Quenching Principle Of The Vacuum Interrupter; Interlocks/Protection Against Maloperation - ABB VD4 Instruction Manual

4.4.5

Quenching principle of the vacuum interrupter

Due to the extremely low static interrupter chamber pressure
of 10 to 10 mbar, only a relatively small contact gap is re-
-4 -8
quired to achieve a high dielectric strength. The arc is extin-
guished on one of the first natural current zeros.
Due to the small contact gap and the high conductivity of the
metal vapour plasma, the arc drop voltage, and additionally,
due to the short arcing time, the associated arc energy, are
extremely low, which has advantageous effects on the life of
the contacts and thus on that of the vacuum interrupters.
4.5 Interlocks/protection against maloperation for the
withdrawable circuit-breaker part
A series of interlocks are provided to prevent dangerous
situations and any maloperation. The interlocks of the panel
system ZS and/or the mounting frame, which are normally
effective, are as follows (concerning the circuit-breaker):
- The withdrawable part can only be moved from the test/
disconnected position into the service position (and back)
with the circuit-breaker open and the earthing switch open
(that means that the breaker must opened before)
- The circuit-breaker can only be closed when the withdra-
wable part is precisely in the defined test position or ser-
vice position (mechanical inter lock, with additional electrical
interlock for circuit-breakers with electrical releases).
- The circuit-breaker can only be opened manually in the
service or test position when no control voltage is applied,
and cannot be closed (electromechanical interlock).
- Connection and disconnection of the control wiring plug
connector (8.1) is only in the test/disconnected position
possible.
- The earthing switch can only be closed when the with-
drawable part is in the test/disconnected position or the
removed position (mechanical interlock).
- The withdrawable part cannot be moved from the test/
disconnected position into the service position when the
earthing switch is closed (mechanical interlock).
- Details of any additional interlocks, e.g. in connection
with a blocking magnet on the withdrawable part and/or
earthing switch operating mechanism, can be found in the
order documents for each individual case (see also section
8.5.6).
Instruction manual 534/01 | VD4 Vacuum-circuit-breaker 23