EMC issues around traction power supply system

Hitoshi Hayashiya East Japan Railway Company

Tokyo, Japan

Abstract— Five examples of EMC issues in traction power

supply system will be shown in this paper. The examples shown in this paper do not cause severe problems in the existing railway system but they should be taken into account to realize reliable traction power supply system and power supply system for station as particular issues in the railway system. Each example is discussed based on the measured data on the field or by the experiments.

Keywords—raiwaly, traction power supply system, energy storage system, d.c. circuit breaker, changeover section, LED light, wireless communicaiton

I. INTRODUCTION About the EMC issues in railway, it is often discussed

about the interference between on board motor control system with VVVF (Valuable Voltage, Valuable Frequency) inverters and on ground signaling system. The malfunction of the signaling system directly intimidates the safety of railway transportation system and to realize high reliability of the signaling system is one of the most important topics in electrical engineering for railway. The general technical book of “Railway and EMC problems” was published [1] in 2008 in Japan.

In this paper, the following five examples of EMC issues in traction power supply system are introduced.

High harmonics measurement in d.c. traction power supply system after the introduction of lithium ion battery system at HAIJIMA substation.

Electromagnetic radiation from d.c. circuit breaker which breaks the fault current more than 10kA with long arc in the air during the breaking process.

Transient phenomena in changeover section of traction power supply system for high speed railway which is caused by the opening and closing of vacuum switchgears measured at TAKASAKI sectioning post.

High harmonic condition after introduction of LED light at YOTSUYA station and compared to that before the introduction.

Radio wave measurement in SHINAGAWA railyard to investigate the possibility to introduce wireless communication for light control.

In chapter II, first three issues in traction power supply system are shown while the last two issues around station are shown in chapter III, respectively.

II. ISSUES IN TRACTION POWER SUPPLY SYSTEM

A. High harmonics measurement in d.c. traction power supply system In d.c. traction power supply system, energy storage system

such as lithium ion battery and nickel metal-hydride battery have been installed for regenerative energy utilization. The purpose for installation is not only regenerative energy utilization but also voltage drop compensation and backup for black out.

East Japan Railway Company has introduced lithium ion battery at HAIJIMA Substation in OME Line since February 20th, 2013[2],[3]. The battery was connected to d.c. 1.5kV bus via d.c. / d.c. converter as shown in Fig.1. The track circuit is utilized for detecting the existence of the train, controlling the railroad crossing gate and automatic train control system (ATC), etc., so that, it have to be confirmed that the higher harmonics from the battery system do not interfere with them.

To reduce the high harmonic influence on the track circuit as small as possible, the following measures were introduced. Both the common mode noise and normal mode noise have to be considered.

Electric filter for d.c. / d.c. chopper

Ferrite core to both power circuit and control circuit of the battery

Single point grounding of controlling system in the Circuit diagram of d.c. traction power supply system with battery

switchboard

Making the wire length of the controlling system as short as possible

The influence of the battery system was confirmed during the night time when the railway operation for customer was stopped and the test train was operated on December 23rd, 24th, 2012 and January 26th, 2013. Fig.2 shows the example of relation between the high harmonic current level and the reference values for the signaling system during the test. As shown in this figure, the influence of the battery system on the signaling system is small enough.

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IGBT Chopper1

2

Lithium ionBattery 1

2Feeding circuits

Track circuit

d.c.circuit breaker

Series Reactor

3456

Catenaries system(Contact wire)

Traction transformer (ex. 22kV/1.2kV a.c.)

Diode rectifier (1.2kV a.c./ 1.5kV d.c)

1.5kV d.c. bus

Power supply from rectifier

Power supply from battery

Fig. 1. Circuit diagram of d.c. traction power supply system with battery

0.0001

0.001

0.01

0.1

1

10

100

10 100 1000 10000 100000

Cur

rent

leve

l (A

)

Frequency (Hz)

Reference values for signaling system

Fig. 2. Relation between measurement and reference values on the high harmonic current for the signaling system

B. Electromagnetic radiation from d.c. circuit breaker In d.c. traction power supply system, an air circuit breaker

are applied for feeding circuit breaker to break d.c. fault current up to 12kA. In the d.c. air circuit breaker, the contacts of the circuit breaker are opened and the arc between the contacts are expanded in the arc shoot to increase arc voltage. The fault current was decreased by the enhanced arc voltage and extinguished within 20 or 30ms.

Because the air arc whose expanded length is more than 1m continues about 20ms in d.c. circuit breaker, the radiation from the circuit breaker is apprehended.

To confirm the electromagnetic radiation from d.c. circuit breaker, d.c. short circuit test was performed on January 14th, 2004 at R&D Center of East Japan Railway Company together with Railway Technical Research Institute. The antennas were arranged 3m away from the circuit breaker facing to the circuit breaker and transient radio field was measured based on the method described in IEC62236 series (Railway applications -Electromagnetic compatibility-)[4]. The measurement parameters were summarized in Table.1.

