Types of Bus Bar Arrangements - Its Diagrams, advantages and Disadvantages

November 12, 2021

Common outdoor bus bar arrangements are given below:

1. Single bus bar

2. Single bus bar system with sectionalization

3. Double bus bar with single circuit Breaker

4. Double bus bar with two circuit breakers

5. Breakers and a half with two main buses

6. Main and transfer bus bar

7. Double bus bar with bypass isolator

8. Ring bus

1. Single Bus Bar Arrangement :

The single bus bar arrangement has the simplest design and is generally used in small outdoor substations (primary distribution level) having relatively few incoming and outgoing lines and feeders.

It consists of a single bus bar and all the incoming and outgoing lines are connected to the same bus bar as shown in Fig.

Incoming lines are connected to the bus bar through isolators and circuit breakers.

Outgoing lines are connected through the isolator, circuit breaker, and step-down transformer from the busbar. Each circuit is protected by its own circuit breaker and each circuit breaker is flanked by two isolators.

The major drawback of this system is that, if the fault occurs on any section of the bus bar, the entire bus bar is to be de-energized for carrying out the repair work so this results in loss of continuity of service of all feeders and lines.

Similarly, periodical maintenance work on the bus bars can also be carried out by disconnecting the whole supply.

The equipment connections are very simple, and hence, the system is very convenient to operate. This arrangement is not popular for voltages above 33 kV. The indoor 11 kV substations often use a single bus bar arrangement.

Merits:

1. Each of the outgoing circuits requires a single circuit breaker. So, this type of arrangement is the cheapest one.

2. The relaying system is simple.

3. The maintenance cost is low.

4. The bus bar potential can be used for the line relays,

Demerits:

1. Maintenance without interruption of supply is not possible.

2. Expansion of the substation without shutdown is not possible.

2. Single bus bar system with Sectionalization :

The sectionalization of the bus bar ensures continuity of supply on the other feeders, during the time of maintenance or repair of one side of the bus bar. The whole of the supply need not be shut down.

The number of sections of a bus bar is usually 2 or 3. Sectionalizing of the single bus is as shown in Fig.

No. of sectionalization is limited by the short circuit current to be handled. Another advantage of sectionalization is that the circuit breakers of low breaking capacity can be used on the sections as compared to the previous case.

In the case of duplicate feeders, they are connected to different sections of the bus bar so that in the event of a fault on one of the bus bar sections, the feeders connected to it are immediately transferred to the healthy bus bar section and the faulty section is isolated.

The two sections of the bus are connected through a section circuit-breaker and two isolators.

Sectionalizing of the single bus improves reliability. Provision of bypass isolators between the bus bar and circuit isolators allows circuit breaker maintenance without loss of that circuit or section.

Advantages :

1. The operation of this system is simple as in the case of the single bus bar.

2. The maintenance cost of this system is comparable with the single bus bar.

3. For maintenance or repair of the bus bar, only one-half of the bus bar is required

4. to be de-energized. So complete shut down of the bus bar is avoided.

5. It is possible to utilize the bus bar potential for line relays.

Disadvantages :

1. In the case of a fault on the bus bar, one-half of the section will be switched off.

2. For regular maintenance also one of the bus bars is required to be de-energized.

3. For maintaining or repairing a circuit breaker, it is required to be isolated from the bus bar.

3. Double bus bar with Single Breaker :

This system is shown in Fig. It consists of two identical bus bars, one is the main bus bar and another is a spare bus bar.

Each bus bar has the capacity to take up the entire substation load.

Each load may be fed from the either bus bar. The infeed and load circuits can be further divided into two separate groups based on operational considerations (maintenance or repair).

Any bus bar may be taken out for maintenance and cleaning of insulators. With the help of a bus coupler, the incoming and/or outgoing lines are connected to any bus bar through an isolator and circuit breaker.

This system is adopted when the voltage is greater than 33 kV. This arrangement does not permit breaker maintenance without causing an interruption in supply.

Advantages :

1. Permits some flexibility with two operating buses.

2. Any main bus may be isolated for maintenance.

3. The circuit can be transferred readily from one bus to another by using bus-coupler and bus-selector disconnect switches.

