Electrical substation (one and half breaker scheme)

Double Bus One and Half Breaker Scheme is mostly adopted in high voltage electrical substations (220 KV or 400KV, 700 KV). Due to many advantages of this arrangement like high selectivity, reliability and less cost as compare to other bus arrangements for power stations or switch yards

1. Electrical Substation; One and Half Breaker Scheme In electrical substation or Switchyard various Bus Bar arrangements are used as it is a common point for various incoming and out going circuits. The most used scheme for high voltage high power switch yard such as a 220 KV or 400 KV is " Double Bus half breaker arrangement"  or more commonly know as " half breaker arrangement"  due to many advantages of this scheme. Schematic diagram of this arrangement is shown 

2. Electrical Substation; One and Half Breaker Scheme It consist of two main buses (Main Bus-I and Main Bus-II), Three bays in each Diagonal Each bay consist two isolators or disconnect switch at both end along with earth switchs , a circuit breaker at middle and other auxiliaries like CT, LA etc. Diagonal Bay

3. Electrical Substation; One and Half Breaker Scheme To understand complete process we will see all conditions step by step.

4. Electrical Substation; One and Half Breaker Scheme Case1; Normal working condition All circuit breakers and isolators are in closed condition So the both of incoming lines form generating plant and outgoing lines for transmission system are remain in contact with both the two busses through circuit breakers.

5. Electrical Substation; One and Half Breaker Scheme Case2; Fault on Main Bus-I Sensing elements will sent tripping signal to CB-A of Diagonal 1 and CB-A of Diagonal 2 to get opened and disconnect Main Bus-I form the system Although Main Bus-I got out from the system, the power continues form remaining CBs in to the Mani Bus-II and evacuate to outgoing lines.

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7. Electrical Substation; One and Half Breaker Scheme Case2; Fault on Main Bus-I To isolate the faulty part perfectly form the system, isolators of that part must be opened To check for the fault and to do repair work on faulty bus it must be earthed through earth switches to drain out completely the remaining electrical charge on the bus. During maintenance work on Bus-1 the personals are safely isolated form the remain part of the system.

8. Electrical Substation; One and Half Breaker Scheme Case2; Fault on Main Bus-I After done with the maintenance or repair work then to connect the bus again in to the system first its earthling switches must be open.

9. Electrical Substation; One and Half Breaker Scheme Case2; Fault on Main Bus-I After done with the maintenance or repair work then to connect the bus again in to the system first its earthling switches must be open. Then isolators associated with it must be close first before circuit breakers.

10. Electrical Substation; One and Half Breaker Scheme Case2; Fault on Main Bus-I After done with the maintenance or repair work then to connect the bus again in to the system first its earthling switches must be open. Then isolators associated with it must be close first before circuit breakers. At last the circuit breakers must be closed to compete the process.

11. Electrical Substation; One and Half Breaker Scheme Case3; Fault on any Breaker During normal working if there is a fault on any breaker the remainin g breakers continues power transfer Example; Fault on CB-B of Diagonal 2 maintain continuity through CB-A and CB-C of Diagonal 2. After trouble shooting and repair the faulty Bay can be again put in to the service by following proper switching sequence as followed in the previous case

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