Online PD Monitoring System With Microstrip Antenna for Rotating Machines

摘要

Online partial discharge (PD) monitoring for high voltage rotating machine is one of useful means from the view point of condition-based maintenance. Up to now, various on-line PD monitoring systems are developed and applied: for instance, using slot RTD wiring, stator slot coupler (SSC) or inductive sensors. An online PD monitoring system using microstrip antenna (patch antenna) has been developed for high voltage rotating machines such as induction motors or synchronous generators. This system consists of microstrip antennas, PD detectors and a personal computer. Microstrip antenna is a small and flat antenna which detects electromagnetically radiated PD signals from stator or rotor windings. The frequency of electromagnetic wave detected with the antenna is normally ultra high frequency (UHF) range and depends on the structure of the antenna. It was designed to detect electromagnetic wave of 1.8 GHz around which background noise level is relatively low. Because of its small and flat shape, it is easily installed inside or outside of the machine housing without interfering with machine design, manufacturing or operation. It also means that microstrip antennas do not cause a failure of stator winding because they are completely insulated from high voltage stator windings. This online PD monitoring system was applied to large turbine generators with rated voltage ranging from 13.5 to 27 kV, and it was confirmed to be sensitive enough to PD signals generated from generator windings. In case of online PD monitoring using nearfield antennas, these antennas can detect PD signals very close to a PD source in the windings. On the other hand, the microstrip antenna designed for PD detection can detect attenuated PD signals sensitively beyond near field. This means that the microstrip antenna can cover large area of PD activities in the windings.