Simulation of Power Transformer Winding Sections Provided with Metal Oxide Surge Absorber Blocks with Faults in Portion of Sections

Recent investigations by few researchers have shown that very fast transient voltage behavior of power transformer winding sections can be improved by providing suitable metal oxide surge absorber (MOA) blocks across sections of the windings. However, it is to be ascertained whether it is possible to identify the fault in the event of occurrence of faults in such type of transformer winding sections. The present investigations have been aimed to analyze and identify the parameters that may change as a result of occurrence of fault in sections of transformer winding for appearance of step voltage wave, 1.2/50 microseconds wave shape full and chopped impulse voltages at line terminal even when these sections are provided with MOA protection blocks. Transformer windings with α value in the range of 6 to 18 have been analyzed. Results of studies carried out to identify presence of faults in winding sections are reported in this paper. These investigations have shown that there is no appreciable change in voltage waveforms even when faults to the extent of 5% of winding length occur in any of the winding sections. Further investigations have indicated that there are changes in waveform of current flowing through transformer winding neutral line when 5% of total winding length faults are present in any one section. These changes are not large in magnitude and are observed to occur at 50 microsecond or 100 microsecond instants on the neutral current waveform.