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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
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 [email protected]
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 [email protected]
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 [email protected]
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