transient stability of conventional generating stations
TRANSCRIPT
Transient stability of conventional generating stations during times of high wind penetration
on the Island of Ireland Marios Zarifakis, Electricity Supply Board, Dublin, Ireland
Stockholm 24.11.2016
www.esb.ie
TCD
© 2016 ESB, TCD
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Contents 1. Introduction of the Irish Grid and ESB
2. Government targets and policies
3. Rate of Change of Frequency (RoCoF) and the Grid Code Definition
4. Mathematical models
5. Impact to generating plant and grid
6. RoCoF impact studies with manufacturers
7. Frequency oscillations
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Contents 1. Introduction of the Irish Grid and ESB
2. Government targets and policies
3. Rate of Change of Frequency (RoCoF) and the Grid Code Definition
4. Mathematical models
5. Impact to generating plant and grid
6. RoCoF impact studies with manufacturers
7. Frequency oscillations
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ESB – Electricity Supply Board • Vertically Integrated Utility
• Involved in most types of generation
• The first ESB generation plant (in 1927) was a hydro station at Ardnacrusha
• The ESB group is one of the largest wind generators in Ireland, and ESB has been involved in development, construction and management of Irelands wind resources since the 1980s.
• Large international business.
• ESB owns a number of international power stations and has O&M contracts for several other generation stations.
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Contents 1. Introduction of the Irish Grid and ESB
2. Government targets and policies
3. Rate of Change of Frequency (RoCoF) and the Grid Code Definition
4. Mathematical models
5. Impact to generating plant and grid
6. RoCoF impact studies with manufacturers
7. Frequency oscillations
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Increase of sustainable energy sources
EU 2020 Policy
20% of the EU’s energy demand to be from renewable sources by 2020
Irish Government Targets
40% of Ireland’s total electricity consumption to be met by renewables
TSO’s DS3 Programme Safe and secure power system with high levels of renewable generation
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ESB Generation Focus
Perspectives and Dependencies
EirGrid & SONI Focus
Mechanical Issues
Turbine Integrity
Generator Integrity
Security of supply
Voltage Stability Loading of Lines
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Contents 1. Introduction of the Irish Grid and ESB
2. Government targets and policies
3. Rate of Change of Frequency (RoCoF) and the Grid Code Definition
4. Mathematical models
5. Impact to generating plant and grid
6. RoCoF impact studies with manufacturers
7. Frequency oscillations
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Generation-Load Balance
Generation
Load
Frequency falls if
is smaller than
48,5 49,0 49,5 50,0 50,5 51,0
-2 -1 0 1 2 3 4 5 6 7 8
Freq
uenc
y (H
z)
Time (s)
Sample Low Frequency RoCoF
Frequency (Hz)
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Proposed Definition of RoCoF The new definition by both TSOs, EirGrid and SONI, for the Grid Code is:
“remain synchronised to the Transmission System for a Rate of Change of Frequency up to and including 1 Hz per second as measured over a rolling 500 millisecond period”
Mathematical Definition of RoCoF
𝑹𝒐𝑪𝒐𝑭𝑨𝑽𝑬𝑹𝑨𝑮𝑬= ∆𝒇/∆𝒕
𝑹𝒐𝑪𝒐𝑭𝑰𝒏𝒔𝒕𝒂𝒏𝒕𝒂𝒏𝒆𝒐𝒖𝒔= 𝒅𝒇/𝒅𝒕
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Definition of RoCoF (500ms window)
Ardnacrusha (AA), Aghada (AD), Cathaleen’s Fall (CF), Louth (LOU), Carrickmines (CKM), Great Island (GI), Ballylumford (BALLY) and Poolbeg (PB) (*1)
Maximum RoCoF measurements for different time windows
RoCoF values at various substations (trip of EWIC) (Eirgrid Study 2012)
Problem: Generator sees actual values…
