The effect of cable motor impedance mismatch on reflected waves is common in all AC VFD applications. The severity of the problem depends on the length of the cable, the rise time of the PWM carrier, the voltage of the VFD, and the impedance difference between the motor and the cable.

Under the correct conditions, pulses from the VFD may increase the reflected pulses from the motor, resulting in a doubling of the voltage level, which may damage the cable or components in the drive. The solution is to use XLPE cable insulation, a material with high pulse voltage breakdown levels. This makes the system more immune to the failures of reflected waves and voltage spikes in VFD applications than PVC materials are not recommended in these applications.

The impedance of the cable relative to the motor will be the main mechanism outlined in this paper. This is done because the cable length depends mainly on the layout of the application, the rise time varies with the VFD output semiconductor, and the VFD voltage is determined by the application.