WELCOME TO IMTC HIGH VOLTAGE SAFETY PROGRAM Please Fill in The Registration Forms SAFETY HAS PRIORITY OVER SERVICE CONTINUITY AND ECONOMICS
IEEE - IEC PROVE DEAD THE PLACE OF WORK
High Voltage System Safety Requirement High Voltage system training is now part of STCW code 2010 ( Manila Amendment ) as mentioned on section B- III /2 The convention is in force till - 2013 The convention covers the responsibility for operating and maintaining the High Voltage ( above 1000 volts) electrical power plants on board ships and process plate forms
MODULE STRUCTURE THE ROUTINE / TIMINGS PRE & POST COURSE ASSESSMENT LAYOUT AND GENERAL SAFETY IN THE PREMISES AND THE high voltage ELECTRICAL LAB DURATION OF THE COURSE ATTENDANCE BRIEF ABOUT IMTC IMTC COMPLIMANTRY BUS
SAFETY IS MORE ABOUT ATTITUDE THAN APPTITUDE GENERAL ACTIVITIES ONBOARD • • • • •
Inspection Operation Maintenance Repair Replacement
BEFORE CARRYING OUT ANY ONE OF THE ABOVEACTIVITIES MAKE SURE: 1. 2. 3. 4. 5.
What is to be done. If required make notes Where. Location. Environment. Elements How. Procedures. Caution. Warning. Risk assessment (Permits) When. Precedent Why.
MODULE : 1
SCOPE:The program is intended for:• Electrical Personnel maintaining, operating and repairing Electrical apparatus • Non Electrical Personnel operating electrical equipment • Engineers • Watch keepers • Those responsible for safe control and management of high voltage power systems in a marine environment
This training includes: • The functional operational and safety requirement for a Marine High Voltage system • Maintain and repair of High Voltage switch gear • Taking appropriate action when dealing with faults in a High Voltage system • Switching strategies for isolating components of High Voltage system • Using suitable apparatus for isolation and testing of High Voltage equipment • Switching and isolation procedures on a Marine High Voltage system • Understanding safety documents for High Voltage systems • Testing of Insulation Resistance (IR) and Polarization Index (P/I) on High Voltage equipment
COURSE OBJECTIVES ON COMPLETION OF THE COURSE THE PARTICIPANTS WILL HAVE SUFFICIENT KNOWLEDGE AND ENABLE THEM TO UNDERSTAND :
Voltage, Voltage levels and High Voltage
Advantages of high voltage
Risks and hazards associated with High Voltage
Familiarize with High Voltage Switch Gear
High Voltage safety, precaution and procedures during maintenance and operations
Understand and demonstrate the functional, operational and safety requirements for a Marine High Voltage system
Assist suitably qualified personnel to carry out the inspection, operation, maintenance and limited repairs on High Voltage apparatus
Safely take necessary remedial action during system faults
Devise a switching strategy for isolating HV system / Apparatus in accordance with specified safety procedures documented and a thorough risk assessment
Select suitable apparatus for isolation and testing HV equipment
Perform 5k V insulation resistance (IR) and Polarization Index ( P I ) on High Voltage equipment
High voltage switch gear construction, operation and safety features
Protection systems and applications
Work permits and company specific High Voltage Safety related documents
Trapped key system for sequential isolation and procedures to “PROVE DEAD” the place of work
Table top Exercises
General Personal safety includes 1 Follow Safety policies: Every company has its own safety policy as per the rules of SOLAS (ISM code). Understand and follow these points but also put them in practice
2 Situational Awareness: Know your surroundings and working environment and the risk involved and tackle the problems
3 Knowhow and Training: Correct operating knowledge of different equipment tools and systems on board, including safety procedures and emergency plans through proper training
4 Use of PPE: Every person on board ships must know what PPE is to be used and when and donning and checking. Maintain your PPE so as it is fit for use all the time as and when required
5 Help Yourself First: When you and your colleagues are trapped in dangerous situation, help your self first to get out of the situation and then help others
6 Know Your Ship Inside - Out: On joining a ship be familiar and know every nook and corner of the ship including location of fire fighting appliances, life saving appliances, alarms , escape routes, life boats and every thing needed in an emergency
7 Know Your Emergency Duties: Every crew member should know his emergency duties
8 Avoid Panic Attacks: It is human to get tensed or nervous in case of an accident. Try to control emotions to maintain mental peace and to act in a quick and smart manner under the pressure of an emergency situation
High Voltage Safety
Isolation and access for Maintenance
DIE Disconnect – Isolate – Earth PROCEDURES • No Electrical conductors should be regarded as being safe unless it has been isolated earthed, secured and proved dead • Precautions should be taken to ensure that isolated equipment can not be re energized. Lock out …. Tag out. Put up Warning and Caution notices • Voltage indicators should always to be tested before and after use • When not attended the barriers should be placed around live conductors • If isolation is done by other than competent person then it should be demonstrated to the competent person
Electricity can kill • More than 3000 non fatal electric shock accidents are reported every year in USA,1000 in UK • About 1000 people die every year from electrocution and surprisingly voltage was < 600 volts • Be careful about Ice berg syndrome in case of Electrical injuries / burns
SAFETY PRECAUTIONS
INTRODUCTIONThe management of Marine High Voltage Power Plant • High voltage safety rules and procedures • Electrical hazardous and precautions a) Electric shock (touch potential) b) Arcs/sparks and blast c) Earthing d) Operation and safety features • Legislative background 1. International Health and safety legislation 2. Flag state health and safety legislation 3. ESR (Electrical Safety Rules). Company specific 4. Code of Safe Working Practices (CSWP) 5. Health and Safety Executive (HSE)
MODULE :- 2 Brief revision of Power system on board
ELECTRICAL POWER SYSTEM The generator ( Alternator ) - Source of power. (Converts mechanical energy into Electrical energy by Electro Magnetic Induction) Brief on power and power factor Advantages of high voltage over low voltage
AC / DC
SERIES OR PARALLEL
POWER AND POWER FACTOR ACTIVE POWER = V x I x Cos. phai = KW REACTIVE POWER = V x I x sine phai = KVAR APPARENT POWER = V x I = KVA POWER FACTOR = KW / KVA
• Impedance ( Z ) of the load decides the Power demand • Resistive component of the impedance decides Active power. kW ( Governor )? • Inductive component of the impedance decides the Reactive power. kVAR (AVR )?
INTRODUCTION The Management of Health and Safety at Work, regulation : Risk Assessment. Every employer (Senior personnel, Manager, Superintendent) shall make a suitable and sufficient assessment of :1. Risk to the health and safety of his employees (subordinates) to which they are exposed whilst they are at work: and 2. In making or reviewing the assessment the employer shall take particular account of ; a) The experience, lack of awareness of risk and immaturity of New joiners, Trainees and Apprentices b) The fitting – out and lay out of the work place c) The nature, degree and duration of exposure to physical biological, chemical agents and radiation ( very high Voltage) d) The form, range and the use of the work equipment and the way it is handled
Contd. e) f)
The organization of process and activities The extent of health and safety training provided to young and new employees (Operators, Maintainers and Trainees)
Capabilities of training:1. 2. a)
Every employer (Senior authorized/ Authorized person ) shall, in entrusting tasks to his employee ( Competent person) take into account their capabilities as regards health and safety Every employer shall ensure that his employees are provided with adequate health and safety training:On their being recruited into the undertaking and on their being exposed to new or increased risk because of :(Transfer, introduction of new work equipment, introduction of new technology and introduction of new system of work, modification etc.)
• THE TRAINING REFERED ABOVE SHALL :a) Be repeated periodically where applicable b) Be adapted to take account of any new or changed risk to the health and safety of the employees concerned c) Take place during working hours
General Safety Principles and Prevention 1. 2. 3. 4. 5. 6.
7. 8.
Avoiding risk Evaluate the risk which can not be avoided Combating the risk at source Adapting to technical progress Replacing dangerous by non dangerous or by less dangerous Developing a coherent overall prevention policy which covers technology, organization of work , working conditions, social relationships and influence of factors relating to the working environment Giving collective protection measure priority over individual protective measures Giving appropriate instructions to employees (subordinates)
Management of high voltage on board ships / platforms • Arrangement of high voltage switch rooms Switch rooms Equipment Switch Boards Transformers Protection Relays • Tripping and auxiliary supplies (110 / 220 dc source) • Earthing • Key safe / trapped key system • Fault levels • Application of protection system • Prove dead the place of work. Switching schedule • Documentation
ENERGY TRANSMISSION Energy can be transmitted by various means: Mechanically Hydraulically
Electrically By Radiation and other means Electricity is the most common “energy transmission” mean ADVANTAGES OF ELECTRICAL MEANS: Most efficient Pollution free Flexible Instant availability over any distance Comparatively less maintenance Low weight to high power ratio for a given capacity
VOLTAGE AND VOLTAGE LEVELS VOLTAGE & LEVELS
Low Voltage : Medium Voltage : High Voltage : Extra High Voltage
Up to 1000 volts 1000 to 6600 volts 6600 to 11000 volts Above 11000 volts
NOTE : ON BOARD ANY VOLTAGE ABOVE 1000 VOLTS IS BE TREATED AS HIGH VOLTAGE • Above voltage figures are in RMS • The peak value of the voltages would be above figures divided by 0.707
• Illustration: • 1000 volts RMS = 1414 volts peak & • 6600 volts RMS = 9335 volts peak • 9000 volts RMS = ? volts peak
MODULE :- 3 SAFETY BOOK / MANUAL
AN OVERVIEW
THE SAFETY MANUAL / BOOK & IT’S PURPOSE Safety has priority over service continuity, equipment damage or economics (IEEE ) Provide safety principles to be used for protecting individuals from potential injuries and even death caused by electrical hazards. The basic safety program is for supervisors, managers, electricians, engineers and the designers / specifiers of equipment used in electrical systems The purpose of the safety book is to increase the safety awareness issues faced by the individuals who work on or near electrical equipment as well the system operators and equipment designers / specifiers Safety guide lines are recommended by various international and national safety organizations like: OSHA
: Occupational Safety and Health Administration(USA)
IEC
: International Electro technical Commission (UNO)
ANSI
: American National Standards Institute (USA)
EAW
: Electricity At Work (United Kingdom ) (Regulation 1989)
ELECTRICAL SAFETY RULES – AN OVERVIEW Rules, scope, responsibilities, authorities, familiarization, objections
See: 1) ESR 1(company specific) 2) Code of safe working practice for merchant Seamen
Integrity
Modifications, adjustments, approvals, records, maintenance
See: 1) ESR 1(company specific)
3
Access
Rooms, locks, duties
See: 1) ESR 1 (Company specific rules)
4
Work
Electrical distribution, operating positions, permits, planning, risk assessment, preparation, completion, testing
See: 1) ESR 1( company specific) 2) Safety Management System (SMS) 3) Hazardous Area Guide
5
Competence
Competence assessment training
See: 1) ESR 1 2) ESR 3
1
Responsibilities Authorization
2
and
HIGH VOLTAGE SAFETY RULES OBJECTIVES- Govern all works undertaken on high voltage system include; • Duties • Variations / amendments • Issue • Approval / sanctions DEFNITIONS• Approved- Of type and method sanctioned in writing • Live /dead – Electrically charged • Isolated – Disconnected from all sources of power • High voltage – Any voltage in access of 1000 volts
• • • • • • • • • • • • •
High voltage apparatus Electrical engineer Senior authorized person Authorized person Competent person Permit to work Sanction to test Limitation of access Caution/Danger notice Circuit main Earth Additional Earth/Earthed Key safe Safety lock
ARRANGEMENTS FOR SAFE WORKING Personal protective equipment (PPE) Guarding (when working in the proximity of live electrical equipment) Use of safety locks, key exchange and lock out boxes Risk assessment “ Matrix” HSE.( HEALTH AND SAFETY EXECUTIVE) Documentation ( permits should be ” in writing “ and not verbal, on telephones or walkie talkies)
EMERGENCY CONDITIONS’ When does an emergency condition arise? How would you define an emergency condition? Fire, flood, gas leak, trapped person, etc. • First preference should be the safety of personnel • Immediate steps to be taken to remove the danger and inform the people/person • Do not enter an area which is prohibited to you • Switch off the power supply.
