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A study on relay setting for AT feeding system protection

using PSCAD/EMTDC

Hosung Jung, Moonseob Han, Changmu Lee, Joorak Kim

Korea Railroad Research Institute

360-1, Woulam-Dong, Uiwang-City, Kyeonggi-Do, Korea

Abstract

This paper presents simulation technique for relay setting of AT feeding system protection. To prove if relay setting

value is proper, AT feeding system and various locomotives are modeled using PSCAD/EMTDC. Operation and fault

data have been extracted by simulating various load operation and fault situations. Using these data, setting values of

distance relay and !I fault selection device for protection of AT feeding circuit could be verified. And due to the inrush

current of unloading transformer and increase of temporary maximum load current, the possibility of protection relays

malfunction is shown.

Keywords: PSCAD/EMTDC, AT Feeding System, Locomotive, Distance Relay, !I Fault Selection Device

1 INTRODUCTION

Electrification of railway was rapidly spread with the

opening of KTX(Korea Train Express) in Korea.

Electric railway system supplies power to rolling stocks

by converting three phase ac power supplied bypower supply company to two single phase ac power of

which phase difference is 90"using scott transformer.

And electric locomotive has been developed from the

thyristor phase controlled locomotive to PWM(Pulse

Width Modulation) controlled locomotive.

Since any fault in these electric railway systems may

cause damages on rolling stork and ground facilities as

well as interruption of railway operation and damages

on life or properties, it requires a more reliable

protection method. For the protection of AT feeding

system, distance relay using impedance magnitude

measured at substation and !I fault selection device

using current increment value in fixed time are installed

for main and backup protection relay[1], [2].

However protection relay is hard to detect fault and

cause malfunction in the normal operation condition

because of increase of train operation frequency,

competition of traction load and regeneration load, and

operation of different type of locomotive in the same

section. To prevent it, protection relay setting value

should be corrected by analyzing load and fault

characteristics of the AT feeding system generally[3].

Therefore, this paper modeled AT feeding system and

locomotives using PSCAD/EMTDC, power system

analysis program, to prove the suitable setting value.

Various operation and fault conditions have been

simulated and the load operation characteristics and

fault are analyzed.In conclusion, we can see the reliable trip of relay to the

various faults and the possibility of protection relays

malfunction due to the inrush current of unloading

transformer and increase of temporary maximum load

current.

2 Protection System for AT Feeding Circuit

For the protection of feeding circuit in AT feeding

system, distance relay(44F) and ! I fault selection

device(50F) are applied in dual mode. The main

protection, distance relay calculates impedance using

voltage and current measured at substation and detects a

fault in case the calculated value converges into a range

of fault impedance. In general, distance relay is setted

to protect up to 120% of line impedance between

substation(SS) and sectioning post(SP) in order to

eliminate any unprotected arear. The secondary

protection, ! I fault selection device compares the

current increment value by notches of load current(1I )

and fault current(2I ) to detect a fault such as

expression (1).

21 III

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Figure 1 shows the protection region of distance relay

and ! fault selection technique.

Figure 1. Protection System for AT Feeding Circuit

Distance relay and ! I fault selection device may

malfunction due to the inrush current of AT and rolling

stocks transformer during unloading or increase of the

maximum load current in case of sudden load increase.To prevent it, the trip of relay is blocked by a certain

amount of low order harmonics using the feature that

low order harmonics in fault current is relatively not

more than that of load current.

3 AT Feeding System Modeling Using PSCAD/EMTDC

3.1 AT Feeding System

AT feeding system generally consists of electric power

company, transmission line, electric railway substation,

sectioning post/subsectioning post and feeding circuit.

This paper modeled it by each component usingPSCAD/EMTDC such as figure 2[4], [5].

Figure 2. Modeling of AT feeding system

First, it receives three phase 154kV from electric power

company through transmission line, and converts three

phase 154kV into two single phase 55kV using scott

transformer at railway substation and then converts the

55kV to 27.5kV using AT transformer for supply to the

rolling stocks. Autotransformer of SP and SSP has been

modeled to supply 27.5kV to upper/lower lines. Andfeeding circuit is modeled by 10 port network divided

into upper/lower catenary line group, upper/lower

feeder line group and rail group. To verify the accuracy

degree of modeling, the magnitude of fault current at

each point and line impedance magnitude of short

circuit between rail and catenary are compared in

manual calculation and simulation results. Table 1 and

figure 3 illustrate the result of comparison[6].

