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Bryx_Electronics > Electrical Machines > Flashcards

Electrical Machines Flashcards

1
Q

A generator machine converts mechanical energy into electrical energy by the principle of what?

A

Faraday’s Law

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2
Q

What is called the source of mechanical power or energy used to turn the rotor of the generator

A

Prime mover

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3
Q

“Whenever conductor is moved within a magnetic field in such a way that the conductor cuts across magnetic lines of flux, voltage is generated in the conductor” this statement is also known as?

A

Electromagnetic Induction by Michael faraday

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4
Q

The magnitude of voltage generated depends upon what 4 factors?

A
  1. ) The strength of magnetic field
  2. ) The angle at which the conductor cuts the magnetic field
  3. ) The speed at which the conductor is moved,
  4. ) the length of the conductor within the magnetic field
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5
Q

What method is used to determine the direction of current in a generator?

A

Right Hand Rule(Conventional Current)

Center - Current
Fore - Field
Thumb - Thrust/motion

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6
Q

The basic or elementary generator is an alternator, Also Known as ______

A

An AC Generator

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7
Q

It is the process of changing the generated voltage in the armature to a pulsating dc voltage

A

Commutation Process

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8
Q

Basic Equation of the generated voltage in DC generator

Sipon Ago

A

E = (ZPϕN) / (a*60)

“Sipon Ago”

P=number of poles
N=speed of the armature core rotation (rpm)
Z=total number of elements or conductors in the armature
ϕ=number of flux per pole (Wb)
a=number of armature paths

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9
Q

In a self-excited shunt wound generator, what is the configuration of the field winding to the armature and load?

A

The field coil is connected in parallel

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10
Q

Relevant formulas for Self-Excited shunt generator

A

(Basically just remember the loop analysis lol)

I(load)=P(load)/V(load)

Ish = V(load)/R(shunt)

Ia = Ish + I(load)

Total generated voltage=V(load) + Ia*Ra

Power generated by generator = Ea*Ia

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11
Q

What are the different classifications of generators?

A

Series-wound
Shunt-Wound
Compound

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12
Q

In a ______ generator, the current that flows in the armature is the same with the one flowing through the field winding and external circuit(load circuit)

A

Series-wound Generator

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13
Q

Relevant Formulas for Series-wound generator

A

Ia = I(se) = I(load)

I(load)=P(load)/V(load)

(just use KVL and you can do it :) )

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14
Q

In a ______ generator, the field consists of many turns of small wires that are connected in parallel with the load

A

Shunt-wound Generator

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15
Q

What is the difference between long shunt and short shunt compound generator?

A

In long shunt, the series field coil is connected in series with the armature. In short shunt, the series field is connected in series with the load.

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16
Q

Total number of elements/conductors formula

A

Z=(elements/slot)*(total number of slots)

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17
Q

Elements per slot of the following types of windings:

Simplex, Duplex, Triplex, Quadruplex

A

Z/slot = 2*m

ex. 
Simplex - 2 elements per slot
Duplex - 4 elements per slot
Triplex - 6 elements per slot
Quadruplex - 8 elements per slot
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18
Q

Total number of brushes if not specified:

A 
Nlap = P
Nwave = 2
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19
Q

number of armature current paths (for Sipon Ago)

A 
a(lap) = mP
a(wave) = 2m

m - ‘m’ - plex
Simplex: m = 1
Duplex: m = 2

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20
Q

Voltage Regulation Formula

A

%VR = (Vnl - Vfl) / Vfl *100%

no, full, full

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21
Q

What are the different losses in an electrical machine?

