GE MULTILIN 269 MOTOR MANAGEMENT RELAY Series, Инструкция по эксплуатации

Страница: 95 / 142

3 SETUP AND USE
3-56
Thermal memory can be cleared to 0% by using the
Emergency Restart feature (see section 3.21).
If the phase current is between 1.00 × FLC and the
Overload Pickup level × FLC, one of two thermal model
algorithms can be observed. If the THERMAL
CAPACITY USED is less than the phase current (as a
multiple of FLC) ×
the FLC Thermal Capacity Reduction
setpoint, the THERMAL CAPACITY USED will rise to
that value. If, on the other hand, the THERMAL
CAPACITY USED is above that value, it will remain
unchanged (neither increase nor decrease) unless RTD
BIAS is enabled, in which case the greater of the two
values will be used.
Thermal capacity reduction may be calculated using
the following formula:
100
Time Stall Motor Cold
Time Stall Motor Hot
1
×






− =
TCR
U/B INPUT TO THERMAL MEMORY - When U/B input
to thermal memory is defeated the 269 relay will use
the average of the three phase currents for all overload
calculations (ie. any time the overload curve is active).
When U/B input to thermal memory is enabled the 269
relay will use the equivalent motor heating current cal-
culated as shown:
Ieq = Iavg (with U/B input to thermal memory disabled;
factory preset)
2 2
ea
ln K lp I
+ + =
(with U/B input to thermal memory
enabled)
where K =
I (Amps)
I (Amps)
LR
FLC
or user entered value
(negative sequence current heating factor; see below)
Ieq = equivalent motor heating current
Iavg = average of three phase currents
Iflc = motor full load current
Istart = learned motor starting current (avg. of last 4
starts)
Ip = positive sequence component of phase current
In = negative sequence component of phase current
Thus the larger the value for K the greater the effect of
current unbalance on the thermal memory of the 269
relay.
RTD INPUT TO THERMAL MEMORY - When the hot-
test Stator RTD temperature is included in the Thermal
memory (Setpoints mode, page 5, factory preset dis-
abled) the maximum measured stator RTD temperature
is used to bias (correct) the thermal model. The RTD
BIAS curve acts as a double check of the thermal
model based on feedback from the actual stator tem-
perature (as measured from the RTDs). When the
hottest stator temperature is at or above the RTD Bias
Maximum value (Setpoints mode, page 5) the thermal
capacity used is 100%. When the hottest stator RTD
temperature is below the RTD Bias Minimum value
(Setpoints mode, page 5) there is no effect on the
thermal capacity used. Between these two extremes,
the thermal capacity used is determined by looking up
the value of the Hottest Stator RTD on the user's curve
(RTD BIAS Min, Center, Max temperatures, RTD BIAS
Center Thermal Capacity) and finding the correspond-
ing Thermal Capacity used. The Hottest Stator RTD
value for Thermal Capacity used is compared to the
value of THERMAL CAPACITY USED generated by the
thermal model, (overload curve and cool times). The
larger of the two values is used from that point onward.
This feedback provides additional protection in cases
where cooling is lost, the overload curve was selected
incorrectly, the ambient temperature is unusually high,
etc.
The two-part curve allows for easy fitting of HOT /
COLD curves to the RTD BIAS feature. The minimum
value could be set to the ambient temperature the mo-
tor was designed to (40
°
C). The center point for ther-
mal capacity could be set to the difference between the
hot and cold curves (eg. 15 %). The center point tem-
perature could be set for hot running temperature (eg.
110
°
C). Finally, the Maximum value could be set to the
rating of the insulation (eg. 155
°
C) The user has the
flexibility to set the RTD BIAS as liberally or conserva-
tively as he/she desires.
It should be noted that the Thermal Capacity values for
the RTD BIAS curve MUST increase with temperature.
For this reason, there is range checking on the tem-
perature setpoints (eg. the minimum setpoint cannot be
larger than the center temperature setpoint). It may
take a couple of attempts to set the parameters to the
desired values (it is best to start with the minimum or
maximum value).
It should also be noted that RTD BIAS may force the
THERMAL CAPACITY USED value to 100%, but it will
never alone cause a trip. If the RTD BIAS does force
THERMAL CAPACITY USED to 100%, when the motor
load increases above the overload pickup value, a trip
will occur immediately (see Appendix B). A trip by
RTDs will only occur when the RTD values exceed the
user's trip level for RTD trip, as defined in page 2 of
setpoints.
Additionally, RTD bias may artificially sustain lockout
times for the O/L and Start Inhibit features as they are
based on thermal capacity.
3.21 Emergency Restart
When production or safety considerations become
more important than motor protection requirements it
may be necessary to restart a faulted motor. Momen-
tarily shorting together the Emergency Restart termi-
nals will discharge the thermal memory to 0% so that
the relay can be reset after an OVERLOAD TRIP. In