Electrical Machines Flashcards Preview

Bryx_Electronics > Electrical Machines > Flashcards

Flashcards in Electrical Machines Deck (134):
1

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

Faraday's Law

2

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

Prime mover

3

"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?

Electromagnetic Induction by Michael faraday

4

The magnitude of voltage generated depends upon what 4 factors?

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

5

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

Right Hand Rule(Conventional Current)

Center - Current
Fore - Field
Thumb - Thrust/motion

6

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

An AC Generator

7

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

Commutation Process

8

Basic Equation of the generated voltage in DC generator
(Sipon Ago)

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

9

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

The field coil is connected in parallel

10

Relevant formulas for Self-Excited shunt generator

(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

11

What are the different classifications of generators?

Series-wound
Shunt-Wound
Compound

12

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)

Series-wound Generator

13

Relevant Formulas for Series-wound generator

Ia = I(se) = I(load)

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

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

14

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

Shunt-wound Generator

15

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

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.

16

Total number of elements/conductors formula

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

17

Elements per slot of the following types of windings:
Simplex, Duplex, Triplex, Quadruplex

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

18

Total number of brushes if not specified:

Nlap = P
Nwave = 2

19

number of armature current paths (for Sipon Ago)

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

m - 'm' - plex
Simplex: m = 1
Duplex: m = 2

20

Voltage Regulation Formula

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

(no, full, full)

21

What are the different losses in an electrical machine?

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

22

Armature Circuit loss formula

Pa=Ia^2*Ra

23

Brush Contact Loss

Pb = Ia*Vbrush

1V (for 1 carbon brush)

24

Core loss formula

P(core) = Peddy + P(hysteresis)

25

Eddy current loss formula

P(eddy) = Ke*(N*Bm*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

26

Hysteresis loss formula

P(hysteresis) = Kh•N•(Bm^1.6)•W

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

27

Field Circuit loss formula

Pf = Ish²•Rsh + Ise²•Rse

28

Stray load loss formula

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

29

Efficiency formula for Generators

Ratio of output power to the input

η=Pload / (Pload+2*Pₗₒₛₛ)

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

30

It is the part that rotates in a generator

Rotor

31

It is the part that remains stationary in a generator

Stator

32

Two different types of alternators

Rotating-Armature Alternator
Rotating-Field Alternator (DEFAULT)

33

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

if >1200 rpm, high speed
if <1200 rpm, low speed

34

Examples of high speed prime mover

Steam and gas turbine

35

Example of low speed prime mover

internal combustion and electric motors

36

Voltage Equation for Generator

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)

37

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

f = P⋅N / 120

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

Note: Used for either Alternators or AC Motors

38

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

Motor

39

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

For Conventional Current, Use Left Hand Rule:

Center - Current
Fore - Field
Thumb - Thrust/Force

40

Types of DC motors

Shunt, Series, short-shunt compound motor

41

What kind of motor should be used for c͟o͟n͟s͟t͟a͟n͟t͟ s͟p͟e͟e͟d͟?

AC motor

42

What kind of motor is preferred for v̲a̲r̲i̲a̲b̲l̲e̲ s̲p̲e̲e̲d̲

DC motor

43

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

Series AC motor

44

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

Synchronous motors

45

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

induction motors

46

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

Shaded-pole motor

47

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

Split-phase motor

48

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

Split-phase motor (with capacitor?)

49

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

Repulsion Motor

50

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

Repulsion-start induction motor

51

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

Repulsion-inductor motor

52

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

Series or universal motors

53

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

Synchronous motor

54

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

Squirrel-cage induction motor

55

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

Wound-rotor type induction motor

56

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

Synchronous motor

57

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

Induction Motor

58

Part of a Generator that serves as the supporting structure

Yoke

59

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

Pole

60

Poles in a generator are always _____ in number

even

61

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

Armature

62

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

Spins along with the commutator

63

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

Commutator

64

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

Spins along with the Armature

65

The part of the generator that keeps contact with the commutator

Brush

66

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

Interpoles

67

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

E = B*L*[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

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

Perpendicular

69

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

Parallel

70

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

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

Formula for 'c' in (2Ponz/c)

Cwave = 2 ------ "Kaway" (w/ 2 hands)