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Contents 1. Introduction of the Irish Grid and ESB
2. Government targets and policies
3. Rate of Change of Frequency (RoCoF) and the Grid Code Definition
4. Mathematical models
5. Impact to generating plant and grid
6. RoCoF impact studies with manufacturers
7. Frequency oscillations
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Magnetic Field in a Synchronous Generator
Stable conditions: Tel=Tmech
or 0=Tmech - Tel Dynamic conditions: J𝛼= Tmech-Tel
J𝜔 = Tmech-Tel - KD𝜔 J𝜔 = Tmech - kBSBRsin𝛿 - KD𝜔
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Conventional Swing Equation
𝜏 ↓𝑎 = 𝜏 ↓𝑚 − 𝜏 ↓𝑒𝑙 =0
𝐽↓𝑔𝑒𝑛 𝜔 ↓𝑚 (𝑡)= 𝜏↓𝑚 − 𝜏↓𝑒𝑙
with 𝜔↓𝑚 (𝑡)= 𝛿 (𝑡)
𝐽↓𝑔𝑒𝑛 𝛿 (𝑡)= 𝜏↓𝑚 –𝜏↓𝑒𝑙
Introducing 𝐻= 1/2 𝐽𝜔↑2 /𝑆↓𝑁
2𝐻/𝜔↓0 𝛿 (𝑡) + 𝐾↓𝐷 /𝜔↓0 𝛿 (𝑡) = 𝜏 ↓𝑚 − 𝜏 ↓𝑒𝑙
And with 𝜏 ↓𝑒𝑙 = 𝑘/𝜔↓0 𝐵↓𝑅 𝐵↓𝑆 sin 𝛿(𝑡)
2𝐻/𝜔↓0 𝛿 (𝑡) + 𝐾↓𝐷 /𝜔↓0 𝛿 (𝑡) + 𝑘/𝜔↓0 𝐵↓𝑅 𝐵↓𝑆 sin 𝛿(𝑡) = 𝜏 ↓𝑚
2𝐻/𝜔↓0 𝛿 (𝑡) + 𝐾↓𝐷 /𝜔↓0 𝛿 (𝑡) +𝑘𝐵↓𝑅 𝐵↓𝑆 𝛿(𝑡)= 𝜏 ↓𝑚
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Negative ROCOF, Steam Turbine 0.25 Hz/s & 4 s 0.5 Hz/s & 2s 1 Hz/s & 1s 2 Hz/s & 0.5s
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RoCoF mathematical definition (simplistic view)
𝒅𝒇/𝒅𝒕 = 𝒇↓𝒏 𝑷/𝟐 𝑯↓𝒔𝒚𝒔𝒕𝒆𝒎 𝑺↓𝒃 With:
𝑓↓𝑛 = System Frequency
𝐻↓𝑠𝑦𝑠𝑡𝑒𝑚 = System Inertia
𝑃 = Lost load or generation
𝑆↓𝑏 = MVA rating of the system
Generation Consumers
50Hz
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G1 G
2 Grid Turbine Torque Sum of all loads (Torque)
Electromagnetic Torque
In the air gap of the generator
Turbine Torque
To create the equation of motion using Lagrange
Damping depends on speed deviation! Asynchronous effect!
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Contents 1. Introduction of the Irish Grid and ESB
2. Government targets and policies
3. Rate of Change of Frequency (RoCoF) and the Grid Code Definition
4. Mathematical models
5. Impact to generating plant and grid
6. RoCoF impact studies with manufacturers
7. Frequency oscillations
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Shaft line, exact modelling required for all stations
Analysis for impact at turbine and generator components
Torsional oscillations can create stresses to:
• Couplings
• Rotors and shafts
• Turbine blades and roots
• Generator rotor end bells
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Risks related to mechanical integrity
Torsional oscillations can create stresses to: • Couplings
• Rotors and shafts
• Turbine blades
• Generator rotor end bells
• Generator stator end windings
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Mech/Elec Integrity Consequences RoCoF Event
Reduced Component Life Time
Consequential Machine Damage
Decreased overhaul intervals and
Increased Inspection Requirements
Forced Outage
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Technical Risks
Technical Risks • Controller & Operational Issues
• Turbine/Governor Controller • AVR/PSS Controllers
• Protection Systems • Turbine Protection • Generator & Transformer
Protection • Mechanical Integrity
• Turbine Components • Generator Components • Lifetime Assessments
• Electrical Integrity • Impact of Auxiliary Systems
• Motors, Fans, Pumps
Action • Studies to be completed to assess
impact (OEM’s, TUV)
• Modelling Scenarios • Rotor Dynamic Analysis • Operational Analysis
• Internal Modelling work • Torsional Probes • Matlab/Simulink Model Build
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Operational Consequences ROCOF Event
Further loss of Electrical Power Generations
Cascade Tripping Event
Load Shedding in the system
System Brown/Black Out
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Calculations with parameters ± 1Hz/s & 1.2s Operational Point RoCoF,
duration Remarks
1.) P=305 MW; Q=180Mvar -1Hz/s; 1.2s The generated active power increases to 540MW. Generator experiences 150% of rated stator current. The stator current limiter in the AVR is triggered.
