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IEEE Std 1653.3™-2012

IEEE Guide for Rail Transit Traction Power Systems Modeling Sponsor

Rail Transportation Standards Committee of the

IEEE Vehicular Technology Society

Approved 5 December 2012

IEEE-SA Standards Board

Approved 30 September 2014

American National Standards Institute


Abstract: A Abstract: A description of the data, techniques, and procedures typically used in modeling and analysis of traction power systems is provided in this guide. Keywords: analysis, Keywords: analysis, IEEE 1653.3, modeling, traction power

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Participants At the time this IEEE guide was completed, the Traction Power Modeling Working Group had the following membership: Michael Dinolfo, Chair Mark Pfeiffer, Vice Chair

Roger M. Avery Amildo Barrio Steven Bezner Alan Blatchford Gilbert Cabral Sean Carney Yunxiang Chen Ron Clark Chuck Dale Prakash Dave Ray Davis Dan Day Ramesh Dhingra James Dietz Dan Ferrante Paul Forquer Derek Foster Alan Friend Rajen Ganeriwal Vitaly Gelman Brian Gerzeny Mike Girdwood David R. Gobelle Lowell Goudge

Mark Griffiths David Groves William F. Hanlon, Jr. Zoltan F. Horvath Andrew Jones Sheldon Kennedy Tanuj Khandelwal Ethan Kim Bih-Yuan Ku Stuart Kuritzky Emil Leutwyler Ming Li Louie Luo Frank Machara Alok Kumar Mandal Ted Manning William Mao Vishwanath Mawley Moustapha Ouattara Henry Oviedo Chris Pagni Vince Paparo Mark Patterson Dev Paul

Gareth Rees David Reinke Richard Rohr Charles Ross Edward Rowe Holali Sathya Richard Shiflet Lee Shostle Pranaya Shrestha Suresh Shrimavle Jeffrey N. Sisson Fernando Soares Benjamin Stell Rick Straubel Raymond Strittmatter Daren Szekely Scott Tollefson Gary Touryan Jefrey Wharton Barry Wilson Robert Wilson Tom Young Gordon Yu Kelvin Zan

The following members of the individual balloting committee voted on this guide. Balloters may have voted for approval, disapproval, or abstention. William Aycock Ronald Bennell Steven Bezner Bill Brown Carl Bush William Bush Keith Chow Timothy Cramond Michael Dinolfo Robert Fisher Paul Forquer H. Glickenstein Randall Groves Werner Hoelzl

Andrew Jones Walter Keevil Udayan Khan Yuri Khersonsky Ethan Kim Saumen Kundu Greg Luri David Mueller Michael S. Newman Hans-Wolf Oertel Mark Pfeiffer D. Phelps Charles Ross Bartien Sayogo Suresh Shrimavle

Gil Shultz Alexander Sinyak Jeffrey N. Sisson Ralph Stell Eugene Stoudenmire Rick Straubel Raymond Strittmatter Brandon Swartley Gary Touryan John Vergis Matthew Wakeham Robert Wilson Jian Yu Daidi Zhong

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When the IEEE-SA Standards Board approved this guide on 5 December 2012, it had the following membership: Richard H. Hulett, Chair John Kulick , Vice Chair Robert M. Grow, Past Chair Konstantinos Karachalios, Secretary Satish Aggarwal Masayuki Ariyoshi Peter Balma William Bartley Ted Burse Clint Chaplin Wael Diab Jean-Philippe Faure

Alexander Gelman Paul Houzé Jim Hughes Young Kyun Kim Joseph L. Koepfinger* John Kulick David J. Law Thomas Lee Hung Ling

Oleg Logvinov Ted Olsen Gary Robinson Jon Walter Rosdahl Mike Seavey Yatin Trivedi Phil Winston Yu Yuan

*Member Emeritus

Also included are the following nonvoting IEEE-SA Standards Board liaisons: Richard DeBlasio, DOE Representative Michael Janezic, NIST Representative Julie Alessi IEEE Standards Program Manager, Document Development Michael Kipness IEEE Standards Program Manager, Technical Program Development

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Introduction This introduction is not part of IEEE Std 1653.3-2012, IEEE Guide for Rail Transit Traction Power Systems Modeling.

During development and updating of various IEEE standards and recommended practices related to rail transit traction power, the Rail Transportation Standards Committee of the Vehicular Technology Society recognized a need for a published document to describe the process of traction power system modeling. This guide provides an introduction to the terminology and methodology of rail transit traction power systems modeling.

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Contents 1. Overview .................................................................................................................................................... 1.1 Scope ................................................................................................................................................... 1.2 Purpose ................................................................................................................................................ 1.3 Limitations...........................................................................................................................................

1 1 1 2

2. Definitions, acronyms, and abbreviations .................................................................................................. 2 2.1 Definitions ........................................................................................................................................... 2 2.2 Acronyms and abbreviations ............................................................................................................... 3 3. Modeling and validation............................................................................................................................. 4 3.1 Introduction ......................................................................................................................................... 4 3.2 Train operations and wayside network modeling ................................................................................ 6 3.3 Faults ................................................................................................................................................. 10 4. Analysis.................................................................................................................................................... 4.1 Introduction ....................................................................................................................................... 4.2 Cable, conductor, and equipment ratings vs. loading ........................................................................ 4.3 Equipment ratings.............................................................................................................................. 4.4 Train voltages.................................................................................................................................... 4.5 Running rail-to-ground voltages........................................................................................................ 4.6 Contingency analysis......................................................................................................................... 4.7 Substation rating and placement........................................................................................................ 4.8 Examples of temporary or permanent mitigation strategies ..............................................................

15 15 16 19 20 20 20 21 22

Annex A (informative) Field validation of train operations and wayside network modeling ..................... 23 A.1 Introduction ...................................................................................................................................... 23 A.2 Field verification............................................................................................................................... 23 A.3 Organizational structure and roles of validation participants............................................................ 25 Annex B (informative) Contents of typical report on train operations and wayside network modeling ..... 26 Annex C (informative) Detailed input parameter list for dc system analysis .............................................. 27 Annex D (informative) Typical feeder characteristics................................................................................. D.1 Conductor characteristics of running rails and contact rails ............................................................. D.2 Inductance of running rails and contact rails (dc traction power systems) ....................................... D.3 DC resistance of typical OCS and feeder conductors .......................................................................

31 31 31 32

Annex E (informative) Tabulation of train voltage limits for dc traction power systems ........................... 33 Annex F (informative) Tabulation of rail-to-ground voltage limits for dc traction power systems............. 35 Annex G (informative) Rolling load calculations........................................................................................ 37 Annex H (informative) Bibliography .......................................................................................................... 40

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IEEE Guide for Rail Transit Traction Power Systems Modeling IMPORTANT NOTICE: IEEE Standards documents are not intended to ensure safety, health, or environmental protection, or ensure against interference with or from other devices or networks. Implementers of IEEE Standards documents are responsible for determining and complying with all appropriate safety, security, environmental, health, and interference protection practices and all applicable laws and regulations. This IEEE document is made available for use subject to important notices and legal disclaimers. These notices and disclaimers appear in all publications containing this document and may be found under the heading “Important Notice” or “Important Notices and Disclaimers Concerning IEEE Documents.” They can also be obtained on request from IEEE or viewed at http://standards.ieee.org/IPR/disclaimers.html .

1. Overview

1.1 Scope This guide provides a description of the data, techniques, and procedures used in modeling and analysis of rail transit traction power systems.

1.2 Purpose This guide provides methods and terminology for rail transit traction power system modeling.

1.2.1 Applicability This guide is intended for application by engineers involved in the design and specification of new traction power systems, and the technical evaluation of existing traction power systems in response to re-definition of operating parameters (e.g., increase in service).

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IEEE Std 1653.3-2012 IEEE Guide for Rail Transit Traction Power Systems Modeling

1.2.2 DC versus ac traction power systems This guide is intended to apply primarily to dc traction power systems. However, many of the techniques can be applied to ac traction power system analysis.

1.3 Limitations While this guide establishes a methodology for determination of various parameters that may be of value to designers of individual traction power system components (e.g., switchgear, transformers, rectifiers, cable), it does not address the detailed design process for those components. Where analysis described in this guide is similar to analyses described in IEEE Std 399 TM [B26], this document does not repeat the information in IEEE Std 399 [B26], but instead highlights how the IEEE Std 399 [B26] recommendations should be tailored to the specific requirements of a traction power system. This document also describes certain studies that may be of value as part of traction power system design but are not usually part of commercial and industrial design.

2. Definitions, acronyms, and abbreviations For the purposes of this document, the following terms and definitions apply. The IEEE Standards Dictionary Online should be consulted for terms not defined in this clause. 1

2.1 Definitions ac traction power system: A transit system in which power is delivered from wayside to on-board vehicular systems via alternating current, at nominally constant (or not deliberately varied) frequency, at the vehicle/wayside interface. auxiliary power (hotel power): Those systems, other than propulsion of the vehicle/consist that draw electrical energy. Examples include lighting, heating and air conditioning, air compressors, etc. AW0: The ready-to-run vehicle, without crew or passengers. AW1: AW0 + crew + every seat occupied by a passenger. For U.S. transit properties, a commonly accepted weight per passenger for this purpose is 70.3 kg (155 lb). 2 2 AW2: AW1 load + weight of standees at 0.251m (2.7 ft ) of suitable standing space per standee.

bunching: Deviation of individual headways (between adjacent trains) compared to nominal or average headway. contact conductor: The part of the distribution system, other than the track rails, that is in immediate electric contact with current collectors of the cars or locomotives. 2

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IEEE Standards Dictionary Online subscription is available at: http://www.ieee.org/portal/innovate/products/standard/standards_dictionary.html. 2 The contact conductor is usually either a contact rail (sometimes known as a third rail), or the contact wire of an overhead contact system.

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dc traction power system: A transit system in which power is delivered from wayside to on-board vehicular systems via direct current at the vehicle/wayside interface. design criteria: A description of required system performance. This may establish different requirements depending on status of the wayside traction power system (e.g., single contingency outage conditions vs. operation with all equipment in service). dwell time: The period of time measured from the instant a train stops at its berth at a passenger station until the instant it resumes motion. headway: The time separation between two trains both traveling in the same direction on the same track. It is measured from the time the head-end of the leading train passes a given reference point to the time the head-end of the following train passes the same reference point. Nominal headway is sometimes used to apply to design headway for a system, or average headway of a group of trains. normal conditions: When the traction power system configuration is not impaired by an outage to a substation or a feeder segment. track stationing: The agreed upon measuring of distance and location identification along the railroad. track-to-ground (rail-to-ground) voltage: The potential difference between track and earth at a given location. train consist: Quantity of cars in an operating train. This is typically a design constraint (e.g., operation with a six-car train consist). When this term is applied in connection with simulation and modeling, it may also be appropriate to establish the types of cars in an operating train (e.g., operation with a train consist of six Type A cars plus two Type B cars). transit property: The organization that operates the traction power system and trains. vehicle/wayside interface: The point(s) at which electrical power is transferred between the wayside electrical distribution network and vehicles. 3 These interface points are the location where vehicle contact shoes or pantographs are in touch with contact conductors and the rail/wheel contact points. vehicle weight: Several vehicle weights are of interest for different purposes, and are often called out as follows:

AW0: The ready-to-run vehicle, without crew or passengers AW1: AW0 + crew + every seat occupied by a passenger. For U.S. transit properties, a commonly accepted weight per passenger for this purpose is 70.3 kg (155 lb). AW2: AW1 load + weight of standees at 0.251m2 (2.7 ft 2) of suitable standing space per standee AW3: AW1 load + weight of standees at 0.167m2 (1.8 ft 2) of suitable standing space per standee AW4: AW1 load + weight of standees at 0.125m2 (1.35 ft2) of suitable standing space per standee

2.2 Acronyms and abbreviations NGD

Negative Grounding Device

OCS

Overhead Contact System

RMS

Root-mean-square (See 3.2.7.1)

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The direction of power flow is usually from the wayside system to the vehicle(s) but can be from vehicle(s) to the wayside power distribution system, during regenerative braking.

