TYPES OF BUS BAR SYSTEM

TYPES OF BUS BAR SYSTEM

1 Single Busbar System

Single busbar system is as shown below in figure 

Single Busbar System

a. Merits

1. Low Cost

2. Simple to Operate

3. Simple Protection

b. Demerits

1. Fault of bus or any circuit breaker results in shut down of entire substation.

2. Difficult to do any maintenance.

3. Bus cannot be extended without completely deenergizing substations.

c. Remarks

1. Used for distribution substations up to 33kV.

2. Not used for large substations.

3. Sectionalizing increases flexibility.

2 Main & Transfer Bus bar System

Main & Transfer Bus is as shown below in figure 

a. Merits

1. Low initial & ultimate cost

2. Any breaker can be taken out of service for maintenance.

3. Potential devices may be used on the main bus.

b. Demerits

1. Requires one extra breaker coupler.

2. Switching is somewhat complex when maintaining a breaker.

3. Fault of bus or any circuit breaker results in shutdown of entire substation.

c. Remarks

1. Used for 110kV substations where cost of duplicate bus bar system is not justified. 

3 Double Bus bar Single Breaker system

Double Bus Bar with Double Breaker is as shown below in figure 

a. Merits

1. High flexibility

2. Half of the feeders connected to each bus

b. Demerits

1. Extra bus-coupler circuit breaker necessary.

2. Bus protection scheme may cause loss of substation when it operates.

3. High exposure to bus fault.

4. Line breaker failure takes all circuits connected to the bus out of service.

5. Bus couplers failure takes entire substation out of service.      

c. Remarks

Most widely used for 66kV, 132kv, 220kV and important 11kv, 6.6kV, 3.3kV

Substations.

4 Double Bus bar with Double breaker System

 Double Bus Bar with Double breaker system is as shown below in figure 

a. Merits

1. Each has two associated breakers

2. Has flexibility in permitting feeder circuits to be connected to any bus

3. Any breaker can be taken out of service for maintenance.

4. High reliability

b. Demerits

1. Most expensive

2. Would lose half of the circuits for breaker fault if circuits are not connected to both the buses.

c. Remarks

1. Not used for usual EHV substations due to high cost.

2. Used only for very important, high power, EHV substations.

5 Double Main Bus & Transfer Busbar System

Double main bus & transfer bus system is as shown below in figure

a. Merits

1. Most flexible in operation

2. Highly reliable

3. Breaker failure on bus side breaker removes only one ckt. From service

4. All switching done with breakers

5. Simple operation, no isolator switching required

6. Either main bus can be taken out of service at any time for maintenance.

7. Bus fault does not remove any feeder from the service

b. Demerits

1. High cost due to three buses

c. Remarks

1. Preferred by some utilities for 400kV and 220kV important substations.

6 ONE & HALF BREAKER SCHEME

a. Merits

1. Flexible operation for breaker maintenance.

2. Any breaker can be removed from maintenance without interruption of load.

3. Requires 1 1/2 breaker per feeder.

4. Each circuit fed by two breakers.

5. All switching by breaker.

6. Selective tripping.

b. Demerits

1. One and half breakers per circuit, hence higher cost

2. Any breaker can be removed from maintenance without interruption of load.

c. Remarks

1. Used for 400kV & 220kV substations.

2. Preferred.

7 RING OR MESH ARRANGEMENT

a.      Merits

Bus bars gave some operational flexibility.

b.      Demerits

1. If fault occurs during bus maintenance, ring gets separated into two sections.

2. Auto-reclosing and protection complex.

3. Requires VT’s on all circuits because there is no definite voltage reference point.

4. Breaker failure during fault on one circuit causes loss of additional circuit because of breaker failure.

These VT’s may be required in all cases for synchronizing live line or voltage indication

c.       Remarks

 Most widely used for very large power stations having large no. of incoming and outgoing lines and high power transfer.

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