Question

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)

This question was addressed to me in a job interview.

I would like to ask this question from Design of Tank in section Design of Transformers of Design of Electrical Machines

Answer 1

The correct answer is:

(c) temperature rise with tubes = total loss / dissipating surface / (12.5 + 8.8x)

Explanation:

The temperature rise with tubes in a transformer is determined by the heat dissipation efficiency of the cooling system (which includes tubes) and the losses generated in the transformer. The formula accounts for:

• Total loss: The total amount of heat generated by the transformer during operation, which needs to be dissipated.
• Dissipating surface: The surface area available for heat dissipation, which can include the surface of the cooling tubes or tank.
• $12.5+8.8x$: This term represents the heat transfer coefficient or the efficiency of the cooling system. It combines the physical properties of the cooling medium and transformer design factors.

Thus, the formula for temperature rise is:

Temperature rise with tubes=Total lossDissipating surface×(12.5+8.8x)\text{Temperature rise with tubes} = \frac{\text{Total loss}}{\text{Dissipating surface} \times (12.5 + 8.8x)}Temperature rise with tubes=Dissipating surface×(12.5+8.8x)Total loss​

This formula ensures that the temperature rise is calculated based on both the transformer losses and the efficiency of the cooling system.