On the basis of numerical simulation of heating of symmetric contacts by flowing current,were drawn conclusions about the accuracy of determining the temperature by the Holm – Kohlraus method for various methods of cooling the contacts, including with intensive air and liquid cooling. The question of the possibility of using this method for pulsed heating of contacts. It is shown how the accuracy of determining the temperature of the contact pads depends on the choice of locations for measuring the surface temperature and the potential difference.
A study of the softening process of contact spots of closed high-current copper contacts caused by recrystallization of the material during short-circuit shock currents has been carried out. An original method has been developed for calculating the magnitude of the pulse current, which initiates the welding of contacts, which does not require preliminary experimental measurements.
Numerical simulation of heating of the vicinity of contact spots of closed copper high-current contacts by short-circuit currents of various shapes is carried out. The relationship between the parameters of thermal and mechanical fields when heated to temperatures exceeding the recrystallization temperature of the material is established. The dynamics of changes in the sizes of elastic and plastic deformations and their localization is shown. It is revealed in which cases the results of heating the contact surroundings may differ significantly with the flow of thermally equivalent currents.
Current passing through electrical contacts causes additional heat release due to the presence of a contact resistance. Heat release in contacts may be considerable. In high-current contacts of high-voltage electrical equipment, the problem of overheating gets worse when fault short-circuit currents pass through the contacts. The maximum permissible level of these currents is limited by heating contact areas to their melting point. Welds due to melting of contacts lead to their failure as a rule. A way of considerably raising maximum permissible short-circuit currents has been suggested. Its idea is impulsive preheating of contacts to a temperature higher than the recrystallization temperature of the contact material. The efficiency of this approach has been confirmed experimentally. Numerical simulation of impulsive heating has been conducted. The results have helped us elaborate recommendations for selecting parameters of a train of current pulses that, acting on a contact, may greatly improve its stability against short-circuit currents.
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