This may not be possible in certain circumstances NOTE; THINK AND BE AWARE OF THE EFFECTS CAUSED BY ANY ACTION TAKEN
MODULE - 4 •
Advantages of High voltage system
•
Risks and hazards associated with high voltage
ADVANTAGES OF HIGH VOLTAGE (3.3/ 4.4 / 6.6 / 11K.v. etc. • TRANSMISSION OF POWER TO LONG DISTANCES • FOR A GIVEN ENERGY LEVEL THE ARC INTENSITY IS LOW (The current is low hence I x I x t is low) • LOW WEIGHT / POWER RATIO. ( COMPACT SYSTEM ) • LOW / NO MAINTENANCE ON METAL ENCLOSED SWITCH GEAR
RISKS / HAZARDS ASSOCIATED WITH HIGH VOLTAGE
Note :- PROPERLY USED ELECTRICITY IS NOT DANGEROUS • FOLLOW THE RULES AND REGULATIONS FOR SAFE WORKING (WARNING AND CAUTION) • OUT OF CONTROL ELECTRICITY CAN CAUSE HARM TO HUMANS, THE EQUIPMENT AND THE ENVIORNMENT • HEATING EFFECTS ( ARCS AND SPARKS )CAN ALSO CAUSE FIRES AND BURNS EVEN WITHOUT CONTACT
RISKS / HAZARDS ASSOCIATED WITH HIGH VOLTAGE Hazards can include : a) Poor work conditions, equipment and practices b) Careless and inadvertent actions on the part of the individuals Common electrical hazards that can cause injury and even death
Electric shock with touch potential (current is the boss)
Arc-flash burns ( from contact, short circuits ) and radiant's (Tissue damage ).Temperatures reaching up to 37,000*C
Arc blast impact from expanding air and vaporized material (vaporized copper expands 67,000 times in volume )
Obnoxious / toxic gases
Formation of HCl from burning PVC insulation on the cables
A high voltage electric shock will almost certainly lead to severe injury or fatality Factors that could increase the risk of receiving an electric shock; • • • • • •
High Voltage work carried out close to a person who is not familiar with High Voltage hazards High Voltage insulation testing Equipment using water as part of High Voltage plant Using test instruments when taking High Voltage measurements High Voltage equipment stores energy even after disconnection If the High Voltage circuit main earth is removed while carrying out any maintenance
Ensure that necessary precautions / safety standards are being followed up during operations & maintenance. 1)Ensure proper electrical connection before charging any switchgear 2)Ensure that we are not leaving any tool within panel, electrical equipment 3) HT breakers – Do not charge without wearing 33KV hand gloves & without closing breaker panel 4) Do not touch pf capacitor terminals without discharging them 5) Ensure all electrical safety standards while
handing any electrical equipment
ELECTRIC SHOCK WITH “TOUCH POTENTIAL” • Muscles in human body are controlled electrically • Brain controls the muscles @ 10 pulses / second
• 60 Hz. Power with 120 pulses / sec is eminently suited to kill • Earth Leakage Circuit Breakers (ELCB,s) should trip in 200 milliseconds or less with a fault current of 30 mA • At 200 mA it would take approx. 400 milliseconds for the heart to stop
EFFECTS OF ELECTRIC CURRENT ON HUMAN BODY(TOUCH POTENTIAL) The severity of an Electric shock, can have dramatic effects and, depends upon the following key factors: Current intensity and type- ac/dc Contact duration Tension (Voltage) Body resistance. (Approx. 1500 Ohms)
Current ”path ways” through the body “FREQUENCY” (Hz) of the shock current Psychological condition of the recipient Sex, age and general health of the recipient Environment Attire etc. (PPE)
EFFECTS OFELECTRIC CURRENT ON HUMAN BODY 0.9 – 1.2 mA
Current just perceptible
1.2 – 1.6 mA
Tickling sensation in the hand as from ants
1.6 – 2.2 mA
Sensation that the hand has gone to sleep
2.2 – 2.8 mA
Same sensation perceptible in the wrist also
2.8 – 3.5 mA
Slight stiffening of the hand
3.4 – 4.5 mA
Considerable stiffening of the hand, the lower arm growing tired
4.0 – 5.0 mA
Feeling of cramps and slight trembling in the hands
4.5 – 5.0 mA
Cramp in the lower arm
5.0 – 7.0 mA
Slight cramp in the upper arm ( unpleasant )
6.0 mA
WOMEN CAN JUST BREAK THIS CONTACT (LET GO)
9.0 mA
MEN CAN JUST BREAK THIS CONTACT
15 – 20 mA
REALEASE IMPOSSIBLE CAN NOT BE TOLERATED
20 – 40 mA
Serious and very painful contractions of the muscles, breathing stops, but normally resumes if current is interrupted within
5 seconds
50 – 100 mA
VENTRICULAR- FIBRILLATION. HEART MUSCLES UNABLE TO RELAX thus pumping stops leading to death
AT HIGH VOLTAGES
The recipient can be thrown off and may survive but with severe burns
AT LOW VOLTAGE
Death can occur at relatively low currents, but
time is important
Importance of Earthing
A rough relationship between the shock current measured in milliamps and time measured in milliseconds, that can be tolerated by a normal healthy person CURRENT = 116 / root TIME Roughly, thus a 50 mA current for 4 seconds would not be very dangerous. Calculate the approx. current that would flow through a human body with 1500 Ohm,s resistance from a touch potential of 230 volts
MODULE – 5
High Voltage systems General Lay out of High Voltage Switch Board Comparison between 440volts and 6600 volts
TABLE OF COMPARISON BETWEEN 6.6 kV AND 440V 6.6 k V high voltage
440 volts
CURRENT(FOR A GIVEN CAPACITY)
LOW
HIGH
TYPE OF CIRCUIT BREAKER
VCB,SF6,OIL,Air Blast
ACB
ACB/VCB MAINTENANCE
VACUUM CHECKER/GAP
VISUAL CHECK
SAFETY DEVICE LOCATION
SEPARATE PROTECTION
INCLUDED INSIDE ACB
CONTROL CIRCUIT VOLTAGE
DC 110V
DC 24 V
BUS BAR
SMALL
LARGE
BUS BAR DISTANCE
WIDER
NARROW
MSB PROTECTION
SEGREGATED COMPARTMENTS
WITHOUT COMPARTMENTS
UNDER SHORT CIRCUIT
EXPLOSION
NO EXPLOSION
PROTECTION AGAINST SHORT CIRCUIT
PRESSURE RELIEF FLAPS AND REINFORCED DOORS
NO PRESSURE RELIEF FLAPS
CIRCUIT BREAKER CONNECTOR
WITH AUTOMATIC SAFETY SHUTTERS
NO SAFETY SHUTTERS
EARTHING DEVICE
WITH EARTHING SWITCH
NO EARTHING SWITCH
MSB DOORS
MECHANICAL INTERLOCK SYSTEM
NO NEED
Diesel Generator Panel
MODULE - 6 High voltage switch gear
STANDARDS AND GUIDE LINES RELATED TO SAFETY Key organizations , agencies and commissions throughout the world associated with the safety are: IEEE
Institute of Electrical and Electronics Engineers (USA)
NFPA
National Fire Protection Agency (USA)
OSHA
Occupational Safety & Health Organization (USA)
BIS
Bureau Of Indian Standards ( INDIA)
IEC
International Electro-technical Commission (Standards - UNO)
CENELEC European Committee For Electro-technical Standards (EU) IEEE 1584 guide for flash/ arc” hazard calculations”:
Incident energy < 1.5 calories / cm2 will cause a burn just curable The guide lines from NFPA- 70 provide guidance on appropriate level of Personal Protective Equipment (PPE) as follows
ARCS / SPARKS / BLASTS Arcs can also take place due to breakdown of air gaps Due to a high voltage across the gap a flash over between phases or phase to earth causing a very large fault currents. (CORONA) Partial Discharge ( P D ). Premature failure of insulation The arc temperature can be as high as 20,000* C. This may cause severe burns, loss / temporary loss of vision. The effects may be dramatic A” blast” may follow the power arc and lead to vaporization of the material involved ( contacts
, bus bars and steel panels etc.)
