Pacific Gas and Electric Company Power Utility System Impact Study

Tristan A. Kneschke

T

© PHOTODISC

Pacific Gas and Electric Company Power Utility System Impact Study

Digital Object Identifier 10.1109/MVT.2009.932544

44 |||

1556-6072/09/$25.00©2009IEEE

he system selected by Caltrain for the commuter rail line electrification is an autotransformer-fed system. The system comprises three major parts: ■ traction power supply system including traction power substations located along the route at predetermined spacing ■ traction power distribution system consisting of overhead catenary system, feeder system, paralleling stations, and a switching station ■ traction power return system comprising running rails, impedance bonds, cross bonds, static wire, and ground. The traction power supply system is being designed to consist of two traction power substations. Each substation will have two equally rated, single-phase traction power transformers, with the primary windings connected phase-to-phase to 115 kV transmission system. Connections to the utility high-voltage (HV) system are required to ensure adequate and highly reliable power supply with low susceptibility to phase unbalance, harmonic distortion, and voltage flicker that may result from the addition of traction load. To limit the system unbalance, the transformer primary windings will be connected to alternate phases of the transmission system. The transformer secondary windings will be rated at 50 kV nominal voltage and will feed the feeder and catenary distribution system. The windings will be center-tapped, with the tap solidly grounded and

IEEE VEHICULAR TECHNOLOGY MAGAZINE | JUNE 2009

connected to the traction power return system. Consequently, this arrangement will result in the feederto-rail system operating at 25 kV nominal voltage and the catenary-to-rail system being energized at 25 kV nominal voltage, hence, the name of the system, 2 3 25 kV. With the train utilization voltage of 25 kV, the power distribution along the system is at a feeder-tocatenary voltage of 50 kV. This is very advantageous, as substations can be located further apart than would be possible with a direct-fed system operating at 25 kV. For the traction power substations, power will be distributed along the system route by the feeder or catenary system. The feeder conductor will be 556.5 kcmil steel reinforced aluminum cable (ACSR) wire, while the catenary system will consist of one 300 kcmil stranded hard-drawn copper messenger wire and one 300 kcmil grooved hard-drawn copper contact wire. The distribution system will be equipped with seven paralleling stations and one switching station. Each paralleling station and switching station will include autotransformers with 50 kV primary windings and 25 kV secondary windings. The autotransformers will transform the 50 kV voltage between the feeder and the catenary to 25 kV voltage between the catenary and the rails. A simplified one-line diagram of the system is shown in Figure 1. The traction power return system will consist of the running rails, impedance bonds, cross bonds, overhead static wire, and the ground itself. The return system will be designed to provide low impedance return path for propulsion currents returning to the substations to limit voltage rise along the rails (rail-to-ground potentials) and to improve catenary fault detection by creating sufficiently high short-circuit currents.

THE SYSTEM SELECTED BY CALTRAIN FOR THE COMMUTER RAIL LINE ELECTRIFICATION IS AN AUTOTRANSFORMER-FED SYSTEM. interference (EMI) in circuits paralleling the utility power lines [2]. The overhead distribution system of electrified railroads generally operates with lower clearances than typical power utility transmission lines and is therefore prone to higher incidence of short circuits. The fault levels need to be determined in each substation to verify that short-circuit interrupting capabilities of commercially available circuit breakers are not exceeded. Depending on the propulsion technology of the rolling stock, the trains may operate at a relatively low power factor, which will have to be either supplied by the utility system or corrected by capacitors. Low power factor in the transmission system may cause excessive voltage drop and inefficient power delivery. Rolling stock of modern design will operate at a high power factor and is likely to meet the power utility requirements for HV systems. Traction power demand is of highly fluctuating nature. This is a result of abrupt, impulse-like changes in power requirements of trains as they accelerate and decelerate, as they encounter or leave track grades, and as they enter and leave distribution system feeding sections. The quick variation of the traction current results in sudden variation of voltage at the substation connection point and, to a lesser degree, on other utility busbars. Voltage flicker is objectionable to people and may cause unsatisfactory operation of electronic equipment [3].

