抄録
In inverter-fed motor systems, output voltage of the inverter has a rectangular waveform with rise time of a few tens of nanoseconds, and consequently a motor suffers from repetitive surge pulses which may have adverse effect on motor insulation. Therefore the behavior of surge pulses should be clarified to devise the optimum insulation design of a motor. We have investigated how cable structure and grounding wire connecting inverter and motor affect the surge behavior with particular regard to peak voltage between motor input terminal and ground and peak voltage across the first coil in serially connected multi coils. As a result, we discovered phenomena whereby, when cross sectional structure of the cable is asymmetrical, the surge voltage of a specific phase can become higher than that of the other phases resulting from asymmetry among capacitances between feeder line and ground line. And we have confirmed these phenomena can be prevented by the following three methods: using cables that have symmetrical capacitance to ground among 3 phases (e.g., a 3-phase shielded cable), providing the grounding wire as a separate cable to reduce the capacitance, inserting capacitors at motor terminals or inverter terminals to cancel out capacitive asymmetry.
