Download Power Quality 101

Power Quality 101
Dr. Adly Girgis
APPA 2005 Customer
Connections Conference
October 2005
Introduction
¾ The
objective of the electric utility is to
deliver sinusoidal voltage at fairly constant
magnitude and frequency throughout their
system.
¾ If
loads are linear, both the voltage and
current waveforms will be sinusoidal at a
fairly constant magnitude and frequency.
¾ Typical
examples of linear loads include
motors, heaters and incandescent lamps.
Voltage
Current
Voltage and Current Waveforms for Linear Loads
¾ The
presence of non-linear and electronic
loads distort this pure sinusoidal
waveform.
¾ Typical
examples of non-linear loads
include rectifiers (power supplies, UPS
units, discharge lighting), adjustable speed
motor drives, DC motor drives and arcing
equipment.
Voltage and Current Waveforms for Non-Linear Loads
Voltage
Non-Linear Load Current
¾
The current drawn by non-linear loads is not sinusoidal but it
is periodic, means that the current wave looks the same from
cycle to cycle.
¾ Periodic
waveforms can be described as a
series of sinusoidal wave forms that have
been summed together.
¾ The sinusoidal components are integer
multiples of the fundamental where the
fundamental, in the united states, is 60 Hz.
¾ The only way to measure a voltage or
current that contains harmonics is to use a
true RMS reading meter.
¾ If an averaging meter is used, which is
most common type, the error can be
significant.
Harmonic Sine Wave
60 Hz Fundamental
180 Hz (3RD Harmonic)
Total Seen By Instruments
Waveform with Symmetrical Harmonic Component
Harmonics distort the sinusoidal waveform and
falls under power quality issue.
Harmonic Sine Wave
60 Hz Fundamental
300 Hz(5th Harmonic)
180 Hz(3rd Harmonic)
Total Seen by Instrument
Waveform with 3rd and 5th Harmonic Component
Main Sources of Harmonics
¾ Power
Electronics, Electric Arc Furnaces,
Fluorescent Lamps, Electrical Machines
and Transformers.
¾ The
increasing use of power electronic
devices for the control of power apparatus
and systems has been the reason for the
greater concern about waveform distortion
in recent times.
¾ The
most common power electronic load
is the single phase rectifier, used to power
most modern office and domestic
appliances.
¾ The
terms rectification and inversion are
used for power transfers from AC to DC or
DC to AC respectively.
Transformer Magnetization
Nonlinearities
Flux (Φ)
Voltage (V)
Normal Ideal Excitation Current
Transformer Inrush Current
Inrush Current Wave & Excitation Saturation Curve
Discharge-Type Lighting
¾
Luminous discharge lighting is highly nonlinear and
gives rise to considerable odd ordered harmonic
currents.
This effect is clearly illustrated
0.6
Current (A)
¾
0.4
0.2
0
-0.2
-0.4
2
4
6
8
10 12 14 16 20 22
Time (ms)
Single Phase Rectification
¾
DC Power Supplies
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Many commercial and domestic appliances require
direct current for their operation.
I
V
C
+
-
TV
Load
Current
¾ TV Receivers
Time
Current Waveform generated by a 23 Inch TV Set
¾ Microwave Oven:
6
Current Waveform Because of 900 W Microwave Oven
Current (A)
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2
0
-2
-4
2
4
6
8
10
12
Time (ms)
14
16
20
22
Three Phase Current Source
Conversion
DC to DC
Regulator
The Basic One Line Diagram
Load
A
B
C
Neutral Current Contains No
Fundamental, but Third
Harmonic is 300% of Phase Current
A Balanced Three Phase System
¾ In summary, Harmonics are due to:
z
z
z
Ripples in the voltage waveform of rotating
machines, due to variations in air gap
reluctance over machine pole pitch, flux
distortion
in
synchronous
machines,
nonlinearity in the operation.
Transformer
saturation.
magnetizing
current,
core
Network nonlinearities from loads such as
rectifiers, inverters, arc furnaces, welders,
voltage controllers, frequency converters.
