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Rail Transportation Standards Committee

IEEE

3 Park Avenue

New York, NY 10016-5997

USA

18 January 2013

IEEE Vehicular Technology Society

IEEE Guide for Rail Transit Traction

Power Systems Modeling

IEEE Std 1653.3™ 2012

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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 of the

IEEE Vehicular Technology Society

Approved 5 December 2012 Approved 5 December 2012

IEEE-SA Standards Board

Approved 30 September 2014 Approved 30 September 2014

American National Standards Institute

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Abstract:

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

analysis of traction power systems is provided in this guide. Keywords:

Keywords: analysis, IEEE 1653.3, modeling, traction power 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

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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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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

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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 399TM [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).

AW2: AW1 load + weight of standees at 0.251m2 (2.7 ft2) 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

1

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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IEEE Std 1653.3-2012

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 ft2) of suitable standing space per standee AW3: AW1 load + weight of standees at 0.167m2 (1.8 ft2) 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)

3_{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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IEEE Std 1653.3-2012

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).

 _{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.

 _{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.

 _{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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IEEE Std 1653.3-2012

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 operating 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)

 _{Maximum allowable temperature limits of equipment}

 _{Temperature ratings (short term and continuous) for insulation systems}  _{Environmental conditions for analysis (e.g., ambient temperature, climate)}

 _{Vehicular performance capabilities and limitations, including performance limitations that may result}

at low train voltages

 _{Wayside civil alignment information}

 _{Electrical distribution network characteristics}  _{Operations levels}

 _{Contingency failure/outage conditions}

 _{Maximum ceiling voltage for regeneration (if regeneration is to be evaluated as part of the simulation}

process)

 _{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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IEEE Std 1653.3-2012

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, 2nd 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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IEEE Std 1653.3-2012

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

 _{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)

 _{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 ignored5

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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IEEE Std 1653.3-2012

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 less 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}  _{Signal system}

 _{Yard, storage track, and mainline track information}

 _{Vehicle data (for each vehicle type proposed to be operating)}  _{Traction power system network data}

 _{Substation data}  _{Operating plan}

 _{Contingency operation criteria—recovery from operation incidents}  _{Traction power system contingencies}

 _{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.

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IEEE Std 1653.3-2012

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 = I2R), 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:

∫

= T

dt

t

x

T

rmsload

0 2

))

(

1

(1)

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

(

)

⎟

⎠

⎞

⎜

⎝

⎛

⋅ =

∑

= = n k k n k

L

k

t

k

t

rmsload

1 1 2 (2)

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.

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IEEE Std 1653.3-2012

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:

1) For transit personnel

2) For the public at passenger station platforms 3) For the public along shared rights-of-way

c) 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

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IEEE Std 1653.3-2012

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

Example in dc traction power system Example in ac traction power system Comments Three-phase faults (1) (may be single-line-to-ground, double-line-to-ground, or three-phase)

Between the incoming utility service and the ac terminals of the rectifier. Transformer-rectifier faults; ferroresonance.

Within a utility supply substation feeding a railroad

This should be studied in the same manner as a commercial or industrial power system Three-phase faults (2) (may be single-line-to-ground, double-line-to-ground, or three-phase)

Some dc railroads have a parallel ac power line

connecting rectifier substations

This should be studied in the same manner as a commercial or industrial power system

Line-to-line A broken OCS wire

landing on the running rails Metallic debris connecting the third rail to the running rail

Transformer-rectifier faults Vehicle faults

A broken OCS wire

landing on the running rails Substation bus fault

Cable fault Vehicle faults

As with

commercial/industrial systems, this will result in the greatest possible magnitude of fault current. Regenerative braking systems can be sources to faults of this nature.

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IEEE Std 1653.3-2012

Type of fault, expressed in terms often used in commercial/industrial power system analysis

Example in dc traction power system

Example in ac traction power system

Comments

Line-to-ground (1) OCS or third

rail-to-ground: flashed-over insulator to structure, broken OCS wire landing

on ground.

OCS to ground: flashed-over 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-to-line fault.

Line-to-ground (2) 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.

Running rail-to-ground fault created by debris, flooding, poor track maintenance

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

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IEEE Std 1653.3-2012

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-to-line 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].

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IEEE Std 1653.3-2012

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 over-specified 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.

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IEEE Std 1653.3-2012

Trolley H V C o n n e c t i o n t o U t i l i t y Rail Feeder Trolley

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 feeder-to-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.

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IEEE Std 1653.3-2012

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 time-varying 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)

Typical range of values

Dry-type and cast-coil rectifier transformers

IEEE Std C57.96 [B31] 1 h to 4 h

Oil filled rectifier transformer IEEE Std C57.92 [B30] 2 h to 4 h

Convection cooled rectifier Multiplication of thermal resistance

times specific heat

30 min to 2 h Feeder cables in air, in conduit, or in

cable tray; OCS conductors

Multiplication of thermal resistance times specific heat (IEEE Std 738 [B27] for overhead conductors)

5 min to 30 min

Feeder cables in ductbank Commercial software programs 4 h to 50 h

Enclosed bus duct Multiplication of thermal resistance

times specific heat

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.

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IEEE Vehicular Technology Society

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IEEE Guide for Rail Transit Traction

IEEE Guide for Rail Transit Traction

Power Systems Modeling

Power Systems Modeling

IEEE Std 1653.3™ 2012

IEEE Std 1653.3™ 2012

IEEE Std 1653.3™-2012

IEEE Std 1653.3™-2012

IEEE Guide for Rail Transit Traction

IEEE Guide for Rail Transit Traction

Power Systems Modeling

Power Systems Modeling

Rail Transportation Standards Committee

Rail Transportation Standards Committee

IEEE Vehicular Technology Society

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Notice to users

Laws and regulations

Copyrights

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Errata

Patents

Participants

Introduction

Contents

IEEE Guide for Rail Transit Traction

Power Systems Modeling

1. Overview

1.1 Scope

1.2 Purpose

1.3 Limitations

2. Definitions, acronyms, and abbreviations

2.1 Definitions

2.2 Acronyms and abbreviations

3. Modeling and validation

3.1 Introduction

3.2 Train operations and wayside network modeling

∫

dt

t

x

T

rmsload

))

(

(

1

(

)

⎟

⎠

⎞

⎜

⎝

⎛

∑

∑

L

t