Question

What is the formula for the temperature rise in the design of field windings?

(a) temperature rise = 1 / copper loss in each field coil at 75°C * cooling coefficient of rotating field coils * dissipating surface of the coil

(b) temperature rise = copper loss in each field coil at 75°C * cooling coefficient of rotating field coils * dissipating surface of the coil

(c) temperature rise = copper loss in each field coil at 75°C / cooling coefficient of rotating field coils * dissipating surface of the coil

(d) temperature rise = copper loss in each field coil at 75°C * cooling coefficient of rotating field coils / dissipating surface of the coil

The question was posed to me in an online interview.

The question is from Design of Field Winding in portion Design of Synchronous Machines of Design of Electrical Machines

Answer 1

The correct answer is (d) temperature rise = copper loss in each field coil at 75°C * cooling coefficient of rotating field coils / dissipating surface of the coil

For explanation I would say: The copper loss in each field coil is first calculated using its formula. Next, the cooling coefficient of rotating field coils is calculated. Finally dissipating surface of the coil is calculated and this gives the temperature rise.