Siemens 3RK1308‑0 00‑0CP0 Series Equipment Manual page 77

Principle of operation
The electronics continuously calculate a model of the thermal load on the motor dependent
on the operating time and the current load. The motor memory model charges when the
motor is switched on. The motor memory model discharges after the motor is switched off.
Figure 6-5
Following an overload tripping operation, the motor memory model is fully discharged after
approximately three minutes. You must wait for this cooling time to elapse before you can
acknowledge the fault. If the control supply voltage fails, the motor starter can store the
remaining cooling time if the relevant parameters have been set. When the control supply
voltage is restored, the remaining cooling time elapses before the load can be switched on
again.
If you initiate a restart within a very short time after switching off the motor, it may be that the
motor memory model has not yet fully discharged. This can result in an extremely fast
overload trip after the restart. In continuous operation (partially charged motor memory
model), the tripping times are reduced depending on the pre-charge.
Warning limit motor heating
The motor starter displays a warning if the motor heating limit is overshot. You use this
parameter to preset a motor heating value in percent as a warning limit.
This function is deactivated with a warning limit for motor temperature rise of 0%.
If the warning limit for motor heating is exceeded, a group warning and the
"Thermal motor model overload" maintenance alarm are output.
Motor starter (3RK1308‑0**00‑0CP0)
Equipment Manual, 11/2019, A5E34821005002A/RS-AC/003
Principle of operation
Functions
6.5 Overload protection
77