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3. Modeling and validation

3.1 Introduction Different model(s) will typically be required during system design, each one developed and tailored to specific issues and needs. 

During initial design, and prior to commencement of construction for a new transit system, analysis can establish preliminary locations for substations and can confirm the feasibility of proposed system characteristics (e.g., overhead contact system (OCS) conductor types/sizes, nominal and minimum system voltages, substation ratings, etc.).



As design is finalized, modeling is of value to confirm and finalize system and equipment characteristics, and to develop engineering estimates of relevant system performance characteristics (e.g., energy consumption, vehicle run times).

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For evaluation of existing systems in response to changes in operations levels or deployment of new vehicles with new performance characteristics, modeling serves to identify areas of the traction power system that may require capacity upgrade.

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Modeling can be performed at any time to evaluate new or previously unforeseen changes in operations levels or outages or reconfiguration of the wayside traction power distribution system.

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Modeling can provide a valuable tool to quantify performance characteristics of new technology systems.

3.1.1 Purpose of modeling Modeling is generally performed with the intent of assessing traction power system performance and reliability. Some of the issues that can be addressed via modeling are described below.

3.1.1.1 Quality of power delivered to trainsets Modeling can provide some indication of the range of voltages that will be delivered to trains during operations. Comparison of these voltage ranges can be made against train voltage limits (high, intermediate, or low). Low voltage criteria must be met to ensure continuous operation of trains. Operation of trains at voltages in the intermediate-to-low voltage range can result in reduced vehicle performance (i.e., reduction in available acceleration and/or top speed).

3.1.1.2 Overloading assessment of wayside equipment and feeders Modeling can provide assessment of expected loading (long time, short time, and instantaneous) on wayside equipment, which can be compared against withstand ratings of equipment, short term or instantaneous ratings of equipment, and relay settings.

3.1.1.3 Establishment of operational restrictions Modeling can be used to evaluate proposed operational restrictions in situations where the traction power system is operating in a reduced capacity (e.g., under selected equipment outages). If analysis of a minor reduction in system performance (e.g., a reduction in speed in the vicinity of an impaired substation) indicates that system operations can be maintained, but that system operations cannot be maintained

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without the performance reduction, then the operations restriction might be considered as a viable option when compared against capital upgrades of the wayside system that would otherwise be required to maintain full performance.

3.1.1.4 Energy management Modeling can be used to evaluate or compare the energy consumption of different technologies, system configurations, and op erating strategies/policies.

3.1.2 Baseline criteria Baseline criteria should be established and verified prior to modeling. Examples of baseline criteria to be considered may include the following; these should be collectively established by the transit property and the modelers: 

Applicable criteria or requirements of the user/owner (e.g., desired train service levels, acceptable train voltage ranges, specific outage conditions to be evaluated)

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Maximum allowable temperature limits of equipment

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Temperature ratings (short term and continuous) for insulation systems

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Environmental conditions for analysis (e.g., ambient temperature, climate)

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Vehicular performance capabilities and limitations, including performance limitations that may result at low train voltages

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Wayside civil alignment information

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Electrical distribution network characteristics

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Operations levels

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Contingency failure/outage conditions

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Maximum ceiling voltage for regeneration (if regeneration is to be evaluated as part of the simulation process)

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Other minimum or maximum voltage levels (associated with reduced vehicle performance, or minimum vehicle cutout voltage, or otherwise established as design criteria limits)

3.1.3 Validation Validation of the modeling process is desirable. A suggested validation process is described in Annex A.

3.1.4 Commonalities between models The modeling techniques addressed in this guide generally require preparation of electrical network model(s) to describe the system and to facilitate analysis. The electrical network(s) require information to describe individual components of the distribution system, including feeders and equipment (e.g., transformers, rectifiers). Power sources (generally utility sources, but also possibly regenerating vehicles) must be included in the model. It may be necessary to model vehicles as non-linear loads for load flow analysis of the distribution system. When conducting short circuit analyses, faults may be modeled as nodes in the system, or possibly as low impedance connections.

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3.2 Train operations and wayside network modeling

3.2.1 Purpose Train operations and wayside network modeling is performed to determine relevant performance parameters of a wayside electrical distribution system when providing power to trains. These parameters can then be compared to equipment and criteria ratings to determine if the wayside system provides an acceptable quality of power and reliability, and other purposes.

3.2.2 Background and legacy modeling approaches Calculations of current flow in and voltage at the load is fundamental to the design of traction power systems, from the earliest use of electric traction. These calculations are straightforward to perform for simple radial fed loads. For small networked loads and generators, various manual techniques were developed to simplify the arithmetic. As these networks became larger, these techniques became laborious and calculation approximations were made as described by De Koranyi [B11]. In many cases, these approximations were acceptable because the input data and load data were of limited accuracy. Analogue models were developed and these proved to be very powerful and were used until computer programs started to become available. Even so, these analogue models also used approximations to limit the physical size of the model and the amount of work to set up the model. These models could even perform transient analysis. The accuracy was again only as good as the input data on the line impedances, loads, generators, and motor starting current. Despite these apparent limitations, robust networks were regularly designed. Digital computer-based models can perform complex calculations quickly and accurately and in very large quantities. All these calculations can be very useful; but just like earlier modeling techniques, they are still only as accurate as the input data.

3.2.3 Process Train operations and wayside network modeling is typically performed according to the following sequence: Vehicle data collection and model development: Available tractive effort vs. speed for tractive vehicle(s) is determined. This data might also include variations in tractive effort as a function of voltage at the vehicle/wayside interface. Subsequently, this data can be used to develop a performance profile (speed vs. time, and acceleration vs. time, for acceleration from a stationary position to maximum speed) for operation of a multicar train consist on level tangent (straight) track. This would be established for a fixed loaded train weight (and, if necessary, at different voltages at the vehicle/wayside interface). Typical equations and procedures applicable to this process can be found in Railroad Engineering, 2 nd Edition [B16]. Collection of data regarding vehicles should also include data describing auxiliary power requirements. In some cases, the acceleration (or speed) vs. time performance profile may already be established (for a given load or train weight) on level tangent track. This may allow for determination of the available tractive effort vs. speed. The criteria for analysis should include definition of the vehicle passenger loading (passenger weight) to be applied during analysis. Vehicle weight AW2 is commonly used for traction power modeling, although the loaded vehicle weight(s) to be utilized in modeling should be established early in the modeling process by the transit property. If this criteria is based on loaded vehicle/train weights which are different from the loaded weight applicable to the initial data described above, then the data (tractive effort vs. speed, speed

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vs. time, and/or acceleration vs. time) must be adapted or revised to reflect the actual weight that is to be modeled. Modeling of operation according to specific civil alignment/route characteristics: Data is collected describing the civil track plan and profile for the actual rail system that is to be analyzed. This would include data such as grades, curves, alignment, station stops, and speed limits. Physical performance (speed/location vs. time) for operation of trains on the transit system can then be determined based on headways and/or train schedules. Train control methodology must also be considered in developing the model. Different methodologies such as automatic train operation (ATO), coasting, speed stepping, or braking methods will generate different results. Electrical network model development and analysis: An electrical model of the wayside traction power system is then developed, including utility source impedances and characteristics. In conjunction with train locations and loads as described above, corresponding train power consumption (including power consumption associated with propulsion, and with auxiliary on-board vehicle loads) can then be determined. Network analysis can also determine currents and voltages (as time-varying functions) in the wayside system. If necessary, interactions between train performance and system voltages (e.g., dependencies between tractive effort and train voltage) can be determined by simultaneous or iterative calculations that consider these parameters. Computer modeling of a rail transit system in this manner generally requires specialized software, and different software packages may be suitable for analysis of some transit systems but not others. 4 The user of software should be sufficiently knowledgeable of the software performance to describe in detail the algorithms and calculations performed by the software, so that suitability for use on a particular transit system can be assessed. In addition, the software should have capabilities for detailed data printout at intermediate stages of calculations so that the correctness of the algorithms and processes can be evaluated. Additional verification/validation against measured data can also be performed, as described in Annex A.

3.2.4 Regenerative braking Regenerative braking is typically implemented on modern transit systems to provide some degree of energy conservation by regenerating kinetic energy from braking trains, and distribution of this power to other loads (other trains that are consuming power, and/or a receptive utility or transit property distribution network), or to energy storage systems. However, regeneration may not always be considered as part of a system modeling effort for the following reasons: 

A network model that considers regeneration may be more complex than a model that ignores regeneration and therefore may not be available for analysis

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Accurate modeling of regeneration requires additional data to properly describe the performance of the regenerating trains during braking and the characteristics of the receptive load(s)

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The benefit of regeneration might be intentionally ignored during design to provide a more robust system because loads on wayside system components are generally greater when the effects of regeneration are ignored 5

4

For example, some software packages provide for analysis of dc traction power systems only, or of ac tracti on power systems only, as the detailed modeling processes can be considerably different. 5 Where a receptive utility or transit property distribution network is present, it is possible that consideration of regeneration actually results in computation of higher load on wayside feeder(s), but this situati on is not commonly encountered.

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If the primary goal during modeling is to develop an estimate of overall system energy consumption, then the impact of regenerative braking should be included.

3.2.5 Model time period and sampling interval Load flow models are, by their nature, steady state rather than transient studies. The time period to be modeled should be somewhat longer than any headway interval, and not le ss than the time required for a train to get from one end of the railroad being studied to the other end. 6 If multiple routes are being modeled at one time, the modeler may have to make some choices as to what constitutes a train run. Similarly, if only a segment of the railroad is under study and the boundary station of the study is not normally an end-of-the-line station, the model must be extended at least one or two stations to generate proper train movements and the associated electrical demand on the system. For sizing of equipment, the analysis should be based on peak headways and typically with AW2 train loading or as defined by the transit property. Energy consumption and/or power demand analysis will use actual train frequency intervals as the headways change and corresponding train loading changes. The sampling interval will have a considerable effect on the computation time and data storage requirements. The sampling interval needs to be fast enough to capture all that is of interest, but not so short as to create an inordinate amount of data. One second is often used. Longer than one second may tend to miss acceleration loading. The modeler should try a series of sampling intervals, say 0.1 s, 0.2 s, 0.5 s, 1 s, 2 s, and 5 s, to see how the results vary, and be prepared to demonstrate that the selected sampling interval is appropriate. In order to capture the highest traction power demands, the train schedule can be slightly offset. This offset is commonly referred to as offset resonance or time offset. This offset in the schedule, which is a common operational reality, can cause two trains starting simultaneously which may not appear in the normal schedule. Typical offsets range from 1 s to 10 s. The shorter the offset, the more iterations the modeling program must compute.

