Figure A3: Cross Section of 25 kV Overhead Catenary System (OCS) of KTMB Double Track Rail.
this system are the 132/25kV feeder transformer
stations (FS), overhead catenary system (OCS) and
booster transformers (BT). As shown in Figure A3,
the OCS comprises the catenary wire, contact wire
and the return conductor. The current demanded
by the train propulsion system flow through
the catenary/contact wire, through the traction
motors, and down to the rail. Booster transformers
are intended to “suck up” the current from the
running rail up to the return conductor. There is
also current return to the earth via earth wire.
However, this current is small and insignificant.
(II) PRASARANA/RapidRail DC Power Supply
Traction
Today, on a global scale, over half of all electric
railways adopt direct current (DC) traction. In mass
transit systems, maximum nominal voltages of
up to 1500V are used because of the potential
danger of higher voltages. The most common
voltages are 750 V and 600 V. The distance
between substations varies from 1.5 to 6 km.
The power rating of direct current transformer
rectifier substations varies from 1 to 2 MW for
tramways/light rail transits and up to 10 MW in
mass transport and main line systems.
The PRASARANA/RapidRail traction vehicles
are supplied with DC 750 V by a third rail (power
rail) using the running rails as the return circuit, as
is typical of worldwide rail transit industry practice.
The Ampang Line LRT system is of this design.
However, the exception is for the Kelana
Jaya Line LRT which utilizes the fourth rail as
the return circuit and hence there is no return
current on the running rails which are bonded to
all other earthing installation systems. Also, the
Kelana Jaya Line LRT traction vehicles utilize the
Bombardier-proprietary Linear Induction Motor
(LIM) propulsion system which does not require
gearbox systems for the rolling axle wheel sets.
Figure A4 shows a typical LRT/MRT 750 V DC
power supply/third power rail distribution system
and feeding arrangement.
In the design and operation of DC traction
railways, special attention has to be paid to the
problems of traction current return on the running
rails to minimize the hazard of stray current
corrosion. This is of concern to the Ampang Line
LRT which operates the third rail scheme.
Figure A5 and Figure A6 show the cross section
of the Kelana Jaya Line LRT 750V DC Power Rail
and Power Collector Assembly.
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