The Voltage Protection function is used with motors 1FE1...-....1-.... and with 2SP1 motor spindles with EMF of U > 820 V to 2000 V (V_eff 570 V to 1400 V) to limit the DC link voltage at the drive system in the event of a fault.

If the line voltage fails at maximum motor speed or if the drive system pulses are canceled as a result of the power failure, the synchronous motor regenerates at high voltage back into the DC link.

The VPM detects a DC link voltage that is too high (> 820 V DC) and short-circuits the three motor supply cables, decelerating the motor. The power remaining in the motor is converted to heat via the short circuit in the VPM and motor.