Technical information

8 – THEORY OF OPERATION
Motor Overload
115
NOTE: When the Independent Starting/Running Overload parameter is set to “OFF”, the running OL is used at all times.
NOTE: When one or the other overload is disabled, the Hot/Cold motor compensation is still active. Therefore the motor overload
content may still slowly increase or decrease depending on the measured motor current. However if the motor overload is disabled in
one of the operating modes, the motor overload content is limited in that mode to a maximum of 99%. Therefore, a motor overload
trip can not occur.
CAUTION: When both overloads are disabled, the accumulated overload content is set to zero (0%) and the starter does not provide
any motor overload protection. External motor overload protection must be provided to prevent motor damage and/or the risk of fire
in the case of a motor overload.
8.1.8 Motor Cooling While Stopped
The Motor Overload Cooling Time parameter is used to adjust the cooling rate of the motor overload. When the motor is stopped
and cooling, the accumulated motor overload content is reduced in an exponential manner.
t
e
eCoolingTim
5
* Stoppeden Content wh OL Content OL =
When the motor is stopped, the motor overload cools as shown in the following figure.
Figure 16 – Motor Cooling While Stopped Curves
MX Motor OL Cooling, Motor Stopped
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800
Time (sec)
Remaining OL Content %
12 min
15 min
20 min
30 min
30 min
12 min
If the motor manufacturer does not specify the motor cooling time, the following approximations for standard TEFC cast iron motors
based on frame size can be used: