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8/12/2019 PowerSystems Introduction for Non Engineer
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Power Systems
for theNon Power Engineer
W.O. (Bill) Kennedy, P.Eng., FEIC
Copyright 2004 W.O. (Bill) Kennedy
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PurposeGive a basic understanding of how
power systems are put togetherand how they work
Concepts will be emphasizedMathematics will be kept to a
minimumMathematics only when necessary
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IntroductionTwo parts
First part covers power systemcomponents
Second part covers how thecomponents fit together and work
along with some measures ofpower system performance
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A little bit of PhysicsHans Christian Oerstead discovered the
relationship between magnetism andelectricity
Michael Faraday discovered that avoltage is induced on a wire when itsmoved in or through a magnetic field
James Clerk Maxwell developed themathematics of electromagnetics
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Real and Reactive PowerReal power does the work
Reactive power helps real power
do the work
Power systems need both or they
wont work
What is reactive power?
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Reactive power Quarterback can
throw a bullet, butnot very far
For long distances,
throws in an arc Real power is the
bullet
Reactive power isthe height of the arc
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Reactive Power Capacitors store energy equal
to CV2
Capacitor banks are used to
boost or raise voltage
Reactors use energy equal to
LI2
Motors and fluorescent lights
require reactive power
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Part 1 - Equipment
Generators
TransformersTransmission Lines
Loads
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Generators
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GeneratorsFundamental Law
E = N d/dt
Where is the flux
Magnetic example
High school physics
Faraday's discovery motionMaxwell mathematical theory
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GeneratorsRotor turns inside of the generator
satisfying Faradays LawVoltage induced on the stator follows
a sine waveTake advantage of space and put three
coils equally spaced, 120o apart
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GeneratorsThree Phase
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
0 45 90 135 180 225 270 315 360
Degrees
Magnitude
Phase A
Phase B
Phase C
Motion of rotor induces a voltage on the stator
Stator doesnt move and waveform reflects effect of
rotor field as it moves inside the machine
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GeneratorsControl
Terminal voltageSpeed
Terminal voltage controlled by varyingthe voltage applied to the dc field of therotor
Speed controlled by governor, as loadincreases, fuel supply increases
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GeneratorsSpeed and frequency (60 Hz)
Frequency (f) = n/60 * p/2Poles are in pairs, hence divide by 2
Speed in revolutions per minute, whereasfrequency in cycles per second, hence
divide by 60
Steam sets high speed, small rotors
Hydro sets low speed, big rotors
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Generators
Generation by Fuel Type (Alberta)
44%
39%
9%
8%
coal
gas
renewables
import
Fuel sources in
Alberta Coal plants west
of Edmonton
Gas variouslocations
Renewables include
water and wind Import from BC and
SK
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Generators Capability curve
Limits Stator heating
Rotor heating
Stability
Whats required
Whats used
Generator Capability Curve
-1-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0.00 0.25 0.50 0.75 1.00
Real PowerReactiveP
ower
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Generator Capability Curve
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0.00 0.25 0.50 0.75 1.00
Real PowerReactive
Power
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TransformersFollow Faradays Law
E1=N1d/dt & E2=N2d/dt
Flux (d/dt) is constant
Therefore voltage change depends onnumber of turns, and basic equations
can be equated with the result:E1/N1 = E2/N2
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Transformers Since conservation
of energy must bepreserved and
voltage varies
inversely, currentmust vary directly
I1N1 = I2N2
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Transformers
Usual connection for the transmission systemis WYE grounded at the high voltage
