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Electrical Engineering Objective Questions { DC Motors }

176.  A 4-pole lap-wound DC generator has a developed power of P watts and voltage of E volts. Two adjacent brushes of the machine are removed as they are worn out. If the machine operates with the remaining brushes, the developed voltage and power that can be obtained from the machine are
A. E, P.
B. E/2, P/2.
C. E, P/4.
D. E, P/2.
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177.  A DC shunt motor is running at 1200 rmp, when excited with 220V DC. Neglecting the losses and saturation, the speed of the motor when connected to a 175 V DC supply is
A. 750 RPM.
B. 900 RPM.
C. 1050 RPM.
D. 1200 RPM.
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178.  The compensating winding in a dc machine
A. is located in armature slots for compensation of the armature reaction
B. is located on commutating poles for improving the commutation
C. is located on pole shoes for avoiding the flashover at the commutator surface
D. is located on pole shoes to avoid the sparking at the brushes.
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179. 1n case of an armature controlled separately excited de motor drive with closed-loop speed control, an inner current loop is useful because it
A. limits the speed of the motor to a safe value
B. helps in improving the drive energy efficiency
C. limits the peak current of the motor to the permissible value
D. reduces the steady state speed error
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180.  An electric motor with "constant output power" will have a torque-speed characteristic in the form of a
A. straight line through the origin
B. straight line parallel to the speed axis
C. circle about the origin
D. rectangular hyperbola
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181.  A dc series motor fed from rates supply voltage is overloaded and its magnetic circuit is saturated. The torque-speed characteristic of this motor will be approximately represented by which curve of Fig. 7.2?TorqueFig. 7.2
A. Curve A
C. Curve C
D. Curve D
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182. A 200V, 2000 rpm, 10A, separately excited de motor has an armature resistance of 20. Rated dc voltage is applied to both the armature and field winding of the motor. If the armature drawn 5A from the source, the torque developed by the motor is
A. 4.30 Nm
B. 4.77 Nm
C. 0.45 Nm
D. 0.50 Nm
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