Studies on impulse behaviour of a transformer winding with simulated faults by analogue modelling

The paper highlights some critical observations made in the course of investigations on surge performance of a transformer winding by analogue modelling. The studies cover winding responses to both full and chopped standard lightning impulses where time-to-chop was varied over a wide range to find the maximum stresses across winding discs. Three specific zones along the winding were selected for studies. These were the line-end and earth-end sections each spanning about 6% of the entire winding length, while the midwinding disc was chosen to represent the midwinding section. Two types of faults were simulated: series faults both permanent and voltage-dependent; and parallel faults through resistance with preset faulting levels. Winding responses to faults under impressed impulses were observed and scanned using both neutral-current (Hagenguth) and tank-current methods of fault detection. Important observations are corroborated by oscillograms of winding responses. The results suggest and confirm appropriate methods of fault detection on fault occurrence in the specified sections along the winding