Delmar12
In many instances, it is necessary to derate the transformer to a point at which it can handle the extra current caused by the harmonic distortion. T F
T
In the formula for calculating output voltage, B represents flux density in gauss. T F
T
Large horsepower motors often have full-load currents that exceed the rating of the largest overload heaters. T F
T
Many split-phase motors are designed for operation on 120 or 240 volts. T F
T
One factor that causes the magnetic field to rotate is that the voltages in a three-phase system are 120° out of phase with each other. T F
T
Overload relays are divided into two separate sections: the current-sensing section and the contact section T F
T
The difference among three-phase motors is the type of rotor used. T F
T
The direction of rotation for a split-phase motor is determined by facing the back or rear of the motor. T F
T
The nameplate current value is used to determine the overload heater size for the motor, but the value found in motor tables is used when determining conductor size and fuse or circuit breaker size. T F
T
The speed of the shaded-pole induction motor is determined by the frequency and number of stator poles. True False
T
The word selsyn is a contraction derived from self-synchronous. True False
T
When determining frequency, P represents the number of poles per phase. T F
T
When pulsating currents are connected to a three-phase four-wire system, triplen harmonic frequencies disrupt the normal phasor relationship of the phase currents and can cause the phase currents to add in the neutral conductor. T F
T
When working with multiple motor calculations, the fuse or circuit breaker cannot be the next larger size. It must be the closest without going over the computed size. T F
T
If a counterclockwise rotation is desired for a split-phase motor, what should be connected to T1? T3 T5 T7 T8
T8
A phase rotation meter compares the phase rotation of two different three-phase connections. True False
True
The set of squirrel-cage bars on the rotor of a synchronous motor is used to start the motor and is known as the _____. amortisseur winding starting bars synchronous starter rotor bars
amortisseur winding
To reverse the direction of rotation of a three-phase motor, reverse _____. any one lead any two leads any three leads all leads
any two leads
The squirrel-cage rotor is constructed of _____ and end _____ embedded in steel laminations. bars; bars rings; rings bars; rings rings; bars
bars; rings
The wound-rotor induction motor is popular in industry because it has _____ starting torque and _____ starting current. low; low low; high high; low high; high
high; low
The capacitor-start induction-run motor produces a starting torque that is ________ that of the resistance-start induction-run motor. higher than lower than equal to
higher than
In order to increase the efficiency of the cooling, some alternators operate in a(n) _____ atmosphere. helium oxygen hydrogen nitrogen
hydrogen
In the shaded-pole induction motor, the direction of rotation of the magnetic field is determined by the _____. generator power rotor construction shading coil diameter magnetic field direction
magnetic field direction
On the phase rotation meter, which leads of the meter connect to the "T" leads of the motor? motor line terminal phase
motor
The stator winding of a three-phase motor is often referred to as ________. motor primary motor secondary phase primary phase secondary
motor primary
Which type of harmonic generally causes problems with motors? positive sequence negative sequence neutral sequence triplen
negative sequence
In a motor that has a rotating magnetic field, the speed of that magnetic field is referred to as the _____. rotor speed stator speed synchronous speed slip speed
synchronous speed
In a repulsion-induction motor, what is added to the armature? copper windings two windings three windings squirrel-cage windings
squirrel-cage windings
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. operating voltage overload current starting torque synchronous speed
starting torque
The non-rotating part of a revolving-field-type alternator is called the _____. stator exciter rotor synchronizer
stator
The torque of a squirrel-cage induction motor will be maximum when the phase angle between the stator and rotor fields is _____. 0° 90° 180° 270°
0°
An alternator containing eight poles per phase is turning at 1500 RPM. What is the output frequency? 70 Hz 80 Hz 90 Hz 100 Hz
100 Hz
The Holtz motor operates at _____ RPM. 1200 1725 1800 3600
1200
NEC Section 430.22 states that conductors supplying a single motor operating in a continuous-duty application shall have an ampacity of not less than _________ of the motor full-load current. 90% 100% 125% 150%
125%
Many of the three-phase motors used in industry are designed to be operated on how many voltages? 1 2 3 4
2
An alternator containing eight poles per phase is turning at 900 RPM. What is the output frequency? 30 Hz 40 Hz 50 Hz 60 Hz
60 Hz
Most dual-voltage motors bring out how many T leads at the terminal box? 7 8 9 10
9
When determining the derating factor for a transformer, how many ampere measurements must be made? one two three four
two
Solid-state inverters are a common method of supplying what to the motor? amperes power voltage torque
voltage
In a universal motor, inductive compensation can be used when the motor is connected to _____. AC only DC only either AC or DC
AC only
What type of motor exhibits slightly higher efficiency than other types of motors, but also has a higher starting current? Design A Design B Design C Design D
Design B
Because synchronous motors are often made to have a leading power factor by overexciting the rotor current, the full-load current rating must be decreased when this is done. T F
F
Because the phasor rotation of a negative harmonic is the same as that of the fundamental frequency, it will tend to weaken the rotating magnetic field of an induction motor, causing it to produce much greater torque. T F
F
Harmonics are produced by linear loads that draw current in a continuous manner. T F
F
If triplen harmonics are present on the neutral conductor, harmonic filters cannot be added at the load. T F
F
In the formula for calculating output voltage, v represents velocity in hertz. T F
F
In the formula for determining torque, T represents the torque constant True False
F
Neutral conductors can help reduce the amount of harmonics on the line. T F
F
One factor determining the amount of torque produced by a DC induction is the strength of the magnetic field of the poles. T F
F
Single-phase motors all operate on the principle of a rotating magnetic field. T F
F
The fact that the three voltages in a three-phase system do not change polarity at regular intervals is one factor that causes the magnetic field to rotate. T F
F
The synchronous motor is an induction motor. True False
F
To minimize interference, telecommunication cables are run as close to phase conductors as possible and as far away from the neutral conductor as possible. T F
F
When a harmonics problem has been determined, it is general practice to remove the equipment that is causing the harmonic distortion. T F
F
When alternators have been paralleled and if Alternator 2 is being driven by a steam turbine, the power of the turbine would have to be decreased. T F
F
If a three-phase motor will be operated at 80% power factor, the full-load current must be increased by 10%. True False
False
In a field-discharge resistor, a special double-pole single-throw switch with a separate blade is used to connect the resistor to the field before the switch contacts open. T F
T
To test for harmonic distortion in a three-phase four-wire system, measure all phase currents and the _______________ current with both a true-RMS indicating ammeter and an average-indicating ammeter.
