TRANSIENT ANALYSIS OF ACTIVE-CAPACITIVE CIRCUITS WHEN CAPACITORS ARE CONNECTED IN SERIES

Abstract

Active-capacitive and inductive-capacitive circuits with series connection of capacitors are widely used in the electric power industry to compensate for reactive power. In traction power supply systems for railways electrified with alternating current, compensation units perform two tasks: under heavy load, they maintain a given railway throughput, and under low load, they reduce power losses in the traction network. Therefore, the installation of compensation in the traction network must be at least two-stage, i.e. have two reactive power values and, accordingly, two capacitance values. The value of reactive power in such installations is regulated in steps by switching individual sections of capacitors, which are connected in series. When switching capacitors in series, previously unknown specific transients can occur. They cause significant overvoltages on the capacitors. It is shown that in some cases the calculation of transient processes in active-capacitive circuits with capacitors connected in series using the well-known classical method gives results that differ from the actual values. The purpose of the article is to provide a previously unknown theoretical basis for calculating transient processes in electrical circuits containing series-connected capacitors using the example of active-capacitive DC circuits. The studies carried out are of practical importance, since in modern electrical installations, thyristor switches are used as switching equipment, in which the shunting of one capacitor in the compensating installation occurs at the maximum voltage on the operating capacitor. In this case, overvoltages exceeding the assumed values ​​are possible, in the limit up to double the amplitude value of the supply voltage. A theoretical substantiation of this phenomenon is given by the example of the analysis of the transient process in an active-capacitive circuit with two consecutively connected capacitors.