Ac/Dc Machinies motor midterm

The method of identifying the orientation or direction of a transformers windings is called the _____

Dot convention

Circulating currents, called ______ cause heating and energy losses within the transformer core decreasing the transformers efficiency.

Eddy currents

Voltage ratio of a transformer is equal to the

Turns ratio

When the nameplate of a motor does not list a service factor rating, a service factor rating of 1.00 is assumed and there is no built-in safety margin for the motor.

True

A transformer with one winding common to both primary and secondary circuits is a(n)

Autotransformer

A variac is a(n) ______ that produces a variable AC voltage from a fixed voltage AC supply.

Autotransformer

The windings of a transformer are wrapped together around a closed magnetic iron circuit called a

Core

An instrument transformer that is designed to produce an alternating current in its secondary winding which is proportional to the current being measured in its primary is a(n) __

Current transformer

Motor manufacturers produce only energy-efficient motors.

False

A transformer where the complete core and coil assembly is enclosed in a metal tank and immersed in an insulating oil, and the oil conducts the heat from the core and coil by means of natural convection to the surface of the enclosure where it is dissipated by radiation into the surrounding air, is a ______ transformer.

Oil-Immersed Self-Cooling

If transformer pad pressure is low, use ______ to raise pressure

Pure dry nitrogen

Eddy current losses within a transformer core can be greatly reduced and controlled by ______ the thickness of the steel core.

Reducing

The output winding of a transformer is the ______ winding.

Secondary

A transformer where the cooling of the coil windings is accomplished by natural convection of the surrounding air and by the radiation of heat from the different parts of the transformer structure is a ______ transformer.

Self-Air-Cooled Dry-Type

Electric motors typically require either direct current (DC), single-phase alternating current (1f AC), or three-phase alternating current (3f AC).

True

For every 1% voltage unbalance, there can be up to a 6% current unbalance.

True

Most motors include light-duty-rated or medium-duty-rated bearings.

True

Since a nameplate has limited space to convey the ratings, most information is abbreviated or coded to save space.

True

Typical operating environments for totally enclosed motor enclosures include the following: wet locations, dirty locations, oily locations, corrosive locations, extremely low- and high-temperature locations, gas and other hazardous locations, and combustible-dust locations.

True

______ has an advantage over ______ because it can be easily generated, transformed into a much higher voltage and then distributed around the country over long distances.

AC voltage, DC voltage

The fact that each winding must be wound for the full line voltage is a disadvantage of the ______ connected transformer.

Delta/Delta

The fact that there is no neutral or common connection is a disadvantage of the ______ connected transformer.

Delta/Delta

Voltage control of a transformer is achieved by changing ______ in the primary winding.

Direction

What is the main concern for distribution type transformers?

Dissipation of heat

AC motors will typically use voltage levels of 24 V, 48 V, 90 V, or 180 V.

False

For fractional-HP frame sizes, the frame number represents the distance from the bottom of the base to the center of the shaft in 8ths of an inch.

False

The voltage applied to a motor must always exactly match the nameplate voltage rating.

False

When the transformer load is increased, the primary current will

Increase

___ motors are used in applications such as compressors, waste-disposal systems, electric hoists, gate-opening motors, and other applications in which the motor need only be turned on for short time periods to meet the application requirements.

Intermittent-rated

A transformer that increases the voltage on its secondary winding with respect to the primary is called a ______ transformer.

Step up

Directly applying any frequency to a motor other than the nameplate rated frequency will change the motor's operating characteristics (speed and output torque) and can damage the motor.

True

Insulation breakdown is the most common cause of motor failure.

True

Which is a type of oil used in wet transformers?

Vegetable oil

Transformers are rated in ___

Volt-amperes

______ of a transformer is the change in secondary terminal voltage when the transformer loading is at its maximum, while the primary supply voltage is held constant.

Voltage regulation

The ______ current transformer primary winding is physically connected in series with the conductor that carries the measured current flowing in the circuit.

Wound

A disadvantage of the ______ connected transformer is that it requires the use of three windings, and if any one winding becomes faulted or disabled, the whole group is disabled.

Wye/Wye

Electrical ratings included on motor nameplates include a ___ rating and phase

all of the above

The ___ rating is the amount of current a motor draws when delivering full rated power output

current

The NEMA ___ letter is a code letter representing a National Electrical Manufacturers Association (NEMA) motor classification for the torque and current curves of a motor.

design

The ___ is a code letter signifying the maximum operating temperature of the insulation used in a motor.

insulation class

A ___ is a machine component used to reduce friction and maintain clearance between stationary and moving parts.

motor bearing

A(n) ___ is a metal tag permanently attached to an electric motor frame that gives the required electrical ratings, operating ratings, and mechanical-design codes of the motor.

nameplate

The ___, or duty cycle, is the amount of time a motor can be operated without being turned OFF to allow for cooling.

operating time rating

The ___ is the difference between the winding temperature of a running motor and the ambient temperature.

temperature rise

A design ___ motor is an integral-horsepower 3-phase induction motor design made for full-voltage starting and high locked-rotor torque, with locked-rotor current not exceeding a specified value.

. C

A transformer that decreases the voltage on its secondary winding with respect to the primary is called a ______ transformer.

. Step down

A design ___ motor is an integral-horsepower single-phase motor design made for full-voltage starting and locked-rotor torque higher than for design M, N, and O motors.

L

___ current, or starting current, or inrush current, is the amount of current a motor draws on startup or when the rotor is locked.

Locked-rotor (LRC)

The process by which a coil of wire magnetically induces a voltage into another coil located in close proximity to it is __

Mutual induction

The difference in voltage between the primary and the secondary windings is achieved by changing the ______ of coil turns in the primary winding compared to the ______ of coil turns on the secondary winding.

Number

The input winding of a transformer is the ______ winding.

Primary

In a three phase transformer the magnetic flux of the three phases are ______ apart.

120 degrees

If a dual winding transformer has two secondary windings, each rated at 120 volt, 50 amp, what would the secondary voltage rating be if these windings were connected in parallel?

240 volt

If a dual winding transformer has two secondary windings, each rated at 120 volt, 50 amp, what would the secondary voltage rating be if these windings were connected in series?

240 volt

If a dual winding transformer has two secondary windings, each rated at 120 volt, 50 amp, what would the secondary current rating be if these windings were connected in parallel?

25 amp

___ type is the type of protection given to a motor to shield the motor from the outside environment as well as to protect individuals from the electrical and rotating parts of the motor.

Enclosure

In an ideal transformer (ignoring any losses), the relationship of power in the primary and secondary winding is

Equal

A device that provides a path for pressure created by an electrical fault inside the transformer to prevent rupture of the tank is a (n) ______ .

Explosion vent

The actual voltage applied to a motor should be within 15% of the motor's nameplate rated voltage.

False

The list of motor nameplate locked-rotor indicating code letters begins with the letter "A" and ends with "Z."

False

A transformer works on ______ law of physics.

Faraday's law

_ is a system that provides the ability for a motor or process to keep running instead of shutting down after one phase has gone to ground.

High resistance grounding

A transformer that produces the same voltage on its secondary as is applied to its primary winding is called a ______ transformer.

Impedance

How much increase rating does a functioning air blast give a dry type transformer?

33 %

The ___ rating is a description of the expected or allowed application of a motor.

usage

If the primary of a transformer is supplied with 480 volts, and the output voltage of the secondary is 120 volts, and the load of the secondary is 4 amps, how much current will flow in the primary winding?

1 amp

If a dual winding transformer has two secondary windings, each rated at 120 volt, 50 amp, what would the secondary current rating be if these windings were connected in series?

100 amp