Generators connected DELTA
Loads can be both
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Surge Impedance Loading
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Surge Impedance Loading
(SIL) Transmission line
consists of:
Shunt capacitance
Series resistance and
inductance
Distributed along lengthof line
Treat as distributed
lumped elements Can ignore resistance
Surge Impedance Loading
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Surge Impedance Loading
(SIL) Close the breaker at
sending end
Shunt capacitance
charges to CV2
Close the breaker at
receiving end and feed
the load
Series inductance usesenergy at LI2
Load
Load
Surge Impedance Loading
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Surge Impedance Loading
(SIL)Equating shunt and series energies
CV2 = LI2
Performing the math yields
SIL (power) = V2/SI
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Properties of Surge Impedance (SI) Remains fairly constant over a wide range of
voltages Starts around 400 at lower voltages and
decreases with bundling to around 225 at
1500 kV Capacitance and inductance also remain
constant
Using this we can construct the followingtable
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Properties of Transmission LinesVoltage (kV) SI () R (/km) X (/km) Charging
(kVAr/km)SIL
(MW)X/R
69/72 370 0.4 0.5 15 13/14 1.2
138/144 370 0.2 0.5 70 50/55 2.5
230/240single
340 0.07 0.45 225 170 6
230/240bundled
300 0.07 0.4 290 180/195 6
345 bundled 285 0.026 0.365 525 415 14
500 bundled 250 0.018 0.345 1340 990 20
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0.000.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
100
200
300
400
500
600
700
800
900
1000
Length (km)
Lin
e
Loading
(SIL)
St. Clair Curve
3.25
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Loads Three types of load models
Constant MVA motors
Constant current resistive loads
Constant impedance reactor & capacitorbanks
For power flow use constant MVA
For transient studies need a combination and
may require frequency
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Summary Part 1Generators make the product
Transformers raise and lower voltageto allow efficient transport of product
Transmission lines are the highwaysLoads are the end user of the product
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Dinner BreakDinner Break
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Part 2 how the power system worksFundamental rules
Maintain reactive power balance andvoltages will be in required range
typically +/- 5% of nominalMaintain load/generation balance and
frequency or speed remains constant
typically 60 Hz +/- 0.02 Hz
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Characteristics of power systems Generation is usually remote from loads
Transmission needed to connect generationto load
Transformers needed to raise/lower voltage
Want as high a voltage as practical fortransmission minimizes losses
Use load size, generator size and line SIL to
get line voltage In Alberta, lines are typically 150 km long
At that distance loading 2 times SIL
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Putting it all togetherGenerators produce real power (P)
Generators produce/consumereactive power (Q)
Generator Q for underexcited
operation is around half overexcited
ability
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Putting it all together Transmission lines consume P in form of
losses, typically 5% to 7% of generation Lines produce/consume Q depending on
power flow on the line as a fraction of SIL
< SIL VArs flow out of line
> SIL VArs flow into line
Half from each end, if voltages are equal
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Putting it all together Loads consume P & Q
P required for resistive loads Q required for reactive loads induction motors
Synchronous motors can produce/consume Q
Switching and/or load stations Use shunt reactor/capacitor banks to
produce/absorb Q
Primarily for voltage control
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Breakers
Breakers used toconnect/disconnect
equipment
Breakers must becapable of picking
up and dropping
loads
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Breakers
Breakers must becapable of switchingunloadedtransmission lines
Breakers must becapable of
interrupting thesymmetrical faultplus any dc offset
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Power flowNeed a model of the system
Per unit system is bestMust have consistent voltage ratios
Base impedances on voltage levelMost models involve some lumping, i.e.
