GE 469 Instruction Manual page 171

469
S9 Voltage Elements
Motor Management Relay
specified by the time delay. Note that pickup levels are multiples of motor
nameplate voltage. The running pickup level also applies when the motor is
stopped, and the setpoint is programmed to "No".
U/V ACTIVE ONLY IF BUS ENERGIZED
An undervoltage on a running motor with a constant load results in increased
current. The relay thermal model typically picks up this condition and provides
adequate protection. However, this setpoint may be used in conjunction with the
time delay to provide additional protection that may be programmed for advance
warning by tripping.
Attempting to start a large motor when the supply voltage is down may also be
undesirable. An undervoltage of significant proportion that persists while starting a
motor may prevent the motor from reaching rated speed. This may be especially
critical for a synchronous motor. As such, this feature may be used in with a time
delay to provide protection for undervoltage conditions before and during starting.
In the event of system problems causing asymmetrical voltage conditions where at
least one voltage remains above pickup, an Alarm condition will occur, indicating
that the voltage on at least one phase is below acceptable levels. The trip relay will
not be energized unless the is set to "1-Phase". The factory
UNDERVOLTAGE TRIP MODE
default setting for is "1-Phase".
UNDERVOLTAGE TRIP MODE
To prevent for nuisance undervoltage trips due to VT Fuse Failure, set the
to "3-Phase". The alarm relay will be energized in the event
UNDERVOLTAGE TRIP MODE
of a single-phase undervoltage, which can also be an indication of a potential VT
fuse failure. Typically a fuse failure is detected when there are significant levels of
negative-sequence voltage, indicating voltage unbalance due to the loss of one
phase, without correspondingly significant levels of negative-sequence current,
indicating current unbalance, measured at the output CTs.
If the conditions for Fuse Failure exist, an alarm will occur after a time delay due to
an undervoltage condition in at least one phase. If the motor is running, the voltage
in the faulted phase will be zero, and the measured load current should not indicate
a significant amount of negative or unbalance currents. Therefore the motor can be
kept in service until the opportunity to replace the faulty fuse is available.
If the alarm is caused by an abnormal system conditions, a significant amount of
unbalance current will be present. If the condition is not detected on time, the
unbalance function or the underpower element will trip the motor.
Set to "3-Phase", when the setpoint
UNDERVOLTAGE TRIP MODE S2 SYSTEM SETUP
is set to "On". The relay assumes a
VOLTAGE SENSING ENABLE SINGLE VT OPERATION
balanced three phase system when fed from a single VT.
NOTE
GE Multilin
5–65
http://www.GEindustrial.com/multilin