Rotating Machinery - Final Exam - Delmar's Standard Textbook of Electricity

The torque of a squirrel-cage induction motor will be maximum when the phase angle between the stator and rotor fields is _____.

0°

The Holtz motor operates at _____ RPM.

1200

Section 430.22(A) states that conductors supplying a single motor shall have an ampacity of not less than ____% of the motor full-load current.

125%

If for some reason this fuse will not permit the motor to start without blowing, NEC Section 430.52(C)(1) Exception 2(b) states that the rating of a dual-element time delay fuse may be increased to a maximum of ____ of the full-load motor current.

225%

​Given a harmonic with a fundamental power frequency of 60 hertz, what would be the frequency of the fourth harmonic?

240 hertz

A square wave voltage varies between 0 V and 12 V. The positive pulses are 25 μs wide and there is a 75 μs gap between them. What is the DC average of the waveform?

3 V

A square wave voltage varies between 0 V and 12 V. The positive pulses are 50 μs wide and there is a 50 μs gap between them. What is the DC average of the waveform?

6 V

An alternator containing eight poles per phase is turning at 900 RPM. What is the output frequency?

60 Hertz

As a general rule the temperature rating of most devices will not exceed ____ degrees C.

75

A square wave voltage varies between 0 V and 12 V. The positive pulses are 75 μs wide and there is a 25 μs gap between them. What is the DC average of the waveform?

9 V

Different tables from the ____ (NEC ®) are used to determine the running current for the different types of motors.

National Electrical Code

The servomotor featuring a fiberglass and copper rotor is the _____ motor.

ServoDisc

A synchronous motor operated with no load and used for power factor correction is sometimes called a _____.

Synchronous Condenser

What is a device that converts mechanical energy into DC electrical energy?

a generator

What machines operate on the same principle of electromagnetic induction as DC generators, but they have no commutator?

alternators

To reverse the direction of rotation of a three-phase motor, reverse _____.

any two leads

The speed regulation of a DC motor is proportional to the _____.

armature resistance

In a compound DC motor control circuit, the field loss relay will disconnect the _____ if power is lost to the _____.

armature; shunt field

The squirrel-cage rotor is constructed of _____ and end _____ embedded in steel laminations.

bars; rings

The _____ ride against the commutator segments and are used to connect the armature to the external circuit of the DC machine.

brushes

The motor that does not contain a wound armature, commutator, or brushes is the _____ motor.

brushless DC

The frequency of the current in a squirrel-cage rotor _____ as the rotor approaches synchronous speed.

decreases

Most motor circuits are protected by ____.

dual-element time-delay fuses or inverse-time circuit breakers

The direct current that is an input to the alternator's rotor is the _____ current.

excitation

The output voltage of a generator is usually controlled by the amount of _____.

field excitation current

What are ​voltages or currents that operate at a frequency that is a multiple of the fundamental power frequency?

harmonics

The wound-rotor induction motor is popular in industry because it has _____ starting torque and _____ starting current.

high; low

In order to increase the efficiency of the cooling, some alternators operate in a(n) _____ atmosphere.

hydrogen

Shunt field windings are connected in parallel with the armature. They are wound with _____ turns of fairly _____ wire.

many; small

A device that converts electrical energy into mechanical energy is called a(n) _____.

motor

The output shaft of a stepping motor _____.

moves through a specific angle for each input pulse

​The _____ of a harmonic refers to whether the harmonic is the second, third, fourth, or so on of the fundamental frequency.

name

Motors especially designed for low speed and high torque, or multispeed motors, shall have their running current determined from the ____.

nameplate rating

What is one factor that controls the output frequency of an alternator?

number of stator poles and rotor rotation speed

If a piece of machinery needs a replacement motor and will be damaged if the new motor rotates the wrong way. The test equipment needed to test the rotation direction of the new motor is a _____.

phase rotation meter

The speed of the disc servomotor can be varied by changing the amount of voltage supplied to the armature. The voltage is generally varied using _____.

pulse-width

The rotating part of a revolving-armature-type alternator is called the _____.

rotor

The _____ winding is made of a few turns of large wire and is located at the bottom of the stator core of a split-phase motor.

run

The _____ of a harmonic refers to the phasor rotation with respect to the fundamental waveform.​

sequence

A compound motor has _____ field windings.

series and shunt

In a generator, the _____ permits part of the current that normally flows through the series field to flow through the resistor.

series field shunt rheostat

Small permanent magnet motors that have lightweight rotors are often used as _____.

servomotors

When a squirrel-cage motor is first started, the value of the current draw is _____.

several times the running current

Three lines supply power to a three-phase motor. If one of these lines should open, the motor will be connected to single-phase power. This condition is known as _____.

single-phasing

What is a special type of motor designed to operate with the rotor stalled without damage to the motor?

torque motor

For most squirrel-cage induction motors the typical percent slip is about _____ percent.

two to five

The formula for determining the transformer harmonic derating factor produces a value somewhere between _____.

zero and one

The non-rotating part of a revolving-field-type alternator is called the _____.

stator

A two-phase power system has two voltages that are _____ out of phase.

90°

The rotating part of a generator is called the _____.

armature

An alternator that has a separate small alternator mounted on the shaft of its rotor is equipped with a(n) _____.

brushless exciter

In single-phase motors such as the resistance start induction-run motor, the start winding is disconnected by the _____.

centrifugal switch

The universal motor has a wound armature and brushes like an AC motor, as well as an added component, the _____.

compensating winding

A generator containing both series and shunt fields is called a _____ generator.

compound

A single-phase synchronous motor is sometimes referred to as a(n) _____ motor.

hysteresis

Multispeed fan motors achieve multiple speeds by inserting additional _____ in series with the run winding.

inductance

The revolving armature type alternator is capable of _____ power output and is, therefore, _____ often used than the revolving field type.

less; less

In the shaded-pole induction motor, the direction of rotation of the magnetic field is determined by the _____.

magnetic field strength

What provide(s) the magnetic field necessary for the operation of a DC machine?

pole pieces

The ServoDisc motor is also often called a _____ motor.

printed-circuit

A(n) _____ motor operates on the principle that like magnetic poles repel.

repulsion

The _____ winding is made of many turns of small wire and is located at the top of the stator core of a split-phase motor.

start

There are two basic methods for determining the locked-rotor current (_________ current) of a squirrel-cage induction motor depending on the information available

starting

The squirrel-cage rotor code letters indicate the shape (type) of rotor bars. Different types of bars have a large effect on the _____ of a motor.

starting torque

A(n) _____ is used to measure the difference in voltage and frequency between two alternators.

synchronoscope

In a three-phase motor, the speed of rotation of the magnetic field is called the _____ speed.

synchronous

The _____ motor can operate on either AC or DC voltage.

universal

When a motor is connected differential compound, the _____ determines the direction of rotation of the motor at no load or light load.

shunt field

A three-phase alternator containing six poles is turning at 1000 RPM. What is the output frequency?

50 Hertz