In case of copper the metal expands 67,000 times in volume when vaporized, leading to an explosion An explosion is a very fast expansion of surrounding air and objects can be knocked out from fixtures and fittings and hurled about with very high force Since the fault energy is calculated as ( i2t,), limiting the current will limit the amount of the fault energy by use of proper/certified protective devices
TYPICAL INCIDENT ENERGY LEVELS AND RISK CATEGORIES The table is based on the calculations to IEEE 1584 for a typical LNG carrier with two 2.5 MW turbine and two 1.25 MW Diesel generator sets connected to an insulated distribution system at 440 volts 60 hz. The distances are measured to the arc source and the figures shown on the table refer to the open doors and covers Table clearly shows that the arc flash energy is much higher close to the source of the power generation Long length of cables, right capacity fuses / fast acting MCCBs help reduce the risk when working on panels and starters remote from the main switch board PPE ( gloves, goggles / glasses and full sleeve boiler suits should be used for all the live work. Face shields with hood should be used where the incident energy is 5 cal/cm2 and above
TYPICAL INCIDENT ENERGY LEVELS AND RISK CATEGORIES Scenario
Fault current
Fault Clearing Time
Arc Safe Distance
Incidence Energy at 455 mm
Risk Category
Main Switchboard* One Turbine Generator connected
20 kA
0.5 sec
3375 mm
24 cal / cm2
4
Cargo switchboard.*Two Turbine and one Diesel Generator connected to Main Switch Board
5.8 kA
0.2 sec
850 mm
3.1 cal / cm2
1
Machinery Space vent fan starter. Two turbine Generators connected to Main Switch board
20 kA
0.2 SEC.
1811 mm
9.6 cal / cm2
3
Machinery space vent fan starter. One Diesel Generator connected to Main Switch board
10 kA
0.2 sec.
1186 mm
5.15 cal / cm2
2
63 kW motor ( supplied via 30m of 3 core 25mm2 )
8 kA
0.2 sec
457 mm
1.26 cal / cm2
0
STANDARDS NFPA 70 E (TABLE FROM NFPA 70) (PPE) Wearing PPE increases the level of incident energy that can be endured without injury PPE basically is to provide a barrier between the arc and the naked skin. Note: From a practical viewpoint , over reliance on PPE is counterproductive PPE is restricting and may not permit the wearer to work effectively
Risk Energy level Category Cal / cm2
PPE
0
<1.5 cal / cm2
Non melting flammable material e.g. Cotton, Rayon, Wool
1
< 5 cal / cm2
Fire resistance shirt, pants or coverall. Face shield
2
< 8 cal / cm2
Cotton underwear + FR pants, shirts or coverall
3
< 20 cal / cm2
As above + FR jacket and hood
4
< 45 cal / cm2
Specially rated flash suit and hood
Personal Protective Equipment • PPE must be used when risk can not be avoided or reduced to an acceptable level by safe working practices • PPE does not reduce the hazard, and can only protect the person wearing it and leaves others vulnerable • It should be noted that the use of PPE may in itself cause a hazard- for example, reduced field of vision, loss of agility etc.
Personal Protective Equipment • PPE should be provided by the ship, free of cost where it is needed and suitable for the job to be performed • Fit the worker correctly (comfortable as far as possible) • Take account of ergonomic requirements and the workers health • Be compatible with any other equipment the worker has to use same time
Personal Protective Equipment • • • • •
There has to a mechanism in place to check and maintain the PPE The wearer should check the PPE before using PPE should fit the wearer and be comfortable The wearer should know the correct use of the PPE PPE should be made available free of charge on board
NOTE ; More PPE related details are available with MCA on request for a particular plant and activity.
HIGH / MEDIUM VOLTAGE SWITCH GEAR Salient features of H.V./ M.V. switch gear : Basic switch gear operation is not different from low voltage system but special safety features are added to high voltage switch gear against :
• Arcs & Sparks that take place when the contacts are making and breaking with normal load currents • Under fault currents ‘ARC’ depends on the following factors: The nature and pressure of the medium of arc The external ionizing and de-ionizing agents present The voltage across the electrodes and variation of time The material and configuration of the electrodes The nature and configuration of the arcing chamber
NON INTERNAL“ARC PROTECTED” SWITCH GEAR Non-Internal Arc protected switch gear : A thorough analysis of arc protection system is to be performed. It is an ITERATIVE process. It can not be performed by ship’s staff however it is done and recorded by the designer / specifies / installers of the switch gear IEE 1584 A has advised the following steps : 1) Acquire the short circuit data for “normal operating conditions” (at sea) - (in port-cargo discharging/ loading ) from the original short circuit study or by new calculations. 2) Determine the arc fault current and duration 3) Determine the arc fault energy at the working distance at 100% and 85% of the arc fault current 4) Determine the flash protection boundary. Risk category and required PPE Note : OTS / 332 will provide the relevant data where ever it does not exist on old ships and to the new buildings obviously in case of new buildings the flash protection and RISK category should be determined and included in the short circuit calculations. (Soft ware programs are available from ETAP and CYNCAL for these procedures)
INTERNAL “ARC PROTECTED” SWITCH GEAR Internal “Arc protected” switch gear : In this case what the arc flash analysis will do is - quantify the flash hazard but will not quantify the physical hazard that switch gear presents during and after the fault . Unless the physical construction is robust enough there is a danger of doors, covers being open and even getting detached. Internal parts may be severely damaged, and safety interlocks compromised, i.e: Earthing connections may be detached. It is difficult to verify the exact mechanical strength by calculation. Testing will verify to a sufficient degree that the switch gear is robust to arcing faults. This is internal arc protected switch gear MV switch gear is almost exclusively internal arc protected Note: The MV switch gear is generally internal arc protected therefore the operation and maintenance of the switch gear is to be performed as per the manufacturer's instructions. An arc fault analysis is not strictly necessary, but it is recommended for the records MV voltage equipment should be classified (IAC) in accordance with IEC 67221-200 or any other acknowledged commission etc.
ARC PROTECTED” SWITCH GEAR It is recommended that the specification include the following when generating the arc flash warning labels: Short circuit calculations must include determination of incident energy for 3 phase arcing faults as per IEEE 1584 Arc flash warning labels based on the normal electrical installations operating conditions should be created and available for installation on switch boards, MCC,s, panels and GSP,s. These operating conditions should be clearly indicated on the level The maximum arcing time for the arc flash calculation should be no greater than 5sec. A motor contribution for at least seven cycles should be included The objective should be to design the electrical installation so that only standard PPE is necessary. If not possible then FLASH warning labels should be posted on the panels etc.
REDUCING THE ARC FLASH HAZARDS ON NEW SHIPS
The energy that a worker might be exposed to can be reduced by : Decreasing the prospective short circuit current Decreasing the time taken to cut off the current Increasing the working distance
Techniques to reduce the Arc fault hazard Design
Preferred Methods
Non Preferred Methods
Reduce the Prospective Fault Current Level
Incorporate current limiting fuses in protection scheme
Install current limiting reactor
Provide the dedicated test supplies
Increase transformer impedance
Limit the Duration of the Fault Current
Ensure that time/current characteristics having the minimum practicable margins, are selected
Use “arc flash reduction” maintenance switches on low voltage circuit breakers to over ride breaker timings settings during maintenance activities
Use instantaneous protection elements, e,g, bus tie circuit breakers, transformers, differential protection elements
Use interlocked zone tripping scheme to provide rapid operation of upstream protection elements
Provide protection elements for power transformers secondary circuits as well as primary circuits to reduce operating time
Use arc eliminators ( diverting the arc to a metallic short circuit by means of fast acting and rapid closing devices)
Use arc fault detection and tripping devices Ensure withdrawal parts are moved from/to the service position with only with panel doors closed Select arc tested equipment Select equipment with segregation
Techniques to reduce the Arc fault hazard Operation
Increase the working distance for personnel
Preferred Methods Operate the switch gear from a remote position. Use local electrical control desks away from switch gear
Provide warning levels indicating the level of arc flash hazard and the appropriate level of PPE for operating, faulting finding and maintenance. Reduce the capacity of power supply source
Have the minimum number of on –line sets generators
Non Preferred Methods Increase the length of tools used for withdrawing functional devices, e.g.circuit breaker racking handle
MODULE 6 (a) Safety and use of portable tools
SAFETY AND USE OF PORTABLE ELECTRICAL EQUIPMENT Electricity can KILL Each year about 1000 accidents at work involving electric shock or burns are reported to the UK Health and Safety Executive, (HSE) - 30 of these are FATAL. Indian figures are much higher and are not available to the public Some of these fatal injuries are not related to electric shock directly but falling down from ladders and other precarious positions etc. Portable electrical equipment in daily use ( hand tools, laundry machines, and pantry items etc.) are connected to an outlet/socket by a flexible wire and plug. The voltage levels are 220 /110 50/ 60 Hz. The user should ensure that the equipment is “ FIT FOR PURPOSE” Portable equipment is also, used by shore work shops and refit yards, should meet the safety requirements and if not, to be brought to the notice of superintendent and concerned authorities
WARNING: VOLTAGES ABOVE 50V CAN CAUSE FATAL SHOCK
SELECTION OF ELECTRICAL TOOLS All tools, leads, plugs and extension should be FIT and suitable for the purpose. Tools including instruments are to be maintained / inspected / checked after and before the use which should include the mechanical wear, leads, plugs There are three categories of equipment protection against electric shock : Class I : The apparatus is provided with basic insulation and the metal work is suitably earthed. Most of the domestic and heavy duty tools are class I. In case of insulation failure the earthed metal will reduce the hazardous voltage LEVEL Class II : Is sub divided into two sub groups: - IIA and IIB Class IIA : All insulated . The apparatus has two layers of insulation eg. Drill chucks and fixing screws Class IIB : Double insulated. All exposed metal work separated from the conductors by two layers of insulation so that the metal work can not become live. There is no earth connection hence the safety of the user depends on the integrity of the insulation. (Hair dryers, Small hand tools) Class III : Apparatus operates on Separated Extra Low Voltages (SELV). The voltage not exceeding 50 V AC or DC between conductors or to earth. The apparatus has basic insulation and no earthing is required
SELECTION OF ELECTRICAL TOOLS
Hazardous area: All electric tools, including battery operated, and test equipment are to be certified for the area (Zones) in which they are to be used Non-Certified equipment may be used when the vessel is in gas free condition Pneumatic tools are to be used in restricted, conductive locations, eg; tanks, crankcase, bilges etc. Regular inspection and maintenance is recommended for damaged insulation, overheating, proper plug socket contacts
Recommended Frequency and Scope of Test and Inspection
Recommended Frequency and scope of Test and Inspection Type of Equipment Battery-operated power tools, <25V Portable hand lamps, tools, extension leads. Supplied by dedicated isolating transformer <50V Portable equipment, handheld tools, extension leads and associated protective devices. Machinery areas 110V/220V Portable equipment in dry accommodation / office spaces 110V/220V
User/Informal checks Physical Condition/ Function check before each use Physical Condition/ Function check before each use Physical Condition/ Function check before each use
Inspection & Testing No
Comment Refer Note 1
9-12 months
Refer Note 2 Refer Note 3
6-9 months
Refer Note 2 Refer Note 3
Physical Condition/ Function 12-18 months Refer Note 2 check Refer Note 3 6-12 months 6-9 months Portable equipment in laundries and Gallery Physical Condition/ Function Refer Note 2 110V/220V check Refer Note 3 1-3 months Refer Note 2 Privately owned portable equipment None Before 1st use on board Refer Note 3 110V/220V Notes: 1. Charges to be treated as separate equipment and tested according to requirements. 2. For double insulated (classII) equipment, limited testing is required. Any associated extension leads having a protective earth conductor should be tested 3. Computer / IT or electronic equipment should not be subjected to Insulation Testing
MODULE - 7 Energy Levels
ENERGY Energy in electrical system is measured in;-
Kilo Watts – Generally in 440 volts system or so called low voltage system
Mega Watts – Generally in High/ Medium voltage system
ARC ENERGY When a fault occurs, the Energy at the fault = Current squired. x time FAULT LEVELS AT DIFFERENT VOLTAGES: Fault level @ 11,000 volts = 1.732. x k V. x Fault current Therefore Fault current = Fault level (MVA ) / 1.732. x Voltage (Kv) Typical Fault level in HV (11,000 /6600 v) system is measured in MVA. Standard 250 MVA Calculate the fault current for the above fault at 11,000 and 6600 volts
Fault level at 440 volts is measured at 31MVA Calculate the fault current.