3.2.6 Input parameters Input parameters for analysis include the following: 

Information for train movement/performance simulation

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Signal system

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Yard, storage track, and mainline track information

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Vehicle data (for each vehicle type proposed to be operating)

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Traction power system network data

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Substation data

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Operating plan

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Contingency operation criteria—recovery from operation incidents

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Traction power system contingencies

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Utility information



Passenger vehicle loading

6

In other words, if the trip time for a train (or bus) is 37 min across the whole railroad, then the simulation time should be 37 min. With experience, it may be possible to shorten this time.

8




A more detailed list of prospective input parameters (for dc traction power systems) is provided in Annex C.

3.2.7 Output parameters Relevant output parameters will be different for different modeling purposes. However, available output parameters are likely to include some or all of the following parameters described below.

3.2.7.1 Root-mean-square (RMS) loads Electrical equipment is almost always limited in capacity by its ability to dissipate heat. As current creates heat (P = I 2R), current is usually the limiting factor. Traction loads can vary substantially in magnitude over short time intervals, so it is necessary to establish a method of determining the equivalent heating effect of a varying current. The root-mean-square (RMS) calculation does this for most components. RMS (root-mean-square) loads on wayside system elements (such as circuit breakers, feeders, buswork, rails, OCS conductors, transformers) are of value because these loads can generally be correlated to appropriate equipment and materials ratings to predict if equipment overloading will occur. These calculations are generally performed over time intervals between several minutes and several hours duration. For a continuous, time varying variable x(t) (such as amperes), RMS loading over a time period from zero to T can be calculated as:

rmsload =

1

T

( x (t )) T ∫

2

dt

(1)

0

For a time varying load comprised of discrete individual time periods, each of constant loading, RMS loading can be calculated as:

rmsload =

⎛ n ( 2k ⋅ t k ) ⎜ ∑ L ⎝ k =1

⎞

n

∑ t ⎠⎟ k

(2)

k =1

Where L1 , L2 , L3 , … are the various load steps in %, per unit, amperes, or actual load, and t 1 , t 2 , t 3 ,… are the respective (time) durations of these loads. The integration intervals need to be chosen in consideration of the thermal characteristics of equipment being evaluated. The values of t 1 , t 2 , t 3 ,… should each be significantly shorter than the thermal time constant of the system element, and the total duration of time over which the integration is performed should be significantly longer than the thermal time constant of the system element.

3.2.7.2 Average load data Average load data for selected wayside system elements is of value in predicting system energy consumption. For dc systems, it is also of value when evaluating rectifier loading to determine if overloading or overheating of rectifiers will occur.

9




3.2.7.3 Train voltages Train voltages must generally be maintained within allowable ranges to ensure proper train operation. At excessively low train voltages, the train performance will deteriorate (and trains may cease to operate altogether). As trains move through a transit system, train voltages can be expected to fluctuate considerably, so the analysis should consider the time-varying nature of train voltages. It may be necessary to concentrate on minimum train voltages and/or on various statistical representations (such as probability distributions) to assess system performance and acceptability. See Annex E for voltage limiting criteria values of various transit properties. Train voltages from simulation should be plotted against wayside track stations (or chain markers) to facilitate the identification of specific geographic area(s) where train voltages are outside of criteria limits. The recommended format for these plots is with voltages along the y-axis and track locations on the x-axis. Scatter plots (presenting a plotted point corresponding to each individual calculated train location and voltage), or density plots, are also of value.

3.2.7.4 Peak current Peak current is of interest to establish proper circuit breaker rating and proper settings for relaying devices.

3.2.7.5 Running rails-to-ground voltages Voltages from running rails-to-ground may be computed during analysis for subsequent comparison against criteria limits. These voltages may be of interest for the following reasons: a)

Stray currents (which can result in corrosion of underground utilities) are directly related to running rails-to-ground voltages.

b)

Running rails-to-ground voltages can result in unacceptably high levels of touch potential on the system. This can be a safety concern:

c)

1)

For transit personnel

2)

For the public at passenger station platforms

3)

For the public along shared rights-of-way

Inadvertent connection(s) from tracks-to-ground can result in current flow of several hundred amperes at the point(s) of connection. This can cause significant equipment damage.

3.3 Faults

3.3.1 Fault (short-circuit) modeling Purpose: Fault modeling is done in traction power systems for the same reasons that fault modeling is done in commercial and industrial power systems: a)

To establish touch-and-step potentials for grounding system design

b)

To establish equipment ratings

c)

To establish protective relay settings

10




Traction power systems differ greatly from commercial and industrial power systems in the way that traction power systems are (or are not) connected to earth. A discussion of whether and how to ground a traction power system is outside the scope of this document, but for the purposes of this discussion, the following assumptions are made: 1. A railroad powered by a dc traction power system uses one or both running rails to conduct propulsion current. One pole of the dc system (usually positive in North America) goes to the OCS, or the third rail, and the other pole (usually negative in North America) goes to the rails. A deliberate effort is made to isolate the running rails from earth to the greatest extent practicable. In modern construction, the dc system is virtually never grounded at the substations; substantial effort is made to insulate the system from ground and to alarm should a ground connection be made. However, older traction systems may be grounded directly or through diodes. In any event, despite the efforts to insulate the rails from earth, many thousands of rail insulating pads of individually high resistance value are connected in parallel, and that plus the effect of rain, dirt, and debris on the tracks results in a net low, and variable, resistance between the running rails and earth. 2. Rubber-tired electric buses and monorail systems which are powered by dc traction power systems keep both the positive and negative conductors well insulated from earth with little chance of accidental contact to earth, because the conductors are both aerial in the case of electric buses, or well protected in the case of monorails. (It is possible that in a city with both rail traction and rubber-tired electric buses, that both the trains and buses are powered by a shared traction power system, in which case the general concerns about the railroad dc traction power system apply.)

3.3.1.1 Types of faults Table 1 categorizes the types of faults that need to be considered.

Table 1 —Types of faults Type of fault, expressed in terms often used in commercial/industrial power system analysis Three-phase faults (1) (may be single-line-toground, double-line-toground, or three-phase)

Three-phase faults (2) (may be single-line-toground, double-line-toground, or three-phase) Line-to-line

Example in dc traction power system

Example in ac traction power system

Between the incoming utility service and the ac terminals of the rectifier. Transformer-rectifier faults; ferroresonance. Some dc railroads have a parallel ac power line connecting rectifier substations A broken OCS wire landing on the running rails

Within a utility supply substation feeding a railroad

Metallic debris connecting the third rail to the running rail

Substation bus fault

Transformer-rectifier faults

Vehicle faults

A broken OCS wire landing on the running rails

Comments

This should be studied in the same manner as a commercial or industrial power system This should be studied in the same manner as a commercial or industrial power system As with commercial/industrial systems, this will result in the greatest possible magnitude of fault current.

Cable fault Regenerative braking systems can be sources to faults of this nature.

Vehicle faults

11




Type of fault, expressed in terms often used in commercial/industrial power system analysis Line-to-ground (1)

Line-to-ground (2)

Table 1, continued Example in dc traction Example in ac traction power system power system

OCS or third rail-toground: flashed-over insulator to structure, broken OCS wire landing on ground.

Comments

OCS to ground: flashedover insulator to structure, broken OCS wire landing on ground. Since ac traction power systems are referenced to ground, this type of fault is very similar to the line-toline fault. Running rail-to-ground fault created by debris, flooding, poor track maintenance

Running rail-to-ground fault created by debris, flooding, poor track maintenance This type of fault is of concern in dc systems because of the possibility of corrosion of railroad or neighboring structures.

In general, traction power systems suffer faults of all sorts more often than industrial or commercial power systems do. Reasons for this include: a)

The traction power system conductors must be bare in order that sliding contacts of pantographs or third rail shoes can make electrical contact with the wayside conductors.

b)

Clearances between tunnel or overbuilt structures and traction power system conductors are generally less than would be built for other types of power systems.

c)

The slipstream following a moving train can draw debris along with it.

Preferred system voltages for dc traction are currently given as 750 V, 1500 V, and 3000 V, while the preferred system voltages for ac traction are currently given as 25 kV and 50 kV at 50 Hz or 60 Hz. Older dc traction system in the 750 V class range down to 570 V; older ac traction systems may operate at 11 kV, 12 kV, or 15 kV nominal, and at 16- ⅔ Hz, 25 Hz, 50 Hz, or 60 Hz. A line-to-line fault will produce the greatest possible fault current and is therefore the easiest type of fault to detect. In dc traction power systems, and particularly with large train consists, it can be challenging to distinguish the starting current of a remote train from a fault. One goal of a dc short-circuit study is to find a way to make the critical distinction between a remote fault and a remote train start. A line-to-ground (1) fault in a dc traction system would ideally result in very low fault current because the rails (the other line) are ideally isolated from earth. At least in dry weather, there may well be an appreciable resistance between the rails and earth, and a line-to-ground fault may result in fairly low current, making detection difficult. This situation can also result in the creation of possibly hazardous voltages (from rails-to-ground). A line-to-ground (1) fault in an ac traction system will result in a substantial fault current because ac traction power systems are deliberately grounded at intervals. A line-to-ground (2) fault for both ac and dc traction addresses the fault from the running rail to earth. Since there is always a fairly low distributed resistance between the running rails and earth, there will

12




always be some leakage current between the running rails and earth. A fault in this case is most likely to be initiated by metallic debris or floodwater than has made a better-than-usual connection between the rails and earth. In dc systems, the leakage current between running rails and earth is a major concern because long-term direct current flow, even at low levels, can produce corrosion damage to railroad or adjacent structures. For this reason, a separate stray current study is usually conducted as part of the design of a dc traction power system, and specific construction techniques are used in tunnels, trackways, and stations to minimize the conductance between track, structure, and earth.

3.3.1.2 Performing the fault study The resistance and impedance of the running rails is significant in fault studies. The rails, being of steel and of non-circular cross-section, will be of different impedance than the OCS or the third rail. The OCS or third rails, as a group, are sectionalized much differently than the running rails. The fact that the circuit conductors are dissimilar, and are switched differently, can make it very difficult to use software intended for commercial or industrial power systems to study traction power systems. (This is also a concern for load flow studies.) One must also select the faults to be studied with an eye toward credibility. In any given power system, a line-to-line fault will produce the greatest magnitude of fault current. In a dc traction power system, however, the positive and negative conductors are routed as far apart as possible in order to prevent line-toline faults from occurring. This is quite different from the practice in ac systems of routing all the conductors of a particular circuit together to minimize inductive heating of raceways. At first glance, a fault within a switchgear lineup in a dc traction substation might be considered worthy of study. However, the typical method of construction, with single pole switchgear on one side of the circuit and the other polarity separately routed, may make a line-to-line fault within the substation itself so unlikely as to not be worth consideration.

3.3.1.3 Considerations specific to dc traction power system fault studies DC circuit breakers are rated in terms of maximum interrupting current and in terms of interrupting energy. Not only must the breaker be capable of breaking the worse credible fault that it will see, but it must be capable of absorbing the energy of the arc that results from breaking the fault. Since the load circuit (OCS or third rail, plus running rails, plus the load) has significant inductance, the energy stored in that inductance is significant, and that energy will be reflected as the energy of the arc when the circuit breaker opens. In many applications, the required arcing energy rating is a more onerous requirement than the maximum fault current. If a given traction power substation has one rectifier, then the worst imaginable fault will be a bolted fault between the positive and n egative terminals of the rectifier. 7 Such a fault will have to be cleared by the ac breaker feeding the rectifier and the first dc breaker between rectifier and the external circuit, which is usually the rectifier dc breaker (sometimes referred to as a cathode breaker). Many traction power substations are equipped with two rectifiers, and in that case, the worst imaginable fault (assuming both rectifiers are on line) is a dc bus fault from positive to negative. Such a fault will have to be cleared by opening up both rectifier dc breakers, or one rectifier breaker and a bus tie breaker, and all trolley or third rail breakers on the affected bus section. But the construction of the substation may make such a fault highly unlikely. Typical traction power substation construction routes the positive and negative conductors well apart, and since the positive bus is a single-conductor arrangement, it is not typical that a bus positive to negative fault is credible. 7

For a derivation of the theoretical short circuit current at the terminals of a traction rectifier, see “Transient and Steady-State Short Circuit Currents in Rectifiers for dc Traction Supply” [B43].

