Midterm Theory Questions

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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


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