Field electron emission current in vacuum interrupters after large inrush current

Field electron emission (FEE) current in the open(ing) gap of nine different designs of 36 kV vacuum interrupters under standard recovery voltage conditions was measured during full-power back-to-back capacitive switching. During closing operation, 20 kA inrush current (@ 4250 Hz) was applied. The measurement system is described, able to measure FEE current with a threshold of 30 μA but that also has to withstand a full capacitor bank discharge current of up to 40 kA after re-strike. It was concluded that in spite of the wide variety of measured FEE current magnitude (up to several mA) there is no direct relationship between magnitude of FEE current and probability of breakdown. Longer arc duration of the normal load current reduces the FEE current level after load current interruption.