Impulse dielectric behaviour of dry air in sphere-plane gap

Abstract

The dielectric strength of dry air is lower than that of SF(6), so it is very difficult to use dry air in extra-high-voltage-class gas-insulated equipment. However, due to its environment-friendly property, dry air is expected to be an alternative to SF(6) in low-voltage level gas-insulated equipment. In order to study the possibility of dry air to be applied in equipment in the power distribution system, streamer and breakdown phenomena of dry-air need to be carefully investigated. This study carried out an experimental study of impulse breakdown phenomena of dry air under a quasi-uniform electric field. Results showed that the impulse breakdown voltage of dry air is higher under the positive polarity. Under the gas pressure of >0.4 MPa, the impulse breakdown voltage of minus 50% (V(50%)) of dry air is >150 kV, which satisfies the basic impulse insulation level of the power distribution system equipment. Further, in the quasi-uniform electric field, once streamer discharge appears, it always triggers an electrical breakdown. The development mechanisms for the breakdown of dry air under both positive and negative polarities are well discussed in this paper.

Keywords

• gas insulated switchgear
• discharges (electric)
• electric breakdown
• electric strength
• extra-high-voltage-class gas-insulated equipment
• dry air
• impulse breakdown voltage
• sphere-plane gap
• dielectric strength
• power distribution system
• quasi-uniform electric field
• electrical breakdown