Measurements of Insulation Parameter C3 on Installed, Faulted Line Bushings

The measuring test lead is an important part of high voltage bushings with capacitor-type insulation. The test lead is connected to the outer capacitor lining of the frame, dividing the input capacitance into two: C1 (pipe - last outer lining of the frame) and C3 (last outer lining of the frame - flange). For diagnostics of the in service condition of the input, it is sufficient to measure the insulation resistance R3, the capacitance C1 and the dissipation factor tgδl. The measured and corrected value tgδ1 is compared with the data of the acceptance test report. In the delivery condition, the obtained value tgδl should be close to the nameplate value. A significant difference of more than 3% between the capacitance value C1 and the value specified in the acceptance test report may indicate damage during transportation or installation, so that the input must not be put into operation. The value of the capacitance C3 depends on how the input is integrated. The article deals with the method of measuring the insulation parameter C3 at the installed, faulted line bushings. The confirmation of the normal contact of the outer lining of the hulls of the already installed line bushings is obtained. The conclusion contains conclusions on the results of measurements and recommendations to the equipment manufacturers to make changes in the operating manuals of the bushings.