The measured electromagnetic field strength is shown in Fig.3. The reference values informatively given in IEC62236-5 (Emission and immunity of fixed power supply installations and apparatus) are also shown in this figure. As shown in this figure, the field intensity for 100MHz is a little bit larger than the reference value. Practically, the circuit breakers are installed in the cubicle and the radiation level would be much smaller than the measured value in the bare condition.

TABLE I. PARAMETERS OF THE MEASUREMENT

Short circuit current 7000A Measured frequency 100kHz, 1MHz, 100MHz, 900MHz Measurement bandwidth

200Hz for 100kHz, 9kHz for 1MHz, 120kHz for 100MHz and 900MHz

Antenna Loop antenna (MP414B) for 100kHz and 1MHz Biconical antenna (BBA9106) for 100MHz Log-periodic antenna (UHALP9108A) for 900MHz

Height of antenna Loop: 1m, Biconical: 3m, Log-periodic: 3m Measured field 100kHz and 1MHz: magnetic field

100MHz and 900MHz: electric field

-40

-20

0

20

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60

80

100

0.01 0.1 1 10 100 1000

Mag

netic

fiel

d (d

BuA

/m),

Elec

tric

field

(dB

uV/m

)

Frequency (MHz)

Magnetic field Electric field

IEC62236-5Annex A, Fig. A.1(informative)

Fig. 3. Measured electromagnetic field strengeth

C. Transient phenomena in changeover section of traction power supply system for high speed railway As high speed railway is driven by a single phase a.c.

electric power, three phase electric power from a utility company is converted to a single phase a.c. voltage at traction substations. To reduce the influence of the three phase unbalance to the power grid, special transformer such as Scott connected transformer is applied and three phase voltage is converted to two single phase a.c. voltages, those are M-phase (main phase) and T-phase (teaser), whose phase difference is 90 degree each other. Because of the phase difference, it is impossible to connect M-phase circuit and T-phase circuit directly. In traction power supply system for high speed railway in Japan, the phase-to-phase changeover sections with neutral section are built in front of substations (SS) and sectioning posts (SP) which are located between the substations.

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Fig.4 shows the configuration of the changeover section in front of substation and the working procedure of the changeover switches at every train passage. Here, vacuum circuit breakers are applied for the changeover switches. Fig.5 shows the example of the voltage change at the neutral section when the VCB-B is closed with train load measured at SHIN-TAKASAKI sectioning post in 2005[5][6]. As shown in this figure, the transient voltage change happens at the main circuit and the electric noise from such a transient phenomenon sometimes caused the malfunction of the protection relay system in the past. The control and protection system of the substation have to be designed taking such a noise condition into account. The noises whose frequencies are from a few kHz to 10 kHz are observed during the closing process of VCB with train load because of the previous discharge between the contacts of VCB. Apart from this frequency level, 100 kHz natural frequency of the neutral section electric circuit is also observed.

T-phaseVCB-B

M-phase

T-phaseM-phase

T-phaseM-phase

T-phaseM-phase

T-phaseM-phase

VCB-A

Open

Close

Open

Close

During the passage of HSR

After the passage of HSR

Fig. 4. Configuration of the changeover section and its working procedure

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-100 -50 0 50 100 150 200 250 300 350 400

Time [ms]

Vol

tage

[kV

]

-80

-40

0

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80

308 309 310 311

Time [ms]

Vol

tage

[kV

]

VCB-A Open VCB-B Close

Time (ms)

Time (ms)

Volta

ge (k

V)

Volta

ge (k

V)

Fig. 5. Example of waveforms of voltage change of neutral section

III. ISSUES AROUND RAILWAY STATIONS

A. Hihg harmonic condition after introduction of LED light at railway station In the railway station, lighting and air conditioning are

major electric loads and reducing them is important for saving electricity at station.

In YOTSUYA station 240 rapid type fluorescent lamps on the four platforms whose total capacity was 26.4kW were replaced to 507 LED light in 2012. Figure 6 shows the comparison of low frequency current high harmonics before and after the introduction of LED light on platform No.1 and 2.

As shown in Fig.6, especially 3rd and 11th order harmonic currents were increased by introducing LED light. Because in d.c. traction power supply system, 5th and 7th, 11th and 13th order high harmonics currents are observed because six phase rectifiers are widely used. They induce high harmonic voltage and result in high harmonic current to the loads in the distribution power system. In distribution line of traction power supply system, it is necessary to pay attention to such low frequency high harmonics.

0

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Rel

ativ

e ha

rmon

ic c

urre

nt c

onte

nt (%

)

Harmonic order

100%

100%

FLR light (before introduction of LED)

LED light (after introduction of LED)

Fig. 6. Change of harmonic current content before and after introduction of LED light

B. Radio wave measurement in the railyard We investigated to introduce wireless lighting control

system for railyard between SHINAGAWA and TAMACHI station in 2012. Wireless communication will be reasonable solution to introduce the system to existing infrastructure.

