Working area:
High voltage research & development

Reference:
Ph.D. project: F. Levring: 'Partial discharge investigations by optical methods and charge measurement' 1989-02-05 and December 1990. Ph.d. dissertation in English, 125 pages.

In order to investigate partial discharges and their deterioration to solid insulation under AC conditions, the photon emission has been measured optically in a cavity of 1 mm height in polymer insulation. This was recorded through time and space and is presented as level curves, i.e. contours. The results confirmed the assumed glow discharge process in rapidly developing discharges.

The charge on the walls inside the cavity has been investigated, partly electrostaticly by non-destructive measurement of projected or apparent charge density, partly by measurement of thermally stimulated current, i.e. conduction current during heating at a constant rate. The electrostatic charge distribution became smoothed by discharges in air, however, it was not influenced in any distinct way by discharges in nitrogen. The thermally stimulated current was mainly uninfluenced by the discharge exposure; regrettably, this method did not clarify the mechanisms of accumulation of charge from the discharges in the insulation.

Further investigations of discharge properties and conditions of deterioration made it a prerequisite to develop an oven for high temperature tests and TSC (thermally stimulated current) tests, an integrating bridge, and other electronics. Some of the equipment was developed in connection with master thesis projects.

Employer: High Voltage Laboratory, Institute of Electric Power Engineering, Technical University of Denmark, Lyngby.

1990