Research on simulating the short circuit faults in dc traction network of hanoi pilot light metro line nhon – Ha Noi railway station

y new in Vietnam. In recent years, numerous works involved in the urban 
railway traction power supply system have been published and implemented on railway transit 
systems worldwide. Authors in [1] provided technologies of the urban railway power supply 
system. In [2], a model for traction system has been proposed to discuss the influence of DC 
traction system on power grid harmonics. In [3, 4], the research has been done with the evaluation 
of the impacts of harmonic traction current on the automatic train control systems. Authors in [13] 
proposed the six - pulse three phase rectifier bridge model for calculating close-up and remote 
short circuit transients on DC supplied railway and used piecewise linear techniques for modelling 
both close-up and remote faults, then compared with practically measured results. In [14], an 
accurate simplified calculation method based on second-order approximation to accurately 
determine the current waveform for remote and close-up short circuit faults currents on DC 
traction supply system were presented. Authors in [15] analyzed the model of the 
transformer/rectifier, utilized Kron's tensor analysis to reformulate circuit equations automatically 
after switching operation, and evaluated the impacts of the ratio DC side resistance to AC side 
inductance and the ratio DC side inductance to AC side inductance on the short circuit transient. 
However, in the above analyzed studies, the short circuit faults in the comprehensive traction 
power supply system have not been considered. 
This paper conducts the research on short circuit faults in the traction network of Hanoi 
pilot light metro line Nhon – Hanoi railway station. The model of traction power supply system 
with 12-pulse rectifier units is simulated on software Matlab/Simulink. The objective of the model 
is to study the short circuit faults and the train starting current in the traction network. 
II. MAIN CONTENTS 
1. DC traction power supply system configuration 
A typical section of traction power supply system of Hanoi pilot light metro line Nhon – 
Hanoi railway station is shown in figure 1. The traction power supply system is the complex 
system that is divided into power source (PS-1, PS-2), traction substations (TRSS-1, TRSS-2), 
traction network, and train. The medium voltage level of 22 kV AC is converted to a lower voltage 
one through the three-winding transformer (TRSS) in each substation and with the aid of rectifier 
(TR), and thus the DC traction voltage is generated and connected to the substation positive and 
negative bus bars. The 12-pulse rectifier unit supplies power at 750 V DC through the third rail 
to the train [2]. 
Each traction substation has two sets of 12-pulse rectifier units. The traction transformer 
has a delta-connected (∆) primary winding, with dual star (Y) and delta-connected (∆) secondary 
windings providing equally secondary line voltages 585 V, and line voltage phase angle of delta-
connected secondary winding lags that of star-connected secondary winding by 30o. 
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The train consists of 3 motorized cars and one trailer car. On each motorized car, there are 
four induction motors in parallel fed by a voltage source inverter. traction electric motor 
parameters use for simulation purposes: 200 kW, 585 V (phase to phase), 3 phases, 4 poles and 
81.3 Hz, 2400 rpm rated speed [2]. 
Figure 1. Typical section of traction power supply system 
2. Simulation model of traction power supply system 
The simulation model of traction power supply section of Hanoi pilot light metro line Nhon 
– Hanoi railway station is performed on Matlab/Simulink simulation platform in figure 2. This 
simulation model corresponds to schematic diagram (figure 1) and includes two power sources of 
external network (PS-1 and PS-2), two traction substations (TRSS1 and TRSS2), track feeder 
(RL-f1, RL-f2), return current lines (RL-r1, RL-r2), section of traction network (Net-1 and Net-
2) and electric rolling stock consisting of three carriages (car 1-car 3), short circuit fault model 
and monitoring and measuring performance system. 
Sources PS-1 and PS-2 are external power supply modules, whose voltage levels are 22 kV 
AC. A three-phase AC 50 Hz source plus some small impedances is included in the equivalent 
external power system. 
At traction substations with 12-pulse rectifier conversion of three phase AC with voltage 
of 22 kV AC is carried out, resulting from the primary power supply system of the electric city in 
DC with nominal voltage on bus bar of traction substation 825 V. Traction substation consists of 
traction transformers and rectifier units. To calculate the parameters of traction transformer, the 
formulas were used given in [5]. In the each traction substations 12-pulse rectifier is modelled as 
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the substation rectifier in actual system and supplies power at 750 V DC through the third rail to 
the train. The diode in the rectifier is modelled with 0.01 Ω as the on-state resistance and 106 Ω 
as the off-state resistance. 
Figure 2. The simulation model of traction power supply system 
Traction network of power supply system comprising of contact rail and track circuits is a 
line with distributed parameters. The total length of traction network is assumed to be 1957 m. 
