Pulsed X-ray induced partial discharge diagnostics for routine testing of solid GIS insulators

Detection of small (<; 2mm) voids in solid dielectric high voltage insulators using partial discharge (PD) measurement demands not only a sufficiently high electric field but also the availability of a start electron for the PD to initiate. The latter problem leads to long waiting times for void PD to initiate, far exceeding typical IEC test intervals (typically 60 seconds), thus making 100 % pre-screening economically infeasible. However, by using radiation to ionize the gas within the void and create start electrons, the test interval can be reduced to 60 seconds without risking small voids being missed. Using this method, known as Pulsed Xray Induced Partial Discharge (PXIPD), a test stand for routine testing of insulators up to 420 kV has been developed and put into commercial operation, with more than 20,000 GIS insulators being tested to date. Trials using insulators with known defects prove the effectiveness and reliability of the system to find voids- with the result that failures in factory tests due to voids were reduced by over 60 % compared to before. The short test cycle time plus knowing which insulators actually contain voids has led to more efficient GIS testing and immediate feedback for the insulator production process.