A 
Armature Circuit loss
Brush-contact loss
core loss
eddy current loss
Hysteresis loss
Field circuit loss
Stray load loss
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22
Q

Armature Circuit loss formula

A

Pa=Ia^2*Ra

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23
Q

Brush Contact Loss

A

Pb = Ia*Vbrush

1V (for 1 carbon brush)

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24
Q

Core loss formula

A

P(core) = Peddy + P(hysteresis)

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25
Q

Eddy current loss formula

A

P(eddy) = Ke(NBm*t)² *W

Ke=proportionality constant/eddy current coefficient
N=armature rotating speed
W=Core weight
Bm=Maximum flux density
t=armature core lamination thickness
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26
Q

Hysteresis loss formula

A

P(hysteresis) = Kh•N•(Bm^1.6)•W

Kh=proportionality constant/hysteresis coefficient
N=armature rotating speed
W=Core weight
Bm=Maximum flux density

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27
Q

Field Circuit loss formula

A

Pf = Ish²•Rsh + Ise²•Rse

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28
Q

Stray load loss formula

A

P(stray loss) = 1% of the output for machine 150kW and over

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29
Q

Efficiency formula for Generators

A

Ratio of output power to the input

η=Pload / (Pload+2*Pₗₒₛₛ)

Pₗₒₛₛ - consists of constant/rotational losses, as well as variable losses

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30
Q

It is the part that rotates in a generator

A

Rotor

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31
Q

It is the part that remains stationary in a generator

A

Stator

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32
Q

Two different types of alternators

A

Rotating-Armature Alternator

Rotating-Field Alternator (DEFAULT)

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33
Q

What rpm describes if a motor is High or Low speed?

A

if >1200 rpm, high speed

if <1200 rpm, low speed

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34
Q

Examples of high speed prime mover

A

Steam and gas turbine

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35
Q

Example of low speed prime mover

A

internal combustion and electric motors

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36
Q

Voltage Equation for Generator

A 
E=4.44⋅f⋅N⋅φ⋅kₚ⋅kd x10^-8
where:
E=total voltage generated
f=frequency
N=number of turns
φ=pitch factor
kₚ=pitch factor (1 if not given)
kd=distribution factor (1 if not given)
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37
Q

Alternator/AC Motor Frequency formula, given number of poles and frequency

A

f = P⋅N / 120

f=frequency, in hertz
P=number of poles
N=speed in RPM

Note: Used for either Alternators or AC Motors

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38
Q

A machine that converts electric energy into mechanical energy by utilizing forces exerted by magnetic fields produced by current flowing through conductor

A

Motor

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39
Q

What rule is used for definite relationship between the magnetic field, direction of current and direction which the conductor tends to move for DC motor

A

For Conventional Current, Use Left Hand Rule:

Center - Current
Fore - Field
Thumb - Thrust/Force

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40
Q

Types of DC motors

A

Shunt, Series, short-shunt compound motor

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41
Q

What kind of motor should be used for c͟o͟n͟s͟t͟a͟n͟t͟ s͟p͟e͟e͟d͟?

A

AC motor

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42
Q

What kind of motor is preferred for v̲a̲r̲i̲a̲b̲l̲e̲ s̲p̲e̲e̲d̲

A

DC motor

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43
Q

It is a familiar type of motor which is very similar to dc motor

A

Series AC motor

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44
Q

It may be considered as polyphase motors of constant speed and whose rotors are energized with dc voltage

A

Synchronous motors

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45
Q

The most commonly used ac motor that uses either single of polyphase whose rotors are energized by induction

A

induction motors

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46
Q

It is a very small induction motor with sizes from about 1/500 hp to 1/6 hp. it has low starting torque, with little overhead capacity and low-efficiency motor

A

Shaded-pole motor

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47
Q

It has sizes up to 3/4 hp and can operate nearly at constant speed. It requires fair starting torque with fair efficiency

A

Split-phase motor

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48
Q

Similar to split-phase motor but with higher starting torque due to starting capacitor

A

Split-phase motor (with capacitor?)

