Influence of DC Component Time Constants on Asymmetrical Fault Interruption of 126 kV SF₆ Circuit Breakers

Recently, the time constant of the DC component of short-circuit current exceeds the standard time constant of the circuit breakers (CBs) significantly in high voltage power systems. This may cause severe economic losses due to interrupting faults. Some studies have shown that the increase of the DC component will lead to a decrease in the interrupting capacity of the CBs. Current zero-zone parameters such as G ₋₂₀₀ (arc conductance 200 ns before current zero), G ₋₅₀₀ , and U _peak (peak value of arc voltage) can be applied to evaluate the interrupting characteristics of CBs. However, the effects of the DC component of short-circuit current on the zero-zone parameters and the interrupting properties have rarely been studied. Therefore, the objective of this paper is to obtain the effects of the DC component on zero-zone parameters of a 126 kV SF6 CB to evaluate its interrupting capacity. The interrupting characteristics of a 126 kV SF6 CB under different DC component time constants such as 45, 75, and 120 ms through the T100a type tests were studied. KEMA current zero-zone measuring system was used to measure the arc current and arc voltage in the zero-zones of the arc. The results show that, under the same arcing time, as the DC component time constant rises, the G -200 and G ₋₅₀₀ increase, the U _peak decreases, and the interruption becomes more difficult. Therefore, a method to evaluate the interrupting capacity of the circuit breaker by the critical value G _max or U _lim is proposed. During the arcing period, If G ₋₂₀₀ ≤ G _max or U _peak ≥ U _lim , the interrupting is successful, or else the interrupting fails. For the tested 126 kV SF6 CB, G _max is approximately 10 mS and U _lim is 800 V.