ABB eVM1 Installation And Service Instructions Manual page 16

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• Undervoltage function: controls circuit-breaker opening if the applied voltage drops below the
tolerance limit (established by the Standards).
To prevent the function intervening when the voltage drops below the specified level (e.g. in the
case of motor starting), it is possible to set a trip time.
The undervoltage function is normally disabled. In this case, it is possible to open and close the
circuit-breaker without applying voltage to the input of the function.
• Monitoring function of the actuator closing and opening coil. This function serves to monitor the
continuity of the closing and opening coils of the magnetic actuator to detect any faults.
If a fault is detected, the luminous "COILS OK" signal on front of the circuit-breaker turns off and
the "READY/NOT READY" signalling contacts are commutated.
• Additional safety opening command function. The second input of the control module for the
opening function is designed so that an opening command is carried out directly even in the case
of a fault in the microprocessor.
7.1.5. Truck locking magnet
The locking magnet is inserted in withdrawable circuit-breakers with manual movement and pre-
vents traverse of the withdrawable truck when there is no power supply voltage. It is also linked to
the interlock between circuit-breaker closed and truck: it guarantees that even in a situation with
main welded contacts, the circuit-breaker cannot be isolated.
7.2. Principle of extinction of the vacuum interrupter
Given the relatively low static pressure of the interruption chamber (between 10
relatively limited distance between the contacts is required to obtain high dielectric strength. The
vacuum arc is extinguished on the first passage of the current through natural zero.
Considering the limited distance between the contacts, the high conductivity of the plasma of
metallic vapours, the drop in voltage of the arc and, moreover, the short arcing time, the energy
associated with the arc is extremely limited, therefore producing benefits for the useful life of the
contacts obtained and, consequently, for the useful life of the vacuum interrupters.
Magnetic latching in end-of-run posi-
tion.
Fig. 9
Magnetic latching and action of the
magnetic field of a coil.
-4 and 10 -8 hPa), a
Moving armature in opposing position
and magnetic end-of-run latching.