Motor Controls Chapter 5 Review

The two factors that determine the synchronous speed of an induction motor are the ____ of the power supply and the number of stator ___.

frequency, poles

A wound-rotor induction motor is normally started with

full external rotor resistance

When the field current of a DC motor is varied both the motor speed and the torque will vary.

true

A voltmeter check of a motor should show voltage within _______ % of the motor's nameplate voltage.

10

NEC 430.22 requires branch circuit conductors supplying a single motor to have an ampacity not less than ________ of the motor FLC.

125%

Direct coupling of the motor shaft to the driven load results in a ______ speed ratio.

1:1

A motor with a speed of 1800-rpm and a drive pulley that is 2-inches in diameter is coupled via a belt drive to a load pulley that is 4-inches in diameter. The speed of the driven load would be

900-rpm

The effective voltage acting on the armature circuit of a DC motor is equal to the applied voltage minus the

CEMF

A three-phase synchronous motor can produce a leading power factor.

True

Placing a core of iron in the center of a coil will increase its magnetic strength.

True

The ___ temperature is the temperature of the air surrounding a motor.

ambient

The _________ nature of induction motor operation comes from the slip between the rotational speed of the stator field and somewhat slower speed of the rotor.

asynchronous

A variable AC motor drive is able to operate the motor

below base speed, above base speed, at base speed

An electric motor uses _________ to operate.

both electric current and magnetism

The ______ motor has the highest starting torque of all the single-phase motors.

capacitor start/capacitor run

___-pole motors are single winding motors that will operate at two different speeds depending on how the windings are connected to form a different ___of magnetic poles.

consequent, number

The three major sections of a variable frequency drive are the

converter, dc filter, inverter

The motor energy losses due to the resistance of the windings are known as the

copper losses

Compared to the split-phase motors, capacitor-start motors provide increase starting ___with less starting ___.

current, torque

An electric motor uses___ energy and ___energy to produce mechanical energy.

electric, magnetic

Both NEMA and IEC use identical letter codes for all the critical dimensions of a motor.

false

DC motors are physically smaller than AC motors of the same horsepower.

false

Thermal protectors inside the motor sense ambient motor temperature.

false

The series-type DC motor has

high starting torque

A polyphase synchronous motor is frequently used to

improve power factor

As the load on an induction motor increases the power factor will

increase

Generators operate on the principle that a voltage is induced in a conductor whenever the conductor is _______ through a magnetic field so as to cut lines of force.

moved

Voltage unbalance is the unbalance that occurs when the voltages at the 3-phase motor terminals are

not equal

The two general classifications of motor enclosures are

open or totally enclosed

The start winding is connected in ____________ with the run winding for a split-phase motor.

parallel

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

phase sequence

The device that provides the mechanical energy input to a generator is called the

prime mover

DC compound motors are used to operate loads that require

relatively constant speed under varying loads

A DC series motor

should never be operated without a load

A compound-type DC motor uses both___ and ___field windings.

shunt, series

A squirrel-cage rotor consists of

single bars short circuited by end rings

Single-phase motors are classified by their___ and ____ characteristics

starting, running

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 increase

Torque is best defined as:

the turning force produced by a motor

When a dual-voltage split-phase motor is operated at low voltage

the two run windings and the start winding are all connected in parallel.

Bearing current is the result of induced voltage in the motor seeking a path

to ground

A high inertia load requires a great deal of torque to get the load up and running, but less torque is required to keep it operating.

true

A separately excited DC motor has the armature and field coils fed from separate supply sources.

true

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

true

Motors that are not fully loaded normally draw less than rated nameplate current.

true

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

3600-rpm

NEC Article ______ is the main code source for electric motor installations.

430

The two basic categories of motors are

AC and DC

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

CEMF

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

NEMA H

The___speed of a DC motor is obtained when rated armature voltage and full field current are applied.

base

The rotating shaft of a motor is suspended in the end bells by

bearings

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

decrease slightly

A permanent capacitor motor

does not require a centrifugal switch, uses identical run and auxiliary windings, provides improvement of motor power factor

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

either the run winding or the start winding

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

false

Loading of an induction motor is similar to that of a transformer in that the operation of both involves changing ___linkages.

flux

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

frequency

The shunt-type DC motor is known to have

good speed regulation

Shunt field coil windings of DC motors

have high resistance, are connected across the supply voltage source, are constructed with many turns of small diameter wire

Metric motors are rated in ________ rather than horsepower.

kilowatts

A ________ is an example of a constant horsepower load.

lathe

At the moment a DC motor starts, the only factor limiting armature current is the of ___the armature windings.

resistance

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

reversing the current flow through the field or reversing the current flow through the armature

A common feature of all AC motors is a___magnetic field.

rotating

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

rotating magnetic field

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

series

When a dual-voltage, 9-lead wye-connected 3-phase motor is connected for high voltage, the individual coils of each phase are connected in

series

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

The base speed listed on a DC motor's nameplate is an indication of how fast the motor will run with rated armature voltage and rated load amps at rated 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

The no-load speed of a series motor can increase to the point of damaging the motor.

true

The only essential difference between an AC and a DC generator is the use of slip rings on the one and a commutator on the other.

true