ONLINE Multiple Choice Questions – Electric Machine Design PART 13



181. The output of a rotating electrical machine is limited by
(A) size of the machine
(B) peripheral velocity
(C) temperature rise
(D) none of the above.

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182. The hum in the transformer is due to
(A) transformer winding
(B) magnetostriction
(C) transformer oil
(D) tank walls.

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183. Turbo alternators are characterized by
(A) short diameters and great axial lengths
(B) short diameters and narrow axial lengths
(C) large diameters and narrow axial lengths
(D) large diameters and great axial lengths.


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184. Short circuit ratio for turbo-alternators is usually
(A) 0.1 to 0.2
(B) 0.2 to 0.4
(C) 0.5 to 0.7
(D) 0.8 to 0.95.

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185. A synchronous machine having large length of the air gap will have
(A) higher noise level
(B) smaller unbalanced magnetic pull
(C) lower limit of stability
(D) higher value of inherent regulation.

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186. Damper windings are provided in synchronous machines to
(A) damp out rotor oscillations
(B) reduce the over-voltages under abnormal conditions
(C) facilitate starting
(D) all of the above.

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187. The use of salient poles on high speed alternators will cause
(A) excessive windage loss and excessive noise
(B) reduced windage loss and low noise
(C) reduced windage loss but excessive noise
(D) excessive windage loss but reduced noise.

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188. Arc welding transformer is basically a
(A) frequency changing device
(B) step up transformer
(C) step down transformer
(D) current transformer.

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189. The output voltage of arc welding transformer is usually
(A) 10 to 30 V
(B) 35 to 55 V
(C) 55 to 65 V
(D) 110 to 135 V.

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190. A welding transformer should have
(A) drooping voltage-current characteristics
(B) open circuit voltage less than 80 V
(C) current controlled continuously over the full range
(D) all of the above.

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191. The drooping characteristics of a welding transformer are usually obtained by
(A) using series reactance
(B) adopting oil cooling
(C) multiple tapings on secondary
(D) none of the above.

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192. The power factor of a welding transformer is usually
(A) 1.0
(B) high
(C) 0.5
(D) very low.

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193. For the load cycle shown in the figure, the rating of the motor should be

(A) 600 kW
(B) 350 kW
(C) 300 kW
(D) 275 kW.

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Questions 194 to 196 refer to data below :

Three cores made up of iron, aluminium and wood have the same
dimensions and are wound with the same number of turns. All these are
fed from the same voltage source at a fixed frequency.

194. The materials in order of decreasing magnetizing currents will be
(A) wood, aluminium, iron
(B) wood, iron, aluminium
(C) iron, wood, aluminium
(D) iron, aluminium, wood.

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195. The materials in order of decreasing
hysteresis loss will be
(A) wood, aluminium and iron
(B) iron, aluminium, wood
(C) iron, wood, aluminium
(D) aluminium, iron, wood.

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ONLINE Multiple Choice Questions - Electric Machine Design PART 14
ONLINE Multiple Choice Questions - Electric Machine Design PART 12

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