Reaction of 25 KV AC Railway Traction System
(Light Rail Transit LRT ) to Lightning Current
Transients
Mohamed R.Hussien
Electrical Power Engineering
Faculty of Engineering Cairo Universty
GIZA 12613,EGYPT
m.refaat191107@gmail.com
Abstract—the implementation of LRT project was a unique
step in the new era of electric traction that Egypt is witnessing
and for sure modeling the whole system and study the effect of
various factors on it, is very important. As one of these factors
is the Lightning current surge which LRT is susceptible to, as
it consists of masts and catenary in exposed areas, which surges
may cause damage to the system. However, there are many
methods to avoid Lightning current surge as Surge arresters
(SA) or earth wire or lightning rods. , we will focus on using SA
and observe the response of various parts as Mast, catenary
and locomotive using PSCAD/EMTDC in presence of SA and
without. We found logically that while using SA the induced
voltage and current from Lightning surge on various parts of
the system is less than without SA. So the main conclusion SA
is very important for the system to keep it reliable, sustainable
and assure the continuity of the service for the passengers.
Our aim will be shorten to apply similar model using
PSCAD/EMTDC with different parameters to prove the importance
of SA on ac railway traction systems especially that there is
significant expansion in the establishment of ac railway projects in
Egypt
II. POWER SYSTEM MODELING
The proposed study was applied to LRT which typically
consist of Train, rail, overhead catenary system (OCS),
earthing rods and SA . [4],[5],[6] and [7]. As shown in fig.1
Keywords—Traction system, Lightning, Surge arrester,
PSCAD/EMTDC, back flashover, catenary and overvoltage.
I. INTRODUCTION
Railway transport performs an important role within the
Egypt financial system. Many commuters rely upon the
trains to travel every day. Even though it isn't always
common, occasional direct lightning strikes on railway
overhead power deliver machines pose the risk of disabling
the operation of railways leading to critical maintenance of
damaged equipment, which inevitably results in the loss of
monetary activity and delivery reliability. Thus, suitable
lightning safety systems are required to ensure the continuity
of service and operation of the railway networks.
In previous projects in Egypt as metro Line 1 and 2 using
of SA was much less than these days as LRT, as Line 1 and 2
were in middle of great Cairo [1] surrounding with high
buildings but for LRT it was implemented in east of Cairo in
the desert with no surrounding buildings which make it more
likely to lightning strikes and referring to annual average
thunder days [2] Egypt recording 5 -9 strokes per km2 per
year especially in desert places.
In light of the above it was essential to use a surge
protection device to protect the whole system also the
passengers and according to IEC [3] there is two methods to
reduce the damage of lightning strokes as earth wire or rods
or surge arrestors we will use surge arrestors beside the earth
wire which is hanged over the catenary to make sure we
avoided the critical damage from switching impulse or
lightning impulse which the typical wave form Is 8/20 μs and
peak current 15-20 KA
It was rational that using SA will decrease the surge impact on
various parts as mast, catenary and locomotive as mentioned in [3]
which is applied on similar project in south Africa.
XXX-X-XXXX-XXXX-X/XX/$XX.00 ©20XX IEEE
Fig. 1. Components of Electric railway LRT
A. Modeling of MAST.
Referring to [8] the mast can be represented as lossy line
mast consists of r-l parallel combination, cylinder surge
impedance, and footing resistance using the below equations
where h and r referring to the height and the radius of
cylinder and the simplified fig.2
Where Ro is the resistance at low current; IR is the
lightning current flowing through the footing resistor;Ig is
the current required to produce the gradient voltage; eo is the
breakdown voltage of soil; fig is the permittivity of soil.
m, and t is time. So that we can build a back flash over
control module on PSCAD as shown in fig. 4
(4)
Fig.4 back flash over control module
D. Modeling of catenary,rail, and earthing rod.
We can simply model the these components as R and
neglect the L as it would be very small values, these values
have been obtained from actual measurement
Rail
0.03 ohm per km
Messenger wire
0.242 ohm per km
Contact wire
0.148 ohm per km
Earthing of rail
1 ohm
Return wire
0.242
Fig.2 lossy line mast model
E. Modeling of locomotive .
We can represent the locomotive of power 8 MW as a
pure resistance which draws a 128 A Using equation
no.(5) so with the same manners the locomotive
equivalent resistance will be 0.0048 ohm
B. Modeling of insulator.
The insulator is modeled as a capacitance of 12pf with a
PSCAD Single phase breaker . the capacity was adopted
from [9] ,the breaker was designed to use back flash over
control method such that when voltage across the insulator
exceeds the rated voltage the breaker will close indicate that
there is flash over . Which clearly shown in figure 4
(5)
F. Modeling of Power source
Power supply can be modeled on PSCAD as a sinusoidal
power supply with rated voltage 27.5 KV as shown in
fig.5
Fig.3 PSCAD model of insulator
Fig.5 power supply source
C. Modeling of back flash over contorl module .
Referring to [10] and equation no. (4) Where Vf is flash
over voltage, Ag arc horn length will be selected as 0.07
G. Modeling of Lightning current source.
Referring to [10] we can represent a typical lightning surge
as addition of two reversed impulse with different
parameters of 8/20 μS and peak of 15 KA as shown in fig.6
III. SIMULTION STUDY
We will add all these components as shown in fig.8
bellow and we will inject the Lightning current at the MAST,
OCS, and LOCOMOTIVE.
