Partial discharge localization on dry-type transformers

In this paper an electrical partial discharge (PD) localization technique for a dry type power transformer is presented. The method has been tested in the laboratory on real transformer coil as well as on a transformer in a test bay. Calibration signal is injected through a plate sensor placed along the winding on the surface of the transformer coil in different positions, thus PD signals can be measured at both coil terminal sites using digitizer. Measured PD signal during test can be then evaluate and compared with calculated transfer function. The described technique enables not only localization of the PD source also determination of the apparent charge. This evaluation can be more accurate than conventional PD measurements by use of quadruple and coupling capacitor calibration and can be used during manufacturing process as well as diagnostic in field.