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Exam 21: Energy-Efficient Motors

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Question 1

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In a brush-riding type of motor, briefly describe how the centrifugal mechanism is involved in causing the motor to operate as an induction motor.

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When the rotor reaches 75% of ...

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Although conductively compensated motors have a low starting torque, the speed regulation is very good.

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Question 3

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Identify two of the main construction features of universal motors?

A concentrated-field universal motor is usually a salient-pole motor with two poles and a winding of relatively few turns.

Armature reaction in AC series motors may be compensated with an inductively coupled winding, which acts as a short-circuited secondary winding of a(n) ____________________.

In a universal motor, severe arcing at the brushes from changing the direction of rotation is prevented by shifting the brushes to the neutral (sparkless) plane or by adding a compensating winding.

Briefly describe how speed is regulated in universal motors.

Article 430 of the National Electrical Code® provides requirements for the motor branch-circuit overcurrent protection, motor overcurrent protection, and wire sizes for motor circuits.

The two types of ____________________ motors are the single-field compensated motor and the two-field compensated motor.

Repulsion motors are divided into three distinct classifications. Name two of these classifications.

When the brushes of a repulsion motor are in the ____________________ neutral position, there is no torque even though a heavy current exists in the armature windings.

Briefly describe the two types of brush arrangements in a repulsion motor.

The direction of rotation of a(n) ____________________ motor is reversed if the brushes are shifted 15 electrical degrees from the stator field pole centers in a clockwise direction.

At start-up of a(n) ____________________ motor, the repulsion winding predominates; however, as the motor speed increases, the squirrel-cage winding is used most.

Universal motors are speed-regulated by inserting resistance in parallel with the motor.