Specifications

F7
GE Limitamp
®
Medium Voltage Motor Control
Protection & Control
F
circuit after a definite elapsed time on either energization or
de-energization.
Incomplete-Sequence Relay
An incomplete-sequence relay is used to shut down the
motor (squirrel-cage induction or synchronous) on reduced-
voltage starting if the control fails to transfer to full voltage.
This standard feature protects the autotransformer from
energization longer than rated time. The relay can be furnished
for other sequencing functions also.
Jogging
Drives requiring “jogging” (or inching) must have the control
circuit arranged for repeatedly closing the line contactor at
short intervals to effect small movements of the driven
machine. The line contactor is held closed only as long as
the JOG button is held depressed.
An anti-kiss circuit is provided with the JOG push button,
including a jog relay. The jog relay closes when the JOG button
is depressed, energizes the line contactor coil, seals itself in
around the JOG button and is dropped out only after the line
contactor has closed and wiped in. This makes possible
repeated opening and closing of the line contactor, but also
assures that the tips wipe closed each time.
Current Interlocking
Current-operated relays indicate when the arc is completely
extinguished after the line contactor opens. These relays
then permit closure of a reversing contactor. A short circuit
may occur if a reversing contactor closes after the forward
contactor opens but before the ar
c has been extinguished.
This circuit is necessary in controllers with “plug stop” or
where pressing one instantaneous contact picks up reversing
contactor while running forward. Current interlocking is not
normally used on overhauling loads such as mine hoists,
since during the lowering cycle enough current may not be
drawn to operate the interlocking relays.
This circuit is not supplied on standard Limitamp reversing
controllers, as the operator is expected to turn the selector
switch to reverse only after pressing the STOP button.
Potential Interlocking
Potential interlocking is used for the same reason as in current
interlocking. Potential transformers and interlocking relays
are added to prevent closure of one primary contactor before
complete interruption of the arcs at the tips of the other
(reverse) contactor. Operation is based on the principle that
by the time the disconnected motor’s generated EMF has
decayed to the point where the interlocking relays have
dropped out, the arc in the disconnected contactor has
extinguished, and closing the reversing contactor is permissible.
Potential interlocking is used on hoists and other applications
having possible overhauling loads.
Instrumentation
Ammeter
An ammeter (panel-type or switchboard-type) is used to
indicate either motor amperes or total incoming amperes. It
can either be hardwired to the current transformer of one
phase or all three phases can be monitored by the use of a
selector switch. One current transformer is required for single-
phase reading; two are required for open delta three-phase
reading; three are required in a wye circuit. Three window-
type current transformers are provided as standard on
Limitamp Controllers.
Voltmeter
The voltmeter (panel-type or switchboard-type) is used to
indicate phase-to-phase potential. One potential transformer
is required if only one phase-to-phase potential is monitored.
Two potential transformers, connected in an open-delta
configuration, are required along with a selector switch to
monitor any one of the three phases. Three potential trans-
formers mounted in an auxiliary enclosure and a selector
switch are required to read both phase-to-phase and phase-
to-neutral potentials.
Power Factor Meter
A power factor meter is used to indicate power factor lead
or lag. It is usef
ul in adjusting power factor in synchronous
motor drives and in determining the power factor of a given
drive. The addition of a power factor meter requires the
addition of potential transformers, or of some other potential
source with correct phase and accuracy. When a synchronous
starter is supplied, the GE-Multilin SPM has a digital power
factor meter built into the device.
Wattmeter
A wattmeter is used to indicate loading or useful power
being deliv
ered to a drive at any instant. The instrument is
typically calibrated in kilowatts. Two potential transformers
connected in open delta are required for operation.
Operation Counter
The operation counter is electrically operated from a control
interlock on the line contactor. It totals the number of times
the contactor has closed and opened, and thus pr
ovides
data for the establishment of maintenance schedules, a
record of the number of batch processes initiated over a
given period of time, or any other purpose where the number
of line contactor closures may be significant.
Varmeter
The varmeter indicates lagging or leading reactive power. It
requires the addition of tw
o potential transformers. In totaling
reactive power on a bus feeding several loads, individual
vars for each load can be measured by means of individual
varmeters on each motor and added directly.