10.1 Introduction

Switchgear is a term used to refer to combinations of switching devices and their interconnection with associated control, measurement and protection equipment. It allows the interconnection of various parts of the electrical network by means of transformers, overhead lines or cables to allow control of the flow of electricity within that network from power station to customer. Switchgear is also designed to be able to safely interrupt any faults that might occur in any part of the network to protect the network itself, associated equipment and operational personnel. It also provides, by means of disconnectors, facilities for isolating sections of the network and, with the provision of earthing switches, to allow the safe application of devices to ensure that the isolated sections of the network are earthed and made safe for maintenance activities or possible fault repair.

A combination of busbar circuits, circuit-breakers, switches, fuse switches, disconnectors, earthing devices, terminations and associated control and protection equipment is referred to as a 'substation'. A substation may or may not include a means of voltage conversion, i.e. one or more transformers.

The typical electrical network may comprise generators feeding directly into part of the transmission system, and the transmission system itself may have interconnection to other transmission networks. Such systems are used to allow the flow of large amounts of power from the generating stations to the distribution load centres which may be many tens or hundreds of kilometers away.

Distribution of the power from the transmission system...