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To drive motors by modern invertors is highly effective for saving energy, but there is fear that the electrical insulation system of motor windings is broken by sharp and excessive invertor surges voltage. Therefore, for manufacturing of motors, useful evaluation and protection technologies are required against such issues. The insulation problem on inverter-fed motors is due to the invertor surge generating a partial discharge (PD) in the motor windings. Various environmental factors (temperature, humidity and atmospheric pressure) affect PD phenomena, leading to their complicated characteristics. Many related researchers are reporting the PD inception voltage (PDIV) varies widely when measuring it. What is the reason for it? For the purpose of predictions, and precautions for PD occurrence, it is important to understand PD mechanisms. Are there also impulse waveform generators and PD sensors capable of detecting a very weak signal? The main purpose of this technical report is to respond to these requests and questions. With the goal of making this report easy for readers to understand, we also desire this report will become useful instruction when evaluating practical motors.
In "chapter 2" for understanding fundamental issues, the following items are described; surge analysis, PDs depending on environmental factors, nanocomposite surge-resistance wire and high PDIV wire. The main selling point of this report is "chapter 5", which reports outcomes from the round-robin insulation tests using actual motors and PD measurement tools (chapter 4) performed by the technical committee members according to the IEC international standard (chapter 3). "Chapter 8" describes interesting contents of development of advanced insulation technology of electric vehicles to realize compactness and higher voltages. Thus, we proceed to open the first page and master "the world of inverter insulation". |
