When the pulse voltage is transmitted on the cable, if the impedance of the cable does not match the impedance of the load, reflection will occur at the load side. The result of the reflection is that the incident wave and the reflected wave are superimposed to form a higher voltage, which can reach a maximum of 2 times the DC bus voltage, which is about 3 times the input voltage of the inverter, as shown in Fig. Too high peak voltage added to the motor stator coil, the coil caused by voltage shocks, frequent over-voltage shock will lead to premature failure of the motor.
The actual life of the motor driven by the inverter is affected by the peak voltage, and its actual life is related to many factors, including temperature, pollution, vibration, voltage, carrier frequency and coil insulation process.
The higher the carrier frequency of the frequency converter, the closer the output current waveform is to the sine wave, which reduces the operating temperature of the motor, thereby extending the life of the insulation. However, a higher carrier frequency means that the number of spikes per second is more, and the number of impacts on the motor is more. For a 200-foot cable, the insulation life is reduced from about 80,000 hours to 20,000 hours (4 times) when the carrier frequency is increased from 3kHz to 12kHz (4x).