Practical Guide to Sf6 Handling Practices

Practical Guide to SF6 Handling Practices

Technical Report

Practical Guide to SF6 Handling Practices 1001945

Final Report, February 2002

EPRI Project Manager L. van der Zel

EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA 800.313.3774 • 650.855.2121 • [email protected] • www.epri.com

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM: (A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I) WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUAL PROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'S CIRCUMSTANCE; OR (B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOUR SELECTION OR USE OF THIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT. ORGANIZATION(S) THAT PREPARED THIS DOCUMENT Electric Power Research Institute, Inc. Powertech Labs Inc.

ORDERING INFORMATION Requests for copies of this report should be directed to EPRI Orders and Conferences, 1355 Willow Way, Suite 278, Concord, CA 94520, (800) 313-3774, press 2 or internally x5379, (925) 609-9169, (925) 609-1310 (fax). Electric Power Research Institute and EPRI are registered service marks of the Electric Power Research Institute, Inc. EPRI. ELECTRIFY THE WORLD is a service mark of the Electric Power Research Institute, Inc. Copyright © 2002 Electric Power Research Institute, Inc. All rights reserved.

CITATIONS This report was prepared by EPRI 3412 Hillview Avenue Palo Alto, California 94304 Principal Investigator L. van der Zel Revised November, 2001 Powertech Labs Inc. 12388 88th Avenue Surrey, B.C. Canada V3W 7R7 Principal Investigator I. Wylie This report describes research sponsored by EPRI. The report is a corporate document that should be cited in the literature in the following manner: Practical Guide to SF6 Handling Practices, EPRI, Palo Alto, CA: 2002. 1001945.

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REPORT SUMMARY Sulfur hexafluoride (SF6) usage in electrical utilities is not only greater than ever but also has come under increased scrutiny for two main reasons. First, the price has increased substantially, and second, it has been identified as the most potent greenhouse gas known—largely due to its extremely stable chemistry that permits emissions to accumulate in the atmosphere for centuries. This guide, organized in outline form for quick and easy access to topics, addresses environmental concerns and suggests procedures and policies related to the safe handling of SF6 gas. Emerging techniques related to the use of SF6 at electrical utilities are also described. While the document does not constitute a standard, it provides suggestions that should save utilities time and effort in developing their own guides for this sensitive area. Background SF6 is widely used in circuit breakers and gas-insulated substations as a dielectric and switching medium due to its excellent dielectric strength as well as its chemical and physical properties. Although very stable and chemically inert, the use of SF6 poses challenges in terms of proper, safe, and environmentally sound maintenance procedures. The Kyoto Accord—drafted in December 1997 under the auspices of the United Nations Framework Convention on Climate Change—identified SF6 gas as a chemical whose emissions should be reduced. Many governments have set policies accordingly, and the U.S. government has instituted a plan to encourage emissions reductions on a voluntary participation basis. EPRI has been active in advising the U.S. EPA about utility needs and abilities with regard to SF6 use. This guide meets part of EPRI’s goal to help utilities answer SF6 challenges. EPRI efforts range from government liaison work to educational conferences to hardware development and implementation. Objective To provide a guide utilities can use as a basis for developing internal standards that ensure their SF6 handling practices are safe, economical, and environmentally sound. Approach EPRI approached utilities that have been active in formulating plant-specific guides and procedures. They generously shared material and provided cooperative assistance. EPRI combined and edited these guides and procedures, selecting the most broadly applicable information from each. EPRI also sought the advice of experts from utilities, laboratories, and manufacturers. Material from the five conferences EPRI has held on SF6 handling practices provided additional information to expand the guide.

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Results This handling guide applies to electrical equipment employing SF6 gas as an insulating and/or interrupting medium. The guide specifically addresses: •

Classifications for switching and non-switching equipment types along with indoor and outdoor applications

•

Risks, warning signs, and written instructions for various low-, intermediate-, and high-risk situations as well as abnormal operating conditions

•

Handling procedures for equipment commissioning, maintenance, and failure situations, with information on the use of gas carts for temporary SF6 storage during maintenance tasks

•

Personal protective equipment, with emphasis on clothing and respiratory devices

•

Disposal and environmental protection practices for clean and contaminated SF6 gas as well as solid decomposition products under normal and abnormal conditions

•

Cylinder transportation, handling, and storage, focusing on U.S. Department of Transportation Regulations

•

Latest and emerging techniques dealing with utility-related SF6 handling issues

The topical organization of this material keeps information at a practical level for easy field access. Appendices offer further explanatory and background information on SF6 handling. EPRI Perspective This guide—which is not to be viewed as an industry standard—is intended for use as a reference in formulating utility-specific policies that will improve SF6 handling practices. The contents are suggestions that should be used in conjunction with manufacturers’ recommendations, and where applicable, with national, local, and state or provincial regulations. In addition to this guide, EPRI’s technology transfer efforts in the area of SF6 safety and handling also include the new “laser camera” technology for locating the source of gas leaks. EPRI worked with a manufacturer to enhance a prototype design and make it more suitable for substation use (EPRI report 1000430). Keywords Sulfur hexafluoride Decomposition products Gas-insulated systems (GIS) Substations Circuit breakers Maintenance

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ABSTRACT Suggestions are provided for a comprehensive handbook for the handling of SF6 gas at an electric utility. Information is organized according to topics to make it easy to find material quickly. The intent is to keep the material at a practical level to make it useful in the field. Supplemental material is added in appendices to make the body of the guide easier to use. It is intended as a starting point for customizing a guide aimed at specific situations and practices encountered at an electrical utility. This guide contains suggestions and procedures and should not be considered a standard.

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ACKNOWLEDGEMENTS Although the author assembled the material of this report, most of it originated from other sources. EPRI has held five Conferences on SF6 Handling Practices and some information was learned from those who spoke or from procedures discussed at those meetings. Even more material came from utility engineers, both Canadian and US, who generously shared material they had prepared for use or consideration at their utility. Several contributions are so large that the individuals deserve to be noted for the work they have done: Sammy Bolton, Nick Dominelli, Bernard Dumont, Pierre Gervais, Patrick Gillan, Harry Haag, Bjorn Holm, Bob Middleton, Peter Ng, Larry Romero, Alex Salinas, A. W. Winningham and Cochrane Yung, Luke van der Zel.

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CONTENTS

1 INTRODUCTION.................................................................................................................. 1-1 Environmental Impact of SF6 Gas ....................................................................................... 1-1 References for Introduction ................................................................................................ 1-2

2 SCOPE ................................................................................................................................ 2-1 3 EQUIPMENT CLASSIFICATION ......................................................................................... 3-1 3.1

Non-Switching Type .................................................................................................. 3-1

3.2

Switching Type.......................................................................................................... 3-1

3.3

Outdoor or Indoor Application.................................................................................... 3-1

3.4

Construction.............................................................................................................. 3-1

4 RISKS, WARNING SIGNS & WRITTEN INSTRUCTIONS................................................... 4-1 4.1

General Considerations............................................................................................. 4-1

4.2

Low Risk Situations................................................................................................... 4-2

4.2.1 Applicable Situations—Normal Operation and Installation .................................... 4-2 4.2.2 Potential Hazards ................................................................................................. 4-2 4.2.3 Safe Work Practices (Also see Section 5.1).......................................................... 4-3 4.3

Intermediate Risk Situations...................................................................................... 4-4

4.3.1 Applicable Situation—Routine Maintenance ......................................................... 4-4 4.3.2 Potential Hazards ................................................................................................. 4-4 4.3.3 Safe Work Practices (Also see Section 5.2).......................................................... 4-5 4.3.4 Workplace and Personal Hygiene......................................................................... 4-6 4.4

High Risk Situations .................................................................................................. 4-6

4.4.1 Applicable Situation—Clean-up after an Arcing Fault............................................ 4-6 4.4.2 Potential Hazards ................................................................................................. 4-6 4.4.3 Safe Work Practices (Also see Section 5.4).......................................................... 4-7 4.5

Purpose of Warning Signs......................................................................................... 4-7

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4.6

Recommended Locations for Warning Signs............................................................. 4-7

4.6.1 On all doors leading into rooms or buildings housing SF6 equipment .................... 4-7 4.6.2 At outdoor SF6 equipment locations ...................................................................... 4-8 4.6.3 At low points in a building ..................................................................................... 4-8 4.7

Recommended Written Instructions for Abnormal Operating Conditions ................... 4-9

4.7.1 Response to Gas Pressure/Density Alarms .......................................................... 4-9 4.7.2 Response to Detection of SF6 and Decomposition Products ............................... 4-11 4.7.3 Re-entry of Building Following an Evacuation Order........................................... 4-11 4.8

First Aid...................................................................................................................4-13

4.8.1 Nonfaulted Gas................................................................................................... 4-13 4.8.2 Faulted Gas........................................................................................................ 4-13

5 HANDLING PROCEDURES ................................................................................................ 5-1 5.1

Commissioning of Equipment.................................................................................... 5-1

5.1.1 Gas Handling Apparatus (Gas Cart) ..................................................................... 5-1 Cart Preparation & Conditioning................................................................................ 5-3 Cart Maintenance Steps............................................................................................ 5-3 Important Performance Factors for Gas Carts ........................................................... 5-5 5.1.2 Filling with SF6 from a Gas Handling Apparatus.................................................... 5-6 5.1.3 Filling or Topping up With SF6 from a Cylinder...................................................... 5-6 5.2

Maintenance of Equipment........................................................................................ 5-7

5.2.1 Normal Maintenance Functions ............................................................................ 5-7 5.2.1.1

Pressure Measurement .............................................................................. 5-7

5.2.1.2

Moisture Measurement............................................................................... 5-8

5.2.1.3

Leak detection ............................................................................................ 5-8

5.2.2 Decontamination................................................................................................... 5-9 5.3

Analytical Procedures for SF6 Gas Assessment ...................................................... 5-10

5.3.1 SF6 Gas Content Measurements ........................................................................ 5-10 5.3.2 Moisture Content Measurements........................................................................ 5-10 5.3.3 Oxygen Content Measurements ......................................................................... 5-11 5.3.4 On Site SF6 Decomposition Products Detection.................................................. 5-12 5.3.5 Multiple Component On Site SF6 Gas Assessment............................................. 5-13 5.4

Equipment Failures ................................................................................................. 5-14

5.4.1 Types of Failures ................................................................................................ 5-14 5.4.2 Exposure to Decomposition Products ................................................................. 5-15

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5.4.3 Cleanup Procedures—In a room or enclosed space ............................................5-15 5.4.4 Cleanup Procedures—Outdoors ...........................................................................5-15 5.4.5 Cleanup Procedures—Washrooms.......................................................................5-16 6 PERSONAL PROTECTIVE EQUIPMENT..............................................................................6-1 6.1

Purposes of Protective Clothing and Devices..............................................................6-1

6.2

Protective Clothing.......................................................................................................6-2

6.3

Respiratory Devices.....................................................................................................6-2

6.3.1 Dust Mask ...............................................................................................................6-2 6.3.2 Cartridge Filter Mask...............................................................................................6-2 6.3.3 Supplied Air Respirator ...........................................................................................6-3 6.3.4 Self-contained Breathing Apparatus (SCBA) ..........................................................6-3 7 DISPOSAL AND ENVIRONMENTAL PROTECTION ............................................................7-1 7.1

Clean SF6 Gas .............................................................................................................7-1

7.1.1 Impact on Environment ...........................................................................................7-1 7.1.2 Recommended Practices ........................................................................................7-1 7.2

Contaminated SF6 Gas ................................................................................................7-2

7.2.1 Impact on Environment ...........................................................................................7-2 7.2.2 Recommended Practices ........................................................................................7-2 7.3

Solid Decomposition Products .....................................................................................7-4

7.3.1 Impact on Environment ...........................................................................................7-4 7.3.2 Recommended Practices (Refer to [1] in Section 8) ...............................................7-4 8 TRANSPORTATION AND STORAGE ...................................................................................8-1 8.1

US Dept. of Transportation (DOT) Regulations ...........................................................8-1

8.2

Cylinder Transportation and Handling .........................................................................8-2

8.3

Cylinder Storage ..........................................................................................................8-4

9 REFERENCES .......................................................................................................................9-1 A REACTIVITY & TOXICITY OF SF6 DECOMPOSITION PRODUCTS................................... A-1 B RECOMMENDED EQUIPMENT FOR PERSONAL PROTECTION ..................................... B-1 Recommended Equipment for Personal Protection ............................................................. B-1

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C SAFE WORKING ENVIRONMENT CHART........................................................................C-1 Safe Working Environment Chart ......................................................................................C-1

D NEUTRALIZING SOLUTIONS ............................................................................................D-1 Neutralizing Solution, Choice and Preparation....................................................................D-1

E RESOURCES FOR PURIFYING OR DESTROYING CONTAMINATED SF6 GAS .............. E-1 F PHYSICAL PROPERTIES OF SF6 GAS AND LIQUID ........................................................ F-1 G US ENVIRONMENTAL PROTECTION AGENCY INITIATIVE FOR SF6 GAS ....................G-1

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LIST OF TABLES

Table 5-1 Weights of Typical SF6 Cylinder .............................................................................. 5-7 Table 5-2 Micro GC Multicomponent Detection ..................................................................... 5-14 Table A-1 Reactivity & Toxicity of SF6 Decomposition Products (DP)1 ..................................... A-1 Table C-1 Risk Level for SF6 Concentrations...........................................................................C-1 Table D-1 Neutralizing Agent Options .....................................................................................D-1 Table E-1 Resource Contacts ................................................................................................. E-1 Table F-1 Physical Properties of SF6 Gas and Liquid .............................................................. F-1

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1 INTRODUCTION

Sulfur hexafluoride (SF6) is an extremely stable gas with excellent dielectric properties that make it desirable for use in circuit breakers, gas-insulated systems (GIS), and related equipment in electrical transmission and distribution systems. It is chemically inert, nonflammable and nontoxic. Its relative ease of liquefaction enables handling of sufficient quantities at field workable pressures. However, the decomposition products formed under electrical arcs can be hazardous to personnel and corrosive to equipment. When subjected to electrical arcing, SF6 molecules dissociate, which aids in quenching the arc, then recombine to their original form once the source of the arc is removed. This tendency to repair itself is called “self-healing” (Allied Signal, 1993). When dissociated in the presence of air and moisture, dissociated or fragmented SF6 will react to form the decomposition products. Handling of SF6 containing these decomposition products requires specific precautions and handling procedures. According to Ko et al. (1993), the major use of SF6 gas in the electrical industry is in circuit breakers, buses, disconnect switches and similar equipment. The use is expanding to lower voltage applications and other non-traditional GIS equipment such as transformers. Use of SF6 in these applications in the United States began in the 1950’s. Since that time, SF6 has progressed to be the main dielectric and insulator for circuit breakers and GIS.