Characteristics of Traction Loads Since the traction load is single phase, the traction power transformers in the substations are connected to only two phases of the utility transmission system. The unequal loading of the three phases will unbalance the utility three-phase voltages and currents to some degree. This unbalance creates negative sequence current flow in rotating machinery that needs to be kept within limits, so that the heating of equipments such as generators and motors is not unduly increased [1]. Because of the presence of electronic propulsion equipment on board rolling stock, the loads are contaminated with harmonics, albeit to small degree due to the design of modern rolling stock. The presence of harmonics will cause some distortion of the utility voltages and currents. The harmonics increases the heating of equipments such as generators, motors, and capacitors and, under particularly adverse conditions, may give rise to system resonance. In very unlikely occurrences, the transmission line harmonics may cause electromagnetic

JUNE 2009 | IEEE VEHICULAR TECHNOLOGY MAGAZINE

Purpose of the Study To analyze the response of the Pacific Gas and Electric Company (PG&E) system to the traction loads, comprehensive computer-aided studies were performed to evaluate impacts because of the disturbances listed in Table 1. The levels of the impacts were calculated at key locations on the PG&E system using specially developed computer programs, and the results were compared to the limits acceptable to the utility.

Study Criteria To define acceptable limits for each cause of disturbance, a comprehensive analysis of applicable U.S. standards was conducted, review of available domestic and foreign literature was undertaken, and limits used in other similar utility impact studies were reviewed. Phase unbalance limits: The phase unbalance limits used in the study are shown in Table 2 [3].

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San Francisco

South San Francisco Substation

PS-1, MP 1.27

ATF-1, MP 9.4 MP 9.65, Alternate Site

PS-2, MP 4.95

T1

PS-3, MP 15.35

PS-4, MP 20.02

SW-1, MP 26.66

T2

Feeder System Catenary System

Track 1 Track 2 Traction Power Return System - Rails, Static Wire, and Ground San Jose Tamien Substation ATF-2, MP 45.28 MP 47.34, PS-5, MP 33.55 PS-6, MP 40.95 PS-7, MP 51.39 Alternate Site T1

T2

Symbols: Traction Power Transformer Autotransformer Section Insulator or Overlap Phase Break High Voltage Circuit Breaker Medium Voltage Circuit Breaker ATF Traction Power Substation PS Paralleling Station SW Switching Station

FIGURE 1 Caltrain 2 3 25 kV proposed electrification system. It is particularly important to maintain a generator negative sequence current within tolerable limits, as utility generators and large motors are protected by negative sequence relays that would trip a machine on excessive unbalance. Harmonic distortion limits: For individual and total harmonic distortion of voltage and current, the limits recommended by the IEEE Standard 519 [4] were used. The harmonic distortion levels are defined by the standard for

the point of common coupling, which is the point of traction power transformer connection to the power utility system. In systems where resonance is not present, distortion levels decrease for busbars more distant from the point of common coupling. Therefore, achieving tolerable distortion levels at the traction power transformer primary connections will achieve acceptable levels for all associated subsystems, and installation of filtering equipment can be avoided.

TABLE 1 Studies performed. Cause of Disturbance

Study Performed

Phase-to-phase connection of load

Voltage and current unbalance Harmonic distortion

Harmonic content of load

Resonance EMI

Short-circuit at transformer secondary winding Load power factor

Feeder-to-catenary short circuit Catenary-to-ground short circuit Power factor study

Load fluctuation

Voltage flicker

46 |||

Results Obtained Voltage unbalance on busbars Current unbalance in lines Negative sequence current in generators Individual harmonic distortion Total harmonic distortion Resonant frequency identification, frequency sweep TIF I·T Primary winding voltages and currents Secondary winding currents Power factor Level of voltage flicker Number of flicker occurrences per hour


