GE MULTILIN 269 MOTOR MANAGEMENT RELAY Series, Instruction Manual

Page: 98 / 142

3 SETUP AND USE
3-59
Figure 3.7 Power Measurement Conventions
Power Factor Lead and Power Factor Lag alarm and
trip setpoints with programmable time delays can be
used to detect such conditions as out of step, loss of
synchronism or loss of field.
Where the motor is started unloaded and the field ap-
plied later in the start, the power factor may be poor
until the motor is loaded and synchronous speed is
attained. It may then be necessary to block power fac-
tor protection until the motor is up to speed.
A setpoint on page 7 allows the user to pick one of two
methods of blocking power factor protection on start.
Answering “NO” to the setpoint “BLOCK PF
PROTECTION ON START?” puts the 269 in a mode
where the “Power Factor protection delay” feature may
be enabled. So, when programmed, after the motor has
successfully completed a start, this setpoint required
that the measured power factor comes between the
user specified POWER FACTOR TRIP LEAD and LAG
setpoints for the specified period of time (user’s value
for Power Factor protection delay) before the power
factor trip and alarm features become active. A stop
condition resets the algorithm.
Answering “YES” to the setpoint “BLOCK PF
PROTECTION ON START?” puts the 269 in another
mode where “Block PF alarm & trip on start by: XXX
seconds” may be enabled. When this delay is pro-
grammed, the 269 blocks power factor lag and power
factor lead alarm and trip protection from start until the
time expires. When programming this delay, consid-
eration must be given to the time it takes the motor to
start, apply the field and the load.
The positive KVAR alarm and negative KVAR alarm
setpoint levels determine the threshold that KVARS
must exceed for an alarm or trip condition to exist. The
time delay set determines the amount of time that
these conditions must persist before an actual trip or
alarm occurs.
All motors (synchronous and induction) require vars
from the system to run. The 269 displays consumed
vars by the motor as positive vars. Conversely, if a
synchronous motor is run overexcited as a synchro-
nous condensor, it may be capable of supplying vars
back to the system. Such motors are typically used to
correct a poor PF in an industrial plant. The 269 dis-
plays motor supplied vars as negative vars when a
synchronous motor is running at synchronous speed,
its power factor is unity and the vars required to run the
motor are completely supplied by the field. So, ideally
the reactive power for a unity synchronous motor com-
ing from the AC system is zero. Hence, another way of
indicating abnormal running conditions on synchronous
and induction motors is by using the positive kvar
alarm and negative kvar alarm levels and the kvar
alarm time delay.
Enabling Voltage Phase Reversal allows the 269 to trip
or inhibit based on phase reversal sensed from voltage
from the MPM. This allows sensing of phase reversal
when the bus is energized before the motor is started.
There is a 3-4 second delay for voltage phase reversal,
and it is also defeated on starts to prevent nuisance
trips caused by distortion of the bus voltage wave-
shape.
The Analog Out Scale Factor setpoint is entered to set
the Full Scale value for the MPM analog outputs
(KWATTS and KVARS). The value entered here is the
multiplier that is multiplied by 100 KW to determine the
MPM analog output Full Scale for KWATTS, or by 30
KVAR to determine the MPM analog output Full Scale
for KVAR. 4 mA represents 0 KWATTS and 0 KVARS
and 20 mA represents full scale. Average RMS current
is produced in analog form where 4-20 mA is equiva-
lent to 0 A to 1xCT rating. Power Factor is produced in
analog form where 4/12/20 mA represents -0/1/+0
power factor values respectively.
NOTE: If a meter Communications Failure occurs,
it may be necessary to press the RESET key to re-
move the message if that alarm is assigned to a
latching relay.
On commissioning of a synchronous motor protected
by a 269 and an MPM, correct wiring of the VTs and
CTs is crucial for accurate measurement and protec-
tion. Typically, commissioning and testing starts with
the motor unloaded. It is also typical to examine the
power factor to verify the wiring and proper operation of