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GN Electric Operations continued
Transition relay TR, located in relay cabinet, is a
voltage type relay operated by D. C. from the field
controller to close D. C. line switch L2 for high speed
motoring or regeneration in the separate field control operation.
Dirty contacts are its only troubles.
Blower relay, called N. V. relay, located in relay cabinet,
is an A. C. voltage operated relay. When there is power
on the transformer its contacts close, and these contacts
allow the blower motors to be started and run. If the
M-G set is running and power surges off momentarily, the
blower relay opens to shut off blowers. After M-G set is
re-started, the blowers will automatically start if blower
control switch is on run position and speed controller shut
off. Otherwise blower control switch will have to be shut
off and brought up to start and run position.
Note: One contact of the line relay controls blowers on
cabs 5004-5006, instead of N. V. relay.
Contact trouble is about only kind found.
Limit relay LR, in relay cabinet, is an A. C. current
transformer operated relay. The synchronous motor
current operates it. The limit relay closes at full load
amperes on synchronous motor 1450-1500. Its contacts, when
closed, close SM5, putting over excitation on synchronous
motor field to keep motor from pulling out of synchronism,
and causes a red overload lamp to be extinguished,
warning engineer of overload danger. These warnings
must not be ignored, or power kickout will follow. The
only troubles this relay give are too low setting. It winks
red light before 1500 synchronous amperes is reached. It
never operates where synchronous ampere full load is not
exceeded.
M-G overspeed relay OS, is located on main exciter end
of shaft. It is a centrifugal relay which trips when M-G
set R. P. M. reach 825. Normally it will not trip except
in regeneration when trolley power or contact is lost.
Otherwise, if it trips while locomotive is pulling or standing
still, its a frequency surge on system or a defective relay.
Bad order contacts sometimes occur.
Line relay LR, located at side of transformer in left
aisle operates by A. C. current transformer in ground lead
of main transformer primary. Its contacts close when
transformer is energized. One contact controls the
synchronous motor switches on all cabs. The other contact
controls blowers on 5004-5006 same as N. V. controls
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blowers on other Westinghouse cabs. Its function is to cut
off synchronous motor and mainly to open the exciter
switches El, E2 in case of trolley power failure.
Otherwise, the main exciter would try to motor from the
battery, as there is no reverse current relay to protect
battery on Westinghouse cabs. Also in case of a locomotive
standing with M-G set shut down but circuit breaker closed
and transformer energized, the blowers would be running
single phase okay until a line surge came along; then if
line relay was not there to cut blowers off, when power was
re-applied to the line, the blowers in trying to start single
phase would overheat and likely burn out. Troubles on line
relays are usual contact oxide and occasionally the air gap
gets out of adjustment to where relay fails to pick up.
Line relay may be blocked in to get over road, and
always remove any relay blocking at end of run, then report
defect.
Traction motor overloads 1, 2, 3, 4 located under motor
cut out switches are D. C. current relays, each one
protecting its own traction motor whose number it bears. In
tripping these overloads, open line switches L1, L2,
disconnecting generator from motor. Dirty contacts, broken
discs, or stuck open relays are only troubles.
AR time delay relay, located in middle of space between
compressor and No. 1 blower motor, is an electro pneumatic
switch with its main contacts removed, and utilizing only
the control interlocks as a relay, delay type. When
synchronous motor field switch SM1 closes, its interlock
energizes the three magnet valves of AR, which admits air
into a large delay cylinder, which in turn must fill before
AR contacts close in about five seconds. AR relay then
changes the synchronous motor over from the reduced
voltage tap to the full voltage tap of transformer at full
speed.
It may fail in three ways: (1) A broken air pipe may
cause AR to be inoperative, in which case M-G set will
be found running on switches ML. SL, SM1 and in a
short time the synchronous motor field resisters will get
red hot and synchronous field amperes will show 50
amperes D. C. (2) A bad connection on SM1 in, would act
same way. (3) AR may close, but its own contacts be bad
order, so that M-G will not change over properly, as AR
must close RL, SM3 and L to synchronize M-G set.