EMI limits: The effects of EMI are very site specific and should be performed only when detailed information is available. Although such detailed EMI study was beyond the scope of this study, it was desirable to get some indication of the possible impact of the traction power system harmonics. The National Electric Manufacturing Association (NEMA) MG 1-32.11.1 [5] provides limits on telephone influence factor (TIF) of synchronous generators, as shown in Table 3. The TIF limits are intended to indicate the measure of possible effect of harmonics in the generator voltage output wave on telephone circuits. Since the traction loads inject harmonic distortion into the system in a similar way, it is believed that, in absence of other standards, the use of these limits is reasonable. The IEEE Standard 368 [6] provides a method of harmonic level classification of the power system in accordance with their balanced (measured on each phase) inductive influence (I·T ) product factor, as shown in Table 4. Although the standard is now obsolete, it was intended to contain information and recommendation pertaining to measurement of induced electrical noise generated by HV direct current (HVDC) power transmission systems and filtering equipment designed to mitigate that noise. Therefore, it is believed that, in absence of other standards, the use of this recommendation is justified. Short-circuit current limits: Review of manufacturers’ catalogs reveals that 25 kV single-phase circuit breakers are commercially available with 25 kA short-circuit interrupting capability. Therefore, considering the utility system short-circuit fault level, the substation traction power transformer rating and impedance has to be selected so that the short-circuit fault level on the transformer secondary is maintained under the aforementioned 25 kA. Standard 115 kV three-phase circuit breakers are selected on the basis of the 115 kV system short-circuit level and commercially available at symmetrical short-circuit interrupting capability of 40 kA and above. Power factor limits: The PG&E’s Interconnection Handbook [7] limits the transmission load power factor to between 0.97 lag and 0.99 lead at the point of common coupling. Therefore, this limit was used in this study for power factor evaluation. Voltage flicker limits: The borderline of visibility and the borderline of irritation curves, as published in IEEE Standard 141 [8], were used for the evaluation of voltage flicker acceptability. The study limits were considered by PG&E as reasonable and applicable to this study.

Utility System Representation The PG&E system was represented by its generator data, transmission line impedances and susceptances,


THE TRACTION POWER SUPPLY SYSTEM IS BEING DESIGNED TO CONSIST OF TWO TRACTION POWER SUBSTATIONS. transformer reactances, external system megavoltampere (MVA) infeeds, and real and reactive loads. Special equipment, such as static VAr compensators used for power factor correction and future HVDC transmission link, was also represented. For analysis of voltage flicker, the instantaneous power demand variation at each substation transformer was used. Since the voltage flicker depends on change of voltage from instant to instant, voltage drops over the utility equivalent impedance were calculated for each two successive snapshots of the traction power demand. For this purpose, power demand profiles in one 1-s snapshots were provided by Caltrain for each traction power transformer. Subsequently, the voltage flicker magnitudes were expressed at the point of common coupling, the interface between PG&E and Caltrain systems.

Traction Power System Representation The traction power system was represented as a singlephase system. Each substation supply transformer was represented as a two-winding transformer, with the primary winding connected phase-to-phase to the PG&E 115 kV transmission system, and the secondary winding center-tapped with the center tap grounded. The

TABLE 2 Phase unbalance limits. Unbalance Type

Unbalance Limits (%)

Voltage unbalance (negative sequence voltage u2) Current unbalance (negative sequence current i2)

2.5 5.0

TABLE 3 TIF limits. Generator Rating (kVA)

TIF Factor Limits

6.25–62 62.5–4,999 5,000–19,999 20,000 and above

250 150 100 70

TABLE 4 I·T product limits. I·T Product Level (kA)

Likelihood of Interference

25,000

Unlikely to cause interference Might cause interference Probably will cause interference

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bullet trains per direction will be dispatched, providing for operation at average headways of 5 min. Traction power system simulation of this traffic pattern resulted in an instantaneous (1-s interval) traction power transformer load profile provided by Caltrain as shown in Figure 3. Since temperature increase in the utility equipment does not occur instantaneously, use of instantaneous loads would not be appropriate. Consequently, it was considered that loads averaged over longer intervals, such as 15 min, would be more realistic for potential heating effects to be identified. The 15-min load averages are shown in Table 5. Load harmonic spectrum: Fundamental and harmonic frequencies of current vintage ALP-44 locomotives with a thyristor-controlled drive is shown in Figure 4(a). The harmonic spectrum is characterized by a third harmonic, with a magnitude of more than 35% of the fundamental frequency magnitude. The resulting waveform resembles a square-shaped waveform rather than a sinusoidal waveform. The waveform current of the Channel Tunnel

LOW POWER FACTOR IN THE TRANSMISSION SYSTEM MAY CAUSE EXCESSIVE VOLTAGE DROP AND INEFFICIENT POWER DELIVERY. feeder and catenary system were represented along the feeding section and connected to the paralleling stations and the switching station autotransformers, as shown in Figure 2. To provide at least some unbalance mitigation, the connection of transformer primary windings in consecutive substations was rotated to phases A-B, B-C, C-A, and A-B of the transmission network.

