Optimal Conditions for Controlled Switching of a Three-Phase Shunt Reactor
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Vol. 54, No. 3, September, 2020
OPTIMAL CONDITIONS FOR CONTROLLED SWITCHING OF A THREE-PHASE SHUNT REACTOR M. I. Aleksandrova,1 V. A. Naumov,2 V. I. Antonov,2 and N. G. Ivanov2 Translated from Élektricheskie Stantsii, No. 4, April 2020, pp. 41 – 47.
The switching of shunt reactors in an electrical network is in many cases accompanied by reignition of the arc in the circuit breaker and the occurrence of dangerous overvoltage in the network. To limit such overvoltage, controlled-switching devices are used to switch off the reactor in the optimal phase of the current. To select the optimal switching conditions, the switching processes are analyzed, taking into account the intuitively clear difference between the switching conditions for three-phase and single-phase shunt reactors due to the electrical and/or magnetic coupling between the phase windings. The proposed method of analysis is universal for all types of three-phase shunt reactors due to the use of a universal four-legged star equivalent circuit. The reactor phases are switched off, synchronized against the phase A voltage curve, in the sequence A ® C ® B to minimize the total switching time. Keywords: controlled switching; three-phase shunt reactor.
current zero) and (ii) reignition of the arc in the circuit breaker [3]. To analyze overvoltage, we will use the circuit in Fig. 1. The reactor is represented by inductance LR and capacitance CR, which includes the interturn capacitance and the capacitance of the overhead or cable line section between the circuit breaker and the reactor. The electric system is modeled by an emf source u(t) = U sin(ùt + ø), leakage inductance LS, and capacitance CS. The inductance LS and capacitance CS connected in parallel to the contacts are the parameters of the circuit breaker. The wires connecting the reactor and the circuit breaker are represented by the inductance LB. In reality, the electric system, connecting wires, and reactor have some ohmic resistance (RS, RB, and RR) causing the damping of transients. However, it is very low and can be neglected when considering the switching processes for a shunt reactor. High-voltage circuit-breakers are intended to interrupt high short-circuit currents; therefore, it takes them a short time to interrupt the relatively low working currents of the
Controlled switching of shunt reactors is used to reduce the probability of occurrence of critical overvoltage in the network [1, 2]. The overvoltage induced by switching can lead to damage of the insulation of the reactor and to unjustified wear of elements of the circuit breaker. The excessive wear of reactor circuit breakers is confirmed statistically: the number of failures of reactor circuit breakers is an order of magnitude higher than that of circuit breakers for power transmission lines and transformers [3]. Controlled-switching devices are set to switch off a shunt reactor in the optimal phase of current. The optimal conditions for switching the phases of a three-phase reactor should be selected taking into account design feat
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