ABB eVM1 Installation And Service Instructions Manual page 14

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Fig. 8
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6.3. Basic structure of the withdrawable circuit-breaker
The withdrawable truck (4) (fig. 8), either manual or motorised, consists of a steel sheet structure
with wheels (3), on which the circuit-breaker with the relative auxiliary components, the isolating
contacts (2) for electrical connection with the switchgear and the multi-pole connector (1) for
connection of the circuit-breaker auxiliary circuits are installed.
After having been racked into the switchgear and hooked up, the withdrawable circuit-breaker
can take up the following positions: racked-out, isolated for test (with connector inserted) and
racked-in. The racked-in circuit-breaker is automatically earthed by means of the truck wheels.
The magnetic actuator of the circuit-breaker and the relative controls and indicators, are accessi-
ble from the front.
Withdrawable circuit-breakers of the same type and characteristics are interchangeable. How-
ever, the code of the connector prevents incorrect combinations between the circuit-breaker and
switchgear.
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7. Operation
7.1. Operation of the circuit-breaker drive
7.1.1. Magnetic actuator
The magnetic actuator used in the eVM1 circuit-breakers generates the run required to operate
the moving contacts of the interrupters and integrates all the functions of a traditional operating
mechanism.
The magnetic actuator is a bistable system where end-of-run positions of the moving armature
are reached by means of magnetic fields generated by two coils (one for closing and one for
opening).
The moving armature is kept in position by permanent magnets.
The circuit-breaker operations are obtained by means of energisation of the opening or closing
coil respectively. The magnetic field generated by each coil attracts the moving armature and
thereby moves it from one of the latching points of the permanent magnets to the other.
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