System Loads

DIgSILENT

Magnitude of the loads: Train ultimate peak-period operation which was simulated allowed for train consists comprising either of eight electric multiple units (EMUs) or one locomotive and eight trailing cars operating in the southbound and northbound directions. It is projected that, for each rush hour, ten limited express trains per direction and two baby

T2 –35.61 –5.34 –0.99 0.00 1.017 1.017 11.05 0.000 1.48 0.99 0.00

50 kV ATF-1 Bus T2 11.05 1.48 0.99 0.00

13.51 2.37 0.98 0.00

0.000

0.00 0.00 1.00 0.00

–0.00 –0.00 –1.00 0.00

0.00 0.02 0.00 0.00

0.00 0.00 1.00 0.00

GS-5

GT-5

0.000

0.000

GT-4

AT-5

0.000

GS-4 –0.00 –0.00 –1.00 0.00

0.00 0.17 0.00 0.00

0.000

0.00 0.00 1.00 0.00

AT-4

–1.83 0.12 –1.00 0.00

1.83 –0.25 0.99 0.00

2 Feeders(4)

PS-3

17.1 MW(1)

0.91 –0.07 1.00 0.00

–0.91 0.00 –1.00 0.00

PS-4

Load Flow Three-phase(ABC) Nodes Line-to-Line Voltage, Magnitude SP [p.u.] Line-to-Line Voltage, Magnitude DP2 [p.u.]

PowerFactory 13.2.333

0.91 –0.07 1.00 0.00

–0.91 0.00 –1.00 0.00

3.46 0.14 1.00 0.00 17.10 –0.00 1.00 0.00

Catenary Tk 2(4)

0.971 0.971 0.000

0.000

0.982 0.982

17.1 MW

Catenary Tk 1(4)

Catenary Tk 2

13.86 0.66 1.00 0.00

17.10 –0.00 1.00 0.00

0.971 0.971 0.000

Catenary Tk 2(1)

3.46 0.14 1.00 0.00

13.86 0.66 1.00 0.00

–10.74 –0.32 –1.00 0.00

Catenary Tk 1(1) Catenary Tk 1

–10.74 –0.32 –1.00 0.00

Catenary Tk 2(3)

0.000

GT-3

Catenary Tk 1(3)

GS-3

–0.00 –0.00 –1.00 0.00

0.00 0.25 0.00 0.00

AT-3

–6.92 –0.21 –1.00 0.00

2 Feeders..

6.99 0.37 1.00 0.00

–13.22 –1.30 –1.00 0.00

2 Feeders(2)

SW-1

Project: PG&E Caltrain Electrification Impact on PG&E Traction Power Supply and Distribution Graphic: ATF-1 T2 Systems Date: 10/2/2007 2 x 25 kV Autotransformer System Annex: Figure 7-2 Substation ATF-1, Transformer 2

FIGURE 2 Traction power system representation.

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THE ALP-46 LOCOMOTIVES FEATURE A RECENT

Power (MW)

PROPULSION SYSTEM DESIGN BASED ON AN INSULATED GATE BIPOLAR TRANSISTOR TECHNOLOGY.

80 70 60 50 40 30 20 10 0

7: 00 7: :01 05 7: :01 10 7: :01 15 7: :01 20 7: :01 25 : 7: 01 30 7: :01 35 7: :01 40 7: :01 45 7: :01 50 7: :01 55 : 8: 01 00 :0 0

locomotives [9] is shown in Figure 4(b). The propulsion system has clearly been refined, and the third harmonic is much suppressed. The resulting waveform shows a slightly distorted sinusoid. Since, at this time, there is little known about the harmonic current spectrum of the prospective Caltrain rolling stock, the harmonic current spectrum of modern locomotive, ALP-46, as operated by New Jersey Transit, was used for this study. The ALP-46 locomotives feature a recent propulsion system design based on an insulated gate bipolar transistor (IGBT) technology. Because of the high efficiency of IGBTs, the locomotives draw current with individual harmonics of relatively low magnitude, imperceptible in Figure 4(c). Further advantage of the ALP-46 design is the propulsion system featuring a four-quadrant inverter. This technology enables the locomotive to operate at close to unity power factor.

