FIELD OF THE INVENTION
The present invention relates to an improved DC Traction system of Air
Conditioned metro Trains.
BACKGROUND OF THE INVENTION
Known Metro system is an EMU system with broad gauge rail of 1676 mm.
System receives power at an average line voltage of 675VDC. The allowable
variation in the line voltage is 500V to 900 VDC.
The current is collected from the top face of a third rail by a pair of Third Rail
Current Collector (TRCC) provided on each side of the train bogie.
The known metro trains having an average weight of 400 tons, with acceleration
of 0.45 m/s2, and a declaration of less than 1 m/s2. Further, the known metro
train does not have Train Information Management System (TIMS). Further,
there is no inverter for auxiliary controls.
OBJECT OF THE INVENTION
It is therefore an object of the present invention, to propose an improved DC
Traction system of Air Conditioned metro Trains.

SUMMARY OF THE INVENTION
The system comprises a high speed circuit breaker (HSCB) for protection against
fault in Power and Auxiliary circuit. Four numbers nose suspended, self-
ventilated Traction motors of 167 KW each are mounted on two bogies of each
of six motor coaches. Two stages of field weakening have been provided. An
inductive shunt in the field system so as to have fast commutation of the Motors
in weak field and during Transition/Interruptions.
The control equipment mainly consists of a Master cum brake controller, a Cam
Shaft Controller (CSC), a Traction Current Control Unit (TCCU), a first housing
having all power devices, a second housing accommodating all control relays,
and Starting Braking resistor (SBRs). The Master controller is mounted on
Driver's desk, and the TCCU is mounted on end wall of motor coaches. All other
main equipment are mounted under frame.
Power and control scheme has been devised such that the DC traction system
works in synergy to achieve the required system performance of air-conditioned
Metro Trains. During the motoring, the current is collected through TRCC,
which is transmitted to HSCB, one coil of the CBR (Current balance relay), and
the Line contactor LB1. Negative terminal of Power circuit is connected to earth
return brushes via another line contactor LB2 and other coil of the CBR. There
are three motoring positions and five braking positions in the Master Controller:

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows Block Diagrams of DC Traction system of Metro Air conditioned
train according to the invention.
Figure 2 : Power Schematic of the DC Traction system of figure 1.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1(a) shows the motoring position at start (shunt) when the power circuit
is at 2P-2S combination.
Shunt:
Train starts at 2P-2S combination of power circuit, when two motors are coupled
together in parallel and two such pairs share common resistances Rl to R13.
Cam Shaft Controller contacts RC1 to RC3 then cut the resistances Rl to R3 to
reach to the shunt position. This allows the train to run at a speed approximately
10 km ph.
Series:
In this position, the power circuit is same as described in ease of shunt position.
Cam Shaft Controller contacts RC4 to RC12 and Gl cut the resistances R4 to R13
thereby proceeding train to 14th notch.

Parallel/WF:
In this, motor combination is rearranged by the power circuit as shown in figure
1(b), to make it 4P combination. Each pair of DC series motors use one set of
resistances between points P4 and P405, P30 and P3005. RP11 to RP15 and
RP21 to RP25 resistance are then cut sequentially by means of CSC contacts
RC13 to RC20 and PB1, PB2. After attaining full voltage notch, Motors are taken
to two stage weak fields sequentially by means of WF11-12, WF 21-22, WF31-
32, WF41-42 contacts of the Cam Shaft Controller.
Braking :
Power circuit is rearranged as shown if figure 1(C) to make two loops of
regeneration circuit with Armature of Motor 1 & 2 in series with fields of Motor 3
& 4 and vice-versa with common set of Resistance RP21 to RP25 and Rl to R13.
Again CSC contacts are used to cut resistances sequentially and reach to the final
braking notch i.e. 19th. 5 KW DC-DC converter is used to feed excitation current
to one pair of motor fields which starts the motor in generator mode and feeds
the excitation current to other pair of motor fields. This ensures simultaneous
generation by both the pairs and equal load sharing.
Control circuit:
Control circuit is designed to ensure operation of power circuit as desired and
with interlocking of all safety requirements.

The output signal generated from the master controller depending upon its
position is fed to the Reverser coil to ensure forward or backward movement of
train. This along with other interlocks ensures energisation of off proving relay
only when all contactors and CSC are in initial condition. This then ensures pick
up of LB1 and LB2 to start traction.
ADVANTAGES OF THE INVENTION
Advantages of the invention over the prior art, is depicted in a comparison table,
shown as under:

WE CLAIM :
1. An improved DC Traction system of Air Conditioned metro Trains, the
improvement is characterized by comprising :
a high speed circuit breaker (HSCB) providing protection against
developing fault in power and auxiliary circuit;
at least four nose suspended, self-ventilated traction motors, each motor
being mounted to cover two bogies of each of six motor coaches;
an inductive shunt provided to effect fast communication between the
motors both in weak field position and transition/interruption; and
a master controller mounted on driver's desk with a traction current
control units (TCCUS) attached on end wall of said motor coaches;
wherein the system is enabled to receive current through a third rail by a
pair of third rail current collector (TRCC) and transmit the current through
the high speed circuit breaker (HSCB), one coil of CBR (Current Balance
Relay) and line contactor (LB1) wherein the negative terminal of the
power circuit is connected to earth return brushes including a second coil
of the CBR, and wherein the master controller generates an output signal
for feeding to a reverser coil to ensure forward and backward movement
of the train.

2. The system as claimed in claim 1, further comprising a cam shaft
Controller, traction current control unit, a first housing the power devices,
a second housing accommodating the control relays, and starting braking
resistor.

ABSTRACT

The invention relates to an improved DC Traction system of Air Conditioned
metro Trains, the improvement is characterized by comprising: a high speed
circuit breaker (HSCB) providing protection against developing fault in power and
auxiliary circuit; at least four nose suspended, self-ventilated traction motors,
each motor being mounted to cover two bogies of each of six motor coaches; an
inductive shunt provided to effect fast commutation between the motors both in
weak field position and transition/interruption; and a master controller mounted
on driver's desk with a traction current control units (TCCUS) attached on end
wall of said motor coaches; wherein the system is enabled to receive current
through a third rail by a pair of third rail current collector (TRCC) and transmit
the current through the high speed circuit breaker (HSCB), first coil of the (CBR)
current balance relay and coil of the line contactor (LB1) wherein the negative
terminal of the power circuit is connected to earth return brushes including a
second coil of the current balance relay, and wherein the master controller
generates an output signal for feeding to a reverser coil to ensure forward and
backward movement of the train.