Download - PQ Fundamentals
-
7/29/2019 PQ Fundamentals
1/57
Copyright 2001 by Prof. S. S. Venkata.
Electric Power Quality
by
S. S. (Mani) Venkata
Iowa State University
Ames, Iowa
-
7/29/2019 PQ Fundamentals
2/57
Copyright 2001 by Prof. S. S. Venkata.
OUTLINE
PART I: Power Quality Definitions & Concepts.
PART II: Sources & Mitigation Schemes.
PART III: Case Study of Practical Example.
-
7/29/2019 PQ Fundamentals
3/57
Copyright 2001 by Prof. S. S. Venkata.
Electric Power Quality
TutorialPart I: Power Quali ty
Definitions & Conceptsby
S. S. (Mani) Venkata
Iowa State University
Ames, Iowa
December 29, 2001
-
7/29/2019 PQ Fundamentals
4/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 4/57
Power Quality Definitions
What is Power Quality (PQ) ?
Why is it important to Energy Suppliers?
Why is it important to Customers?
Typical PQ Problems.
Impact of PQ on Utilities and Customers.
Focus on Three Aspects of Power Quality Harmonics
Voltage Sags
Voltage Flicker
Review of Power Concepts under Non-sinusoidalConditions.
-
7/29/2019 PQ Fundamentals
5/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 5/57
Classical Distribution Systems
-
7/29/2019 PQ Fundamentals
6/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 6/57
Future Distribution Systems
-
7/29/2019 PQ Fundamentals
7/57Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 7/57
What is Power Quality?
Power quality broadly refers to the
delivery of a sufficiently high grade ofelectric service.
In general, it involves maintaining a
sinusoidal load bus voltage at stipulatedmagnitude and frequency.
-
7/29/2019 PQ Fundamentals
8/57Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 8/57
Voltage/Current Waveforms at
a Veneer Plant
-
7/29/2019 PQ Fundamentals
9/57Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 9/57
Typical Power Quality Problems
1. Disturbances
- Voltage Dip (SAG)
- Brief Voltage Increases (SWELLS)
- Outages
- Transients
- Voltage Notches
2. Unbalance
3. Distortion
- Voltage Harmonics
- Current Harmonics
4. Voltage Fluctuation- Step Voltage Changes (regular or irregular)
- Cyclic or Random Voltage Changes
5. Flicker
-
7/29/2019 PQ Fundamentals
10/57Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 10/57
Typical Power Quality Problems (cont.)
-
7/29/2019 PQ Fundamentals
11/57Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 11/57
Typical Power Quality Problems (cont.)
-
7/29/2019 PQ Fundamentals
12/57Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 12/57
Typical Power Quality Problems (cont.)
-
7/29/2019 PQ Fundamentals
13/57Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 13/57
Why is Power Quality
Important?
It affects both utilities assuppliers and customers as
users
-
7/29/2019 PQ Fundamentals
14/57Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 14/57
Impact on Customer Side
Computers and communication equipment are
susceptible to power system disturbances which
can lead to loss of data and erratic operation.
Automated manufacturing processes such as
paper-making machinery, chip-making
assembly lines, etc. can shutdown in case of
even short voltage sags.
-
7/29/2019 PQ Fundamentals
15/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 15/57
Impact on Customer Side (cont.)
Induction and synchronous motors can have excessive
losses and heating.
Home electronic equipment are vulnerable to powerquality problems - e.g., blinking VCR machines and
digital clocks.
Equipment and process control malfunction translatesto dollars of expense for replacement parts and for
down time, impacting adversely on profitability and
product quality.
-
7/29/2019 PQ Fundamentals
16/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 16/57
Impact on Utility Side
Failure of power-factor correction capacitors
due to resonance conditions.
Increased losses in cables, transformers andconductors, especially neutral wires.
Errors in energy meters, which are calibrated
to operate under sinusoidal conditions.
-
7/29/2019 PQ Fundamentals
17/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 17/57
Impact on Utility Side (cont.)
Incorrect operation of protective relays,particularly in solid-state and microprocessor-
controlled systems.
Interference with ripple control and power line
carrier systems used for remote switching, load
control, etc.
Unhappy customers as well as malfunction and
failure of system components and control
systems, impacting adversely on profitability.
-
7/29/2019 PQ Fundamentals
18/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 18/57
Total Cost of PQ Problems &
Solutions Annual Cost of Problems
Estimated as $ 180 M to Users + $ 300 M to Utilities,
Total of $ 480 M per year
Total cost of solutions
Estimated as $3+ Billion by EPRI based on the amount
expended by the industry to mitigate PQ problems
-
7/29/2019 PQ Fundamentals
19/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 19/57
Focus on Three Aspects of Power
Quality
Harmonics
Voltage Sags
Voltage Flicker
-
7/29/2019 PQ Fundamentals
20/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 20/57
Harmonics and Their Impact
on Equipment and Systems Linear Loads: draw Currents proportional to
applied voltages.
