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Interview Question of Bus Bar system of Substation

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1. What do you mean by electrical busbar ? What are the types of busbars used in a substation and how are they supported ? How are long lengths of busbars obtained ?

Ans : Electrical busbar is the collector of electrical energy at one location operating at a constant voltage. The busbars used in a substation are either rigid type or flexible type. Rigid busbars are made up of aluminum alloy tubes of 50 to 250 mm diameter and supported on post insulators with clamps and connected at both ends by strain insulators with clamps and connectors. Flexible busbars are made up of A.C.S.R. conductors and supported at both ends by strain insulators, clamps & connectors. Long length of busbars are obtained either by welding or by clamping adjacent sub-lengths.

2. What is the necessity of busbars ?

Ans : Busbars are necessary for acting as common point when a number of generators or feeders operating at same voltage are to be connected together.

3. What are the different types of busbar arrangements generally used in the system ?

Ans : The different types of busbar arrangements are as following :-
a) Single busbar system in which the generators or incoming feeders outgoing lines and transformers are connected to the busbar, and it is used in small outdoor substation.
b) Single busbar with sectionalisation in which the busbar is sectionalized by means of a circuit breaker with both end isolators and it is used in the large generating station where several units are installed.
c) Duplicate busbar system in which two busbars, a ‘main’ busbar and a ‘spare’ busbar are used for the benefit of maintenance work without interrupting the supply and it is used in the large important substation.
d) Ring busbar arrangement in which all the sectionalized buses are connected in a ring to receive supply from any adjacent section.
e) Mesh busbar arrangement in which the circuit breakers are arranged in the mesh formation by the buses so that the number of circuit breakers needed will be exactly half the feeders to be controlled.
f) One and a half breaker arrangement in which three circuit breakers are needed for controlling two circuits.

4. What are the advantages of duplicate busbar arrangement over single busbar arrangement ?

Ans : The advantages of duplicate busbar arrangement over signal busbar arrangement are as follows :- a) In the case of repair and maintenance work of the main bus of the duplicate busbar arrangement the supply need not be interrupted, as the entire load can be transferred to the spare bus which is not at all possible in single busbar arrangement.
b) In the case of any fault occurred on the duplicate busbar arrangement, the continuity of supply of the circuit can be maintained by transferring it to the other busbar which is not at all possible in single busbar arrangement.
c) The testing of feeder circuit breaker can be done by putting them on the spare busbar without disturbing the main busbar which is not possible in the single busbar arrangement.

5. What are the advantages of sectionalisation arrangement of busbars ?

Ans : The advantages are as follows :-
a) Each section of the busbar can be withdrawn from the circuit for maintenance work other remaining active.
b) By introducing current limiting reactor in between sections the fault MVA can be reduced.

6. Where and why is one a half breaker arrangement used ?

Ans : One and a half breaker arrangement is generally used in the extra high voltage system for reducing the cost of circuit breakers.

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