I/Ie[%]
Thermal
Motor
Model
Cooling
Time
Running
Load >
Restart
Level
Trip
&
Cooling Mode =
Load based
>
Tcooling
&
Cooling Mode =
Time-based
Load
Trip
Load >
Warning
Level
Prewarning
Thermal
Overload
Electronic Overload Protection
The UMC protects single - and three-phase AC motors in compliance with IEC 60947-4-1. The tripping class can be set to class 5, 10,
20, 30 or 40. The advanced thermal motor model considers both the copper and iron parts of the motor thus providing the best
protection of the motor.
Before an overload trip actually happens, a pre-warning can be generated. During high overload situations the prewarning might
be raised just a few seconds before the actual trip happens.
The presently used time to trip for the
current load situation. If the motor is switched off the time to trip shows 6553 sec (never trips). If the motor is running the predic-
ted trip time is updated regularly. The smaller the value the earlier the trip happens.
After an overload trip, the remaining cooling down time (=time to restart) is calculated regularly and also available to the user.
The motor can be restarted if the cooling time is 0 sec.
Block Diagram:
—
Signal flow of the thermal overload protection
The thermal information of the motor is cyclically stored (thermal memory) 1). After a thermal overload trip the motor must cool
down before it can be started again. There are two options to define the necessary duration of the cooling time.
• Fixed cooling time:
The user has to specify a fixed duration e.g. 15 minutes. After a thermal overload trip a further motor start is inhibited for that time.
The time that has to be adjusted depends on:
Motor size, motor with or without ventilation, the environment temperature etc. Considering these points the appropriate cool-
ing time can be estimated.
Some examples of motor cooling time constants (t.c.) (motor standstill) can help:
Size
c.t.
•
is possible again.
1)
If the UMC was switched off while the cooling time was running and the power down time was shorter than 20 min, the UMC restarts the cooling timer with the
remaining cooling time.
Otherwise the cooling time is set to zero.
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