Examples: incandescent lighting, heatingand motor loads
Non-linear loads: draw current only a part of
the voltage cycle.
Examples: computers, adjustable speed
drives and programmable logic converters.
-
7/29/2019 PQ Fundamentals
21/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 21/57
Harmonics and Their Impact
on Equipment and Systems The resulting current from nonlinear
loads contains 3rd, 5th, 7th, ...harmonics.
Harmonic currents permeate into source
currents.
Source currents having harmonic content
impact source voltage.
-
7/29/2019 PQ Fundamentals
22/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 22/57
Metering Errors
Induction Watt-Hour Meter
Induction watt-hour meters work on the same principles
as an induction motor.
Positive sequence harmonics aid disk rotation.
Negative sequence harmonics retard the disk.
1 2 3 4 5 6 7 8 9 10
+ - 0 + - 0 + - 0 +
0
0.2
0.4
0.6
0.8
1
0 120 240 360 480 600Hz
Reading/Actual
Meter Frequency Response
-
7/29/2019 PQ Fundamentals
23/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 23/57
Linear Load: the consumer pays for unused energy
due to voltage distortion.
Non-Linear Load: the consumer pays even more forunused energy due to both voltage and current
distortion
Both Cases: the metering error is more significantwhen the load is light and the harmonic energy is alarge % of the energy transferred through the meter
Metering Errors (cont.)
Linear
Load
>
>
W
>
-
7/29/2019 PQ Fundamentals
24/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 24/57
Harmonic Resonance
Parallel Resonance Series Resonance
HarmonicSource
EQUIVALENT CIRCUIT
Capacitor
Capacitor HarmonicSource
ONE-LINE DIAGRAM
Source
Impedance
Cap.
Capacitor
ONE-LINE DIAGRAM
Line
EQUIVALENT CIRCUIT
Line
impedance
Harmonic
Source
HarmonicSource
Source
Impedance
-
7/29/2019 PQ Fundamentals
25/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 25/57
Harmonic Resonance (cont.)
Series resonance caused bytransformer and secondarycapacitor.
Harmonic source on theprimary can cause a highvoltage distortion on thesecondary.
This can result in capacitor
failure if the capacity ofharmonic source(s) on theprimary is larger than thecapacitor rating.
Primary
Loads
EQUIVALENT CIRCU IT
Harmonic
Source
Capacitor
Transformer
Reactance
ONE-LINE DIAGRAM
Capacitor
Secondary
Harmonic
Source
Loads
-
7/29/2019 PQ Fundamentals
26/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 26/57
Example of Resonance
-
7/29/2019 PQ Fundamentals
27/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 27/57
Harmonics Analysis
The Fourier Series:
Any periodicwaveform can be
represented by aninfinite series of sinewaves havingfrequencies which aremultiples of the
fundamentalfrequency, i.e.,harmonics.
-
7/29/2019 PQ Fundamentals
28/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 28/57
Fourier Series-Basic Equations
Let f(t) be a periodic waveform with fundamental frequency 0
The Fourier Series Representation of f(t) is:
f(t) = a0 + a1cos0t + a2cos20t + + b1sin0t + b2sin20t + (1.1)
= a0 + ancos(n
0t) + bnsin(n
0t) (1.2)
1n
1n
-
7/29/2019 PQ Fundamentals
29/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 29/57
Fourier Series - Basic Equations (cont.)
where
a0 = (d.c. component) (1.3)
an = (1.4)
bn = (1.5)
T
0
dtf(t)
T
1
T
0
0dttnsinf(t)
T
2
dttncosf(t)T
2T
0
0
-
7/29/2019 PQ Fundamentals
30/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 30/57
We have from Eq. 1.3 to Eq. 1.5:
0.1.1T
1T
0
T2
T
0
dtdta i.e., no dc component
0.cos.1.cos.1T
2T
0
2
00
T
T
n dttndttna
T
0
T2
T
0n t.dtnsin.1t.dtnsin.1T
2b
0
n
4
if n is odd
0 if n is evenThus f(t) can be represented as :
...7sin7
15sin
5
13sin
3
1sin
4)(
0000tttttf
-
7/29/2019 PQ Fundamentals
31/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 31/57
Example of Fourier Series
-
7/29/2019 PQ Fundamentals
32/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 32/57
Harmonics Indices
THD: Total Harmonic Distortion: Ratio of rmsvalue of total harmonic content to rms value offundamental
TIF:Telephone Interference Factor
C-Message Weights
V.T and I.T Products
-
7/29/2019 PQ Fundamentals
33/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 33/57
Total Harmonic Distortion (THD)
The most commonly used power quality measure
It is defined as the ratio of the root-mean square of the
harmonic content to the root-mean square value of the
fundamental quantity. Frequently the THD is
expressed in percent
1
2
5
2
4
2
3
2
2 ...
