Location of PD sources in power transformers by UHF and acoustic measurements

The paper presents the experience of unconventional methods for partial discharge (PD) measurement to detect and localise PD sources in power transformers. The UHF PD measurement method is usable as stand-alone measurement and as a supporting measurement for off- and on-line PD detection. The sensitivity of UHF PD measurements is sufficient and is normally not affected by external disturbances. Especially in noisy surrounding it might be a very helpful method to support other PD measurement techniques for example dissolved gas analysis and acoustic location of PD. Propagation time of UHF signals can be used for geometrical PD location. The accuracy seems to be adequate to determine the phase limb where the PD is located. Additionally, different measurable UHF amplitudes support an estimation of the PD location. However, since transformers rarely possess more than three oil valves for installation of UHF probes, an additional acoustic measurement is usually required for location. Using the knowledge gained from the UHF location, acoustic sensors can be placed near to the PD source at the transformer tank. The paper explains first the fundamentals of PD measurements and PD source location and presents two case studies.