Function library
Thermal motor monitoring, error detection
7−82
L
EDB82MV752 EN 5.2
7.12 Thermal motor monitoring
7.12.1 I
2
t monitoring
Description
With I
2
t monitoring, self−ventilated three−phase AC motors can be thermally monitored without using
sensor.
( Stop!
l I
2
t monitoring does not fully protect the motor since the calculated motor
temperature is reset after every mains disconnection!
l After renewed mains connection the connected motor can be overheated, if
– it is already hot and is still overloaded.
– the cooling air supply is interrupted.
– the air is too hot.
l Full motor protection can be achieved by using a PTC thermistor or thermostat in
the motor.
( 7−84)
Codes for parameter setting
Code Possible settings IMPORTANT
No. Name Lenze Selection
C0120 I
2
t switch−off 0 0
= not active
{1 %} 200 Reference: Apparent motor current (C0054)
Ref. to active motor current (C0056)
possible, see C0310
7−82
Adjustment
1. Calculate C0120. This value corresponds to a motor load of 100 % :
C0120[%]
I
r
I
N
100%
I
r
Rated motor current
I
r
Rated controller current at a chopper frequency of 8 kHz
2. If you reduce C0120 based on the calculated value, the monitoring already starts at a motor
load of < 100 %.
3. If you increase C0120 based on the calculated value, the monitoring only starts at a motor
load > 100 %.
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