Lecture 10
AUXILIARY CIRCUITS
Motor Generator
The H.T. supply is taken from the main isolating switch , through HRC
Fuse (50A)M.G. contactor, overload relay and motor generator protective
resistor. The fuse protects the circuit under short circuit conditions and the
overload relay protects the motor against overload and fault conditions by
de-energizing the contactor coil and opening the same.
Though a connection at MG3,the motor can be earthed by operating the
main isolating switch the purpose being to protect anyone entering the high
tension auxiliary compartment before the MG set has stopped and while the
motor is still generating a high voltage. Permanently connected in the circuit
is a 9.7 ohm protective resistance which limits the current in the event of a
fault on the MG set . The motor current passes through the series winding of
the generator, and ensure that the generator EMF builds up in the correct
polarity.
Starting circuitIt is assumed that the O/L relay has not operated. The battery supply from
wire 16 is taken through MG and COMPRESSOR miniature circuit breaker,
drivers control rotary switch and MG set push button thus, energizing train
line wire No. 14 as shown in M.G. Control Circuit. This energized M.G. set
and Trip Relay set coil and closes its interlock. The current from wire 14
also passes through the MG miniature circuit breaker, blocking rectifier,
M.G. set and trip relay interlock M.G. over voltage and M.G. overload
interlock, which are closed and M.G. contactor interlock (normally close) to
energies the time delay relay (TDR) coil and close the time delay relay. The
overload hold coil is energized and prevents the overload relay from being
operated by the starting current of the MG set. The contactor now closes and
breaks the supply to the time delay relay coil. This is retained closed for a
further 1.5 seconds by which time the starting current will have passed its
peak and the time delay relay will have dropped out de-energizing the
overload hold coil and interrupting the direct feed to the MG cont. coil . The
MG contactor coil is still supplied through an economy resistance retained
closed by its own interlock.
Retaining circuit
Retaining circuit is provided to keep the MG set running in order to
maintain continuous supply to lights and fans. This also helps in retaining
the supply to lights and fans when driver changes over from one end to the
another.
Supply is taken from wire 16 through the MG retain miniature circuit
breaker, low tension relay (LTR) interlock which is closed when the MG is
running, blocking rectifier, MG set and trip relay interlock MG over voltage
relay interlock and MG overload relay interlock to the MG contactor coil.
Overload condition
In the event of an overload caused by a flash over of the motor or
excessive load current the overload relay will operate and the interlock of
the MG overload relay will interrupt the supply to the MG contactor coil and
open the MG contactor. Failure of a MG set opens the LT relay and wire 17
is energized by LT relay contact from wire 19 which is supplied from the
drivers control switch through the GUARD’s –2 miniature circuit breaker.
This lights up the Gen. supply failure lamp in the driver’s cab.
The overload is reset by pressing the MG and comp. O/L reset push button
with driver’s control rotary switch in ON position. This energizes train wire
15 and the overload reset coil. The MG set is now restarted by pressing MG
set push button and retained as before.
To shut down the MG set, energies trip coil of MG set and trip relay by
pressing MG trip push button. Also fed from the negative side of the MG
retaining miniature circuit breaker is the traction motor overload indicating
circuit which consists of an interlock of the traction motor overload relay in
series with a lamp.
Over voltage condition
The over voltage relay (set and trip type) has been provided to protect the
equipment and the regulator from damage due to over voltage, in the event
of the regulator failing to control the output of MG set. The relay does not
permit the voltage to exceed 125 volts when the voltage rises to 125V the
relay operates and its interlock provided in the feed wire to MG contactor
operating coil opens. This opens the MG contactor and stops the MG. The
relay can be reset by pressing MG and COMP. O/L reset push button.
CircuitsFollowing are fed directly from the generator at 110V DC supply
(i) HT compartment blower motor
(ii) Main lights
(iii) Ventilation fans
(iv) Control circuits
(v) Battery
Control circuits and battery are fed through a blocking rectifier across which
a surge suppressing condenser is connected.
When MG set is not running the battery may be required to supply the
following:
i) Control circuits
ii) Auxiliary compressor circuits
iii) Emergency lights
A double pole isolator switch is provided in the battery circuit which
permits external charging of the battery from a charging socket. The battery
is protected by fuses and the charging current is limited by a resistor
provided in the battery circuit, which is also known as buffer resistance.
AUXILIARY COMPRESSOR
L.T. supply is taken from the battery to operate this compressor. It is
assumed that enough compressed air is not available to raise the pantograph
and the auxiliary compressor governor is closed . By bringing the toggle
switch mounted on the auxiliary compartment panel to the ‘COMPRESSOR
START’ position. The contactor coil is energized and the contactor closes,
thus starting the auxiliary compressor. Immediately after the contactor
closes, an economy resistor is connected in series with the contactor coil.
When the required pressure pre-determined by the governor setting is built
up in the air line the compressor governor cuts off the supply to the
contactor coil thus opening the contactor and stopping the compressor
motor. The auxiliary compressor can also be stopped by switch up the toggle
switch to compressor stop position. In case of emergency the auxiliary
compressor governor can be by passed by closing sealing switch.
MAIN COMPRESSOR
The HT supply is taken from the main isolating switch through HRC
fuse, a contactor, and an overload relay to the compressor motor and a
protective resistor which is permanently connected. The circuit is not earthed
because the motor comes to rest very quickly, after the supply has been cut
off.
