AC Distribution Interview Questions and Answers:

1. What is primary distribution system and what is normal operation voltage of primary distribution ?

Ans. Primary distribution system is that part of the distribution system which operates at voltages such as 3.3, 6.6 or 11 kV. The normal operation voltage of primary distribution is 11 kV.

2. What is usable voltage for secondary distribution ?

Ans. The secondary distribution usable voltage is 415/240 V (415 V for 3-phase loads and 240 V for single-phase loads).

3. Differentiate between open-loop system and ring-loop system.

Ans. In a loop feeder system, two or more radial feeders originating from the same or different secondary substations are laid on different routes of load areas. The arrangement having the ends of two feeders tied together through normally open switching devices is known as open-loop system while the arrangement having the ends of two feeders tied together through normally closed switching devices is called the ring main feeder or the ring-loop.

4. What is interconnected system and where is it employed and why ?

Ans. When the feeder ring main is energized from two or more than two generating stations or substations it is called the interconnected network system. Because of interconnected feeders, power can be supplied to all the distribution transformers even though a part of network may be out of service. Such a system provides better reliability and flexibility and is employed in large metropolitan cities where continuity of supply is the most important.

5. What is radial system of distribution ? What are its advantage and drawbacks ?

Ans. In radial system, the low voltage distributors radiate out from the distribution transformer and run through the areas to be supplied by them. This system is the simplest and the least expensive system. This system generally not used because of the following drawbacks.

• The end of the distributor nearest to the supply end would be heavily loaded.
• The consumers at the farthest end of the distributor would be subjected to serious voltage fluctuations with the variation in load.
• The consumers are dependent on a single distributor so that a fault on the distributor cuts off the supply from all the consumers who are on the side of the fault away from the station.