A model for fast switching transients in power systems: the near zone concept

The author presents a simple time-domain model which makes it possible to predict the order of magnitude of the highest di/dt values generated by closing switches in electrical power systems. The model is based on traveling-wave analysis. It is demonstrated that two different approaches must be applied, according to whether (a) the closing time, T/sub s/, of the switch is faster than twice the traveling time to the first reflection point or (b) T/sub s/ is much slower. Under condition (b) the well-known quasistationary approach di/dt/sub max/=U/sub 0//L can be used, where U/sub 0/ is the switched voltage and L is the self-inductance of the line between the stray capacitances located to the left and the right of the switching device. Under condition (a) a new formula must be applied: di/dt/sub max/ approximately=2 U/sub 0//ZT/sub s/, where Z is the line impedance of the line in which the switching device is installed and T/sub s/ is the time during which the voltage across the switch collapses from U/sub 0/ to zero. Experimental results are given from both fast and slow closing switches. >