Experimental characterization of current chop in 126kV vacuum interrupters

Because of great harmfulness of greenhouse effect, SF₆ gas has to be limited, and it is necessary to develop high voltage vacuum circuit breakers to replace SF₆ circuit breakers. Current chop is a well-known phenomenon for vacuum interrupters and results in high overvoltage. The chopping current depends not only on material parameters and gap parameters, but also on the parameters of the electrical network. In this paper, current chop phenomena of 126 kV single break vacuum interrupters have been researched in an experimental circuit where current is limited either by a resistor or an inductance. In the experiment, contact gap is 20 mm or 30 mm and arcing current is 32 A or 66 A. A serial of experiment has been carried out for two 126kV vacuum interrupters with CuCr₅₅ and CuCrTa contact material. It has been found that the current chop phenomenon shows a significant dependence on contact materials, arc current and the capacitance parallel to the switching gap. The results showed that the chopping current of CuCrTa contact material is lower than that of CuCr55 contact material for 126kV vacuum interrupters.