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
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 system
6
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
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
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
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 Control
Design and Optimization of
AVR/PSS
Special Protection Scheme
Restoration 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
• 09.2010
• 02.2011
• 06.2011
• 09.2012
Trial parallel operation started
Non-commercial energy exchanges
Commercial energy exchanges
(https://tcat.teias.gov.tr/)
Expected date of the end of trial parallel
operation
37
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
Frequency of Turkey and Spain in Case of an Accident
50.01
Frequency of Turkey
Frequency of Spain
50
Frequency (Hz)
49.99
49.98
49.97
49.96
49.95
49.94
0
20
40
60
80
100
120
140
160
180
200
Time (Sec)
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
Daily Frequency
50.1
50.05
Frequency (Hz)
50
49.95
49.9
49.85
0
5
10
15
Time (hr)
20
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
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
46
Present State
• Frequency Stability (1&2)
• Rotor Angle Stability (3)
• Operational Issues
– On progress
47
Part 2
Section - 3
The Possible Effects of Rapid
Growing Intermittent Generation
on Turkish Electricity Transmission
System
48
Current Situation in Turkey
Distribution of Installed Power with respect to
Electrical Energy Generation Sources
3,0 %
6,7 %
THERMAL - TOTAL
GEOTHERMAL
HYDRO - DAM
26,6 %
HYDRO - RUN OF THE RIVER
63,5 %
WIND
0,2 %
• 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
Hydro
Wind
Geothermal
Solar
Biomass (incl. LFG)
–
–
–
–
–
–
First 10 years of operation ($cent/kWh)
7.3
7.3
10.5
13.3
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.
56
– Capacity reserve agreements!!!
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 - 1
Grid Code Improvements
59
Voltage Ride-Through Capability
60
Voltage Ride-Through Capability
61
Active Power Control
62
Reactive Power Support
63
Reactive Power Support
64
Reactive Power Control
65