Online UHF PD Monitoring for Step-up Transformers of Hydropower Plant

As we known, to evaluate and diagnosis the insulation faults of large-size power transformers, partial discharges (PDs) can be detected via ultra high frequency (UHF) technique. In this paper, an UHF PD online monitoring system was developed for large-size step-up transformers. The principle of UHF PD monitoring method was introduced., and the hardware structure and software key techniques in the system were described. In order to achieve the integrated PD monitoring and ensure the accuracy of PD analysis, the operating environments and operating conditions of the transformers have been acquired synchronously. Meanwhile, the correlative analysis of PDs with respect to operating conditions can be performed and the characteristics of PD activities with respect to relevant states can be studied. The association analysis of PDs is performed as follows: (a) periodical PDs caused by power frequency voltage under stable operating conditions, (b) stochastic PDs caused by transient over-voltages under unstable operating conditions. At present, the system has been applied into several large-size step-up transforms and achieved large mount of on-site monitoring results, and the reliability of PD analyzing results is verified by the analysis of the onsite data.