In- situ On-line Acoustic Emission Measurement and Off-line Recovery Voltage Measurement for periodic condition monitoring of oil-filled 220kV transformers- comparison of results

Periodic condition monitoring of Transformers -play a key role right from generating station to the distribution of power-ensuring uninterrupted power supply. Transformers have complex insulation system and assessing condition of the insulation system for defects like partial discharges, hot spots, ingress of moisture due to loosening of gaskets etc., is very essential. Condition monitoring techniques such as off-line and/or on-line are adopted to assess the condition of insulation system. This paper presents the in-situ findings of the periodic condition monitoring of 220kV class transformers in a power generation station in India. Acoustic emission technique which is one of the on-line test tools for periodic condition monitoring and also to study the relative performance by carrying out the test over different years, is used in this paper. Recovery voltage measurement is an off-line test being used to assess the moisture content in the paper-oil insulation system of the transformer. The results obtained with on-line acoustic emission measurements using acoustic emission technique were found to be comparative in terms of their respective magnitude with the results obtained with off-line Recovery Voltage Measurement (RVM) test.