ATMOSPHERIC STABILITY Hydrodynamic stability Parcel method Stability criteria
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Transcript of [height=1.5cm,width=9cm,keepaspectratio]CREWlogo ECE … on Power System Stability 12 Significance...
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StabilityCharacteristics of a good verbal presentation
References
ECE 566: Grid Integration of Wind EnergySystems
S. Suryanarayanan
Associate ProfessorECE Dept.
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Outline
1 Stability
2 Characteristics of a good verbal presentation
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Disclaimer
The following slides have been taken directly from the publicdomain source [1] for the purpose of educational objectives.All copyrights are reserved by and remain with the originalowner of these slides.
Suryanarayanan ECE 566 Lecture/Week 15
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Fundamentals on Power System Stability 1
Power System Stability
On Island Networks
DIgSILENT GmbH
Prepared for IRENA Workshop, 8 - 12 April 2013, Palau
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Fundamentals on Power System Stability 2
• Definition of power system stability
• Rotor angle stability
• Frequency Stability
• Voltage stability
• Renewable energy integration and stability
Overview
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Fundamentals on Power System Stability 3
What is Power System Stability?
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Fundamentals on Power System Stability 4
Definition of stability:
Power system stability is the ability of an electric power
system, for a given initial operating condition, to regain a
state of operating equilibrium after being subjected to a
physical disturbance, with most system variables bounded
so that practically the entire system remains intact.
Source: IEEE/CIGRE Joint Task Force on Stability Terms and Definitions, “Definition and Classification of Power System Stability”, IEEE Transactions on Power Systems, 2004
Power System Stability
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Fundamentals on Power System Stability 5
• Rotor angle stability (transient stability, small-signal stability)
• Frequency stability
• Voltage stability (short-term, long-term, small disturbance, large disturbance)
Types of Stability
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Fundamentals on Power System Stability 6
Rotor Angle Stability
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Fundamentals on Power System Stability 7
What is Rotor Angle?
Reference Machine Synchronous Machine 2
Rotor angle
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Fundamentals on Power System Stability 8
Large signal rotor angle stability (Transient stability)
Ability of a power system to maintain synchronism during severe
disturbances, e.g.
– Short circuit fault
– Loss of generation
– Large step loading (or loss of load)
Large signal stability depends on system properties and the type
of disturbance (not only a system property)
– Analysis using time domain simulations
– Critical fault clearing time
Transient Stability
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Fundamentals on Power System Stability 9
Transient Stability
Left: Active power (red) and reactive power (green) Right: Generator speed
Case 1: Stable
10.008.006.004.002.000.00 [s]
1500.00
1000.00
500.00
0.00
-500.00
-1000.00
G1: Positive-Sequence, Active Power in MW
G1: Positive-Sequence, Reactive Power in Mvar
10.008.006.004.002.000.00 [s]
1.013
1.008
1.003
0.998
0.993
0.988
G1: Speed in p.u.
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10.008.006.004.002.000.00 [s]
2000.00
1500.00
1000.00
500.00
0.00
-500.00
G1: Positive-Sequence, Active Power in MW
G1: Positive-Sequence, Reactive Power in Mvar
Fundamentals on Power System Stability 10
Transient Stability
Left: Active power (red) and reactive power (green) Right: Generator speed
Case 2: Critically Stable
10.008.006.004.002.000.00 [s]
1.0325
1.0200
1.0075
0.9950
0.9825
0.9700
G1: Speed in p.u.
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Fundamentals on Power System Stability 11
Transient Stability
Left: Active power (red) and reactive power (green) Right: Generator speed
Case 3: Unstable
10.008.006.004.002.000.00 [s]
1.90
1.70
1.50
1.30
1.10
0.90
G1: Speed in p.u.
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Fundamentals on Power System Stability 12
• Significance of transient stability depends on several factors,
e.g.