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49
Q

It has a stator winding connected to the source of power and the rotor winding to the commutator. It has a varying speed characteristics

A

Repulsion Motor

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50
Q

It operates as a repulsion motor during starting then as induction motor when running. It has high starting motor torque for long duration

A

Repulsion-start induction motor

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51
Q

It has a squirrel-cage winding in the rotor. It can be constant or variable speed repulsion motor

A

Repulsion-inductor motor

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52
Q

It has high starting torque which is constructed to operate on alternating current up to 60 cycles. It has good efficiency and excellent overload capacity with variable speed that can be controlled over very wide limits

A

Series or universal motors

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53
Q

It operates at synchronous speed with constant speed(its obvious advantage) that can be determined only by the supply frequency and the number of poles on the machine

A

Synchronous motor

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54
Q

It is widely used because of its all-purpose characteristics. good starting torque and good overload capacity

A

Squirrel-cage induction motor

55
Q

It is with rotor construction distinct from squirrel-cage but with similar stator construction with easily controllable variable speed

A

Wound-rotor type induction motor

56
Q

It has a stator similar to induction motor but its rotor consists of a set of salient-poles with constant speed even load changes

A

Synchronous motor

57
Q

The most commonly used type of AC motor. It is simple, rugged and costs relatively little to construct

A

Induction Motor

58
Q

Part of a Generator that serves as the supporting structure

A

Yoke

59
Q

Part of a Generator that provides the magnetic field through electromagnetic Induction

A

Pole

60
Q

Poles in a generator are always _____ in number

A

even

61
Q

Part of the generator that contains windings, in which produces the output current

A

Armature

62
Q

The Armature (spins/does not spin) along with the ________

A

Spins along with the commutator

63
Q

The part of the generator that allows the basic alternator(AC) output a DC Current

A

Commutator

64
Q

the Commutator (spins/does not spin) along with the _____

A

Spins along with the Armature

65
Q

The part of the generator that keeps contact with the commutator

A

Brush

66
Q

An optional part of the generator that will cancel the magnetic field produced by the armature windings, since it is not desired

A

Interpoles

67
Q

Formula for Generated Voltage across a moving conductor, in the presence of a uniform magnetic field

A

E = BL[Vsin(θ]

B - Flux Density (Tesla)
L - Length of Conductor (meter)
V - Tangential Velocity (m/s)
θ - Angle Between Velocity vector and flux lines

68
Q

Voltage across a moving conductor in the presence of a magnetic field is maximum when Velocity Vector is ________ to the Flux Lines

A

Perpendicular

69
Q

Voltage across a moving conductor in the presence of a magnetic field is minimum when Velocity Vector is ________ to the Flux Lines

A

Parallel

70
Q

Alternative Formula for Generated Voltage in a DC Generator (2Ponz/c)

A

E = 2PΦNZ / c*(m)

Z - # armature winding conductors
P - Number of PAIRS of poles (Actual #poles / 2 )
N - Revolutions per second (R/s)
Φ - Flux per Pole

71
Q

Formula for ‘c’ in (2Ponz/c)

A

Cwave = 2 —— “Kaway” (w/ 2 hands)

Clap = 2P ——“Clap”“Palakpak”
P - # PAIRS of poles

72
Q

When not mentioned in a problem, the DEFAULT assumption is to use a _______ Wound Generator

A

Shunt Wound

73
Q

Both Rse and Rsh are ____________

A

Field Windings

74
Q

A Compound Wound Generator where the H-Fields produced by Rse and Rsh Aid each other

A

Cumulative Compound

75
Q

A Compound Wound Generator where the H-Fields produced by Rse and Rsh Oppose each other

A

Differential Compound

76
Q

A Compound Wound Generator Classification where The No-Load Voltage is equal to the Full-Load Voltage

A

Flat Compounded

0% Voltage Regulation

77
Q

A Compound Wound Generator Classification where The No-Load Voltage is Less than the Full-Load Voltage

A

Under Compounded

Positive Voltage Regulation

78
Q

A Compound Wound Generator Classification where The No-Load Voltage is Greater than the Full-Load Voltage

