A Novel Surface Charge Accumulation Behavior on Downsized Spacers in C4F7N/CO2 Mixture

Charge accumulation becomes an important bottleneck to restrain the development of DC transmission system. Since SF
6
is a gas with strong greenhouse effect. C
4
F
7
N/CO
2
mixture, as a potential substitute, has been widely concerned by researchers. Some researchers have focused on the surface charge accumulation characteristics of C
4
F
7
N/CO
2
mixture, but the reported results do not coincide well. Therefore, the surface charge accumulation of C
4
F
7
N/CO
2
mixture is detailly and deeply investigated in this paper. Active electrostatic probes and surface charge inversion algorithms are used to calculate the surface charge distribution in C
4
F
7
N/CO
2
mixture under 0.1 MPa in this paper. It is found that there is a homo-charge injecting area near HV electrode in C
4
F
7
N/CO
2
mixture. However, a hetero-charge spot is observed. In addition, hetero-charges are also deposited on middle area between two electrodes and the area closed to GND electrode. As hetero-charges are mainly deposited on spacer surface by gas conduction in this electrode-spacer configuration, it is concluded that the gas ionization and gas conduction in C
4
F
7
N/CO
2
mixture are enhanced. Compared with SF6, more charges are deposited on spacer surface in C
4
F
7
N/CO
2
mixture. Thus, C
4
F
7
N/CO
2
mixture needs certain treatment for practical GIL applications. The results can provide a feasible reference for practical industrial applications of
C4
F
7
N/CO
2
mixture.