Check for Insulation Defects and Deterioration
Even If No Non-Defective Part is Available
On a standard, properly configured 3-phase motor, the phases (U,V,and W) are balanced. Consequently, the response waveforms obtained when an impulse voltage is applied between phases (U-V,V-W,W-U) will be almost identical.
By tentatively identifying the response waveform obtained from one phase as the waveform for a non-defective part and comparing it to the response waveforms from the other phases, you can detect insulation failures and deterioration.