288. Which of the following loss of D.C.motor decreases with increase in load?
A. Friction and windage loss
B. Core loss
C. Brush contact loss
D. none of the above
289. In an overloaded motor main danger arises due to
A. winding getting overheated
B. busbars getting heated
C. starter getting damaged
D. bearing getting overheated
290. A wide and very sensitive speed control is usually required in case of
A. elevators
B. steel rolling mills
C. colliery winders
D. all of the above
291. For which application a D.C. motor is preferred over an A.C. motor?
A. High speed operation
B. Low speed operation
C. Fixed speed operation
D. Variable speed operation
292. Regenerative braking on D.C. shunt motors is used when
A. the load has overhauling characteristics
B. the load is variable
C. the load also acts as a braking force
D. the load is constantly decreasing
293. Which motor should be used for centrifugal pumps?
A. Series motor
B. Shunt motor
C. Either of the above
D. None of the above
294. Which of the following methods is most effective in finding out the no load losses in a large D.C. shunt motor?
A. Field's test
B. Ward-Leonard test
C. Block rotor test
D. Swinburne's test
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