V
VVVVTHD
(for voltage)
1
2
5
2
4
2
3
2
2 ...
I
IIII (for current)
-
7/29/2019 PQ Fundamentals
34/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 34/57
THD (cont.)
The THD is zero for a perfectly sinusoidal wave. It
increases indefinitely as the waveform distortion
increases.
A THD of5% is commonly cited as the border line
between high and low distortion for distributioncircuits.
Balanced THD includes only positive and negative
sequence signals
Residual THD includes only triplen or zero-sequence signals only.
-
7/29/2019 PQ Fundamentals
35/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 35/57
-
7/29/2019 PQ Fundamentals
36/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 36/57
-
7/29/2019 PQ Fundamentals
37/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 37/57
Telephone Influence Factor (TIF)
The TIF is a variation of the THD in which the
harmonic components are weighted by factors whichreflect:
The frequency response of the human ear and
The variation of the inductive coupling between adjacent
circuits with frequency.
It is defined as: TIF =
(Frequently, the TIF is expressed in percent.)
The ANSI 368 Standard recommends truncation of the
infinite series at 5.0 kHz.
.. .
.. .IIIII
2
5
2
4
2
3
2
2
2
1
2
5
2
4
2
3
2
2
2
12
5
2
4
2
3
2
2
2
1
IIIII
wwwww
-
7/29/2019 PQ Fundamentals
38/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 38/57
Telephone Influence Factor (TIF)
(cont.) The TIF is often used to asses interference of
power distribution circuits with audio
communication circuits.
It is useful for assessing interference withanalog telephone circuits, but is not indicative
of interference with circuits which usetechniques such as pulse code modulation(PCM).
Table. C-message and TIF weighting coefficients
-
7/29/2019 PQ Fundamentals
39/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 39/57
g g g
TIF weighting factors vs. frequency
-
7/29/2019 PQ Fundamentals
40/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 40/57
C-message weights
The C-message weighted index is similar to the TIF
except that weights ci are used instead of w
C=
The C-message weights are related to the TIF weights
as follows:
...
...IcIcIcIcIc2
5
2
4
2
3
2
2
2
1
252423222125
24
23
22
21
IIIII
ii wcif 05
-
7/29/2019 PQ Fundamentals
41/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 41/57
C-message weights
Unlike the TIF weights, the C-message
weights do not take into consideration
linear variation of mutual coupling ofcircuits with frequency.
-
7/29/2019 PQ Fundamentals
42/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 42/57
V.T and I.T products
The THD does not take into account the strength (level)
of the signal. The V.T product is an alternative index
which incorporates the voltage amplitude.
V.T =
ws are weights that are listed in Table 2.2 of Heydts
book
The I.T product is a similar index for line currents.
I.T =
...VVVVV2
5
2
4
2
3
2
2
2
125
24
23
22
21
wwwww
Vrms TIFV .
...IIIII2
5
2
4
2
3
2
2
2
12
5
2
4
2
3
2
2
2
1 wwwww
Irms TIFI .
-
7/29/2019 PQ Fundamentals
43/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 43/57
Voltage Sags
A voltage sagis when a customer experiences
temporary voltage levels lower than a specified
level (between 0.9 and 0.1 pu)
Causes:
Short-circuit conditions (Faults)
Starting large motors, etc.
-
7/29/2019 PQ Fundamentals
44/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 44/57
Voltage Sags
Effects:
Duration-dependent
Failure of computer equipment
Outages of sensitive process plants
Measures
CBEMA Curve (1978): less stringent restrictions ITIC Curve (1996): demands more severe
performance standards
-
7/29/2019 PQ Fundamentals
45/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 45/57
The CBEMA (Computer Business Equipment manufacturers
Association) Curve
0.0001 0.001 0.01 0.1 1 10 100 1000
-100
-50
0
50
100
150
200
250
TIME IN SECONDS
PERC
ENTCHANGEINBUSVOLTA
GE
8.33ms
OVERVOLTAGE C ON DITION S
UNDERVOLTAGE CONDITIONS
0.5CYCLE
RATED
VOLTAGE
ACCEPTABLE
POWER
-
7/29/2019 PQ Fundamentals
46/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 46/57
The ITIC (Information Technology Industry Council) Curve
0.0001 0.001 0.01 0.1 1 10 100 1000
-100
-50
0
50
100
150
200
250
TIME IN SECON DS
PERC
ENTCHANGEINBUSVOLTAGE
8.33ms
OVERVOLTAGE CONDITIONS
UNDERVOLTAGE CONDITIONS
0.5CYCLE
RATED
VOLTAGE
ACCEPT ABLE
POWER
10%+--
-
7/29/2019 PQ Fundamentals
47/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 47/57
Alternative Power Acceptability Curves
Curve Year Application Source
FIPS poweracceptability
curve
1978 Automatic dataprocessing
(ADP)
equipment
U.S. federalgovernment
CBEMAcurve
1978 Computer businessequipment
ComputerBusiness
Equipment
Manufacturers
AssociationITIC curve 1996 Information
technologyequipment
InformationTechnology
IndustryCouncil
Failure ratecurves for
industrial
loads
1972 Industrial loads IEEE Standard493
AC linevoltage
tolerances
1974 Mainframecomputers
IEEE Standard446
IEEEEmerald
Book
1992 Sensitiveelectronic
equipment
IEEE Standard1100
-
7/29/2019 PQ Fundamentals
48/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 48/57
If loads such as arc furnaces cause
variation in the distribution bus voltage
which has a spectral characteristicwhich lies between a fraction of a Hertz
and about one third of the system
frequency, this condition is calledflicker.