A

Over Compounded

Negative Voltage Regulation

79
Q

Type of Winding that forms loops as it expands around the armature core

A

Lap Winding

80
Q

Lap winding is used for High _______ Applications

A

Current

81
Q

The term used to describe the coil span at the back end of the armature (opposite side of the commutator)

A

Back Pitch

82
Q

The term used to describe the coil span at the Front end of the armature (The side of the commutator)

A

Front Pitch

83
Q

Formula for Back Pitch(Yb) in Lap Winding

A

Yb = Yf +- 2m

Yf - Front Pitch
m - ‘m’-plex
+ if Progressive
(- if Retrogressive)

84
Q

When the Lap Winding expands from Left to Right, it is considered as __________

A

Progressive

85
Q

When the Lap Winding expands from Right to Left, it is considered as __________

A

Retrogressive

86
Q

Type of Winding that forms Waves as it expands around the armature core (Hmmm… ano kaya yun?)

A

Wave Winding :v

87
Q

Wave winding is used for High _______ Applications

A

Voltage

88
Q

Formula for Average Pitch in a Wave Winding

A

Y = ( Z +- 2*m)/P

Z - # of elements on armature
m - ‘m’-plex
P- #Poles

89
Q

Alternate Formula for Average Pitch in a Wave Winding

A

Y = (Yb + Yf) / 2

Yb - Back Pitch
Yf - Front Pitch

90
Q

Formula for Coil Pitch(Ys)

A

Ys = Coil span (unit is in #slots) / Slots per Pole

91
Q

For Alternators (AC OUTPUT), ________ are used on the rotor instead of Commutators (since Commutators are responsible for AC»>DC)

A

Slip Rings

92
Q

Alternators can either be ________ or _______

A

Single Phase, 3-Phase

93
Q

Alternators are best used for _____

A

Electrical Power, connected parallel to the load

94
Q

Rotor type that is high-speed, and uses 2 or 4 poles

A

Turbine Driven

95
Q

Rotor type that is low-speed, and uses several poles

A

Salient-Pole

96
Q

Formula for Alternator EMF per Phase

A

E(per Phase) = 2.22kpkdfΦ*Z

kp - pitch factor (1 by default)
kd - distribution factor (1 by default)
f - frequency (Hz)
Φ - Flux PER POLE (Wb)
Z - #conductors PER PHASE
97
Q

Formula for Force on a Conductor(for motors)

A

F = BIL*sinθ

B - Flux Density (T)
I - Current (A)
L - Length (m)
θ - Angle Between Current Vector and Flux Line

98
Q

DC Motor Back EMF

A

Same formula used for Generator EMF (either sipon ago or 2ponz/c )

99
Q

Why the need for the formula: E = KΦN

A

E = ZPΦN/a*60

BUT Z,P,and a are parameters that are not easily configured on the fly because it is part of the motor/generator’s physical construction

therefore, we set these variables as a constant: K = ZP/60a

Finally: E = KΦN
This formula is used for problems with Φinitial, Φfinal, Ninitial, Nfinal, etc.

100
Q

Formula for DC motor Speed

A

Nrpm = 60a(Eback)/PZΦ
Derived from “sipon ago”

or

reverse engineer motor speed ‘N’ from 2ponz/c

101
Q

Motors Operate by the principle of _________

A

Lenz’s Law

102
Q

Mathematical Expression for Powers involved in DC Motor

A

[Vin * Ia] = [Ea * Ia] + [Ia² * Ra]

[Vin * Ia] - Electrical Input
[Ea * Ia] - Mechanical Output
[Ia² * Ra] - Armature Losses

103
Q

Formula for Torque of a DC Motor

A

EaIa = τω

τ = Ea*Ia / ω 
τ = Ea*Ia / 2πn

n - Rev/s

104
Q

Unit for Torque (τ)

A

N*m or Joules

105
Q

Alternative Formula for Torque (Using 2ponz/c variables)

A

τ = PIaZΦ / πc
“Piso Spicy”

Note: use 2ponz/c variables

106
Q

Why the need for the formula: τ = KΦIa

A

τ = PIaZΦ / πc

But P, Z, π, and c are constant (not easily changed)
so: K = PZ/π*c

Therefore: τ = KΦIa
This formula is used for problems with Φinitial, Φfinal, Ia(initial), Ia(final), etc.

