Controlled switching of high voltage shunt reactor

Abstract

This thesis characterized models and investigations into switching transient phenomena related to the shunt reactors and for reactive power control in the transmission system. Reactor banks play an important role in mitigating the voltage rise, otherwise known as Ferranti effect, which is characteristic to long lightly loaded transmission lines having high capacitive charging current. The energizing and de-energizing of the reactor bank introduces high frequency transients that might stress the insulation of the switching equipment leading to equipment failures. The work presents different phenomena associated with reactor bank de-energisation and addresses the issue of circuit breaker application when interrupting low inductive currents from an engineering stand point. The work illustrates a case study simulated in the Alternative Transients Program part of the Electromagnetic Transients Program package (ATP\EMTP) to demonstrate current chopping and re-ignition phenomenon associated with reactor bank switching. Mitigation methods for the aforementioned issues are also evaluated. This work focus on finding the transient overvoltages in case of single and three phase’s system and determine the ideal switching case that gives the lowest overvoltage magnitude at the shunt reactor components. Also in this study, varying opening times of circuit breaker for three-phase connections were used to determine the stress of shunt reactor components. We can stimulate the synchronous switching state of the shunt reactor by variation in the circuit breaker times. First, in case of the single-phase analysis, Laplace transform were used to calculate the transient overvoltages, while ATP simulation for validation were used to compare the acquired results. In order to reproduce the switching operation of shunt reactor, the Alternative Transient Program (ATP/EMTP) was applied. The reason ATP was applied here is because it gives solution in time domain and very helpful in the comparisons with analytical method conducted. On the other hand, in case of the three- phase shunt reactor, the de-energisation of the shunt reactor was used to identify the transient overvoltages for synchronous switching. The first method applied in this study are uncontrolled switching that depend on opening the circuit breaker at one time for all phases, while the second method is controlled switching, in other words, to give the circuit breaker limited time for each phase, the opening time is based on the value of the current across the circuit breaker that allows the lowest transient overvoltage. The final method applied in this work is the surge arrester for the protection and minimize the transient overvoltages.