– Distribution of synchronous generation: highly centralised
vs highly dispersed
– Types of machines and controllers: same type of prime
mover, AVR and governor vs completely different types
• Highly centralised power systems with generators of the same
make / model are typically more robust against transient instability
Transient Stability in Island Networks
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Fundamentals on Power System Stability 13
Small signal rotor angle stability (Oscillatory stability)
Ability of a power system to maintain synchronism under small disturbances
The following oscillatory phenomena are of particular concern:
– Local modes
– Inter-area modes
– Control modes
– Torsional modes
Analysis using modal / eigenvalue analysis
Small Signal Stability
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Fundamentals on Power System Stability 14
Small Signal Stability
• Td = damping torque
• Ts = synchronising torque
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Fundamentals on Power System Stability 15
• Most studies suggest that small-signal stability is not a
significant issue
– In the EirGrid study [1], increased wind penetration actually
improved damping in the oscillatory modes
– A study by Potamianakis and Vournas [2], which reflects small
systems in the Greek isles, also shows that small-signal stability
is not a major issue
Small-Signal Stability in Island Networks
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Fundamentals on Power System Stability 16
Frequency Stability
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Fundamentals on Power System Stability 17
Frequency stability
Ability of a power system to compensate for a power deficit
Frequency Stability
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Source: EirGrid [1]
Fundamentals on Power System Stability 18
Frequency Stability
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Fundamentals on Power System Stability 19
How a typical power system compensates for a power deficit:
1. Inertial reserve (network time constant)
– Lost power is compensated by the energy stored in rotating masses of all generators -> Frequency decreasing
2. Primary control (1s to 15s):
– Lost power is compensated by an increase in production of primary controlled units. -> Frequency drop partly compensated
3. Secondary control (15s to 3min):
– Lost power is compensated by secondary controlled units. Frequency and area exchange flows reestablished
4. Re-Dispatch of Generation
Frequency Stability
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Fundamentals on Power System Stability 20
• Frequency disturbance following an unbalance in active power
Frequency Deviation according to UCTE design criterion
-0,9
-0,8
-0,7
-0,6
-0,5
-0,4
-0,3
-0,2
-0,1
0
0,1
-10 0 10 20 30 40 50 60 70 80 90
dF in Hz
t in s
Rotor Inertia Dynamic Governor Action Steady State Deviation
Frequency Stability
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Fundamentals on Power System Stability 21
• Effects of off-nominal frequencies:
– Resonances in rotating machines causing mechanical vibration
damage
– Overheating of transformer and generator core laminations if
Volts/Hz ratio is too high
– Change in induction machine operating speed
– Flicker in lighting equipment
– Time error in AC powered clocks
Frequency Stability
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Fundamentals on Power System Stability 22
Frequency Disturbance Example – Ireland 2005
Source: Lalor [3]
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EAST-WEST INTERCONNECTOR
HVDC
TRANSMISSION SYSTEM400, 275, 220 AND 110kVJANUARY 2014
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StabilityCharacteristics of a good verbal presentation
References
Description of freq. disturbance example [2]
The electricity grid in the island is an interconnectionbetween NIE (northern Ireland Electricity) and ESB(Electricity Supply Board) systemsPower flows from the north to the south via normalconnectionsHVDC line (Moyle interconnection) imports active powerfrom ScotlandWhen NIE and ESB lose synchronism, north will be powerrich and south will be power poor; frequencies will deviate
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Description of freq. disturbance example [2]
To stop frequency deviations when the NIE-ESB line is out,signals are sent to curtail the flow of active power in theHVDC lineBy curtailing a pre-defined quantity of power, systemfrequency deviations can be limited
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Description of freq. disturbance example [2]
on 8/5/2005, the system was operating normallyApproximately 370 MW of power was flowing N-S on theNIE-ESB lineHVDC lines were importing 115 MW from Scotland
Around 10 : 30AM, a wrongly generated signal caused a−280 MW step change in the HVDC flow causing 165 MWexport to ScotlandNIE-ESB line was operational and the above action causeda drop in frequency to 49.52 HzPrimary controls for operating reserves pulled the systemfreq. back to 49.86 Hz
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Description of freq. disturbance example [2]
Following this, in 2 more minutes, another wrong sginalwas sent to the HVDC interconnection causing anotherstep change of −280 MWTotal export from Ireland to Scotland on the HVDC lineswent from 165 MW to 445 MWSystem frequency dipped further causing two generationunits (475 MW) to trip from the system
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Description of freq. disturbance example [2]
This was due to the action of ‘Rate of change of frequency’relaysIreland grid experienced a loss of over 1000 MW in under 5minutesUnder freq. load shedding relays helped stop the decreasein freq. at 48.41 HzSystem freq. recovered to 49.5 Hz in 11 minutes from thestart of the event
Suryanarayanan ECE 566 Lecture/Week 15
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Fundamentals on Power System Stability 23
• Frequency stability is a significant issue in small island grids
due to low system inertias
– Low system inertia => high sensitivity to frequency deviations
– Large frequency deviations after a disturbance are more likely
– Frequency deviations may cause activation of load-shedding,
over/under-frequency or ROCOF relays
Frequency Stability in Island Networks
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Fundamentals on Power System Stability 24
• Considerations:
– Spinning reserve to cover contingencies and limit frequency
deviations
• More spinning reserve = higher level of contingency that can
be suffered by the system without collapse
• More spinning reserve = more inertia = smaller freq deviations
• More spinning reserve = higher generator running costs
– Minimum loading of thermal generators (e.g. typically 40 – 60%
for diesel generators to avoid cylinder bore glazing)
Frequency Stability in Island Networks
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Fundamentals on Power System Stability 25
Voltage Stability
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Fundamentals on Power System Stability 26
Voltage stability refers to the ability of a power system to
maintain steady voltages at all buses in the system after being
subjected to a disturbance.
