Online Monitoring for the Safety of Insulation of Inverter-Fed Equipment Under Varying Working Condition

The online condition method for the safety of insulation can give prognosis for potential failure in inverter-fed equipment such as motors, which can avoid the huge losses caused by the unexpected failure. In the existing methods, the equivalent impedance of the stator winding is estimated in frequency domain by measuring the terminal voltages and leakage current. Because the output voltage of the inverter has many harmonics, the frequency resolution of the monitoring method should be as high as 1~10 Hz to distinguish different harmonics. For the traditional method such as FFT (Fast Fourier Transform), the window length should be very long. If the fundamental frequency of the inverter-fed machine changes in the window in varying work condition, the existing method cannot estimate the impedance parameters accurately. Therefore, a sliding window matrix pencil method is proposed to solve this problem. The online experimental results prove that it can estimate the groundwall and phase-to-phase insulation parameters accurately in varying work condition.