Environmental Impact of SF6 Gas SF6 has properties that impact the environment. Reflecting its stable chemistry, it is very long lived in the atmosphere. The Intergovernmental Panel on Climate Change (IPCC) estimates its lifetime to be on the order of 3,200 years. It has the highest global warming potential (GWP) for gases studied by the IPCC until now. Global warming potential refers to the ability of a specified emission of a greenhouse gas to contribute to a change in future radiative forcing. (IPCC, 1995, p. 1215.) Relative to an equivalent amount of carbon dioxide (the most prevalent greenhouse gas), SF6 has a GWP of 24,900 (IPCC, 1995). Thus, it is the most potent greenhouse gas known. Its long atmospheric lifetime implies that emissions of the gas will accumulate for centuries. Recent measurement studies of SF6 show atmospheric concentrations to be on the order of 3.2 parts per trillion (ppt) but increasing. Several researchers report the annual growth of SF6 concentrations to be approximately seven to eight percent (Maiss, 1994; Rinsland, 1993; Zander, 1991). Growth in atmospheric concentrations of SF6 during the period when measurements have been made has been steady, from less than one ppt to currently more than three ppt. A recent publication by the Max Planck Institute for Chemistry (M. Maiss and C.A. Brenninkmeijer, 1999), however, states that the annual global emissions of SF6 has declined by 27% from 1995 to 1998. This is due to better handling practices of electrical utilities especially with regards to release abatement. Better tracking and reporting of SF6 losses and consumption has also 1-1

Introduction

contributed to the decline in SF6 emissions. In 1992, the United States signed, but has yet to ratify, an international agreement, the Framework Convention on Climate Change, to address the threat of global climate change posed by increasing greenhouse gas emissions. In response, President Clinton directed his administration to develop the Climate Change Action Plan (CCAP). The CCAP has the goal of reducing greenhouse gas emissions in the United States. In addition to CO2, the dominant source, the CCAP also focuses on lesser known greenhouse gases such as the hydrofluorocarbons and perfluorocarbons that are mainly used as refrigerants. SF6, a fully fluorinated compound, is included with these gases for consideration in the Climate Change Action Plan. Since the major use of SF6 is in electrical systems, the U.S. Environmental Protection Agency organized a voluntary Partnership to focus on reducing emissions of SF6 gas. US utilities have been invited to join by signing a Memorandum of Understanding (MOU.) Material describing this program in more detail, the latest draft of the MOU and the current list of participants are found in Appendix 7. The EPA has also prepared and initiated a parallel memorandum for the metallurgical industry, the second largest user of SF6 gas.

References for Introduction Clinton, President William J. and vice President Albert Gore, Jr. 1993. The Climate Change Action Plan. October, 1995. IPCC. Intergovernmental Panel on Climate Change. 1995. Climate Change 1994. Radiative Forcing of Climate Change. The Press Syndicate of the University of Cambridge. New York, NY. Ko, M.K.W., Dak Sze, N., Wang, W. C., et al. 1993. “Atmospheric Sulfur Hexafluoride: Sources, Sinks, and Greenhouse Warming.” Journal of Geophysical Research 98(D6):1049910507. Maiss, M., and I. Levin. 1994. “Global Increase of SF6 Observed in the Atmosphere.” Geophysical Research Letters 21(7):569-572. Rinsland, C.P., et al. 1993. “ATMOS/ATLAS 1 Measurements of Sulfur Hexafluoride (SF6) in the Lower Stratosphere and Upper Troposphere.” Journal of Geophysical Research 98(Dll):20491-20494. Zander, R., et al. “Infrared Spectroscopic Measurements of the Vertical Column Abundance of Sulfur Hexafluoride, SF6 from the Ground.” Journal of Geophysical Research 96(D8):1544715454 (1991). M. Maiss and C.A. Brenninkmeijer: “A Reversed Trend in Emission of SF6 into the Atmosphere” 2nd Int. Symposium on Non-CO2 Greenhouse Gases (NCGG-2), Noordwijkerhout, The Netherlands, 8-10 September, 1999, van Ham et al. eds., Kluwer Academic Publishers, Dordrecht 1-2

2 SCOPE

This Handling Guide applies to electrical equipment employing SF6 gas as an insulating and/or interrupting medium. It defines handling procedures including SF6 gas filling of equipment and the storage or disposal of clean or contaminated gas under both normal and abnormal conditions. It outlines requirements for safe working conditions and describes the degrees of protection to be provided for personnel and the environment. Although this guide does not deal specifically with the handling of SF6 blends (SF6 is blended with N2 and CF4 and is used for low ambient temperature operation and also for cost and environmental reasons), many of the environmental and safety procedures are applicable. Filling procedures and specific handling of SF6 blends can be found in the references and elsewhere [14]. This Guide does not cover equipment design specifications, nor does it detail the properties and adverse effects of SF6 and its decomposition products. Such information is available from the publications listed in the Reference section. This Guide is intended for use by electrical utilities for the purpose of reference and guidance in formulating standard practices, but is not to be taken as required or as an industry standard. The contents are suggestions that should be used in conjunction with manufacturers’ recommendations, and where applicable, with national, state or provincial and local regulations. It does not reflect specific legal requirements applicable in any given state or province; reference for these requirements should be made to appropriate local, state or province Acts and Regulations.

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3 EQUIPMENT CLASSIFICATION

The type and the construction of SF6 equipment and its operating environment determine the level of risks. How to continually assess those risks as work progresses are explained in Section 4. The handling procedure to be followed at a given level of risk is detailed in Section 5 Personnel protection is described in Section 6 and environmental concerns and procedures in Section 7. SF6 equipment in an electric system is listed below under switching and non-switching types and under indoor and outdoor applications.

3.1

Non-Switching Type This group of SF6 gas filled electrical equipment includes: gas insulated transmission lines and bus ducts, cable terminators and bushings, instrument transformers, power transformers and capacitors.

3.2

Switching Type This group of SF6 gas filled electrical equipment includes: circuit breakers, disconnect and ground switches, circuit switchers and reclosers.

3.3

Outdoor or Indoor Application Outdoor application includes all the electrical equipment types listed in sections 3.1 and 3.2. This group consists of equipment filled with pure SF6 for operation down to -35°C (-31°F) ambient and equipment filled with mixed gas for operation down to -55°C (-67°F) ambient. Indoor application includes most gas insulated switchgear (up to 550 kV) and most medium voltage (15 kV to 36 kV) metal enclosed switchgear, operating at ambient down to 0°C (32°F).

3.4

Construction Almost all SF6 equipment has pressurized enclosures. The enclosures may be made of porcelain, metal or composite material. 3-1

Equipment Classification

In most designs, the enclosures are equipped with: •

A pressure relief safety feature.

•

A pressure/density monitoring device.

•

Valves for filling, draining and sampling the SF6 gas.

Many medium voltage equipment enclosures are sealed for life with typical gas leakage rates below 0.1% per year. The design discourages onsite gas sampling and refilling, a factor that is balanced by less leakage in equipment that seldom requires maintenance.

3-2

4 RISKS, WARNING SIGNS & WRITTEN INSTRUCTIONS

4.1

General Considerations When working with SF6 equipment, continuous emphasis needs to be placed upon personal protection and safe work procedures. Work can be performed in a safe and reliable manner by recognizing the potential hazards associated with the particular working situation and assessing risk then following the appropriate procedures and precautions presented in this guide. The hazards include working with pressurized enclosures, asphyxiation from displacement of air and chemical hazards especially during fault conditions. The recommendations for personal protection and safe work procedures are based on the level of risk in particular situations described in the following sections. When a situation is unclear, it is prudent to assume the higher risk level is appropriate. The guide offers a practical approach to risk assessment and use of personal protective equipment (PPE). It is always good practice to treat SF6 enclosures that are entered by personnel as confined spaces. Personnel entering an enclosure should exercise confined space procedures, which include checking the air quality (especially oxygen content) with a calibrated sensor, constant fresh air ventilation, and never working alone. Confined space training is essential. There are three risk levels outlined here. Level one being the lowest and often include working with new equipment or non-switching equipment. Level two involves intermediate risk where normal levels of decomposition products may be present due to normal operation of switchgear. Level three is the highest risk level and occurs where there has been a fault or suspected fault and where high levels of decomposition products may be present. All situations involve working with a pressurized enclosure and the potential of displacement of breathable air. Recognizing and detecting the presence of decomposition products, both in the form of gases and solids, is essential. This may involve laboratory analysis, field assessment and, under unexpected circumstances, the sense of smell. SF6 decomposition products produce a pungent odour that may smell like rotten eggs or a burning battery and can produce an irritation to the throat or eyes. Any residual odor or discomfort to the throat or eyes when working in the proximity of any SF6 filled electrical equipment indicates a problem and the area should be evacuated and this will involve increasing the level of risk. The sense of smell must never be used intentionally to locate a faulted enclosure. It is very hazardous to inhale highly concentrated SF6 decomposition gases from a faulted enclosure.

4-1

Risks, Warning Signs & Written Instructions

Always analyze suspect gas for SF6 decomposition products by field assessment and/or by laboratory analysis. Each situation will determine which personnel require personal protective equipment (PPE). Anybody potentially exposed to decomposition products should wear PPE. As clean-up proceeds, the level of risk can be reduced once all the decomposition products have been safely removed. This should be confirmed before personal protective equipment is removed. Where faults have occurred, there is normally a requirement to document initial findings before anything is disturbed. This is often limited to taking a few photographs after a compartment is opened. A compartment is opened, of course, only after the SF6 has been safely removed – as per company and manufacturer guidelines and instructions.

4.2

Low Risk Situations 4.2.1 Applicable Situations—Normal Operation and Installation The usual cases in the Low Risk Situation are: working with new equipment during assembly, testing and commissioning; working with existing nonswitching equipment which has been problem free; operating and working around any existing equipment. In all these situations, harmful SF6 breakdown products are not expected to be present. 4.2.2 Potential Hazards Asphyxiation: Although SF6 is non-toxic, it acts as an asphyxiant in high concentrations in air due to the displacement of oxygen. It has no other additional adverse physiological effects. It is five times heavier than air and will collect in low lying areas. Confined space training for personnel working with indoor GIS is beneficial. Inhalation of a small quantity of pure SF6 for a short period is not dangerous. The danger of asphyxiation due to SF6 gas is present in the fall line of a major SF6 spill. Being five times heavier than air, SF6 gas will accumulate temporarily in low lying areas until it diffuses into surroundings and becomes uniformly dispersed. Simple asphyxiants exert their effect solely by decreasing or excluding oxygen from the work environment, thus leading to suffocation. Nitrogen, SF6, and Argon all belong to this class. The oxygen concentration of breathing air must not be less than 13% (20.9% is normal). Stating this requirement in a different way, the concentration of a simple asphyxiant must not exceed 35% in breathing air. The standard precaution is to insure there is sufficient ventilation at the work

4-2


site. The use of air quality monitors such as those used for confined space entry is recommended. Pressurized Enclosures: The SF6 gas used in electrical equipment is usually pressurized, and that pressure seldom exceeds 640 kPa (93 psia). Although the enclosure may be under relatively low gas filling pressure, nevertheless, the normal safety precautions applicable to pressure vessels need to be observed.

4.2.3 Safe Work Practices (Also see Section 5.1) New equipment is filled with clean SF6 gas, either pure or blended with other gases such as N2 or CF4 for low ambient temperature operation. Blends reduce the amount of SF6 required and are increasing in application for both cost and environmental reasons. The insulating gas and insulating parts have to meet very stringent requirements for purity, dryness and cleanliness. Working with clean SF6 gas is harmless if the following safety practices are observed: Carry out work only in well ventilated areas. Prior to entering areas where accumulation of SF6 is suspected, the use of air quality monitors such as those used for confined space entry is recommended. A portable SF6 gas detector could also be used to detect the presence of SF6 gas. If SF6 is present, use forced ventilation to disperse the gas. Use only properly calibrated instruments. Do not smoke during work and remove sources of heat (heaters, engines, welding machines, etc.) and open flame from the working vicinity. Since SF6 gas may decompose with heat at temperature as low as 200°C (392°F), a temperature reached by items such as: burning cigarette tips, electric heaters and gas fired space heaters, all areas housing SF 6 equipment should be designated as NO SMOKING areas. This prohibition should be strictly enforced. Decomposition products in high concentrations are toxic. Any arc welding that occurs in an area housing SF6 equipment should also be controlled, as arc welding can also cause SF6 gas to dissociate to form hazardous decomposition products. Therefore, if there is a risk of a high concentration of SF6 in the ambient (for example, during gas filling operations), no welding or other heat producing activities (for example, use of spot heaters) should be permitted in the vicinity. Inspection and other access covers of an SF6 enclosure should not be removed until the pressure inside the enclosure has been determined to be at atmospheric pressure. Open all access covers with caution.

4-3


4.3

Intermediate Risk Situations 4.3.1 Applicable Situation—Routine Maintenance During normal maintenance when a switching device is opened for inspection, there may be a thin coating of metallic fluoride powder on the inside of the enclosure. This indicates an intermediate risk situation that requires appropriate PPE. These solid decomposition products form because of arcs, which occur during normal switching operations. Often, no odor (rotten egg smell) is present as the gaseous decomposition products either are absorbed by the desiccant or react with components within the enclosure. The metallic fluoride powders, however, require appropriate procedures for handling. See section 5.4.

4.3.2 Potential Hazards Asphyxiation and Pressurized Enclosures: See Section 4.2.2 Decomposition products (normal levels): SF6 gas has excellent dielectric properties, unique arc-quenching ability, excellent thermal stability, and good thermal conductivity. Because of these characteristics, it is used extensively in electrical and electronic equipment such as circuit breakers, switches, and microwave components. SF6 gas absorbs free electrons generated during a circuit interruption arc by fragmenting (dissociating) the SF6 molecule. After exposure to the extreme temperature of an electric arc, the dissociated molecules recombine to form SF6. This recombination is not always 100 percent efficient and in the presence of trace contaminants such as oxygen and moisture, some of the dissociated SF6 will react to form decomposition products. The type and amount of SF6 decomposition products depend on the magnitude and duration of the arc, any contaminants present in the gas, and the type of materials (metals, plastics, composites etc.) comprising the electrical equipment. SF6 gas-insulated circuit breakers are equipped with desiccants designed to remove moisture and SF6 decomposition products. The commonly used desiccants are aluminum oxide, activated alumina and molecular sieve. These desiccants are not designed to handle large amounts of moisture and SF6 decomposition products. Units, which have experienced electrical problems or internal failures, may contain abnormally high levels of byproducts, which could exceed the absorption capacity of the desiccants. Desiccants should always be replaced whenever possible. Proper storage conditioning of new desiccants is important. New desiccant that has been exposed to the air for extended periods may have reached its absorbent capacity for moisture and will be less effective. New desiccant can be conditioned or “activated” by following the manufacturer’s instructions. Never apply heat to used desiccant as decomposition products may be released [1]. Disposal of spent desiccant, especially after a fault, should be 4-4


done in an environmentally sound and safe manner. Decomposition products are absorbed by the desiccant and may degas and hydrolyze when contacted with air and moisture. Secondary decomposition products result from byproducts chemically reacting with other byproducts or contaminants. As an example, sulfur fluorides and metal fluorides may react with trace moisture that may yield hydrofluoric acid. Hydrofluoric acid is extremely corrosive and will react with electrical equipment components and is also very harmful to personnel in high concentrations Electrical decomposition of SF6 can produce a very wide variety of decomposition products, many of which may exhibit differing degrees of toxicity, dependent upon exposure concentration, time of exposure and many other factors. [11] For example, the metallic fluoride powder may cause a burning sensation of the skin, which, for a short term exposure, would disappear with time and would leave no permanent damage. Extreme faults can produce significant amounts of decomposition products, both gaseous and solid, and contact with skin results in hydrolysis of these products and the formation of HF. Severe exposure not only produces a burn on the skin but can also have some serious chronic effects. If personnel show symptoms of burns on the skin, application of HF cream (available from first aid suppliers) is advisable to the affected areas and medical attention is advisable. Since SF6 decomposition products are detectable by smell at low concentration levels where toxicity is practically non-existent. If any odur is detected, personnel should immediately evacuate the area. See the Reactivity and Toxicity chart in Appendix 1.

