ABB’s new VMAX medium voltage vacuum circuit breaker for primary distribution offers safe and cost effective performance with minimal maintenance. Suitable for voltages from 12 to 17.5kV, currents from 630 to 1250A and capable of handling 15,000 operations without maintenance, the VMAX circuit breaker provides reliable protection against electrical faults. VMAX circuit breakers feature an insulating monobloc comprising of three vacuum interrupters. These vacuum interrupters house the contacts and act as interrupting chambers. To ensure that arcs are quickly extinguished, these interrupters contain no ionisable materials.
When a fault occurs, the contacts separate, forming an electric arc made up of melted and vaporised contact material. This arc only survives until the external energy that caused it is cancelled by passing through natural zero.
The spiral geometry of the VMAX’s contacts ensures electrical faults are dealt with quickly and safely. When an arc forms, a radial magnetic field is created in all areas of the arc column. This results in the formation of an electromagnetic force, which forces the arc to rotate rapidly around the contact axis, reducing its strength and minimising thermal stress on the contacts.
By reducing wear caused by thermal stress, the operational life of the contacts is greatly prolonged. Furthermore, with no air present in the vacuum interrupter chambers, oxidation and contamination of the contacts is also prevented.
The design of the chambers also prevents the risk of an arc restriking. The rapid condensation of the metal vapours in a zero current environment enables recovery of maximum dielectric strength between the interrupter contacts within microseconds.
As well as a fixed installation version, VMAX circuit breakers are also available in a withdrawable design for UniGear ZS1 type switchgear, which helps to greatly reduce the amount of downtime required for installation, testing and maintenance. Both types have a front operating mechanism.
As protection against incorrect installation or removal, VMAX circuit breakers incorporate key locks, ensuring that the units can only be worked on by authorised operators. This feature is supported by padlock devices on the switching pushbuttons, which prevent unauthorised tampering. As a further safety feature, the design of the units also prevents the incorrect installation of circuit breakers with the wrong current ratings.
As with other ABB vacuum circuit breakers, the VMAX series features a mechanical operating mechanism, with stored energy, free release and anti-pumping device as standard. These features allow the circuit breakers to open and close independently of the operator. The mechanical operating mechanism is simple to use and is offered with a wide range of accessories that can be quickly and easily installed.
VMAX circuit-breakers are suitable for electrical distribution applications involving control and protection of cables, overhead lines, transformer and distribution substations, motors, transformers, generators and capacitor banks.