Time (h:min:s)

FIGURE 3 Traction power load.

Transmission Line Selection The Caltrain electrification system is planned to be supplied by two traction power substations, one located in the South San Francisco area and one located in the San Jose area. For the South San Francisco substation, PG&E identified six suitable transmission lines for substation supply. For the San Jose substation, only one line was identified as suitable. Review of the PG&E transmission network revealed that two of the lines in the South San Francisco area supply Bay Area Rapid Transit (BART) system loads. These two lines were not the first choice for supply of Caltrain unbalanced loads. This is due to the fact that any voltage unbalance at the rectifier ac input terminals increases harmonics at the rectifier dc terminals. Furthermore, one of the transmission lines was supplied by a cogenerating plant, as shown in Figure 5. A preliminary study revealed that, when all systems are in service, the system operates satisfactorily. However, in the event of circuit breaker Brk 1 opening, the traction load would be supplied mainly by the cogenerating plant and without the support of strong busbar Bus A, and the negative sequence current in the cogenerators would

exceed the study limit. Therefore, this line was also deemed unsuitable. Finally, for each location, a transmission line with a substation located in the vicinity of the proposed traction power substation was selected, and the traction power transformers will be supplied directly from the PG&E substation busbar.

Studies Performed The commuter rail system experiences two load peaks during which the utility system unbalance, harmonic distortion, and EMI are likely to be the highest. The load peaks occur every weekday for 2–3 h in the morning and, in the afternoon when the passenger density is the highest, the train headways are the shortest and the train consists are the longest. This period of operation is characterized by the highest traction system loads and coincides with relatively high utility system loads. Normally, during the peak period of operation, it may be assumed that all utility generators will be in service and the requirement for power factor correction will be at the maximum, requiring all shunt

TABLE 5 Traction power transformer loading. Transformer Load (MW) Averaged Over 15 min Substation ATF-1 South San Francisco

Substation ATF-2 San Jose

Substation Loading Condition

Transformer 1

Transformer 2

Transformer 1

Transformer 2

Highest total system load demand Highest substation load demand Highest substation load difference

6.4 6.0 6.0

34.2 34.8 34.8

28.6 26.5 26.5

2.7 2.1 2.1


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150 120

Bus A

Magnitude (%)

90

Brk 1

60 Traction Power Load

30 0

Cogeneration Plant

–30 –60 –90 BART Load

–120

0 36 0

0

0

32

28

0

0

0

24

20

16

12

80

40

0

–150

FIGURE 5 Cogeneration plant supplying traction load.

Angle (°) (a) One Cycle of Waveform

150 120 90 60 Magnitude (%)

30 0 –30 –60 –90 –120

0 36

0 32

0 28

0

0

24

20

0 16

0 12

80

40

0

–150 Angle (°) (b) 150 120

Magnitude (%)

90 60 30 0 –30 –60 –90 –120

0 20 0 24 0 28 0 32 0 36 0

16

0 12

80

40

0

–150 Angle (°) (c)

FIGURE 4 One cycle of load current waveform of propulsion systems for various rolling stock developed over the last 20 years. (a) Thyristor-control locomotive, (b) Channel Tunnel locomotive, and (c) IGBT ALP-46 loco. capacitors to be connected to the utility system. Also, all transmission lines will be assumed in service.

