FORCE FUNCTION AS AN EFFECTIVE TOOL FOR BUILDING PROTECTION OF ELECTRICAL NETWORKS AND ELECTRIC MOTORS

At present, different parameters are also used to construct various protections, such as the effective value of the current, the Joule integral, the inverse sequence current, the reactive and active power. This makes it difficult to combine all the protections of power grids in one device. In order to concentrate all types of protections in one device, namely, in a switch, it is proposed to use a new parameter. Such a parameter is the sum of the squares of the instantaneous values of the currents of the three phases. The dependence of the change with time of the specified sum of the squares of the currents is denoted as the force function. The article substantiates the possibility of analyzing the nature of the power function for the construction of virtually all types of protection of electric networks, as well as for the thermal protection of electric motors. When implementing thermal protection of electric motors, the analysis of the force function allows you to use the windings themselves as sensors for the temperature of the windings of electric motors. As for the protection of electrical networks, the analysis of the force function in transient mode allows you to reliably identify the starting current of electric motors. Interlocking the tripping of protection against the specified current increases the reliability of protection of networks against short-circuit currents, since this implements protection against remote short-circuit current and redundancy of the failure of the feeder circuit breaker by the input one. Steady-state force function analysis allows you to implement protection against neutral wire breakage and the resulting overvoltages. To build these protections, only information from current sensors is sufficient, so they can be combined with current protections in the circuit breaker trip. This makes it possible to abandon the use of other protection devices and thereby significantly reduce both the size and the cost of the entire power grid protection system.