Explanation: There are 3 types of cooling methods available for transformers. They are natural cooling, air blast cooling, forced oil circulation.

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.

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.

Explanation: Air blast cooling helps in increased heat dissipation. The minimum value of increased heat dissipation is 50% and maximum value is 60%.

Explanation: The increases in velocity of the air circulation increases the temperature. The temperature rise increases the transformer output.

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.

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.

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.

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.

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.

Explanation: Width of tank = 2*distance between adjacent limbs + external diameter of h.v windings + 2*clearance between h.v windings and tank is the formula for three phase transformer. For single phase transformers, the distance between adjacent limbs is not multiplied.

Explanation: The external diameter of h.v winding is obtained. Next, the clearance on each side between the winding and tank along the width is calculated and is substituted in the above formula.

Explanation: Firstly, the height of the transformer frame is calculated. Next, the clearance height between the assembled transformer and tank is also calculated. Substitute the values to obtain the height of transformer tank.

Explanation: The minimum value of the rating of the transformer for a voltage of about 11 kV should be 1000 kVA. The maximum value of the rating of the transformer for a voltage of about 11 kV should be about 5000 kVA.

Explanation: 1000-5000 kVA is the rating of the transformer for the voltage of about 11 kV. When the voltage rating is about 11-33 kV, then the rating of the transformer is less than 1000 kVA.