PD monitoring of power transformers by UHF sensors

Abstract

Electrical energy networks' reliability is driven by both, the quality and the reliability of its electrical equipment, e.g. power transformers. Local failures inside their oil/paper insulation can cause breakdowns and resulting high outage and penalty costs. Power transformers are tested on partial discharge (PD) activity at a factory routine test. Complementary, UHF PD monitoring can be used to prevent these events during service. Therefore, continuous monitoring can be beneficial compared to singular diagnostic measurements: Diagnostic PD measurements provide snapshot information which lacks trend information. Also, temporary measurements can cause misleading interpretations due to the volatile nature of PD, e.g. measurements performed during low PD activity could falsely indicate a general absence of PD. In its first part, this contribution presents two different types of ultra-high frequency (UHF) sensors for PD measurement and explains the installation process at power transformers including an UHF PD monitoring system. The second part provides a use case concerning three years of UHF PD monitoring data of a power transformer. Correlation of PD data with the transformer's load, temperature and the dissolved gas analysis are discussed.