Mid Term

Question 1

Connection to the armature of an alternator is normally done using what

Answer 1

Slip rings

Question 2

The higher power output alternators use a

Answer 2

Revolving field

Question 3

Non rotating part of an alternator

Answer 3

Stator

Question 4

Rotating part of an alternator

Answer 4

Rotor

Question 5

An alternator that has a separate mall alternator mounted on the shaft of its rotor is equipped with a

Answer 5

Brushless exciter

Question 6

Output frequency of an alternator is controlled by

Answer 6

Number of stator poles

Rotor speed

Question 7

Alternators should be connected in

Answer 7

Parallel

Question 8

What is a field discharge resistor used for?

Answer 8

A field discharge resistor is used to limit voltage and prevent damage to an alternator when rotor dc excitation is removed.

Question 9

What can be used instead of a field discharge resistor?

Answer 9

Diode

Question 10

What does a synchroscope do?

Answer 10

Test phase angle of an armature

Question 11

Advantages of a brushless exciter?

Answer 11

Less parts to wear. (No brushes)

Question 12

Max kva of a rotating armature alternator?

Answer 12

25kva

Question 13

The amount of emf produced in an alternator is proportional to what?

Answer 13

Number of conductors in the armature
Magnetic field strength
Speed of rotation

Question 14

Describe a salient pole rotor

Answer 14

Has many poles on the outside of the rotor. Turned at low speeds.

Question 15

Describe a cylindrical pole rotor

Answer 15

Have 2-4 poles
Used at high speeds
Cylindrical shape with poles inside

Question 16

Purpose of “f” leads on an alternator

Answer 16

Provide excitation or field current

Question 17

Two types of stators in a rotating armature alternator?

Answer 17

Permenant magnet

Electro magnet

Question 18

Purpose of a rotor in a rotating field alternator?

Answer 18

The rotor is rotated by the prime mover to produce a current

Question 19

What is a prime mover?

Answer 19

The force used to rotate the armature in an alternator. (Harry)

Question 20

What are 4 conditions that must be met when paralleling alternators?

Answer 20

Phase rotation must be the same
Phase sequence must be the same
Frequency
Voltage output

Question 21

Output frequency of an alternator is dependent on?

Answer 21

Speed

Number of poles

Question 22

3 factors that determine output voltage of an alternator

Answer 22

Number of conductors in armature
Magnetic field strength
Speed of rotation

Question 23

What is electromagnetic induction?

Answer 23

When a conductor cuts magnetic lines of force, a voltage is induced into the conductor

Question 24

Describe lenzs law

Answer 24

When a closed loop of wire cuts through magnetic lines of flux, current is induced into the loop, creating a magnetic field. This magnetic field opposes the original field.

Question 25

Is a synchronous motor an induction motor?

Answer 25

No

Question 26

What is synchronous speed?

Answer 26

Speed of rotating magnetic field in a motor

Question 27

How is a squirrel cage rotor constructed?

Answer 27

Bars between 2 end rings

Question 28

Motor with high starting current?

Answer 28

Squirrel cage

Question 29

Typical percent slip of a squirrel cage motor?

Answer 29

2-5%

Question 30

Describe single phasing

Answer 30

Lose a single phase of a 3 phase of a three phase motor.

Question 31

Motor with low starting current and high starting torque?

Answer 31

Wound rotor motor

Question 32

What are amortisseur windings?

Answer 32

A set of squirrel cage bars on the rotor of a synchronous motor used to start the motor.

Question 33

What is a synchronous condenser?

Answer 33

A synchronous motor with no load used to correct the power factor of another motor or set of motors.

Question 34

How is the rotor in a seldom motor constructed?

Answer 34

3 windings connected in wye

Question 35

What are wound rotors motors used for?

Answer 35

High starting torque, low inrush current | Variable speed control

Question 36

How are 3 phase motors alike?

Answer 36

All operate on the principle of a rotating magnetic field | All have the same stator design

Question 37

How are 3 phase motors different?

Answer 37

Have different rotor designs

Question 38

What is the purpose of the m leads?

Answer 38

Connect your rotor circuit to the resistors in a wound rotor motor.

Question 39

Describe the starting sequence of a wound rotor motor

Answer 39

Resistance is connected to the rotor circuit to limit inrush current Energize stator, creating rotating magnetic field Voltage induced in the rotor is shunted out through the resistors Resistance is removed making the rotor start to turn At full rpm all resistance is removed

Question 40

Starting sequence of the synchronous motor

Answer 40

Energize stator, creating rotating magnetic field Field cuts amortisseur winding Current through the amortisseur winding produces a magnetic field that is attracted to the stator field causing the winding to turn When close to synchronous speed dc is applied to the rotor, causing the rotor windings to become electromagnets Rotor and stator fields lock in step and rotate at synchronous speed

Question 41

Describe the wiring configuration of the stator in a wound rotor motor

Answer 41

Windings 120 degrees apart setting up a rotating magnetic field Stator is the same in all 3 phase motors

Question 42

Describe the construction of a squirrel cage rotor

Answer 42

Bars connected to 2 end rings

Question 43

Describe the construction of a wound rotor motor

Answer 43

Has 3 separate windings 120 degrees apart Same poles per phase as the stator Coils connected to slip rings on the rotor shaft

Question 44

Describe the construction of a synchronous motor

Answer 44

Dc excited wound coil with a squirrel cage added to it

Question 45

What are the brushes in a synchronous motor used for?

Answer 45

Dc excitation to the rotor

Question 46

Describe how a rotating magnetic field is set up by the stator

Answer 46

The pairs of poles in the stator are wound so that when current flows flow through the winding they develop opposite polarities. When the stator is energized a rotating field is set up which we call phase rotation. It rotates at synchronous speed Windings are 120 degrees apart

Question 47

How are shynchronous and wound rotor motors the same?

Answer 47

Same stator | Both use wound coils. Wound rotor has 3, synchronous has 1

Question 48

How are synchronous and squirrel cage motors the same?

Answer 48

Same stator | Synchronous motor used a set of squirrel cage bars in the rotor that are used to start the motor. (Amortisseur winding)

Question 49

Why are motors important

Answer 49

Cause fuck you that’s why