1. How many types of cooling methods are available for the transformer?
a) 3
b) 2
c) 1
d) 4
Explanation: There are 3 types of cooling methods available for transformers. They are natural cooling, air blast cooling, forced oil circulation.
2. How are the radiators cooled in the present time?
a) by natural cooling
b) by forced cooling using small fans
c) by forced cooling using large fans
d) by using external air
Explanation: At present time the radiators are cooled using forced cooling. The forced cooling takes place with the help of the small fans mounted on each radiator.
3. What type of cooling is being made use of in transformers having a capacity of less than 11MVA?
a) natural cooling
b) forced cooling
c) air blast cooling
d) forced cooling and air blast cooling
Explanation: For transformers having capacity less than 11MVA, natural cooling is made use of. For transformers having capacity more than 11MVA, air blast cooling is used.
4. Compared to the natural cooling, how much of heat dissipation is increased by air blast cooling?
a) 50-70%
b) 60-70%
c) 50-60%
d) 40-60%
Explanation: Air blast cooling helps in increased heat dissipation. The minimum value of increased heat dissipation is 50% and maximum value is 60%.
5. Increase in the velocity of oil circulation increases the transformer output.
a) true
b) false
Explanation: The increases in velocity of the air circulation increases the temperature. The temperature rise increases the transformer output.
6. What is the relation of the increase of the oil circulation rate with energy losses?
a) increase of the oil circulation rate is not depending with energy losses
b) increase of the oil circulation rate is directly proportional to the energy losses
c) increase of the oil circulation rate is directly proportional to the square of energy losses
d) increase of the oil circulation rate is indirectly proportional to energy losses
Explanation: The increase in the oil circulation rate is unsuitable because this increases the large energy losses In the pumping unit. To cool the oil, it is circulate through a special oil cooler.
7. What is the flow rate of the circulating oil in an air cooler with natural air cooling?
a) 12.5 litre per minute per KW of losses
b) 12 litre per minute per KW of losses
c) 14 litre per minute per KW of losses
d) 13 litre per minute per KW of losses
Explanation: When natural air cooling is used, the flow rate is 12 litres per minute per KW of losses. Even when the air blast cooling is used, the transformer output increases roughly to the same extent.
8. What is the range of the cooler surfaces per 1 KW of losses?
a) 0.1-0.25 m2
b) 0.18-0.2 m2
c) 0.1-0.2 m2
d) 0.18-0.25 m2
Explanation: The minimum value of the cooler surfaces per 1 KW of losses is 0.18 m2. The maximum value of the cooler surfaces per 1 KW of losses is 0.25 m2.
9. What is the range of the flow rate of circulating oil per KW of losses?
a) 6-7 liters per minute
b) 5-6 liters per minute
c) 6-8 liters per minute
d) 6-7 liters per minute
Explanation: The minimum value of the flow rate of circulating oil per KW of losses is derived to be 6 liters per minute. The maximum value of the flow rate of circulating oil per KW of losses is derived to be 8 liters per minute
10. The temperature difference between the incoming and outgoing water is greater than 10°C.
a) true
b) false
Explanation: The water flow rate is about 1.5 litres per minute. The difference in temperature between the incoming water and outgoing water is 10°C.