Structurally, the vacuum circuit-breaker series VM represents a metal housing on which three poles are fixed. The housing with the operating mechanism is made of structural steel sheet and powder coated. Inside the housing, there are three electromagnetic actuators with a magnetic latch, the connection circuits to which are brought to external terminals covered in a casing. The main element of each pole is a vacuum interrupter installed inside a pole of a polymer material.
The vacuum interrupter has a silicone coating to provide additional protection against surface breakdown in-service conditions of high humidity and dust. The special geometry of the VI contacts creates an axial magnetic field in the entire area of the arc. Due to the AMF effect, a compressed-type arc takes the form of a diffuse arc uniformly distributed over the contact surface at any value of the breaking current. Thus, the thermal load on the contacts is reduced, thus reducing their point overheating and subsequent erosion.
The structure of the pole is stack-mounted, made of high-strength polymer material, which provides high dielectric characteristics and pole strength. The vacuum interrupter is located inside the pole. The upper contact terminal of the pole is connected to the fixed contact of the vacuum interrupter. The lower contact terminal of the pole is connected through a flexible connection to a movable contact of the vacuum interrupter. The movable contact in return is mechanically connected to an electromagnetic drive and synchronized by means of cross-shaft.
The operating mechanism of circuit-breaker is electromagnetic with a magnetic actuator. The closing operation is carried out by discharging the capacitor banks located in the control module CVM and passing a large current impulse through the coils of operating mechanism. The opening operation is also carried out by discharging the capacitor banks and passing a reverse current impulse. The circuit-breaker kept in the closed position by permanent magnets. A distinctive aspect of the magnetic actuator is its high performance of keeping the circuit-breaker closed. The holding force of the magnetic latch does not weaken over time and the circuit-breaker can firmly be in the closed position for an unlimited period of time if a loss of control voltage supply occurs. When the circuit breaker is manually opened by means of the manual trip pushbutton, the opening shaft is rotated and the arc is disconnected from the stator through a system of levers. In this case, the closed magnetic circuit formed by the magnetic latch breaks, the holding force of the magnetic latch weakens and the opening spring opens the circuit-breaker.
