Search

Partial discharge (PD) in gas insulated switchgear (GIS) has been studied extensively under AC voltage or transient voltage applied alone. However, the transient voltage in an actual system is superimposed on the AC operating voltage, which has rarely been studied. In this paper, the effect of AC and switching impulse superimposed voltage on PD characteristics was studied in SF6 gas. A test platform of generating superimposed voltage with controllable phase was used to study free particle and floating potential defect models. When the AC voltage was 90 and 110% of PD inception voltage (PDIV), the standard switching impulse with amplitude of about twice the PDIV was superimposed on different phases of the AC voltage. When the AC voltage is below the PDIV, results show that PDs of free particle defect model can be initiated when switching impulse is superimposed on 45 and 90° of AC. The PDs in the subsequent cycles of AC reignited into a self-sustaining discharge. For the floating potential defect, PDs have a marked difference duration, which is initiated by switching impulse in different phase. However, there is no change in PDs in each model when the AC voltage is above the PDIV. [ABSTRACT FROM AUTHOR]

Recent studies suggest that fluoronitriles compound Novec 4710 possesses a dielectric strength two times higher than that of SF6, while with a low global warming potential of only 2400. Mixed with CO2 buffer gas, the Novec 4710 mixtures offer excellent dielectric properties and the possibility to be used as an eco-friendly alternative to SF6 for medium voltage switchgears. This paper focuses on the comparative study of the breakdown strength and partial discharge (PD) characteristics between the fluoronitrile/CO2 mixtures and SF6 under AC voltages. Breakdown tests are conducted under different electrode configurations, i.e., planeplane, sphere-plane, rod-plane, and needle-plane, at different pressures and electrode gaps. In the uniform field, equivalent dielectric strength to SF6 at 100 kPa can be reached by a mixture containing 15% fluoronitrile at identical total pressure; while in non-uniform and highly non-uniform fields, SF6 exhibits higher dielectric strength than 20% mixture. The PD analysis suggests that SF6 has much more PDs with lower magnitude and the 20% fluoronitrile/CO2 mixture has less PDs but with higher magnitude. Due to the different PD characteristics, the corona stabilization effect may be responsible for the higher breakdown strength of SF6 under highly non-uniform field. [ABSTRACT FROM AUTHOR]