4.3.3 Safe Work Practices (Also see Section 5.2) During the initial inspection of any apparatus, protective equipment should be worn—i.e. coveralls, rubber boots, rubber gloves, chemical cartridge respirator and acid resistant goggles. It is always a good idea to have any suspect gas analyzed for decomposition products prior to handling. The respirator should be equipped with an organic vapor/acid gas cartridge as indicated as well as a HEPA (High Efficiency Particle Arresting) filter. This will ensure protection from vapors of the solvent used in cleaning and for protection from degassing of the solid decomposition products as gaseous decomposition products are readily absorbed by the solids. If there is no appreciable amount of dust and no detected decomposition products, subsequent work may be carried out according to the safe work practices for low risk situations. Always wear gloves when handling components before they have been properly cleaned especially when any evidence of dust is found. During any maintenance procedure, if any odor or irritation is noticed by any personnel, the level of risk should be increased and respirators and PPE should be employed. Always follow procedures, clean up immediately, and never handle metallic fluoride powder with bare hands

4-5


4.3.4 Workplace and Personal Hygiene A clean workplace and personal hygiene are important aspects for the safe handling of SF6 and any potential decomposition products during SF6 equipment maintenance and restoration work. Therefore, –

the workplace where maintenance/restoration work is carried out should be regularly cleaned. All cleaning materials such as rags and soiled protective clothing should be disposed of in accordance with the recommended practices of Section 7.3.2.

–

the workplace should never be used for eating and drinking or for the storing of outdoor clothing or other materials not associated with the maintenance of contaminated SF6 equipment.

–

upon completion of clean-up work, personnel should wash all exposed skin areas (hands, forearms, face, and neck) before changing into street clothing and/or handling any food.

The required equipment for personal protection is discussed in Section 6 of this guide.

4.4

High Risk Situations 4.4.1 Applicable Situation—Clean-up after an Arcing Fault If there has been a fault in a gas enclosure, large amounts of decomposed SF6 may be present. If possible and practical, have the SF6 analyzed before commencing work. The amount and type of arc product produced depends on the arc energy, the moisture content and the materials near the arc.

4.4.2 Potential Hazards Asphyxiation and Pressurized Enclosures: See Section 4.2.2 Decomposition products (high levels): If a fault occurs inside an enclosure, normally it is cleared before any damage to the equipment can occur. However, if the primary protection should fail, the heat generated by the arc could cause the pressure of the SF6 gas to rise to the point where the pressure relief device ruptures. This will release large quantities of gaseous SF6 decomposition products into the building or surrounding area if outside. Under these conditions, percent by volume levels of decomposition products can form. This will require all personnel coming into any contact with the faulted gas to wear appropriate safety equipment.

4-6


A few of these SF6 decomposition products are highly toxic [11]. Most are highly irritating when in contact with moisture as in the mouth, respiratory tracts and eyes. They have a nauseating odor and smell like rotten eggs. Evacuate the area on any detected odor and follow appropriate safety precautions.

4.4.3 Safe Work Practices (Also see Section 5.4) Evacuate the building when the smell of decomposition products is detected or when the SF6 alarm is activated. For proper evacuation and re-entry, refer to Sections 4.7.2 and 4.7.3. When working on equipment containing decomposed SF6 (and the pressure relief device has not burst) follow the precautions detailed in Section 6.2.3. Once exposed to atmosphere, SF6 decomposition products absorb moisture and become corrosive. Cleanup must be affected as soon as possible to prevent damage to equipment (insulator surfaces) and protect personnel from undue exposure to the toxic material.

4.5

Purpose of Warning Signs Warning signs posted at strategic locations provide an effective line of final caution. They should carry emergency instructions; identify vital controls, equipment locations, display evacuation maps and evacuation plans. For example, signs could be prominently displayed at the SF6 equipment or in buildings housing SF6 equipment to warn personnel of potentially hazardous circumstances such as: •

the accidental release of SF6 and in particular, its decomposition products, into the immediate work environment,

•

the rupture of pressurized porcelain or epoxy SF6 enclosures due to impact,

•

the arcing associated with disconnect or ground switch operation in SF6 switchgear while the viewing port is being used, and

•

the momentary transient high voltages on the equipment enclosures caused by disconnect switch operations or internal fault conditions.

Only the first two points pertaining to SF6 handling are dealt with in this guide.

4.6

Recommended Locations for Warning Signs 4.6.1 On all doors leading into rooms or buildings housing SF6 equipment The warning signs should be: –

CAUTION 4-7


–

THIS IS A NO SMOKING AREA

–

THIS BUILDING CONTAINS SF6 EQUIPMENT

If additional signs are desirable, it is suggested that they include the following information where applicable: –

equipment fault may release hazardous decomposition products

–

immediately evacuate the building if a pungent odor is present or upon activation of the SF6 detector alarm system

–

location of nearest first aid treatment equipment

–

location of self contained breathing apparatus (SCBA)

–

location of building ventilation fan switch

–

location of marshaling point (map)

–

location of instructions to firemen

–

location of instructions for medical response personnel.

4.6.2 At outdoor SF6 equipment locations Where applicable, the warning signs should be: –

CAUTION

–

PRESSURIZED EQUIPMENT

–

PORCELAIN MAY RUPTURE UPON IMPACT

4.6.3 At low points in a building Since SF6 gas is much heavier than air, warning signs should be placed at any low points in the building such as kiosks or pits where personnel may be required to work. Personnel entering such areas should have confined space training and be equipped with calibrated sensors to assess the air quality. SCBA’s are recommended. The warning sign should be: –

CAUTION

–

SF6 GAS MAY ACCUMULATE IN THIS AREA

–

VENTILATE WORK AREA IF REQUIRED

In addition to warning signs, buildings containing gas insulated switchgear should have an audible alarm system, which activates upon detection of potentially harmful levels of SF6 gas and/or decomposition products in the environment. SF6 detectors should be strategically placed throughout the building and in particular in connected areas below the switchgear room, such as basements, cable ducts, shaft pits and other similar areas. 4-8


Confined space entry procedures should be adhered to following an alarm situation from any detector in these areas.

4.7

Recommended Written Instructions for Abnormal Operating Conditions 4.7.1 Response to Gas Pressure/Density Alarms The SF6 gas used in electrical equipment is usually pressurized. Therefore, the normal safety precautions applicable to pressure vessels should be observed. 1. Overpressure Alarm An overpressure alarm may be an indication of a fault condition, or an indication of a temperature rise due to overloading or an indication of gas contamination inside the SF6 enclosure. If the alarm condition persists, personnel should be dispatched to the site to investigate. Pressure readings, compensated for the ambient temperature, should be taken to ensure that the pressure monitoring device is functioning correctly. If the over-pressure is a genuine alarm, it is recommended that the enclosure be isolated and gas samples be taken for analysis. The cause of the over-pressure condition should be established and the necessary corrective action taken prior to returning the equipment to service. 2. Refilling Alarm The annual leakage rate for a sound SF6 installation is typically far less than one per cent per year. Most of this leakage will occur at such places as the interconnecting flange seals, the pressure sampling ports and piping joints. Flows through porous metal castings have also been observed. All refilling alarms should be addressed as soon as possible. Corrective action, however, may be deferred, depending on the leakage rate, the type of equipment and its history. For instance, circuit breakers should maintain their dielectric and interrupting capabilities down to the lockout gas pressure level. Many circuit breakers also maintain a dielectric withstand to ground and even across the open gap of the contacts at normal operating voltage when the gas pressure falls to one atmosphere. Therefore, for circuit breakers, it is safe to continue operating the equipment at the refilling pressure, though the utility should be aware that continued leakage would eventually result in a lockout or failure. The alarmed enclosure should be “topped up” to the rated pressure level at the first opportunity. The actual leakage rate and source of leakage should also be determined. The service crew should check the gas tightness of all enclosure

4-9


seals. The work may be carried out with the equipment in operation, provided it is safe to do so. 3. Low Pressure Alarm At this pressure value, the equipment maintains its rated dielectric withstand capability. Switching equipment also maintains its interrupting capabilities and depending on the safety practice of the user, will perform one of the following functions: – breaker will trip and lockout the electrical closing circuit. (Typical for feeder or line circuit breakers) –

breaker will lockout both the trip and close circuits. (Typical for all circuit breakers including feeder or line circuit breakers)

The urgency of corrective response and even the repair procedure depend upon the system operational requirements and the time elapsed between the refilling alarm and the low pressure alarm. If the time interval between the two alarms is at least one week, under emergency conditions, SF6 gas could be added to the affected equipment to bring the pressure back to the normal operating pressure. The equipment could then remain energized and in service until it can be removed from the system for the necessary corrective repair work. Should the interval between the two alarms be less than one week, this indicates the presence of a substantial leak. In this case, the affected equipment should immediately be de-energized, the source of the leak pinpointed, the leak repaired and gas replenished prior to returning the equipment to service. If the low pressure alarm occurs immediately after the refilling alarm, this indicates that a major leak has occurred, and one of the following situations may have occurred: an enclosure may have burned through, an enclosure pressure relief device may have operated or a connecting pipe may have broken. In this instance, the affected gas enclosure should be de-energized as quickly as possible. Personnel responding to this particular case of gas pressure alarm activation should wait until the area is ventilated to a safe level (see Appendix 3) before entry. However, if the situation demands that they must enter the area immediately, they must be equipped with high personal protective level breathing equipment and protective clothing as defined in section 6 of this SF6 handling guide. They must have adequate training covering such situations, and there must be relevant company procedures in place. Section 4.7.1 clauses 2, 3 & 4 do not apply to gas enclosures that are designed to be “sealed for life”. These enclosures have only one pressure switch. In case of a pressure drop, the faulty enclosure should be replaced.

4-10


4.7.2 Response to Detection of SF6 and Decomposition Products 1. If the audible SF6 detection alarm sounds, all personnel should leave the building. 2. If, at any time while working in a building housing SF6 equipment, personnel detect a pungent odor—like rotten eggs or a burning battery—they should evacuate the building and sound the building evacuation alarm. 3. If, at any time personnel have a burning sensation on the skin, have difficulty in breathing or have suspicions they were exposed to SF6 decomposition products, they should evacuate the building and seek the appropriate first aid and/or medical attention. 4. If a fault occurs inside the SF6 equipment that results in the release of SF6 decomposition products, all personnel should immediately leave the building by the nearest exit. All should avoid the faulted area if possible. It is recommended that the nose and mouth be covered until one is clear of the faulted area. The sound of the fault, accompanied by the characteristic “rotten egg” smell, and possibly also by the sight of a dust cloud over the fault area, are warnings that the fault has resulted in the release of SF6 decomposition products. 5. Following exit from the building, all personnel should assemble at a predetermined location. A head count should be taken. The work crew person in charge should ensure that all personnel are present and accounted for. 6. Following an evacuation from the building and the accounting of all personnel, all building entrances should be secured and marked with safety tape to avoid unauthorized entry by personnel unaware of the building evacuation order. 7. If the building ventilation fans are not running, they should be started as soon as possible to reduce the concentrations of any potentially hazardous decomposition products that may be present. Care should be taken to ensure that building exhausts do not vent in locations that can endanger personnel. Choose assembly locations that are not near exhaust points. 8. If forced ventilation is not available or not functioning, open all doors, windows etc. to encourage natural ventilation. All possible access points should be marked with safety tape.

4.7.3 Re-entry of Building Following an Evacuation Order 1. Personnel should not routinely re-enter a building following an evacuation order until SF6 concentration has been reduced to a safe level by mechanical 4-11


or natural ventilation. It is suggested that the exhaust flow be checked before anyone enters the building to check the air there. 2. If any personnel were unable to exit the building, rescue re-entry should only be attempted by personnel wearing protective clothing and gloves and equipped with SCBA (self contained breathing apparatus). 3. The cause of the building evacuation order should be investigated by trained personnel wearing appropriate protective clothing and respiratory protection corresponding to the appropriate levels as defined in Section 6 of this Guide. The following procedures should be followed: 3.1

The investigator(s) should have a communication system established with an observer located outside the building. Communication frequency intervals between these individuals should be established (for example, reports every five minutes).

3.2

If the pre-determined communication signal has not been received, standby rescue personnel should be dispatched to investigate. All rescue personnel entering the building must be equipped with protective clothing, self contained respiratory equipment and communication equipment.

3.3

Initial equipment investigations should be done using “hands off inspection” in order to minimize skin contact with any potentially hazardous solid decomposition products.

3.4

The investigator(s) should determine the cause of the evacuation order, establishing whether a gas leak has occurred (High SF6 concentration), if a fault has occurred, and if so, if a SF6 enclosure has ruptured, or whether an alarming system malfunction has occurred.

4. Following completion of the investigation as to the cause of the evacuation order, an assessment should then be made to determine the level of personal protection required for building re-entry by all personnel. All employees reentering the building should wear the designated level of personal clothing and respiratory protection equipment. 5. Restrictions on all building entrances should only be lifted once an “all clear” communication has been given by the designated responsible person. (i.e. work can resume without any special respiratory or personal protection requirements).

4-12


4.8

First Aid 4.8.1 Nonfaulted Gas Recommended first aid procedures for treating contact with nonfaulted SF6 liquid or gas are as follows: (1) Skin or Eye Contact with Liquid SF6 (a) Symptoms—Frostbite, redness, pain, open wounds. (b) Treatment—DO NOT wait for symptoms to appear. Treat the affected body area immediately as follows: (1) DO NOT: apply direct heat to the affected body area, rub the affected area, or remove the victim’s clothes. (2) Slowly warm the affected body area with lukewarm water. (3) Seek medical treatment. (2) Inhalation (a) Symptoms—Pale or blue skin, headache, sluggish, tingling in the arms and legs, altered hearing, possible unconsciousness. (b) Treatment (1) (2) (3) (4) (5)

Move victim to fresh air. Remove or loosen all restrictive clothing. If breathing is difficult, administer oxygen if available. Seek medical treatment. If not breathing, call for immediate medical assistance and administer cardiopulmonary resuscitation (CPR).

4.8.2 Faulted Gas Recommended first aid procedures for treating contact with faulted SF6 are as follows: (1) Eye Contact (a) Symptoms—Irritation, redness, blurred vision, pain. (b) Treatment (1) Flush eyes immediately with water for a minimum of 15 minutes while lifting eyelids to ensure a complete rinse. (2) After flushing with water, irrigate eyes with a saline solution, if available, and cover both eyes with sterile bandages.

4-13


(3) Having a small portable eyewash, such as that used in battery rooms, at the worksite for emergency use is a good idea. (4) DO NOT use boric acid because of its drying qualities. (5) Seek medical treatment immediately. (2) Skin Contact (a) Symptoms—Redness, irritation, swelling, pain. (b) Treatment (1) Flush area with water for a minimum of 15 minutes. (2) Remove contaminated clothing carefully so that other skin does not become irritated. (3) Again, flush area with water. (4) Seek medical treatment immediately. (3) Inhalation (a) Symptoms—Shortness of breath, pale or blue skin, headache, sluggish, tingling in the arms and legs, altered hearing, possible unconsciousness. (b) Treatment (1) (2) (3) (4) (5)

Move victim to fresh air. Remove or loosen all restrictive clothing. If breathing is difficult, administer oxygen if available. Seek medical attention immediately. If not breathing, call for medical assistance and administer CPR.