Traction network section is implemented to simulate the equivalent resistance and inductance of 
the third contact rail and the running rails [3, 9, 10, 11 and 12]. The circuit model of traction 
network section is shown in figure 3. 
Figure 3. Circuit model of traction network 
The model of train consists of 3 carriages models (Car-1, Car-2 and Car-3), each of which 
has a traction drive with asynchronous motors. Model of the main scheme of power circuit of 
electric equipment of traction drive of each carriage includes a LC-filter, a voltage source inverter 
with the pulse width modulation (PWM) generator. Traction inverter with PWM converts DC 
voltage are taken from the contact rail into three-phase voltage with variable voltage and variable 
frequency (VVVF) to supply four parallel asynchronous traction motors. Switching frequency of 
PWM inverter in traction mode of rolling stock is 2400 Hz. 
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Figure 4. The simulation model of AC motor drive system 
A circuit branch consists of an ideal switch block and a small impedance block stands for 
the short circuit fault. The fault impedance used in the simulation model is purely resistive. The 
block “step” is to count the time and gives the trigger signal to the switch to let the fault “happen”. 
Figure 5. Short circuit fault model 
3. Simulation results analysis 
The traction power supply system of Hanoi pilot light metro line Nhon – Hanoi railway 
station has been modeled and simulated on Matlab/Simulink. Simulation results are obtained for 
the starting-up process and short circuit conditions, which include traction current profiles 
observed from the traction substation. The 23tb ode with variable simulation steps is chosen as 
the simulation method. 
When the train is being started from 0 to 50 km/h, feeder line currents at each substation 
are given in figure 6. The maximum starting current of feeder line of traction substation TRSS1 
can reach about 1650 A. Both the starting-up currents depend on the train location when the 
starting–up occurs. As shown in figure 6, both the current rising rate and current increment 
decrease when the distance from traction substation is increased. 
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Nearby substation TRSS 1
Remote substation TRSS 1
Figure 6. Train starting of different feeder lines on traction power supply section 
Remote short circuit current
Near short circuit current
Figure 7. Short circuit current profile of near and remote away from TRSS 1 with the train 
The most common type of faults in traction power supply system is the short circuit 
between contact rail and running rail [7, 8 and 9]. Short circuit fault of track feeder to rail consists 
of near and remote short circuit faults. The distances are 0.1 km and 1,857 km respectively under 
the condition that the distance between two traction substations is 1,957 km. In both cases, the 
fault resistance is 100 m [10]. Traction current profiles of external faults occurring near and 
remote the traction substation are given in figure 7 and 8. Figure 7 presents the short circuit current 
profiles with the train running at 50 km/h. When the short circuit fault occurs at location of 0.1 
km along the track, the impulse current with large amplitude can be generated rapidly. The 
maximum short circuit current can reach about 7.06 kA. With the increasing of the distance from 
the fault location to the traction substation, the value of the short circuit current will be reduced 
to 1520 A, so as to the current rise rate. Figure 8 illustrates that when the short circuit fault occurs 
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at location of 0.1 km along the track without train, the maximum short circuit current can reach 
about 6.3 kA while the remote short circuit current is 1300 A. 
a)
b)
Figure 8. Short circuit current profile of near and remote away from TRSS 1 without the train 
Comparing the simulation results of train starting current in figure 6 with short-circuit 
current in figure 7 and 8, it is found out that depending on the train location, the increment and 
rising rate of the short circuit current can be smaller than those of the starting current of the train 
owing to the high series impedance of the traction supply. 
III. CONCLUSIONS 
To study the short circuit faults in traction power supply system of Hanoi pilot light metro 
line Nhon – Hanoi railway station, a comprehensive model of traction power supply system and 
the short circuit fault model of the system have been presented in this paper. Simulation studies 
were conducted with respect to variations of the starting-up process and short circuit conditions. 
The short circuit current depends on the fault location. Close-up faults result in short circuit 
current with high magnitudes and high rising rate of current. Thus these defects can be quickly 
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and properly detected. Remote short circuit fault currents are no more than train starting currents. 
It is pointed out that the phenomena of mis-operation and mal-operation cannot avoid with 
traditional protection without protection of the whole feeder line. Therefore, it is important to 
choose the main protection elements that could discriminate the short circuit current from the train 
starting currents. 
According to the simulation results of short circuit current, short circuit fault may cause 
accidents, and threaten the safe operation of electrical equipment as well as the personal security 
of operating personnel. Therefore, choosing protection scheme and the principle of setting 
protection relay for the traction system supply in the technical design of Hanoi pilot light metro 
line Nhon – Hanoi railway station is very important. 
Acknowledgment 
This work is funded by University of Transport and Communications (UTC) under the 
project code T2020-DT-002. 
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