Mayr´s Model of the Arc Applied to 50-and 60-Hz Interruption in Low-Voltage Devices

Mayr and Cassie made assumptions about thermal properties of arcs about 40 years ago. The resulting mathematical models of the arc have been applied by others to various arcing structures, usually large circuit breakers, and have had good success in predicting performance of the arcing devices for both high currents using Cassie´s model and low currents using Mayr´s model. The thermal properties of the arc from Mayr´s model are investigated for low-voltage devices such as relays and motor starters. Mayr´s model applied to low-voltage device circuit interruption predicts that 60-Hz current is harder to interrupt than 50-Hz current and experimental data verify this result. The 60-Hz current is higher than the 50-Hz current in the last critical microseconds of the arc. The arc volume is hotter at current zero for the 60-Hz arc than for the 50-Hz arc. The actual interruption, however, is not completely described by Mayr´s model of the arc, but instead the interruption may be dependent upon the dynamics of the space charge layer formed at the contact surface.