(4) Ingestion—To avoid ingestion, DO NOT eat or smoke while handling SF6. Workers shall wash their hands after handling SF6 gas and byproducts. (a) Symptoms—Nausea, vomiting, sluggishness. (b) Treatment (1) Rinse mouth to remove any contaminants. (2) Give plenty of water to drink to dilute the ingested chemicals. DO NOT induce vomiting. (3) Seek medical treatment immediately.

4-14

5 HANDLING PROCEDURES

SF6 is normally supplied as a liquefied gas in cylinders painted silver. However, there is no North American Industry Standard for color coding SF6 bottles, so, many manufacturers have their own color coded bottles and these have been changing over the last few years. Generally, SF6 cylinders range in sizes from 5 kg to 52 kg (11 lb to 115 lb), most common being the 52 kg (115 lb) size. Normal pressure is about 2.1 MPa (305 psig) at 20°C (68°F). Normal safe handling procedures are: •

do not drop or roll cylinders

•

do not apply direct heat to cylinders

•

do not allow cylinder temperature to exceed 50°C (122°F)

•

do not store cylinders in direct sunlight

•

do not use cylinders if they are chilled below -29°C (-20°F)

•

do not exhaust gas so fast that icing of the valve develops

•

store cylinders vertically and securely with valve cap in place and at a dry, well ventilated location, away from flammable material

5.1

Commissioning of Equipment Gas enclosures are often filled at the manufacturer’s works with nitrogen or SF6 gas at a pressure well below the nominal operating pressure (usually at 25kPa (3.6 psig)) at the time of shipment and will require gas replacement or topping up before placing the equipment into service. In such instances, gas handling equipment will be required during commissioning to evacuate the enclosure and to allow gas to be stored and to fill the enclosure with clean gas up to rated pressure. Caution should be observed with new equipment filled with this nominal operating pressure in colder climates. If the equipment cools below freezing with this low pressure of gas, a vacuum may develop inside the enclosure increasing the risk of air or moisture contamination. Preferably, the gas handling equipment should have re-processing facilities for removing moisture, gaseous and solid decomposition products.

5.1.1 Gas Handling Apparatus (Gas Cart) A gas handling apparatus or gas cart is essential for filling and evacuating SF6 equipment. Air and moisture content must be minimized. 5-1

Handling Procedures

A commercially available gas handling apparatus, usually a wheeled vehicle or cart, has the following major components: a. A storage vessel, suitable for storing gaseous or liquid SF6, designed in accordance with ASME Section VIII and equipped with an ASME approved safety valve. If the cart is expected to travel between substations while carrying SF6, the storage vessel must have US Department of Transportation approval; see section 8.1. b. An oil-less, gas tight compressor to transfer SF6 from the SF6 enclosure to the storage vessel. c. A vacuum pump to remove air and moisture, including remnant SF6 below atmospheric pressure, from the enclosure. Notice if the output of the vacuum pump and its associated plumbing are connected to the SF6 handling side of the apparatus. This can be a source of oil contamination of the SF6, depending on the design of the vacuum pump. Some substations are equipped with central vacuum systems, which permit venting of the exhaust outside and away from the work area. d. A filtering system consists of: a particle filter located at the connection to the SF6 enclosure; decomposition products and moisture filters located between the compressor and the storage vessel. The compressor withdraws gas in the SF6 enclosure from its rated pressure down to atmospheric pressure, or, with an additional oil-less vacuum compressor in series, down to a pressure near 5 kPa (0.8 psia or 37 Torr). The compressor compresses the gas into the storage vessel mounted on or near the apparatus, either in gaseous or liquefied form. A cooling system can be utilized to ensure liquefaction at more moderate pressures. A system of desiccant dryers and filters in the circuit purifies the gas as it is passed through. The vacuum pump may not be oil free and should be used to evacuate the moisture and air only if it poses no risk of contamination. It may be used to exhaust remnant SF6 to atmosphere through the filtering system. Vacuum and pressure tight, automatic, SF6 gas couplings should hold any pressure or vacuum inside the hoses or the apparatus when disconnecting the service hoses from the apparatus or from the enclosure. Gas handling hoses should be capped off when they are not in use to minimize exposure to moisture. e. If the switchgear being drained of SF6 is of the dual pressure type, it is advisable to have a pre-filter unit outfitted with an activated charcoal cartridge to remove any oil that might be present [13]. All hoses must be evacuated before gas transfer starts. It is preferable to use the shortest possible length of hose to minimize SF6 losses. The filters and desiccant units of the gas cart are crucial for maintaining gas quality. It is important that they be checked and maintained regularly. 5-2

Handling Procedures

Gas carts should be regularly checked for leaks. This is important not only to reduce emissions of SF6 gas, but also to avoid the simultaneous contamination of the stored gas with air. Cart Preparation & Conditioning The following process should be followed on a regular basis, preferably in the shop, prior to transporting the cart to the work site. If the drive to the work site is long and involves rough roads, consider repeating these steps at the site. If sample cylinders are to be used, they should be attached to the cart during the conditioning process. Consult appropriate transportation regulations when transporting on public roads. Restrictions apply in many jurisdictions that prevent transport of pressurized or liquefied SF6 gas in the gas cart. Step 1: Place the cart, hoses, and test vessels under vacuum for 5 minutes. The vacuum gauge should approach 0.1 kPa (1 mbar). Step 2: Pressurize the cart, hoses, and test vessels with nitrogen at 500 kPa (72 psi) absolute for 3 minutes Step 3: Evacuate for 5 minutes. Step 4: Repeat steps 2 & 3 twice more. Step 5: Vacuum the cart to 0.1 kPa (1 mbar) and hold for 20 minutes. Step 6: Pressurize the cart with nitrogen at 200-300 kPa (30 – 45 psia) absolute for storage and transport. Cart Maintenance Steps Loss of Pressure Check List: 1 Check all connections on every fitting and hose. Tighten if necessary Inspect fittings used to make connections to the breaker. 2 Pressurize the cart with Nitrogen gas to approximately 500 kPa (5 bar). Ensure all valves are open (except the valve for the vacuum gauge). Begin closing the valves at the pressure gauge and work backwards until the cart is sectionalized into many smaller areas. 3 Wait at least 4 hours. 4 Start opening the valves at the pressure gauge and work backwards. Note any pressure drops. Any noticeable decreases in pressure indicate leaks.

5-3

Handling Procedures

Investigate and repair or replace the defective fittings. Repeat the above steps until pressure is maintained. Loss of Vacuum Check List: 1 With all valves open, evacuate the cart to 0.1 kPa (1 mbar) (or other predetermined value). 2 Beginning at the vacuum gauge, close valves to sectionalize the cart 3 Wait at least 4 hours. 4 Start opening the valves at the vacuum gauge and work backwards. Note any loss of vacuum. Any noticeable increases in pressure indicate leaks. Investigate and repair or replace the defective fittings. Repeat the above steps until vacuum is maintained. ii)

Scrubber Testing: If the following tests indicate decomposition products, the dry type gaseous filter (scrubber) contents are to be replaced. SF6 decomposition product tube—Connect dry nitrogen to the inlet of the scrubber unit. Route the gas from the outlet of the scrubber through a SF6 by-product tube as per manufacturers instructions for testing SF6 gas. Moisture Test—As with the SF6 by-product tube test, nitrogen is passed through the scrubber unit and into a moisture tester. Decomposition products may exist if the dew point is noticeably higher (wetter) than the dry nitrogen (-50°C dewpoint or 39 ppmv). If decomposition products exist, damage to the moisture sensor may occur.

Never use a molecular sieve with a pore size greater than 4 Angstroms (e.g. 13X) as thermodynamic reactions can occur under certain conditions resulting in severe overheating of dessicant towers. Never use Soda Lime (NaCO3) as a filter material for SF6 as it produces CO2 upon contact with decomposition products and is hard to remove from the gas.

5-4

iii)

Flow Meter Testing: Using the above scrubber tests, check the flow meters on the gas cart for byproduct contamination.

iv)

Vacuum Pump Maintenance: Change the oil in the vacuum pump twice a year or if exposed to high levels of decomposition products using only oil specified by the manufacturer. Overhaul the pump when performance deteriorates.

Handling Procedures

v)

Moisture Tester: The unit should be calibrated at least once a year, preferably prior to any high maintenance seasons. Once calibrated, check the dew point of a single SF6 (preferred) or nitrogen cylinder, which can be kept as a reference throughout the year to confirm the moisture tester’s accuracy. SF6 percentage tester: The unit should be field calibrated at least once a year, preferably prior to the high maintenance season. Again, use the same reference SF6 cylinder as a check of the instrument.

vi)

vii) By-product tube inspection: The tube O-rings should be inspected yearly for signs of wear or deterioration. Expiry dates on the tubes should be checked regularly. Shelf life is increased if the tubes are kept in a refrigerator. viii) Gauge Calibration: The cart gauges should be calibrated as specified by the manufacturer Important Performance Factors for Gas Carts When selecting gas carts, consider carefully these factors in your decision: 1. Pump rate expressed in SCFM –

A faster pump will pay off in reduced time required for maintenance tasks.

2. Pump limiting pressure ratio, usually in the range of 500:1–1000:1 –

Because the stored SF6 gas will be liquefied in the gas cart, the pressure ratio determines the amount of gas that will remain in the equipment and be lost when it is opened. For good systems, this loss is about 1%. To put that in perspective, every time a circuit breaker with 500 kg (1000 pounds) of gas is opened, the cost of gas lost in this step can exceed $100. Reducing the residual gas in equipment after evacuation also reduces the environmental impact.

3. Storage capacity –

Insure that the tank can hold all the gas from the largest breaker or GIS section it is likely to service. The tank should be ASTM certified and DOT compliant if serving multiple substations.

5-5

Handling Procedures

5.1.2 Filling with SF6 from a Gas Handling Apparatus Connect the gas handling apparatus to the gas enclosure valve of the equipment. Stainless steel hoses or stainless steel with Teflon lining hoses is recommended to minimize moisture contamination. The following operations should be performed: –

Initiate vacuum pumping and open the gas enclosure valve. Develop a vacuum of less than 0.1 kPa (1 mbar), hold vacuum by sealing off the SF6 enclosure and observe its leakage rate over a 2 to 3 hour period. An initial pressure rise prior to leveling off would indicate some moisture problem. A continuous steady pressure rise would indicate a leak condition.

–

Filling is done by transferring the high pressure SF6 in the storage vessel to the evacuated enclosure until the equipment rated pressure is reached or until pressure equalization occurs, then if necessary, the compressor is used to complete the process. It is recommended that the SF6 be circulated through a dryer and purifier prior to entering the gas enclosure.

–

During the filling process, the SF6 will be cooled by expansion as it leaves the storage vessel (it will also be heated up by a compressor) and is transferred into the enclosure. Therefore, the gas in the enclosure will be at a temperature different from ambient. Allow the temperature of the gas to stabilize (at least 12 hours) and check the filling pressure. Pr = Pn + P1 + P2 Where; Pr = Relative filling pressure Pn = Given pressure at a temperature of 20°C (68°F) and an atmospheric pressure of 101.1 kPa (14.70 psia). P1 = Pressure correction for temperature. P2 = Pressure correction for atmospheric pressure.

–

Moisture content should be checked after filling. The typical value of moisture is a dewpoint of -50°C (-58°F) at atmospheric pressure, corresponding to 40 ppmv.

–

O2 content may be checked after filling. The typical value of O2 content is between 500-1000 ppmv.

5.1.3 Filling or Topping up With SF6 from a Cylinder For small volume SF6 equipment and for topping up purposes, it may be more practical to fill the enclosure directly from certified SF6 cylinders instead of using a gas handling apparatus. 5-6

Handling Procedures

–

To facilitate the transfer of SF6 gas, the gas cylinder may be warmed by submerging in warm (about 40°C (100°F)) water to half of its height or by using a blanket heater of appropriate design. Heating also reduces the amount of residual gas in the cylinder.

Never use an open flame to heat the cylinder. –

Do not invert the gas cylinders to speed up the transfer of SF6, unless the filling apparatus is designed for this purpose (equipped with a gas warmer) and personnel are familiar with such a process. The gas cylinders may contain particulate metal oxides that can result in failures if transferred into the gas enclosure. In addition, by inverting the gas cylinders, liquid SF6 could be forced into the enclosure, which upon evaporation, will cause extreme localized cooling and can result in over-pressure. The pumps of gas carts are designed for transfer of gas and some can be damaged if liquid is passed through them. The full-capacity weight or pressure is stamped on the cylinder. The approximate quantity of gas in a partially filled SF6 cylinder can be best determined by weighing the cylinder and comparing it to the initial weight. It is necessary to establish the weight of the empty cylinder plus its valve assembly. Consult the manufacturer and, if possible, mark the cylinder. Caution: some cylinders are marked with their empty weight, but this may not include the valve. SF6 is commonly shipped in pressurized cylinders filled with liquid SF6:

Table 5-1 Weights of Typical SF6 Cylinder

Weight of SF6 gas

Cylinder weight

Total weight

52 kg

50 to 52 kg

102 to 104 kg

115 lbs.

110 to 114 lbs.

225 to 229 lbs.

Prior to topping up, all filling pipework, valves, etc. should be clean and dry. (purged with dry nitrogen or vacuumed)

5.2

Maintenance of Equipment 5.2.1 Normal Maintenance Functions 5.2.1.1

Pressure Measurement The gas pressure should be checked regularly. 5-7

Handling Procedures

–

three months after commissioning;

–

once a year after one year in service or longer depending on equipment type and operating experience.

– a record should be maintained of all pressure readings and of any gas additions to each piece of equipment. This will help with tracking losses. Where pressure drops indicate an SF6 leak, a portable leak detector should be used to locate the leak(s). An alternative is to use the EPRI laser camera – see section 5.2.1.3. While corrective action could be limited to occasional topping up with SF6, it is not desirable to let leaks continue. The dielectric strength of SF6 depends on the gas density in the enclosure and the purity. The gas density is approximately proportional to pressure. Any leak will reduce the gas density and thus reduce its dielectric strength. Typically, two stage pressure switches are provided to monitor pressure of the SF6. An alarm is given if the gas pressure falls to the first stage level of “minimum service pressure.” Should the pressure fall to the second stage level of “loss of SF6”, breaker operation will be blocked. 5.2.1.2

Moisture Measurement Moisture content should be checked approximately three months after commissioning. The regular maintenance interval recommended by the manufacturer should be followed until it is learned from experience how much this interval can be extended. Frequent moisture measurements are undesirable because the total volume of SF6 exhausted to make these measurements is significant. Newer techniques for gas assessment are being developed which reduce the volume of gas required substantially and are field portable. See section 5.3.5.