HIGH VOLTAGE EARTHING CONDUCTOR The cross sectional area of the earthling conductor for Copper and Aluminum There are tables ( IEE ) and regulations: Cross sectional area – S = Root ( I square x time ) % k I = fault current t = time duration of the fault current K = properties of earthling conductor (resistivity, temp. coefficient etc. )
Earthing conductor:For a copper conductor with PVC insulation (thermoplastic) and a temperature range from 30 C – 160 C, k = 143 and For a aluminum conductor k = 95 Typical Copper Earthing conductor used = 70mm2 It can withstand a fault current of 10,010 A for 1 sec Aluminum conductor of 120 mm2 will handle a fault current of the same magnitude
In maritime high voltage installation the minimum size of Earthing conductors required is = 30 mm2 . As per Norwegian regulations
MODULE:- 8 SAFETY AND PROTECTION SYSTEM
SAFETY AND PROTECTION SYSTEM The safeties incorporated in any power system include protection against • Normal over loads but, with time and % • Short circuit between phases • Short circuit between phases and earth Faults cause Heavy sparks and Arcs
HEAT FROM ARCS / SPARKS As seen above the heat from high voltage arcs and sparks is measured in MVA Heat loss from an arcing chamber: Conduction; Convection and Radiation Arc extinction: The final extinction of arc requires a rapid formation of the dielectric strength of the medium between the circuit breaker contacts and cooling of the arcing chamber Cooling: Cooling is achieved by conduction through baffles, splitters, insulating walls or forced gas blast directed along the discharge as is done in air blast and SF6 circuit breakers
ARC- ENERGY AND CURRENT Besides normal / routine switching operations the arc energy which is generated by faults is a serious concern in designing the high voltage systems Fault generated by arc energy= (I2arc x t ). Magnitude of the fault current (The current in the Arc) and the duration in seconds Fault magnitudes fault level in HIGH VOLTAGE systems are expressed in “ MVA“ This is the “ fault level” Fault currents are expressed in kilo amperes ( k.A.)
MODULE 8 MEDIUM VOLTAGE SWITCH GEAR
There occurs a fault Then the current should halt Otherwise the fault current would increase And the service continuity decrease But the relay acts quick And the circuit breaker trips The faulty circuit is disconnected And the power system is protected Thank you Mr. Switch gear Because of you there is no fears
MEDIUM VOLTAGE SWITCH GEAR CONSTRUCTION AND “SALIENT “ SAFETY FEATURES
SWITCH BOARDS/ SWITCH ROOMS On ships with installed capacity in access of 3MW the switch boards are segregated. Links / interconnecting breakers are installed to interconnect the switch boards 1. Marine switch rooms containing switch gear and control gear 2. Transformers 3. Protection relays 4. Tripping and auxiliary supplies (Batteries) 5. Earthling
• PROTECTION; Current transformers and associated relays placed as close as possible with special features
• SECURITY; Unauthorized entry to switch rooms is restricted Special “key safe / trapped key” system is incorporated. Doors are “secured’
• ACCESS AND LIGHTING; Switch boards should have an unobstructed well lit passage not less than one Meter width Anti slip certified insulated coverings are required NOTE; NEVER USE SWITCH ROOMS AS WORKSHOPS OR STORAGE SPACES
SWITCH GEAR CLASSIFICATION OF CIRCUIT BREAKERS: • Based on Voltage Low – Less than 1kV Medium – 1kV to 52 kV High/extra high – 66kV to 765 kV Ultra high – above 765 kV • Based on location In door Out door
SWITCH GEAR • Based on interrupting Media Air break Air blast Bulk oil Minimum Oil SF6 Gas Insulated Vacuum
SWITCHGEAR AND SAFETY FEATURES 3300 / 6600 volt switch gear is metal enclosed • ISOLATORS - DISCONNECTORS a) Where isolation is required for other than electrical purposes b) On duplicate bus bar system to facilitate the change over without interruption c) All withdraw able circuit breakers, contactors SAFETY FEATURES:- Most isolators are OFF LOAD devices
SWITCH GEAR SWITCHES: Load break- fault make devices. Not capable of handling the fault currents • EARTHING SWITCHES: Normally not designed to break fault current Features; a) Independent manual operation. May have stored energy b) Inter lock is provided when connected to circuit main earth c) Some switches are fitted with anti - flex handles
•
SWITCH GEAR CONTACTORS ; Mechanical switching devices operated other than by
hand. Not capable of breaking the fault current hence fitted with fuses Features; a) Frequent operations with vacuum interrupter b) Are “dependent power operated” c) Withdrawal not possible with contactor “ON” d) Can not be closed until the isolating contacts are fully engaged e) Automatic shutters cover the exposed live contacts when withdrawn f) The contactor opens on failure of a single fuse to prevent the single phasing g) In some cases the earthing switch automatically closes on withdrawal
SWITCH GEAR
CIRCUIT BREAKERS; Mechanical switching devices
Features; a)
b) c)
Capable of making, carrying and breaking currents under normal circuit conditions and also making carrying for a specified time and breaking currents under specific abnormal conditions Arc quenching medium may be SF6, vacuum, oil etc. Operations may be independent manual
CIRCUIT BREAKERS
SAFETY FEATURES ; a) b) c) d) e)
Can not be isolated whilst in closed position Automatic shutters are in all withdrawal able units Oil circuit breakers have a pressure relief valve Gas circuit breakers are fitted with alarms for low gas pressure and subsequent lock out Locking facilities are provided
INTERNAL ARC PROTECTED SWITH GEAR
Metal enclosed Switch gear » The switch Ready to install assemblies requiring high voltage and low voltage cable connections » assemblies have earthed metallic enclosures » These switch gears have generally three high voltage compartments separated by partitions
DESIGN AND CONSTRUCTION • The design is such that the normal operation, inspection and servicing can be carried out safely • Removable parts and fixed parts should withstand the insulation level of the switch gear • Interlocks between different components are provided to ensure the safety and the desired sequence of operation (Trapped key system)
Metal enclosed Switch Gear with removable parts • The withdrawal or engagement of the Circuit Breaker should be impossible unless it is in open position • The operation of the circuit breaker should be impossible unless: 1- It is in the service 2- Disconnected, removed, test position •
It should be impossible to close the circuit breaker in the service position unless it is connected to the auxiliary circuit
Metal enclosed Switch Gear without removable parts with disconnector • The operation of the disconnector should be impossible unless the associated circuit breaker is in open position • The operation of the circuit breaker should be impossible unless the associated disconnector is in the closed, open or earth position
ENCLOSURES
Gas filled Enclosures : • Sheet Metal Gas filled enclosures house the main circuits • The gas is non corrosive inert gas with very good dielectric properties, such as SF6 ( Sulfur Hex Fluoride) in a thoroughly dried state • Service pressure is relatively low (2`5bar ) as per IEC 298
SF6 CIRCUIT BREAKER SULPHUR HEXAFLUORIDE : • Contacts close and open in a chamber filled with SF6 Gas • SF6 gas IS A GREEN HOUSE GAS • The gas has very good dielectric properties • Well suited to high and very high voltages
Physical properties of SF6 gas Colourless Odourless Non toxic, pure SF6 gas is not harmful to health Non inflammable. However impure SF6 gas contains toxic impurities • Gas is 5 times heavier than air @ 20*C • • • •
Chemical properties of SF6 gas • • • •
Stable upto 500*C The gas is inert Electro negative Does not react with structural material
Vacuum Circuit Breaker
VACUUM TECHNOLOGY Another media used in metal enclosed switch gear is vacuum for dielectric between contacts and cooling the arcing chamber NOTE :Vacuum switch gear is the most commonly used switch gear in systems up to 65 kV .