13




It is often the case that the worst (maximum current) credible fault is from OCS or third rail to running rail immediately outside the substation, and that the worst (maximum energy) credible fault is from OCS or third rail to running rail some distance to the next substation. An example of the first case is shown in Figure 1.

Figure 1 —Contact line to track fault outside substation Strictly speaking, the inflow of fault current from adjacent traction power substations should be considered. However, the inductance of the traction power circuit from substation to substation is often enough to delay the rise of current from an adjacent station so that the adjacent station contribution is not significant. If the railroad has more than two tracks, the effect of parallel inductances may reduce this current limiting effect to the point where adjacent station contribution is significant.

3.3.1.4 Considerations specific to ac traction power system fault studies In many respects, the fault analysis of an ac traction power system is very similar to that of commercial and industrial power systems. However, the engineer involved in such studies should keep the following in mind: a)

OCS-to-running rail faults would, formally, include the impedance of the rail network-to-ground. Determining the actual impedance of a network of steel rails is difficult, especially when the impedance bonds necessary for (signal) track circuits are considered. It is conservative to ignore the rail impedance and simply treat these as OCS-to-ground faults, but this might result in overspecified circuit breakers. Not considering the rail impedance may lead to difficulties in sensing remote faults.

b)

Autotransformer electrifications introduce special complications. In an autotransformer system, three wires are employed: the trolley or OCS, the rail, and a feeder (see Figure 2). The impedance between trolley and ground is a complex, non-monotonic function that changes at every autotransformer station. See Lin and Li [B37], Pilo and Rouco [B42], and Kneschke, Hong, Natarajan, and Naqvi [B35] for further discussion.

14




Trolley n o i t y c t i e l n i t n U o o C t

Trolley Rail

V H

Feeder

Figure 2 —Autotransformer system In Figure 2, a high voltage supply (e.g., 115 kV or 230 kV) from a commercial power system is tapped single-phase to a transformer with a center-tapped low voltage winding. The center tap is grounded and connected to the rails. One hot becomes the trolley (OCS), and the other hot becomes the feeder. Rolling stock loads are not normally connected between the feeder and the rail. Trains connect between the trolley and the rail. At intervals, autotransformers bridge trolley-to-feeder and are center-tapped to the rail. This arrangement is most often realized symmetrically, i.e., the trolley-to-rail voltage is the same as the feederto-rail voltage (but 180 degrees out of phase) as for example the 2×25 kV system. However, asymmetric systems are known, for instance the 12 kV trolley-to-rail, 24 kV feeder-to-rail system. c)

The X/R ratios of ac traction power systems can be quite different from typical values for commercial or industrial systems. In the 16⅔ Hz traction systems widely used in Europe, the X/R ratio is approximately 1.

3.3.2 Fault interruption At some point, the current interrupting device(s) should interrupt the fault. Depending on the particular application and selection of dc interrupting devices for a fault that is close to the substation, the fault interruption might occur significantly before the peak current available (prospective current) is attained, or at any time thereafter.

4. Analysis

4.1 Introduction Analysis provides for determination of the suitability of selected ratings and configurations for components and materials in the traction power system, to comply with applicable system design criteria and constraints, to provide an acceptable level of system reliability, and to avoid significant loss of life of system components due to overloading. It also includes consideration of characteristics of non-traction power systems and components (such as vehicles) with the intent of satisfying necessary performance parameters or requirements of those systems/components. Analysis can often include evaluation of alternate system configurations until one or more configurations are found that meet all design constraints.

15




4.2 Cable, conductor, and equipment ratings vs. loading

4.2.1 Process overview Modeling of a traction power system can result in the generation of considerable data describing the loads that components of the traction power system can be subjected to. Comparison of these loads against characteristics and ratings of the wayside equipment should be conducted, but is complicated by the timevarying nature of the loads. To simplify this task wherever possible, condensation of the output data from modeling into appropriate metrics is employed. The most commonly applied metric that can be determined from modeling data is RMS load. Other metrics that can be of use include average load, accumulated I2t (ampere-squared-time) values, and instantaneous load. Any RMS calculation should be made using discrete time intervals that are (a) much smaller than the thermal time constants of the affected components, and (b) much smaller than typical durations of peak current draws (at trains) associated with train acceleration and movement. A suggested time interval for this purpose is one second. The intent of this process is to calculate load data that can be used to establish that the individual components of the traction power system will not be subject to loads that are excessive for the expected conditions of service.

4.2.2 Thermal time constants For wayside system elements, a determination of thermal time constants should be made. The determination does not need to be particularly accurate (and in most cases, cannot be), but is valuable because it establishes relative time frames over which calculations should be made.

Table 2 —Thermal time constants Component

Suggested process to calculate thermal time constant (in lieu of measurement) IEEE Std C57.96 [B31]

Dry-type and cast-coil rectifier transformers Oil filled rectifier transformer Convection cooled rectifier

IEEE Std C57.92 [B30] Multiplication of thermal resistance times specific heat Multiplication of thermal resistance times specific heat (IEEE Std 738 [B27] for overhead conductors) Commercial software programs Multiplication of thermal resistance times specific heat

Feeder cables in air, in conduit, or in cable tray; OCS conductors Feeder cables in ductbank Enclosed bus duct

Typical range of values

1 h to 4 h 2 h to 4 h 30 min to 2 h 5 min to 30 min

4 h to 50 h 30 min to 2 h

4.2.3 Loading data calculation Loading data that should be calculated for evaluation include the following. For the purposes of these determinations, durations of time that are less than one-fifth of the respective component’s thermal time constant can be considered to be significantly shorter than that of the time constant; and durations of time that are greater than five times the respective component's thermal time constant can be considered to be significantly longer than that of the time constant.

16




4.2.3.1 Peak currents Peak (i.e., very short duration) currents (including fault currents) should be compared against equipment ratings (if defined) and used for protective devices and relay settings.

2

4.2.3.2 I t data, calculated over time intervals significantly shorter than that of the respective component These calculations are most commonly applied in evaluation of cable and conductor short-time heating due to faults or short-time overloads. For insulated conductors, I 2t values should be compared against I 2t values which are associated with operation at the limiting (destructive) insulation material temperatures (generally, a value between 150 °C and 250 °C, depending on the insulation type). This process and calculation are described in greater detail in IEEE Std 242 [B25]. For overhead conductors, I2t values should be compared against I2t values which are associated with avoidance of annealing of the copper conductors. A suggested limit is 125 °C for hard-drawn copper as noted by Stell [B49]. For overhead conductors, I2t values should additionally be compared against I2t values which are associated with design limits for tensioning of conductors; typical limiting values are 75 °C or 100 °C for copper and copper alloys, respectively. 8

4.2.3.3 Average load data for rectifiers, calculated over intervals significantly longer than the time constants of the rectifier(s) Average load currents should be calculated over rolling time intervals of total duration significantly longer than rectifier thermal time constant. 9, 10 This calculated load should be used as input for the rectifier rating evaluation.

4.2.3.4 RMS load data calculated over intervals significantly longer than that of the respective component Other than for rectifiers, for routine (normal condition) operation, RMS load values calculated over rolling time intervals significantly longer than that of the thermal time constant of the respective component should not exceed the continuous rating of that component. 11 Continuous ratings of rectifier-transformers can be considered to be the nameplate continuous rating. Continuous ratings for cable feeders can be considered to be the ampacity at an operating temperature.12

8

However, this requirement should be applied prudently. For example, an I 2t calculation for a fault or a transient load that is close to a substation may produce a high value, but since the calculation applies only to the short length of overhead conductor that is close to the substation (between the substation and the fault), the resulting temperature rise of the conductor in this short length might be allowable, even if it considerably higher than the tensioning limit temperature, if it is part of a much longer tensioned span. 9 Refer to Annex G. 10 Average load rather than RMS load is an appropriate metric to compare against ratings for rectifiers because the heat loss (and by extension, temperature rise) of rectifiers is usually primarily due to diode forward junction voltage drop (which is relatively constant over wide ranges of current flow) rather than resistive losses. 11 Refer to Annex G. 12 Although for cables in ductbank, ampacity values are typically established based on a specific 24-h loss factor. Unfortunately, ampacity values are often published for specified values of load factor rather than loss factor. Although load factor and loss factor are related, the correlation between them is dependent on the 24-h load cycle, and the load cycle that is typically assumed for the purpose of determining published ampacity values is quite different from the load cycle that is typically encountered in traction power systems.

17




Ampacity values for conductors should be determined based on RMS load current and limiting temperature. It may be appropriate to have different limiting temperatures for different conditions of operation. For example, conventional solid dielectric insulated cables may have a temperature limit for normal operation (indefinite duration) of 90 °C, but a short-time contingency rating of 130 °C for limited durations. The long-time loading computation generally provides for determination of the RMS ampere load (or for rectifier units, the average ampere load). For cable feeders and OCS conductors, load ratings are generally established as ampacity ratings (based on temperature ratings of conductors) (see Neher and McGrath [B40], Stell [B46], and Stell [B45]). Ampacity ratings are then compared against RMS loads that are determined as part of the train operations and wayside network modeling. The ampacity values should be not less than the RMS loads to avoid conductor overheating, annealing, or reduction of service life. Conductor ampacities are established differently depending on whether the circuit is ac or dc, and are also dependent on the physical configuration. Extensive published information is available establishing ampacities for 60 Hz ac circuits, but these may not be applicable to traction power design (because the traction power system is a dc system, or a different frequency ac system, or has a different physical configuration for conductor installation than is addressed in the published information, or is for a different load factor). It may be necessary to provide calculation of RMS load(s) over different time intervals for evaluation of different feeders. For example, OCS contact conductors (with typical thermal time constants of a few dozen minutes) should be evaluated against RMS loads that are calculated over comparably short time periods (see IEEE Std 738 [B27]), but conductors in duct banks (with thermal time constants of several hours) should be evaluated against RMS loads calculated over longer time intervals. Determination of conductor ampacity in duct banks may also require consideration of conductor load cycle over extended time periods (e.g., over a 24 h period), to consider the extent to which the surrounding environment (soil, concrete) cools (or continues to heat, but at a slower rate) between peak loading periods.

4.2.4 Short time (overload and fault) ratings Short time temperature ratings of conductors may be evaluated against temperature rise experienced for short durations that may occur during outages of equipment (when other in-service equipment and feeders will be subjected to higher-than-normal loads). Analysis based on fault modeling can include the following: 

Selection of required equipment ratings to interrupt faults



Comparison of withstand ratings for feeders and equipment against peak or prospective fault durations and magnitudes



Determination of touch and step potentials during fault conditions



Selective coordination and relay studies to provide for selective operation of overcurrent devices during fault conditions, and to establish requirements and settings for overcurrent relays and devices

Instantaneous cable temperature ratings of conductors may be evaluated against instantaneous temperatures that will be experienced during fault conditions.