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z
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Load nonlinearities
High
voltage
dc
power
conversion,
transmission and power exchange.
Interconnection of non conventional energy
generation sources such as wind, solar,
geothermal etc. with distribution systems.
Active and Passive VAR compensators.
¾ Harmonic currents can produce a number
of problems, namely:
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Equipment heating
Equipment malfunction
Equipment failure
Communications interference
Fuse and breaker mis operation
Process problems
Conductor heating
Capacitor Switching of Normal
Operating Conditions
I
¾ Benefits:
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z
z
P.F. Improvement
Loss Reduction
Voltage Improvement
Load
Φn
Φ0
ILD
V
V
I
Ic
Φn < Φ 0
PFn > PF0
Improved PF
I < ILD
I2Rf < I2LDRf
Reduced Losses
¾ The process of capacitor switching is done
frequently to improve power factor and
voltage regulation.
z
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Time of Day control
Voltage Control
Capacitors Switching Concerns
¾ Harmonic Resonance
¾ Voltage Rise
¾ Transients
A STUDY CASE
HARMONIC DISTORTION WITH CAPACITOR
CORRECTION
Zsj (h)
I(h)
I
Zcj (h)
RESULTS
Capacitor switching in this case caused
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An increase in current RMS value
An increase in apparent power
Reduction in power factor
Increase in total harmonic distortion
Solution – Replace capacitor with a filter.
Capacitor Switching Transients
other line
L1
L2
C1
L1
C2
C1
L2
C2
Voltage Flicker Phenomena
¾
¾
¾
Voltage flicker refers to a fluctuation in the
magnitude of the supply voltage envelope,
created by large non-stationary loads.
These large industrial loads draw high irregular
currents which produce voltage fluctuation
problems for power systems.
If commercial or residential loads are electrically
close to such loads, customers may experience
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z
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Uncomfortable light flickering
Television picture distortion
Computer error and memory loss
Misoperation of industrial devices.
Typical Voltage Flicker Disturbance
Arc Furnace Operations
¾ Arc
furnace often represent the single largest
customer on an electric utility supply system.
¾ From the power quality point of view, electric
arc furnace loads can result in serious
electrical disturbances on a power system.
¾ This is due to the characteristics of the
electric arc phenomena.
¾ Arc
furnaces
represent
non-linear,
asymmetric loads with a rapidly varying
demand for reactive power.
¾ In
the power supply, there are generally
strong power quality impacts appearing as
fluctuations, harmonics and unbalances of
the voltage.
¾ An arc furnace installation consists of a
refractory lined shell which holds the scrap
metal charge.
Movable
Arms
Electrodes
Water
Cooled
Leads
Scrap
Charge
Furnace
Transformer
¾ Due
to the random motion of the arc and the
resulting change in the arc length, the
random demand in power demand produces
irregular fluctuations in current.
¾ These
current fluctuations produce the
voltage drop across the furnace transformer
leads to a voltage flicker.
¾ The
arc furnace load will vary from a
complete open-circuit to a full three phase
short-circuit several times during the melting
process.
Voltage Flicker Limitation
¾ At
higher levels of flicker magnitude variation
for a given frequency, the lamp flicker
became annoying and objectionable.
¾ This led to the establishment of a tolerance
threshold or borderline of objection.
¾ From the electric utility’s point of view, the
tolerance threshold may be used to aid in the
design and operation of a power system
while minimizing the possibility of flicker
complaints from its customers.
At higher frequencies of voltage fluctuation above 1
hertz, there is little difference between a perceptible
flicker and an objectionable flicker.
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5
4
3
2
1
0
10
0
10
1
0.
1
Objectionable
Visible
0.
00
01
0.
00
1
0.
01
Percent Voltage Change
¾
Frequency of Voltage
Fluctuation (Hz)
Faults in Power Systems
Looks Like a Snake !!
Time for a nap?
