Electrical Machines Midterm 6261-ELPT-1351

Magnetic permeability

is a measure of the ability of a material to conduct magnetic flux.

Magnetic saturation

____________________ is the condition where a magnetic core has substantially all the magnetic domains aligned with the field and any increases in current no longer result in a stronger electromagnet.

Magnetic force

____________________ is a force caused by a magnet that acts at a distance on other magnets.

Mutual

____________________ induction is the ability of an inductor (coil) in one circuit to induce a voltage in another circuit or conductor.

relative motion

The three requirements for induction are a conductor, a magnetic field, and ____________________ between the conductor and the magnetic field.

increases

The current and the strength of the magnetic field decrease if the resistance of the circuit ____________________.

reversed periodically

In order to create the continuous motion needed in a motor, the direction of the current must be ____________________.

current

The direction of an electromagnetic field is determined by the direction of the ____________________ flowing though the conductor.

voltage

A motor's nameplate ____________________ rating is the optimal voltage that should be connected to the motor for best operating performance.

Operating

____________________ ratings include the power rating, usage rating, service factor rating, speed rating, operating time rating, motor efficiency rating, ambient temperature rating, and insulation class.

power

The ____________________ rating is the amount of power a motor can deliver to a load.

speed

The ____________________ rating of a motor is the approximate speed at which the rotor of a motor rotates when delivering rated power to a load.

Motor efficiency

____________________ is a measure of the effectiveness with which a motor converts electrical energy to mechanical energy.

totally enclosed

A(n) ____________________ motor enclosure is a motor enclosure that prevents air from entering the motor.

service factor rating

The ____________________ is a multiplier that represents the amount of load, beyond the rated load, that can be placed on a motor without causing damage.

general-purpose

Motors that are rated for ____________________ usage are used in a wide range of applications and for mechanical loads such as conveyors, machine tools, and belt-driven equipment.

Open

____________________ motor enclosures include general, drip-proof, splashproof, guarded, semiguarded, and drip-proof fully guarded types.

40

A motor without an ambient temperature rating is assumed to be rated at ____________________°C.

brushless exciter

A(n) ____________________ is a rectifier assembly mounted on the main rotor shaft along with the exciter generator.

revolving rotor

A(n) ____________________ alternator is an alternator where a fixed magnetic field is created in the stator, with the rotor turning within the stator, and AC power is supplied through the rotor slip rings and brushes.

Torque

____________________ is turning or twisting force that causes an object to rotate.

overload rating

The ____________________ of an alternator is the load above the normal load that can be carried for a specified period.

alternator

A(n) ____________________ is a synchronous machine that produces alternating current (AC).

exciter

A(n) ____________________ generator is an assembly consisting of a small three-phase alternator used to supply current to an alternator rotor.

automatic

With ____________________ synchronization, a controller monitors the frequency, phase angle, and voltage of the incoming source and the busbar.

rotor

A(n) ____________________ is the rotating moving part of an alternator or generator, consisting of a core and windings, that convert torque to magnetic energy.

stator

A(n) ____________________ is the fixed unmoving part of a generator, consisting of a core and windings, that converts the energy of a magnetic field to electrical energy.

rotor

A(n) ____________________ is the rotating, moving part of a motor, consisting of a core and windings, which convert the rotating magnetic field of the stator into the torque that rotates the shaft.

dual voltage

A(n) ____________________ motor is a motor that operates at more than one voltage level.

True power

____________________ is used by the resistive part of a circuit that performs the work and can be produced only when current and voltage are both positive or both are negative.

Torque

____________________ is typically measured in foot-pounds (ft-lb), pound-feet (lb-ft), and inch-ounces (in.-oz).

rotor frequency

The ____________________ is the rate at which the stator magnetic field passes the poles in the rotor.

Locked rotor

____________________ torque is the torque a motor produces when the rotor is stationary and full power is applied to the motor.

energy

All motors have motor ____________________ losses that reduce motor efficiency.

synchronous speed

The ____________________ is the theoretical speed of a motor based on line frequency and the number of poles of the motor.

magnetic field

Mutual induction requires the presence of a(n) ____________________ and relative movement of a conductor within that field.

D

Motor Design ____________________ has high starting torque, high slip, and low starting current.

Induction

____________________ motors are the most common 3-phase motors used in industry today.

shaft

The rotor consists of a core and windings, which converts the rotating magnetic field of the stator into the torque that rotates the ____________________.

squirrel-cage

A(n) ____________________ rotor is an induction motor rotor consisting of conductors made from solid bars assembled into a cage frame resembling a squirrel cage.

stator

At startup, the magnetic field in the ____________________ interacts with the stationary conductor bars in the rotor windings and induces a current.

fan blades

In many motor styles, the shorting rings contain ____________________ that move the air through the motor for cooling.