Disadvantages :

1. One extra breaker is required for the bus coupler.

2. Three switches are required per circuit.

3. High exposure to bus faults.

4. If the bus coupler fails, the entire substation runs out of service.

4. Double Bus bar with Two Circuit Breakers :

Fig. shows the schematic diagram of a double bus bar arrangement with two breakers per circuit.

This is a simple and flexible arrangement.

.

It is expensive and hence is rarely used. When it is used, it is used in large generating stations which require a high-security connection.

It provides the best maintenance facilities for maintenance to be carried out on the circuit breakers.

Thus, when one circuit breaker is opened for maintenance or repair works, the load can be transferred to the other circuit breaker very easily. Between the main buses are two breakers and one circuit.

This arrangement allows for any breaker to be removed from service without interruption to service to its circuit.

A fault on either of the main buses will cause no circuit disruption. A breaker failure will result in the loss of one circuit. The scheme provides a double feed to each circuit.

Thus, it gives very high reliability and operational flexibility. However, the scheme involves a high cost of having two circuit breakers per circuit.

Advantages :

1. Two circuit breakers in each circuit.

2. Has the flexibility to connect the feeder circuits to any bus.

3. For service maintenance, any breaker can be taken out.

4. High reliability.

Disadvantages :

1. More expensive.

3. If circuits are not connected to both buses, the bus bars lose half the circuits for breaker failure and interrupt supplies.

5. Breakers and a half with Two Main Buses :

The schematic diagram of this arrangement is shown in Fig.

This method is an improved version of a double bus bar with two circuit breakers and uses a lesser number of circuit breakers.

In this method, one spare circuit breaker is provided for every two circuits. Both the

buses are normally energized. Between the buses, are three circuit breakers and two circuits.

This arrangement allows for breaker maintenance without interruption of service. A fault on either bus will cause no circuit outage.

A breaker failure results in the loss of two circuits if a common breaker fails and only one circuit if an outside breaker fails.

Fewer breakers are needed for the same flexibility as in the double-breaker system

Advantages :

1. This system is more economical as compared to a double-bus double-breaker arrangement.

2. A fault in a breaker or in a bus will not interrupt the supply.

3. The addition of circuits to the system is possible.

4. High reliability

5. Any main bus can be taken out of service at any time for maintenance.

Disadvantages :

breaker per circuit.

1. The relaying becomes more complicated as compared to that in a single bus arrangement

2. The maintenance cost is higher.

6. Main and Transfer Bus bar :

The schematic diagram of this commonly used arrangement is shown in Fig.

This arrangement is an alternative to the double bus bar scheme.

It consists of two independent buses, one of which is normally energized. Under normal conditions, all circuits are tied to the main bus.

The transfer bus is used to provide service through the transfer bus tie-breaker (bus coupler).

When it becomes necessary to remove a breaker from service only one breaker at a time can be removed from service and the transfer breaker takes its place when it is out of service.

In a substation, to work on a bus bar it is often necessary to remove it from service.

This is possible only by transferring the load to the other bus bar. This is not possible in this scheme. Hence the absence of this facility to remove any bus bar from service is the only drawback.

Advantages :

1. It ensures supply in case of a bus fault. In case of any fault in a bus, the circuit can be transferred to the transfer bus.

2. It is easy to connect the circuit from any bus.

3. The maintenance cost of the substation decreased.

4. The bus potential can be used for relays.

5. Ease of expansion.

Disadvantages :

1. Requires one extra breaker for the bus tie.

2. Switching is somewhat complicated while maintaining a breaker.

3. Failure of bus or any circuit breaker results in shut down of entire substation.

7. Double Bus bar with Bypass Isolator :

This is a commonly used arrangement also known as sectionalized double bus bar arrangement and is shown in Fig.

This is a combination of a double bus and a main and transfers bus scheme.

Any of the bus bars can act as the main bus and another bus is used as the transfer bus.

The advantage of this method is that any circuit breaker or any busbar can be taken out for service without affecting the supply.

In substations, it is frequently necessary to take the bus bar or the circuit breaker out of service for maintenance or repair. So this scheme is recommended one both because it is simple and economical.

8. Ring Bus :

This is an extension of the sectionalized bus bar arrangement. By using two bus couplers as shown in Fig. the ends of the bus bars are returned upon themselves to form the ring.