CHAPTER 4 Power Factor _ Power Quality.pptx

CHAPTER 4
Power Factor & Power Quality

Outlines
• Introduction to PQ
• Power Factor
• Power Factor Correction
• Harmonics in Power Systems
• Voltage Sags
• Voltage Swells
• Transients
• Standards for Power Quality
2
BEX 42803/ BEF 33203/ BEE 4213 – Utilisation of Electrical Energy

Introduction to PQ
• What is PQ? Different perspectives…
– Equipment designer or manufacturer:
“A perfect sinusoidal wave, with no variations in
the voltage, and no noise present on the
grounding system.”
– Electrical utility:
“Voltage availability or outage.”
– Industrial / end-user:
“The power that works for whatever equipment
the end-user is applying.”
3

Introduction to PQ
• None of the hypothetical point of view is properly
focused!
“the concept of powering and grounding sensitive
electronic equipment in a manner suitable for the
equipment.”
“any power problem manifested in ,
, and deviations that results in
failure or mis-operation of customer equipment.”
4

Introduction to PQ
5
POWER SYSTEM
(SUPPLY POWER)
CONSUMERS
(LOADS)
Voltage
Quality Current
Quality
Power
Quality

Introduction to PQ
• Modern load & equipment are to
power quality variations.
• High efficiency and
results in increasing harmonic levels
(distortion in frequency).
• Increased of the power quality issues by
the end users.
6

Reasons for concern with PQ
• End-user equipment become more sensitive to PQ due
to many controls.
• Complexity of .
• Large systems in many businesses facilities.
equipment used for enhancing
system stability, operation and efficiency. They are
major source of bad PQ and are vulnerable to bad PQ
as well.
7

Examples of Disturbing Loads
8
Adjustable-Speed
Motor Drives
Computers High-intensity
Lighting (HID)
Microprocessor-
controlled Equipment

Power Quality Concerns
Power
Quality
Power
Factor
Harmonics
Voltage
Sag/Dip
Voltage
Swell
Transients
9

Power Quality Overview
10

Effects of Poor Power Quality
• Equipment
• Excessive wear or of equipment
• Increased from downtime
• Increased , repair time and expenses
• Outside expense
11

Information Technology Industry Council (ITIC)
Curve
12

PQ Categories Based on Duration
PQ Category Time Range
Nanoseconds to 3 cycles
Instantaneous
Momentary
Temporary
0.5 seconds to 30 cycles
30 cycles to 3 seconds
3 seconds to 1 minute
 1 minute
Continuous
13

Transients
14

Short Duration
15

Long Duration
16

Computer Equipment Disturbance Table
17

Causes of Power Quality
Power Quality Typical Causes Example Solutions
Impulse Transient Lightning, Electrostatic
discharge, Load switching.
Surge arresters, Filters,
Isolation transformers.
Oscillatory Transient Line/ Cable switching,
Capacitor switching.
Surge arresters, Filters,
Isolation transformers.
Voltage Sags/ Swells Remote system faults. Ferroresonant
transformers, UPS.
Under/ Over Voltage Motor starting, Load
variation.
Voltage regulators,
Ferroresonant
transformers.
Harmonics Distortion Nonlinear load, System
resonance.
Active/ Passive Filters,
Transformer with zero
sequence components.
Voltage Flicker Intermittent loads, Motor
starting, Arc Furnaces.
Static Var systems.
18

What is Power Factor
• Industrial loads are mostly inductive type.
• Motors require REACTIVE power (Q) to set up
the magnetic field, and ACTIVE power (P) to
produce the useful work (shaft Horse Power).
19
 REACTIVE power (Q)
ACTIVE power (P)
(Power Factor Angle)

What is Power Factor
• Power Factor is a measure of how efficiently
electrical power is consumed.
20
100% of the energy burned is being used
to move the runner from A to B.
Say, =30, only 87% of the energy burned
is being used to move the runner in the
horizontal direction of B, and so extra
energy will be required to achieve the
same objective.

