Different BusBar Schemes in Electrical Substations

Selection of right Busbar Scheme is the most Important components of Electrical Substation, It is responsible for efficient and reliable flow of power and transmitting and distributing electricity from generation plants to consumers. Busbars are the metallic conductors that used as the central connection points within these substations. The arrangement of busbars, known as a busbar scheme. It is also important for functionality, flexibility, and overall performance of Electrical Substation.

Following are the common Busbar schemes used in Electrical Sub-station

1. Single Busbar Scheme:

The simplest and most economical busbar scheme is the single busbar arrangement. It consists of a single busbar to which all incoming and outgoing feeders are connected. While this scheme is cost-effective, it has the lowest level of redundancy, as a fault on the busbar can disrupt power supply to all connected feeders.

Single Busbar Scheme
Single Busbar Scheme
AdvantagesDisadvantagesRemarks
1. Low cost1. Fault of bus or any circuit breaker results in shut-down of entire substation.1. Used for distribution substation upto 33kv.
2. Simple to Operate2. Difficult to do any maintenance.2. Not used for large substation.
3. Simple Protection3. Bus can not be extended without completely de-energizing substations. 4. Can be used only where loads can be interrupted or have other supply arrangements.3. Sectionalizing increases flexibility.
Advantages and Disadvantages of Single Busbar Scheme

2. Main and Transfer Bus Scheme:

For increased redundancy, the main and transfer bus scheme utilizes two busbars – a main bus and a transfer bus. The main bus is normally energized, while the transfer bus remains de-energized. In the event of a fault on the main bus, the feeders can be quickly transferred to the transfer bus, minimizing the outage duration.

Main and Transfer Bus Scheme
Main and Transfer Bus Scheme
AdvantagesDisadvantagesRemarks
1. Low initial & ultimate cost.1. Requires one extra breaker coupler.1. Used for 132kv substations where cost of duplicate bus bar system is not justified.
2. Any breaker can be taken out of service for maintenance.2. Switching is somewhat complex when maintaining a breaker.
3. Protentail devices may be used on the main bus.3. Fault of bus or any circuit breaker results in shutdown of entire substation.3. Sectionalizing increases flexibility.
Advantages and Disadvantages of Main and Transfer Bus Scheme

3. Double Main Bus Scheme:

The double Main bus scheme offers the highest level of redundancy among common busbar schemes. It employs two busbars and two circuit breakers for each incoming and outgoing feeder. This redundancy ensures continued power supply even if a circuit breaker fails.

Double Main Bus Scheme
Double Main Bus Scheme
AdvantagesDisadvantagesRemarks
1. High flexibility1. Extra bus-coupler circuit breaker necessary.1. Most widely used for 66kv, 132kv,220kv and important 11kv, 6.6kv, 3.3kv substations.
2. Half of the feeders connected to each bus.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 coupler failure takes entire substation out of service.
Advantages and Disadvantages of Double Main Bus Scheme

4. Double Main with By-pass Isolator

This bus arrangement provide the facility of a double bus arrangement & a main and transfer bus arrangement.The bus to which the transfer bus isolator is connected can be used as a transfer bus also. During the time a circuit is under bypass, the bus coupler will act as the breaker for the bypass circuit.

Double Main with By-pass Isolator
Double Main with By-pass Isolator
AdvantagesDisadvantagesRemarks
1. High flexibility1. Extra bus-coupler circuit breaker necessary.1. Most widely used for 66kv, 132kv,220kv and important 11kv, 6.6kv, 3.3kv substations.
2. Half of the feeders connected to each bus.
3. Either main bus can be taken out of service at any time for maintenance.
2. Bus protection scheme may cause loss of substation when it operates.
3. High exposure to bus fault.
5. Bus coupler failure takes entire substation out of service.
Advantages and Disadvantages of Double Main with By-pass Isolator

5. Double Main with Transfer Bus

•Since separates transfer bus is available there will be no need of transferring the load from one bus to the other bus unlike in a double main cum transfer bus arrangement.

•Other feature are similar to the one described in double bus with by-pass isolators scheme.

double main & Transfer bus
Double main & Transfer bus
AdvantagesDisadvantagesRemarks
1. Most flexible in operation.
2.Highly reliable
3.Breaker failure on bus side breaker removes only one circuit, 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.
1. High cost due to three buses.1. Preferred by some utilities for 400kv and 220kv important substations.
Advantages and Disadvantages of Double Main with Transfer Bus

6. Ring Main Scheme

As long the mesh is closed, load has two sources of supply and any circuit breaker can be taken out of service without affecting the supply. Extension of mesh station is almost impossible. No bus bar protection required.

Ring Main Bus Scheme
Ring Main Bus Scheme
AdvantagesDisadvantagesRemarks
1. Busbars gave some operational flexibility.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. These VT’s may be required in all cases for synchronizing live line or voltage indication.
4. Breaker failure during fault on one circuit causes loss of additional circuit because of breaker failure.
1. Most widely used for very large power stations having large no. of incoming and outgoing lines and high power transfer.
Advantages and Disadvantages of Ring Main Scheme

Choosing the Right Busbar Scheme

The selection of the most appropriate busbar scheme for a particular substation depends on several factors:

  • Substation Size and Complexity: Larger and more complex substations typically require more sophisticated busbar schemes to handle higher power flows and ensure reliability.
  • Reliability Requirements: Critical substations demand higher levels of redundancy, necessitating busbar schemes like double breaker bus or mesh bus systems.
  • Cost Considerations: Simpler busbar schemes like single busbar or single busbar with bus sectionalizer offer lower initial costs, while more complex schemes like mesh bus systems involve higher upfront investments.
  • Maintenance Needs: Busbar schemes should be designed to facilitate maintenance activities without compromising power supply.
  • Future Expansion: The busbar scheme should accommodate potential future expansions, such as additional feeders or transformers.

Conclusion

Busbar schemes are the backbone of electrical substations, enabling the efficient and reliable transfer of power. By carefully considering the specific needs and constraints of a substation, engineers can select the most suitable busbar scheme to ensure a safe, reliable, and cost-effective power supply.

Leave a Comment