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.
Design and implementation of control of solid state relay switches using MSP 430 for instantaneous high current supply
Main objective of the project is to control the switches, through the microcontroller MSP430 to supply a very high current. Solid state relays are used as switches which energises Contactors to pass the high current using Capacitor discharge system. High current is passed to the sample specimen placed inside the heater which needs to be heated at a very high temperature. The current pulse is generated by the capacitor discharge system. Capacitor discharge heating is an extra amount of heat in the heating element, the power supply for regular heater is suspended for a while and the capacitor is allowed to discharge during this period. This is done using the microcontroller MSP430. Software is written so as to control the operation of solid state relay switches such that the current injection happens at the particular instant. This can be initiated by an interrupt from the computer. By this the interrupt pin of the microcontroller port becomes high and the corresponding operation initiates. Thus computer commands the MSP430 to give this pulse of current for heating whenever required. Feedback control of the solid state relay switches is given to MSP430 to check the SSRs status and this is displayed on the PC. Thus by controlling the SSR switches it is possible to pass the required amount of current to the heater where the sample is placed. PC is interfaced to the supercomputer using RPC, for fast and precise calculations where the result is received back on PC.
Polarity effect of unsymmetrical material combination on the arc erosion and contact resistance behaviour
The arc duration, material transfer, contact morphology, surface composition, and contact resistance of dissimilar contact combinations of palladium and silver were experimentally examined with breaking inductive load from 0.5 A to 4.0 A for 6/spl times/10/sup 4/ times of operations in air at atmospheric pressure. The test results have led to the conclusion that the polarity significantly affects the arc erosion and electrical contact resistance behaviours. By comparing with the previous results, it is known that the cathode material plays a main role in arc erosion, such as mass transfer, arc duration, and erosion pattern. The contact resistance is, however, dominated by the anode material due to surface contamination, especially the anode oxidation in late gaseous phase. Also, evidence is found in this work that the material transfer between two electrodes greatly influences the arc erosion and contact resistance behaviours.