Further description of load factor and loss factor as it relates to ampacity determination can be found in the Electric Power Research Institute’s “Increased Power Flow Guidebook” Final Report [B13]. It i s therefore important to verify that any ampacity value for cables in ductbank are based on a loss factor that corresponds to the traction power system load cycle.

18




4.3 Equipment ratings

4.3.1 Continuous ratings Major equipment units (e.g., transformers) typically have an established continuous output load rating (measured in amperes), which may be compared against predicted RMS ampere loads from the simulation(s).13 Rectifier long term loading can be considered by comparing average rectifier o utput load rating (measured in amperes) against predicted rectifier average loads from the simulations. 14 Breaker loading can be considered by comparing simulated RMS loads against breaker continuous ampere ratings. The time required for a cable to reach its operating temperature for a given load varies greatly with the type of installation. A traction power cable in air, or in conduit which is in air, will have a thermal time constant of several minutes. A traction power cable in an underground ductbank may have a thermal time constant of tens of hours. When computing the effective or rms ampere load to be carried by any piece of equipment, a rolling time interval should be selected which is significantly shorter than the thermal time constant of the apparatus under consideration.15

4.3.2 Overload ratings based on ultimate temperature rise It is sometimes reasonable to apply equipment in traction power applications where the RMS load exceeds the continuous load rating, provided that the duration of the calculated load is short enough, when evaluated against the thermal time constant of the equipment and the overall load cycle, that the temperature limit(s) of the equipment will not be exceeded. A procedure for applying such an analysis to transformers is presented in IEEE Std C57.92-1981 [B30]. Such an evaluation considers the thermal time constant for average temperature rise of the equipment and a known or inferred maximum allowable average temperature.

4.3.3 Overload ratings based on insulation aging and loss-of-life It is sometimes reasonable to apply equipment in traction power applications where the RMS load exceeds the continuous load rating, provided that the equipment will not be subjected to an unacceptable shortening of life due to aging of insulation systems operating at higher temperatures. A procedure for applying such an analysis to transformers is presented in IEEE Std C57.91 [B29] and IEEE Std C57.96 [B31]. Such an evaluation requires knowledge of Arrhenius constants for the insulation materials, thermal time constant(s) for the equipment, and expected equipment and insulation system lifespan when operated at rated load.

4.3.4 Short time overload ratings Some equipment units may have defined short-time overload ratings which should be compared against corresponding short time peak loads. As an example, dc feeder breakers are typically not rated to supply short time loads in excess of four times the breaker continuous ampere rating.

13

RMS loads generally correlate closely to average internal heat loss, and average internal heat loss generally correlates closely to temperature rise, for transformers and feeders. 14 This assumes that most of the internal heat loss is generated in the rectifier diode semiconductor junctions. Since the forward bias voltage in silicon and thyristor diodes does not greatly vary with load (certainly not in a linear manner, in any event), the average internal rectifier heat loss is closely correlated to the average ampere load served by the rectifier. For rectifiers with significant resistive losses, it may be necessary to consider not only average value of the load current, but also RMS value of the load current, to determine average internal rectifier heat loss. 15 Refer to Annex G.

19




4.4 Train voltages Train voltages that are determined as part of the simulation should be compared against vehicle criteria and/or traction power system performance criteria limits. Comparison of calculated train voltages against criteria limits should be done with consideration of the source of the train voltage limit established in the criteria. For example, if the minimum criteria limit value correlates to dropout voltage of on-board equipment (propulsion equipment and/or auxiliary equipment), then the criteria limit might be considered as an absolute limit because dropout of the on-board equipment could result in significant service disruption or passenger inconvenience. On the other hand, a minimum train voltage criteria limit that correlates to reduction in vehicle performance (e.g., acceleration) might be interpreted as more of a soft limit if it can be demonstrated that occasional voltage dips below the criteria limit do not result in significant reduction of system performance (e.g., that the average system speeds do not significantly drop off due to occasional sag in train voltage). For this purpose, it may be valuable to determine probabilistic train voltages to establish relative portions of time during which train voltages are within different voltage ranges to estimate overall reduction in vehicle performance.

4.5 Running rail-to-ground voltages Running rail-to-ground voltages should be compared against traction power system performance criteria limits.

4.6 Contingency analysis Traction power systems are generally expected to provide reliable service under a multitude of conditions. Failures or outages of equipment should not generally result in significant interruption of service. It therefore is important for the designers of traction power systems and components to realistically and accurately accommodate such conditions. Contingency analysis can begin with an effort to itemize expected troublesome conditions. Originating conditions can be classified as to expected likelihood and duration. For each such condition, the allowable traction power system response can be defined. Examples of failure/outage conditions, or aberrant operational conditions, are the following (note that multiple conditions can be combined into one contingency simulation depending on the particular railroad/agency’s requirements): 

Failure of one or more traction power system components (e.g., a de-energized traction transformer, or a track feeder breaker in a not-closable condition)



Loss of a utility feeder (or losses of multiple utility feeders)



Complete de-energization of one (or more) substation(s) (e.g., during maintenance). It is important to distinguish between power loss in which a substation’s bus does not provide power but serves to equalize voltages on the contact conductors, as opposed to a power loss in which track feeder breakers are open.



Unexpected bunching of trains in a track area, leading to highly localized system loading



Special operations (e.g., increased service conditions due to special events)

Examples of response limits to such conditions might include the following: NOTE—These examples are generally unrelated to the specific examples provided above.

20






No impact on traction power system performance



Reduced voltage to trains with (or without) a concurrent reduction in system performance (e.g., reduction in acceleration, train consist, or speed, or increase in system headway)



Temporary allowance for operation of equipment at a higher-than-normal operating condition (e.g., operation for limited time of cables at temperatures above nominal rated temperature)



Establishment of physical time limit(s) for operation with the aberrant operating conditions



Avoid simultaneous train starts

These statements then constitute a significant part of the design criteria for the traction power system and can be considered as part of a strict reliability analysis.

4.7 Substation rating and placement The determination of required size (ratings) and locations for substations involves many tradeoffs between often conflicting requirements. To a limited degree, an increase in substation quantity can compensate for insufficient substation capacity, and an increase in substation capacity can compensate for insufficient substation quantities. The construction cost of increased substation capacity is generally much less than the cost of increased substation quantity, so most system designs will attempt to provide for larger individual substation ratings in order to maximize substation spacing. However, this approach quickly leads to diminishing returns, and substation spacings will generally approach a design maximum that is strongly correlated to voltage drop limits. Longer substation spacings will also promote higher track-to-ground voltages and greater stray currents. Other requirements (e.g., real estate availability) may also dictate specific substation locations.

4.7.1 Rating of substations Considerations in determining the electrical rating (electrical size) of individual substations include the following: 

RMS load: The substation RMS load over a predetermined time frame (often a peak rush period) must be evaluated against overall substation capacity.



Overload rating: Peak equipment loading, such as during multiple train accelerations, should be evaluated against equipment rated overload capabilities (e.g., heavy traction rating, or extra heavy traction rating).

4.7.2 Placement of substations Placement of substations is likely to involve consideration of many factors, including: 

Site specific constraints: Availability, quality, and reliability of utility feeders, land availability, maintenance vehicle access, and architectural/civil issues can all influence comparative evaluations of different substation locations.



Load determination and substation ratings: Loads at substations will vary depending on the physical location of the substation(s) with respect to grades, curves, speed limits, passenger stations, adjacent substation locations, etc.



System performance: Specific locations may improve certain aspects of system performance. For example, some substation locations may be preferred over other locations because they are closer to

21




peak loads (e.g., accelerating trains) that are served, and therefore result in less voltage drop in the OCS/rails to the trains and/or lower rail-to-ground voltages. 

Multiple functionality: Special trackwork (e.g., switches or crossovers) in an electrified rail transit system generally require dedicated electrical switching devices and controls. These switching devices can be part of passive control units (e.g., tie breaker stations or switching stations) or they can be the feeder breakers at substations.



Design criteria: Specific criteria requirements (including contingency analysis)

4.7.3 Redundancy Redundancy should be considered in design when establishing substation ratings and locations. For example, a transit property may require that train operations be maintained (either at normal full load, or at some prescribed reduced operating capacity) in the event of the loss of any one piece of traction power substation equipment, or loss of multiple equipment units, or complete loss of one or more traction power substations. These criteria will likely result in increased loads (both RMS and short time overloads) on remaining in-service traction power equipment or adjacent in-service substations, and will have significant impact on determination of substation location(s) and rating(s).

4.8 Examples of temporary or permanent mitigation strategies The following is a list of possible mitigation measures to correct substandard voltage or current rating conditions for either temporary or permanent situations: 

Increase headways (temporary)



Shorten trains (both temporary and permanent)



Lower speed or acceleration (temporary)



Energy storage substations (permanent)



Temporary substations (temporary)



Facility or equipment upgrades (permanent)



Wayside temporary jumpers (temporary)



Feeder or conductor upgrades (permanent)



Route or operational restrictions (e.g., at turnbacks) (temporary)



Avoidance of simultaneous starts (both temporary and permanent)



Transformer tap changes (temporary)



Reduce substation spacings (permanent)



Reduce transformer impedance (to improve voltage regulation) (permanent)

22




Annex A

(informative) Field validation of train operations and wayside network modeling A.1 Introduction This annex describes general guidelines for conducting an effort to validate a simulation effort to compare simulation output data against field measurements. Such an effort may be considered to be of value by the transit property, or others. If such a validation effort is desired, then the parties involved should refine and expand on these guidelines to establish a more definitive effort. This annex does not address the initial validation of simulation software that should be performed during software development. The responsibility for initial verification and validation of software lies with the original software developer and/or the software user as part of sound systems and software engineering practices, and is not addressed in this annex. 16 This annex addresses only supplemental validation of the process of applying the software and conducting an analysis for an individual transit system.17

A.2 Field verification A validation should be conducted as a joint and collaborative effort involving the organization performing the simulation, the transit property, and the party reviewing the results. 18 A validation effort can require considerable commitment of manpower and resources from both the consultant and the transit property to be of value. The extent of the required validation effort should be agreed to early in the simulation/modeling effort and be subject to periodic re-evaluation and refinement. The validation effort should be documented in writing. The field validation process consists of measurement of parameters on the transit property’s operating system (for controlled non-revenue test conditions and/or for known in-service operating conditions) and comparison of the measured parameters against output data from the modeling/software simulation. Subsequent adaptation of the core simulation software, revision of the simulation input data followed by resimulation, and/or re-interpretation of the simulation output data can be performed by the software user until an acceptance or rejection of the simulation process is made by the reviewer and the transit authority. Any such acceptance by the transit authority would only be a conditional acceptance of the modeling process for the intended purpose, but would not constitute a blanket acceptance by the transit authority of subsequent use or application of the software used during the validation effort. Furthermore, the acceptance by the transit authority could be withdrawn in the event of subsequent discovery of significant inaccuracies or other deficiencies in the software or process. Comparison of simulation results against measured data for the purpose of validation can be subject to certain pitfalls:

16

IEEE Std 1012 [B28]. While portions of IEEE Std 1012 are referenced for information within this document, it is not the intent of this document to require conformance with IEEE Std 1012. 17 Hovever, validation of the software application process here might also include limited re-validation of the software, such as (a) verification of software output data against that of another software package that is already considered to be of adequate quality for the intended function, with comparable input data sets, or (b) comparison of software output data against results of manual calculations. Either method requires that a suitable range of test cases be established. Both methods may also require that the software be capable of producing intermediate data printouts that allow for checking/verification of individual subroutines within the software. 18 The reviewing party can be the transit property.