Example: Fault Condition (A-G)
F
Va
Area of voltage variation
during fault “A-G Fault
Vc
Vb
Industrial Park
F
I1
Feeder 1
S
Feeder 2
P
Recloser
I1
S
Distribution Substation
P
Sources of Continuing Education
and Professional Development
¾
IEEE Tutorials
Conferences.
in
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Coming Conferences:
General
and
Regional
Power Systems Conference 2006
Advanced Metering, Protection, Control,
Communication and Distributed
Resources
March 14-17, 2006
Clemson, SC, USA
http://www.ces.clemson.edu/powsys2006
Preliminary Technical Program
¾ Panel Discussions:
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Distribution automation advancements to
improve system reliability and power quality.
BPL past, present and future technology and
applications.
Advanced Metering Technology.
Power Quality Issues in Metering and Relays.
Cyber Security for SCADA and Protection
Systems.
¾
Technical Paper Session:
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Innovation in Distribution System Protection.
State Estimation, Load Shedding and Restoration.
Substation and Line Protection.
Innovation in SCADA and Communication Systems I
& II.
Distribution System Operation, Automation and
Reliability.
Tutorials:
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All Tutorials are offered at no additional cost, but
advanced registration is required.
A – Power System Protection and Automation
Innovation – Ed Schweitzer, Schweitzer Engineering
Laboratories (Full Day)
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B – State of the art in Power Systems
Communications, Control and Protection – Mark
Adamiak, GE (Full Day)
C – Cyber Security best practices in the context of
NERC – CIP Regulations – Jason Stamp, Sandia
National Laboratories (Full Day)
D – Distribution Automation – John McDonald,
President of PES (Half Day)
Important Dates:
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January 15, 2006 ÆPP Presentation and Advanced
Registration
March 14-17, 2006 Æ Pre-Conference Tutorials and
Conference
More Information
¾
For updated information, hotel reservation and
registration visit the conference website
http://www.ces.clemson.edu/powsys2006
or Contact the Conference Chair
Dr. Adly Girgis
[email protected]
864-656-1053
864-656-5936
ONE DAY TUTORIAL
March 14, 2006
Clemson, SC
IEEE Power Engineering Society
Power System Basics
for Non-Engineering Professionals
Course Description
This one-day course is intended to give non-engineering
professionals a better understanding of electric power systems
planning, operations and regulatory frameworks. Basic electrical
terminology and concepts are explained in simple to understand
terms with regard to design, construction, operations and
maintenance of power plants substations and transmission and
distribution lines. Basic electrical safety concepts are included.
¾ Who Should Attend?
z Regulatory Affairs, Legislators, Commission Staff Professionals,
z Power Brokers, Power Marketers, Consumer Groups and related
organizations,
z Policy Makers, Public Affairs Administrators, Legal Councils,
Media Communications Staff Experts,
z Energy
Agency Leaders, Business Executives, Education
Institution Board Members,
z Utility Management, or anyone interested in learning about
electric power systems.
¾ Benefits of Attending
¾ Participants gain more insight into the concerns of engineers, the
demands of regulators and consumer groups and a perspective of
how these factors play a major role in the operation of today’s
electric power systems. This course will help participants become
more productive and proactive in professional situations.
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Course Outline
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Introduction and Brief History
Fundamentals of Electric Power
Discussion of how natural recourses such as coal, gas, water, solar,
wind, etc. are converted into useable electrical energy.
Generation and Transmission
The operation of generation plants, substations and transmission
lines are explained plus how these systems work together to
efficiently transport electrical power long distances.
Distribution and Utilization
Power delivery to residential, commercial and industrial customers is
explained including emergency backup generators.
Power System Protection
Design concepts of power system protective relaying and
coordination are explained for local and interconnected systems.
Power System Operation
How electric power systems are monitored, controlled and operated
under normal and abnormal conditions, including the use of
telecommunications channels are included in this course.
Interconnection and Regulation
The benefits of interconnected power systems and regulatory
requirements of electric power systems are discussed.
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