To locate which kind of trouble exists, proceed as
follows: When relay SR1 closes at 250 R. P. M., switches
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ML and SL should close and M-G set speed up to 600
R. P. M., when relay SR2 should close, followed by SM1
closing, (50 amperes synchronous motor field shows,), then
SM1 in interlock closes AR in five or six seconds. Relay
AR closes switches RL and SM3, switch SL opens, then L,
L1, E2 close. M-G should run normal with following
switches closed: ML, RL, L, SM1, SM3, E1, E2.
If AR air pipe is broken, put a match stick in SM1 in
interlock to stop air wasting, then after set is up to full
speed, short out both contacts on AR and set will change
over properly. Caution: Be sure to only short out or
connect together the same finger contacts that relay contact
block would connect if it operated properly. The
synchronous field amperes should indicate about 100-150
amperes D. C. with M-G running properly, and battery
amperes should never indicate discharge.
Ventilation relay VR, is located on main transformer air
duct in right aisle. It is merely a floating diaphragm with
contacts on it, that air stream from transformer blower
forces up so contacts make and cause blower signal light to
burn. If transformer blower motor stops, the diaphragm
falls and signal light is extinguished.
Note: Blower signal light only protects the transformer
and not the traction blowers.
Relay SR1, located in relay cabinet, is a D. C. voltage
relay operated by main exciter at 250 R. P. M. To
connect synchronous motor to transformer, relay SR1 closes
switch SL whose interlocks cut off D. C. starting switches
between battery and generator. Failures occur as follows:
(a) Relay SR1 fails to close at all, and M-G will not speed
up beyond 250 R. P. M. Remedy: Leave start controller
wide open, then close SR1 by hand and hold it closed
until relay SR2 closes and M-G hits full speed. Then let
SR1 drop out. (b) SR1 closes normally, but drops out as
soon as SR2 closes and M-G drops switch SL with a loud
report. Remedy: Start M-G normally, and as M-G set
reaches change over from battery generator to transformer
synchronous motor, and SR1 closes, hold SR1 closed, so
it cannot drop out until after SR2 closes and M-G settles
down at full speed, then let SR1 go — it's no longer needed.
Most of relay troubles experienced with SR1 and SR2 are
caused by relay resister tubes breaking or shorting.
Relay SR2, in relay cabinet, is same kind of relay as
SR1, only it's set to close at 600 R. P. M. when its contacts
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close switch SM1, putting 50 amperes D. C. field on
synchronous motor. The synchronization is completed from
here on by SM1 in interlock operating AR relay.
Special: Relay SR1 and SR2, by either of them closing
prematurely, will kick out A. C. overloads and liable to
damage switches. Never close them except at 250 R. P. M.
SR1, and 600 R. P. M. SR2.
Relay SR2 can fail as follows: (a) Will not pick up
or close at all. Remedy: Close it at 600 R. P. M. or full
speed and block it closed.
Note: Never let a relay flutter in and out or you will
blow up the switches it controls, (b) Relay apparently
closes okay, but it drops out shortly after closing. This
causes all the switches SM1, relay AR, switch RL to open
with a roar, then close again, usually kicking out A. C.
overloads, and the M-G set cannot be synchronized.
Remedy: Watch the relay SR2 while M-G is being started, and
when SR2 does close, hold it tight closed until M-G steadies
down at full speed, then careful not to let it open at all,
block it in and it will run okay. The common sense
application of your ordinary knowledge will help find these
troubles, as: If M-G starts on battery, but does not change
over to transformer, it is bound to be SR1, and if it starts
and changes over to transformer, but will not synchronize,
SRl is either dropping out or (1) SR2 has not picked up,
(2) it picked up, but dropped out again.
Both of these relays SR1 and SR2 should close and stay
closed, once they pick up.
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