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to radiation and convection is respectively 6 and 6.5 W/m7°C. Assume that the
convection is improved by 35% due to provision of tubes.
PART C
Answer any two full questions, each carries 10 marks.
Explain the criterion for the selection of number of poles in a ‏عل‎ machine.

What are the design procedure of the field winding of a dc machine?

A shunt field coil has to develop an mmf of 8000A. The voltage drop in the coil
is 40 ५ and the resistivity of the round wire used is 0.021 Q/m and mm’. The
depth of the winding is 35 mm approximately and the length of the mean turn is
1.8 m. Design a coil so that the power dissipated is 800 W/m‘ of the total coil
surface. Take the diameter of the insulated wire 0.2 mm greater than that of bare
wire.

Derive the output equation of a synchronous machine.

Estimate the diameter, core length, size, number of conductors and number of
slots for stator of a ISMVA, 1110५, 50117, 2 pole star connected turboalternator
with 60° phase spread. Assume Byy=0.55Wb/m’, ac=36000Amp/m, current
density=5A/mm’, peripheral speed=160m/sec. The winding should be arranged
to eliminate 57 harmonics.
PART 0

Answer any two full questions, each carries 10 marks.
What are the factors to be considered for the selection of air gap length of an
induction motor?
Derive an expression for the end ring current of a squirrel cage induction motor.

Describe about finite element methods. What are its advantages and
applications?

What is computer aided design? How does it help in designing electrical
machines?

Estimate the stator core dimensions, number of stator slots and number of stator
conductors per slot for a 10014 W,3300V, 50117, 12 pole star connected slip ring
induction motor. Assume average gap density 0.4Wb/m?, ampere
conductors/m=25000A/m, efficiency=0.9, Power factor=0.96. Choose main
dimensions to give best power factor. The slot loading should not exceed 500
Ampere conductors.

بد بد ‎ಸಸ್ಯ‏

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