Midterm Theory Questions
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 motor that does not contain a wound armature, commutator, or brushes is the _____ motor.
brushless DC
A device that converts electrical energy into mechanical energy is called a(n) _____.
motor
The ability of one coil to induce a voltage into another coil is called _______.
mutual induction
A transformer supplying a house with 240/120 V has a secondary which is center tapped. The conductor connected to the center is called the _____ conductor.
neutral
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 windings are connected in _____.
parallel
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
When closing a delta, connections should be checked for proper ____ before making the final connection and applying power.
polarity
The ServoDisc motor is also often called a _____ motor.
printed-circuit
Some motors are constructed so that they will operate on either of two voltages. When they are connected to operate on the higher of the two voltages, the windings are connected in _____.
series
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
In a single phase motor the speed of the rotating magnetic field is called ______.
Synchronous speed
There are three basic types of three-phase motors, the squirrel-cage induction motor, the wound-rotor induction motor, and the synchronous motor, the difference among them is the type of _____ used.
Rotor
A motor that has 60 stator poles per phase at 60 hz would have an RPM of ______.
S = 120 * f/P 120 * 60 / 60 = 120 RPM
The torque of a squirrel-cage induction motor will be maximum when the phase angle between the stator and rotor fields is _____.
0
DC motors operate on the principle of _______.
Repulsion and Attraction
Which of the following is not a standard type of single phase motor.
Resistance Start / Resistance Run
Motors that use high pole count for low speed high torque applications are often referred to as ______.
Ring torquers
Single-phase motors are used almost exclusively to operate _______?
Fans Well pumps Home Appliances
______ is the amount of magnetic flux lines that do not follow the metal core and are lost to the surrounding air.
Flux leakage
The _____ relay functions as both a starting relay and an overload relay.
Hot-wire
In a split phase motor the current flow through the run winding lags the applied voltage due to _____.
Inductive reactance
A tape-wound core is also called a(n) _____ core.
toroid
In a transformer, the turns of primary wire compared to the turns of secondary wire is called the _____ ratio.
turns
All values of a transformer are proportional to its _______.
turns ratio
For most squirrel-cage induction motors the typical percent slip is about _____ percent.
two to five
In general, what type of compound-motor connection should be avoided?
Differential-compound
A motor is operating at 3450 RPM and is producing a torque of 32 lb-in. What is the output horsepower of the motor?
1.75 hp
A squirrel-cage rotor induction motor has a synchronous speed of 3600 RPM and an actual rotor speed of 3450 RPM. What is the percent slip?
4.17%
One horsepower is equal to how many watts of power?
746
A two-phase system is produced by having an alternator with two sets of coils wound _____ apart.
90
Another common way to create a second current wave for a single phase motor is by using ___________.
A Shading Coil
The start winding of a resistance-start induction-run motor is intended to be energized only during the period of time that the motor is actually starting. If the start winding is not disconnected, it will be damaged by excessive ______.
Current flow
In a universal motor, inductive compensation can be used when the motor is connected to _____.
AC only
To change the direction of rotation of a compound motor, the connection of the ______ will need to be reversed?
Armature leads
_______ are one-winding transformers. They use the same winding for both the primary and secondary.
Autotransformers
To disconnect one of the windings, after the motor has started, a ___________ is commonly used.
Centrifugal Switch
A common type of isolation transformer is the ________. This type of transformer changes the high voltage of power company distribution lines to the common 240/120 volts used to supply power to most homes and many businesses.
Distribution transformer
A capacitor is connected in _____ with the winding to provide a continuous leading current in the ______ winding.
Series; start
The servomotor featuring a fiberglass and copper rotor is the _____ motor.
ServoDisc
Split phase motors start by creating __________.
Simulated 2 phase power
Single phase motors generally have two stator winding called ________ and __________.
Start and Run
The ____ winding of a motor is often referred to as the motor primary, and the rotor is referred to as the motor secondary.
Stator
The direction of rotation of any three-phase motor can be changed by reversing two of its _________.
Stator leads
Which is not a standard repulsion type single phase motor?
The Repulsion-Capacitance Motor
The amount of starting torque produced by a split-phase motor can be determined by_____.
The strength of the magnetic field of the stator
What two forces determine the torque of a dc motor?
The strength of the magnetic fields of the poles and the armature
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 the consequent pole motor, if the number of poles is doubled, the motor speed will be _____.
cut in half
The frequency of the current in a squirrel-cage rotor _____ as the rotor approaches synchronous speed.
decreases
In a transformer, even when there is no load connected, there will be some small current flow known as _____ current.
excitation
What frequency should be applied to a six-pole motor to produce a synchronous speed of 400 RPM?
f = PS/120 6 * 400 / 120 = 20 Hz
Permanent magnet motors have _____ efficiency than conventional field-wound motors.
higher
A single phase synchronous motor is sometimes called a
hysteresis motor
A(n)_____transformer is magnetically coupled, not electrically coupled. This means that the secondary winding is physically and electrically isolated from the primary winding.
isolation transformer
Most transformer cores are assembled from many thin sheets of metal. This type of construction is called _____.
laminated
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 operating principle of all three-phase motors is the _______.
rotating magnetic field
A compound motor has _____ field windings
series and shunt
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
The DC motor, known as a "constant speed motor," is the _____ motor.
shunt
When the field winding of a DC motor is connected in parallel with the armature, the motor is called a _____ motor.
shunt
When a motor is connected to a differential compound, the _____ determines the direction of rotation of the motor at no load or light load.
shunt field
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
