Investigation of the relative impulse strength of magnet wires

This investigation was conducted to determine if shielded magnet wire was really superior to heavy and quad build wire for use in large (up to 900 hp), random wound AC motors. Since all motors start cold (at least once), we determined that testing at room temperature was not unreasonable and that further testing at elevated temperatures could be done, if needed. We also tried to establish a relationship between the AC and impulse breakdowns. To this end, we manufactured 150 medium sized three turn coils with two 15 AWG wires in parallel. We used five types of magnet wire (heavy build from two manufacturers, shielded wire from the same two manufacturers and quad build from one of these manufacturers). We applied voltage between the parallel wires at an increasing rate (of 1000 volts per second) till breakdown to ten coils of each type. We used AC voltage and 0.1 microsecond wavefront pulses using a commercial surge test set (60 impulses per second). Two voltages were used for each test sequence, so that rudimentary voltage endurance curves could be developed. The results are shown for each of the five types of wire.