Influence of fire on DC corona current.

Abstract

Corona discharge is one of the undesirable consequences associated with HVDC transmission. Corona discharges are the visible result of the partial electrical breakdown of ionised air in the non-uniform fields surrounding energised conductors. Corona produces undesirable effects such as corona loss, audible noise, radio interference, ozone and nitric oxides. The performance of high voltage transmission lines is presumably affected by the occurrence of wild forest fires beneath these lines. Fire under transmission line generates heat and increases the temperature of the air surrounding the conductors. The increase in temperature due to the presence of fire decreases the breakdown strength of air insulation that can result on flashovers and interruption of power supply. This thesis presents the experimental results of the investigation conducted on a short test line using a small corona cage. The results of the corona current magnitudes obtained from the investigation on the dominant frequencies of the corona current pulses under the influence of high-temperature gas fire are presented. The propagation of the dominant frequency signals is studied in isolation of other sources of high frequency signals within controlled laboratory conditions. The corona current signature technique, which is the combination of the magnitudes of dominant frequencies and the repetition rate of the corona pulses, was introduced to evaluate the impact of fire on the corona current. Results obtained from the dc corona current investigation are then compared with those obtained from ac corona current investigation and presented.