Motors Test 1

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% Slip Formula

% Slip = (No load speed - Full load speed)/ Full load speed

A variable AC motor drive is able to operate the motor

-Below base speed -Above base speed -At base speed

Shunt field coil windings of DC motors

-High resistance -Constructed with many turns of small diameter -Are connected across the supply voltage source

The direction of rotation of a shunt wound DC motor is changed by

-Reversing the current flow through the armature -Reversing the current flow through the field

The direction of rotation on a split-phase motor can be reversed by interchanging the connections to

-The run winding -The start winding

The synchronous speed of a 2-pole, 60 hertz AC motor is

3600 RPM

A________ is an example of constant HP load

A lathe

On a 3-phase motor, the stator windings are arranged to create

A rotating magnetic field

The two basic categories of motors are

AC and DC

The voltage induced into the armature of a DC motor is know as the

CEMF

The _____ motor has the highest starting torque of all single phase motors

Capacitor start/capacitor run

The ________ motor has the highest starting torque of all the single phase motors

Capacitor start/capacitor run

When a load is applied to a 3 phase squirrel cage induction motor the rotor speed will

Decrease slightly

An electric motor uses what to operate

Electric current and magnetism

A current-carrying conductor , placed in and at right angles to a magnetic field, tends to move parallel to the field

False

Direct current motors can normally operate directly from the power supplied by the electric utility system

False

Direct current permanent magnet servo motors are used in cranes to start heavy loads

False

Single phase operation of a three phase motor will reduce the current in the two remaining phases

False

The locked-rotor starting current of an induction motor is several times less than the full load current

False

Unlike three phase induction motors, single phase types are self starting

False

The speed of as squirrel cage motor can be varied by varying the supply

Frequency

A wound-rotor induction motor is normally started with

Full external rotor resistance

The shunt type DC motor is known to have

Good speed reevaluation

The series type DC motor has

High starting torque

Armature Current Formula

Ia = (motor terminal voltage - CEMF)/(armature circuit resistance)

A polyphase synchronous motor is frequently used to

Improve power factor

As the load of an induction increases the power factor will

Increase

Which of the following NEMA insulation classes had the highest safe operating temperature?

NEMA H

The direction of rotation of 3 phase induction motor is determined by

Phase sequence

DC compound motors are used to operate loads that require

Relative constant speed under varying loads

The synchronous speed of an induction motor refers to the speed of the

Rotating magnetic field

Synchronous Speed Formula

S = 120f/ # of poles

The universal motor is constructed similar to that of a ______ type DC motor

Series

A DC series motor

Should never be operated without a load

A squirrel cage rotor consists of

Single bars short circuited by end rings

Which is not a requirement for motor action

Source of mechanical energy

If the field current of a shunt-type DC motor is held constant and the armature voltage is increased, as a result

The speed of the motor will decrease

Torque can best defined as

The turning force produced by a motor

One advantage DC type motors have over AC types is that

Their speed can be easily varied

The purpose of a commutator on a DC motor is

To maintain the proper direction of current flow in the armature conductors

A DC series motor runs fast with a light load

True

A good capacitor will hold a charge even when power is removed

True

A split phase motor relies on the start winding to create a phase shift

True

A three phase synchronous motor can produce a leading power factor

True

Compared to s squirrel cage motor of equivalent HP, a wound rotor motor has a higher starting torque and a lower starting current

True

Overheated bearings may cause motor noise

True

Single phasing refers to the operation of a 3 phase motor on two phases is lost

True

The commutator in a DC motor reverses armature coil current flow to produce continuous armature rotation

True

The direction of rotation for a 3-phase AC motor can be changed by exchanging L1 and L2 of the voltage supply

True

The speed of a 3-phase synchronous motor is the same as that of the rotating magnetic field

True

The speed of a DC shunt motor is inversely proportional to the field current

True

A series type DC motor uses field coils

With low resistance made up of a few turns of large diameter wire

A DC shunt motor should never be operated

With the field circuit open


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