Table 1. Comparison of fault Current by Manual

Calculation and Simulation

Unit : [kA]

Fault point and typeManual

CalculationSimulation

3 phase short 39.13 39.08Substation of

power

company 1 line ground 37.20 37.12

3 phase short 12.63 12.63End of

transmissionline 1 line earth f 9.47 9.61

2nd of Scott

Transformershort fault 2.31 2.42

2nd of AT

TransformerShort fault 10.71 10.79

0 2 4 6 8 10 12 14 16 18 20

2

4

6

8

10

12

14

16

Comparison of the Line Impedance

Impedance[Ohm]

Calculation Value

Simulation Value

Figure 3. Comparison of Line Impedance by Manual

Calculation and Simulation

It is reasonable that AT feeding system modeling isaccurate, considering the values of calculation and

simulation. It is also shown that the short-circuit

impedance between rail and catenary is not linear but

slightly curved due to the boost of autotransformer of

SP and SSP. And there is a little difference between

calculation and simulation, it is assuming that it is

calculated in the single line condition and

autotransformer is not considered.

3.2 Locomotive Modeling

Due to the development of power electronicstechnology, locomotive has been developed from

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resistance control to thyristor phase control and up to

PWM control method. So locomotive with different

controls are inevitably operated in a same section and

the protection relay should be set considering the load

characteristics.

To model locomotive using PSCAD/EMTDC, the speedis divided into 10 levels from start to the maximum

speed and the effective/reactive power by speeds is

converted into impedance. Meanwhile, harmonics,

which occurs when locomotives are operated, is

expressed with the maximum values of each order as its

constant current source and modeled accordingly.

Thyristor phase controlled locomotive, using ac power

supplied from catenary and a rectifier combining

semi-bridge type thyristor and diode, controls thyristor

phase, changes speed and alternates its traction force by

field-weakening control. The currently operated

thyristor phase controlled locomotives is EL 8000electric locomotive and KTX. The power factor at the

maximum traction is about 0.7~0.8 and the harmonics

seems to be relatively huge generally.

Figure 4 illustrates the load region by modeling

thyristor phase controlled and simulating them in

various operation conditions. It shows that power factor

is better than that of thyristor phase controlled

locomotives, because it was compensated the power

factor using power factor compensation device in

locomotive.

0 100 200 300 4000

100

200

300

400

44F

X[Ohm]

Load

Thyristor Phase Control Vehicle

Figure 4. Load area of thyristor phase controlled

locomotive

PWM controlled locomotives convert electric power

from feeder voltage of single phase ac power and 60Hz

frequency to dc constant voltage while ac voltage

generated from voltage transformer is structured as

pulse voltage, converting pulse width to ac voltage. The

currently operated PWM controlled locomotives are EL

8100 locomotives and High Speed Railroad(HSR-350),G7 trains. Since the voltage and current wave are

almost closed to sine wave, it is controlled that power

factor is to be 1 regardless of sizes of feeder voltage

and traction motors. And unlike other controlled

locomotives, it contains a little low order harmonics.

Figure 5 illustrates the load area by modeling PWM

controlled locomotives and simulating them in various

operation conditions, showing that in traction, thepower factor is maintained 1.

0 100 200 300 400

0

100

200

300

44F

X[Ohm]

Load

PWM Control Vehicle

Figure 5. Load area of PWM controlled locomotive

Harmonic components, which are generated when

locomotive is operated, have an influence on the

fundamental wave, making it difficult to detect faults

while they are used to the factor of low order harmonics

in order to prevent maloperation of distance relay and

I fault selection device. Since the generation of

harmonics is, however, different depending on vehicles,

it is required to analyze the generation by control types.

1 5 9 13 17 21 25 29 33 37 41 45 490

5

10

15

20

25

30

35

40

Maximum H arnomic Current

Harm

onicCurrent[A]

Harnomic Degree

Thyristor Phase Control

PWM C ontrol

Figure 6. Comparison of Harmonic Current by Control Types

Figure 6 illustrates the comparison of harmonic currents,

which occur from thyristor phase controlled locomotive

and PWM controlled locomotive respectively. In

general, PWM controlled locomotives THD is within

5% while thyristor phase controlled locomotive is about

15%.

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4 Relay Setting and Impedance Convergence Characteristics

4.1 Relay Setting for Feeding Circuit Protection

To verify setting values of distance relay and !I fault

selection device, the following feeding system has been

modeled. In the modeling, the full length of line is up to

50km considering extension feeding, and the lineimpedance is 0.159+j0.695(0.73 77.15 ") !/km. In

addition, for the maximum load condition, it is

simulated with the maximum load current of 945A

(based on 55kV) because up to 3 locomotives could be

operated to each direction in the same section.

( ) Distance Protective Relaying Scheme

R = 0.159 !/km # 50 km # 120 % = 9.54 !

X = 0.695 !/km # 50 km # 120 % = 41.7!

() !I fault selection device (in maximum operation)

)2/(/0 hLFF kIIVZ += = 55000 / (945/2 + 945 * 0.5) = 58.2 !

Figure 7 illustrates the protection region according to

setting values of protection relay drawn on impedance

map. Distance relay could protect up to 120% of the

line impedance from a substation to its neighboring

substation, considering extension feeding while ! I

fault selection device could protect up to maximum

load current.