VACCUM ARC General characteristics : The vacuum arc is really a metal vapor discharge The vacuum arc is different from general low or high pressure arcs since the arc forming particles are the electrons, ions and neutral atoms , derived from the electrodes itself. ( Contact material ) The base gas pressure here is very low ( vacuum). Therefore conduction process role is not significant
VACUUM CIRCUIT BREAKERS GENERAL CONSTRUCTION : • Arc interruption takes place in vacuum • Arcing contacts are placed in the metal chamber • Moving contacts are attached to metal bellows • The interrupter is finally enclosed in a metallic body • Proved to be most suitable for medium voltage
• The material of the contacts plays very important role in overall performance of the breaker [ Cu Bi, Cu Cr, Cu Ag ]. • Cu Cr is most common material used • Contact geometry ( VERY IMPORTANT)
Vacuum Interrupter Design aspects; • Interrupter length ( 8-20 mm) depending upon voltage • Contact travel (contact gap) 6 – 10 mm for 6.6 k.V. • Contact shape • Contact size • Time of travel Contact Gap
8 to 12 mm
Contact speed Opening Closing
0.5 to 0.8 mm/ms 0.5 mm/ms
Construction of Vacuum Interrupter Parts 0f the interrupter; • Enclosure made of impermeable insulating material • Enclosure retains a vacuum of 10/10x11 Torr • End flanges. Made of non magnetic material • Contacts are “disc shaped” with symmetrical grooves, segmented (misaligned fixed and moving) • Contacts (Sintered) Copper Bismuth • Vapour condensing shield. Metallic tube around the contacts • Metallic bellows welded to metallic flange • Seals. Metal glass or ceramics
Interrupter
VACUUM CIRCUIT BREAKER Vacuum Interrupter technology has some distinct advantages: • SMALL CONTACT GAP • TRAVEL DISTANCE • LONGER ELECTRICAL LIFE • ENVIORNMENTLY BENIGN • OVERALL SUPERIOR PERFORMANCE
Vacuum interrupter
• Vacuum testing Checking VACUUM. 1. Check the pull on moving contact 2.
Connect the power to the OPEN terminals of the interrupter from a dedicated vacuum checker available on board/plant ( usually 15 kV – 50kV )
Merits and Demerits of VCB and VCT 1. 2. 3. 4. 5. 6. 7. 8.
Self contained unit. No gas or oil required Pollution free Modest or no maintenance Compact unit .Easy installation Non Explosive Silent operation Large nos. of operations. Well suited for repeated operation of almost all types of loads (30,000) Sealed unit keeps the elements out, maintains the contact resistance
Demerits • The vacuum interrupter is more expensive • Restriction on rated voltage • High technology involved in designing the interrupter • Loss of vacuum will render the switch gear useless • Surge suppresser are required for certain switching operations
Vacuum Contactor • Capable of millions of operations on load and overload • Short circuit interruption capability is limited • Back up fuses give the short circuit protection • Strikers are provided to take care of single phasing and short circuits • Sustaining power is required ( 110 volt DC on board )
OPERATING MECHANISM • SPRING MECHANISM • PNEUMATIC MECHANISM • HYDRAULIC MECHANISM • SF6 DYNANAMIC MECHANISM • MOTOR DRIVEN MECHANISM
SYSTEM REQUIREMENTS OF CIRCUIT BREAKERS The main function of the circuit breaker is to interrupt short circuit currents and protect their loads against the effects of such faults. This function must be carried out with a high degree of safety and reliability
• Terminal faults • Short line faults • Transformer magnetizing and reactor currents • Switching of unloaded capacitor banks • Out of phase switching
TESTING SWITCH GEAR
ROUTINE TESTS 1. Di electric test on the main circuit 2. Di electric test on the auxiliary and control circuits 3. Measurement of the resistance of the main circuit 4. Tightness test 5. Design and visual checks.( name plate details and values ) 6. Mechanical operation tests. ( minimum/maximum operating test. At least five closing opening time and pressure where applicable)
• TYPE TESTS: All type tests should be carried out by using the number of samples specified in IEC 60694
MODULE 9 REMEDIAL ACTION SCHEME
FAULTS AND PROTECTION SYSTEM
FAULTS AND PROTECTION SYSTEM Electrical safety regulations clearly specify:EFFICIENT MEANS, SUITABLY LOCATED, SHALL PROVIDE PROTECTION ; FROM EXCESS OF CURRENT IN EVERY PART OF A SYSTEM AS MAY BE NECESSARY • TO PREVENT DANGER TO PERSONNEL AND THE EQUIPMENT •
WHAT IS A FAULT? WHAT IS FAULT LEVEL? FAULT ENERGY? FAULT ENERGY IS MEASURED AS ( I x I x t ) Consequently, the FAULT ENERGY is to be kept to a minimum level to limit the damage to plant and more importantly, to
prevent injury to personnel
FAULT LEVELS
In high voltage system the faults are measured in MVA Fault = 1.732 multiplied by voltage multiplied by current = 1.732 x Voltage x Current = 1.732 x V x I
TABLE FOR FAULT CURRENT SYSTEM VOLTAGE (kV)
FAULT LEVEL( MVA )
FAULT CURRENT (kA)
400
35000
50
275
15000
31.4
132
7500
32
66
2500
21.8
33
1500
26.2
11
500
26.2
6.6
150
13.1
3.3
50
8.8
.415
31
43.0
TYPES OF FAULTS AND EFFECTS
Active faults:- Current flow between two
a) b) c) d) e)
phases due to complete break down of insulation. This will result in an EXPLOSION. These faults are to be cleared as rapidly as possible CONSEQUECES – Increased damage at fault location due to very high energy. Danger to operating personnel (flashes, arcs, sparks ) Increased probability of earth faults spreading to healthy phases Very high electromechanical stresses on cores of transformers Sustained voltage dips on motors and generators
FAULTS CONTD. • SOLID FAULTS:- These faults occur due to suddenly the complete break down of insulation due to external damage resulting in very high fault currents and an explosion. Such faults also must be cleared as rapidly as possible otherwise it will result in any of the following consequences;
FAULTS CONTD. • Increased damage at location of the fault since fault energy = (current)2 x time • Danger to personnel ( arcs and flashes) • Enhanced probability of earth faults spreading to healthy phases • Higher mechanical and thermal stressing in all items of the plant carrying the fault current, particularly in transformers • Sustained voltage dips
FAULTS CONTD. The incipient faults:- The small faults developing into catastrophic failure
Passive Faults :- Not really direct faults but may result into active faults if not attended to:-
a) Over loading- leading over heating and insulation deterioration. b) Over voltage which stresses the insulation c) Under frequency d) Power swing:- Generators running in parallel can go out of synchronism e) In adequate cooling f ) Bearing failure
FAULTS CONTD. • TRANSIENT AND PERMANENT FAULTS :- These faults occur mostly
on out door equipment • PERMANENT FAULTS:- Faults with permanent damage to insulation • SYMMETRICAL AND ASYMMETRICAL FAULTS:- Faults related to power factor
PROTECTION SYSTEM Protection system provides protection to the complete electrical system; • From source to the consumers • Maintainer and the operator. The system also activates alarms and indicates the cause of the faults and abnormalities
PROTECTION SYSTEM SHOULD: • DETECT THE FAULT AS EARLY AS POSSIBLE • DISCRIMINATE • DISCONNECT ONLY THE FAULTY CIRCUIT
THE ROLE AND PURPOSE OF PROTECTIION SYSTEM Protection system, however sophisticated, can not prevent a fault • A good number of faults are caused by human error • Condition monitoring has its limitations So the role of the protective system is to detect a fault at the lowest possible level consistent with the ability to supply full load to the plant. That is;; TO MINIMISE BUT NOT PREVENT DAMAGE TO THE AFFECTED PLANT TO DETERMINE THE AREA OF THE FAULT AND DISCONNECT THE AFFECTED AREA
PROTECTION SCHEME 5-S principles ;-
1.SECURITY: The system should be reliable so that security of supply is ensured
2.SENSITIVITY: The system should be able to sense minimum value of the fault current, thereby reducing the consequent damage
3.SPEED: Protective system should be able to isolate the fault in the shortest possible time
4.SELECTIVITY: Protective system should be able to select and trip only the nearest circuit breaker
5.STABILITY: Protective system should not operate for external faults
PROTECTION SYSTEM Protection System includes the :• Generator Protection • Switch Board Protection • Feeder Protection • Transformer Protection • Motor protection
COMPONENTS OF SAFETY AND PROTECTION SYSTEM PROTECTION SYSTEM INCORPORATES :•The relays; Electro mechanical relays Static relays Numerical relays •Transformers; Required for the measurements of currents and voltages Current transformers Potential transformers (voltage transformers) Instrument transformers The above transformers are classified as instrument (measuring) and protection transformers
THEORY OF CURRENT TRANSFORMER The ideal CT• Primary and Secondary AT (Ampere Turns) should be exactly equal IN MAGNITUDE • The AT should also should be in perfect phase opposition Two basic factors can effect the performance of a CT 1. The phase error 2. The current error ( the Ratio Error)
The CT performance can be improved by• Using a core of very high permeability and low hysteresis loss • Maintaining the rated burden (load) • Ensuring a minimum length of flux path • Lowering the internal secondary burden • Use of wound type primary • Keeping the secondary burden to minimum possible value
PARAMETERS OF INSTRUMENT TRANSFORMERS • CURRENT RATING • RATED BURDEN • ACCUEACY CLASS FOR PROTECTION CT,s ( 5P,10P,15P.) • INSTRUMENT SECURITY FACTOR (In case of short circuit) • KNEE POINT VOLTAGE Knee point; The point on the magnetization curve at which 10% increase in flux density causes a 50% increase in exciting ampere turns
CURRENT TRANSFORMERS (CT,s) • Most current transformers are supplied in the ratio of 100/1, 200/5, 400/5, 800/1, 1600/5, 2000/1 etc. • Metering CT,s are linear to a value of 20% • Protection CT,s are linear during a large fault current • Typical burden on CT,s is 2.5 – 15 VA • Summing CT,s are used to add different currents
Sequence Components: 1. Positive sequence, caused by locked rotor 2. Negative sequence, caused by current imbalance 3. Zero sequence, caused by earth faults
Zero – phase sequence systems 1. Placing a CT around earthed neutral 2. Using a core balance CT 3. Current balance system
APPLICATION OF INSTRUMENT TRANSFORMERS • DIFFERENTIAL PROTECTION; Used for the protection of generators, transformers, transmission lines and large motors etc. (Vector differences between two or more electrical quantities) • RESTRICTED EARTH FAULT PROTECTION; Generally incorporated in generators with earthed neutral. In this arrangement usually up to 15% or less earths are not included • CORE BALANCE CT; A core balance CT is used in sensitive earth fault protection system. The CT is put around all the three phase cables to detect the zero sequence current. These CT,s are very sensitive and can detect the leakages of 500mA • SUMMATION CT,s • CURRENT BALANCE CT,s
NON RELAY OPERATEDP ROTECTION
• SURGE PROTECTION • FUSES
EXAMLES 0F HRC FUSE SELECTION
EXAMLES 0F HRC FUSE SELECTION Fig. 1 Illustrates the HRC Fuse operation in the cut off region. Key points to note are: • Cut off Current • Pre-arcing time • Arcing time
EXAMLES 0F HRC FUSE SELECTION Fig. 2 Shows “I squire t” rating of some different sizes of HRC Fuses. It should be noted that the “I squire t” parameter is given on a logarithmic scale
EXAMLES 0F HRC FUSE SELECTION Fig. 3 Shows the time / current characteristic of the fuses given in fig. 2
EXAMLES 0F HRC FUSE SELECTION Fig. 4 (a) Shows simple distribution system with fuse discrimination using the “2 to 1” rule. The discrimination is achieved by doubling the rating of the fuse at each ascending stage of the distribution system Fig. 4 (b) Shows the corresponding system with discrimination achieved by using the ‘I squire t ; method based on the “I squire t” characteristics shown in fig 5.
