1. What is the loss dissipated by tubes by convection, given area of the tubes = 3.5?
a) 12.3 W per °c
b) 2.51 W per °c
c) 5.3 W per °c
d) 30.8 W per °c
Explanation: Loss dissipated by tubes by convection = 8.8 * Area of tubes
Loss = 8.8 * 3.5 = 30.8 W per °c.
2. What is the formula for temperature rise with tubes?
a) temperature rise with tubes = total loss / dissipating surface*(12.5 + 8.8x)
b) temperature rise with tubes = total loss * dissipating surface*(12.5 + 8.8x)
c) temperature rise with tubes = total loss / dissipating surface / (12.5 + 8.8x)
d) temperature rise with tubes = total loss + dissipating surface*(12.5 + 8.8x)
Explanation: The total losses in the transformers are obtained firstly the iron loss and copper loss. Next the dissipating surface temperature is obtained and substituting in the above formula gives the temperature rise.
3. What is the formula for number of tubes?
a) number of tubes = (1/ 8 * area of each tube) * (total loss / temperature rise with tubes – 12.5 * dissipating surface)
b) number of tubes = (1* 8 * area of each tube) * (total loss / temperature rise with tubes – 12.5 * dissipating surface)
c) number of tubes = (1/ 8 * area of each tube) / (total loss / temperature rise with tubes – 12.5 * dissipating surface)
d) number of tubes = (1/ 8 * area of each tube) + (total loss / temperature rise with tubes – 12.5 * dissipating surface)
Explanation: First the temperature rise with tubes is obtained. Then the iron loss and copper loss are obtained and added. Area of each tube is also obtained. Substituting all the values in the above formula provides the number of tubes.
4. What is the range of the diameter of the tubes used?
a) 50-60 mm
b) 60-70 mm
c) 70-80 mm
d) 50-70 mm
Explanation: The minimum value of the diameter of tubes is derived to be around 50 mm. The maximum value of the diameter of tubes should be less than 70 mm.
5. Elliptical tubes with pressed radiators are increasingly been used.
a) true
b) false
Explanation: Elliptical tubes with pressed radiators are on high demand now a days. This is because they give a greater dissipating surface for the small volume of oil.
6. What is the formula for width of the tank for single phase transformers used?
a) width of tank = 2*distance between adjacent limbs + external diameter of h.v windings + 2*clearance between h.v windings and tank
b) width of tank = distance between adjacent limbs + external diameter of h.v windings + 2*clearance between h.v windings and tank
c) width of tank = 2*distance between adjacent limbs * external diameter of h.v windings + 2*clearance between h.v windings and tank
d) width of tank = distance between adjacent limbs * external diameter of h.v windings + 2*clearance between h.v windings and tank
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.
7. . What is the formula for the length of the tank?
a) length of the tank = external diameter of h.v winding + clearance on each side between the winding and tank along the width
b) length of the tank = external diameter of h.v winding * clearance on each side between the winding and tank along the width
c) length of the tank = external diameter of h.v winding + 2*clearance on each side between the winding and tank along the width
d) length of the tank = external diameter of h.v winding / 2*clearance on each side between the winding and tank along the width
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.
8. What is the formula for height of transformer tank?
a) height of transformer tank = Height of transformer frame + clearance height between the assembled transformer and tank
b) height of transformer tank = Height of transformer frame * clearance height between the assembled transformer and tank
c) height of transformer tank = Height of transformer frame/clearance height between the assembled transformer and tank
d) height of transformer tank = Height of transformer frame – clearance height between the assembled transformer and tank
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.
9. What is the rating of the transformer for the voltage of about 11 kV?
a) 1000-2000 kVA
b) 100-3000 kVA
c) 1000-5000 kVA
d) 100-500 kVA
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.
10. What is the rating of the transformer for the voltage of above 11 kV upto 33 kV?
a) 1000-5000 kVA
b) less than 1000 kVA
c) above 1000 kVA
d) 100-500 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.