107
Q

When a motor initially starts, the armature draws ______________ at t = 0, due to ____________

A

High Current due to Back EMF

108
Q

What solution can be implemented for the initial high current in a motor?

A

Add a Rheostat in series to the armature winding, initially at high resistance to prevent high current overdraw, and then it gradually decreases in resistance for normal operation

109
Q

Formula for Starting Armature Current when starting the DC motor

A

Assuming Back EMF = 0:

Iastart = Vs / (Ra - Rrheo)

Vs - Supply Voltage
Ra - Armature Resistance
Rrheo - Rheostat Resistance

110
Q

Formula for Speed Regulation(%SR)

A

%SR = (Snl - Sfl) / Sfl x100%

111
Q

The three configurations for Speed Control in a DC Motor

A
  1. ) Rheostat in Series to Armatire
  2. )Rheostat in Series to Shunt Winding
  3. )Rheostat in Parallel Series Winding
112
Q

Which Speed Control Configurations have the Control Speed Inversely Proportional to the Rheostat Resistance?

A

Rheostat in Series to Armature, and

Rheostat in Parallel Series Winding

113
Q

Which Speed Control Configurations have the Control Speed Directly Proportional to the Rheostat Resistance?

A

Rheostat in Series to Shunt Winding

114
Q

What Determines the speed of an AC Motor

A

Frequency of Supply Voltage

115
Q

3 Types of AC Motors

A
  1. ) Series AC (Similar to DC Motor)
  2. ) Synchronous Motors
  3. ) Induction Motors
116
Q

Another Term for Series AC Motor

A

Universal Motor

Since it can operate on either AC or DC

117
Q

AC Motors are either _________ or ________

A

Single Phase or Polyphase

118
Q

Synchronous Motor VS Induction Motor:

Which one requires a Separate DC Exciter?

A

Synchronous Motors Require a separate DC Exciter

Induction Motors are Self Excited

119
Q

The Speed of the Synchronous motor is _______ to the load Resistance

A

Not related to the load resistance (Constant Speed)

120
Q

The Speed of the induction motor is _______ to the load Resistance

A

Directly Proportional

121
Q

The Speed of the induction motor is (Controllable/not controllable)

A

Controllable

122
Q

The Speed of the Synchronous motor is (Controllable/not controllable)

A

Not Controllable (No Questions will appear regarding the speed of a synchronous Motor)

123
Q

The Power Factor Required to operate a Synchronous Motor is __________

A

Any Power Factor can operate a synchronous motor

124
Q

The Power Factor Required to operate an Induction Motor is __________

A

A Lagging Power Factor

125
Q

The Synchronous motor is relatively (Cheap/Expensive) Compared to Induction Motors

A

Expensive

126
Q

Another use for synchronous motors

A

can be used to improve the Power Factor of an electrical power distribution

127
Q

Can induction motors be used to improve Power Factor of a line?

A

No.

Only used for mechanical loads

128
Q

________ Motors are often used to drive DC Generators

A

Synchronous

129
Q

Induction Motors have a ________ Construction

A

Simple and Rugged

130
Q

Two Types of Induction Motors

A
  • Squirrel Cage

- Wound Rotor

131
Q

The speed of rotation of a rotating Magnetic Field, when the Field is the rotor

A

Synchronous Speed (Ns)

132
Q

The Actual Speed of the Rotor

A

Rotor Speed (Nr)

133
Q

Formula for Slip

A

Slip = Ns - Nr

Ns - Synchronous Speed
Nr - Rotor Speed

134
Q

The Synchronous speed is (>,

A

Greater than

Bryx_Electronics (11 decks)

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