PWM inverter output high voltage square wave pulse with a steep edge, because the vibration frequency of the wave drag plate and cable does not match the steep rise in the frequency producing a vibration plate side reflected voltage spikes, which is superimposed on the high-voltage square wave pulse , with the impact of the stator winding insulation effect. This traction inverter for variable speed vibration plate insulation system put forward higher requirements.

Dielectric capabilities. Electrical equipment insulation can safe and reliable operation, mainly to see if it withstand voltage capability. The size of insulation withstand voltage capability is called insulation level. Insulation level should ensure the continuing role of the maximum operating voltage exceeds the maximum operating voltage and under a certain value under the action of short-term over-voltage, insulation can operate safely.

Insulation should have a high electrical strength, that is the minimum thickness, the electrical strength of the insulation is minimal dispersion frequency vibration plate provides maximum operating voltage. For supplied by the inverter VVVF traction frequency vibration plate, the insulation system should have adequate anti-overshoot voltage capability.