ELECTRICAL MACHINES DESIGN QUESTIONS FOR PRACTICES

10. Find the amount of cooling air required in m³ per second at the inlet temperature of 25^OC for a 25000KVA alternator working at full load. The efficiency is 96% and the power-factor is 0.87. The temperature of air coming out of machine is 50^OC. Determine also the amount of hydrogen required with the same data.

11. Discuss, briefly, about the “Frame Size” and “Standard Frames”.

12. Explain heating and cooling process of electrical machines also define heating & cooling time constants.

13. What do you understand by the term “Impregnation of winding”?

14. Does the selection of current density Amp /mm² in the design of electrical machines, depend on duty-cycle of the respective machine? Explain in brief.

15. Justify the statement, “By exceeding the rate of cooling, the overload capacity of an electrical machine can be enhanced.”