CLINK II SCU MANAGER
functional description scu
version 5.0
49
Figure 20: Temperature curve after start with blocked rotor in hot condition
5.8.5
Motor overload
The motor overload protection uses the motor temperature calculated by the thermal model and the motor
current to protect the motor against overload.
The motor is switched off if it is overloaded during a certain time. The length of this time depends on the size
of the overload. The corresponding current/time characteristic complies with IEC 947-4-1 concerning motor
starters.
IEC 947-4-1 distinguishes 4 temperature classes. In table 37, the trip time is stated as a function of the motor
current for each temperature class.
The times at 1.05 In and 7.2 In are from cold condition, the times at 1.2 In and 1.5 In are from hot condition. At
In there is a thermal equilibrium.
Table 37: Trip times according to IEC 947-4-1
Class
Trip time
1.05 In
1.2In
1.5In
7.2 In (stall)
10 A
> 2 hours
< 2 hours
²<= 2 min.
2 < t <= 10 s
10
> 2 hours
< 2 hours
<= 4 min.
4 < t <= 10 s
20
> 2 hours
< 2 hours
<= 7 min.
6 < t <= 20 s
30
> 2 hours
< 2 hours
<= 7 min.
9 < t <= 30 s
Tcu
T_ambient
t (min)
T_stall
T_nom
Temp. rise
Tfe
Temp. rise interlock level
Time to reset