B

Design ____________________ motors are designed for a broad variety of applications, such as in HVAC applications providing power for fans and blowers and in industrial applications providing power for pumps.

drum switch

A(n) ____________________ is a rotating control device used to switch resistors in or out of a wound-rotor circuit.

brush rigging

A(n) ____________________ is the entire assembly of the brush, brush holder, insulators, and any wiring included in the assembly.

starter

A wound-rotor motor ____________________ is a device containing low-wattage resistors that is designed to provide rotor circuit resistance during startup and remove that resistance when the motor is up to speed.

resistance

When some of the resistors in the rotor circuit are shunted, the ____________________ in the rotor circuit is decreased and the rotor current is increased.

resistance

The ____________________ is changed during startup to keep the maximum torque near the actual operating speed throughout the acceleration period.

windings

The rotor ____________________ of a wound-rotor motor consist of coils of insulated copper conductor wound into the slots in the rotor.

microswitch

A drum switch often contains a(n) ____________________ to pull in the stator contactor.

slip ring

A spring placed behind a brush forces the brush to make contact with the ____________________.

brush

A(n) ____________________ is a sliding contact that rides against a rotating component to provide a connection to a stationary circuit.

leading

A(n) ____________________ power factor is a circuit with current leading voltage by some angle between 0° and 90°.

synchronous condenser

A(n) ____________________ is a synchronous motor operated at no load in order to provide power factor correction.

synchronous

A(n) ____________________ motor is a motor that rotates at exactly the same speed as the rotating magnetic field of the stator.

B

Synchronous motors are used for applications in which a NEMA Class ____________________ motor is designed.

synchronous

When a(n) ____________________ motor is running at synchronous speed, there is no relative motion between the rotor and stator magnetic fields and no eddy currents are induced in the iron.

field monitor

A(n) ____________________ relay measures the power factor of the motor and trips the motor offline if synchronization is not achieved within the proper amount of time or if the motor pulls out of step while running.

DC

The power factor of a synchronous motor is determined by the amount of ____________________ power applied to the rotor.

Torque

____________________ angle is the angle between the rotor and stator fields as a synchronous motor is running under load.

Protective relays

____________________ are needed to shut down a synchronous motor if it slips out of synchronous speed.

capacitor start

The ____________________ motor is the most common type of capacitor motor.

90

In a single-phase motor stator, the start winding is placed ____________________ mechanical degrees from the run windings.

auxiliary windings

Capacitor-run motors are available as two- or three-speed motors with the addition of ____________________ that are placed in series with either the start or the run windings.

rotor

A(n) ____________________ is the rotating, moving part of a motor, consisting of a core and windings, that converts the rotating magnetic field of the stator into the torque that rotates the shaft.

capacitor-run

A(n) ____________________ motor is also known as a permanent split-capacitor motor.

start winding

Reversing the ____________________ is the standard method used in industry for reversing the direction of rotation of a single-phase motor.

stator core

A(n) ____________________ is constructed of many notched thin sheets (laminations) of steel to limit eddy currents.

dual-voltage

In a typical ____________________ motor, the run winding is split into two sections.

split-phase motor

A(n) ____________________ is a single-phase AC motor that includes a run winding and a resistive start winding that creates a phase-shift for starting.

centrifugal switch

A(n) ____________________ is a switch that opens to disconnect the start winding when the rotor reaches a certain preset speed and reconnects the start winding when the speed falls below a preset value.

cartridge

A(n) ____________________ fuse is a snap-in cylindrical fuse constructed of a fusible metallic link or links that is designed to open at predetermined current levels.

interrupting rating

The ____________________ is the maximum amount of current that can be safely applied to an OCPD while still maintaining its physical integrity when reacting to fault currents.

instantaneous-trip

A(n) ____________________ circuit breaker is a circuit breaker with no delay between the fault- or overload-sensing element and the tripping action of the device.

circuit breaker

A(n) ____________________ is an overcurrent protection device with a mechanical mechanism that automatically opens a circuit when an overload condition or short circuit occurs.

electronic overload

A(n) ____________________ relay is a device that has built-in circuitry to sense changes in current and temperature.

bimetallic-strip overload

A(n) ____________________ relay can be designed to reset automatically.

overcurrent protection device

A(n) ____________________ is a set of fuses or circuit breakers added to provide overcurrent protection of a switched circuit.

inverse-time

A(n) ____________________ circuit breaker is a circuit breaker with an intentional delay between the time when the fault or overload is sensed and the time when the CB operates.

cartridge

Fuses are commonly available as plug fuses and ____________________ fuses.

field windings

____________________ are magnets or stationary windings used to produce the magnetic field in an alternator or motor.

Interpoles

____________________ are used to reduce sparking at the brushes of larger DC motors.

compound

A(n) ____________________ motor is a DC motor with the field connected in both series and shunt with the armature.

motor

Armature current in a(n) ____________________ is forced to flow in the opposite direction to that of the countervoltage.

commutator

A(n) ____________________ is a ring made of insulated segments that keep the armature windings in the correct polarity.

series-wound

A(n) ____________________ generator is a generator that has its field windings connected in series with the armature and the external circuit (load).

shunt-wound

A(n) ____________________ generator is a generator that has its field windings connected as a shunt in parallel with the armature and the external circuit.

DC

____________________ motors provide excellent speed control for acceleration and deceleration, with effective and simple torque control.

series

A(n) ____________________ motor is a DC motor that has the field winding connected in series with the armature.