50 |||

BART Load

During system outages and light load conditions, adverse impacts may be increased. Therefore, in addition to the all systems in study, additional studies were performed, as follows: ■ All system in service: This is a base case run that represents the normal system configuration under peak system loads and reveals the system performance by identifying its strengths and weaknesses. The purpose of the base case study is to establish the system performance benchmark for comparison with studies representing utility system outages, traction power system outages, and light load condition study. ■ Utility system outage conditions: Outages of utility equipments, such as generators, transformers, and transmission lines, increase the utility system impedance. The higher the system impedance, as viewed from the traction power substations, the higher values of unbalance and distortion are obtained. ■ Traction power substation transformer outages: During a traction power transformer outage in a substation, the in-service transformer will supply the entire substation load and increase loading on the supply power utility line. ■ Light load conditions: The utility system loads are represented as busbar shunts and act as dampers for harmonics in the potentially resonant transmission circuits. Should a particular study indicate a real possibility of resonance, the computer run would be repeated with light loads at the utility busbars. The light loads would decrease damping and increase the possibility of higher harmonic distortion and resonance. ■ Traction substation outages: In the unlikely event of outage of the entire South San Francisco Substation ATF-1, the transformer T1 in San Jose Substation ATF-2 will supply the traction load to the end of the system in South San Francisco. Similarly, in the event of outage of entire San Jose Substation ATF-2, the transformer T2


in the South San Francisco Substation ATF-1 will supply the traction load to the end of the system in San Jose. For outage of an entire substation, some degradation in rolling stock performance or schedule can be expected. Therefore, the traction loads for these two studies were reduced.

100 SVC 215 MVAr: Harmonic Distortion A in % SVC 215 MVAr: Harmonic Distortion B in % SVC 215 MVAr: Harmonic Distortion C in % 10

1

0.1

Study Results

[-]

1. 00 3. 00 5. 00 7. 00 9. 00 11 .0 13 .0 15 .0 17 .0 19 .0 21 .0 23 .0 25 .0 27 .0 29 .0 31 .0

Results of the studies under normal and contingency conditions show 0.01 that the busbar voltage unbalance and the generator current unbalance (the negative sequence current) are 0.001 well below the study criteria limits. The worse case results occurred at SVC 215 MVAr Date: 10/2/2007 Caltrain Electrification Impact on PG&E 115 kV System substation ATF-1 and are presented Annex: /7 South San Francisco Substation AFT-1 Area All Systems in Service in Table 6. The harmonic distortion study has shown acceptable individual FIGURE 6 Individual harmonic distortion in a system capacitor. and total harmonic distortion. An example of the individual harmonic distortion result is operating conditions and under various system outshown in Figure 6, where each individual harmonic is age conditions, including transmission line, generator, plotted with the IEEE Standard 519 limit. As each harand traction power system contingencies. The utility monic distortion is well below the study criteria limit, system voltage and current unbalance, harmonic disthe results are acceptable. tortion, EMI levels, short-circuit level, power factor, The EMI study shows that the TIF and the I·T product and voltage flicker were found to be within the defined are well below the limits, and the short-circuit study limits and are therefore acceptable. Based on the produces fault currents well below capabilities of study results, it is concluded that no remedial actions off-the-shelf circuit breakers. The power factor study within the utility power system are necessary. indicates that the power factor on the traction power The harmonic distortion study results are dependent transformer 115 kV primary windings is within the mainly on the harmonic spectrum of the rolling stock. requirements of the PG&E Interconnection Handbook, as Because, at this time, assumptions have been made shown in Table 7. with regard to the characteristics of the rolling stock The worst voltage flicker is well within the requirements that will be serving the Caltrain system in the future, it of IEEE Standard 141, with all flicker points being below is recommended that the propulsion and regeneration the borderline of visibility curve, as shown in Figure 7. system harmonics of the new cars or locomotives are no higher, and preferably, are lower than those used in the study. Conclusions and Recommendations The information regarding the transmission line The results of the studies show that the PG&E system capability and loading provided by PG&E indicates that stands up well to the traction loads under normal

TABLE 6 Unbalance and harmonic distortion study results. Phase Unbalance Study

Harmonic Distortion Study

Negative Sequence Bus Voltages u2 and Generator Currents i2 (%)

Bus Voltage IHD and THD Distortion (%)

Transformer IHD and THD Current Distortion (%)

Bus

u2

Generator

i2

Bus

IHD

THD

Xfmr

IHD

THD

ATF-1 T1 ATF-1 T2

0.5 1.0

United Co-Gen SFAERP

2 1

ATF-1 T1 ATF-1 T2

Within IEEE 519 Within IEEE 519

0.02 0.03

T1 T2

Within IEEE 519 Within IEEE 519

0.6 0.5


||| 51

TABLE 7 EMI, short-circuit current, and power factor study results. EMI Study

Short-Circuit Current Study

Power Factor Study

TIF and I·T Product (kA)

Short-Circuit Currents (kA)

Power Factor (p. u.)