To confirm its validity, field measurements of signal strength around 2.4GHz band were carried out. Fig.7 shows the measuring points at railyard between SHINAGAWA and TAMACHI station. The measured electric field power at Point C is shown in Fig.8.

The results of investigation are as follows:

At Point A & B, arch shape strong field intensities for wireless local area network were observed around 2.41 and 2.47GHz.

At every measuring point, needle-shaped strong intensities were observed and those are obvious at Point C.

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Error rate increases when the field intensity becomes more than -70dBm.

The distance for stable communication is about 15m for 1mW wireless communication in -70dBm field power condition.

If there is an idle channel, wireless communication is realized for 35m interval.

There is no common idle channel for all measuring points, from point A to point E.

Because the average interval length of electric poles in the railyard is about 50m and 35m wireless communication is insufficient. Even for the idle channel, the communication error rate was 46.0% for 50m wireless communication in the railyard.

200mNorthSouth

West

East

SHINAGAWASTATION

TAMACHISTATION

TOKAIDO LINEPoint A

Point BPoint C Point D

Point E

Fig. 7. Measuring points at railyard near SHINAGAWA station

-110-100-90-80-70-60

Rec

eive

d po

wer

(dB

m)

Frequency Time

2.4GHz

2.5GHz0s

5s

Point C

Fig. 8. Measured electric field power

IV. CONCLUSIONS In this paper, five examples of EMC issues in and around

traction power supply system are shown.

In d.c. traction power supply system, the influence of d.c./d.c. converter have to be confirmed not to interfere with signaling system. Such a confirmation is important when a new energy storage system such as lithium ion battery is introduced to 1.5kV d.c. traction power supply system for regenerative energy utilization.

There happens transient electromagnetic phenomenon during the arcing process of d.c. air circuit breaker to break

fault current more than 10kA in d.c. traction power supply system. The reference value for electromagnetic radiation from electric machines is informatively given in IEC standard.

In the changeover section for high speed railway in Japan, the rapid voltage changes during the opening and closing process of vacuum switchgears are happens. In the traction substation, the controlling and protection relay system have to be designed to endure the noise radiated from such voltage changes.

In the railway stations, LED lights are actively introduced replacing for conventional fluorescent lamps during last a few years. The interactions between LED lights and existing 11th and 13th low order high harmonics have to be noted in the future when a lot of LED lights are introduced to the railway stations and offices.

The electric field intensity is measured at railyard to discuss the possibility to introduce wireless lighting control system. It was confirmed that the 2.4GHz band has already crowded around the railway station in Tokyo metropolitan area and it is difficult to establish reliable wireless communication system.

ACKNOWLEDGEMENT The measurements and experiments shown in this paper

are supported by the following colleagues and I really appreciate for their supports and contributions.

(Railway Technical Research Institute) K.Kawasaki, K.Nakamura

(East Japan Railway Company) M.Tojo, T.Kato, M.Hino, K.Watanabe, T.Koshiishi, S.Kikuchi, T.Sato, K.Kudo, S.Matsuzawa, J.Obama, D.Hayakawa, H.Suzuki, T.Kondo, Y.Noda, T.Ishii

(Hitachi Co., Ltd.) H.Takahashi

REFERENCES [1] The Institute of electrical engineering of Japan, “Railway and EMC

problems”, Ohmusha, Ltd., 2008 (in Japanese) [2] H.Hayashiya, S.Kikuchi, K.Matsuura, M.Hino, M.Tojo, T.Kato, M.

Ando, T.Oikawa, M.Kamata, H.Munakata, “Possibility of energy saving by introducing energy conversion and energy storage technologies in traction power supply system”, 15th European Conference on Power Electronics and Applications Vol.LS5d, No.73, September 2013

[3] M.Tojo, T.Kato, T.Koshiishi, M.Hino, S.Kikuchi, H.Hayashiya, H. Takahashi and M.Teshima, “Improvement of control for energy storage system for traction power supply”, The Papers of Technical Meeting, IEEJ, No.TER-13-050, November 2013 (in Japanese)

[4] K.Kawasaki: “Trends of international standardization of electromagnetic compatibility in railway systems”. The Journal of the institute of electrical installation engineers of Japan. Vol.31, No.6, pp.420-423 (2011) (in Japanese)

[5] H.Hayashiya, M.Hino, T.Sato, K.Kudo and S.Matsuzawa, “Comparative study of the surge phenomena of the changeover section”, The Papers of Technical Meeting, IEEJ, No.TER-05-037, pp.43-48, July 2005 (in Japanese)

[6] H.Hayashiya, Y.Ueda, K.Ajiki, M.Ando and M.Nakajima, “Investigation of Closing Surge in Shinkansen Power System and Proposal of a Novel Power Electronics Application for Changeover Section”, The 2005 International Power Electronics Conference (IPEC-Niigata 2005), No.S45-3, April 2005

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