Comparison of Partial Discharge Performance of Identical Generator Transformers in a Thermal Power Station by Acoustic Emission Technique - Case Studies

Generator transformers in thermal power stations are capital intensive and form a vital link between generation and transmission of bulk power to the grid stations of ac power system. Condition assessment of these transformers is very essential and important in order to avoid unforeseen breakdown, thereby causing inconvenience to the end user and financial loss. Insulation system of transformer is very complex and periodic condition assessment for partial discharges in the insulation is very crucial. There are several techniques like off-line and on-line techniques to assess the condition of these transformers for partial discharges. Except the tests on oil, all other tests are off-line and require outage of the transformers, thereby causing disruption of the power supply. Presently, a few on-line techniques have been developed to assess the condition of these transformers. Of several on-line techniques, acoustic emission technique is gaining focus among most of the researchers for monitoring the performance in terms of partial discharges in the insulation of the generator transformers. Acoustic emission technique for detecting partial discharges is being tried as a tool for assessment of the condition of the transformer insulation and also to compare the performance of identical generator transformers. The principle of acoustic emission technique along with in-situ findings of the performance of identical single phase generator transformers of 400kV class for partial discharges, in a thermal power station are discussed in this paper as case studies Some of the observations during the field trials are also discussed.