Preface

Switchgear is a generic term and includes the entire range of switching devices and their combination with associated control, measuring, protecting and regulating equipment. The assemblies of such devices and equipment with associated inter-connections, accessories, enclosures and supporting structures, intended, in principle, for use in connection with the generation, transmission, distribution and conversion of electric energy also form a switchgear.

We all are familiar with low voltage switches and re-wireable fuses in our homes. A switch is used for opening and closing an electric circuit while a fuse is used for over-current and short-circuit protection. Every electric circuit needs a switching device and a protective device. The switching and protective devices have been developed in various forms. Thus switchgear can be taken as a general term covering a wide range of equipment concerned with the switching, protection and control of various electrical equipments.

Similarly, switching and current interrupting devices play a significant role in the modern electrical network, right from generating stations, transmission sub-stations at different voltages, distribution sub-stations and load centres. The switching device here is called a circuit breaker. The circuit breaker, along with associated devices for protection, metering and control regulation, is called a switchgear.

A switchgear has to perform the functions of carrying, making and breaking the normal load current like a switch. In addition, it has to perform the function of clearing the fault current for which sensing devices like current transformers, potential transformers and various types of relays, depending on the application, are employed. There also has to be provision for metering, controlling and data, wherein innumerable devices are used for achieving the switchgear function. Thus a switchgear can include a circuit breaker, current transformers, potential transformers, protective relays, measuring instruments, switches, fuses, MCBs, surge arrestors, isolators and various associated equipments.

Switchgears are necessary at every switching point in the power system for the reasons mentioned above. There are several voltage levels and fault levels between the generating stations and final load points. Hence in the various applications, the requirements of switchgears vary depending on the location, ratings and local requirements. Besides the supply network, switchgear is required in industrial works, industrial projects, domestic and commercial buildings.