Post-Arc Current in High Voltage SF6 Circuit-Breakers When Breaking at up to 63 kZ

There is little literature available dealing with the post-arc current in high voltage circuit-breakers breaking in SF6. Or at least, little providing curves either of the current in the breaker or of the voltage across its terminals. This article is intended to contribute to a better understanding of the postarc conditions during the interruption of short-circuit currents between 40 and 63 kA. These currents although high, are nevertheless common in high voltage systems. Les Renardieres Power Test Laboratory (LEP) has developed an original method using a measurement shunt protected by a pyrotechnic device. Particular attention has been given to the resolution of the measurement and to minimizing at source the capacitive component superimposed on the useful signal. An example is given in Figure 1 of a test at 40 kA. The stray capacitance value is 50 pF only, and the post-arc current level is 0.5 A. Other tests, performed at current values up to 63 kA, gave post-arc current levels up to 2 A. The interest of these trickly measurements is in coming closer to the tendency of international standard IEC 56 to increase the constraints during periods when there is a fear of thermal failure of the circuit-breaker. Interpretation of the experimental results by the generalized Mayr model: 1/g.dg/dt = (U.I/P - 1)/¿ where: U = arc voltage I = arc current P = Po. gß: cooling power ¿ = ¿o.