A METHOD FOR MONITORING THE THERMAL CONDITION OF A DETACHABLE CONTACT CONNECTION OF A SURGE PROTECTOR

An increase in the resistance of an electrical contact connection in the electrical network of a residential flat causes spot heating or a series of electrical arcs, which often lead to fires. However, this heating is not detected by the usual protective devices implemented in surge protectors and therefore the risk of fires remains. The purpose of the research is to increase the efficiency of protection of plug contacts of the surge protector from excessive overheating by justifying the parameters of the protective device with thermoelectric effect. Scientific novelty consists in determination of its structural scheme, as well as in obtaining quantitative characteristics of its operation. Materials and methods. The object of the research is electric surge protectors. The subject of the research is a schematic solution for protection of a surge protector against overheating of the contact connection, which contributes to the prevention of fires at rated currents. The method of mathematical modelling of conductor heating in the contact connection of the surge protectors, based on the solution of the heat balance equation, as well as methods of analysis and generalisation have been used. To measure the heating temperature of the plates of the disassembled connection of the surge protectors, a group of temperature sensors is installed, the place of installation of which and the setting of the protection operation temperature are determined by experiments. Results. A mathematical model of conductor heating in a contact connection subject to weakening or degradation, which takes into account its transient resistance, load current strength, dimensions of structural heat dissipating elements, is proposed for a surge protector with a rated current of 10 A. The dependence of the contact connection surface temperature on its transient resistance in emergency and normal operation modes has been determined experimentally. The time characteristic of heating of the contact plate of a 5-socket surge protector, as well as the distribution of its heating along the longitudinal coordinate are established. It is shown that the electrical scheme of the surge suppressor protection from a large transient resistance of the contact system includes a thermorelle installed in the middle of the plug socket seats (two on each contact plate), as well as a trigger circuit to fix the damage and an indication system. Conclusion. Due to mechanical weakening of tightness of adhesion of surfaces of current-carrying elements, the increase of resistance of contact connection in 6–8 times in relation to the standard leads to overheating of connection up to 160–250 °С with further appearance of short circuit in the network and fires. The given circuit-technical solution of protection of a surge protector from a mode of overheating of a defective contact connection disconnects the network until the moment when melting or burning of non-metallic components of a plug connection can occur. The established temperature overheating of the contact connection of typical 3- and 5-socket surge protectors with rated current of 10 A in normal operation does not exceed 11°C, therefore the additional protection is based on the thermoelectric method of control (by excess or difference of temperature). The required temperature of triggering of sensors of thermo relay of this protection is 45±5°C at various combinations of load current and resistance of contact connection, which allows to make a tune-up against undesirable starts in normal load modes.