12 January 2011

Electical Objective Questions: Transmission and Disribution ( Set1)

Electrical Objective Questions With Answers:

1) Feeders are designed mainly from the point of view of:
a) Current Carrying Capacity
b) Voltage Drop in it
c) Operating Voltage
d) Operating Frequency

2) Electrical Distributors are designed from the point of view of:
a) Current Carrying Capacity
b) Voltage Drop in it
c) Operating Voltage
d) Operating Frequency

3) 3 phase 4 wire system is commonly used for:
a) primary Distribution
b) Secondary Distribution
c) Primary Transmission
d) Secondary Transmission

 4) Which of the following distribution systems are more economical:
a) DC system
b) Single Phase ac system
c) Three phase 3 wire ac system
d) Three Phase 4 wire ac system


5) In Over head transmission systems, the conductors used are: 
a) Copper Conductors
b) All Aluminium Conductors
c) ACSR conductors
d) Aluminium and Zinc alloy Conductors 

6) Large Industrial Consumers are supplied voltage at:
a) 220kV
b) 11kV
c) 66kV
d) 132kV

7) The Conductors used in high tension over head lines are:
a) Solid
b) Stranded
c) Both a and b

8) Conductors used in high tension transmission lines are stranded because of:
a) Increased Tensile Strength
b) ease in handling
c) Cheap in cost
d) reduced resistivity

Answers:  

(1) a (2) b (3) b (4)
(5) c (6) b (7) b (8) b



Explanation for Objective Questions:
1.  Answer (a). Feeders are the conductors which connect the substations or generating stations to the areas to be fed by these stations. Generally from feeders no tappings is taken to the consumer, so current loading in the feeder remains the same through out the conductors. so feeders are designed based on the current carrying capacity.
2. Answer (b).Distributors are the conductors from which numerous tappings are taken for providing power supply to the consumers. Therefore the current loading on the distributors varies along the length. So distributors are designed from the point of view of voltage drop in them.
3. Answer (b).3 phase 4 wire type of connections are made at the secondary distribution. Secondary distribution consists of stepping down of volatge from 11kV to 415v . This voltage is used for connecting to the consumer terminals. In 3 phase 4 wire system, 4 th wire is the neutral wire. Therefore using one of the phases and neutral wire single phase power supply can be given to the house hold purposes. 
4. Answer (a). DC distribution is more economical compared to cost wise because it requires two conductors, no inductance capacitance phase displacement and surge problem , no skin effect in dc hence cross section of the conductor is completely utilized, no charging currents, and saving in the copper. However ac distribution is superior compared to dc system because voltage control is easy in ac system becuase of the transformers.
5. Answer (c). In over head lines the conductors used are ACSR conductors.ACSR (Aluminum Conuctor Steel Reinforced), consists of galvanised steel strand surrounded by a number of aluminum strands.
6. Answer (b).large industrial suppliers are supplied power at 11kV. All the motor and drive loads  will have high voltage rating of 6.6kV and can be start and run with out any voltage drop on other loads.So 11kV is sufficient.
7. Answer (b). Conductors used in the high voltage transmission are stranded.
8. Answer (b). Flexibility of the conductor increases when  they are stranded and also reduces the skin effect.

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