Power Factor Triangle
• Power Factor is the ratio of Active Power (P) to
Apparent/ Total Power (S):
21

cos
S(kVA)
P(kW)
Factor
Power 

Lagging (Inductive Loads)
Leading (Capacitive Loads)
 REACTIVE power (Q)
ACTIVE power (P)
(Power Factor Angle)

Phasor Relationship between P, Q, and S
22

Impact of Poor Power Factor
23
Wasted Power

Power Factor Correction
• 2 ways of improving power factor:
lagging reactive current demand of the
loads
lagging reactive current by supplying
leading reactive current to the power system
24

Capacitor units for PFC
25

Static VAR Compensator (SVC) for PFC
26

Static VAR Compensator (SVC) for PFC
27

Leading p.f obtained from over
excitation synchronous compensator
28

Synchronous compensator
29

Advantages of PFC – Overview
• Power consumption reduced
• Electricity bills reduced
• Reduced heating in equipment
• Increased equipment life
• Transformer & distribution equipment I2R losses
reduced
• Extra kVA availability from the existing supply (Q
= 0 kVAr)
• Reduction of voltage drop in the electrical system
30

• Benefits of installing Capacitors:
– Supply reactive power required by inductive loads.
– Decrease conductor size
31
Utility
supplies Q
Capacitor
supplies Q

• Benefits of installing Capacitors: (Cont…)
– Reduce
– Reduce (minor). Anyway,
will cause a voltage rise that can
damage insulation & equipment.
32
















2
PF
Desired
PF
Original
-
1
100%
reduction
loss
%
kVA
r
Transforme
%Z
r
Transforme
kVAr
Capacitor
Rise
Voltage
%



An industrial consumer has the following loads:
i. 9 kW of lighting at unity PF
ii. A motor taking 12 kVA at 0.75 PF lagging
iii. A number of small motors taking 15 kW at 0.6 PF lagging.
The loads are balanced over the three phases of 400 V supply
system. Determine:
a) The total kW, kVAr, kVA.
b) The overall power factor
c) The line current
33

34
Load kW kVAr
i 9 0
ii 9 7.936
iii 15 20
Total 33 27.936
kVA
43.23
27.936
33
kVA
Overall 2
2



lag
0.763
kVA
43.23
kW
33
factor
power
Overall 

V.I)
A...(S
62.4
V
400
3
kVA
43.23
I
current
Line L 




Calculate:
a) The total kVAr to be supplied by a capacitor bank in order to
improve the overall power factor of the system of Example 1
to 0.9 PF lagging;
b) The value of capacitance required assuming that the
capacitors are connected (i) in star, (ii) in delta.
35

36
1
27.936 kVAr
33 kW
2
?? kVAr
A
B
C
O



25.84
.9
0
Cos
2
2


phase)
-
(1
kVAr
3.989
11.966/3
BC
phase)
-
(3
kVAr
11.966
)
25.84
tan
(33
-
27.936
BC





C
2
X
V
Q 

37
V
230
400V
3
1
V
,
connection
star
For the 


F
240
13.26
50
2
1
C
13.26
kVAr
3.989
V)
(230
X
2
C









400V
V
,
connection
delta
For the 
F
79.4
40.1
50
2
1
C
40.1
kVAr
3.989
V)
(400
X
2
C










Practical PFC Guide-Table
38
   
 
2
1
1
1
2
1
cos
tan
cos
tan PF
PF
P
Q
Q
QC






PFDesired
PFOriginal
0.85 0.86 0.87 0.88
0.50
0.51
0.52
0.53
K-Factor

Effective Reactive Power
• Differences in voltage level between the
and the used will produce different
injected reactive power into the system.
• The factor to be considered:
where,
QCAP = Effective reactive power provided by capacitor
QS = Effective reactive power injected into supply system
VCAP = Capacitor voltage level
VS = Supply system voltage level
39
2









