Final Review Flashcards by Stacey Unger

What is the prime function of all DC motors?

To maintain starting current within safe limits

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What type of protection does a three-point starter provide?

It provides low voltage protection

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What type of compounding is used when constant voltage or speed is required?

Flat compounding

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What type of manual starter provides a great ability to control speed

A four-point starter

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What components ride against the commutator segments and connect the armature to the external circuit of a DC generator?

The carbon graphite brushes

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What is the purpose of a field winding in a DC machine?

To create the main magnetic field

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Once the DC motor is started and all the resistance is removed, what limits the current through the armature?

Counter EMF

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What does a successful starting up a self-excited DC machine depend on?

Residual magnetism

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How should the direction of rotation of a DC motor be reversed?

By changing the armature leads A1 and A2

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What protective device connected in series with a shunt field do most large compound motors have?

A field loss relay

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What is an advantage of a separately excited DC machine?

Constant field strength

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If resistance is removed from the shunt field winding circuit, what will happen to the magnetic field?

It increases strength

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If resistance is added to the shunt field winding circuit of a DC shunt motor, what will happened to the motor speed?

Less field strength equals less CEMF
More current through the armature equals more speed

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What type of wound armature have their windings connected in parallel?

Lap wound

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What is the distortion or bending of the main magnetic field of a DC machine caused by its interaction with a magnetic flux developed by the armature current called?

Armature reaction

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What type of compounding occurs when a cumulative long-shunt compound motors full loaded speed is greater than no load speed?

Over compounding

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What type of compounding occurs when differential short shunt compound generators full load voltage is less than it’s no load voltage?

Under compounding or differentially compounded

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What is the function of the series field rheostat?

To divert current around the series field, thus controlling compounding

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What is the commutator of a DC machine constructed of?

Each of the segments of the commentator are insulated from one another with a heat proof insulating material known as Mica

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What is the position at which the armature windings are parallel to the lines of flux and there is no induced voltage called?

The neutral plane

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What happens to the counter EMF generator as load is added to a series motor?

Speed decreases which causes counter EMF to decrease

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What is the main disadvantage of a manual 3-point starter?

It has no speed control

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What is the best way to slow or stop a DC motor under normal operation?

Dynamic braking

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Will increasing the number of turns of wire in an armature coil of a DC generator cause an induced EMF to increase or decrease?

Increase

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What is the function of the shunt field rheostat on a DC shunt motor?

To control the current through the shunt field

Are resistance and voltage directly or inversely proportional in a DC shunt generator?

Inversely

What two components are used to hold the brushes in place and maintain an even pressure?

Brush holders and springs

What component of a DC machine supports their shaft and allows it to rotate freely?

The bearings

What are the three factors that determine the strength of electromagnetic?

1: Turns 2: Core Strength 3: Current

What is the component of a DC generator that converts AC to DC called?

The commutator

What is the force that causes a motor to rotate known as?

Lorentz Force

What type of compound motor has its fields winding wound in such a matter that they aid each other in the production of magnetism?

Cumulative compound

Will increasing the number of turns of wire in an armature coil of a DC motor cause the CEMF to increase?

Increase

Name two industrial processes in which differential compound generator may be used?

Welding and electroplating

When starting a DC motor, what percentage of FLA shall the starting current be limited to?

150%

What type of DC motor is used when constant or adjustable speed is extremely important?

Separately excited shunt

In reference to the left hand rule for generators, what do the thumb forefinger and middle finger represent?

Thumb: Thrust Forefinger: Main magnetic field Middle finger: current through the armature

What are the windings embedded in slots or holes in the main pole face called?

Compensating windings

What are two types of magnets?

Electromagnets and permanent magnets

When a generator supplies current to a load, what is produced, which makes the armature assembly harder to turn?

Counter torque

What causes the shift of the neutral plane on a DC motor under load?

Current through the armature causing it to react with the main field

When a DC motor is first started, why is the armature current so high?

Not involving low armature resistance before counter EMF develops

Where are magnetic flux lines most densely concentrated?

At the pole face or shoe

What is the insulation separating the copper segments of the commentator constructed of?

Mica

What are the four components that comprise an armature assembly?

1: Shaft 2: Commutator 3: Armature Windings 4: Iron Core

When electromagnetic reaches to a point where strength increases only slightly when an increase in current, it is known as a point of?

Saturation

What are the three factors that determine the output of a generator?

1: Speed of the armature 2: strength of the main magnetic field 3: turns and configuration of the armature windings

What are the three ways that armature reaction can be corrected?

1: Interpoles 2: Compensating windings 3: rotate the brushes to the neutral plane

When proper communication is taking place, what color is a commutator?

Dark chocolate

What happens to the torque of DC series motor as the load is increased?

It increases

If resistance is added to the shunt field winding circuit of a DC generator, what will happen to the output voltage?

It decreases

Is the resistance of a shunt field winding higher or lower than the resistance of the serious field winding?

