Abslrod-This paper describes a method which determines the operating instants of the circuit breaker for controlled switching of shunt reactors independent of the network configuration, in order to reduce overvoltages and inrush currents. Some other previous papers offered the favorable instants for both isolated and directly earthed neutral case, but not for the earthed neutral through a reactor. The proposed method in this paper is based on two facts. First, the instant of a maximum voltage between contacts of the circuit hreaker(CB) is the optimum point for closing to minimize the inrush current. And secondly, both the minimum arcing time of the CB and the current interruption instant of each poles should he considered as the reference for the opening instant. The performance of the proposed method was verified by the results of simulation studies using the electromagnetic transients program(EMTP). The behaviors of CB treated in the simulation involve the rate of decay of dielectric strength between contacts and the scatter of the operating time. Especially, the results of EMTP show that the closing and opening instants of the second one among the three poles shift continuously with the ratio of the impedance of a shunt reactor to that of the neutral reactor in the range of 30 phase angle, respectively. And also the maximum scatter of the CB dosing time to ensure the inrush current of less than a certain level can he provided.Index Ierms-circuit breaker, controlled switching, inrush current, optimum instant, reignition, shunt reactor. 0-7803-7525-4/02/$17.00 Q 2002 IEEE.

This paper presents the pwformane prediction technique of a disconnecting switch in case of short circuit current conduction The thermal characteristics caused by the applied force to the contacts and contact resistance are analyzed by solving a coupled electrical-mechanical-thermal problem Extra high voltage @HV) disconnecting switch (DS)consists of electrical contacts and mechanical parts which actuate the contacts. When the short circuit condition occurs, large current flows through the electrical contacts and this causes amount of Joule heating. If the temperature rise due to the Joule heating is higher than the melting point of the contact material, then the contacts become melting.This paper presents the calculation of the DS performance according to the applied f m and the Joule energy using a couplcd clcctricd-mcchanicd-thmal analysis. Thc prcscntcd analysis technique is verified through the test results. IL MECHANICAL ANALYSIS OF THE ~~ECHANICAL PARTSFirst, the force distribution at the interface between the contacts is calculated using a mechanical analysis. Next the heat W e r analysis is conducted. The flowchart of t h~s analysis is shown Fig. 1. Analpis of the force diatributim 3 I Calculation of the contact resistance with respect to the force I Calculation of the temperature rise I Vcrificatim of thc analysis through thc ternpeatun tile tent Fig. 1. Flowchart of the analysisThe structure of DS for an analysis is shown in Fig. 2 (a). Fig. 2 (b) shows the force distribution at each blade of the moving contacts. IIL CALCULATION OF THE CONTACT RESISTANCE To cd~ulale Ihe w n k l resislmcx wilh respect lo lhe applied force, the calculation method is developed and the contact resistance is measured using a rnicroahm meter. Fig. 3 shows the measurement system of a contact resistance and the comparison of calculations and measured results. (a) m u l u u e n t system @) c o m p~o n of contact resistance Fig. 3. Comparison of contact resistance with respect to the applied force.

No abstract