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 www.esb.ie 1

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

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

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.

European Transmission System ROCOF Project Board Meeting

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

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

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

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

Frequency Scale 50Hz 49Hz 51Hz Generation Consumers

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

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

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

RoCoF Trace

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…

RoCoFAverage with Δt = 100ms and Δt = 500ms

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

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

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

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

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

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

BR BS No gravity!!!

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

Swing Equation for light systems

Model verification Real event Model ROCOF Project Board Meeting

Frequency trace depends on system inertia

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

Swings depend on electromagnetic torque

SN Curve

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.

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

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

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

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

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

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

Frequency Traces

Frequency traces

Frequency traces

Study Scope

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

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

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??

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

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)

Typical Turbine Generator control circuit

Questions? Fragen? ErwthseiV;

Thank You and Vielen Dank Footer

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,