Integrating Intermittent Renewable Energy Resources Mahmut Erkut Cebeci 27.03.2012, Amman

Outline Part 1 – Quality Introduction: Background Effects of Wind Turbines on Power Quality International Standards and Local Directives in Turkey Technical Details Parameters Effecting Wind Power and State of the Art Wind Power Technology Parameters Characterising the Power Quality of Wind Turbines Case Study Part 2 – Integration and Operational Challanges ENTSO-E CESA interconnection studies ENTSO-E CESA trial parallel operation and frequency control performance indices The possible effects of rapid growing intermittent generation on Turkish Electricity Transmission System a) The current situation b) Geographical distribution of renewable generation c) The expected challenges Conclusions Part 3 – Grid Code Improvements 2

Outline Continued Part 3 – Grid Code Improvements 3

Power Quality Concerns Part 1 Power Quality Concerns

Part 1 Section – 1 BackGround

Some Facts about Turkish Grid >52 GW installed capacity More than 36 GW of peak demand (occured in summer, last year’s peak demand was >32 GW in summer) Annual increase in demand and consumption is 7–8 % Hydro, coal and combined cycle power plants Increasing interest in renewables Deregulated generation sector Privatized(ing) distribution sector TEIAS is natural monopoly in transmission business (regulated by EMRA) Interconnected operation with ENTSO-E CESA system

Background A wind turbine is a prime mover that converts the kinetic energy of wind to electrical energy via a generator. Not an energy capacity but an energy source. Output power is very dependent on enviromental conditions. Exponential growth in interest in wind power brings exponential penetration level to grid.

Background Not considered in traditional power system approach. A wind turbine may operate synchronised to the grid or independently. (Island Mode) May have adverse effects on the grid.

Wind Power Interest in Turkey Before November the 1st, TEİAŞ has stated 4916MW of available wind penetration, 3274MW of which is licenced. After November the 1st, TEİAŞ has stated 7453MW of extra available wind penetration to EPDK. Total available capacity is increased to 12369MW. Close to 13000MW licence applications to EPDK upon this event. TEİAŞ has prepared a competition directive.

Turkish Wind Speed Map (REPA-50m)

Turkish Wind Power Intensity Map

Effects of Increasing Wind Power Penetration Level to Power Quality Problems: - Voltage Sags - Flicker Emission - Harmonics Injection Solutions - Developing Wind Power Technology and Power Electronics Technology - Enhanced Grid Codes

International Standards and Local Directives IEC 61400-21 IEEE 1547 (Draft) Turkish Grid Code – Appendix 18

Section – 2 TECHNICAL DETAILS Part 1 Section – 2 TECHNICAL DETAILS

Parameters Effecting Wind Power

Constant Speed vs. Variable Speed Constant Speed have 8 poles for low speed and 4-6 poles for high speed

Power Control Concepts Stall Control: The design of rotor aerodynamics causes the rotor to stall (lose power) when the wind speed exceeds a certain level Pitch Control: the blades can be turned out or into the wind as the power output becomes too high or too low Active Stall Control: At low wind speeds the blades are pitched similar to a pitch-controlled wind turbine, in order to achieve maximum efficiency. At high wind speeds the blades go into stall by being pitched slightly into the direction opposite to that of a pitch-controlled turbine

State of The Art Technology

State of the Art Technology

Terminology

Power Quality Characteristics of Wind Turbines IEC 61400 is the de-facto standard for wind power technology IEC 61400-21 is about the power quality characteristics of wind turbines

Power Quality Parameters Rated Data (Pn, Qn, Sn, Un, In) Max Permitted Power (10 Min Avg.) Max Measured Power (60 sec & 0.2 sec Avg.) Q as a function of P (As 10 min Avg. Values) Flicker Coefficient c(Network Impedance Phase Angle, Annual Average Wind Speed) Max # of specified switching operations of the wind turbine for 10 minutes and 120 minutes Flicker Step Factor kf(Network Impedance Phase Angle) Voltage Change Factor ku(Network Impedance Phase Angle) Max harmonic currents Ih, during continuous operation as 10 minute period averages up to 50th 60 and 0.2 sec max powers are important for relay settings and island operation Q should be given as a function of P for turbines with induction generator The turbines utilizing frequency converter can supply and consume reactive power but this is limited by the size of the converter Flicker coefficient changes depending on the grid strength and impedance angle, hence this value shpuld be known for specific values of the impedance angle and annual average wind speed The voltage change factor and flicker step factor are normalised measures of the voltage change flicker emission due to a single switching operation of a wind turbine Harmonic currents should be investigated in case of power electronic converters IEC 61400-21 does not require measurements of harmonic emissions from wind turbines with induction machines

Case Study

Case Study

Case Study Procedure Slow Voltage Variations – Load Flow Study for minimum and maximum loading conditions of both the wind turbines and the grid to check whether the voltages remain within the limits and no overloading in any of the instruments. Flicker Calculations for Long Term and Short Term (Rapid Changes) Pst is a measured value over 10minutes and Plt is a calculated value as given, the limits for both parameters are to be defined in the grid code

