Development of Portable Partial Discharge Monitor for Generator Stator Windings in Hydro Power Stations

摘要

Reducing maintenance cost is very important for electric power utilities in order to have the advantage in competitive power market. Besides the reliability of facilities is required to be kept in certain level. In such situation, it is necessary to know the machine condition surely in order to conduct condition based maintenance (CBM). Generator stator windings in hydro power station are one of the most important parts. Problems of generator stator windings tend to cause prolongation of the repair period and waste power (lost water usable for generation). Detection of partial discharge (PD) is a good method to check the condition of stator windings. Several methods have been proposed to detect the PD. We have developed and use a new portable on-line monitor to measure PD in hydro generators while the units are operating. The best feature of the monitor is installed resistance temperature detectors (RTDs) between top and bottom coils of the slots in a generator stator, can be used. We utilize these RTDs as sensors of PD pulses that occur in the stator windings. The noise removal function, which was the most difficult to develop the portable on-line PD monitor, is performed by a microprocessor in the system. The obtained PD pulses are analyzed and displayed in real time on the screen so that operators can monitor the PD trend. This method has following advantages: -RTDs have been already installed in the stator, additional cost is unnecessary. -Reliability of RTDs has been well proven, so we do not have to worry about the reliability by adding additional sensors. In order to check the performance of the PD monitor, we applied it to several generators in actually operating hydro power stations and it was confirmed the effectiveness of the monitor enough to check the condition. Monitoring the trends of the PD signals gives us good information about the insulation condition of stator windings. We have been using the monitor to measure PD in generator stator windings at all 245 hydro generators for decision of criteria.