EXAMLES 0F HRC FUSE SELECTION Fig. 5 Shows the “I squire t” characteristics of some of the HRC fuses ( supplied by the fuse manufacturers )
PRACTICAL EXAMPLE OF HRC FUSE SELECTION AND DISCRIMINATION
PRACTICAL EXAMPLE OF HRC FUSE SELECTION AND DISCRIMINATION Fig. 6 Calculate the capacity of fuse A and the capacities of fuses feeding 20 k W lighting , 30 kW heating and 30 kW motor circuits. Lighting load @415 Volts. 20 kW = 20 x 1000 / 1.732 x 415 = 28 Amperes . Therefore 32 Amps fuse will be suitable Heating load @ 415 Volts. 30 kW = 30 x 1000 / 1.732 x 415 = 42 Amperes Therefore 50 Amps fuse will be suitable
PRACTICAL EXAMPLE OF HRC FUSE SELECTION AND DISCRIMINATION Fig. 6 (Continued) MOTOR :- 30 kW 4 pole DOL starting current ( 7 x FLC ) for 10 seconds would require a fuse to with stand a starting current of 378 amperes for 10 seconds Therefore a 100 Amps fuse will be required to withstand the motor starting current of 378 Amps for 10 seconds as per fig 7
PRACTICAL EXAMPLE OF HRC FUSE SELECTION AND DISCRIMINATION Fig. 7 Shows time current characteristics of some of the fuses. Therefore fuse “A” in figure 6 will have to withstand the following load conditions 1. STEADY STATE – current = 28 + 42 + 54 = 124 Amps continuously 2. TRANSIENT - current = 28 + 42 + 378 = 448 Amps for 10 seconds
PRACTICAL EXAMPLE OF HRC FUSE SELECTION AND DISCRIMINATION Fig. 8 Shows the “I squire t “discrimination characteristics associated with the fuse time/current character shown in fig. 7, 125 A fuse will withstand 448 amps for 10 seconds. However on checking fig. 8 “I squire t “ characteristics it can be seen that the pre arcing time of a 125 A mps fuse is LESS than the total operating time (ie. Pre arcing time + arcing time) of 100 Ampere fuse in the motor circuit and therefore WILL NOT BE SUITABLE
PRACTICAL EXAMPLE OF HRC FUSE SELECTION AND DISCRIMINATION Fig. 8 (Continued) Consequently Fuse A will need to be rated at 160 Amperes NOTE :-160 A FUSE PRE ARCING TIME IS GREATER THAN THE TOTAL OPERATING TIME OF 100 Amps fuse
PRACTICAL EXAMPLE OF HRC FUSE SELECTION AND DISCRIMINATION Fig. 1 depict a diagram showing two squirrel cage induction motors connected to a 415 volts distribution system and their starters Motor 1 (M 1) is 37 kW 4pole, (In = 67.5 A) with DOL starting current = 7 x In for 10 seconds (67.5 x 7 = 472.5 A) Motor 2 (M2) is 110 kW 4pole, (In = 189A) with ESS (Electronic Soft Starter) starting current = 3.5 x In for 40 seconds (189 x 3.5 = 661.5 A) Refer the time /current and I squire t characteristics, determine the required HRC fuse rating for fuses F1, F2 and F3.
SURGE PROTECTION SURGE; A transient over voltage steeply rising followed by slowly decaying voltage wave •
EXTERNAL SURGE;- On transmission lines due to lightning and it travels in both the direction. This results in an increase, of voltage several time, of the rated voltage and subsequently gets attenuated. Protection is normally provided by lightning arresters
• INTERNAL SURGE / SWITCHING SURGES ;- These surges are caused due to switching action of certain types of circuit breakers, connected to inductive loads in particular. SF6 and Vacuum circuit breakers
SURGE PROTECTION TYPES OF SURGE PROTECTION CONNECTED TO ANY SYSTEM DEPENDS UPON THE VOLTAGE AND THE INSULATION OF THE SYSTEM • OIL INSULATED SYSTEM; - This type generally doesn’t require protection due to inherent properties of the oil used. • DRY INSULATED SYSTEM; - Rotating machines, dry core transformers can not withstand large switching surges. This type of apparatus requires surge protection NOTE- SURGE ARRESTER/SUPPRESSORS ARE CONNECTED ON THE ON LOAD SIDE ,FROM ALL THE THREE PHASES TO GROUND
SURGE PROTECTION S0URCE OF SURGE
TYPE OF SURGE
PROTECTION DEVICE
MOUNTING
EXTERNAL
LIGHTNING
LIGHTNING ARRESTER OUT SIDE SUBSTATION
INTERNAL
SWITCHING
SURGE ARRESTERS SUPRESSORS
LOAD SIDE OF THE BREAKERS
SURGE PROTECTION DEVICES USED FOR SURGE PROTECTION;-
1. 2.
Metal oxide type surge
arresterCapacitance Resistance surge suppressor-
Metal Oxide type surge arrester The metal used is Zinc Oxide(90-95%) and 5-10% additives such as Alumina, Antimony Trioxide and Bismuth Oxide etc. Principal Ratings • Rated Voltage and continuous operating voltage • Basic Insulation level expressed to withstand lightening impulse and frequencies • Thermal rating. Discharge capability and current rating • Impedance
CAPACITANCE RESISTANCE TYPE – Simple surge protection device with a power capacitor and a resistance in series The power capacitor rating is important and the operation depends• C-R value. The inductance voltage surges are balanced by the capacitance. L component is reduced • The surge energy is dissipated by the resistor • The device lowers the rising rate of voltage appearing across the contacts and suppresses the re ignition across the contacts • High frequency currents are attenuated with the C-R time constant
C - R VALUES FOR MEDIUM VOLTAGE C – 0.04 mF to 0.3mF R – 20 Ohms to 1000 Ohms For Medium Voltage motor control the values are C- 0.1 mF R – 100 Ohms
FUSES Simple construction and consistency Last resort against faults if the protection system fails Selecting a right fuse will meet the discrimination requirement Excursions of currents can affect the safety factor of a fuse
Check the time / current curve of the fuses
TYPES OF FUSES • Semi enclosed or rewire able type • Totally enclosed cartridge • Drop out fuse • HRC fuse ( Used on Medium Voltage ) • Striker Fuse ( used with High Voltage contactors)
SPECIFICATION OF A FUSE LINK • • • • • • • • •
Voltage rating ( To be specified by the manufacturer) Frequency Current rating ( Continuous RMS Value) Minimum Fusing current Fusing factor (Ratio between maximum fusing current to current rating ( This factor is more than 1 ) Prospective peak current Breaking capacity. Highest prospective current Operation of fuse link ( Process of pre arcing ) Cut Off ( melting of fuse element before the current reaches the prospective current)
OPERATION OF A FUSE There are two distinct periods in blowing of a fuse
1. Pre-arcing time. Time during which the fuse element is melting. (depends on current)
2. Arcing time. This is the period during which arcing exists. (depends on voltage)
3. Total arcing time.
Characteristics and classification of a Fuse ; • Check the characteristic curves • Duty of category – AC1 – AC5 etc. Classification 1. Class P fusing factor less than 1.25 2. Class Q fusing factor less than1.75 3. Class K fusing factor more than 1.75 FUSING FACTOR = Minimum fusing factor/ Rated current
RELAYS
MODULE -10 • Detect • Discriminate • Disconnect
PROTECTION RELAYS The most vital component in power safety system is the PROTECTION RELAY. Senses the current and voltage A protective relay is an electrically operated device designed to : Sense the identified circuit parameters and To initiate the disconnection with or without a warning signal, of the intended part of an electrical section in case of any abnormal condition in the installation
Discrimination Discrimination can be achieved by one of three methods • Comparison: - The basic principle of such protection is the zone protection. Incorporates the differential relays
• Time:- Discrimination by time is basis for many simple devices which include the time limit fuses and IDMTL relays. There is a drawback in this arrangement, the operation may be delayed
• Magnitude:- In this arrangement the discrimination is
achieved by the magnitude of the large change in the fault currents, for example in transformers primary and secondary currents
TYPES OF PROTECTIVE RELAYING • Directional- comparison Relaying • Directional – comparison Blocking • Phase comparison Relaying • Differential Relaying • Loss of field • Field grounding
TYPES OF RELAYS Electromechanical Relays 1 Attracted Armature 2 Moving Coil 3 Induction 4 Thermal 5 Motor operated 6 Mechanical
RELAYS • Most commonly used relays are the IDMTL relays • Relays may be non directional or bidirectional and directional • The relays may be typically 1A or 5A • IDMTL characteristics can be adjusted according to criticality of system involved like: -
Current setting • For a given current setting as the current increases the operating time decreases. • British and most of the other standards require that the relay does not operate below the 110% setting • For electromechanical over current relays of 1A, the typical settings range as0.5A (50%) to 2A (200%)
NUMERICAL RELAYS- Features available
1. 2. 3. 4.
Thermal protection Unbalance protection Under-current protection Over-current and earth fault protection and temperature protection (RTD) 5. Number of starts 6. Hour run meter 7. Ampere meter
PROTECTION SYSTEM TOPOLOGY The instruments shall be connected through a multi drop system using RS 485 MODBUS Protocol to PC/server. On line data is available.