S
CAP
S
CAP
V
V
Q
Q

If the three phase capacitor bank of 525 V rms
is chosen as the PFC component for the power
quality issue encountered in Examples 1 and
2, determine the effective reactive power of
the capacitors so that the overall system
power factor can be improved to 0.9 lagging.
40

41
kVAr
V
V
kVAr
V
V
Q
Q
S
C
S
C
61
.
20
400
525
966
.
11
2
2


















Harmonics in Power Systems
“a sinusoidal component of a periodic wave or quantity
having a frequency that is an integral multiple of the
fundamental frequency”
“a periodic non-sinusoidal function of a fundamental
frequency may be expressed as the sum of sinusoidal
functions of frequencies which are multiples of the
fundamental frequency”
42

• Types of harmonics in power systems:
– Voltage
– Current
• Harmonics Classifications
– Subharmonics (fh  f)
– Integer/ Characteristics harmonics (fh = nf)
– Non-integer/ Non-characteristics harmonics
(fh  f and fh ≠ nf)
where,
f = fundamental frequency
fh = harmonic frequency
n = integer = 1,2,3,…
43

44
DC 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
System Frequency (Hz)
Spectral
Component
(RMS)

• Sinusoidal voltage/current function:
45
)
sin(
)
(
)
sin(
)
(






t
I
t
i
t
V
t
v )
sin(
)
( t
V
t
v 

)
sin(
)
( 
 
 t
I
t
i
V
I

T
f


2
locity
Angular ve



/
2
Period


T

• The presence of harmonic components in the normal
sinusoidal waveform produced a
waveform :
46
...
)
)
1
sin((
)
sin(
...
)
3
sin(
)
2
(
)
sin(
)
(
1
3
2
1
0









 t
n
V
t
n
V
t
V
t
V
t
V
V
t
v
n
n





Fourier Series

47

• The Fourier series is simplified to express the
periodic voltage waveform with fundamental
frequency,  = 2 f,
48
)
to
1
k
(for
)
sin
cos
(
)
( 0 



  t
k
b
t
k
a
V
t
v k
k 

)
,
,
3
,
2
,
1
(
,
cos
)
(
1
n
k
dt
kt
t
f
ak 



 





)
,
,
3
,
2
,
1
(
,
sin
)
(
1
n
k
dt
kt
t
f
bk 



 





where ak and bk are the coefficient of the
individual harmonic components,

Ratio between the root mean square (RMS) value of the
individual harmonic and the RMS value of the fundamental.
Ratio between the RMS value of the harmonics and the RMS
value of the fundamental.
49
)
,...
4
,
3
,
2
(
%,
100
1
2




 n
I
I
THD
n

Harmonics Sources in Electrical Systems
• Many nonlinear loads, drawing
from electrical power systems.
computer equipment with switched power
supply, variable speed motors and drives,
photocopiers, laser printers, fax machines, battery
charges, UPS, ballast fluorescent light ballast,
medical diagnostic equipment etc.).
• These non-sinusoidal currents pass through
in the power systems and produce
voltage harmonics.
• These propagate in power systems
and affect all of the power system components. 50

Fluorescent Lighting
• The amount of harmonics no. 3, 5, 7, and 9 are high.
51

Adjustable Speed Drives (ASD)
• ASDs are widely used to control the speed of AC
motor nowadays, compared to the application of
belts and pulleys in the 1970s.
52

Personal Computers
53
Odd orders
harmonics!