2.) P=305MW; Q=0Mvar The generated active power increases to 503MW. Generator experiences 140% rated stator current. The stator current limiter in the AVR is triggered.
3.) P=305MW; Q=-120Mvar The generated active power increases to 530MW. The stator current limiter in the AVR is triggered. The reactive power triggers the under-excitation limiter and under-excitation protection. I> protection picks up.
4.) P=100MW; Q=-160Mvar The reactive power triggers the under-excitation limiter and the under-excitation Protection.
1.) P=305 MW; Q=180Mvar +1Hz/s; 1.2s ΔP/Δt is substantial and can lead to trigger the “Remote Breaker Opening” logic which would close the control valves.
2.) P=305MW; Q=0Mvar ΔP/Δt is substantial and can lead to trigger the “Remote Breaker Opening” logic which would close the control valves.
3.) P=305MW; Q=-120Mvar ΔP/Δt is substantial and can lead to trigger the “Remote Breaker Opening” logic which would close the control valves.
4.) P=100MW; Q=-160Mvar ΔP/Δt is substantial and can lead to trigger the “Remote Breaker Opening” logic which would close the control valves. Reverse Power Pick up (-125MW). Torsional Oscillations become more evident on low loads.
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Contents 1. Introduction of the Irish Grid and ESB
2. Government targets and policies
3. Rate of Change of Frequency (RoCoF) and the Grid Code Definition
4. Mathematical models
5. Impact to generating plant and grid
6. RoCoF impact studies with manufacturers
7. Frequency oscillations
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Study Scope Type MW
(Exp) Unit #
Studies Required
Study Priority
CCGT 2094 4 4* 1 Peat 228 2 1 1 Coal 855 3 1 1 Gas 258 1 1 3 OCGT 517 6 2 3 Pump Storage 292 4 1 1 Hydro 206 17 2 3
12 studies to be completed Timeframe for Priority 1 Units 18 months
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Timeline going forward ● Studies required to demonstrate compliance
– High priority – 18 months - high run hours, frequently constrained on, frequently run during high wind
– Mid priority – 24 months - units not in other categories
– Low priority – 36 months - low run hours, infrequently constrained on, infrequently run during high wind
– Exempt units – units soon to retire, very low runs hours or units which in EirGrid’s operational experience have ridden through high RoCoF events in the past
ESB will need to be compliant (or derogated/exempted) by these dates to ensure it incurs zero penalties.
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Project Timeline
2010 – 2012 Consultation Period • Risk Paper • OEM Engagement • Understanding & Education
• Financial Appraisal • Regulatory
2013 – 2014 CER ROCOF Paper • Consultation Paper • Decision Paper • KEMA Challenge Study • No Cost Recovery Position
• Procurement Strategy
2014 – 2016 Studies • Tender Process • Priorities 1 studies • Digsilent Study • Matlab/Simulink Model • Torsional Probe Analysis • Quality & Validation
2016 – 2018 Post Studies • Level of Compliance • Level of Investment • Development of individual Business Cases
• Implementation
That’s it??
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Contents 1. Introduction of the Irish Grid and ESB
2. Government targets and policies
3. Rate of Change of Frequency (RoCoF) and the Grid Code Definition
4. Mathematical models
5. Impact to generating plant and grid
6. RoCoF impact studies with manufacturers
7. Frequency oscillations
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Real Event, DBP, 26.12.2014
• C30 in Coolkeeragh Trip at 22:38 • DB1 MW; Hz • 7 Min Oscillation • Pk-Pk: ~0.3 – 0.4 Hz • Period of Osc: 15 s (0.066 Hz)
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Response to a sinusoidal disturbance
Currently installed turbine controllers need major attention….
Output of controllers swing almost in phase with disturbance which amplifies the disturbance
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Acknowledgements Models used:
Matlab from Mathworks with Simulink and SimPowerSystem
Literature:
“Power System Stability and Control”, Prabha Kundur
“Handbook of Electrical Power System Dynamics”, M. Eremia, M. Shahidehpour
“Elektrische Schaltvorgaenge”, Reinhold Ruedenberg
Various publications by Eirgrid and CER (www.eirgrid.com and www.cer.ie)
DNV GL Study on ESB Fleet
Some animations were used from www.wikipedia.de, Dreiphasenwechselstrom
Contributions by: Stephen Carrig, ESB GWM Manager C&I
Prof. Dr. William T. Coffey, Trinity College Dublin,