Switching the Magnetizing Current of Large 345-kV Transformers with Double-Break Air Switches

The results of a field test of a 345-kV double-break air disconnect switch interrupting magnetizing current of 400-MVA autotransformers are reported. Waveforms of typical currents are shown, and high-speed sequence photos are included to illustrate arcing for opening and closing. Restriking of the arc during opening is charted for two conditions of excitation energy source impedance. Comparisons of the double-break arcing time with that of previous single-break switch tests at similar currents indicate that the double-break switch interrupts with half the arc time. An experimental high-velocity interrupter system with sequence photos showing 4-cycle arcing time for a 6-ampere interruption and a new design concept in the arrangement of the terminal pad and connector hardware for EHV disconnect switches are shown.