Dynamic control of contact pressure in distribution electric contacts with use alloys with effect of memory form
DOI:
https://doi.org/10.31548/energiya2018.02.005Abstract
The greatest influence on the state of collapsible contacts is created by factors of contact pressure and temperature. Reduction of contact pressure leads to increased transient resistance, contact temperature, increase in the rate of oxidation of contacting surfaces. Reducing the contact pressure twice causes an initial increase in the transient resistance by 2.5-3 times. At the same time, an increase in the rate of growth of oxide films leads to a further increase in transient resistance and a decrease in the period of normal operation of contacts 3-4 times. The theoretical analysis has shown that the passage of short-circuit currents through collapsible contact systems, for example, aluminum tires leads to their increased heating (temperature + 200 ... + 250 °C) and excess (above the nominal level) of mechanical stress in bolts - 220 ... 270 MPa, tires - 80 ... 120 MPa. The specified level of excessive mechanical stress creates residual deformations in bolts and connection joints.
Existing range of technical methods and means of reducing the growth of the main contact pressure with increasing temperature does not allow to provide effective control of contact pressure in collapsible contacts. Application of the most effective means - steel plate springs according to GOST3057-90 allows to reduce the growth of mechanical stress in contacts when passing currents short circuit only to the level of 30%.
Studies of electro thermal and thermo-mechanical processes in the contacts have established that the stabilization of contact pressure provides stabilization of the resistance of collecting current lines of the RC and only partially reduces the growth rate of oxide films and the resistance of the tunneling effect of the quasimetallic contact of adhesive and reactive films RTP. It is proved that the process of film growth and transition resistance RPER can be slowed down as much as possible by dynamic control of contact pressure, depending on the contact temperature.
It is theoretically proved and experimentally proved that electrothermal, thermo mechanical and electromechanical processes in contact systems of electrical equipment and their modes of operation by their nature coincide with the physical conditions of the occurrence of the phenomenon of EPR in functional alloys.
The method of dynamic control of contact pressure in collapsible contact systems on the basis of the use of properties of functional alloys was substantiated in the paper for the first time by theoretical and experimental research. Application of this method allows to stabilize the pressure within 5% and extend the life of collapsible contacts 3-4 times.
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