A comparative analysis of performance of well-known methods for conforming distribution of impulsive voltage along regulating winding

On-load tap changer is a crucial component of power transformer since it dynamically performs the adjustment of load voltage to an adequate level, without interrupting its current. That is why its price is relatively high. However, for any designer of power transformer a correct rating of an on-load tap changer is not an easy task and the reason does not lie in any current concern. In fact, main reasons concern about the right BIL-Basic Impulse Insulation to be taken, because during standard test of impulse voltage intense and thus harmful overvoltage can seriously damage tap changer and condemn the whole power transformer. Thus, the aim of this work is to show how efficient most of the commonly used types of regulating windings can be for conforming any impulsive overvoltage. An important result is how significant the influence of the intrinsic and parasitic series capacitance of winding is. However, in some cases the use of varistor can be the most effective measure. On the other hand, even the use of electrostatic shielding for the enhancement of that capacitance cannot give as interesting results as varistor does. Basis of presented analysis includes economic aspects besides results from circuit modeling and computational simulation.