Clap = 2P ------"Clap""Palakpak"
P - # PAIRS of poles

72

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

Shunt Wound

73

Both Rse and Rsh are ____________

Field Windings

74

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

Cumulative Compound

75

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

Differential Compound

76

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

Flat Compounded
(0% Voltage Regulation)

77

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

Under Compounded
(Positive Voltage Regulation)

78

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

Over Compounded
(Negative Voltage Regulation)

79

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

Lap Winding

80

Lap winding is used for High _______ Applications

Current

81

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

Back Pitch

82

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

Front Pitch

83

Formula for Back Pitch(Yb) in Lap Winding

Yb = Yf +- 2m

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

84

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

Progressive

85

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

Retrogressive

86

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

Wave Winding :v

87

Wave winding is used for High _______ Applications

Voltage

88

Formula for Average Pitch in a Wave Winding

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

Z - # of elements on armature
m - 'm'-plex
P- #Poles

89

Alternate Formula for Average Pitch in a Wave Winding

Y = (Yb + Yf) / 2

Yb - Back Pitch
Yf - Front Pitch

90

Formula for Coil Pitch(Ys)

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

91

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

Slip Rings

92

Alternators can either be ________ or _______

Single Phase, 3-Phase

93

Alternators are best used for _____

Electrical Power, connected parallel to the load

94

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

Turbine Driven

95

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

Salient-Pole

96

Formula for Alternator EMF per Phase

E(per Phase) = 2.22*kp*kd*f*Φ*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

Formula for Force on a Conductor(for motors)

F = B*I*L*sinθ

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

98

DC Motor Back EMF

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

99

Why the need for the formula: E = KΦN

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 = K*Φ*N
This formula is used for problems with Φinitial, Φfinal, Ninitial, Nfinal, etc.

100

Formula for DC motor Speed

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

or

reverse engineer motor speed 'N' from 2ponz/c

101

Motors Operate by the principle of _________

Lenz's Law

102

Mathematical Expression for Powers involved in DC Motor

[Vin * Ia] = [Ea * Ia] + [Ia² * Ra]

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

103

Formula for Torque of a DC Motor

Ea*Ia = τ*ω

τ = Ea*Ia / ω
τ = Ea*Ia / 2πn

n - Rev/s

104

Unit for Torque (τ)

N*m or Joules

105

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

τ = P*Ia*Z*Φ / π*c
"Piso Spicy"

Note: use 2ponz/c variables

106

Why the need for the formula: τ = K*Φ*Ia

τ = P*Ia*Z*Φ / π*c

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

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

107

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

High Current due to Back EMF

108

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

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

Formula for Starting Armature Current when starting the DC motor

Assuming Back EMF = 0:

Iastart = Vs / (Ra - Rrheo)

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

110

Formula for Speed Regulation(%SR)

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

111

The three configurations for Speed Control in a DC Motor

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

112

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

Rheostat in Series to Armature, and
Rheostat in Parallel Series Winding

113

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

Rheostat in Series to Shunt Winding

114

What Determines the speed of an AC Motor

Frequency of Supply Voltage

115

3 Types of AC Motors

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

116

Another Term for Series AC Motor

Universal Motor
(Since it can operate on either AC or DC)

117

AC Motors are either _________ or ________

Single Phase or Polyphase

118

Synchronous Motor VS Induction Motor:
Which one requires a Separate DC Exciter?

Synchronous Motors Require a separate DC Exciter

Induction Motors are Self Excited

119

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

Not related to the load resistance (Constant Speed)

120

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

Directly Proportional

121

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

Controllable

122

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

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

123

The Power Factor Required to operate a Synchronous Motor is __________

Any Power Factor can operate a synchronous motor

124

The Power Factor Required to operate an Induction Motor is __________

A Lagging Power Factor

125

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

Expensive

126

Another use for synchronous motors

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

127

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

No.
Only used for mechanical loads

128

________ Motors are often used to drive DC Generators

Synchronous

129

Induction Motors have a ________ Construction

Simple and Rugged

130

Two Types of Induction Motors

-Squirrel Cage
-Wound Rotor

131

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

Synchronous Speed (Ns)

132

The Actual Speed of the Rotor

Rotor Speed (Nr)

133

Formula for Slip

Slip = Ns - Nr

Ns - Synchronous Speed
Nr - Rotor Speed

134

The Synchronous speed is (>,

Greater than