Long term behavior of corona resistant insulation compared to standard insulation of magnet wire

Low voltage motor turn insulation has been aged under stresses similar to those caused by PWM voltage pulses. Commercial standard turn insulation was tested in parallel with a new inverter grade corona resistant (CR) insulation. Both types of insulation were subjected to fast bipolar pulses at 80°C and at 130°C. When the maximum peak voltage was set to 620 V, below the discharge inception voltage (DIV), no failure was recorded on either insulation system, after aging times of 280 days. When the pulse peak voltage was increased to 830 V, failures rapidly occurred on all specimens with standard insulation and later for all specimens with CR insulation. A third aging test was carried out at 750 V. Here, at 80°C, all specimens with CR insulation failed before the specimens with standard insulation. The mean time to failure for CR material was of 133 hours, while it was larger than 1070 hours for the standard type insulation at the same temperature. This behavior was not observed at 130°C and 750 V