Mitigation of switching overvoltages in transmission lines via controlled switching

The goal of this work is to present a controlled switching strategy to reduce overvoltages due to transmission line closing and re-closing. Controlled closing and re-closing of transmission lines eliminates the need of pre-insertion resistors, reducing in this way the costs of transmission line circuit breakers. The switching strategy consists on finding a suitable circuit breaker making instant, i. e., the time in which the voltage across the circuit breaker contacts is zero and the time span between the closing instant of the first and the last pole is as small as possible, minimizing in this way, the effect of the electromagnetic coupling between transmission line phases. The method is based on a very simple zero crossing algorithm with constraints and is implemented in the Alternative Transients Program (ATP) using the MODELS language. Data from the North-Northeast Brazilian Power System Grid, planned to be in service by 2009, are used to produce a few case studies. Some line switching events are analyzed: line closing and re-closing taking into account trapped charges and shunt compensation effects. The controlled switching performance is compared to the pre-insertion resistorpsilas method. The simulations attest the efficiency of the method, limiting switching overvoltages to nearly 1.55 per unit for shunt compensated transmission lines. In addition, controlled switching provides an increase of power apparatus life time, improvement on power quality and possibly the elimination of impositions that makes prohibitive some switching operations.