Voltage Flicker Definition
-
7/29/2019 PQ Fundamentals
49/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 49/57
Flicker is a characteristic where a high frequency
(0) sinusoid is modulated by a low frequency
sinusoid (f).
Mathematically,
v(t) = (1 + Vfcos(ft)) Vmcos (0t)
Side-band frequencies of (0f) will be present.
Voltage Flicker Definition
-
7/29/2019 PQ Fundamentals
50/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 50/57
Intensity of Flicker, F
where Sscf = short-circuit kVA at electrode tip
Ssc = short-circuit kVA at PCC(point of common coupling)
Perceptibility of Flicker depends on both
Vfand f.
Voltage Flicker Definition
SS
VV
sc
scf
m
f
Power Component
-
7/29/2019 PQ Fundamentals
51/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 51/57
Power Component
Definitions:P,Q,S,...
Sinusoidal System Power Concepts
tsin2 Vv ; )-t(sin2 Ii
t2sinsint2cos1cos* VIVIivp
t2sint2cos1
QP powerorcos activerealVIP
powersin reactiveVIQ
power22 apparentQPVIS
cos/.. SPfp
Graphical Interpretation
-
7/29/2019 PQ Fundamentals
52/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 52/57
Graphical Interpretation
-
7/29/2019 PQ Fundamentals
53/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 53/57
Physical Interpretation
Real power, P is the average value of instantaneous
power. It represents the useful power being
transmitted.
Reactive power, Q is the peak value of that power
component which travels back and forth on the line,
resulting in the zero average.
Apparent power, S determines the loading of the
system and is used for rating power apparatus.
Power factor of a system is an indicator of the
efficiency with which power is transmitted. It is
desirable to have a power factor close to 1.
-
7/29/2019 PQ Fundamentals
54/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 54/57
Non-Sinusoidal System Power Concepts
Total Harmonic Distortion (THD)
Rms voltage =V = VRMS =
Rms current = I = IRMS =
Apparent power, S = VI = VRMS IRMS
Real power, P =
1
2
4
2
3
2
2 ...
VVVV
.. .2
4
2
3
2
2
2
1 VVVV
...2
4
2
3
2
2
2
1 IIII
...coscoscos 333222111 IVIVIV
-
7/29/2019 PQ Fundamentals
55/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 55/57
Reactive Power = ?
Budeanu
s Definition:
Distortion power, D =
Fryzes Definition:
Reactive power,
...sinsinsin 333222111 IVIVIVQB
222QPS
22PSQF
222DQQ
BF
-
7/29/2019 PQ Fundamentals
56/57
Copyright 2001 by Prof. S. S. Venkata. PQ TUTORIAL: PART I 56/57
Power Components for Non-sinusoidal
Conditions
-
7/29/2019 PQ Fundamentals
57/57
References
S. S. Venkata, G. T. Heydt, Proceedings of the NSF Workshop
on Electric Power Quality,Jan. 1991, Grand Canyon, AZ, USA.
2. J. Arrillaga, N. R. Watson, S. Chen, Power System Quality
Assessment,John Wi ley & Sons, England, 2000.
3. R. C. Dugan, M. F. McGranaghan, H. W. Beaty, Electrical
Power Systems Quality,McGraw-Hil l, USA,1996.
4. G. T. Heydt, Electric Power Quality,Stars in a Circle, USA,
1991.
5. E. Acha, M. Madrigal, Power Systems Harmonics: Computer
Modeling and Analysis,John Wi ley & Sons, England, 2001.
6. A. E. Emanuel,
IEEE Tutorial Course: NonsinusoidalSituations Effects on The Performance of Meters and
Definitions of Power,I EEE, USA,1990.