A switchgear is an integrated assembly of switches, buses fuses and other components used to isolate electrical equipment at an electrical installation, for example, an electrical power sub-station. Switchgear is used to both de-energise equipment to allow work to be done and to clear faults downstream of the switchgear. Switchgear is often housed in a metal cabinet at the installation.
A distinction is made between so called ‘fixed switchgear’ and so called ‘withdrawable switchgear’. In fixed switchgear the main circuit breaker is fastened within the installation by fasteners, for example bolts, and cannot be removed from the installation without using tools to undo the fasteners. In withdrawable switchgear additional constructional features enable the main circuit breaker to be withdrawn from the installation (and put back in) with a minimum usage of tools or with no usage of tools. Accordingly, in a withdrawable switchgear, the main circuit breaker can be removed quickly for maintenance or replacement or to provide easy access to other components in the installation.
Conventional switchgear comprises a number of electrical terminals or poles, typically two or more, each electrically isolated from the other, and comprising an insulating housing containing an electrical contact. The insulating housings may be made of epoxy resin. In one known arrangement, one such terminal has an electrical contact for a bus or power rail and another such terminal has an electrical contact for a cable connection routed to a load. An electrical connection is established between the bus and the load by inserting into each terminal housing a respective one of a pair of electrical contacts of a circuit breaker. In this way, one circuit breaker's contact engages the contact of one of the terminals and the other circuit breaker's contact engages the other terminal's contact so that the electrical path is established between the bus and the load through the breaker. Each terminal's housing is generally conical in shape, with a circular cross section. In air insulated switchgear the terminals must be separated by a certain gap for insulation purposes.
U.S. Pat. No. 3,889,722 describes a plastic insulated switching unit for a multiphase high voltage switchgear. The switching unit comprises an insulating housing defining a cylindrical cavity and fixed ring-shaped contacts at an inside wall of said housing. A drawout switching device comprises a projecting tubular pole, having an operating mechanism. The tubular pole comprises ring-shaped contact pieces mounted on its outside. The switching device is moveable between a fully inserted position and an isolating position. In U.S. Pat. No. 3,889,722 the fixed ring-shaped contacts are each located in a recess formed in the inner surface of the insulating housing.
It is desirable to provide an improved terminal for an electrical switchgear and in particular one that allows for a more compact switchgear.