The system on board usually has features as ;1 Data which is required to be viewed/logged 2 Trend graphs ( spread sheets) 3 Define lower and upper limits. Deviation will initiate alarms/standby system readily available 4 Mimic representation of the system with data and status 5 Archiving of the collected data for reference 6 Comparison 7 Data exchange to/from other units and many more features including SCADA
STATIC RELAYSThese relays have replaced most of Electromagnetic relays but not fully. BECAUSE• Highly sophisticated isolation/filtering • Very reliable power supply source • Stringent quality control since many manufacturer are involve • Testing at every stage is important • Many interconnected modules are required to achieve the complex functions
APPLICATION OF NUMERICAL PROGRAMMABLE RELAYS – Functions available • Remote computer/HMI capability • Sequence quantity (positive, negative, zero) • Power ( active, reactive, power factor) • Average, RMS, Peak values • Harmonic quantities • Frequency • Temperature (RTD) • Motor start/stop
Numerical Relay for Motor ProtectionFeature:• Self check feature – Ability to detect and correct a failure before the protection system operate • Data Acquisition System • Memory Testing • Set Point Testing • Watch Dog Timer
HI - MAP RELAYS Hyundai- Intelligent Measurement and Protection Relays
HIMAP RELAYS PTOTECTION FUNCTIONS ANSI No.
PROTECTION FUNCTION
24
Over Excitation protection
25/A
Automatic Synchronizing
27
Under Voltage, instantaneous, Definite time
27B
Bus under voltage definite time
32
Over voltage relay
37
Under current relay
40Q
Loss of excitation
46
Reverse phase
47
Phase sequence voltage
49
Thermal overload
50BF
Breaker failure
50GN
Current earth fault
51LR
Locked rotor
59
Over voltage relay
59B
BUS over voltage relay
59N
Residual over voltage
64
Ground over voltage
66
Start inhibit
HIMAP RELAY PROTECTION FUNCTIONS (Hyundai Intelligent Measurement and Protection) ANSI No
Protection function
67
AC directional over current
67GS/GD
AC directional earth faults definite time
78
Vector surge supervision
78 S
Out of step tripping
79
Auto Reclosing
81
Frequency supervision
81 B
Bus frequency supervision
86
Lock out
87M
Motor differential
87T
Transformer differential
87G
Generator differential
87LD
Line differential
87N
Restrict earth fault relay
94
Trip current supervision
95 i
Inrush blocking
- FF
Fuse failure
Other AdvantagesRemote communication is very cost effective • Change of Settings • Change of Group setting • Control of Breaker (closing and opening) • Instrumentation viewing • Event Recorder down loading
Any three general categories of protective relays technology is used :1. Electromechanical: Uses magnetic flux to create torque from voltage and current 2. Solid state relay: Uses low voltage analog signals sensed from current and voltage. Uses discrete electronic and logic circuits and may contain a basic microprocessor for logic and mathematical operations 3. Numeric relays: A multifunction, programmable logic relay ; digitized sensed current and voltage, then calculates an RMS or phasor equivalent value. Also uses high end microprocessor
TRANSFORMERS INSULATION Oil, Fluorogas, Nitrogen, On ships, dry type resin encased transformers are common
COOLING Marine transformers are air cooled and placed in separate well ventilated rooms ( In some cases in A/C rooms. ( Avoid moisture ingress) Special protection against surges is integral part of safety system associated with transformers Precautions are also taken against shock and vibration due to heavy seas
TRANSFORMER PROTECTION • High set Over Current :- HSOC [50/51] – I >>or inst.-To provide operation for high levels of fault current associated with primary side phase /phase faults. Set to be stable for phase to phase faults on the secondary side. – Trip primary and inter trip the secondary circuit breaker • IDMTL OVER CURRENT:- To provide non directional IDMTL protection for over current discrimination external to the transformer as a back up • IDMTL DIRECTIONAL OVER CURRENT:- DOC [67] I > To provide directional discrimination protection for over current external to the transformer in the opposite direction to the normal current flow. • INTER TRIP:- INT. [94] – To inter trip another circuit breaker which could possibly feed into the fault • DIFFERENTIAL RELAYING (87) – Measured difference between the input and output current initiates the tripping of the breaker
OTHER PROTECTIONS INCLUDE : • In rush detection and trip blocking • Energizing inrush • Recovery inrush – This occurs at clearing an external fault as a result of sudden increase of voltage • Sympathetic Inrush • Over excitation due to over voltage or under frequency • Ground fault sensing • Turn to turn fault ( differential relay )
MOTOR PROTECTION Sequence Components and supply unbalance Three sequence Components 1.
Positive Sequence Component (locked rotor effect)
2.
Negative sequence Component (caused by supply unbalance)
3.
Zero Sequence Component ( earth fault)
MOTOR PROTECTION Although environment and load may affect the life and integrity of the motor by and large all motors are liable to the same types of failure, namely:Primary cause of motor failure is the “ EXCESSIVE HEATING “ •
Negative sequence Protection : CAUSES : a) Voltage unbalance in the feeder supply b) Phase reversal c) SINGLE PHASING
•
Some kind of mechanical over load resulting in an electrical over load
•
Stalling due to mechanical failure
•
Phase failure
•
Insulation failure
Motor protection • • • • • •
Short circuit protection is provided by fuses The fuses are large in size in comparison with low voltage Access to fuses is available only after isolation Fuses are firmly bolted on the contactor and are part of the contactor When working on Medium voltage, level 3 or 4 safety is required as per NFPA 70E All modern motor protection relays have computer interface such as RS – 232 or RS – 485 communications that allows the user to ; a) Set the parameter b) Look at real time running data c) observe vectors of currents and voltages d) Event recording e) Start inhibit for number of starts etc.
MOTOR PROTECTION. Contd. • MOTOR PROTECTION :- MP - Generally consists of number of elements incorporated into the same relay Thermal – [46] [49] :- Over current due to mechanical loading, out of balance due to single phasing and failure of power factor correcting components/capacitor • Earth fault:- cable breaking down to earth • HSO/C: [50/51] :- Instantaneous operation for motor / cable phase to phase fault ( only with circuit breakers ). Contactors are fitted with fuses • UNDER VOLTAGE ( Fitted with circuit breaker fed motors ) UV – [27] < V
HIGH VOLTAGE GENERATORS Types and starting arrangements Voltage on the stator and the rotor Excitation arrangement Safety systems on prime mover and the Alternator • Parallel operation of the generators • Load sharing ( DROOPS ) • Governor and Automatic Voltage Regulator • • • •
GENERATOR PROTECTION INSULATION : • Corona in the Armature of generators generating voltages in excess of 5000 Volts • Insulation failure: a) Excessive temperature b) Excessive voltage c) Contamination d) Physical damage • Inspection:a) Swelling b) cracking
HIGH VOLTAGE GENERATORS:Some considerations : • Insulation class – 1 . Class B, Mica, Glass fibers and suitable binder temperature 130* C 2 . Class F, above material but with higher binding temperature 155*C 3 . Class H, includes silicone and higher class binding, temperature 180* C • • • • • •
Air gap ( armature reaction) Cooling Special added protection in certain cases (turbines) Insulated pedestal bearing De- Excitation arrangement Earthing
GENERATOR PROTECTION STATOR SIDE The protection installed on generators circuits varies with :The size of the generators a) types of prim movers. Note : -Tripping of the generator circuit breaker should be accompanied by a complete shut down of the generatorsthat includes the disconnection of field excitation circuit, shutting of fuel/steam etc. • OVER CIRRENT PROTECTION:- Standard IDMTL. For external faults. [50 V / 51V] • INTERNAL PROTECTION :- Voltage restrained over current relay. VR/OC [51V] .Slow IDMTL characteristics • THERMAL OVERLOAD (49) : -
GENERATOR PROTECTION Contd. • RESTRICTED EARTH FAULT :- To operate for an earth fault on the generator winding and associated switch gear and wirings. REF- [50] or [64] calibrated CBCT • DIFFERNTIAL:- DIFF - [87]. Operates for a phase or earth fault • REVERSE OPOWER: - RP - [32R] . Operates for motoring. • PHASE UNBALANCE:- PU/B – [46]. To detect system unbalanced loading which gives rise to negative and zero sequence currents as well as positive sequence currents . • OVER SPEED/UNDER POWER:- O/S – [32L]. • UNDER/OVER VOLTAGE :- O/V – [27 / 59]. Failure of AVR or sudden loss of load • FIELD FAILURE:- FF – [40] • UNDER / OVER FREQUENCY – [ 81] particularly while synchronizing
GENERATOR PROTECTION Contd. • Negative Sequence Protection due to unbalanced load ( single phasing ) • Out of step protection. Load swing • Thermal protection. Relay BE1- 49 takes signal from an RTD • Check synchronizing and auto synchronizing. Relay [25] takes care of this arrangement (use the provision regularly )
GENERATOR PROTECTION ROTOR SIDE :The generator of MVA capacity need rotor protection as follows :-• Rotor Excitation Under Current [ UBC/A/37 ] • Rotor Excitation Under Voltage[ UV 80 ] • Diode Failure Relay • Rotor Earth fault Relay [ 64R ]
Polarization Index and Insulation Resistance test on Motors, Generators and Transformers as per IEEE standard 43 – 2000 ( P/I – I/R ) Partial Discharge; premature failure of insulation Causes.. 1. 2. 3.
Salt laden atmosphere Hydrocarbon contamination AVR feed back re strike etc
Purpose: • Evaluate the condition of the insulation between the ground and the conductor • IR value measured with Meggar may not be the actual reliable I/R value. • To obtain the reliable I/R value, P/I and I/R values are needed • What does the Meggar actually measure ?
Insulation resistance is made up of four components: 1.
Capacitive Current - ic
2.
Conduction Current - il
3.
Surface Leakage Current - ir
4.
Polarization current - ip
Capacitive current: ic • Any insulation behaves like a capacitor when subjected to D. C. voltage • A high charging current will flow through the capacitor and then it will decay • In case of generators, motors and transformers the decay time of the current is less than 10 seconds, however the IR value is taken for 1 minute
Conduction Current: il • This current is galvanic current which flows between copper and core • This can happen if the moisture is absorbed by the insulating material like thermoplastic or crack in the insulation or some contamination • This current is constant with time
Surface leakage Current :ir • This is constant D.C. current and flows through the surface of the insulation • The cause for this current is conductive contamination on the surface of the winding • This current is constant with time
Polarization Current : ip • Electrical insulation is hygroscopic in nature and absorbs moisture in low quantity or in excess • Applying D.C. potential (Electric Field) from Meggar results in the absorption of electrons from the hydrogen molecules resulting in the ionization of Hydrogen • The energy (current) required for this to happen comes from Meggar D.C. voltage • This current is called “ POLARIZATION CURRENT”
• The water becomes completely polarized when electrons from Hydrogen are merged with oxygen • When the alignment (merge) is complete, the current flow from Megger stops • The approx. time to complete polarization (merge) is 10 minutes of applying voltage • Now add all these four currents
Total current It It = ic + ir + il + ip After 1 Min. ic = 0 (As analyzed earlier) So, It after 1 min. it = ir + il + ip After 10 min. ip is zero ( seen earlier ) So, it after 10 min. = ir + il Therefore, PI = ir + il + ip / ir + il, = R10/R1 That is .Resistance after 10 min. / Resistance after 1 min Note : Minimum IR value acceptable = 100 M Ohms with 2500/ 5000 volt Meggar for 1 min.