23






Uncertainties or variabilities in operations that cannot be predicted nor simulated in advance will generally contribute to differences between measurements vs. simulation output data. 19 It is difficult to separate the effects of these discrepancies from other differences arising from actual deficiencies in the software.



The cost in time, materials, electrical energy, and personnel resources to conduct instrumented tests may dictate that (a) the instrumented tests be of very limited duration and scope, (b) the tests be conducted on a system that is less chaotic than would be experienced during peak period revenue operation (perhaps operating during non-revenue periods), and/or (c) the tests be conducted on a system operating at reduced operations levels compared to the ultimate system that will be modeled.

Considering these difficulties, the following test program is suggested. a)

First, instrument a single train to measure energy consumption and power consumption (at the rails/OCS interface) and operate the train on the transit system (either during non-revenue or revenue periods). Make measurements of station-to-station runtimes (in seconds) for comparison against output data from simulations. Conduct simulations concurrently with tests. Make comparisons between measured system performance and simulated results. Example metrics to be compared are: 1)

Average energy consumption for individual station-to-station runs

2)

Individual station-to-station runtimes

3)

Power consumption vs. time

4)

Peak power consumption

Resources permitting, validation can optionally proceed to a more involved level. b)

Secondly, instrument wayside traction power substations (as many as possible, subject to financial and other constraints) for collection of electrical and other performance data. Conduct simulations concurrently with tests. Make comparisons between measured system performance and simulated results. Example metrics to be compared are: 1)

Average power consumption at individual substations

2)

RMS loads on selected wayside distribution system components and equipment

3)

Schedules of operation and/or headways 20

4)

Train voltages and line currents

5)

Station-to-station runtimes

Any validation effort should include effort to resolve inconsistencies between measured data vs. output data from simulations. The determination of actual metrics to be assessed in the validation effort, and the allowable deviations between measured data vs. simulation output data, should be established jointly between the consultant and the transit property. It may not be possible to establish allowable acceptance limits for accuracy of simulations in advance. The validation effort should be documented in report(s) as agreed upon between the consultant and the transit property.

19

Examples might include variations in station-to-station runtimes or station dwell time (passenger boarding) that cannot be explained despite operation with automatic train control and (perhaps) a known passenger load. 20 The headway or schedule of operations for trains may be a metric that the transit property will need to provide to the consultant to be utilized as input data for the validation simulation effort.

24




A.3 Organizational structure and roles of validation participants The observation, instrumentation, measurement, and collection of real-world data on the transit system for utilization in the validation effort will necessarily require technical, managerial, and financial support. 21 Managerial and financial support will be provided by the transit property. The preferred source for technical support is also from the transit property but can be provided by the consultant if necessary. It is recommended that the validation effort occur according to the definition of integrated validation as described in Annex C of IEEE Std 1012-2005 [B28] (with the consultant operating in the role of the development organization, and the transit property operating in the role of integrated IV and V organization). This approach recognizes the possible benefits of, but does not mandate, technical independence between the development organization and the integrated IV and V organization.

21

Refer to IEEE St d 1012 [B28], Table C.1.

25




Annex B

(informative) Contents of typical report on train operations and wayside network modeling The following is a summary description of the contents of a typical simulation report. This guide suggests the following format for reports: Report cover/title page (including task identification, client, and date of report) Table of Contents Executive Summary (including overall management-level description of findings and conclusions) The executive summary should include a brief description stating the purpose of the analysis and the intended outcome (e.g., (a) to define traction power system requirements to serve a new system or to facilitate operation at a higher service level, or (b) to determine service levels that can be met with an existing system). The executive summary should also provide an overview of the conclusions reached via analysis. Introduction (describing purpose of report and issues/questions addressed) The introduction should provide a complete description of the process through which the scope of work was developed. If prior reports/analyses dealt with similar issues, they can be referenced here. Assumptions and Criteria The underlying data applicable to the modeling effort related to operations levels, failure criteria, etc. To the extent that specific design criteria standards of the transit property are applicable, they should be stated or referenced here. Operations and criteria should include a complete description of the relevant technical parameters and assumptions that have been utilized in modeling and analysis. Results and Discussion (presentation of technical findings) This section should include technical description of the output parameters that were developed during the analysis, and their impact on final determinations made under the study. Conclusions and Recommendations Conclusions and recommendations should provide a more detailed description of the final recommendations (compared to the description in the Executive Summary). Appendices (Charts, graphs, tables, input and output data as appropriate) Appendices should include listing of relevant input data used in analysis (if input data has not otherwise been documented as data of record), or references to relevant previously published or documented items. Output data from simulations and analysis should be reproduced (condensed if and as necessary) to allow for review by the reader to follow the process by which final recommendations have been made.

26




Annex C

(informative) Detailed input parameter list for dc system analysis Table C.1 provides a detailed list of input parameters for dc system analysis, including consideration of vehicle performance. Not all of these parameters are necessarily required for any given analysis:

Table C.1—Parameters list for dc system analysis Item 1

Description of data required Plan and profile of the track route, including proposed passenger stations

2

Train voltages: Maximum tolerated Maximum under regenerative braking Unloaded voltage of power supply Nominal voltage of power supply (i.e., at 100% load) Lowest voltage for specified or required tractive effort Diminished tractive effort (possibly several points) Lowest allowable operating voltage for propulsion Undervoltage cutout of vehicle

Example or comments Starting from passenger stations uses considerable energy; and passenger station locations, as well as grades and curves (speed restrictions), largely dictate the locations of maximum energy use. Stationing of switch points, platform ends, beginning and ends of curves, etc., and of traction power facilities should be identified. The list to the left shows, in ord er from highest to lowest, the voltages that are often defined in traction power engineering. Not all voltages are applicable to all transit agencies.

27




3

4

5

6 7 8

9

10 11

Table C.1, continued Rail-to-earth voltages Touch and step potentials are a safety concern. There are Max under normal operating conditions no U.S. standards, but 50 V to 70 V is often cited as a Max under defined contingency operation design goal for normal operating conditions, and 70 V to Track leakage resistances are needed to 100 V as a design goal for contingency conditions with compute this substations out of service. IEC 62128 [B23] specifies this potential as a function of time. Refer to 3.2.7.5. Track leakage resistance varies with the types of track construction and with the weather. The maximum resistance values are used to determine the rail-to-earth voltages. Representative values: New direct fixation track: 1000 ohms to 1500 ohms – 304.8 track m (1000 track ft) Aging direct fixation track: 500 ohms to 1000 ohms – 304.8 track m (1000 track ft). Dirty direct fixation track: 50 ohms to 250 ohms – 304.8 track m (1000 track ft) Timber tie special track work 250 ohms to 500 ohms – 304.8 track m (1000 track ft) Any type of wet track - 2 ohms to 10 ohms- 304.8 track m (1000 track ft) Note that track leakage resistances are often, but incorrectly, spoken of using terminology such as “X ohms per 1000 track m (ft).” The “per” is improper here because it suggests that the total resistance increases with track length. A longer length of track will result in lower total resistance, measured from the track section to ground. Locations of traction power facilities These need to be defined in terms of the stationing of the Traction power substations connection points to the OCS or contact rail and the dc: Switching stations (a/k/a circuit breaker running rails as well as a cabling distance from the actual house, tie breaker station, paralleling station) TPSS location to the railway. Often, the objective of the engineer’s work is to determine where traction power facilities need to be placed in terms of electrical performance, or to verify adequate traction power system performance when the locations of the facilities are determined by available real estate or other factors. This will be an iterative process. Speed limits and signal design At any point on the railroad, the speed limit is the lower of: (1) any applicable law, as may be the case for street running (2) the capability of the vehicle (3) braking distance considering train control and station stops (4) track limits, especially curves. Minimum end-to-end run time requires making maximum possible speed all along the way, but accelerations due to speed limit changes can have a dramatic effect on total energy consumption. Design headway and consists station dwell times Vehicle weights See 2.1. Vehicle dimensions, including frontal area and Train resistance is an important factor in energy use; rotational portion aerodynamic wind resistance becomes particularly significant at higher speeds. Tractive effort curves A curve showing tractive effort as a function of speed for the vehicle is necessary to model the train performance. Tractive effort at speeds above initial start will generally be reduced with diminishing voltage, so a family of curves is used to describe the performance o f the vehicle. Acceleration rates, adhesion data 1.341 m/sec2 (3 mphps) is often specified as the maximum acceleration rate Braking effort curves, braking rates for friction, Service braking is often specified as 0.67 m/sec 2 (1.5 resistive, regenerative, and blended modes mphps), with emergency braking of 1.117 m/sec2 to 1.341 m/sec2 (2.5 mphps to 3 mphps).

28




Table C.1, continued The use of regenerative braking can return substantial energy to the line. A net reduction in purchased energy of 10% to 30% is often found when regenerative braking is fully deployed. Shorter headways and more frequent stops result in percentages toward the higher end of the range. In addition to the simple savings in money, regenerative braking will substantially reduce the heat rejected to the atmosphere, which is of particular value in tunnel operation, as this makes for a far more comfortable environment in underground stations. Also refer to 3.2.4.

12

Regenerative braking

13 14

Vehicle current or power limits Overall mechanical efficiency

15

Auxiliary power requirements

16

Traction power schematic diagram, impedances of traction power system

17

Utility voltage considerations

Considering tractive effort of the vehicle vs. power in at the pantograph or contact rail shoe, this is often in the 80% to 85% range. The vehicle auxiliary power system provides energy to lights, heating/ventilating/air conditioning, and other systems. These are usually considered “always on” for modeling purposes, and in fact will comprise the vast majority of the load for sub stations feeding yards and shops. 30 kW to 100 kW per car is normal and is generally related to the length of the car. Resistance heating usually draws more power than air conditioning, so in cold climates, the peak load will occur in winter, while in hot climates, the peak load will occur in summer. Tentative ratings of equipment are necessary to commence modeling but are likely to be refined as the design progresses. For dc substations, the following values are often fou nd: Utility supply at 12.5 kV to 34.5 kV Rectifier ratings of 0.5 MW to 5 MW (light- and heavyrail systems; streetcar systems use smaller). Transformer-rectifier voltage regulation of 4% to 6% Typical values for conductor impedances are given in Annex D. A return diagram is useful to show where double-rail and single-rail returns are used (if mixed), where isolation in the return circuit is employed (i.e., yard-to-mainline junctions, line-to-line interchanges if applicable) Lengths and impedances of track-to-substation feeder cable should be defined. Track-to-track crossbonds, where used, should be placed and sized. Supplementary (parallel) positive and negative feeder cables should be placed and sized. Utilities normally expect to deliver voltage to the customer’s service entrance within ±5% of nominal (see ANSI C84.1 [B1]). The modeler may wish to evaluate the performance of the traction power system with the utility voltage at its low normal limit, as with passive equipment (diode rectifiers for dc systems) this low utility voltage will pass through the traction power system. It may also be worth considering the utility voltage at its high normal limit if it is found that regenerative braking is b eing limited by high line voltage.