not practical to model every detail
However, this depends on the type ofstudy
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Power flow To solve a power flow need to solve for four
variables at each bus Bus voltage V
Bus angle
Real power P Reactive power Q
However, some variables already known
Load P & Q
Generator bus V
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Solution methodsFour solution methods
Gauss-Siedel solves phasor equationsNewton-Raphson solve for P & Q by
separation of variables
dc solves circuit as a dc circuit by
treating jX as a resistance
Decoupled load flow variant of Newton-Raphson. Separates V &
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Solution methods Solution results
Balance generation with load and lossesKeep all bus voltages within tolerance +/-
5%
Require a slack or swing bus. Can be afictitious generator to supply/absorb P & Q
Solution achieved when swing bus P & Q
equal zero Not practical, therefore minimize swing bus
P & Q
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Types of studiesDynamic studies
All of the above: Operations, Planning &Fault
Transients what happens as powersystem moves from one steady state toanother
Additional studies determine equipmentratings, e.g. breaker duty
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ContingenciesContingencies test the system for
robustnessContingency loss of one or more
components at a time
Costs escalate if system designed formore than two contingencies
Example loss of a generator and line ortransformer N-G-1
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Power system exampleGo to example
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Power System PerformanceLosses weve ignored losses up
to this pointMeasuring outages
Lines & Stations
Delivery Point measures
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Transmission LossesTransmission Losses
0
100
200
300
400
500
4750 5000 5250 5500 5750 6000 6250 6500 6750 7000 7250 7500 7750
Net Generation to Supply Alberta Load (MW)
Losses
M
W
Losses are
stochastic Simple system
losses vary as a
square of current Complex system
losses display a
linear variance
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Transmission LossesTransmission Losses Histogram
0
100
200
300
400
500
197
210
223
236
249
262
275
288
301
314
327
340
353
366
379
392
405
418
431
Losses (MW)
Count
Histogram demonstrates a normal
distribution pattern for losses
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Transmission lossesTransmission Generation, Load and Losses by Day
4000
4500
5000
5500
6000
6500
7000
7500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Hour
Geenration&Load(MW)
0
100
200
300
400
500
600
700
800
900
1000
Losses(MW)
Net Gen
Net Load
Losses
+3-sigma
-3-sigma
Ave Losses
Losses on AIES are very linear
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Power system performanceNeed measure system performance
Measure frequency and duration ofoutages
Reason outages occur infrequently
Measures of performance look at allcomponents and causes
Usually stated as an average of wholesystem
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PerformanceFor Alberta, AESO publishes data to its
website on line and terminal outages asan overall average for the voltage class
For Delivery Points frequency and
duration data also published as asystem average
For comparison, all Canada data isincluded for Delivery Points
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PerformanceTwo types of duration are measured
Momentary < 1 minuteSustained > 1 minute
Following are examples of chartspublished on the AESO website
http://www.aeso.ca/transmission/5548.html
http://www.aeso.ca/transmission/5548.htmlhttp://www.aeso.ca/transmission/5548.htmlhttp://www.aeso.ca/transmission/5548.html8/12/2019 PowerSystems Introduction for Non Engineer
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Transmission - line
1.721,7010.05%6.074,5980.7675798,997Total
5.96950.03%2.64370.88141,595500
0.943200.04%4.931,1590.6923533,968240
1.266850.05%7.062,2720.5932254,417138/144
6.676010.14%6.081,1302.061869,01769/72
Frequency
per 100 km.a(faults/100
km.a)
Number ofMomentary
Faults
Unavailabilityper 100 km.a
(%)
Average
OutageDuration
(hrs/fault)
Total
OutageDuration
(hours)
Frequency
per 100 km.a(faults100
km.a)
Number ofSustained
Faults
KilometerYears
(km.a)
VoltageClass (kV)
For the Period From 1997 - 2001
Summary for Line Related Forced Outages
Transmission Outage Statistics
Alberta Interconnected Electric System
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System Average Interruption FrequencySAIFI-MI
0.0
0.4
0.8
1.2
1.6
1997 1998 1999 2000 2001
Year
Frequency
Alberta
Canada
Ice Storm
Removed
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System Average Interruption DurationSAIDI
0
100
200
300
400
1997 1998 1999 2000 2001
Year
Duration
(minutes) Alberta
Canada
Ice Storm
Removed
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Summary Part 2Power flow studies model and test
the system for robustnessyesterday, today and tomorrow
N-G-1 is used to test the system foroperation today and into the future
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Summary Part 2Losses are an important part of
power system design and operationHigher voltage lines reduce losses
However, losses are fixed when theconductor is chosen
For a system like Albertas, lossesare fairly flat
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Summary Part 2Outages are measured using
frequency and duration techniquesPresented as system average
numbersAlbertas performance not bad
when compared to rest of Canada
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Thats all folks!
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