5.2.1.3

Leak detection It is advisable to check equipment regularly for leaks, especially if the pressure gauge indicates a drop or if refilling has been required. Leaks can be located by hand-held refrigerant detectors to determine the general area. “Sniffers” are capable of detecting Halogen gases, including SF6. If it is difficult to locate the leak, try wrapping the

5-8

Handling Procedures

suspect areas in plastic film held by tape to trap gas. When the general area is identified, follow up by the use of a soapy solution applied to suspect surfaces. Bubbles in the solution show the precise location. This procedure generally requires that the equipment be removed from service and can be tedious. A newer technique developed in collaboration with EPRI is to use a laser camera that can visualize the leaks of SF6 gas without requiring an outage. The laser camera can see leaks as small as will be economical to fix. The laser camera’s sensitivity can be so high as to cause problems when there is insufficient wind—a cloud of gas is evidence of a leak, but the exact site cannot be seen because the cloud obscures the leak site. In such cases, it is useful to use a small portable fan to provide some airflow. Because only observation from a distance is required, almost all leak surveys made with the laser camera can be conducted without removing the equipment from service. The far infrared wavelength of the laser presents no risk of eye damage despite the several watts of output. Utilities have the option of purchasing a laser camera or contracting for a service. Another emerging technique for SF6 leak detection involves detecting SF6 using a specially modified infrared camera. This technology is still in development and has yet to match the sensitivity of the laser camera. However, it does show one advantage in that it can be used in an open air substation without requiring a background. The laser camera requires a background to detect SF6 leaks, as the laser light generated by the camera needs to be reflected back to the observer. 5.2.2 Decontamination Refer to Section 6 for personal protective equipment to be used for the decontamination process. In the presence of corona or an electric arc and contaminants such as oxygen and moisture, SF6 will decompose to form gaseous and solid decomposition byproducts, which are toxic. Internal inspection of a breaker after a number of years of normal operation usually reveals a light coating of solid decomposition byproducts (metallic fluorides) at the bottom of the enclosure and on the interrupter mechanism exposed to the arc. These metal fluorides appear as a fine white powder and skin contact and inhalation should be avoided. During normal maintenance the gas should be reclaimed using a gas cart with field replaceable filter units, consisting of: a particle filter filtering particulate solids down to 1 micron, activated alumina (dried Al2O3) to remove moisture and a molecular sieve (such as 3A) to remove decomposition products. If there has been a fault, it is desirable to remove the fault gases through a scrubber filter upstream to the connection to a gas cart. To avoid cross contamination, separately 5-9

Handling Procedures

designated hoses should be used for gas removal where practical. Metal fluoride powders should be vacuumed with a HEPA rated vacuum cleaner with exhaust filter capable of removing particles down to 0.3 microns. The area should be wiped clean with suitable neutralizing solutions. Adequate ventilation must be maintained when cleaning with a solvent especially in confined areas such as inside a gas enclosure. The proper use of personal safety equipment is essential to any personnel being exposed to decomposition products and solvent vapors. Good ventilation prevents reduces solvent vapors in the work area. Powders removed from the apparatus as well as activated alumina filters should be disposed of in accordance with the Recommended Practices detailed in Section 7.3.2.

5.3

Analytical Procedures for SF6 Gas Assessment 5.3.1 SF6 Gas Content Measurements SF6 gas content measurement is not required for equipment filled with pure SF6 unless there is reason to suspect that prolonged leaks or mishandling have allowed air to enter the enclosure in more than trivial amounts. Ideally, routine laboratory analysis would be conducted before maintenance to check for decomposition products, after filling to check for quality and every two years thereafter for normally operating equipment. Where equipment is filled with blended gas for cold temperature application, SF6 gas content measurements may be performed in the field with velocity of sound measuring instruments or equivalent. With SF6 gas bled through the instrument at about 500cc per minute, a reading of the percent SF6 content can be obtained very quickly. Suspect gas should be sampled and analyzed by gas chromatography for confirmation. These instruments are calibrated for determining percent SF6 in air or nitrogen. Blends of SF6 with CF4 require a factor be applied to the reading to get an accurate result. Always check manufacturer’s instructions. Recommendations: Measure SF6 gas content in conjunction with moisture measurements during commissioning, also before and after each gas handling.

5.3.2 Moisture Content Measurements Moisture in SF6 gas promotes the formation of various decomposition byproducts. Water on solid insulators will reduce the flashover withstand voltage. It is therefore important to control moisture content in SF6 gas. Moisture seldom penetrates into a gas enclosure from outside. If the equipment is known to leak, there is a strong possibility of moisture migrating inside the 5-10

Handling Procedures

enclosure, the equipment should be checked for moisture content, and the leak located and repaired. Moisture inside enclosures is often absorbed and trapped in solid insulators before the enclosure is sealed and filled with gas. This moisture will slowly degas in the dry SF6 atmosphere and is usually absorbed by internal dessicants. An instrument with a silicon or aluminum oxide sensor can be used to measure moisture content. The purging feature of the instrument provides a fast response time. The instrument is sensitive to oil contamination, therefore, a slow purge response indicates sensor contamination. The sensor is temperature dependent, so an instrument to be used outdoors should be equipped with a temperature compensated sensor. “Chilled mirror” (electronically chilled) devices are now available and appear to be less susceptible to damage or calibration shifts from SF6 gas byproduct contamination. About 500cc per minute for 5-30 minutes (depending on the sensor) should be bled through the instrument at atmospheric pressure. Most manufacturers specify moisture levels in ppm by volume, which can be read directly on the instrument scale only at atmospheric pressure. Measurements performed at elevated pressures must therefore be read in dewpoint and converted to ppm if required. Recommendations: Measure moisture content before, after gas handling, and during commissioning. Repeat moisture measurements after one year of service. If the readings are within rated limits, no further moisture measurement is required for approximately another 5 years unless significant leaks occur. Use upper limits provided by individual manufacturers. Any SF6 equipment which is evacuated at a temperature less than 10°C (50°F) may have moisture frozen inside the enclosure. It should be subjected to moisture testing once the temperature exceeds 10°C (50°F) when the any ice present changes to moisture vapor. These tests should be repeated monthly, during warmer temperature when accurate verification of moisture content can be undertaken.

5.3.3 Oxygen Content Measurements SF6 may become contaminated with air during gas transfer operations. The most common problems are leaks in transfer hoses, connections and fittings while operating at below atmospheric pressure. The oxygen content of SF6 gas may be used as an indication of air contamination. (Air is approximately one fifth oxygen with most of the remainder nitrogen.) Measurements of oxygen content in SF6 gas may be performed in the field with various instruments. 5-11

Handling Procedures

For example, a trace oxygen analyzer that makes use of a fuel cell can measure oxygen content concentrations of 1 ppm to 10,000 ppm with SF6 gas at atmospheric pressure bled through the instrument at about 500cc per minute. A stable reading is obtained very quickly. The instrument is calibrated with atmospheric air. The fuel cell has a typical life of about one year, depending on the amount of oxygen exposure. Erratic readings of the instrument mark the end of fuel cell life. Proper gas handling procedures will ensure oxygen content levels below 500 ppm in new equipment. Unless otherwise specified by a manufacturer, oxygen content of in-service equipment must not exceed 6,000 ppmv (about 0.6% oxygen or 3% air). Recommendations: Use a portable trace oxygen analyzer as a diagnostic tool to determine the extent of air contamination in SF6. Use in conjunction with SF6 gas content measurements (see 5.3.1).

5.3.4 On Site SF6 Decomposition Products Detection Various disposable indicator tubes are available for field detection of SF6 decomposition products. In use, a fixed amount of gas is passed through the tube. The presence of decomposition products causes discoloration of the tube packing material. The length of discoloration along the tube corresponds to the concentration of decomposition products. EPRI sponsored research has resulted in the development a prototype portable SF6 Decomposition Products Detector (DPD). The major application of the DPD is to provide a quick and accurate measurement of SF6 decomposition products in field situations. This instrument is portable, rugged and easy to operate and is able to handle sampling from energized equipment at system pressure. It is advantageous to test the gas at the source due to the unstable nature of low level decomposition products and to detect faults quickly without having to wait for lab analysis. With this detector, rapid screening of SF6 is possible to quickly locate problems and minimize outages. Personnel safety can also be rapidly assessed before maintenance begins so that appropriate procedures and precautions can be implemented. Recommendations: Check decomposition products content with a portable detector or with indicator tubes when there is reason to believe abnormal impurities exists. Filtration of the gas is required if any decomposition products are detected. Appropriate safety and handling procedures must be followed. (See section 4) Check decomposition product content again before gas is reused. Refer to “Reactivity and Toxicity of SF6 Decomposition Products” chart in Appendix 1. 5-12

Handling Procedures

5.3.5 Multiple Component On Site SF6 Gas Assessment Multiple component detection involves using one instrument for detection of all components. Portable gas chromatography is the most obvious option. The best muticomponent detection method found in ongoing work sponsored by EPRI was a portable micro gas chromatograph. This instrument was customized for this application. One analysis was required to get all the necessary results for evaluation of SF6. Sample volumes required for the actual analysis are in the order of microliters (10-6 liters), the major losses of SF6 arising from sampling is in the volume of the sampling lines. Short, one-sixteenth inch O.D. stainless steel sampling lines are used. With a sampling time of 30 seconds at a sample gas flow rate of 50 to 100 cc/min, the volume of gas required for purging and analysis is less than 50 cc. This is equivalent to less than one gram of gas. In comparison, routine moisture measurements using hygrometers can consume up to fifteen liters of gas, this equates to approximately one hundred grams of gas. Routine sampling of SF6 using a typical150cc sample cylinder requires flushing of the cylinder and sampling lines (usually twice) and consumes approximately 15 grams of SF6 for each gas compartment. By using a high pressure sampling manifold attached to the inlet of the micro gas chromatograph (maximum pressure of 500 psig), direct sampling from SF6 equipment and from SF6 cylinders and pressurized tanks containing up to 35% air (any higher air content results in a gas mix with a pressure greater than 500 psig) can be performed. Sampling and analysis can be done without the need of a pressure regulator. A frit is in-line at the sample gas inlet to remove particulates and, to a certain extent, oil. There is also provision for collecting the possible 100 cc of gas that is vented for sampling and purging of sample lines. Field operation is straightforward and the software prints or displays a report giving the results in ppmv or %v in a simple report. The following table summarizes the results using this instrument. This method of SF6 gas assessment is able to meet CIGRE criteria for in service gas. For complete SF 6 gas assessment to criteria for new gas, this in combination with the decomposition products detector (DPD) described earlier is required. This is due to the lower limits of decomposition products required for new gas.

5-13

Handling Procedures Table 5-2 Micro GC Multicomponent Detection

Component

Detection Limit

Expected Levels

Comment

(ppmv)

(ppmv)

SF6

<50

50-100%

Usually >95%

CF4

<50

0-4,000

Up to 50% for SF6/CF4 blends

O2

<50

0-20,000

N2

<50

0-100,000

Up to 50% for SF6/N2 blends

H2O

Not determined

0-2,000

Estimated 50 ppmv detection

SOF2

10

0-200

Dominant byproduct

SO2F2

Not determined

0-200

Interference from SF6

COS

10

0-100

Generally low levels

SO2

Approx. 50

0-200

Difficult to detect below 50 ppmv*

* Difficulty in low level detection due to adsorption in lines and columns

5.4

Equipment Failures 5.4.1 Types of Failures During an electric arc in SF6 equipment, the predominant proportion of the arc energy is used to heat up the SF6 gas. This heat will cause the pressure of the gas to increase. The most common method used to limit the pressure in SF6 equipment is by installing pressure relief devices. Pressure relief devices are designed to rupture at a pressure much lower than the withstand capability of the enclosure. If the pressure relief device ruptures, or if there is a burn-through of the enclosure, large quantities of SF6 arc products will be released into the air. There are safety hazards in such cases and it is important to observe proper procedures near any such occurrence; see below.

5-14

Handling Procedures

5.4.2 Exposure to Decomposition Products If SF6 arc decomposition products are detected by smell and/or irritation, the area or building should be evacuated and the re-entry procedures detailed in Sections 4.7.2 and 4.7.3 should be followed. Solid (dust) decomposition products react vigorously with moisture. Contact with the human body must be avoided. It is particularly important to avoid dust contact with the nose, eyes and mouth

5.4.3 Cleanup Procedures—In a room or enclosed space 1. Use protective clothing as detailed in 6.2 and the appropriate safety equipment as detailed in 6.3. No personnel should enter without respirators until SF6 concentration is below 20 ppmv (see Safe Working Environment Chart in Appendix C). 2. Enter and locate the point(s) of burn-through or rupture of the enclosure. 3. Clean up the deposits, if in powder form, using a high efficiency vacuum cleaner equipped with a HEPA filter, otherwise use lint-free rags to wipe off deposits. (See 5.2.2.) The rags can be moistened with isopropyl alcohol, but separate rags should be used for metal and insulating areas. It is better to do this as quickly as possible since exposure to the moisture of the air will begin chemical reactions, making the deposits more harmful and more difficult to remove. 4. Force ventilate the room or enclosed space with a fresh air blower. 5. Treat contaminated clothing, tools and other material as detailed in 7.3.2. 6. Decomposition products can compromise the surface dielectric strength of insulators. If nearby equipment has been exposed, the insulating surfaces should be wiped and washed with soapy water followed by a thorough rinse with water.

5.4.4 Cleanup Procedures—Outdoors 1. Use protective clothing as detailed in 6.2 and the appropriate safety equipment as detailed in 6.3. 2. Clean up the deposits, if in powder form, use a high efficiency vacuum cleaner equipped with a HEPA filter; otherwise use lint-free rags to wipe off deposits. (See 5.2.2) The rags can be moistened with isopropyl alcohol, but separate rags should be used for metal and insulating areas. 3. Wash the outside area surrounding the release with water.

5-15

Handling Procedures

4. Treat contaminated clothing, tools and other material as detailed in 7.3.2. 5. Decomposition products can compromise the surface dielectric strength of insulators. If nearby equipment has been exposed, the insulating surfaces should be wiped and washed with soapy water followed by a thorough rinse with pure water.

5.4.5 Cleanup Procedures—Washrooms Such measures as constructing dedicated washrooms at the substation facilities or storing large volumes of water at the worksite during breaker maintenance have been proposed for rinsing a worker’s body in the event of coming in contact with any faulted SF6 or its toxic byproducts. These measures are not only costly but also impractical, and may not be environmentally sound. Discussion: Having a dedicated washroom at the substation facility may not be feasible or practical because of the following reasons: 1. A dedicated washroom will most likely be located a far distance from the location of the breakers, making its use inconvenient and difficult during an emergency. 2. A water source is not always available at the substation facility and providing such a source may be very costly, if not prohibited. Transporting a large volume of water to the worksite using a tanker or tank trailer is not very practical or safe because of the following reasons: 1. Additional personnel will be required to transport the water to the worksite and depending on the location of the worksite, transporting the water poses additional risks to maintenance personnel. 2. Locating a large water container near the breakers may not be possible due to the spacing limitations and/or reduced electrical clearances around the equipment. 3. The disposal of the water, whether used or not, may be a problem because of the drainage system and/or the environmental surroundings of the substation facility. 4. Having a small portable eyewash, such as that used in battery rooms, at the worksite for emergency use is more convenient and practical.

5-16

6 PERSONAL PROTECTIVE EQUIPMENT

Persons working with SF6 should avoid possible hazards by recognizing the risks described in Section 4, by following the handling procedures described in Section 5 and by using protective clothing/devices recommended in this section. The degree of personal protection required when working on SF6 equipment is dictated by the type of work being undertaken and by the conditions likely to be encountered inside the SF 6 enclosure. These conditions will be dependent upon the type of equipment housed inside the enclosure in question and on the service history of the equipment. Non-switching equipment enclosures (e.g. bus ducts) will likely contain only uncontaminated SF6. Enclosures containing switching equipment such as circuit breakers and disconnect switches may contain mildly contaminated SF6. Nevertheless, any enclosure, regardless of whether it contains non-switching or switching equipment, in which a power fault has occurred or has experienced partial discharges over a period, will contain decomposed SF6 and these decomposition products should be treated with caution.