29




18

Contingency design

19

Wayside loads

20

Track leakage characteristics

Table C.1, continued Under what failure conditions is the traction power system expected to deliver normal, or fairly normal, performance? What degradation in performance is acceptable under first and second contingencies? Many transit operations are designed so that any one substation may be off line without ov erloading the adjacent substations past their short term ratings. Off line may mean that only the power supply has been lost while switchgear remains in service to act as an equalizing bus between the tracks. Off line can also mean that the switchgear is out of service, leaving no connection between the tracks at the substation location. The difference between these two interpretations of off line can be significant. Wayside loads powered from the traction power system often include: Switch heaters Contact rail heaters This is of concern for rail-to-earth voltage calculations and determination of stray current.

30




Annex D

(informative) Typical feeder characteristics The following are typical data, or sources of data, for feeder characteristics applicable to modeling of traction power systems.

D.1 Conductor characteristics of running rails and contact rails Jones [B32] cites a typical per-unit-length resistance of 8 micro-ohms per foot for 115 RE steel running rail in dc traction power applications, and a per-unit-length resistance of 1.4 micro-ohms per foot for aluminum contact rail as used in New York’s Second Avenue Subway project. Skin effect parameters for steel running rails are provided in Experimental Researches on the Skin Effect of Steel Rails [B33]. Values of dc resistance for various rail types used in Europe are provided in Table 3.2 of Contact Lines for Electric Railways [B34]. An analytical method for calculation of impedance of non-ferrous contact rails is provided in “Modeling of Frequency-Dependent Impedance of the Third Rail Used in Traction Power Systems” [B52]. Extensive data describing resistance and inductance of rails and OCS systems for dc traction power systems is provided in “Direct Current Coordination for Electrified Transit” [B48].

D.2 Inductance of running rails and contact rails (dc traction power systems) Inductance of rails and OCS systems in dc traction power systems is provided in “Direct Current Coordination for Electrified Transit” [B48]. Kennelly, Achard, and Dana [B33] provide values as follows: For 100 lb/yd running rails, 1.31 μH/m to 1.86 μH/m; for 69.3 lb/yd and 86.5 lb/yd contact rails, 1.75 μH/m to 2.52 μH/m. Helfrich, Hall, and Reynolds [B17] provide values for mining systems with trolley wires: 2.03 μH/m to 0.947 μH/m. Tylavsky [B51] provides values for mining systems with trolley wires: Trolley feeder, 1.70 μH/m. Trolley, 1.71 μH/m. Rails, 1.66 μH/m. Hill and Carpenter [B18] provide values of 0.635 μH/m to 0.644 μH/m for rail at 50 Hz. Hill and Carpenter [B19] provide values by FEM analysis (differential mode): running rail inductance @ 50 Hz, 1.96 μH/m theory, 2.83 μH/m experimental; contact rail inductance @ 50 Hz, 1.32 μH/m theory, 1.95 μH/m experimental. Fracchia, Hill, Pozzobon, and Sciutto [B14] provide values (per Figure 2 of [B14]) of Ls = 0.08 μH/m, L1 = 1.01 μH/m, L2 = 0.055 μH/m. Hill, Fracchia, Pozzobon, and Sciutto [B20] provide values of system resistance and inductance, as varying functions of frequency.

31




Mariscotti, and Pozzobon [B39] provide measured values of resistance and inductance, for 1.5 m and 0.5 m rail separation, as functions of current. Wang and Wang [B52] provide values for steel third rail of 0.246 μH/m @ 1 Hz to 0.1948 μH/m at 105 Hz. Fracchia, Mariscotti, and Pozzobon [B15] provide values for inductance of system of 1.37 μH/m, r = 0.5 mΩ/m, c = 20 pF/m, for OCS 3 kV dc system.

D.3 DC resistance of typical OCS and feeder conductors Typical dc conductor characteristics for OCS conductors and feeder conductors can be found in ASTM B1 [B3], ASTM B2 [B4], ASTM B3 [B5], ASTM B8 [B6], ASTM B9 [B7], ASTM B47 [B8], ASTM B105 [B9], and ASTM B116 [B10].

32




Annex E

(informative) Tabulation of train voltage limits for dc traction power systems Table E.1 provides a tabulation of train voltage limits on various transit properties, or from industry guides/standards. This table is provided for information only and is not intended to establish recommended values for new or existing system design. While the information contained in Table E.1 is believed by the authors of this document to be accurate, this information should be verified before application in new design or analysis efforts.

Table E.1—Train voltage limits for dc systems

Transit agency or guide/standard

PAac, Pittsburgh Sound Transit, Seattle MTA, Baltimore Light Rail St. Louis CC Metrolink LRT

Type

) s t l o v ( e g a t l o v l a n i m o n m e t s y S

Substation voltage (volts)

d a o l o N

d a o L % 0 0 1

Train voltage limits (volts)

) n o i t a r e n e g e r (

m u m i x a M

e c n a m r o f r e p l l u f u m u i n i M

OCS

650

690

650

750

450

300

OCS

1500

1590

1500

1800

1500

900

OCS

750

832

750

980

600

400

OCS

800

400 to 500

n i t n e e c m i p v i u r e s q e l l A

s e n o g i t a i t u d O n o c

525

525

900

525

CTA, Chicago

3rd R

600

640

600

750

550

CATS, Charlotte

OCS

750

795

750

900

DART, Dallas

OCS

845

845

845

RTD, Denver

OCS

825

870

MATA, Memphis

OCS

600

VMR, Phoenix

OCS

RTD, Sacramento BART San Francisco LIRR

d e c e u c d n e a r - m m r o u f r m i e n p i M

Traction power system design requirements (delivered voltage to trains; minimum) (volts)

450

400

525

525

525

950

525

600

525

825

950

600

640

600

650

350

450

400

850

850

850

900

600

525

OCS

800

850

800

900

525

525

3rd R

1000

850

750

3rd R

750

525

525

1150 795

750

800

500

500 to 400

33




Table E.1, continued

NYCT

3rd R

Miami SEPTA Philadelphia

3rd R

Minneapolis HPO

OCS

San Jose LRT Salt Lake City TRAX Houston SE/EE/NC extensions WMATA (Washington, DC)

OCS

TTC, Toronto NJT, HudsonBergen

3rd R

662

625

450

700 650

550

450

600

525

750 795

750

800

900 900

OCS

800

750

OCS

825

786

900

525 600

525

525 475 or 450

750

500

600

650

430

525

350

3rd R Both OCS & 3rd R

700

742

700

570

607

570

720

500

OCS

750

795

750

900

525

720

600

400

900

750

500

1800

1500

1000

3600

3000

2000

525

IEEE Std 16 [B24]

IEC 60850 [B22] 600

800

400

400

400

750

1000

500

500

500

1500

1950

1000

1000

1000

3000

3900

2000

2000

2000

750

975

525

450

1500

1950

1050

900

3000

3900

2100

1800

AREA Manual for Railway Engineering Volume 3 [B1] recommended voltages

34




Annex F

(informative) Tabulation of rail-to-ground voltage limits for dc traction power systems Table F.1 provides a tabulation of rail-to-ground voltage limits on various transit properties. This table is provided for information only and is not intended to establish recommended values for new or existing system design. While the information contained in Table F.1 is believed by the authors of this document to be accurate, this information should be verified before application in new design or analysis efforts.

Table F.1—Rail-to-ground voltage limits for dc traction power systems

System/type

Is rail-to-ground limit established as a system design parameter or limit?

Rail-to-ground voltage limit notes

Are negative grounding devices applied?

Notes regarding negative grounding device (NGD) application

WMATA Washington, DC (heavy rail)

No

Not to exceed 50 V under normal operations

No

—

Yes

Located at substations. Trigger setpoint of 50 V-100 V; delay of 0.1 s-0.6 s. Commutation via reverse bias. NGD adjustment for sustained current (adjustable 5 A-50 A, 15 s-150 s) results in substation lockout.

No

—

Yes

NGD to automatically connect the running rail to the substation ground bus if the voltage rises above a preset value of 35 V

Phoenix East Valley VMR (light rail)

Not known

Salt Lake City UT (light rail)

Yes

Pittsburgh (light rail)

BARTD San Francisco CA (heavy rail) Miami Dade County (heavy rail) Chicago CTA (heavy rail)

—

Maximum rail-toground voltage 50 Vdc System capable of maintaining the negative rail potential rise to within 70 V under substation outage condition

Yes

Not known

—

Yes

Set at 80 V

No

—

Yes

Set at 50 V

No

Rarely exceeds 50 V

No

Substations partially diode grounded via utility drainage (stray current) bonds

35




Table F.1, continued

DART Dallas TX (light rail)

Sacramento CA (light rail) VTA San Jose CA (light rail)

Yes

Initial design limit established at 50 V; later revised to 72 V (Phase II buildout)

Yes

Back-to-back thyristors. Initial (early phase) construction provided setpoint of 52 V; currently set to 62 V to avoid nuisance operation. If thyristor current exceeds 700 amps, a spring loaded mechanical switch is closed to bypass the thyristor units. The bypass switch can only be manually opened. Bypass switch rating is 750 amps continuous, 15 000 amps for 0.3 s.

Yes

Initial design criteria limit was set at 50 V

Not known

—

Not known

—

No

—

Not known

—

No

—

Not known

—

Denver CO RTD (light rail)

Yes

MTA/LIRR ESA New York City (heavy rail)

Yes

Minneapolis MN HPO (light rail)

Yes

Exposition LRT Los Angeles CA (light rail)

Yes

Maximum track-to-earth potentials do not exceed 50 V during normal operations Maximum track-to-earth potentials do not exceed 75 V (goal) during normal operation. Maximum track-to-earth potentials do not exceed 50 V during normal operations. Running rail touch potential below 45 V dc during normal operation.

Yes

Baltimore MD (light rail)

Not known

—

Yes

Located at substations. Back-to-back thyristors. Trigger setpoint of 50 V (adjustable); no intentional time delay. Commutation via reverse bias. NGD adjustment for sustained current (set at 35 A, adjustable time delay of 0.1 s-102 s with 15 s initial adjustment) results in substation lockout.

Baltimore MD (heavy rail)

Not known

—

No

—

Yes

Mechanical contactor is provided; closes at approximately 50 V and stays closed for approximately 10 s. Three immediately consecutive close operations result in system lockup (contactor closed permanently) with alarm to central control.

Hudson-Bergen line; NJ

Yes

Limited to 50 V

36




Annex G

(informative) Rolling load calculations This IEEE guide makes reference to rolling calculations of load over time. Rolling load calculations are suggested as a method of evaluating changing electrical loads on equipment, and correlating those loads to changes in equipment temperature, to facilitate predictions as to whether or not limiting equipment temperatures will be exceeded. The rolling load calculation consists of exponential smoothing of load data, p erformed as follows: Assume that a wayside system element is subjected to loading and that the loading is modeled as discrete loads, each lasting for time interval of ∆t . The value of ∆t should be significantly shorter than the thermal time constant ∆ of the wayside system element: ∆t << τ

For the purposes of this explanation, the discrete load values are represented as: L1 L 2 L3 L4 L5

load from time 0 to ∆t load from time ∆t to 2∆t load from time 2 ∆t to 3∆t load from time 3 ∆t to 4∆t load from time 4 ∆t to 5∆t etc.

