Comparison of on-line and off-line PD measuring system for hydro generator stator winding

Partial discharge (PD) is one of the most promising phenomena to utilize in detecting deterioration of high voltage rotating machine insulation. PD test can be performed either when the machine is not operating (off-line) or during normal machine operation (on-line). Off-line PD test is a well-known method to assess the stator winding insulation and on-line PD test has proven to be a successful technique of monitoring stator insulation condition. This study carried out on-line and the off-line PD tests on a hydro-generator using the same PD sensor and measuring instrument and analyzed various PD characteristic parameters. We used the contact-type CC (Ceramic Coupler) sensor for PD tests. To test reliability of this sensor, we analyzed the frequency response characteristic test using S parameter and PD signal characteristic test for the simulated defect winding. Also, we checked the similarity between the test results of diagnostic system (PDMS-HG) was installed on the test hydro generator and of the on-line and off-line PD tests.