Investigation of Partial Discharge Localization based on Electrical Measurements

The health of power transformer is important for a stable and reliable power supply. Besides, power transformer is a cumbersome and capital-intensive static device, of which the repair or replacement necessitates Iong- term outage. As a consequence, a transformer failure is burdensome for both electricity utilities and end customers. In extreme cases, a power transformer failure can lead to the malfunction of the whole transmission network. Therefore, it is imperative to guarantee the reliable operation of the power transformers. Partial discharge PD is one of typical initiate defects in power transformers. PD in power transformers can deteriorate the insulation, which can eventually turn into a catastrophic failure. IEC standard 60270 prescribes the measurement procedures and evaluation criteria of partial discharge measurement. In IEC 60270, the basic PD quantity is the apparent charge q. It is used to evaluate the severity of partial discharges. However, it has not been used for PD Iocalization, where other methods like acoustic or UHF (Ultra High Frequency) is the priority option. This implies that normally two different measuring procedures should be carried out to determine the presence and the location of PD. However, the measurement of the apparent charge can be useful to localize the source of PD. By analyzing the values of apparent charge measured in the three phases of the transformer, a possible location of the PD source can be estimated. In the investigation described in the following a specific amount of charges was injected to different discs of all three phases and the corresponding outputs were determined at different bushings. Afterwards, representative functions of the windings were established by comparing the detected output charges.