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.
Comparison of properties of silver-metal oxide electrical contact materials
Changes in physical properties such as density, porosity, hardness and 
 electrical conductivity of the Ag-SnO2 and Ag-SnO2In2O3 electrical contact 
 materials induced by introduction of metal oxide nanoparticles were 
 investigated. Properties of the obtained silver-metal oxide nanoparticle 
 composites are discussed and presented in comparison to their counterparts 
 with the micro metal oxide particles as well as comparable Ag-SnO2WO3 and 
 Ag-ZnO contact materials. Studied silvermetal oxide composites were produced 
 by powder metallurgy method from very fine pure silver and micro- and 
 nanoparticle metal oxide powders. Very uniform microstructures were obtained 
 for all investigated composites and they exhibited physical properties that 
 are comparable with relevant properties of equivalent commercial silver based 
 electrical contact materials. Both Ag-SnO2 and Ag- SnO2In2O3 composites with 
 metal oxide nanoparticles were found to have lower porosity, higher density 
 and hardness than their respective counterparts which can be attributed to 
 better dispersion hardening i.e. higher degree of dispersion of metal oxide 
 in silver matrix.
Prophets praying for, or preying on people’s faith: A reflection on prophetic ministry in the South African context
In mainline churches, the ministry of prophecy or the prophetic ministry involves the proclamation of the gospel. This, in turn, is related to the every-believer ministry. However, there is now a resurgence of the prophetic ministry as a special office as evidenced by the establishment of neo-prophetic churches. This article argues that neo-prophetic churches are tapping into people’s longing for the fresh divine word to speak directly into their personal situations. The article also probes whether neo-prophets in the prophetic activities are not also preying on people’s faith.