1. How do the walls of the transformer tank dissipate heat?
a) by radiation
b) by convection
c) by conduction
d) by convection and radiation
Explanation: The plain walled tanks of the transformer also dissipate heat through convection and radiation. The property is similar to that of the rotating machinery.
2. What is the specific heat dissipated by the plain walled tanks of the transformer by radiation and convection?
a) 6.5, 6 W per m2 – °C
b) 6, 6.5 W per m2 – °C
c) 6.5, 6.5 W per m2 – °C
d) 6, 6 W per m2 – °C
Explanation: The heat dissipated by the plain walled tanks of the transformer by radiation is 6 W per m2 – °C. The heat dissipated by the plain walled tanks of the transformer by convection is 6.5 W per m2 – °C.
3. What is the formula for the temperature rise of the transformers?
a) temperature rise = total loss * specific heat dissipation * surface temperature
b) temperature rise = total loss / (specific heat dissipation * surface temperature)
c) temperature rise = total loss / specific heat dissipation / surface temperature
d) temperature rise = total loss * specific heat dissipation / surface temperature
Explanation: Firstly the surface temperature is calculated along with the specific heat dissipation which is nothing but 12.5. Then the losses are calculated and substituted in the above formula.
4. Can the plain walled tanks accommodate the transformer for both large and small outputs?
a) the plain walled tanks can accommodate for large outputs but cannot accommodate for small outputs
b) the plain walled tanks can accommodate for large outputs and small outputs
c) the plain walled tanks cannot accommodate for large outputs and small outputs
d) the plain walled tanks can accommodate for small outputs but cannot accommodate for large outputs
Explanation: The plain walled tanks are large enough to accommodate the transformer and oil has sufficient surface to keep the temperature rise within limits for small outputs. But the plain walled tanks cannot accommodate the transformers for large outputs
5. How are the ratings of the transformer, losses and temperature rise related?
a) increase, decrease, increase
b) decrease, increase, increase
c) increase, increase, increase
d) decrease, increase, decrease
Explanation: As the rating of the transformer increases, the losses also increase. As the losses increase the heat dissipated increases and gives high temperature rise
6. What is the usage of the tanks with tubes?
a) if the temperature rise with plain tank is very low
b) if the temperature rise with plain tank is very high
c) if the temperature rise is zero
d) if the temperature rise with plain tank exceeds the specific limits
Explanation: Temperature rise in transformers is calculated with plain walled tanks. If the limits is exceeded then the plain walled tank is replaced by tank with tubes.
7. What is the relation of the provision of tubes with respect to dissipation of heat?
a) the provision of tubes is directly proportional to the dissipation of heat
b) the provision of tubes is indirectly proportional to the dissipation of heat
c) the provision of tubes is directly proportional to square of the dissipation of heat
d) the provision of tubes is indirectly proportional to square of the dissipation of heat
Explanation: The provision of tubes increases the dissipating area. The increase in dissipation of heat is not proportional to area because tube screen some of the tank surface preventing radiation from there.
8. What is the relation of the transformer surface with respect to dissipation of heat?
a) transformer surface has no relation with respect to dissipation of heat
b) transformer surface has minor changes with respect to dissipation of heat
c) transformer surface has major changes with respect to dissipation of heat
d) transformer surface has no change with respect to dissipation of heat
Explanation: When the tanks with tubes are provided, the dissipation of heat increases. The dissipation of heat has no effect on the transformer surface.
9. How is the circulation of oil improved in tanks with tubes?
a) it can be improved by using dissipating heat
b) it can be improved by using more effective air circulation
c) it can be improved by using more effect power flow
d) it can be improved by using more effective heads of pressure
Explanation: The circulation of oil is improved in tanks with tubes. It takes place with the help of using more effective heads of pressure.
10. An addition of 35 percent should be made to tube area of the transformers.
a) true
b) false
Explanation: An addition of 35 percent should be made to tube area of the transformer. This should be done in order to take into account this improvement in dissipation of loss by convection.