Case Study Procedure Switching Operations (Flicker Emission due to Switching) Continuous Operation (Flicker Emission due to Continuous Operation) Pst and Plt are related with number of switching operations as well as flicker step factor For continious operation c, flicker factor becomes more important

Case Study Procedure Voltage Dips Harmonic Currents The results obtained with respect to mentioned detailed procedure should be investigated with respect to the grid codes and other related regulations of the specific country or site. The start up of a wind turbine can cause a reduction of voltage followed by a recovery within few seconds, utilizing the voltage change factor the sudden votage reduction can be calculated. The grid code also can define a limit for this variable

Case Study Conclusion The simplified rules (such as 5% rule in Turkey) would conclude that the grid had to be reinforced or the wind farm had to be limited with a less capacity. According to the results obtained with respect to the previous procedure, it is concluded that the wind farm can be connected to the existing grid without any reinforcements to the grid (except for the MV transformers and related cabling etc. to connect the wind farm to the grid)

Part 2 Security Concerns

Outline Part 1 – Quality Introduction: Background Effects of Wind Turbines on Power Quality International Standards and Local Directives in Turkey Technical Details Parameters Effecting Wind Power and State of the Art Wind Power Technology Parameters Characterising the Power Quality of Wind Turbines Case Study Part 2 – Integration and Operational Challanges ENTSO-E CESA interconnection studies ENTSO-E CESA trial parallel operation and frequency control performance indices The possible effects of rapid growing intermittent generation on Turkish Electricity Transmission System a) The current situation b) Geographical distribution of renewable generation c) The expected challenges Conclusions 30

Interconnection Studies Part 2 Section - 1 ENTSO-E CESA Interconnection Studies

Organization Chart of the Project Rehabilitation of the Frequency Control Performance of TPS for Synchronous Operation with UCTE Survey of Power Plants Site Tests & Studies Design of Governor Control and Parameter Optimization Secondary Control Design and Optimization of AVR/PSS Special Protection Scheme Restoration Plan Training

Preliminary Studies Site Survey Identification of the Problems Power Plant Dynamical Data Generator Parameters AVR, PSS, Speed Governor Models and Parameters Reliability of the data is very important!!! Identification of the Problems Very Low Frequency Periodical Frequency Oscillations (b/w 20-30 sec, depending on the state of the system) Governor Rehabilitation and Retuning Studies (mostly concentrated on HPPs) Poor Quality of Frequency Control Coordination with PPs, Balancing & Settlement Market Expected Low Frequency Inter Area Oscillations (caused by static excitation systems and longitidunal structure of the system) PSS Rehabilitation and Retuning Studies Innovative Measures History of frequency control in Turkey 33

Periodical Frequency Oscillations Major HPPs in service, before synchronization After synchronization

Basic Problem (Challenging !!!) Periodical frequency oscillations have been resolved by rehabilitation & governor retuning of Ataturk & Karakaya HPPs. According to the simulation studies, the expected inter area mode after interconnection of Turkey is ~0.15Hz. ~0.15Hz oscillations are inside the control bandwidth of: PSSs Governors Conclusion: The speed governing structures of power plants (Governors and Turbines) should not contribute to inter area power swings of ~0.15Hz.

Part 2 Section - 2 ENTSO-E CESA Trial Parallel Operation and Frequency Control Performance Indices

ENTSO-E CESA Interconnection 09.2010 Trial parallel operation started 02.2011 Non-commercial energy exchanges 06.2011 Commercial energy exchanges (https://tcat.teias.gov.tr/) 09.2012 Expected date of the end of trial parallel operation

Inter Area Oscillations – After Interconnection Mode shape after the interconnection of Turkish Power System to ENTSO-E CESA system.

Simulation Studies - Time Domain Analysis DIgSILENT Power Factory 39

Low frequency modes (~0.15 Hz) are present in the system!!! Steady State Stability of the Interconnected System Low frequency modes (~0.15 Hz) are present in the system!!!

Steady State Stability - Solution Methodology Road map for enhancing the steady state stability of the interconnected system

Interconnected System Frequency δf ~ 25 mHz faverage ~ 50.00 Hz Total 30 sec reserve (i.e., primary reserve) of the CESA system including Turkey is ~3000 MW Turkey as a control area provides ~300 MW of this reserve

Performance Indices The hourly integral of ACE should not exceed ±60 MWhrs (the target value is ±20 MWhrs) To limit unintended energy exchanges Number of cases with ACE > ±175 MW (measured per 2 seconds, evaluated per 4 seconds) over an hour should not exceed 10% of the cases in normal operation To prevent overloads in the electricity transmission systems of the neighboring Balkan countries The amount of sum of tie line flows due to inter area oscillations should not exceed 30 MWs in normal operation To prevent overloads due to inter area power oscillations in the CESA countries

