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.
Effect of arc behavior on material transfer: a review
One of the serious problems of arcing in relays and switches is leading to material transfer, thus resulting in the loss of contact material and the early end of lifetime. Although this phenomenon has been studied for many years, there are still many unsolved problems. This paper is a review of material transfer due to arcing based on published work by the authors and by the other investigators. Included are a discussion of transfer mechanism, called PSD model (particle sputtering and deposition model); a survey of contact materials, circuit parameters, electrode temperatures, and surrounding gases which have been determined to affect arc behavior and material transfer; the effect of contact surface temperature distribution, arc spot dimension, arc root stability, and arc duration on wearout or loss of contact material from two contacts; and an idea of balance transfer ("zero" loss) operation. It is expected that this paper could supply some basic considerations for controlling material transfer in practical applications.
The distribution of 54-Mn in the enamel and dentine of the rat incisor.
Abstract The distribution of 54 Mn was studied in the lower incisors of rats. Autoradiograms show 54 Mn to be present in the enamel and dentine 5, 10 and 15 days after its administration. In the dentine, the radioisotope is first localized in a zone near to and encircling the pulp and later becomes more diffuse. Pre-existing as well as the newly formed enamel incorporates the isotope. In both enamel and dentine 54 Mn appears to be principally associated with the inorganic portion.