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.
SOLID STATE RELAY SWITCHES CONTROL USING MSP 430 FOR INSTANTANEOUS HIGH CURRENT SUPPLY CONTROL USING MSP 430 FOR INSTANTANEOUS HIGH CURRENT SUPPLY.”
Microcontroller MSP430 is used to control the SSR switches to supply a very high current. PC is interfaced to the supercomputer for computations. SSR and contactor switches are used to pass the current. Capacitor discharge system is also used to supply a very high current around 170-200A. 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. Power supply for regular heater is suspended temporarily and capacitor is allowed to discharge using the Capacitor discharge heating. This is achieved by the instructions through the computer to the microcontroller. Current injection at the particular instant is done with the help of a software by initiating an interrupt from the computer. The interrupt pin of the microcontroller becomes high by this and the operation is initiated correspondingly. Thus the MSP430 receives the command to give the necessary pulse of current for heating at the required time. Feedback is received with regard to the position of the switches whether the particular SSR is ON or OFF. Injection of power depends on the corresponding switch positions by giving the necessary instructions by the computer.
Time lapse photography of clouds from high altitude balloons.
Time lapse pictures of clouds taken by cameras flown at altitudes of 30 km on balloons provide valuable insights into the convection and electrification of cloud systems. Simple camera arrangements for taking such pictures are described.