Interpretation of PI value PI
Condition of winding
Measure to be taken
< 1.0
Hazardous
Dry winding
1-1.5
Bad
Dry winding
1.5-2
Doubtful
Drying recommended
2.0-3.0
Adequate
3.0-4.0
Good
>4.0
Excellent
“PROVE DEAD” THE PLACE OF WORK
• High voltage test probe:Practical demo • Discharge rod:• Portable earthing cables
Test probe / Hot rod Read the instructions printed on the probe • Prove the test probe before using. (Read the safety precaution on proving unit) • The typical unit available on board may also have provision for discharging the stray voltages. • Connect the earth knuckle to the earth strip firmly • It is safe to work only when the LIGHT ON THE PROBE DOES NOT LIGHT, probe connected to earth
Discharge Stick
6 ft Insulated Rescue Hook
Salisbury Discharge Stick
8 ft Insulated Rescue Hook Static Discharge Stick Attachment Gripall Hotstick
“PROVE DEAD” THE PLACE OF WORK After switching off, withdrawal, and earthing 1. Check and confirm the continuity of the discharge rod 2. Connect the flexible end to the earth strip firmly 3. Touch the points of work with the tip of the rod to discharge any residual voltages
110 VOLTS POWER SYSTEM • UPS WITH BATTERY FLOATING • AVRCONTENUOSLY MONITORS THE CURRENT AND VOLTAGE OF CHARGER AND THE BATTERY • EARTH FAULT AND VOLTAGE DEVIATION ALARMS • EARTH LAMPS
KEY EXCHANGE/ TRAPPED KEY SYSTEM EXERCISES MODULE - 11
General safety Rules and definitions
GENERAL HIGH VOLTAGE SAFETY RULES These rules apply to all work carried out on high voltage system within the regulation laid down by ; • The Health and Safety at Work Electricity Act 1989 • The Code of Safe Working Practices for Merchant Seamen • The safety rules are only a general guide lines and that safety rules should be written specifically for individual installation or system
General Safety Rules 1.
2. 3.
4.
No work shall be carried on any high voltage system or apparatus until an assessment has been carried out to high light the dangers or consequences of that work No work shall be carried on any high voltage system or apparatus by persons not authorized or qualified to do so No work shall be carried on any high voltage system or apparatus until; A. The system or apparatus has been isolated from the supply B. The system or apparatus has been properly earthed C. The system or apparatus screened from any other apparatus as may be necessary and Danger or caution notices posted in the relevant areas No work shall be carried out on any high voltage system or apparatus until a high voltage permit to work has been issued
General safety rules cotd. 5.
6.
7.
8.
No high voltage permit to work shall be issued until all competent persons who carry out work have been A. Made aware of the full extent of the work to be carried out B. Made aware of the points of isolation and earthing C. Made aware of any dangers that may be present in the immediate vicinity of the work No person shall carry out any work on high voltage system or apparatus whilst unaccompanied by a person who is competent to do so On completion of the work the competent person shall demonstrate to the authorized person that all work has been completed in line with the work instruction On completion of the work the permit to work shall be cancelled and all personnel should be made aware that it is no longer safe to work on the high voltage system or apparatus
General safety rules
9.
10.
11.
On completion of the work where necessary a sanction for test shall be issued and all persons involved shall be made aware of any danger that may arise during the test and be made aware of any points of isolation that may be necessary On completion of the tests the competent person in charge of the test shall demonstrate to the authorized person that all the equipment used in the test has been removed and that the system or apparatus is ready to be returned to normal service after the sanction for test has been cancelled Once the permit to work or sanction for tests have been cancelled the authorized person shall ensure that all isolators and earths have been removed and that it is safe to energize the system
DEFNITIONS :Additional Earth- An approved earthling device that may be applied by the competent person in addition to circuit main earth
Authorized- Given authority in writing by STASCO. Chief Engineer, superintendent, Manager etc.
Approved- Sanctioned in writing by STASCO Caution notice- A portable notice warning against the interfere with or to operate the Electrical Equipment
Chief Engineer- Person responsible for maintaining safe conditions
on the ship and the Electrical power system under his control. The C/E should have sufficient Electro –technical knowledge and experience to recognize and avoid danger and fully familiar with STASCO SMS Chief engineers may delegate part or the whole of their electrical role, including authority for issuing electrical safety document, to others at their discretion but in doing so retains personal responsibility
Definitions contd.
Circuit main earth- An earthling device applied to main circuit
conductors prior to the issue of an electrical safety document as • A closed earth switch • A circuit breaker selected and closed to earth • A set of approved portable Earthling leads Competent Person – A person with the necessary knowledge , training and experience to undertake tasks and activities assigned to them and in particular has sufficient electro technical knowledge and experience to recognize and avoid danger Danger- Risk of injury or loss of life from electric shock, burns or other causes Dead – Equipment at or about zero potential and disconnected from any live power system Electric equipment – The electrical machines, apparatus and circuits forming part of an electrical installation Electrical Permit to Work ( EPTW ) - A form issued by a permit issuer (authorized person ) to a permit holder ( competent person ) in charge of the work to be carried out on specified Electrical Equipment
Definitions contd.
Electrical person- There are three categories of electrical Person A. Electrical Person – A person with necessary knowledge, training and experience who MAY or MAY not be a trained electrician or electrical engineer but is competent to carry out work on low voltage electrical equipment
B.
Electrical person – MV – A person with the necessary knowledge, training and experience who may or may not be a trained electrician or electrical engineer but is competent to carry out work on medium voltage electrical equipment.( The electrical person MV MUST BE COMPETENT TO CARRY WORK ON LOW VOLTAGE ELECTRICAL EQUIPMENT)
C.
Senior Electrical Person – An electrical person who has demonstrated superior knowledge and skills. The category of Senior Electrical Person is intended for electrical engineer appointed to ships with particularly complex electrical plant and equipment
Testing and Maintenance’ 1. Insulation testing (Phase to Earth and between phases ) 1000 / 5000 Volts Meggar 2. Contact resistance with micro Ohm meter 3. P/I tests 4. Time of operation ( closing/opening) 5. Battery supply 110 volts DC 6. Connections of PTs and CTs 7. Risk assessment
POWER MANAGEMENT SYSTEM (PMS)
The system addresses the key energy needs: • Industry’s dependence on scare energy resources • The volatile energy costs • Growing environmental consciousness • Very stringent legislations The other names: What is in a name ? • Power Distribution Control System ( PDCS ) • Load Management System ( LMS ) • Electrical Network Monitoring & Control System (ENMCS) • Electrical Control System ( ECS ) • Electrical Integrated Control System (ELICS ) • Integrated Protection and Control System ( IPCS )
PMS An overview and salient features Power management is a group of functions • Design of power management system and power plants installed on ship types • Black out prevention system • Minimization of fuel consumption and operation • Power redistribution control • Integrated net work power control • Speed control of generators and motors
PMS Functions • Generator allocation. Compare the total demand with the available power • Auto start / stop of generators to consider with the load changes as per pre calculated load dependent start /stop table • Transient frequency deviation limit • Under frequency limit will trip the circuit breaker of an on line generator resulting in a black out
PMS Load limiting features Types of consumers • Sheddable loads; All non essential loads can be regarded as sheddable loads • Non sheddable loads; Consumers with high importance of supplying the energy eg; Nav. aids and control net work etc. • Controllable consumers; thrusters, compressors etc. • Non controllable loads; switch ON /OFF
PMS • There are consumers that rely on power rather than Energy. These can operate with reduced power for limited time ( HVAC, HEATERS) • There are consumers which rely on POWER. These consumers need full power all the time ( controllers, control equipment, Nav. aids)
PMS Black out prevention control Electrical Causes of black out • • • •
Short circuit Earth fault Overload Sharing of KW and KVAR load
PMS • •
•
•
SUMMARY The plant definition phase: Tighter dimensioning and thus reduced costs Plant start up: The PMS will ensure the power system capacity is not violated at any time by holding load start command until the system can provide the required power. This helps the plant safety All phases of plant operation: The PMS will control all generators, transformers and motors to ensure stable power system operation as well as monitoring and controlling active and reactive power with other generators running in parallel Maintenance planning: Comprehensive data are recorded and aggregated on the conditions of the electrical power plant. The data can be monitored automatically and responsible person can be notified
PMS Non Electrical causes • • • •
Temperature Pressure Level Rpm
• Inadvertent operation etc.
“Remedial Action Scheme” during system faults
Def; The measures activated by the system…Manually or Automatically…to ; • Isolate the consequences of fault • Maintain a normal state or move towards a normal state ( Pre fault or post fault ) • Maintain rotor angle stability after being subjected to disturbances or faults
Remedial Action during system faults Other names ; RAS ; Remedial Action Scheme SPS ; Special Protection System SIPS ; System Integrity Protection Scheme Common RAS Classification; principles for contingencies and Disturbances • Event based • Parameter based • Combination of both above
Criterion Without exceeding the safety limits….. means; • Healthy elements should remain in operation • Available generator on line • Available standby generator • Available fuel supply • The reserve or standby power should be able to accommodate the new operational situation Situation…? The fault has happened to a particular section or part of a plant
Criterion Situation • Active power available • Alert state… System operating normally but a contingency is detected • Section control. Frequency • Black out state • Exceptional contingency. Fault on generator / transformer or DC line failure • Short circuit / Open circuit
Components of RAS; •Load shedding •Harmonic domain analysis in case of electronic switching devices •Thermal problems caused harmonic frequency leakage
Components of RAS • • • • •
Fast acting IED CT’s / PT’s with fast response PLC’s Very efficient and comprehensive SCADA system Relays with good IDMTL Characteristics
EXERCISES • • • •
HYUNDAI SWITCH GEAR TERASAKI SWITCH GEAR K.T. SWITCH BOARD TAPTI 3300 VOLTS SWITCH BOARD
