Abstract
The processes of electric arc quenching of an electromagnetic contactor during testing for ultimate breaking capacity are considered. The conditions for facilitating the successful arc quenching when turning off the limiting currents are shown: by reducing the phase shift between current and voltage, by reducing the amplitude of the restriking and recovery voltages. The processes of anode heating during arcing (heat saturation mode), after the change of polarity and transition of the current through zero, processes on the cathode in the temperature equalization mode are considered. The mathematical models of cathode thermal processes adressed the heat fluxes of the ionic component and evaporation. The mathematical models of anode thermal processes in the temperature equalization mode took into account the heat fluxes of the ionic component, thermionic emission, and evaporation. The calculations were carried out for the averaged values of thermophysical coefficients for copper, since the arc base moves from the contacts to the contact holders, which are made of copper or its alloys. The calculation results showed that the used mathematical models of thermal processes are appropriate both for the cathode and for the anode. This was confirmed by the results of previously performed and published experimental and theoretical studies of thermal processes at the switching contacts of electrical devices.
Highlights
The microprocessor devices are being actively introduced in the power industry
The electrical contacts are exposed to significant thermal loads, which can cause the contactor failure and lead to an accident in the electrical equipment it controls
It is proposed to evaluate the device reliability using the reliability index basing on the analysis of the main failure types of AC contactor under various load conditions [16]
Summary
Electromechanical devices are still the key elements in products for which reliable operation is especially important. The reliability of electromechanical devices, in particular electromagnetic contactors, is confirmed by testing for the ultimate switching capacity. The main switching elements of an electromagnetic contactor are electrical contacts that pass currents that are many times higher than the rated ones. The electrical contacts are exposed to significant thermal loads, which can cause the contactor failure and lead to an accident in the electrical equipment it controls. It is proposed to evaluate the device reliability using the reliability index basing on the analysis of the main failure types of AC contactor under various load conditions [16]. The reliability index is the degree of failure rate, which is determined by six levels in accordance with the maximum failure rate
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