6.1

Purposes of Protective Clothing and Devices The solid decomposition products produced during an arcing fault are generally very fine particulates, with approximately 70 percent of the dust particles being below 5 microns (0.0002 in.) in size. The major components of the solid decomposition products are copper and aluminum fluorides and tungsten oxide. The amount of powder produced will depend on factors such as the electrode material, the arc energy, duration and behavior. The small particle size provides a large surface area onto which the arced gases can adsorb. Both the arced gases and the solid dust particles can be very irritating to the skin upon contact. In the absence of ventilation in an indoor building, the very small decomposition particles can float in the air for a considerable period after their release into the ambient air (two hours or more). Workers potentially exposed to these gaseous and/or solid SF6 decomposition products will require clothing and devices for protection from these contaminants. (See Appendix B for a sample list of safety/protective equipment).

6-1

Personal Protective Equipment

6.2

Protective Clothing 1. Protective clothing to cover skin should be worn by all personnel who are required to perform any of the following: –

remove and handle solid SF6 arc byproducts,

–

enter a building where a fault has occurred and solid byproducts have been ejected into the ambient air (burn through or bursting disc operation),

–

work with solvent cleaning,

–

generally, anyone entering the building within the first four hours of a fault releasing SF6 byproducts into the ambient air.

2. The protective clothing should include:

6.3

–

pocketless, hooded, coated polyester or paper disposable coveralls, having elastic ankle and wrist grips, overlapping protective footwear and gloves

–

protective footwear

–

industrial type rubber gloves, preferably manufactured from nitrile or neoprene rubber or chlorinated polyethylene (CPE), shall be worn and securely taped to the coveralls

–

chemical type, acid resistant industrial goggles for eye protection.

Respiratory Devices 6.3.1 Dust Mask Generally, after the building ventilation system(s) have been operating for four hours, the concentration of gaseous and solid contaminants released into the air by a fault will have dropped to a level where minimum respiratory protection is adequate. In this situation, a HEPA rated dust mask is sufficient. Any detected odor from decomposition products and a cartridge filter is required.

6.3.2 Cartridge Filter Mask Either a full face dual cartridge or a half face dual cartridge air purifying respirator, with combination HEPA, acid gas and organic vapor cartridges, is appropriate for intermediate to high risk situations. (re: section 4.3 and 4.4) A full face respirator is superior to a half face respirator because it provides eye protection and has a higher protection factor. Because of their natural moisture, the eyes are especially vulnerable to damage from SF6 arcing byproducts. Workers should be alert to stinging of their eyes, which might indicate a problem.

6-2


Due to the requirements for cleanliness in SF6 insulated equipment, most components need to be cleaned with solvents before returning the equipment to normal service operation. Workers should wear an organic vapor cartridge mask to protect their respiratory system from the solvent vapor generated during the cleaning process. For inspections, cleaning of the compartment after initial vacuuming, and for working in a ventilated location for a short period, the use of a half face cartridge mask will provide adequate respiratory protection. Always maintain good ventilation in the workplace. Especially when using solvents, a poorly ventilated workplace might require an air supplied respirator. Always inspect a mask after use and restore it to proper condition or replace it. There will be no time for this following the next incident.

6.3.3 Supplied Air Respirator Complete respiratory protection should be used during initial vacuuming of heavy concentrations of solid particles in a faulted enclosure, when working around enclosures where the faulted gas cannot be removed (for example, where a burnthrough has occurred), and when working in an enclosed area where prolonged arcing has taken place and the ventilation is poor. Generally, everyone who is required to enter the building within the first four hours following the occurrence of a fault, which resulted in the release of SF6 byproducts into the ambient air, should have complete respiratory protection. This level of protection can be obtained using an air supplied respirator with a full face piece operated in a pressure demand or other positive pressure mode, such as with a compressed air source.

6.3.4 Self-contained Breathing Apparatus (SCBA) Self-contained, pressure demand breathing apparatus (e.g. Scott Air Pack, MSA401 etc.) should be worn by all personnel entering the building under special emergency conditions such as: –

during fire fighting;

–

entrance into an indoor substation in which a major burn through or pressure relief device operation has just occurred and where solid and gaseous SF6 decomposition products ejected into the ambient air remain high in concentrations;

–

emergency re-entry into an indoor substation to rescue personnel who are unaccounted for following an evacuation order.

6-3


Only personnel trained in the use of SCBA should respond to the emergency conditions described above. No one should enter the indoor substation alone under these circumstances. If the wearer engages in strenuous work, the actual time useful for breathing with SCBA will be less than the estimated time. Always inspect SCBA after use and restore to proper condition or replace. Inspect at regular intervals (one year suggested) if not used. There will be no time for this following an incident.

6-4

7 DISPOSAL AND ENVIRONMENTAL PROTECTION

7.1

Clean SF6 Gas 7.1.1 Impact on Environment Clean SF6 gas released into atmosphere has only a minor impact on the environment for the following reasons: 1. It does not contribute to ozone destruction. 2. It contributes less than 0.1 percent of the total greenhouse effect caused by man-made gases such as CO2, O3, CH4, H2O and the CFC’s. However, SF6 is chemically extremely stable and therefore has a long atmospheric lifetime. Consequently, when released to the atmosphere, accumulations remain for long periods. To keep the atmospheric concentration of SF6 from rising too fast and becoming a significant contributor to global warming, the international electrical community is recommending that SF6 in electrical equipment should be reclaimed and recycled to the extent that is economically feasible. [4] In the USA, the EPA has begun a voluntary program aimed a reducing the release of SF6 gas (See Appendix 7.)

7.1.2 Recommended Practices 1. Federal and state or provincial regulations on release limits must be observed. Deliberate release of SF6 gas during equipment maintenance, repair, or decommissioning should be avoided. Release should be limited to the minimum amounts necessary for testing and measurement purposes. All reasonable and economic effort should be made to prevent release and to reclaim SF6. EPRI is sponsoring work aimed at SF6 release abatement during sampling where the gas vented during sampling is collected and recovered. Venting from sampling is greatest during moisture measurements using conventional hygrometers where up to 0.1 kg of gas may be vented. Emerging techniques such as the portable gas chromatograph (see section 5.3.5) will greatly reduce these emissions.

7-1

Disposal and Environmental Protection

2. Equipment routine leakage should be kept as low as possible. 3. New SF6 applications should be introduced only if they are designed for recycling gas.

7.2

Contaminated SF6 Gas 7.2.1 Impact on Environment Toxic gaseous SF6 decomposition products, which are released to the atmosphere, react with moisture and oxygen and are transformed into more stable and less toxic substances. The same substances are produced in much higher quantities by industrial processing and fossil fuel burning. The concern about releasing SF6 decomposition products into the atmosphere is of a localized nature.

7.2.2 Recommended Practices 1. Contamination that occurs under normal operation of equipment constitutes the overwhelming majority of all SF6 contamination. This includes SF6 gas that is mixed with N2 or CF4 gas for use in blends and SF6 that has become contaminated with air and moisture. SF6 containing only small amount of gaseous and solid decomposition products should be reclaimed. It can be reprocessed for reuse. Most recovering equipment have filtering system returning the SF6 to a reusable state. CIGRE recommends that gas put in switchgear have less than 2% air and that subsequently the air level should not exceed 3% [12]. If the air content is too high for normal recycling, the gas can be shipped to a purification center, which can reduce the air content to a very low level. Appendix 5 gives some details on commercial options for cleaning gas. 2. Contamination, which occurs under abnormal operation of equipment, may result in gas that is too heavily contaminated to be reprocessed on site. In this case, the contaminated gas should be evacuated into a storage vessel and held in storage until it can be shipped to a purification center (Appendix 5) or disposed of in a safe manner. 3. Release of SF6 decomposition products should be limited except as necessary for testing and measurement purposes. Large volume releases such as those that result from an equipment failure may be classified as a “reportable spill” by local regulations. Released decomposition products must be mixed and diluted with a sufficient quantity of atmospheric air to reduce their concentration to a safe level. 4. In order to determine the amount of SF6 in a cylinder, weighing the contents is the most common method. If any liquid exists in the cylinder (even if the gas is contaminated with air or nitrogen), the majority of the weight of the 7-2


contents will be SF6. The pressure inside the cylinder can give an indication of the air or nitrogen content. A cylinder containing pure SF6 will have a pressure equal to the vapour pressure of SF6 at that temperature (2.1 MPa at 20°C.). As the air or nitrogen content increases, so does the pressure in the cylinder. If the air or nitrogen content is high enough (typically when SF6 content is about 62%v), conventional compressors will be unable to liquefy the gas. To determine the weight of SF6 in a cylinder containing gas that cannot be liquefied, the weight of the gas in the cylinder will need to be multiplied by a factor that is calculated from the percent by volume SF6. The following formula gives the “weight factor” that needs to be multiplied by the total weight of the gas to get the weight of SF6. The following is only valid for cylinders containing air or nitrogen contaminated SF6 and no liquid SF6. Weight Factor =

(%vSF6) × 146 ((%vSF6) × 118) + 2800

Where: %vSF6 = percent by volume SF6 (see section 5.3.1) For example, 50.0%v SF6 gives a weight factor of 0.839 and if the cylinder has fifteen pounds of gas, 12.6 pounds is SF6 (0.839 x 15 pounds). Always check the condition of the gas in the enclosure before taking any other actions. 7.2.2.1


The air content in the tank or cylinders in the gas cart will increase slowly over time due to inevitable air ingress from constant handling. Recycling of high air contaminated gas requires removal and shipping of the gas to some recycling facility. SF6 gas can be classified according to the degree of contamination. New gas, non-arced gas, normally arced gas, and heavily arced gas (>200 ppm decomposition products) [13]. Usually only the heavily arced gas cannot be reclaimed by gas carts. Filter maintenance in gas carts is essential after handling any arced gas. Technologies using semipermeable membranes are emerging as alternatives to large, expensive SF6 gas recovery systems. These may be more suitable to SF6 gas with high air content and SF6/N2 blends. As these modules require only a flow of the gas through the membranes, they could easily be plumbed into a gas stream resulting in significant energy savings compared to cryogenic methods of purification. Other advantages include treatment on site or at a utility central SF6 handling site. Savings in terms of shipping and compliance with transportation regulations is also realized. 7-3


The advantages of such a system include operation at room temperature and moderate pressure (<150 psig), energy efficiency (require no power to operate), scalability to any size (multiple modules), and ease of incorporation into gas carts. They are particularly suitable for purifying SF6 with high air content and for SF6/N2 blends. Recovery of SF6 with these modules can be easily incorporated into existing gas handling procedures. Gas carts should not be relied upon to remove air from SF6. Other technologies under development use pressure swing adsorption or a combination of membranes and pressure swing adsorption. Many utilities are establishing central SF6 handling facilities that will not only monitor consumption and quality assurance but also maximize recovery of used (and new) gas. Depending on temperature, new cylinders have much more residual gas in them at atmospheric pressure and low temperature than they do at atmospheric pressure and high temperature. Recovery of this residual gas is fiscally prudent but may lead to air contamination during handling, as vacuum is required for recovery. Simple adaptation of these modules to gas handling equipment at these facilities will allow on site recovery and purification of gas collected from in service and decommissioned GIS equipment. Scrubbers for oil, moisture and decomposition products are readily available and widely used but field methods for removal of air from SF6 are not.

7.3

Solid Decomposition Products 7.3.1 Impact on Environment Solid decomposition products are powders with very small particles that tend to float in atmosphere for a considerable time (two hours or more). They are chemically toxic and are acidic when combined with moisture. The impact is usually of a localized nature and as with gaseous decomposition products, will dissipate and react with the oxygen and moisture in the air. 7.3.2 Recommended Practices (Refer to [1] in Section 8) 1. Disposable Material Collect disposable material such as dust, absorbers (desiccant) and rags in double plastic bags for treatment. Empty the contents into a barrel and submerge the material and the plastic bags in neutralizing fluid (see Appendix 4). Leave this for at least 24 hours. The solid waste has now been neutralized and can be disposed of in a landfill.

7-4


Used neutralizing fluid should be disposed according to local regulations, for example, by pouring into sanitary sewer or, in remote areas, to ground. Applicable municipal sewer use by-laws and state or provincial water discharge standards should be consulted prior to discharging neutralized wastes in order to ensure compliance. 2. Non-Disposable Material and Clothing Place the material and clothing in a container ensuring that they are well covered in neutralizing fluid. Allow them to stand for at least one hour in this liquid, poking with a rod if necessary to ensure that the solution reaches all contaminated parts. Following the neutralization the clothing may then be removed, rinsed thoroughly in clean water and laundered in the normal way. The neutralizing solution and the rinsing water can be disposed of in the sanitary sewer according to local regulations. 3. Tools Tools such as a vacuum cleaner should be washed in a neutralizing solution and thoroughly rinsed with water. 4. Neutralizing Solutions Refer to Appendix 4 for choosing and preparing neutralizing solutions.

7-5

8 TRANSPORTATION AND STORAGE

Suppliers of SF6 gas should be aware of pertinent regulations involved in shipping cylinders to customers. Electric utilities need to be aware of regulations and appropriate precautions for moving gas carts containing gas from one substation to another.

8.1

US Dept. of Transportation (DOT) Regulations There are elaborate U. S. federal regulations covering rules for transporting materials that are hazardous or pressurized. Most significant for substation equipment maintenance people are the segments relating to highway transport. The pertinent portions of the Code of Federal Regulations (CFR) are found in Volume 49 and you may see such citations as: CFR 49, 173 meaning part 173 within volume 49. The government prefers the citation version: 49 CFR 173.1 for the first section of part 173.

http://mcregis.fhwa.dot.gov/regtoc.htm is the appropriate web site for reading the Federal regulations regarding motor vehicles. It appears that the entire volume is posted at this site, but it can be difficult to follow the intricate citations, references and incorporations by reference while reading from a computer screen. “CFR 49, Parts 100 to 185” can also be purchased in hard copy (paperback book) from US Government printing offices, which are located in major cities for $50 each. This is a thick book with intricate cross-references and the hard copy is recommended for those who become more than superficially involved. Below are some citations to sections of the CFR 49 followed by our interpretations of what is required. EPRI can make no claim or warranty that this is accurate. 172.101 contains a table listing SF6 as a hazardous material (pg. 222) and putting it in hazard class 2.2 172.101 Appendix A contains a table listing hazardous substances, which have reportable quantity (RQ) ratings. SF6 does not appear in this table, so references to RQ regulations within CFR 49 do not apply. 173.304 contains a table listing SF6 gas and limiting the gas pressure in proper cylinders to the maximum pressure which would produce a density of contents 20% greater than filling the cylinder with water. At 15°C (60°F), one pound of water occupies 27.74 cubic inches, so a user is not allowed to exceed a density of one pound of SF6 per 23.12 cubic inches in an approved cylinder. 8-1

Transportation and Storage

173.301-d-1 allows several approved cylinders to be manifolded together provided each cylinder also has an individual valve. 173.6,a.2 allows exception from other regulations for chemicals defined as “material of trade” provided the amount and pressure of these materials does not exceed defined limits. As a division 2.2 material, SF6 is limited to a cylinder whose gross weight does not exceed 100 kg or 220 pounds or, if a permanently mounted tank (i.e. a recycling cart) meeting ASME standards is used, the tank capacity is not to exceed 70 gallons if the gas is not liquefied. 173.6.c.4 requires that the operator of a motor vehicle carrying material of trade must be informed of the fact and what his material is and what regulations are involved 173.34.d provides a table listing the retest period for pressure cylinders 173.115.d gives a definition of liquefied compressed gas that includes SF6 in many cases 173.315 give regulations for cargo tanks and portable tanks carrying SF6 gas. SF6 is not individually listed in the table of this section, but is covered by the line, “Division 2.2 materials not specifically provided for in this table” Comment: If you have tanks, which are ASME rated, but are not DOT approved, the proper procedure is to remove SF6 gas and put it in a local storage tank before driving the cart to another substation by highway. Gas suppliers prefer that you have a dedicated storage tank for this purpose rather than using a cylinder they have supplied because of the possibility that recycled gas contains contaminants.