• Small disturbance voltage stability (Steady-state voltage stability)
– Ability to maintain steady voltages when subjected to small
disturbances, e.g. increasing load, change in solar PV output
• Large signal voltage stability (Dynamic voltage stability)
– Ability to maintain steady voltages after following large disturbances,
e.g. transmission line trip
Voltage Stability
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Fundamentals on Power System Stability 27
Small-Signal:
- Small disturbance
Large-Signal
- System fault
- Loss of generation
Long-Term - PV Curves (load flows)
- QV Curves
- Long-term dynamic models
including tap-changers, var-
control, excitation limiters, etc.
- PV Curves (load flows)
of the faulted state.
- Long-term dynamic models
including tap-changers, var-
control, excitation limiters, etc.
Short-Term - Typically not a problem and not
studied
- Dynamic models (short-term),
special importance on dynamic
load modeling, stall effects etc.
Voltage Stability - Analysis
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Fundamentals on Power System Stability 28
Voltage Stability – QV and PV Curves
1762.641462.641162.64862.64562.64262.64
1.40
1.20
1.00
0.80
0.60
0.40
x-Achse: SC: Blindleistung in Mvar
SC: Voltage in p.u., P=1400MW
SC: Voltage in p.u., P=1600MW
SC: Voltage in p.u., P=1800MW
SC: Voltage in p.u., P=2000MW
P=2000MW
P=1800MW
P=1600MW
P=1400MW
DIgS
ILEN
T
1350.001100.00850.00600.00350.00100.00
1.00
0.90
0.80
0.70
0.60
0.50
x-Achse: U_P-Curve: Total Load of selected loads in MW
Klemmleiste(1): Voltage in p.u., pf=1
Klemmleiste(1): Voltage in p.u., pf=0.95
Klemmleiste(1): Voltage in p.u., pf=0.9
pf=1
pf=0.95
pf=0.9
DIgS
ILEN
T
Vo
lta
ge
Active power
Vo
lta
ge
Reactive power
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Fundamentals of Power System Stability 29
Voltage Stability: Example (PV Curves)
Outage of large generator
All generators in service
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Fundamentals on Power System Stability 30
• Voltage instability is mainly caused when a power system
cannot meet its demand for reactive power.
• Problem is much the same for islands as for interconnected grids.
Factors influencing voltage stability include:
– Weaknesses in the network (subject to local voltage instability)
– High system loading
– Distances between generation and load
– Availability of reactive power support
– Dynamic effects, e.g. OLTCs, field excitation limiters, SVCs, etc
– Load characteristics, e.g. induction motors (air-conditioning)
Voltage Stability in Island Networks
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Fundamentals on Power System Stability 31
Renewable Energy Integration and Stability
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Fundamentals on Power System Stability 32
• Frequency stability:
– Renewable energy sources are often connected via a converter
interface and have no inertia (as seen from the grid)
– Replacing synchronous generators with sources using a
converter interface therefore reduces total system inertia and is
more sensitive to frequency deviations
– Thermal generators may run under minimum load if displaced
by renewable energy sources
• Potential mitigation measures:
– Minimum system inertia, i.e. minimum number of synchronous
generators online (spinning reserve)
– Under-frequency load shedding
– Energy storage with fast response [4]
– Demand side management (DSM), i.e. smart grid technologies
Renewable Energy Integration – Key Stability Issues
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Fundamentals on Power System Stability 33
Renewable Energy Integration – Key Stability Issues
Source: Lalor [3]
No wind
FSIG
DFIG
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Fundamentals on Power System Stability 34
• Transient stability:
– Effects of renewable energy integration on transient stability
must be assessed on a case-by-case basis and depends more
on distribution of synchronous generators and controller types
– Some past studies indicate that for moderate penetrations e.g.