Fig.8 Full model on PSCAD.
Fig.6 Modeling of surge .
H. Modeling of SA
SA is a protection device that’s in normal operation
voltage it works as an open circuit and at certain voltage
have impulse shape acts as low resistance conducts the
surge to the ground using its characterizes equation no.
(6) where I is current is thermal constant , V is the
operating voltage and alpha is non linearity exponent
(6)
Two models are normally used The IEEE [11] or The
pinceti-giannetoni model [12] we will work with the last
model as it more simplified and can be reprenseted in fig
.7 and equation no.7 bellow.
(7)
Where Vn is the arrester rated voltage,Vr/t is the resdiual
voltage for lightning current of 1/T2 μS and Vr8/20 is the
residual voltage for lightning current of 8/20 μS
Fig.7
A. At the MAST
When lightning strikes directly on top of a railway mast,
the lightning current splits into two paths: one that travels
down the mast and the other that travels along the phase
conductor where it encounters the insulator, and this can
cause back flashover in the conductor's direction. In this
simulation, the mast and insulator are the components that
were observed. The transient voltage and current of the mast
and insulator are shown in Fig. 8. The high voltage across the
mast components suggests that the insulation has failed, and
the voltage across that insulator demonstrates that the
breaker was open when the voltage reached the breakdown
point. Fig. The voltage across the insulator with surge
arresters present is shown in Figure 9 along with the current
and voltage of the mast after protection was applied. The
surge arrestor and mast were connected in parallel for this
current injection. The parts of interest were the mast
components and the insulator, which were similar to those in
the simulation on top of the mast without any protection.
B. At the OCS
Current can flow over the catenary wire when lightning
strikes on top of the overhead wires and this can result in
flashover voltages across the insulator separating the mast
from the rest of the wires. The catenary wires' transient
voltage and current, as well as the insulators, were observed
through simulations. Fig. The voltage across the insulator
and the catenary transients are shown in figure 10. The
transient response of these components in conjunction with
the surge arresters is shown in Fig. 11.
C. At the LOCOMOTIVE
The locomotive and pantograph are both susceptible to
the direct lightning strike that strikes the top of the
pantograph. In order to avoid damaging the locomotive, the
locomotive drives, and the wagons, simulations were
performed for both the pantograph and the locomotive. The
pantograph is where the majority of the current will be drawn
to flow. Figure illustrates the transient current and voltage
caused by the lightning strike on the pantograph and the
locomotive. 12 and 13. Fig. shows the transient response of
these components in conjunction with the surge arresters. 14
and 15.
IV. RESULTS AND DISCUSSIONS.
Here it the list of figurers after the simulation have been
done in presence of SA
It’s obviously that using SA have been reduced the
induced current and voltage and keep the equipment safe,
reliable and sustainable.
V. CONCLOUSINS .
Fig.8 Transient response of the mast and insulator.
For a traction power supply, a lightning protection system's
design, simulation, and analysis have been presented. The railway
is a direct feed 25 kV AC system. A mast, an insulator with
backlash overvoltage control, overhead catenary wires, a
pantograph, an AC locomotive, and the railway lines make up the
system. Using an ABB datasheet and a 30 kV operating voltage,
the surge arrester varistors were created. The outcomes of
the model's simulation in the presence and absence of surge.
Surge arresters may be used to limit over voltages that are caused
by strong lightning currents, according to arresters. System
efficiency was determined to be within a margin of error by a
worst-case analysis.
ACKNOWLEDGMENT
Fig.9 Transient response of the mast and insulator in presence of SA
We acknowledge the facilities rendered by Cairo
University and national authority for tunnels for making this
work a success
REFERENCES
W.Essam. ‶ Implemented projects ″national authortiy for tunnels
,Acesseddate(12/6/2022), http://www.nat.gov.eg/Location.aspx?id=27
[2] ‶annual average thunder days ″,Acessed date (12/6/2022), https://lionlightningprotection.com/r-1-annual-average-thunder-days.html
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[1]
Fig.10 Transient response of the catenary and the insulator
Fig.11 Transient response of the catenary and insulator in presence of
SA
Fig 12,13 . Transient response of the LOCOMOTIVE .
Fig. 14,15 Transient response of the LOCOMOTIVE in presences of SA.