A HT connection is also taken between fuse and comp. contactor for
High Tension Relay (HTR) which is fed through a fixed resistor and an
economy resistor.
These resistance provide a large closing current which is reduced after the
relay has been closed, thus permitting the relay to operate at voltage down to
800V from the overhead supply.
Control circuit
Feed wire 16 is connected to synchronizing wire 13 through compressor
governor miniature circuit breaker, blocking rectifier and compressor
governor. Across the compressor governor a sealed switch is connected
which enables the driver to control the compressor manually in the event of
the governor failing on low air pressure.
The supply to contactor circuit is then taken through the compressor
contactor miniature circuit breaker, HT relay (HTR) interlock, compressor
overload relay interlock and compressor set and trip relay interlock.
Assuming that these relays are closed, the time delay relay closes and
energizes overload relay hold coil and closes the compressor contactor. The
time delay relay is now de-energizes by compressor contactor closing. After
a delay of 1-2 seconds the time delay relay opens, de-energizes the overload
hold coil and the compressor contactor is retained closed by its own
interlocks and economy resistor. Set and trip coils of compressor set and trip
relay are connected to wire 12 and 49 respectively, which can be energized
by pressing comp. set or comp. trip push button as desired, assuming that the
supply is available from wire 16 through MG and COMP. Miniature circuit
breaker and driver’s control rotary switch .
Once the relay is set by pressing ‘Comp. Set’ push button it allows
continuous supply to the compressor circuit until it is interrupted by pressing
‘Comp. Trip’ push button. This has the advantage of switching the
compressor ON and OFF along with allowing the compressor to run when
the driver charger ends.
Loss of HT voltage
In this event the HT relay is de-energized, and opens the compressor
contactor, when the supply is restored, the compressor is started up , in the
sequence given above.
Should a fault develop from a flashover of excessive overloading, the
compressor overload relay will operate and open the circuit to the
compressor contactor coil. This opens the compressor contactor and isolates
the compressor from the supply.
The overload is reset by pressing the MG and COMP. O/L reset push
button with the driver’s control rotary switch in ON position. This energizes
train wire 15 and overload reset coil.
COMPRESSOR CONTROL CIRCUIT
In EMU Train compressor is required to build air pressure which is use
in brake system, raising pantograph, RPC contactors, hooter, wipers. A
compressor is fitted in each motor coach. The compressor work on 1500V
obtained from OHE through MIL (Link) In HT circuit fuse is provided for
protection and any over loading due to earth path or any shorting in working
is protected by resistance.
The wire no. 16 main control positive supply is given to the push button of
compressor , but compressor trip and MG and compressor overload reset
through MG and compressor MCB and DCS.
When the compressor trip push button is pressed wire no.49 is
energized, which energies the trip coil of compressor set and trip relay
(STR). So the N/O of O/L STR in compressor contactor coil circuit open
and the compressors stops working.
When the compressor set push button is pressed wire no 12 is energized
which energize the set coil of STR and the N/O inter of STR is closed in
compressor or contactor coil circuit,
The supply of 1500 V DC is fed to high tension relay (HTR). Coil HTR is
energized when OHE voltage is above 800 V when OHE voltage is less than
800V. The HTR Relay is deenerzise and its interlock N/O open and
compressor contactor coil circuit and trip the compressor. The N/O interlock
of HTR closes and supply from wire no. 16 given to TDR coil through
compressor MCB, Close interlock of HTR. STR and N/C interlock of
compressor overload relay and compressor contactor. The negative is given
to TDR (Oil through compressor governor MCB and N/C interlock of
compressor
Or its seal switch. This energize the TDR coil, after energies TDR coil, but
one N/O inter closed in compressor overload relay compressor at initial
stage current also compressor contactor coil is energized hold coil, and
another in compressor contactor circuit, thus the compressor hold coil
energized so that compressor overload hold coil, does not trip and its
compressor contactor is HT circuit closed.
In HT circuit when compressor contactor closed 1500V DC supply
from MIL to given to armature of compressor motor through compressor
fuse, compressor contactor, compressor overload relay coil, series field and
negative is completed through the positive resistance and the compressor
start working.
When the pressure is at 7.0Kg/Cm2 the interlock of compressor
governor opens and the negative path is out. Hence the compressor
contactor coil deenergized and the compressor contactor in HT circuit is
open and compressor stop the working. Compressor again starts when the
pressure is reduced to 5.8 Kg/Cm2 and compressor governor interlock is
closed. If the interlock of governor are not proper, the compressor governor
can be bypassed by seal switch.
Before compressor governor the negative path of contactors is also
connected to wire no.13.This causes synchronization of all the compressor in
the train. If any one or two compressor governor open its interlock, then all
to the compressor contactor coil circuits will be completing negative path,
through wire no.13 and closed compressor interlock, so its compressor
governor MCB and the compressor will be until all the compressor governor
interlock opens.
Also if any one compressor governor closes its interlock first all the
compressor governor coil circuit will be completing negative path through
wire no.13, thus all the compressor starts at a time, when any one of the
compressor governor interlock and all the compressor stop only when the
compressor governor interlock opens.
If any of the seal switch is any motor coach or additional by pass switch
for compressor in driving cab is closed all the compressor will be working
continuously.
Also if any of the MCB of the compressor governor is tripped and so the
pressure is not building quickly , then additional by pass switch in driving
cab is switch on to by pass all the compressor governors and compressors
governors MCBs.