GE MULTILIN 269 MOTOR MANAGEMENT RELAY Series, Инструкция по эксплуатации

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3 SETUP AND USE
3-55
3.19 Thermal Capacity Alarm
The Thermal Capacity Alarm setpoint level determines
the threshold that thermal capacity must equal or ex-
ceed for an alarm condition to exist. The time delay set
determines the amount of time that these conditions
must persist before an actual alarm occurs.
3.20 Thermal Memory
The 269 relay uses an internal thermal memory register
to represent the thermal capacity of the motor. To "fill"
this register, the square of the equivalent motor heating
current is integrated over time. This equivalent current
is a biased average of the 3 phase currents. The rate
at which the memory fills is thus dependent on the
amount of overload as well as RTD bias. The RTD bias
can be defeated using a setpoint in page 5 of
SETPOINTS mode. When the thermal memory regis-
ter fills to a value corresponding to 100% motor ther-
mal capacity used, an OVERLOAD TRIP will be
initiated. This value is determined from the overload
curve.
Thermal memory is emptied in certain situations. If the
motor is in a stopped state the memory will discharge
within the motor STOPPED COOL TIME (factory value
= 30 min.). If the motor is running at less than full
load, thermal memory will discharge at a programmed
rate to a certain value. This value is determined by the
"FLC Thermal Capacity Reduction" setpoint. For exam-
ple, a value of 25% may be chosen for this setpoint. If
the current being drawn by the motor drops below full
load current to 80%, then the thermal memory will
empty to 80% of the FLC Thermal Capacity Reduction
setpoint, namely, 20% (0.8 ×
25%). In this way the
thermal memory will discharge to an amount related to
the present motor current in order to represent the ac-
tual temperature of the motor closely. Thermal memory
will discharge at the correct rate, in an exponential
fashion, even if control power is removed from the 269.
Figure 3.6 Hot Motor Thermal Capacity Reduction