Only seven moving parts are used

For many years, circuit breakers have used energy stored in springs, charged either manually or using motors, to perform the opening and closing operations. This requires complex latching mechanisms and hundreds of moving parts.

Now a vacuum circuit breaker has been developed by ABB Control for use in industrial and utility power networks, with only seven moving parts, known as VM1. The hundreds of moving parts of a conventional breaker are replaced by an electronically controlled magnetic actuator.

The actuator consists of two permanent magnets located between ‘close’ and ‘open’ coils, and an armature that moves in between.

During normal operation, the permanent magnets hold the armature in a stable ‘closed’, or ‘on’ position. The ‘open’ coil is energised if the breaker is tripped, or the ‘0’ button on the front panel is pushed. A magnetomotive force of 12,500ampere-turns then overcomes the permanent-magnet field, pulling the armature to the ‘open’ position. The coil is de-energised, and the armature is held in position by the permanent magnets, without the need for mechanical interlocking.

The magnetic actuation is bi-directional: pushing the ‘1’ button actuates the second, ‘close’ coil that pulls the armature in the opposite direction back to the stable ‘on’ position.

The breaker contains a capacitor that stores sufficient energy to power the ‘open-close-open’ auto-reclosing sequence required by IEC standards in the event of failure of auxiliary power, and as a further backup, the breaker can be operated with an emergency handle.

No maintenance over a lifetime of 100,000 operations is needed (triple the lifetime of traditional circuit breaker designs, says ABB), and the breaker’s electronic control unit performs monitoring of switching functions and can indicate any fault locally and remotely.

A 12-page technical brochure describing the VM1 breaker is available from the company on request.

ABB Control Tel: 01203 368500