1. Marios Zarifakis, Electricity Supply Board, Dublin, Ireland
TCD
Transient stability of conventional generating stations during times of high wind penetration on the Island of Ireland
Marios Zarifakis, Electricity Supply Board, Dublin, Ireland
© 2016 ESB, TCD 1

2. Contents Introduction of the Irish Grid and ESB
Government targets and policies
Rate of Change of Frequency (RoCoF) and the Grid Code Definition
Mathematical models
Impact to generating plant and grid
RoCoF impact studies with manufacturers
Frequency oscillations

3. Contents Introduction of the Irish Grid and ESB
Government targets and policies
Rate of Change of Frequency (RoCoF) and the Grid Code Definition
Mathematical models
Impact to generating plant and grid
RoCoF impact studies with manufacturers
Frequency oscillations

4. 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.

5. European Transmission System
ROCOF Project Board Meeting

6. Contents Introduction of the Irish Grid and ESB
Government targets and policies
Rate of Change of Frequency (RoCoF) and the Grid Code Definition
Mathematical models
Impact to generating plant and grid
RoCoF impact studies with manufacturers
Frequency oscillations

7. 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

8. Perspectives and Dependencies
EirGrid & SONI
Focus
ESB Generation
Focus
Security of supply
Turbine Integrity
Increase of Wind
Voltage Stability
Mechanical Issues
Loading of Lines
Generator Integrity

9. Contents Introduction of the Irish Grid and ESB
Government targets and policies
Rate of Change of Frequency (RoCoF) and the Grid Code Definition
Mathematical models
Impact to generating plant and grid
RoCoF impact studies with manufacturers
Frequency oscillations

10. Frequency Scale
50Hz
49Hz
51Hz
Generation
Consumers

11. Frequency and the Rate of Change of Frequency
RoCoF= 𝑑𝑓 𝑑𝑡
Frequency
RoCoF

12. 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
50Hz
Consumers

13. 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

14. RoCoF Trace

15. Definition of RoCoF (500ms window)
RoCoF values at various substations (trip of EWIC) (Eirgrid Study 2012)
Maximum RoCoF measurements for different time windows
Ardnacrusha (AA), Aghada (AD), Cathaleen’s Fall (CF), Louth (LOU), Carrickmines (CKM), Great Island (GI), Ballylumford (BALLY) and Poolbeg (PB) (*1)
Problem: Generator sees actual values…

16. RoCoFAverage with Δt = 100ms and Δt = 500ms

17. Contents Introduction of the Irish Grid and ESB
Government targets and policies
Rate of Change of Frequency (RoCoF) and the Grid Code Definition
Mathematical models
Impact to generating plant and grid
RoCoF impact studies with manufacturers
Frequency oscillations

18. 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 𝐽 𝜔 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 +𝑘 𝐵 𝑅 𝐵 𝑆 𝛿 𝑡 = 𝜏 𝑚

19. Negative ROCOF, Steam Turbine
0.25 Hz/s & 4 s
0.5 Hz/s & 2s
1 Hz/s & 1s
2 Hz/s & 0.5s

20. Positive ROCOF, Steam Turbine
0.25 Hz/s & 4 s
0.5 Hz/s & 2s
1 Hz/s & 1s
2 Hz/s & 0.5s

21. Real Frequency Event, 27.04.2014, DBP
Power Output
Frequency
Pnom=390MW
Frequency and Power traces

22. Magnetic Field in a Synchronous Generator
Stable conditions:
Tel=Tmech or
0=Tmech - Tel
Dynamic conditions:
J𝛼= Tmech-Tel
J 𝜔 = Tmech-Tel - KD𝜔
J 𝜔 = Tmech - kBSBRsin𝛿 - KD𝜔

23. BR BS
No gravity!!!

24. Damping depends on speed deviation! Asynchronous effect!
Turbine Torque
Grid
Turbine Torque G1
Sum of all loads (Torque) G2
Electromagnetic Torque
In the air gap of the generator
To create the equation of motion using Lagrange

25. Swing Equation for light systems

27. Model verification
Real event
Model
ROCOF Project Board Meeting

28. Frequency trace depends on system inertia

29. Contents Introduction of the Irish Grid and ESB
Government targets and policies
Rate of Change of Frequency (RoCoF) and the Grid Code Definition
Mathematical models
Impact to generating plant and grid
RoCoF impact studies with manufacturers
Frequency oscillations

30. Swings depend on electromagnetic torque

31. SN Curve

32. 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.
+1Hz/s; 1.2s
ΔP/Δt is substantial and can lead to trigger the “Remote Breaker Opening” logic which would close the control valves.
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.

33. 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

34. 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

35. Technical Risks Action 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
Modelling Scenarios
Rotor Dynamic Analysis
Operational Analysis
Internal Modelling work
Torsional Probes
Matlab/Simulink Model Build
Digsilent Study

36. Mechanical Integrity Consequences
RoCoF Event Reduced Component Life Time Consequential Machine Damage Decreased overhaul intervals and Increased Inspection Requirements Forced Outage

37. Operational Consequences
ROCOF Event Further loss of Electrical Power Generations Cascade Tripping Event Load Shedding in the system System Brown/Black Out

38. Contents Introduction of the Irish Grid and ESB
Government targets and policies
Rate of Change of Frequency (RoCoF) and the Grid Code Definition
Mathematical models
Impact to generating plant and grid
RoCoF impact studies with manufacturers
Frequency oscillations

39. Frequency Traces

40. Frequency traces

41. Frequency traces

42. Study Scope

43. RoCoF 2Hz/s (Northern Ireland)
Max and Min Load Leading
Comparison.
In both cases the allowed
Stress is possibly exceeded

44. Impact on lifetime is unknown
Life time and maintenance
analysis to be undertaken

45. Project Timeline That’s it?? 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??

46. Contents Introduction of the Irish Grid and ESB
Government targets and policies
Rate of Change of Frequency (RoCoF) and the Grid Code Definition
Mathematical models
Impact to generating plant and grid
RoCoF impact studies with manufacturers
Frequency oscillations

47. 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)

48. Typical Turbine Generator control circuit

49. Questions? Fragen? ErwthseiV;

50. Thank You and Vielen Dank
Footer

51. 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 ( and DNV GL Study on ESB Fleet Some animations were used from Dreiphasenwechselstrom Contributions by: Stephen Carrig, ESB GWM Manager C&I Prof. Dr. William T. Coffey, Trinity College Dublin,