SWITCHES

A switch is used in an electric circuit as a device for making or breaking the electric circuit. switches may be classified as 

1. Oil switches: These are usually use  voltage heavy current circuits,

2. Air switches : These are further classified into

(a) Air-break switches

(d) Isolators

(o) Disconnected switches

BUS- BAR ARRANGEMENTS

Bus-bars are arranged to achieve

(a)dequate operating flexibility

(b) sufficient reliability

(c) minimum cost.

The cost can be minimised by reducing the number of  circuit breakers to a minimum but complication

 of  the protective gear are increased.  Some bus-bar arrangements.  

(1) Single bus-bar arrangement. In this arrangement a set of bus-bars is used for complete power station and to this bus-bar are connected all generators, transformers and feeders through circuit breakers and isolating switches. Such a bus-bar arrangement is cheaper in initial as well as in maintenance cost  and simple in operation and relaying.

(2) Single bus- bar system with sectionalization . With increased number of generators and outgoing

feeders connected to the bus-bars, it becomes essential to provide arrangement for sectionalizing the bus-bars so that a fault on any one section of the bus-bars may not cause a complete shutdown. ‘This is achieved by providing a circuit breaker and isolating switches between the sections.

(3) Ring bus-bar system. In this arrangement each feeder is supplied from two paths, so that in case of failure of a section, supply is not interrupted.  

(4) Duplicate bus-bars system. Duplicate bus-bar system with sectionalization is usually adopted in order to maintain continuity of supply. Such a system consists of two-bus-bar couplers and sectionalizing breaker converts the duplicate bus- bars into a ring system having greater flexibility.