Experience with on-line PD testing on 653 instrument transformers

The traditional method of insulation condition assessment is to perform off-line dissipation factor tests on 653 HV instrument transformers to assess the condition of those units. This paper presents on-line PD testing on the transformers. Acoustic measurements were made to identify PD activity in the instrument transformers. Electrical measurement was used to evaluate the severity of PD activity. The test results identified the medium levels of PD activity in 6 transformers of 653 instrument transformers. DGA analysis was performed in six current transformers removed from service due to a precision issue. The DGA test results of six current transformers were consistent with the on-line PD test results.