A new life-test equipment designed for medium-duty electromagnetic contactors

In this study, a new test equipment, which is capable of performing arc-erosion experiments of electrical contacts on a medium-duty contactor, was designed and manufactured. The current load value of the system was gradually adjustable up to 30 A via control buttons located on the device. The make/break counts (cycle) and delay times of electrical contacts were adjusted by an electronic flasher. The number of operations was readily adjusted to desired counts before tests, and was monitored along the whole test on the LCD display of up/down counter. Inductive loads consisting transformers were used to achieve real-life operating conditions. A contactor having pole number of 3, switching power of 37 kW, and switching current of 75 A was used to conduct arc-erosion experiments. The test conditions for this contactor were 220 V operating voltage, 50 Hz frequency, and 20 A switching current. The switching frequency and delay time were selected as 1,000 times per hour and 2.6 s, respectively. Arc-erosion experiments were carried out by using the contactor up to 40,000 operations. The contact surfaces were analyzed by using scanning electron microscopy. The chemical compositions nearby arc were determined by energy dispersive x-ray spectroscopy. The experimental results showed that the contact surfaces were reasonably affected by the arc-erosion, which leads to mass loss by material migration and/or evaporation. Arc-affected zones were enlarged with the increasing operation number. It was concluded that the stationary contacts underwent major erosion.