We now calculate exponentially smoothed data, as terms S 1 , S 2 , S 3 , S 4 , …. The first term is S 1 = L1. Subsequent terms are calculated as S n+1 = α ( Ln) + (1-α )S n Where = ∆t / τ

α

The resulting data is smoothed data for the corresponding thermal time constant. As an example, consider a wayside system element with a thermal time constant of τ = 300 seconds, for which per-unit load values L1 , L2 , L3 , L4 , … are known. Each load value represents a load which lasts for 60 s (=∆t ). α

= ∆t / τ = 60/300 = 0.2

Also, assume that the system element is modeled as a resistive element, for which heat loss is proportional to L2. If we assume that the steady-state temperature rise above ambient for the element is proportional to steady-state heat loss, then we can assign heat loss value s as H 1 , H 2 , H 3 , H 4 , … where H n = K * ( Ln)2. Assume that K =1.0; also assume the following load values: 22

22

In other words, maximum allowable steady-state temperature rise is reached when per-unit load is established at 1.0.

37




Table G.1—Sample load values L1 L2 L3 L4 L5

0.1 0.3 0.5 0.7 1.0

1.2 1.4 1.5 1.6 1.2

L6 L7 L8 L9 L10

0.8 0.9 0.6 0.2 0.3

L11 L12 L13 L14 L15

0.4 0.6 1.1 1.4 1.1

L16 L17 L18 L19 L20

L21 L22 L23 L24 L25

0.9 0.9 1.1 1.0 1.0

The smoothed per-unit temperature rise values are then computed as H 1 = L12 = 0.01 H 2 = 0.2( L2)2 + (1-0.2) H 1 = 0.2(0.3)2 + 0.8(0.01) = 0.026 H 3 = 0.2( L3)2 + (1-0.2) H 2 = 0.2(0.5)2 + 0.8(0.026) = 0.0708 Etc. Shown below is a graph of Ln: 1.8

1.6

1.4

1.2

) t i n u 1 r e p ( d0.8 a o L 0.6

0.4

0.2

0 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

15

16

17

18

19

20

21

22

23

24

25

Time interval

and H n: 1.6

1.4

1.2

) t i n u r 1 e p ( e s i r 0.8 e r u t a r e 0.6 p m e T 0.4

0.2

0 1

2

3

4

5

6

7

8

9

10

11

12

13

14

18

19

20

21

22

23

24

25

Time interval

From the graph of Ln vs. time, it can be inferred that the per-unit load limit is exceeded during intervals 6, 7, 8, 9, 10, 18, 19, 20, and 23; limiting temperature rise ( H n) will be exceeded during time intervals 8, 9, 10, 11, 12, and 13.

38




Note that this analysis is greatly simplified for the purpose of explanation. A typical traction power simulation might have time intervals of individual duration lasting only a few seconds (versus the 60 s interval presented here) and might cover a total time period of several hours or more (versus the 300 s time duration presented here.)

39




Annex H

(informative) Bibliography Bibliographical references are resources that provide additional or helpful material but do not need to be understood or used to implement this standard. Reference to these resources is made for informational use only. [B1] American Railway Engineering and Maintenance-of-Way Association (AREMA) Manual for Railway Engineering, Volume 3: Infrastructure and Passenger. [B2] ANSI C84.1, Electric Power Systems and Equipment—Voltage Ratings (60 hertz). [B3] ASTM B1, Standard Specification for Hard-Drawn Copper Wire. [B4] ASTM B2, Standard Specification for Medium-Drawn Copper Wire. [B5] ASTM B3, Standard Specification for Soft or Annealed Copper Wire. [B6] ASTM B8, Standard Specification for Concentric-Lay-Stranded Copper Conductors, Hard, MediumHard, or Soft. [B7] ASTM B9, Standard Specification for Bronze Trolley Wire. [B8] ASTM B47, Standard Specification for Copper Trolley Wire. [B9] ASTM B105, Standard Specification for Hard-Drawn Copper Alloy Wires for Electric Conductors. [B10] ASTM B116, Standard Specification for Figure-9 Deep-Grooved and Figure-8 Copper Trolley Wire for Industrial Haulage. [B11] De Koranyi, L., “Design of dc Power Supply for Rapid Transit Systems,” IEEE Transactions on Industry and General Applications, March/April 1965. [B12] Dietz, James H., “Integrating New Railcars into Existing Traction Power Systems,” Proceedings of the American Public Transit Association 2010 APTA Rail Conference, Vancouver, Canada. [B13] Electric Power Research Institute, “Increased Power Flow Guidebook” Final Report, November 2005. [B14] Fracchia, M., Hill, R. J., Pozzobon, P., and Sciutto, G., “Accurate track modeling for fault current studies on third-rail metro railways,” Proceedings of the 1994 ASME/IEEE Joint Railroad Conference, 1994 (in Conjunction with Area 1994 Annual Technical Conference), pp. 97-102, March 22-24, 1994. [B15] Fracchia, M., Mariscotti, A., and Pozzobon, P., “Track and traction line impedance expressions for deterministic and probabilistic voltage distortion analysis,” Proceedings of the Ninth International Conference on Harmonics and Quality of Power, 2000, vol. 2, pp. 589-594, Oct. 1-4, 2000. [B16] Hay, W. W., Railroad Engineering, 2nd Edition. New York: Wiley, 1982.

40




[B17] Helfrich, W. J., Hall, P. M., and Reynolds, R. L, “Time constants of direct current trolley systems,” Proceedings of the Fifth West Virginia University Conference on Coal Mine Electrotechnology, pp. 9-1 to 9-13, September 1-13, 1980. [B18] Hill, R. J., and Carpenter, D. C., “Determination of rail internal impedance for electric railway traction system simulation,” IEEE Proceedings-B, vol. 138, no. 6, pp 311-321, November 1991. [B19] Hill, R. J., and Carpenter, D. C., “Rail track distributed transmission line impedance and admittance: theoretical modeling and experimental results,” IEEE Transactions on Vehicular Technology, vol. 42, issue 2, pp. 225-241, May 1993. [B20] Hill, R. J., Fracchia, M., Pozzobon, P., and Sciutto, G., “A frequency domain model for 3 kV dc traction dc-side resonance identification,” IEEE Transactions on Power Systems, vol. 10, no. 3, pp. 13691375, August 1995. [B21] House, H. E., and Tuttle, P. D., “Current-Carrying Capacity of ACSR,” Power Apparatus and Systems, Part III, Transactions of the American Institute of Electrical Engineers, vol. 77, issue 3, pp. 11691173, April 1958. [B22] IEC 60850, Railway Applications—Supply Voltages of Traction Systems. [B23] IEC 62128-1, Railway Applications—Final Installations—Part 1—Protective Provisions Relating to Electrical Safety and Earthing. [B24] IEEE Std 16, IEEE Standard for Electrical and Electronic Control Apparatus on Rail Vehicles. [B25] IEEE Std 242, IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems. [B26] IEEE Std 399, IEEE Recommended Practice for Industrial and Commercial Power Systems Analysis. [B27] IEEE Std 738, IEEE Standard for Calculating the Current-Temperature of Bare Overhead Conductors. [B28] IEEE Std 1012, IEEE Standard for Software Verification and Validation. [B29] IEEE Std C57.91, IEEE Guide for Loading Mineral-Oil-Immersed Transformers. [B30] IEEE Std C57.92-1981, IEEE Guide for Loading Mineral-Oil-Immersed Power Transformers Up to and Including 100 MVA with 55 °C or 65 °C Average Winding Rise. [B31] IEEE Std C57.96, IEEE Guide for Loading Dry-Type Distribution and Power Transformers. [B32] Jones, A. L., “A Comprehensive Short Circuit Analysis of a Low Voltage dc Traction Power System,” Proceedings of the American Public Transit Association 2006 APTA Rail Conference, New York. [B33] Kennelly, A. E., Achard, F. H., and Dana, A. S., Experimental Researches on the Skin Effect of Steel Rails, J. Franklin Institute, vol. 182, no. 2, pp. 135-190, August 1916. [B34] Kiessling, Puschmann, and Schmieder, Contact Lines for Electric Railways, Munich: Publicis Corporate Publishing, 2001, Table 3.2.

41




[B35] Kneschke, Hong, Natarajan, and Naqvi, “Impedance Calculations for Septa’s Rail Power Distribution System,” Transactions of the 1995 ASME-IEEE Joint Railroad Conference. [B36] Lanctot, E. K., Peterson, E. L., House, H. E., and Zobel, E. S., “Ice Build-up on Conductors of Different Diameters,” Transactions of the American Institute of Electrical Engineers, Power Apparatus and Systems, Part III, vol. 78, issue 4, pp. 1610-1614, December 1959. [B37] Lin Guo-song and Li Qun-zhan, “Impedance Calculations for AT Power Traction Networks with Parallel Connections,” Proceedings of the 2010 IEEE Asia-Pacific Power and Energy Engineering Conference. [B38] Mariscotti, A., and Pozzobon, P., “Resistance and Internal Inductance of Traction Rails at Power Frequency: A Survey,” IEEE Transactions on Vehicular Technology, vol. 53, no. 4, pp. 1069-1075, July 2004. [B39] Mariscotti, A., and Pozzobon, P., “Measurement of the internal impedance of traction rails at 50 Hz,” IEEE Transactions on Instrumentation and Measurement , vol. 49, issue 2, pp. 294-299, April 2000. [B40] Neher, J. H., and McGrath, M. H., “The Calculation of the Temperature Rise and Load Capability of Cable Systems,” Transactions of the American Institute of Electrical Engineers , Power Apparatus and Systems, Part III, vol. 76, October 1957. [B41] Olmsted, L. M., “Safe Ratings for Overhead Line Conductors,” AIEE Transactions, vol. 62, issue 12, pp. 845-853, December 1943. [B42] Pilo and Rouco, “A Reduced Representation of 2x25 kV Electrical Systems for High-Speed Railways,” Proceedings of the 2003 ASME-IEEE Joint Railroad Conference, Chicago, IL. [B43] Pozzobon, P., “Transient and Steady-State Short Circuit Currents in Rectifiers for dc Traction Supply,” IEEE Transactions on Vehicular Technology 47:4, New York: Institute of Electrical and Electronics Engineers, November 1998. [B44] Schurig, O. R., and Frick, C. W., “Heating and Current-carrying Capacity of Bare, Conductors for Outdoor Service,” General Electric Review, vol. 33, no. 3, pp. 141-156, March 1930. [B45] Stell, R. W. B., “Cable Ampacity Tables for Direct Current Traction Power Systems,” Proceedings of the American Public Transit Association 2005 Rapid Transit Conference. [B46] Stell, R. W. B., “Cable Rating Considerations for Direct Current Traction Power Systems,” Proceedings of the American Public Transit Association 2003 Rapid Transit Conference. [B47] Stell, R. W. B., “Cost Effective Traction Power System Design: An Analytical Approach,” Proceedings of the American Public Transit Association 1997 Rapid Transit Conference. [B48] Stell, R. W. B., “Direct Current Coordination for Electrified Transit,” Proceedings of the American Public Transit Association 1992 Rapid Transit Conference. [B49] Stell, R. W. B., “Protection of Trolley and Messenger Wire from Thermal Damage Due to Short Circuits,” Proceedings of the American Public Transit Association 1994 Rapid Transit Conference. [B50] Steimel, A., Electric Traction—Motion Power and Energy Supply: Basics and Practical Experience. Muinch: Oldenbourg Industrieverlag GmbH, 2007. [B51] Tylavsky, D. J., “Track/trolley system transients,” IEEE Transactions on Industry Applications, Vol. 24, issue 4, pp. 672-681, July-Aug. 1988.

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