Bus

TIF

Xfmr

I·T

Xfrm

HV Winding

LV Winding

Xfrm

cos

ATF-1 T1 ATF-1 T2

1.2 1.1

T1 T2

1.6 2.9

T1 T2

4.1 4.1

9.4 9.2

T1 T2

1.0 0.98

Voltage Flicker (%)

6

Borderline of Irritation (%) Borderline of Visibility (%) Voltage Flicker, Phase C Voltage Flicker, Phase A

5 4 3 2 1 0 1

10

100 1,000 Fluctuations/h

10,000 100,000

For the voltage flicker study, an in-house developed program was used. To determine the phase currents and voltage drops in a three-phase system unbalanced by a phase-to-phase load, it was necessary to use a symmetrical component theory [10] to develop the relevant equations for A-B, B-C, and C-A phase load connections. For this purpose, Microsoft Excel spreadsheet software was used to obtain all numerical results and plot all graphs.

Author Information FIGURE 7 Voltage flicker compared to IEEE Standard 141 Curves. the transmission lines supplying the substations considered for supply of the Caltrain electrification system loads operate with sufficient spare capacity and are able to accommodate the additional traction loads. Upon PG&E’s acceptance that the proposed substations are suitable for Caltrain system supply, it is recommended that PG&E approves the locations and supply points selected for the traction power supply substations planned to serve the San Francisco to Tamien Corridor. Further, it is recommended that Caltrain proceeds with service application at the appropriate time.

Appendix Software Used For the studies, except for the voltage flicker study, the PowerFactory software by DIgSilent was used. The software is capable of representing the three-phase utility transmission network, the utility generators, transmission network, static VAr devices, loads, as well as the singlephase traction power supply, distribution, and return systems. The study included representing the three-phase utility loads as well as the unbalanced and distorted single-phase traction loads. The software is capable of calculating voltage unbalance on busbars, current unbalance in lines and generators, individual and total harmonic distortion of voltages and currents, EMI indices, short-circuit fault levels, and power factors at various locations in the system.

52 |||

Tristan A. Kneschke is a senior engineer with Louis Tobias Klauder (LTK) Engineering Services, a rail transit consulting group headquartered in Ambler, Pennsylvania. Over his 20-year association with LTK, Tristan participated in more than 100 assignments of varying complexities and durations. The projects included system studies, preliminary designs, final designs, and construction-related services.

References [1] T. Kneschke, “Control of utility system unbalance caused by single-phase electric traction,” presented at the 1984 IAS Annu. Meeting, Chicago, IL, Paper CH2060-2/84/0000-0259. Republished in the IEEE Trans. Ind. Applicat., vol. IA-21, pp. 1559–1570. Nov./ Dec. 1985. [2] T. Kneschke, “Electrical traction power supply configurations on 10,000 route miles of U.S. railroads,” Final Rep. No. DOT/FRA/ORD82/50, NTIS Accession No. PB83-147975, National Technical Information Service, Springfield, VA, June 1982. [3] T. Kneschke, “Power supply system for electrification of the North Jersey coast line,” presented at the 1985 Joint IEEE/ASME Railroad Conf., New York, NY, Paper CH2167-5/85/0000-0029. [4] IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems, IEEE Standard 519, 1992. [5] Motors and Generators, National Electrical Manufacturer’s Association Standards Publication MG-1, 2006. [6] IEEE Recommended Practice for Measurement of High-Voltage DirectCurrent Systems, IEEE Standard 368, 1977. [7] PG&E Interconnection Handbook (Section L3, Substation Design for Load Only Entities), Revision 01, San Franciso, CA; Pacific Gas & Electric Co. Dec. 15, 1997. [8] IEEE Recommended Practice for Electric Power Distribution for Industrial Plants, IEEE Standard 141, 1993. [9] R. Barnes and K. T. Wong, “Unbalance and harmonic studies for the channel tunnel railway system,” IEE Proc. B, vol. 138, no. 2, pp. 41–50, Mar. 1991. [10] Westinghouse Electric Corporation, Electrical Transmission and Distribution Reference Book, 4th ed., East Pittsburgh, PA, 1964.
