On line PD measurements and diagnosis on power transformers

On line partial discharge (PD) measurements provide information on the dielectric integrity of the high voltage insulation of oil insulated power transformers during service. These PD measurements are performed using a broadband antenna on an oil valve and UHF detection of PD signals. The sensitivity of this new detection technique is high and immunity for electromagnetic (EM) interference and corona discharges in air outside the transformer is very good. Dielectric faults can be detected in this way in an early stage of development and are classified in four categories. Automatic pattern recognition techniques of phase resolved pulse sequence (PRPS) data are very useful in risk assessment of dielectric faults.