The voltage protection function is deployed on 1FE motors and on the synchronous version of 2SP1 motor spindles with an EMF of Г› > 820 V to 2000 V (U_rms 570 V to 1400 V) in order to limit the DC link voltage in the drive system in the event of a fault.

If the line voltage fails with the motor operating at maximum speed, or if the drive system pulses are suppressed as a result of a line voltage failure, the synchronous motor feeds energy at high voltage back into the DC link.

The VPM detects that the DC link voltage is too high (DC > 820 V) and shorts the three motor feeder cables in order to brake the motor. The residual motor energy is converted to heat via the short circuit in the VPM and motor.