On-line condition monitoring for diagnosis and prognosis of insulation degradation of inverter-fed machines

Real-time winding insulation condition monitoring is becoming an important research topic in response to increase in high availability and reliability demands in modern drives. In this paper, a novel method is proposed to monitor ground-wall insulation of low voltage inverter-fed machines based on a multi-frequency measurement of equivalent insulation ground-wall capacitance and dissipation factor. The monitoring is applied to four machine stator samples subjected to accelerated aging until failure. Insulation degradation is continuously tracked via the capacitance and dissipation parameters. A link between ground-wall insulation capacitance and final lifetime is established. The relationship between capacitance progression and its value at final machine failure is used to develop a method for prognosis of the final failure time.