232. Which of the following motors is most suitable for signalling devices and many kinds of times?
A. D.C. shunt motor
B. D.C. series motor
C. Induction motor
D. Reluctance motor

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233. Which motor should not be started on no-load?
A. Series motor
B. Shunt motor
C. Cumulatively compounded motor
D. Differentially compounded motor

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234. Ward-Leonard control is basically a
A. voltage control method
B. field divertor method
C. field control method
D. armature resistance control method

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235. For constant torque drive which speed control method is preferred?
A. Field control
B. armature voltage control
C. Shunt armature control
D. Mechanical loading system

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236. In Ward-Leonard control the lower limit of speed is imposed by
A. residual magnetism of the generator
B. core losses of motor
C. mechanical losses of motor and generator together
D. all of the above

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237. The main dis-advantage of the Ward-Leonard control method is
A. high initial cost
B. high maintenance cost
C. low efficiency at light loads
D. all of the above

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238. Which of the following can be used to control the speed of a D.C. motor?
A. Thermistor
B. Thyristor
C. Thyratron
D. Transistor

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