0 10 20 30 40 50 60

0

10

20

30

40

50

60

R [Ohm]

44F

Line Impedance

50F

X

[Ohm]

Protection Region

77.15

Figure 7. Protection Region of Protection Relay

4.2 Impedance Convergence Characteristics

To analyze the convergence characteristics of fault

impedance in case of any condition, the short fault

between catenary and rail and short fault between

catenary and feeder have been simulated. Figure 8

illustrates the simulated short fault between catenary

and rail at the maximum load operation and shows theimpedance convergence for faults, which occurred at

10%, 30%, 50%, 70% and 90% from a substation.

0 10 20 30 40 50 60

0

10

20

30

40

50

60

R [Ohm]

10%

30%

50%

70% 90%

44F

Line Impedance

50F

X[Ohm]

Catenary-Rail Short Fault

Figure 8. Fault Impedance Convergence

(Catenary-Rail Short Fault)

Figure 9 shows the simulated short-circuit between

catenary and feeder at the maximum load operation and

illustrate impedance convergence for faults, which have

occurred at 10%, 30%, 50%, 70% and 90% from a

substation.

0 10 20 30 40 50 60

0

10

20

30

40

50

60

R [Ohm]

10%

30%

50%

70%

90%

44F

Line Impedance

50F

X[Ohm]

Catenary-Feeder Short Fault

Figure 9. Fault Impedance Convergence(Short Fault of Catenary-Feeder)

As seen in the above results, it is verified that the

setting values of distance relay could be used to detect

faults regardless of type or distance of faults.

Figure 10 shows the characteristics of changes in

impedance due to inrush current of unloading

transformer or sudden load increase. It can be expected

that a relay may maloperation as impedance temporarily

converges into protection region due to sudden load

increase or inrush current. Therefore, low orderharmonic restriction is essential to prevent a relays

maloperation.

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0 10 20 30 40 50 60

0

10

20

30

40

50

60

R [Ohm]

Maximum Load Curren

Inrush Current

44F

Line Impedance

50F

X[Ohm]

Maloperatoin Condition

Figure 10. Load Impedance Convergence

(maloperation condition)

5 CONCLUSION

This paper presents simulation technique for relay

setting of AT feeding system protection. To prove if

relay setting value is proper, AT feeding system and

thyristor phase controlled and PWM controlled

locomotives are modeled using PSCAD/EMTDC.

Operation and fault data have been extracted by

simulating various load operation and fault situations.

Using these data, setting values of distance relay and

I fault selection device for protection of AT feeding

circuit could be verified. And due to the inrush currentof unloading transformer and increase of temporary

maximum load current, the possibility of protection

relays malfunction is shown.

It is required in further studies that AT feeding system

and locomotives considered moving load characteristics

are modeled in detail.

REFERENCES

[1] Gao Shibin, He Weijun, Chen Xiaochuan, Study

on Microprocessor-Based Adaptive Protective Relay

for Heavy Duty Electric Traction System,

Developments in Power System Protection Conference

Publication No. 434, pp319-322, 1997

[2] Tevfik Sezi, Frank E. Menter, Protection Scheme

for a New AC Railway Traction Power System, IEEE

Transmission and Distribution Conference vol 1,

pp388-393, 1999

[3] Hosung Jung, A Study on Protection system to the

Load Characteristics on the AC Feeder System,

Proceeding of the KIEE Summer Annual Conference

2004, No. B, pp 1370-1372, 2004

[4] Hanmin Lee, Kwanghae Oh, Fault Analysis of AC

Electric Railway System Mode by EMTDC, Trans.

KIEE vol. 52A, no. 9, pp 1-7, 2003.

[5] PSCAD/EMTDC Users mannual.

[6] Korea Railroad Research Institute, A Study on the

Overhead Contact-line Constant and Optimal Strategy

of Protection Circuit in the Electrical Railway

Substation, Korea Railroad, 1998

Biographies

Hosung Jung

1998 Master Degree in Sungkyunkwan

Univ. 1998-2002 Ph.D in

Sungkyunkwan Univ. 2002-Present

Researcher in KRRI (Korea Railroad

Research Institute) E-mail

hsjung@krri.re.kr

Moonseob Han

1989 Master Degree in Inha Univ.

1989-1995 Researcher in ADD

(Agency for Defense Development)

1995-Present Senior Researcher in

KRRI (Korea Railroad Research

Institute) E-mail mshan@krri.re.kr

Changmu Lee

1994 Master Degree in Hanyang Univ.

1994-1997 Researcher in Korea

Institute of Industrial Technology

1997-Present Senior Researcher in

KRRI (Korea Railroad Research

Institute) E-mail cmlee@krri.re.kr

Joorak Kim

1999 Master Degree in Hongik Univ.

1999-2000 Researcher in Hongik Univ.

2000-Present Researcher in KRRI

(Korea Railroad Research Institute)

E-mail jrkim@krri.re.kr