Functions of Different Switching Devices

Source:

Circuit breakers:

Make and break all currents within the scope of their ratings, from small inductive and capacitive load currents up to the full short circuit current, and this under all fault conditions in the power supply system, such as earth faults, phase opposition, and so on.

 

Switches:

Switch currents up to their rated normal current and make on existing short circuits (up to their rated short circuit making current).

 

Disconnectors (isolators):

Used for no-load closing and opening operation. Their function is to isolate downstreamdevices so they can be worked on.

 

Three-position disconnectors:

Combine the functions of disconnecting and earthing in one device. Three-position disconnectors are typical for GIS - Gas insulated switchgear.

 

Switch disconnectors (load break switches):

The combination of a switch and a disconnector, or a switch with isolating distance.

 

Contactors:

Load breaking devices with a limited short circuit making or breaking capacity. They are used for high switching rates.

 

Earthing switches:

To earth isolated circuits.

 

Make-proof earthing switches (earthing switches with making capacity):

Are used for the safe earthing of circuits, even if voltage is present, that is, also in the event that the circuit to be earthed was accidentally not isolated.

 

Surge arresters:

To discharge loads caused by lightning strikes (external overvoltages) or switching operations and earth faults (internal overvoltages). They protect the connected equipment against impermissibly high voltages.

 

Fuses:

Consist of a fuse base and a fuse link. With the fuse base, an isolating distance can be established when the fuse link is pulled out in de-energized condition (like in a disconnector). The fuse link is used for one single breaking of a short circuit current.

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