Electric Furnace
• High-power and devices in
power systems. Producing
during melting process. High 5th and 7th
harmonics also produced.
54

AC/DC Converters
• If the number of converter/inverter is p, then
the of harmonic current in AC side will be
(n = 1, 2, 3…).
55

Effects of Harmonics
** Note: Please read the provided note, “Harmonics”
for the sub-title, “Effect of Harmonics on Power
System Devices”.
56

– Harmonics cause disturbance in in power
systems such as sensitive medical devices, control circuits, and
computers.
– Control circuits that work on current or voltage
have higher sensitivity to harmonics and may not work properly
in the presence of harmonics.
57

– With the presence of harmonics,
– Excessive losses and torque fluctuation also
appear in in the presence of
harmonics because only the fundamental
component yields average torque in motors and
harmonics yield and
.
58

– The presence of current harmonics especially
in electrical power systems increases .
– Higher neutral currents, in four-wire, three-phase systems,
in addition to the of the , can
cause power feeders, overloaded
transformers, , and common mode .
– Typical PC power supply:
59

– The presence of current and voltage harmonics of
may lead to of
conventional that utilise
induction watt-hour meters
60

– Current and voltage harmonics, when passing through the
power system or another load, may cause a
.
– Figure below shows a kind of resonance where the load
has a close to the .
61

Voltage Sags – Example
62

63

64

Voltage Sags – Definitions
Sag : 0.1 pu to 0.9 pu
Interruption : < 0.1 pu
Instantaneous : 0.5 cycles - 30 cycles
Momentary : 30 cycles - 3 seconds
Temporary : 3 seconds - 1 minute
65

Voltage Sags – Sources
• Any , if large enough,
will cause a voltage sag:
 Motors
 Faults
 Switching
66

Voltage Sags – Sources
• Motors typically draw times their
running current when they are .
• Motors may start and stop frequently.
• Common cause of voltage sags in
facilities – the facility’s own can
cause the voltage sag.
67

Voltage Sags – Motor Example
68

A “stiff” 14.4kV three-phase system serves a
distribution line with an impedance of 1.2+j6
ohms. If the voltage at the sending end
remains 14.4kV, what is the voltage drop in
the line due to a balanced 3-phase load of
10+j5 ohms per phase?
69

Given variables:
Zload = (10+j5), Zline=(1.2+j6), V=14.4kV/3
Line current:
70
A
Z
Z
V
I
line
load
line 




 48
.
44
598
.
529


Use the line current to find the voltage drop and load
voltage:
Voltage sag (%),
71
kV
Z
I
V line
line
drop 



 21
.
34
241
.
3
kV
V
V
V drop
load 




 92
.
17
921
.
5

%
22
.
71
%
100
1









 




V
V
V
Sag load
magnitude

Typical voltage sag tolerance – IEEE 1346
Equipment Upper Range Average Lower Range
PLC 20ms, 75% 260ms, 60% 620ms, 45%
PLC, I/O card 20ms, 80% 40ms, 55% 40ms, 30%
5HP AC drive 30ms, 80% 50ms, 75% 80ms, 60%
AC control relay 10ms, 75% 20ms, 65% 30ms, 60%
Motor starter 20ms, 60% 50ms, 50% 80ms, 40%
PC 30ms, 80% 20ms, 60% 70ms, 50%
72

Transients
73

Transients – Types
5ns rise, lasts <50ns
1μs rise, lasts 50ns – 1ms
0.1ms rise, lasts >1ms
by lightning, removal of an inductive load,
loose wiring, and other arcing events.
74

Transients – Types
• Capacitor switching, ferroresonance, transformer
energisation
– Back-to-back capacitor switching, cable switching,
impulse response
– Response of system to an impulsive transient
75

Transients – Impact on Loads
• Hard disk crash
• Power supply failure
• Component failure
• SCR failure
• Circuit board failures
• Process interruptions
76

Transients – Sources
– Lightning
– Switching Operations (Breakers, Capacitors,…)
– Fault Clearing/Breaker Operations
– Lightning
– Arcing Devices
– Starting & Stopping Motors
– Breaker Operations
– Capacitor Switching
77

Transients – Lightning
78
High Frequency!

Transients – Faults
79

Transients – Motor Starting
80

Transients – Cap. Bank Switching
81

Standards for Power Quality
82
PQ
Standards
IEEE IEC

83

84

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