Part winding resonance: Demerit of interleaved high-voltage transformer winding

Interleaved transformer winding is a new and promising development in the f ield of design of high-voltage transformer windings. Although the strengths and weaknesses of the interleaved winding concept against surge voltages a re theoretically known, implementation in a practical multiwinding EHV tran sformer may lead to various complications and the winding can show unpredic table behaviour contrary to existing knowledge. A comparative assessment of interleaved transformer winding has been made by EMTP simulation of two id entical multiwinding EHV transformer models having interleaved and noninter leaved conventional disc windings. The observations regarding relative surg e performance of interleaved and noninterleaved windings may throw some lig ht on optimum interleaving of the disc coils in transformer winding. The ta p changer or regulating winding forms a weak point in HV transformers and i s found to be responsible for the majority of failures. Distribution of imp ulse voltage in the regulating or tap-changer winding has also been studied . The results of these observations may be useful in finding suitable expla nations for the failure of tap-changer windings in EHV power transformers.