Using leakage currents to evaluate the induction motor insulation condition

The need to improve the reliability and reduce the stator winding-related accident rates of asynchronous electric drives is what makes this topic relevant. The goal hereof is to find how capacitive leakage currents could be used to indicate the condition of the stator winding insulation in an asynchronous motor. The paper presents some results of studies into the stator winding insulation leakage currents generated by rectangular voltage pulses at 100 to 2000 Hz. The researchers have verified the ability to register leakage current parameters as a function of voltage pulse amplitude and frequency in order to use such data to find the insulation condition. It is shown that rectangular voltage pulses can produce sufficiently large leakage currents for easier use. Even rather simple and low-cost equipment is usable to that end. However, reliable determination of the leakage current peaks amplitude requires a very long measurement with numerous transmitted pulses; alternatively, one could use very high-resolution equipment with a sampling time of 10-6 s or less. Nevertheless, the equipment used in the tests does extract the data regarding the effective capacitive leakage currents, which could be used to diagnose the insulation.