Partial Discharge Diagnostics of High Voltage Instrument Transformers – Case study

This paper presents a complete measurement procedure to detect partial discharge (PD) in instrument transformer under on-site scenario. The objective of this paper is to illustrate how to utilize the commonly available methods to improve the accuracy, reliability and effectiveness of PD diagnostics regarding the high voltage instrument transformers. Three PD measurement methods are used to detect and confirm the defect in the high voltage current transformer (CT) under normal exploitation. In the first step, a directional UHF antenna is used to screen the device under test and to find the possible source of PD signals. In the second step, acoustic sensor is used to confirm the presence of PD in the object pointed in the previous step. These two steps can be performed under normal working conditions of the tested object, as they are completely noninvasive. In the last step, electric method is used to finally confirm the presence of PD and to assess its intensity.