8.2

Cylinder Transportation and Handling Cylinders must be securely lashed in an upright position or loaded into racks securely attached to the vehicle or packed in boxes or crates of such dimensions to prevent their overturning, or securely loaded in a horizontal position. Transport in accordance with Federal, State or Province, and local regulations. Cylinders are extremely heavy. Workers must use caution when handling them. Hoses, valves, gauges, and fittings will be regularly inspected and kept in good working order. The following precautions shall be observed while storing, transporting, or handling the cylinders:

8-2

(1)

Use mechanical lifting devices, such as cranes and dollies.

(2)

Do not lift by the protective cap, drop, throw, or roll. After securing the protective cap, the cylinder may be lifted from a horizontal position to a vertical position by the bottleneck or using a lifting device.


(3)

Store away from a direct source of heat, including direct sunlight, to avoid dangerous pressure from developing. Do not allow cylinders to be subjected to the temperatures above 120° F (49°C).

(4)

Store in an area free of exposure to flammable material.

(5)

Store with protective cap on and in an upright and secured position.

(6)

Do not store on damp ground or in contact with moisture.

(7)

Do not slam cylinders together or against other solid objects.

(8)

To prevent contamination, do not add unfiltered gas to cylinders.

(9)

Always keep the protective cap in place when not in use or during transportation.

(10) Identify a leak using gas detecting devices. (11) Defective cylinders should be marked “DEFECTIVE” and returned to the supplier. (12) Check cylinder labels for contents before using. Color coding used by vendors may vary. (13) Always direct cylinder openings away from personnel when opening a valve. Open valves slowly. Never test for pressure by placing body parts in front of a valve. (14) Personnel should not manipulate safety devices on valves and cylinders unless they are qualified to do so. (15) Cylinder contents should not be changed, gases mixed, cylinder colors changed or lettering removed without proper authorization. (16) Use of a direct flame to raise the gas pressure of a cylinder is prohibited. (17) Cylinders should never be allowed to come into contact with electrical circuits or direct flames. (18) Always close cylinder valve and relieve the pressure on regulators when they are not to being used for any extended length of time. (19) A positive pressure should be left within the cylinder at all times. (20) Use regulators with cylinder when connecting to containers of lower pressure ratings. Only regulators approved for specific gases should be used.

8-3


8.3

Cylinder Storage A. All cylinders should be stored in a safe, dry, well-vented place that is not exposed to direct sun. B. Flammable substances should not be stored in the same area as flammable gases. C. Cylinders should be stored on a level, fireproof floor in the vertical position and each cylinder secured with a restraining device so it cannot fall over. D. Cylinders containing different gases should not be intermingled. E. Never store cylinders near a source or potential source of heat. Cylinder steels are not to be subjected to temperatures below -29 °C (-20°F). F. Valves on all cylinders not in use should be kept closed. Caps should be installed on cylinders so equipped.

8-4

9 REFERENCES

1. G. Mauthe, K. Pettersson et al, “Handling of SF6 and its Decomposition Products in Gas Insulated Switchgear (GIS), 1st and 2nd Part”. CIGRE Working Group (WG) 23.03. Electra, No. 136 and 137 (1991) 2. Analysis of Gaseous SF6 Decomposition Products. Canadian Electrical Association. N. Dominelli. 1986 3. Concept of the Reuse of SF6, Published by Dilo and Solvay. 4. SF6 and the Global Atmosphere, G. Mauthe, K. Pettersson et al. Members of CIGRE WG23.10 Task Force 01. 5. L. Niemeyer and F.Y. Chu, “SF6 and the Atmosphere”, IEEE Transactions on Electrical Insulation. Vol. 27 No. 1 p. 184-187 (Feb. 1992) 6. The Use of Sulphur Hexafluoride (SF6) Gas in High Voltage Switchgear and Controlgear, IEC 1634. 7. Allied Chemical Manual on SF6, Allied Chemical Corporation, (1973 and 1976). 8. KC—Sulphur Hexafluoride (SF6), KALI-CHEMIE AG, Hanover (Germany). 9. The Use of Sulphur Hexafluoride (SF6) as an Arc Quenching Medium in Circuit Breakers for Medium Voltages, BBC Brown Boveri (Publication No. CH-A 555270 E). 10. E. Berthold Ganger and A. A. Leibold, “The Influence of Foreign Particles on Dielectric Strength in SF6 Installations”, Paper No. A 76 152-9 presented at the IEEE PES Winter Meeting, New York, NY, January 25-30, 1976 11. Investigation of S2F10 Production and Mitigation in compressed SF6-Insulated Power Systems. Final Report, Volume 1: Executive Summary. October 1995. Sponsored by Cooperative Research and Development Agreement (CRADA) Number ORNL 90-002, between BPA, CEA, EPRI, OH, HQ, DOE of US and five other organizations. 12. SF6 Recycling Guide, Re-Use of SF6 Gas in Electrical Power Equipment and Final Disposal Guide 117, International Conference on Large High Voltage Electrical System (CIGRE) Task Force 23.10.01. 13. SF6 Handling Guide for Switchgear, version 04. ABB T&D High Voltage Switchgear SF6 Recycling Team, Greensburg PA, 2000 14. CIGRE Guide for SF6 Gas Mixtures. Application and Handling in Electrical Power Equipment. ABB Corporate Research Center, Baden, Switzerland

9-1

A REACTIVITY & TOXICITY OF SF6 DECOMPOSITION PRODUCTS Table A-1 1 Reactivity & Toxicity of SF6 Decomposition Products (DP) DP2

Chemical Stability in the Atmosphere

Stable End Products

Smell Detection5 threshold

Toxicity Data [ppmv] TLV3

LD504

[ppmv]

odor

S2F2

fast decompose

S.HF.SO2

0.5

pungent, acrid

SF2

fast decompose

S.HF.SO2

5

pungent, acrid

SF4

fast decompose

HF.SO2

0.1

pungent, acrid 6

SOF2

slow decompose

HF.SO2

0.6...1

SOF4

fast decompose

SO2F2HF

0.5

SO2F2

stable

SO2F2

5

2000-4000

none

SO2

stable

SO2

2

ca 100

0.3-1

pungent

HF

stable

HF

1.8...3

50-100

2.0-3

acrid

WF6

fast decompose

WO3.HF

0.1

50-100

acrid

SiF4

fast decompose

SiO2HF

0.5

50-100

acrid

stable

CF4

non toxic

CF4 AlF3

7

stable

FeF2

7

CuF2

7

stable stable

AlF3 FeF2 CuF2

100

0.1-0.01

rotten egg acrid

none 3

none

3

none

3

none

2.5 mg/m as fluoride 2.5 mg/m as fluoride 2.5 mg/m as fluoride

1) This table was extracted from a draft CIGRE 23-03 Working Group document (Reference [1], Annex F) and expanded to include metal fluorides. 2) S2F10 is not included because the generated amount in a fault is negligible and its contribution to the overall toxicity of SF6 decomposition has not been substantiated. 3) TLV—threshold limit value of the non-decomposed gas for 8 hours daily exposure (MAK = German equivalent of TLV. The range of values indicates differences between different countries) 4) 50% lethal dose for mice or rats after 60 minutes exposure 5) Smell characteristics refer to the underlined gas(es) 6) Estimated odor threshold range. 7) Solid decomposition produced according to enclosure material.

A-1

B RECOMMENDED EQUIPMENT FOR PERSONAL PROTECTION

Recommended Equipment for Personal Protection1 Depending on the installation, the work to be carried out, the quantity of SF involved and the 6 expected degree of decomposition of the SF6, some or all of the following equipment should be available: a) Protective clothing. Pocketless, hooded, non-permeable industrial grade white polyethylene disposable coveralls with elastic ankle and wrist grips, overlapping the footwear and gloves. b) Overall type protective footwear. c) Industrial type rubber gloves, preferably nitrile or neoprene, for skin protection. It is to be noted that heavy gloves reduce the ability to work effectively with small parts, therefore, double layer of latex or polyethylene disposable gloves such as medical type will be more appropriate. d) Chemical type, acid resistant industrial goggles for eye protection. e) Fibrous cup like dust masks, with HEPA designation, to cover mouth and nose for light duty respiratory protection. f) Half face or full face dual cartridge air purifying respirator, with combination HEPA, acid gas and organic vapor cartridges, for intermediate duty respiratory protection. g) Full face supply air respirator for heavy duty respiratory protection. h) Self-contained pressurized breathing apparatus for the highest degree of respiratory protection. i) Normal industrial first-aid equipment including eyewash equipment containing a saline solution. j) An SF6 detector capable of detecting 20, 200 and 1000 ppmv SF6 in air. 1

Adapted from IEC 1634 (Reference [6], Annex E).

B-1

Recommended Equipment for Personal Protection

k) Equipment for forced ventilation of enclosed spaces and other inaccessible areas, e.g. cable trenches/ducts, SF6 chambers etc. Such equipment may be portable or permanently installed, depending on the size of the installation and must be of sufficient capacity to ensure that satisfactory working conditions, as recommended in the relevant sections of this Guide, can be maintained. l) A dedicated vacuum cleaner, equipped with a HEPA designated filter capable of trapping particles in the sub-micron range, and a non-metallic open ended nozzle.

B-2

C SAFE WORKING ENVIRONMENT CHART

Safe Working Environment Chart 1 When working with SF6, it is necessary to ensure that the concentrations of decomposition products, possibly toxic, remain at safe levels in the work area. Ideally, these concentration levels could be verified by direct measurement using a variety of disposable indicating tubes or specific detectors, ideally one for each decomposition product. See Section 5.3.4.A more practical alternative is to measure the SF6 in the air with a low cost, battery powered, and portable detector capable of sensing SF6 down to 10 ppmv. This is an indirect method which uses estimated quantities of SOF2, SO2 and HF present in the SF6 at the risk levels described in Section 4, to calculate the maximum concentrations of SF6 in air necessary for the TLV’s of these decomposition products to be reached. (See Appendix 1 for TLV levels.) The values in the table below are derived from this approach. The SF6 concentration of the chart should be the maximum exposure that personnel handling SF6 will be allowed to work under for up to 8 hours, under the described situations. Forced ventilation should be used if necessary to ensure that the limiting concentration is not exceeded. Personnel should wear a protective respirator if the suggested concentration cannot be met. Table C-1 Risk Level for SF6 Concentrations Risk Level for the situation *

Low

Limiting SF6Concentration 1000 ppmv

(Working on equipment with no contamination)

Intermediate

200 ppmv

(Working with equipment that has seen only normal service)

High

20 ppmv

(Working with equipment that has seen failure, or repeated operation at high fault levels) *For detailed definitions of the risk levels, refer to Sections 4.2, 4.3 & 4.4.

1

Adapted from IEC 1634 (Reference [6], Annex F).

C-1

D NEUTRALIZING SOLUTIONS

Neutralizing Solution, Choice and Preparation1 Each of the three formulations for neutralization listed here has slightly different properties. They are all solutions of an active agent in water, made up according to the concentrations given in the table, in kg of active agent per 100 litters of water. In choosing a neutralizing solution the following criteria should be considered: •

the solution chosen should not be unduly corrosive or irritating if it is necessary to apply it by hand.

•

it should be sufficiently alkaline during the neutralization process to ensure that acidic residues are effectively neutralized.

•

it should not be too alkaline at the end of the process such that it cannot be disposed of as normal waste. Table D-1 Neutralizing Agent Options Active Agent Hydrated Lime Sodium carbonate (washing soda)

Formula Ca(OH)2 Na2CO3

Concentration kg/100 litters saturated 1.1 10 3 1

Soaking Period Hours 24 24 0.25 Wash --

Recommended Application Note 1 Note 1 Note 2 Note 3 Note 4

Sodium bicarbonate NaHCO3 Notes: 1. Used for soaking and neutralizing contaminated material. 2. Used only if contaminated material must be neutralized in a very short time. (Caution: When using alkaline solutions at high concentrations, care should be taken to avoid contact with the skin, eyes, etc. 3. Used for washing contaminated tools, footwear, equipment etc. 4. When the supply of clean fresh water is limited, this weak solution is used to rinse area of skin that may be contaminated.

1

Adopted from IEC 1634 (Reference [6], Section 6.5.3).

D-1

E RESOURCES FOR PURIFYING OR DESTROYING CONTAMINATED SF6 GAS

Gas which contains up to 60% air and any level of particulates, moisture and decomposition products which can be generated in use can be purified to a level that exceeds the CIGRE recommendations [12] for reuse. At some point, it will be more expedient to destroy the gas (have it broken down into environmentally benign components) than to have it reclaimed. The utility must consider the cost of storage, shipment and processing in making its decision as to the proper path to take, but the CIGRE guide, which permits up to 2% air in the SF6 gas used to fill apparatus, makes purification a viable option that is responsive to the environmental concerns and usually cost effective. Below are purification resources known at this time. Contacting your gas supplier is also suggested, if they are not listed below.

Table E-1 Resource Contacts Company

Contact

Phone

Air Products, Allentown, PA

Joe Munley

610-481-6254

Allied-Signal, Buffalo, NY

Dawn Hamilton

618-524-6343

Dilo, Oldsmar, FL

Eric Campbell or Lukas Rothlisberger

727-376-5593

Solvay Fluorides, Inc., Houston, TX

Sherry Kacherski

203-629-7900

Spectra Gases, Branchburg, NJ

Matthew Adams

800-932-0624

Polar Technolgy, Amesbury MA

603-394-8041

Advanced Specialty Gases, San Francisco, CA

415-398-7167

E-1

F PHYSICAL PROPERTIES OF SF6 GAS AND LIQUID Table F-1 Physical Properties of SF6 Gas and Liquid Property Density at standard temperature and pressure

Value

Units 3

6.12

kg/m

0.382

lb/ft

Density ratio with air

5.07

-

Molecular weight

146.05

g/mole

Density of liquid at boiling point

1168

kg/m

73

lb/ft

Expansion ratio from liquid to gas

225

-

Boiling point at 1 atmosphere

-64

°C

-83

°F

3,772

KPa

547.1

lb/in

232

KPa

33.7

lb/in Absolute

-50

°C

-58

°F

0.00813

BTU/ft/hr/°F

435

Cal/cm-sec-°C

Critical pressure Triple point pressure Triple point temperature Thermal conductivity at 32 °F at 0 °C

3

3

3

2

2

F-1

G US ENVIRONMENTAL PROTECTION AGENCY INITIATIVE FOR SF6 GAS

Below is the standard text prepared by the EPA for consideration by electric utilities. Following the text is a listing of current participants. Participation is a decision to be made by individual utilities weighing many factors. The EPA manager of this program is Jerome Blackman, 202 564-8995 ([email protected]). MEMORANDUM OF UNDERSTANDING between The United States Environmental Protection Agency and “Partner” I.

PREAMBLE

A. This is a voluntary agreement between the United States Environmental Protection Agency (EPA) and the “Partner” (collectively, the “Parties”), by which the Partner joins the SF6 Emissions Reduction Partnership for Electric Power Systems. B. SF6 (sulfur hexafluoride) is used for electrical insulation and for arc quenching and current interruption in equipment used in the transmission and distribution of electricity. C. The Partner and EPA recognize that the primary purpose of this agreement is to achieve environmental and economic benefits by reducing emissions of sulfur hexafluoride (SF6) during the operation and maintenance of equipment used in the transmission and distribution of electricity. II.