Yes

What are the windings wound around the interpoles called?

Commutating windings

What is the amount of magnetism left in a material after magnetizing force has stopped called?

Residual magnetism

What type of DC machine converts mechanical input into electrical output?

Generator

What is the rotating assembly of a DC machine called?

Armature assembly

What are the six components that comprise most DC machines?

1: enclosure 2: bearings 3: pole pieces 4: armature assembly 5: field windings 6: brushes 7: terminals

What are the three basic types of armature? Windings?

1: lap wound 2: wave wound 3: frog leg wound

In a series field winding in a DC machine considered a load or a source?

Load

What are two types of bearings found in a DC machines?

Sleeve and ball

What is a DC generator that uses permanent magnetics as its field known as?

Magneto

What are the three types of field windings used in DC machines?

1: series 2: shunt 3: compound

What is the mechanical force used to turn a generator called?

Prime mover

Field windings are wound on to magnetic poles to form?

Electromagnets

What is the proportion of the pole piece closest to the armature called?

Pole shoe

How can the ripple effect be smooth in the output of a DC generator?

More winding average output voltage is higher, less pulsation or slots

What are the three types of DC machine field structures?

1: Permanent magnetic 2: separately excited 3: self-excited

What type of armature winding provides modern voltage and modern current?

Frog leg wounds

What type of wound armature have their windings connected in parallel?

Lap wound

What type of armature windings provide high voltage and low current?

Wave wound

Is the voltage induced into the armature windings of a DC generator AC or DC?

How is the winding of an interpol connected in relation to the armature?

Commutating winding is connected in series

Is a polarity of each interpol in a DC generator the same polarity or opposite in polarity of the main pole ahead of each interpole in the direction of rotation?

Same polarity

What are the two main factors that affect the amount of torque developed in a DC motor?

Main magnetic field and armature magnetic flux

Do series motors have an extremely low or extremely high starting torque?

Extremely high

What happens to the torque of a DC series motor as a load is increased?

Torque increases

What happens to the speed of a DC series motor as a load is increased?

Speed decreases

Is a shunt generator considered a constant voltage generator?

Yes, because of its excellent voltage regulation characteristics

What type of compound motor has its field windings wound in such a matter that they oppose each other in the production of magnetism?

Differential compound

What type of DC machine converts electrical input to mechanical output?

Motor

What type of wound armature have their windings connected in series?

Wave wound

What type of armature winding provides low voltage and high current?

Lap wound

Does the armature winding carry the same current as the shunt field windings?

In a serious motor are torque and speed directly or inversely proportional to each other?

Inversely

What is an advantage of a separately excited DC machine?

Better control of output voltage generator and speed control motor

What type of compound generator has its shunt field winding connected in parallel with both the armature and series field windings?

Long shunt

Is the armature reaction proportional to the armature current?

Yes

With a constant load, can armature reaction be corrected by shifting the brushes and therefore adjusting the neutral plane setting?

Yes

What are the four types of enclosures for DC machines?

1: Open type 2: weatherproof 3: drip proof 4: totally enclosed type

Is the commentator an electric or a mechanical switch?

Mechanical

What type of DC motor is used when constant or adjustable speed is extremely important?

Shunt motor

three factors for Right hand rule for motors

Thumb: is the direction of force Forefinger: magnetic field by the field windings Middle finger: current in armature conductor

How is compounding controlled in a compound DC motor or generator?

By changing the strength of the series field via the series field diverter

What type of compounding is used when constant voltage or speed is required?

Flat compound

How is the output voltage of a DC shunt generator controlled?

A voltage regular changes the current to the shunt field

What happens to the speed of a DC series motor as a load is increased?

Decreases speed

What happens to the Counter EMF generated as load is added to a series motor?

Decrease counter EMF

What is a function of the shunt field? Rheostat

To control current through the shunt field

What is the function of the series field rheostat?

To divert current around the series field

What type of armature winding provides high voltage and low current?

Wave wound

What type of generator is considered a constant voltage generator?

Separately excited Shunt

Are resistance of the shunt field rheostat and voltage output directly or inversely proportional and a DC shunt generator?

Inversely

Are resistance of the shunt field rheostat and speed directly or inversely proportional in a DC shunt motor?

Directly

If resistance is added to the shunt field winding circuit of a DC shunt generator, what will happen to the output voltage?

It will decrease

What are the two main factors that affect the amount of torque produced in a DC motor?

Maine field strength and armature field strength

How is compounding controlled in a compound? DC motor or generator?

By changing the relationship of series and shunt fields through the series field diverter

What are the three most common methods of automatically starting a DC motor?

1: counter EMF starter 2: current limit starter 3: time delay starter

What type of wound armatures have their windings connected in series parallel?

Frog leg wound

What is the main disadvantage of a manual 4 point starter?

It does not provide protection against field loss

If resistance is removed to the shunt field winding circuit of a DC motor, what will happen to the motor speed?

It slows down