The LMVP vacuum circuit-breaker is mounted on a steel carriage, having four flanged wheels to facilitate location within the enclosure. A central screw mechanism operated by a removable handle is provided for raising and lowering the circuit-breaker.
A moulded silica-filled epoxy resin housing contains three vacuum interrupters, which are air insulated and separated by integrally moulded phase barriers. Primary thoroughfare bushings are also incorporated in the housing and at their upper end, accommodate self-aligning multi-finger isolating contacts. Guide pins are fitted to the top plate to ensure correct location of the circuit-breaker, and a copper contact provides positive earthing of the unit.
The LMVP vacuum circuit-breaker is interchangeable with the Reyrolle LMT oil circuit-breaker.
The housing has moulded inserts, which provide accurate and simple location of components. The main operating shaft is coupled to the moving contacts of the interrupters through a drive insulator.
Current transfer is through multilaminated sliding contacts and the added contact load in the closed position is provided by disc springs.
Copper-chrome contact material is used in the interrupters to minimise contact erosion. The added contact load spring assembly can be checked visually for allowable erosion with a 0.5mm feeler gauge. If required, allowable erosion can be measured accurately on the moving contact with a vernier calliper.
The interrupters have a typical life expectancy of 20,000 mechanical operations, 10,000 to 20,000 load current operations, and between 30 to 100 fully rated short-circuit operations.
Should interrupter replacement be required, this and resetting are achieved without the need for special tools.
There are three models of circuit breaker available, having ratings of 630/800 Amp, 1250 Amp and 2000/ 2500 Amp. The first model is rated 630 Amp in a 630 Amp enclosure, and 800 Amp in a 1250 Amp enclosure. The 2000/2500 Amp model has paralleled primary thoroughfare bushings and a single interrupter per phase.