30 – 40%, renewable energy sources do not significantly affect
transient stability [1]
• Potential mitigation measures:
– Depending on grid characteristics, it may be necessary to limit
penetration of renewable energy sources (case-by-case)
Renewable Energy Integration – Key Stability Issues
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Fundamentals on Power System Stability 35
• Voltage stability:
– Renewable energy sources with limited or no reactive power
control (e.g. fixed-speed induction wind turbines, household-
scale PV inverters) will decrease voltage stability
– Integrating renewable energy sources into weak parts of the
grid can actually improve voltage stability
• Potential mitigation measures:
– Use renewable energy sources that are capable of reactive
power control
– Connect renewable energy sources at weak parts of the grid
Renewable Energy Integration – Key Stability Issues
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Fundamentals on Power System Stability 36
1. EirGrid, “All Island TSO Facilitation of Renewables Studies”, 2010,
http://www.eirgrid.com/renewables/facilitationofrenewables/
2. Potamianakis, E. G., Vournas, C. D., “Modeling and Simulation of
Small Hybrid Power Systems”, IEEE PowerTech Conference, 2003
3. Lalor, G. R., “Frequency control on an island power system with
evolving plant mix”, PhD Dissertation, 2005
4. Kottick, D., Blau, M., Edelstein, D., “Battery energy storage for
frequency regulation in an island power system”, IEEE Transactions
on Energy Conversion, Vol 8 (3), 1993
References
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StabilityCharacteristics of a good verbal presentation
References
Disclaimer
The following slides have been generated directly usingmaterial from [3] for the purpose of educational objectives. Theauthor of [3] has provided explicit permission via email to thisinstructor for doing so.All copyrights are reserved by and remain with the originalowner of these slides.
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Characteristics of a good verbal presentation [3]
Underlying principals
Speak clearly and loudly for everyone to hear andcomprehendStay in the time limitPay attention to making your slides and do itsemi-professionallyPublic speaking is a skill honed by practiceSpeaking, more than writing, makes an instant impression(double-edged dagger)
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Characteristics of a good verbal presentation [3]
General deportmentDress appropriately for the occasionIf you are thinking about using slides or not, use themSlides are indispensable for technical talks; do not usehandwritten notes
However, feel free to annotate the slides if you have accessto a SmartBoard and if you feel comfortable using it
Use extreme caution in using humor in talks.Practice and time your presentationsMake your slides and graphics visible for the in-class andthe online audienceView your recorded presentation. It will help improve yourperformance.
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StabilityCharacteristics of a good verbal presentation
References
Characteristics of a good verbal presentation [3]
Slides for presentationProfessionally prepare slides using software such asPowerPoint or BeamerAvoid gaudy background for slides. Use colors sparingly toachieve a professional appearanceAvoid animations, clip art, and other comical or tackyaccessoriesAvoid using elaborate slide transitions and audio clipsduring the same
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StabilityCharacteristics of a good verbal presentation
References
Characteristics of a good verbal presentation [3]
Slides for presentationAvoid commonly seen templates of slide backgroundsDo not rush through your slides. You will lose youraudience almost immediately if you do soHave a few hidden slides at the end of the presentation
Hip-pocket slides are usually used to answer anyanticipated questions which may require more details thanthose presented.Use them if needed; also, this shows preparedness onbehalf of the presenter
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StabilityCharacteristics of a good verbal presentation
References
Characteristics of a good verbal presentation [3]
FontsRecording requires large, bold fonts – the larger the fontsize, the betterUse bold, italics, and color highlighting some text foremphasisNever use any font size less than 36 (or at the very least28)
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StabilityCharacteristics of a good verbal presentation
References
Characteristics of a good verbal presentation [3]
FontsDo not load your slides with too much informationDense slides are to be avoided at all costsComplicated slides will get you in troubleIf you must show a table, then do NOT show a huge tablethat cannot be readIf you have to show a huge table (which is to be avoided),at least consider highlighting the most relevant dataDo NOT use webdings, wingdings, or uncommon bulletmarks – they tend to show up as junk on most projectors
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Characteristics of a good verbal presentation [3]
PointersUse of pointers can be an effective highlighting toolBut, be cautious of minor hand movements which maycause significant jumps in the use of the pointerLaser pointers are preferred and can be impressive tools ifthey are bright enough
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Characteristics of a good verbal presentation [3]
Timing
Keep to the time limit; make sure you are aware of the timelimit and of the passage of timeRecruit a person from the audience to warn you as the endof your time slot approaches
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Characteristics of a good verbal presentation [3]
Language and proofreading
Have your slides checked by a native speaker of thelanguage usedProofread slides. Try to get a second opinion of thepresentationUSe the default spell-checkerDo not present information, especially important ones,near the edge of the slide.
Suryanarayanan ECE 566 Lecture/Week 15
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StabilityCharacteristics of a good verbal presentation
References
Power system stability on island networks. DigSILENTGMbH, prepared for IRENA Workshop. URL:http://goo.gl/RQnQO1 (visited on 04/08/2013).
Gillian R. Lalor. “Frequency control on an island powersystem with evolving plant mix”. PhD thesis. The NationalUniversity of Ireland, 2005. URL:http://goo.gl/gJzWQq.
Gerald T. Heydt. Technical Writing for Power Engineering.Tech. rep. Arizona State University, 2006.
Suryanarayanan ECE 566 Lecture/Week 15