Dc Motors Objectives Part 03

41 . In base of dc shunt motors as the load is increased the speed of motor reduces slightly

42 . Regenerative braking on shunt motors is used when the load has overhauling characteristics.

43 . In hemostatic braking for dc series motors motor is run as a generator.

44 . In Hopkinson’s test for dc motors both machines are mechanically coupled

45 . A 230V dc motor is connected to 230V ac supply then it will run with less efficiency and high spark

46 . A dc series motor should always started on load.

47 . Which figure represents the speed-torque characteristics of a dc shunt motor is

48 . Which dc motor has approximately constant speed shunt motor

49 . The armature current of a dc motor is given by Ia=(V–Eb)/Ra

50 . Which motor will have highest percentage increase of input current for the same percentage increase in torque Shunt motor

51 . Which of the following method is most effective in finding out the no losses in a large dc shunt motor Swinburne’s test

52 . The retardation test in case of shunt motors and generator is use to determine stray losses.

53 . A dc series motor develops a torque of 20N-m at 3A of load current is increased to 6A, the torque developed will be 80N-m .

54 . The back emf of a dc motor depends on field flux

55 . A series motor never started without some mechanical load on it because at no load series motor develops infinite speed.

56 . A conductor 10cm long lies across a magnetic field of 0.8 weber/sqm.

The force acting on the conductor when a current of 20A passes through it will be 1.6 N.

57 . The armature of a shunt motor contains 0.8-ohm resistance. The motor is to run on a 120V circuit. If the motor is suddenly thrown on the circuit while the armature is standing still (back emf in normal running being 110V) the current drawn by the motor will be 600A .

58 . The airgap b/w stator and armature of an electric motor is kept small in order to provide stronger magnetic field .

59 . Small dc motor up to 50HP usually have 2 POLES.

60 . A dc generator can be termed as Rotating amplifier.