Mahmut Erkut Cebeci27.03.2012,

Amman

Integrating Intermittent Renewable Integrating Intermittent Renewable Energy ResourcesEnergy Resources

OutlinePart 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 Systema) The current situation

b) Geographical distribution of renewable generation

c) The expected challenges

• Conclusions

Part 3 – Grid Code Improvements2

Outline ContinuedPart 3 – Grid Code Improvements

3

Part 1

Power Quality Concerns

4

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 system6

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.

• 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.

Background

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

Part 1

Section – 2

TECHNICAL DETAILS

Parameters Effecting Wind Power

Constant Speed vs. Variable 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

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)

Case Study Procedure

• Switching Operations

(Flicker Emission due to Switching)

• Continuous Operation

(Flicker Emission due to Continuous Operation)

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.

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

29

OutlinePart 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 Systema) The current situation

b) Geographical distribution of renewable generation

c) The expected challenges

• Conclusions30

Part 2

Section - 1

ENTSO-E CESA

Interconnection Studies

31

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 ControlDesign and Optimization of

AVR/PSS

Special Protection SchemeRestoration Plan

Training

32

Preliminary Studies

• Site Survey– 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

33

Periodical Frequency Oscillations• Major HPPs in service, before synchronization

• After synchronization

34

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.

35

Part 2

Section - 2 ENTSO-E CESA Trial Parallel

Operation and Frequency Control Performance Indices

36

ENTSO-E CESA Interconnection

37

• 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.

38

Simulation Studies - Time Domain Analysis

0 20 40 60 80 100 120 140 160 180 20049.94

49.95

49.96

49.97

49.98

49.99

50

50.01

Time (Sec)

Fre

qu

en

cy

(H

z)

Frequency of Turkey and Spain in Case of an Accident

Frequency of TurkeyFrequency of Spain

39

Steady State Stability of the Interconnected System

• Low frequency modes (~0.15 Hz) are present in the system!!!

40

Steady State Stability - Solution Methodology

• Road map for enhancing the steady state stability of the interconnected system

41

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

0 5 10 15 2049.85

49.9

49.95

50

50.05

50.1

Time (hr)

Fre

qu

ency

(H

z)

Daily Frequency

42

Performance Indices

1) The hourly integral of ACE should not exceed ±60 MWhrs (the target value is ±20 MWhrs)– To limit unintended energy exchanges

2) 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

3) 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

43

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)44

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.

45

46

Small Signal Stability - Consequences

Present State

• Frequency Stability (1&2)

• Rotor Angle Stability (3)

• Operational Issues – On progress

47

Part 2

Section - 3The Possible Effects of Rapid

Growing Intermittent Generation on Turkish Electricity Transmission System

48

Current Situation in Turkey

• Percentage of renewables in total installed power is almost 10%.

49

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!!!

50

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

51

Geographical Distribution of Renewable Generation

•Geographical distribution of wind potential

52

Geographical Distribution of Renewable Generation

•Geographical distribution of solar potential

53

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

54

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

55

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!!! 56

The Expected Challenges – Very Long Term

• Two scenarios are possible:1) Intermediate term pain for long term gain (long term

electricity price stability)• Balanced distribution of electrical energy generation

sources

2) 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

57

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)

58

Part 3

Section - 1Grid Code Improvements

59

60

Voltage Ride-Through Capability

61

Voltage Ride-Through Capability

62

Active Power Control

63

Reactive Power Support

64

Reactive Power Support

65

Reactive Power Control