Description: The switching equipment of power substations is made on electromechanical drives (sometimes manual), the duration of the signal passing from the moment of signal supply and the direct response of contacts can take several periods, due to the inertia of mechanical processes. It is impossible to obtain identical electromechanical systems for each phase. Therefore, the moment of switching on, both in relation to the voltage sinusoid, and in relation to the phases is random, which provokes significant current surges, which in a number of cases are perceived as a short circuit and equipment malfunction. Using modern transistor assemblies I J B T makes it possible to create switching equipment for a fixed time,, now the term control commutation is used. Transient processes when triggering switches occur as they are switched on and off. Switching overvoltages can be minimized by using soft switching methods. The periodic component when switched on can be substantially weakened if the circuit of the supply circuits occurs near the maximum voltage, or eliminated altogether, at several times turning on the same load (memory element used). When unlocking a consumer with a low power factor there is a risk of repeated breakdowns of the contacts, in order to eliminate the contact of the contacts should occur far enough from the zero value of the current and until the moment of transition through zero and the arcing of the arc, the distance between the contacts should be sufficient and corre-spond to a significant strength of the gap between the contacts. In some cases, with the arbitrary switching of an unloaded trans-former, there are current jets comparable to short-circuit currents, which provokes a false alarm of relay protection. To elimi-nate this phenomenon, “memory” is used for phase values of currents and the calculation of residual magnetism in them at the transformer's center, which allows it to choose a time moment that minimizes the transitional aperiodic process when re-switching. In the article the method of determination in automatic mode of the switching moment is offered depending on the size of the load, its nature and the history of the switching off of the transformer. Together, these parameters allow you to find the instant of each phase's activation without initiating the transient process.
Keywords: load parameters, transformer, short circuit, harmonious signal.
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