COMMON AGREEMENTS AND PRINCIPLES

A. SF6 emissions from electric power systems are the result of releases from properly functioning equipment (due to static and dynamic operation), from leakage (e.g., due to old and/or deteriorated gaskets or seals), and from gas escaping into the atmosphere when gas is either transferred into equipment or extracted from it for disposal, recycling, or storage. B. The Partner and EPA acknowledge that only technically and economically feasible actions to reduce SF6 emissions will be sought. The determination of what is technically and economically feasible will vary among Partners, and it is at the discretion of each Partner to make that determination.

G-1

US Environmental Protection Agency Initiative for SF6 Gas

C. The Parties assume good faith as a general principle in fulfilling the obligations of this Memorandum of Understanding (MOU). D. The Parties agree to informally notify each other if any problems arise and to work together to maximize the effectiveness of the MOU. E.

III.

Nothing in this agreement constrains EPA or any Partner from taking actions relating to SF6 that are authorized or required by law. EPA RESPONSIBILITIES

A. SF6 has been identified by the Intergovernmental Panel on Climate Change as an extremely potent greenhouse gas. EPA believes that reducing emissions of this gas will help to address global climate change. B. EPA will provide a single representative for the Partnership. EPA will notify the Partner within 30 days of any change in the representative’s identity. C. EPA agrees to serve as a clearinghouse for technical information on successful strategies for reducing SF6 emissions, and to sponsor research relating to such strategies, contingent upon the availability of funds. D. EPA agrees to provide the Partner with recognition for its achievements in reducing SF 6 emissions and for its public service in protecting the environment. EPA also agrees to produce brochures, public service announcements (PSAs), and articles for publication describing the partnership and companies that have been successful in implementing the partnership. EPA agrees to obtain Partner’s approval on any pieces, prior to publication, that discuss Partner’s participation. EPA further agrees to conduct one or more technical conferences on issues relating to the Partnership and to recognize the environmental and technical leadership of those Partners whose contributions to reducing SF6 emissions are particularly noteworthy. E.

EPA will seek to establish Partnerships to reduce SF6 emissions with all U.S. electric power systems that employ SF6-bearing equipment.

F.

EPA will identify protocols to inventory and report SF6 emissions. A detailed description of these protocols and an inventory reporting form is included in Attachment B of this MOU.

G. Information submitted to EPA will be treated in accordance with the EPA regulations at 40 CFR Part 2, including the provisions on protecting confidential business information. EPA will treat any information not explicitly designated as confidential by the Partner as nonconfidential.

G-2


IV.

PARTNER RESPONSIBILITIES

A. The Partner agrees to appoint a single representative for the Partnership (designated in Attachment A of this MOU). The Partner will notify EPA within 30 days of any change in the representative’s identity. B. The Partner agrees that it will, where possible, estimate its SF6 emissions during one of the years between 1990 and 1998, choosing the year for which the most accurate information is available. The chosen year will serve as the starting year for the Partner’s emission reduction efforts. The Partner will also include a written explanation of the method used to generate this estimate, indicating the accuracy and completeness of the estimate. The estimate will be included in the first Annual Report. Any changes to this estimate and/or the chosen year will be communicated to EPA in the subsequent Annual Report. The Annual Report, as referred to in this paragraph and subsequent paragraphs, is to be submitted during the first quarter of each year (between January 1 and March 31). C. The Partner agrees that in its first Annual Report it will provide EPA with the total estimated nameplate capacity of SF6 (in pounds) of its SF6-bearing equipment in service. This number will be updated as appropriate in subsequent annual reports. Equipment which is sealed-for-life or which contains less than 15 pounds of SF6 is exempted from this agreement. D. The Partner agrees that it will, on an annual basis, inventory emissions of SF6 and will report its emissions of SF6 to EPA in accordance with a uniform reporting protocol identified by EPA and described in Attachment B. The Partner will use the form included in Attachment B to report its annual emissions to EPA as part of its Annual Report. The Partner will maintain records that could be used to verify the accuracy of data reported in the annual inventory of emissions, e.g., gas purchase and sale records, and gas returns to suppliers. E.

The Partner agrees that, within one year of signing the MOU, it will develop and distribute a company-wide policy for the proper handling of SF6. The policy will include, to the degree technically and economically feasible: a commitment to recycle (recover and reuse) SF6; a commitment to establish a maintenance program for all equipment with a goal of reducing emissions; a replacement strategy for all SF6 equipment that leaks to such an extent that leakage cannot be controlled through normal maintenance procedures; and a commitment to purchase and use equipment that eliminates or reduces the possibility of SF6 leaks. A copy of the policy will be included in the Partner’s first Annual Report to EPA, and updated as appropriate in subsequent years.

F.

The Partner agrees to establish and implement handling procedures for SF6 within one year of signing the MOU. The Partner agrees that only knowledgeable personnel will handle SF6 equipment. If the Partner hires outside parties for maintenance and/or recycling/disposal, the Partner agrees that those parties will follow in-house policies pertaining to maintenance, recycling and disposal. A description of the handling procedures will be included in the Partner’s first Annual Report to EPA, and updated as appropriate in subsequent years.

G-3


G. Within 18 months of signing the MOU, the Partner will establish an emissions reduction goal. This goal will be quantified relative to the Partner’s emissions during the year chosen by the Partner as their starting year (see IV B), and should be expressed in terms of either pounds of SF6 and/or the percentage reduction e.g., “the Partner commits to reducing SF6 emissions X% and/or by X pounds from 199X levels [the starting year] by the year 200X.” If the Partner does not choose a starting year as indicated in IV B, then the first year in which the Partner joins the Partnership and inventories its emissions will serve as the starting year. The emissions reduction goal will reflect technically and economically feasible options available to the Partner. The Partner will notify EPA of the goal with a letter outlining the goal’s content and the rationale for choosing it. If, due to changing circumstances, the Partner decides to change its emissions reduction goal, the Partner will inform EPA of this change and provide a description of why the change was deemed necessary. H. The Partner agrees that it will share with EPA information about successful SF6 emission reduction processes and technologies that the Partner considers non-confidential, and it will share such non-confidential information with others who operate electric power systems. I.

The Partner agrees that participation in the Partnership, use of the Partnership logo, or any publicity relating to its participation in the Partnership does not constitute EPA’s endorsement of the Partner for anything other than its participation in the SF6 Emissions Reduction Partnership for Electric Power Systems and its commitment under Section IV of this agreement. The Partner agrees that it will not claim or imply otherwise. The logo and the logo use guidelines will be forwarded to the Partner as soon as the logo is created.

J.

The Partner agrees that the activities it undertakes connected with this MOU are not intended to provide services to the Federal government, and that the Partner will not submit a claim for compensation to any Federal agency.

K. The Partner may, after collaboration with EPA, attach additional provisions to this MOU. Such additions must contribute to the goal of SF6 emissions reduction and not conflict with any of the provisions contained in the MOU. V.

TERMINATION OF AGREEMENT

A. This agreement can be terminated by either the Partner or EPA 30 days after the receipt of written notice by the other Party with no penalties or continuing obligations. If either Party terminates the MOU, both Parties will refrain from representing that the Partner is participating in the partnership. VI.

SIGNATORIES The undersigned hereby execute this Memorandum of Understanding on behalf of their parties. This agreement takes effect when signed by both parties.

G-4


For the United States Environmental Protection Agency: On: Paul M. Stolpman, Director Office of Atmospheric Programs For Partner: On: Company Representative Typed name and title

G-5


ATTACHMENT A—PARTNER REPRESENTATION Designated Partner Representative: Name:

Title:

Mailing Address:

Phone Number: Facsimile Number: E-mail Address:

Official Partner Signatory: Name: Mailing Address:

Phone Number: Facsimile Number: E-mail Address:

G-6

Title:


ATTACHMENT B — SF6 EMISSIONS INVENTORY REPORTING PROTOCOL AND FORM This protocol provides a template for reporting annual SF6 emissions based on annual changes in a company’s SF6 inventory. Use of the protocol requires the following data: •

SF6 gas in inventory at the beginning of the reporting year

•

SF6 gas in inventory at the end of the reporting year

•

SF6 gas additions to inventory (i.e., purchases)

•

SF6 gas subtractions from inventory (i.e., sales or returns)

•

Changes in nameplate capacity

Gas in inventory refers to SF6 gas contained in cylinders (such as 115-pound storage cylinders), gas carts, and other storage containers. It does not refer to SF6 gas held in operating equipment. Gas additions and gas subtractions refer to SF6 gas placed in or removed from the stored inventory, respectively. Gas additions also include SF6 provided by equipment manufacturers with or inside new equipment. Complete Tables 1 and 2 (see the form on the following page) to estimate annual emissions. Use the comments box to describe the means used to obtain a specific quantitative value, e.g., measured, estimated using rough data, or other comments including perceived accuracy of the form entries. If there is not enough room in the tables to record all your comments, please attach additional sheets. Accounting for Acts of Nature and Other Non-preventable Events An act of nature (e.g., lightning or earthquakes) or another non-preventable event (e.g., equipment failure) which destroys or damages a piece of equipment might result in the loss of SF6 to the atmosphere.1 If acts of nature or other non-preventable events occur that result in a loss of gas to the atmosphere, the Partner should contact EPA prior to submitting the annual inventory so that EPA and the Partner can discuss how best to account for this gas loss in the annual inventory process. The Partner need only inform EPA about such events prior to submitting the annual inventory, and not after each event occurs. Under no circumstances would the loss of gas from an act of nature or other non-preventable event be added to the Partner’s annual emissions estimate.

1

The term “non-preventable event” does not include releases from properly functioning equipment (due to static and dynamic operation) or leakage (e.g., due to old and/or deteriorated gaskets or seals).

G-7


WORKSHEET

Table 1 Inventory

Amount (lbs)

A

Beginning of year

B

End of year

Comments

Table 2 Additions to Inventory Amount (lbs)

Comments

1. Purchases of SF6 (including SF6 provided by equipment manufacturers with or inside new equipment) 2. SF6 returned to the site after off-site recycling C: Total Additions (add items 1-2)

Subtractions from Inventory Amount (lbs)

Comments

3. Sales of SF6 (to other entities) 4. Returns of SF6 to supplier 5. SF6 taken from storage and disposed of 6. SF6 taken from storage and sent off site for recycling D: Total subtractions (add items 3-6)

Change to Nameplate Capacity Amount (lbs)

Comments

7. Total nameplate capacity of new equipment 8. Total nameplate capacity of retiring equipment E: Change to nameplate capacity (subtract item 8 from item 7)

Total Annual Emissions = A - B + C - D - E = UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460 OFFICE OF AIR AND RADIATION

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SF6 Emissions Reduction Partnership for Electric Power Systems List of Partners (September, 2001) Listed below are the 64 partners in the United States Environmental Protection Agency’s SF6 Emissions Reduction Partnership for Electric Power Systems. A current list can be found on the EPA website at: http://www.epa.gov/highgwp1/sf6/partners.html EPA is pleased to be working with these electric utilities and local governments on this new voluntary initiative. The partners are to be congratulated for taking a leadership role in reducing these emissions. Their decision to work with EPA to reduce emissions of this potent greenhouse gas demonstrates a true commitment to protecting the environment. SF6 is used in a variety of applications including as an insulating material in electrical transmission and distribution equipment such as circuit breakers. SF6 has been recently identified as a persistent and potent greenhouse gas. The partners are among the first users of this material to act to protect the climate. Electric power systems that join the partnership agree to estimate their emissions of SF6; establish a strategy for replacing older, leakier pieces of equipment; implement SF6 recycling; ensure that only knowledgeable personnel handle SF6; and submit annual progress reports. Eighteen months after joining, partners agree to come up with an emissions reduction goal that they determine to be technically and economically feasible. EPA will be a clearinghouse for technical information on successful strategies to reduce emissions; serve as a repository for data on the emissions reduction achievements of the partners; and work to obtain commitments from all electric power system operators to join the partnership. The partners, listed alphabetically by state, are: Alabama Athens Electric Department (Athens, AL) Arizona Salt River Project (Phoenix, AZ) Wellton-Mohawk Irrigation and Drainage District (Wellton, AZ) Arkansas City Light, Water & Cable (Paragould, AR) California Edison International (Rosemead, CA) Kings River Conservation District (Fresno, CA) PG & E Corporation (San Francisco, CA) Silicon Valley Power (Santa Clara, CA) G-9


Connecticut Connecticut Light and Power Company (Berlin, CT) Northeast Utilities Services Company (Hartford, CT) Town of Wallingford (Wallingford, CT) Florida Florida Power and Light Company (Juno Beach, FL) Fort Pierce Utilities Authority (Fort Pierce, FL) Georgia Southern Company (Atlanta, GA) Crisp County Power Commission (Cordele, GA) Illinois Commonwealth Edison (Chicago, IL) Indiana Northern Indiana Public Service Company (Merriville, IN) Iowa Muscatine Power and Water (Muscatine, IA) Kentucky Big Rivers Electric Corporation (Henderson, KY) Louisiana Southwestern Electric Power Company (Shreveport, LA) Maine Bangor Hydro-Electric Company (Bangor, ME) Central Maine Power Company (Augusta, ME) Maine Public Service Company (Presque Isle, ME) Massachusetts Commonwealth Electric (Wareham, MA) Western Massachusetts Electric Company (West Springfield, MA)

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Montana Montana Power Company (Butte, MT) Nebraska Hastings Utilities (Hastings, NE) Grand Island Utilities Department (Grand Island, NE) Nebraska Public Power District (Doniphan, NE) New Hampshire North Atlantic Energy Service Corporation (Seabrook, NH) Public Service Company of New Hampshire (Manchester, NH) New York Consolidated Edison Company of New York, Inc. (New York, NY) New York Power Authority (New York, NY) Rochester Gas & Electric (Rochester, NY) North Carolina City of Monroe (Monroe, NC) Ohio American Electric Power (Columbus, OH) Cinergy Services, Inc., on behalf of The Cincinnati Gas & Electric Company and PSI Energy, Inc. (Cincinnati, OH) First Energy Corporation (Akron. OH) FirstEnergy Corporation (Akron, OH) Oklahoma OG&E Electric Services (Oklahoma City, OK) Oregon Bonneville Power Administration (Portland, OR) Columbia River PUD (St. Helens, OR) Eugene Water & Electric Board (Eugene, OR) Pennsylvania

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Allegheny Power (Greensburg, PA) Duquesne Light Company (Pittsburgh, PA) GPU Energy (Reading, PA) South Carolina South Carolina Electric & Gas Company (Columbia, SC) Tennessee Nashville Electric Service (Nashville, TN) Tennessee Valley Authority (Chattanooga, TN) The Memphis Light, Gas & Water Division (Memphis, TN) Texas Austin Energy (Austin, TX) El Paso Electric Company (El Paso, TX) Reliant Energy—HL & P (Houston, TX) San Antonio City Public Service Board (San Antonio, TX) Texas Municipal Power Agency (Bryan, TX) TXU (Dallas, TX) West Texas Utilities (Abilene, TX) Vermont Central Vermont Public Service Corporation (Rutland, VT) Washington PUD No. 1 of Douglas County (East Wenatchee, WA) PUD No. 1 of Pend Oreille County (Newport, WA) Wisconsin Manitowoc Public Utilities (Manitowoc, WI) Menasha Electric and Water Utilities (Menasha, WI) Village of Prairie du Sac (Prairie du Sac, WI) Wisconsin Electric Power Company (Milwaukee, WI)

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Target: Substation Operation and Maintenance

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