Bipolar HVDC transmission system study between +- 600 kV and +- 1200 kV: insulation studies. Final report

The insulation strengths for line and station insulators tested with various switching surges in the presence of dc voltage bias are described. This is part of a larger research effort to pinpoint technical problem areas in overhead line design and operation at voltages of +-600 kV to +-1200 kV. The results reported can be used to determine conductor-to-tower clearances, length of the insulator column supporting a station bus, and clearances between buses. In testing station buses it was observed that the presence of the second bus, which is connected to ground or is under a negative bias voltage, affects the level of voltage needed to produce a breakdown across the insulator column supporting the first bus. Bus height above ground also affects the breakdown voltage across the insulator column and between buses. In order to assure that all bus-to-ground breakdowns terminate on the lower part of the insulator column and not to the ground plane, a proper coordination between insulator column length and bus height above ground should be maintained. Because of the many parameters affecting the breakdown voltage of air gaps, and the preliminary nature of this research investigation, the results obtained should be considered ''typical'' and should notmore » be used for final specification of air insulating clearances. When testing with mixed voltages, the breakdown voltage decreased for the conductor-to-tower arrangement as the impulse component was increased. On the other hand, the flashover voltage increased for the bus-to-bus arrangement with an increasing impulse component. These apparent inconsistencies were not expected from the limited amount of existing data. No reasonable explanation was developed. Power supply requirements for dc insulator contamination tests have also been investigated. Separate reports contain the results of this work.« less