Neutral
A capacitor-start capacitor-run motor operates on the principle of a rotating magnetic field in the stator. T F
T
A factor that must be considered when installing a motor is the size starter used to connect the motor to the line. T F
T
After alternators have been paralleled, the power input to Alternator 2 must be increased to permit it to share part of the load. T F
T
Because the instantaneous peak value of current is equal to the RMS value times 1.414, if the current waveforms are sinusoidal, the formula produces a derating factor of 1.0. T F
T
Capacitors in permanent split capacitor motors are generally the oil-filled type. T F
T
Frequent starting of a capacitor-start induction-run motor can damage the start capacitor because of overheating. T F
T
Harmonics are classified by name, frequency, and sequence. T F
T
Harmonics can have very detrimental effects on electric equipment. T F
T
Hydrogen is less dense than air at the same pressure. T F
T
If phase currents are unequal, find an average value by adding currents together and dividing by three. T F
T
An alternator that has a separate small alternator mounted on the shaft of its rotor is equipped with a(n) _____. electric starter primary exciter brushless energizer brushless exciter
brushless exciter
The universal motor has a wound armature and brushes like an AC motor, as well as an added component, the _____. inductive winding compensating winding neutral plane synchronous winding
compensating winding
In what type of selsyn system does the third unit turn by the same amount when one unit is held in place when a second unit is turned? differential transmitter single-phase three-phase
differential
Which of the following would not be associated with harmonics on single-phase power lines? electronic ballasts triac light dimmers computer power supplies electronic drives for DC motors
electronic drives for DC motors
The direct current that is an input to the alternator's rotor is the _____ current. excitation starting synchronizing initiating
excitation
One method of determining harmonic problems on single-phase systems is to make two separate current checks. When this is performed, a ratio of average to true-RMS equal to one indicates _____ harmonic distortion. no moderate extreme
no
What is one factor that controls the output frequency of an alternator? number of stator poles and rotor rotation speed input voltage number of stator poles and number of rotor bars input voltage and torque
number of stator poles and rotor rotation speed
Which measuring instrument responds to true RMS current when checking for harmonics problems? wattmeter ohmmeter ohmmeter galvometer
ohmmeter
When the field-discharge switch is closed and DC is connected to the field, the circuit connecting the resistor to the field is __________. open closed
open
By increasing or decreasing the strength of the magnetic field of the rotor, the _______________ of an alternator is controlled.
output voltage
Some motors are constructed so that they will operate on either of two voltages. When they are connected to operate on the lower of the two voltages, the phase windings are connected in _____. series parallel
parallel
What are capacitor-start capacitor-run motors generally called? single phase permanent split-capacitor dual run multiphase dual run
permanent split-capacitor
Which type of harmonic would cause the magnetic field to rotate in the same direction as the fundamental frequency?
positive sequence negative sequence neutral sequence triplen
Which of the following is not a common symptom of harmonics problems? overheated conductors overheated transformers circuit breakers that trip when they should not pulsations of current
pulsations of current
Split-phase motors operate on the principle of a _____ magnetic field. fixed pulsating vibrating rotating
rotating
The rotating part of a revolving-armature-type of alternator is called the _____. stator exciter rotor synchronizer
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. start run synchronous disconnect
run
Selsyn motors operate on _____ voltage. two-phase single-phase three-phase
single-phase
Power is carried to the outside circuit of a revolving armature type of alternator via brushes riding against the _____. commutators diodes sliprings wires
sliprings
The ______ is the temperature rating of the devices and terminals as specified in NEC Section 110.14(C). termination measurement termination temperature temperature measurement heat rating
termination temperature
Which of the following is a factor in determining the synchronous speed of the rotating magnetic field? the number of inverse rotations the number of magnetic rotations the frequency of the applied voltage the frequency of the voltage drop
the frequency of the applied voltage
Each time the rotor position of the transmitter of a selysn motor is changed, the rotor of the receiver changes by what amount? more torque less greater the same
the same
The differential selsyn has three stator windings connected in a wye and a rotor made of _____. three windings connected in a wye one winding
three windings connected in a wye
What is a special type of motor designed to operate with the rotor stalled without damage to the motor? servo motor torque motor repulsion motor capacitor-start capacitor-run motor
torque motor
Harmonics on single-phase powerlines are generally caused by a device such as a _____. triac light dimmer lamp with an incandescent bulb single-speed motor heater
triac light dimmer
Which type of harmonic generally causes trouble in a three-phase four-wire system? positive sequence negative sequence neutral sequence triplen
triplen
The formula for determining the transformer harmonic derating factor produces a value somewhere between _____. zero and one zero and ten zero and the RMS phase current zero and the instantaneous peak value
zero and one
