Evaluation of the UHF method based on the investigation of a partial discharge case in post insulators

The ultra-high frequency (UHF) method is treated as an effective means for partial discharge (PD) detection in field monitoring in smart substations due to its outstanding noise rejection capacity and satisfying sensitivity to typical insulation defects. However, abundant evidence is still lacked to prove its universality. In this paper, the PD test of an actually manufactured post insulator with potential defects is carried out using several kinds of PD detection methods. Nevertheless, the UHF signal is not able to be detected with the coupler, while PD current pulses with large magnitude are already observed within the coupling device connected to the test object. The balanced measuring system is used to verify the origin of the detected pulses, and the limitation of the UHF method on detecting PD of this type is proved. Attempt are made to locate the defect on the test object by measuring the distribution of the temperature on the surface of the insulator. All the results and data analysis show the specific characteristics of the defect compared with those well investigated before, and demonstrates its value to be further researched in the future.