Fluoronitrile (FN) – CO2, Fluroroketone (FK) – CO2 mixtures present interesting properties such as: high dielectric strength, non-flammability, and low Global Warming Potential and show thus high interest to replace SF6 in high voltage equipment, in particular in Gas Insulated Switchgear. However, all developed monitoring systems, in particular partial discharge (PD) measurement, is specified for equipment filled with SF6, the question is quickly raised to know if the existing systems can be adapted for the new gases. To respond to this question, understanding of PD phenomena is mandatory to evaluate the performance of PD measurement systems in function of gas composition. Despite the fact that broad simulations on PD, i.e. corona discharge pulse have been performed in air, N2, few studies involved SF6 and none of them addressed the FN – CO2, FK-CO2 mixtures.
2D axisymmetric model is used to simulate PD pulse in point-plane configuration. Three charge carriers model including electrons, positive and negative ions are used to describe the initialization and the development of PD pulse in SF6, in FN-CO2 mixtures and in FK-CO2 mixtures. The simulation was performed for different gases in negative DC polarity at room temperature and at SF6 equivalent dielectric strength. The swarm parameters of different gases are also included.
The PD current pulses of different gases are simulated. The time evolution of electric field and of charge carriers are also analyzed. Both investigated gases showed short pulse time (subnanosecond) and very short pulse rise time. Finally, a comparison on pulse rise time was also made between SF6 and the studied SF6 alternative gases.
This study showed the difference in term of PD current pulse in function of gas and it might lead to a difference in term of performance between different PD measurement systems, especially the UHF system which is based on very high frequency component of PD pulse.
T. Vu-Cong, C. Toigo, G. Ortiz, M. Dalstein, F. Jacquier and A. Girodet
Presented at CEIDP