ABB Selective main circuit breakers S750 series Function

Function

STOTZ selective main circuit breakers operate voltage

independent. They do not require auxiliary energy for swit

ching the device on or off or for their protection functions.

A straight forward design ensures the reliable protection

function. The functional elements consist of proven electro

mechanical components specifically designed for these

requirements.

For overload tripping, a thermostatic bimetal is used,

as in the case of a standard circuit-breaker.

And also as for circuit-breakers, it is necessary to separate

main contacts quickly by using a short-circuit “hammer trip”

solenoid to ensure effective short-circuit limitation. When the

downstream protective device has tripped because of a short

circuit, the contact tips reclose again. This occurs without

auxiliary energy through a simple spring-type system.

If a short circuit occurs between the S 750 and the down

stream mcb, another bimetal release enables the short-time

delay tripping. Both the selective release and the overload

release trip the mechanism and ensure that contact tips

remain in the open position to comply with isolation require ments.

The current is limited and the arc is quenched as in the case

of circuit-breakers.

The underlying switching principle enables a special selectivity

behaviour: current-limiting selectivity. When a short circuit

occurs, the S 750 supports the downstream mcb and also

limits the energy that has an impact on the installation and –

subsequently – on the network of the supplier. The selectivity

behaviour of the S 750 offers major advantages compared to

fuse-based technologies.