"3 phase TPC"
Because the rotor of a synchronous motor does not depend on induction to produce current, the ____________ can be larger than in an induction motor.
Air gap
In which of the following motors does torque vary inversely with speed?
Constant horsepower
When removing grease and oil from a motor, you should avoid using too much solvent because it
can damage the insulation
The two kinds of multispeed induction motors are the multiple-winding motor and the ____________ motor.
consequent-pole
At full load, a motor connected to the line will do all of the following EXCEPT
decrease its internal temperature
In a dual-voltage motor, the potential difference across one phase in a Y-connected winding equals the potential difference across the line
divided by the square root of 3
In a constant-horsepower motor, the torque
doubles when the speed is cut in half
If the load driven by an alternator is purely inductive, the current
lags the potential difference
With a low dc field current, the ac current
lags the potential difference
The rotor core of an induction motor is made from slotted sheet steel ____________, generally punched from the same material used for the stator.
laminations
To ensure that three-phase motor control equipment is in good operating condition, you should
maintain a regular plan of inspections
A wound-rotor motor is always started with _____ in the rotor circuit.
maximum resistance
In an induction motor, maximum torque is always developed when the
reactance and the resistance of the rotor are equal
An inductor connected in series with the motor winding is found in a(n)
reactor starter
Reducing the potential difference applied to a motor during the starting period ____________ the starting torque and ____________ the time required for the motor to come up to speed.
reduces; increases
To improve a motor's service life, you should do all of the following EXCEPT
remove the winding insulation
If the load driven by an alternator is purely ____________, the current is in phase with the potential difference.
resistive
Reduced potential difference in a primary-resistance starter is obtained by connecting ____________ in series with each stator lead, then shunting them out of the circuit at high speed.
resistors
The main difference between low-voltage release and low-voltage protection concerns how the motor is
restarted
Whenever an engine starts, it should run until all parts reach
their normal operating temperatures
Although alternators can be built with any number of phases, there is little advantage in using more than
three
When considering power factor, remember that the induction motor is electrically equivalent to a ____________ with a short-circuited secondary winding.
transformer
A four-pole, three-phase motor has _____ coils.
twelve
In a cascade system having large air-gap circuit- breakers, there should not be more than _____ cascade step(s)
two
In a cascade system having large air-gap circuit- breakers, there should not be more than _____ cascade step(s).
two
A relay with inverse-time characteristics operates
faster as the current increases
A lack of torque, a decrease in speed, and growling noises are all indications of a(n)
open rotor circuit
During plugging, the current in an induction motor is higher than the locked-rotor current, causing a(n)
power loss
In establishing a schedule for inspecting generators, you should match the schedule to the maintenance schedule of the
prime mover
The instant that a synchronous motor changes from induction to synchronous operation is called the
pull-in point
To prevent motor starter "chatter" on some motor starter circuits, it may be necessary to employ surge and backspin protection for motors that operate
pumps
In a squirrel-cage induction motor, motor conductor bars inserted in the slots of the rotor core are not insulated from the core because the voltage across each bar is seldom more than ________ V.
10
A motor rated at 2 hp at full load can develop __________ hp if it delivers its maximum torque.
3 to 4.5
Plants where considerable moisture exists often select a 240 V distribution system because it is considered ____________ than a 480 V system.
safer to use
An engine operating at 1714 rpm and driving a 28 pole generator or one operating at 1846 rpm and driving a ____________ pole generator is the most practical generator set for 400 Hz otput
26
When using compressed air to blow out dust from motor windings, the pressure at the nozzle tip must be less than ________ psi.
30
The frame of the stator of an induction motor is sometimes called the
Yoke
When dc power is applied to the rotor of a synchronous motor,
a set of north and south poles is produced
If an induction motor ran at synchronous speed, it would develop zero torque because of the lack of
slip
n automatic transfer system installations that back up critical electronic gear, action is initiated when the potential difference of any phase drops near ____________%.
90
Which of the following is true of a reactor starter, as compared to a resistance starter?
Its connections are the same except that it uses induction coils
The winding in a squirrel-cage rotor consists of copper or aluminum bars, pressed into slots and ____________ at both ends of the rotor.
Short Circuited
All of the following are benefits of system grounding, EXCEPT
allows service to be maintained in entire circuit until the fault is located
Hunting can be reduced on engine-driven and some turbine-driven salient-pole alternators by including a(n)
amortisseur winding
Variable-torque motors are designed to give
an increase in torque with an increase in speed
Acceptable methods of cleaning insulation in auxiliary generating equipment include wiping it with a clean cloth, blowing it off with low-pressure air, using a vacuum cleaner, and cleaning it with a(n)
approved solvent
Reduced-voltage starters for three-phase motors change the potential difference across the motor by means of
autotransformers or resistors
Angular loads are caused by forces applied to the bearing
both parallel and perpendicular to the shaft
The supply winding in an alternator
can be part of either the rotor or the stator
A variable-torque motor produces torque that ____________ and power output that ____________ when the speed doubles.
doubles; quadruples
The power factor of a synchronous motor will be less than 100% if the dc current in the rotor winding is
either too high or too low
The permanent joining of motor frames, conduits, control boxes, and other metal parts not intended to carry current in normal operations is known as
equipment bonding
Induction motors can be connected directly across the line on starting. However, the starting current may be ____________ the rated (running) current.
four to nine times
A synchronous motor is unique in that its speed is controlled by the ____________ of the power supply and is not affected by variations in the ____________ on the motor.
frequency; load
In general, the power factor of an induction motor increases with the load until the maximum power factor is reached at
full load
The frequency of a generator set is controlled by a ____________, which controls engine speed.
governor
200°F (95°C) is the
maximum temperature at which bearings may be safely operated
On a magnetic across-the-line starter, the incoming power lines are connected to terminals L1, L2, and L3 on the top of the motor starter, and the ____________ leads are connected to terminals T1, T2, and T3 on the bottom of the motor starter.
motor
Many electric motors are manufactured as dual-voltage three-phase motors that are either Y or delta connected with ____________ of twelve leads brought out.
nine
Wound-rotor motors are used most often in applications that require high starting torque and low starting current, where the driven machine starts
slowly
A synchronous motor using an amortisseur winding for starting is electrically the same as a ____________ motor
squirrel-cage induction
When removing abrasive dust and particles from the windings of a large motor, a ____________ works better than compressed air.
vacuum cleaner