Instrumentation & Measurement Magazine 24-4 - 98

Fig. 1b, there are four working earthings and the traction control
unit (TCU) speed sensors on the above TBs. Also, there is
one protective earthing between the 08 TB and 09 TB.
Interference of the PCA on TCU Speed Sensors
The PCA is generated at the moment the pantograph is separated
from the power supply line, which produces EMR and
overvoltage on the TBs. Only one end of the TCU speed sensor
cable is connected to the TB, as shown in Fig. 2a. The overvoltage
generated by the PCA creates a parasitic capacitance
between the cable shield and the core wire of the sensor, as
shown in Fig. 2b.
According to Fig. 2b, the inductive voltage generated by
the overvoltage on the sensor core wire can be calculated by:
UU
jwC Z Z
s 
where Us
1( )
s
jwCZ
1
1 ,
s
is the interference voltage, which can impact the signal
of the TCU speed sensor [12]. Z1
and Zs
of sensor cable shield and core wire, respectively, U1
are the impedance
is the overvoltage
between the sensor cable shield and the steel rail, and C
is the parasitic capacitance generated by the overvoltage.
In addition, the EMR from the PCA can also affect the TCU
speed sensors because the outer conductor of the sensor cable
shield is made of metal wire with many tiny holes and is
not completely shielded. The inductive electric field (E) will
be generated on the surface of the cable because of the EMR.
As described in Fig. 3, a part of the inductive electric field (E')
will be coupled on the core wire through the tiny holes. Due
to E > E', the potential difference (U) between the cable shield
and core wire will be caused.
The value of U can be obtained by:
U IZ L
 
where I is the inductive current, Zt
tm ,
(2)
is the transfer impedance
per meter cable, and Lm is the effective length of the cable [16].
Based on the above analysis, there will be the inductive
voltage on the core wire and the potential difference between
the cable shield and core wire because of the overvoltage and
the EMR, respectively. They are two different interference
(1)
Composite Model of the High-speed
Train
Structure of the High-speed Train Model
The pantograph will be connected to the power supply line (25
KV/50 Hz) when the high-speed train is running. The current
is transmitted to four traction transformers located in 02 TB,
07 TB, 10 TB, and 15 TB. In addition, four TCU speed sensors
are installed separately at the end of the wheel shaft of those
TBs. As long as one of the TCU speed sensors detects that the
train speed exceeds 5 km/h, all the train doors will be closed
automatically [17].
As shown in Fig. 4, the current flows into the earth by working
earthings on the primary side of the transformer. The high
voltage cable, sixteen TBs, and steel rail are also included in the
composite model. There is a switch to simulate the separation
of the pantograph from the power supply line by opening it.
The relevant parameters in the model refer to the equivalent
parameters of the Beijing-Tianjin high-speed railway in
China, as listed in Table 1 [18].
In addition, an arc model will be added to the model to
simulate the PCA generated at the moment the pantograph is
separated from the power supply line, as described in Fig. 5.
The relevant parameters are shown in Table 2 and the numbers
(No.) correspond in turn to those in Fig. 5.
Establishment of the PCA Model
The current common arc models are Mayr Model, Cassie
Model, and Habedank Model [19]. Among them, the Habedank
Model combines the other two models, which makes up
for their shortcomings. The mathematical model of Habedank
Model is:
 

 
dt
 

dgC
 
 
 
gM
dgM
dt


Fig. 2. Connection diagram of TCU speed sensor (a) before and (b) after the
pantograph separation.
98


IEEE Instrumentation & Measurement Magazine
 u g
i
1

M
2
P
11 1
 
gg g
CM
 gC
C CC
,
(3)
1
i
2
Fig. 3. The diagram of speed sensor cable.
modes from the PCA on the TCU speed sensor at the moment
of the pantograph separation.
June 2021

Instrumentation & Measurement Magazine 24-4

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