Frequency Control Problems The basic challenge is related to the quality of secondary frequency control, due to the transition between secondary reserve/tertiary reserve, as a result of: Intermittent loads (arc furnaces, etc.) Hourly load variations up to 2500 MW/hr (annual average peak demand is ~30000 MW) Balancing and settlement market problems (mostly related to market conditions) IT infrastructure of TEIAS Intermitttent and/or uncontrolled generation Mostly due to small (<50 MW) renewable power plants, a potentially serious problem) Day ahead balancing – Day ahead market transition Physical unavailability of qualified secondary reserve Large hydros are the main providers of secondary reserve – Peakers, availability of water, etc.!! Efficiency constraints of NGCCPPs Slow nature of TPPs (boiler dynamics)

Frequency Control Problems - Consequences High standard deviation of ACE (causing overload in the weak Balkan electricity transmission systems) due to: Intermittent loads & uncontrolled generation Hourly load variations up to 2500 MW/hr (annual peak load is ~32000 MW) Balancing and settlement market problems (mostly related to market conditions) IT infrastructure of TEIAS Solution Effective management of tertiary reserve (long term, not possible with the current market regulations) Increased amount of secondary reserve under the influence of the AGC system (short term) for certain periods of the day.

Small Signal Stability - Consequences Highest East-West mode observed on 23rd April 2011 (Minimum load conditions due to Easter and Turkish National Holiday) The system is unstable in the steady state (i.e., the equilibrium point) By operation of the innovative measures (FACTS devices), the repeating undamped oscillations are damped after a threshold

Present State Frequency Stability (1&2) Rotor Angle Stability (3) Operational Issues On progress

Part 2 Section - 3 The Possible Effects of Rapid Growing Intermittent Generation on Turkish Electricity Transmission System

Current Situation in Turkey Percentage of renewables in total installed power is almost 10%.

Current Situation in Turkey As of March 2011, according to TEIAS statistics: Small Hydro ~3400 MW in operation >4500 MW is licenced and/or under construction Some projects are uncertain Renewable Power Plants (except small hydro) ~1700 MW in operation >770 MW is licenced and/or in construction Dominated by wind projects, increasing interest to solar projects Renewables are not only used for electricity generation!!!

Current Situation in Turkey Incentive mechanism for renewable generation Technology First 10 years of operation ($cent/kWh) Hydro 7.3 Wind 7.3 Geothermal 10.5 Solar 13.3 Biomass (incl. LFG) 13.3 90 % discount in system usage tariff & 99% discount in license fees Extra incentives in the case of usage of domestic equipment Technical previleges (ancillary services & market regulations) Priority in system interconnection Land usage incentives For further details see Turkish Law #6094

Geographical Distribution of Renewable Generation Geographical distribution of wind potential

Geographical Distribution of Renewable Generation Geographical distribution of solar potential

The Expected Challenges – Short Term Increased standard deviation of ACE due to Intermittent generation in short term (turbulent peaks/dips) Balancing and settlement market problems due to bad prediction of renewable generation capacity for the next day IT infrastructure of TEIAS Special monitoring/prediction/control system requirement especially for renewables Expansion of the existing system

The Recent Developments RITM Project (http://www.uzay.tubitak.gov.tr/ritm/tr/root/) EIE, TUBITAK UZAY, DMI Wind Electricity Generation Forecast Currently applied to 480 MW of 1500 MW installed capacity

The Expected Challenges – Long Term Ancillary Services Provision Demand Coverage Generation – Demand balance in off-peak hours, downward reserve management is an issue Wind generation curtailment seems to be the only solution in some cases Market conditions (purchase guarantee, etc.) Solution Effective management of tertiary reserve (current market conditions do not encourage generation curtailment) Optimal amount of secondary reserve under the influence of the AGC system (both upward and downward directions) for the entire day. Capacity reserve agreements!!!

The Expected Challenges – Very Long Term Two scenarios are possible: Intermediate term pain for long term gain (long term electricity price stability) Balanced distribution of electrical energy generation sources Unexpectedly low energy prices may end up with generation investment unstability (boom boost, long term electricity price unstability) causing either Surplus of generation Lack of generation (an example of such phenomenon was experienced in 2011 spring) Not technical but economical issues

Conclusions The frequency stability of TETS has been drastically enhanced with the ENTSO-E CESA Interconnection Intermittent generation characteristics due to the stochastic nature of renewable resources in short term, together with balancing and settlement market conditions will definitely have adverse effects on this issue. Possible solution: Effective management of tertiary reserve (current market conditions do not encourage generation curtailment) Optimal amount of secondary reserve under the influence of the AGC system (short term) for the entire day. Monitoring and control infrastructure investments (both hardware and software)

Grid Code Improvements Part 3 Section - 1 Grid Code Improvements

Voltage Ride-Through Capability

Voltage Ride-Through Capability

Active Power Control

Reactive Power Support

Reactive Power Support

Reactive Power Control