Partial Discharge Monitoring of Power Transformers by UHF Sensors

The reliability of electrical energy networks depends on both, the quality and the reliability of its electrical equipment, e.g. power transformers. Local failures inside their insulation can lead to breakdowns and hence to high outage and penalty costs. Usually, power transformers are tested on partial discharge (PD) activity before commissioning. UHF PD monitoring can be used to prevent these events during service. Continuous monitoring exceeds the benefits of singular diagnostic measurements. Diagnostic PD measurements can provide snapshot information but no trend information. Also, temporary measurements can cause misleading interpretations due to the volatile nature of PD as measurements performed during low PD activity do not prove the general absence of PD. These drawbacks can be avoided by using continuous PD monitoring. In the first part, this contribution presents two different types of ultra-high frequency (UHF) sensors for PD measurement and their installation at power transformers including an UHF PD monitoring system. The second part is about a use case providing three years of UHF PD monitoring data of a power transformer, where the PD data is correlated with the transformer’s load, temperature and the dissolved gas analysis.