Impact of Past, Present and Future Wind Turbine Technologies on Transmission System Operation and Performance
Publication Number: CEC-500-2006-050
Publication Date: May 2006
PIER Program Area: Renewable Energy Research
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The purpose of this document is to provide technical context on wind energy technology for those parties involved in the intermittency analysis efforts being undertaken to support the anticipated near term increases in wind generation capacity in California. These increases in wind capacity are being driven by the state's implementation of its Renewable Portfolio Standard (RPS) authorized under SB 1078. In this document, the electrical characteristics of modern-day wind turbines and the impact of those characteristics on electric power transmission system planning and operation are emphasized.
This document describes the evolution of utility-scale wind turbine technology and wind plant development over the past 25 years with an emphasis on the electrical impacts related to performance, reliability, power quality and operation of the interconnected transmission network. The target audience for the paper is the engineer with some basic familiarity with electric power systems and the transmission planning process, but with little or no background in wind energy conversion technology and its impact on the grid. Prior Energy Commission and CWEC reports have provided technical background on the aerodynamic and mechanical aspects of modern wind turbines, including the turbine rotor (blades) and drive train, up to and including the gearbox. This report expands upon that body of work by focusing on the electromechanical conversion of wind energy to electrical energy, from the gearbox output shaft all the way to the bulk power transmission network.
The scope of this document is limited to utility scale wind plants with interconnections at the high voltage transmission level. Neither residential scale wind turbines nor wind turbine "clusters" connected at primary distribution level are addressed. These applications are not anticipated to have significant operating impacts on California's bulk power transmission system. Further, interconnection issues with these applications are being addressed by the Commission through its involvement with the CPUC Rule 21 technical and policy working groups.
The balance of the report is organized into six additional sections, as follows:
- � Section 2 - A Brief History of Wind Power Development in California. This section provides historical context for the current state of wind integration within California's electric power transmission system.
- � Section 3 - Historical Transmission and Interconnection Issues at California's Major Wind Development Areas. Transmission and interconnection issues which occurred in conjunction with the interconnection of California's early wind plants are reviewed. In addition, problem solutions, either through specific wind facility modifications or through wind turbine technology improvements, are presented.
- � Section 4 - Present Day Wind Energy Technology Review. This section provides an overview of modern wind turbine technology, with a particular emphasis on electrical characteristics. Wind turbine electrical topologies and their impacts on grid integration are examined.
- � Section 5 - New Transmission and Interconnection Issues for High Wind Penetration Scenarios. California's current modest level of penetration of wind power has resulted in such minimal impacts to the transmission system that wind generation receives presently little or no consideration in the planning and operations of the state's transmission network. With the penetration levels envisioned under the RPS, wind will be a significant component of generation in the state, and additional considerations for planning and operational studies will be an absolute necessity. This section describes additional transmission impacts that will accompany these higher penetration levels.
- � Section 6 - New and Evolving Wind Power Interconnection Standards and Procedures. Interconnection practices and regulatory processes have changed significantly in the time since most of California's existing wind capacity was commissioned. This section provides an overview of these evolving standards and practices and their potential impacts on future wind project interconnections in the state.
- � Section 7 - Future Wind Turbine Technology Enhancements for Improved Grid Compatibility. The final section describes wind turbine technology enhancements that are already under development to improve the performance of wind power with respect to transmission system operational impacts. California will benefit from these technology developments, which are being driven largely by grid compatibility needs in areas (primarily in Europe) already experiencing penetration levels similar to those anticipated under the California RPS.
The Intermittency Analysis Project (IAP), funded under the California Energy Commission's Public Interest Research (PIER) Program, was undertaken to assess power system impacts resulting from the implementation of California's Renewable Portfolio Standard (RPS). Given the current state of commercial viability of the various renewable energy technologies, it is envisioned that RPS goals will be achieved largely through significant increases in the state's installed base of wind energy facilities. The preparation of this report was the first task of this system impact assessment.
The objective of this task was to provide technical context on wind energy technology for those parties involved in the intermittency analysis effort. In this document, the electrical characteristics of modern-day wind turbines and the impact of those characteristics on electric power transmission system planning and operation are emphasized. The evolution of utility-scale wind turbine technology and wind plant development over the past 25 years, with an emphasis on the electrical impacts related to performance, reliability, power quality and operation of the interconnected transmission network, are described. This report expands upon previous CWEC reports by focusing on the electromechanical conversion of wind energy to electrical energy, from the wind turbine gearbox output shaft to delivery of energy to the bulk power transmission network.
Keywords: Interconnection, intermittency, ramping, stability, wind energy
Table of ContentsPreface v
Section 1 - Introduction and Scope 1
Section 2 – A Brief History of Wind Power Development in California 3
Section 3 – Historical Transmission and Interconnection Issues at California’s Major Wind Development Areas 6
Section 4 - Present Day Wind Energy Technology Review 10
Section 5 - New Transmission and Interconnection Issues for High Wind Penetration Scenarios 20
Section 6 - New and Evolving Wind Power Interconnection Standards and Procedures 28
Section 7 - Future Wind Turbine Technology Enhancements for Improved Grid Compatibility 31
Footnotes and References 36
LIST OF FIGURES
Figure 1. Major Wind Development Areas in California 4
Figure 2. Wind Farm in San Gorgonio Pass 5
Figure 3. Constant Speed Wind Turbine System 11
Figure 4. Constant Speed Wind Turbine Torque-Speed Characteristic (A) and Current (B) 13
Figure 5. Turbine using a Two Speed Generator to Improve Aerodynamic Performance 15
Figure 6. Torque-Speed-Pitch Relationships in a Variable Speed Wind Turbine 18
Figure 7. Doubly-Fed Generator and Power Converter for a Variable Speed Wind Turbine 19
Figure 8. Full-Conversion Variable Speed Generator and Converter System 20
Figure 9. Sample Output of Power Flow Analysis for 3-Bus Transmission System 22
Figure 10. Example of Transient Stability Simulation Output 24
Figure 11. PV Curves for Voltage Stability Analysis at a Load Bus 27
Figure 12. E.ON-Netz Low Voltage Ride-Through Requirement for Wind Turbines 29
Figure 13. Real Time Curtailment Via Pitch Control 32
LIST OF TABLES
Table 1. Summary of Grid Code Requirements in Countries with Largest Wind Power Capacity 31
Table 2. Summary of Technology Enhancements to Address Transmission Integration Issues 34