By Andrew Leon
The wind power industry has experienced rapid growth resulting in more than 60 gigawatts of installed wind capacity in the United States and over 300 gigawatts worldwide. Despite the similarity to traditional utility power generation infrastructure, a number of critical design considerations and issues unique to wind power plants (WPPs) have become evident. This recent expansion of utility-scale renewable energy facilities led to the creation of the Wind and Solar Plant Collector Design Working Group within the IEEE Power & Energy Society. This group serves as a focal point within the PES for addressing topics related to the practical design issues of collector systems for wind and solar plants.
Diverse challenges are encountered during the design and construction of wind power plants. Typical WPPs consist of an interconnection substation, collection circuits, reactive compensation equipment, step up transformers, as well as five main types of WTGs - each with their own power conversion and performance characteristics. Improper system grounding can lead to premature failure of collection circuit equipment, potentially resulting in costly repairs and reduced availability. Utilities and system operators outline local reactive power requirements. Mandatory compliance with these requirements can be approached in a number of different ways each having its advantages and disadvantages. Additionally, the combination of complex capacitive and inductive elements in a WPP can cause significant power quality issues related to harmonics and resonance. Conventional utility design practices prioritize reliability, which is addressed with increased levels of redundancy. In contrast, maximum economic availability of wind turbine generators (WTGs) is the ideal focus for optimizing a new WPP.
This special publication is a compendium compiled from a series of 11 technical papers by 45 authors. These papers were published and presented by the working group to provide general design guidance as well as to address specific issues encountered in WPPs. Covered design principles include considerations for underground versus overhead collector lines, power transformer specifications, reactive power compensation guidelines, as well as SCADA and Control philosophy. Industry specific issues such as the system grounding of WPPs and harmonic/resonance issues are discussed along with available protection and mitigation options that may address these concerns.
The compendium is organized into two parts. A brief summary of the papers within each section is provided for the reader. An appendix includes abbreviations & terms related to WPP collector systems.
PART 1 Wind Power Plant Design Principles
1. “Wind Power Plant Collector System Design Considerations”
A summary of the most important design considerations for wind power plants are presented. The configuration of feeder strings is discussed aside important design aspects such as conductor sizing and the thermal characteristics of site-specific soil. Substation design and equipment specifications are explained as well as the various engineering studies required to support the overall design of a wind power plant.
2. “Characteristics of Wind Turbine Generators for Wind Power Plants”
Summary of the most important characteristics of wind turbine generators applied in modern wind power plants is presented. Various wind turbine generator designs, based on classification by machine type and speed control capabilities are discussed highlighting their operational characteristics, voltage and power factor control capabilities, voltage ride-through characteristics, behavior during short circuits, and reactive power capabilities.
3. “Wind Power Plant Substation and Collector System Redundancy, Reliability, and Economics”
Basic guidelines on design considerations for wind power plant substations and collector systems are discussed. Wind power plant design often prioritizes aspects not normally considered in traditional utility systems. Power loss and overall economic analysis in a typical wind power plant is explained.
4 .“Design and Application of Cables and Overhead Lines in Wind Power Plants”
This paper presents a summary of the most important considerations for wind power plant collection system underground cable and overhead designs. Various characteristics, including conductor selection, soil thermal properties, installation methods, splicing, concentric grounding, and NESC/NEC requirements are discussed.
5 .“Power Transformer Application for Wind Plant Substations”
Here, the application of wind power plant transformers with regard to the selection of winding configuration, MVA rating, impedance, loss evaluation, on-load tap changer requirements, and redundancy is presented. Wind power plants use power transformers to step plant output from the medium voltage of the collector system to the high or extra high voltage transmission system.
6. “Wind Power Plant SCADA and Control”
This paper discusses the range of application for SCADA and control systems in a wind power plant, the most important SCADA and control system considerations, and contractual requirements for SCADA and control systems.
7 .“Reactive Power Compensation for Wind Power Plants”
The basic guidelines for the application of reactive compensation systems to be used as part of a wind power plant are presented. A brief history of wind plant reactive compensation systems is discussed, including the fundamental need for reactive power compensation. This paper provides alternatives for reactive compensation, reactive compensation analytics, and an overview of the operating principles in various compensation devices.
PART 2 Wind Power Plant Equipment Protection and Safety
8 .“Wind Power Plant Grounding, Overvoltage Protection, and Insulation Coordination”
Presents a tutorial description of the process of selecting and applying surge arresters to wind plant medium voltage collector systems, with emphasis on the peculiar properties of this application. Proper insulation coordination is critical to preventing premature failure in wind plant equipment. The collector systems of large wind plants require the application of surge arresters to protect the equipment insulation from transient overvoltages. This application is constrained by maximum operating and temporary overvoltage levels.
9. “Arc-Flash Hazard in Wind Power Plants”
A brief review of the concept of arc flash and a methodology for arc-flash hazard analysis on a WPP collector system follows. Addressed topics include faults fed by multiple sources and modeling of the resultant wind turbine generator fault current. The paper concludes with two examples using the presented methodology.
10. “Wind Plant Collector System Fault Protection and Coordination”
Presents a summary of the most important protection and coordination considerations for wind power plants. Short-circuit characteristics of both aggregate wind plant and individual wind turbine generators, as well as general interconnection protection requirements are discussed. Many factors such as security, reliability, and safety are considered for proper conservative protection of the wind power plant and individual turbines.
11. “Harmonics and Resonance Issues with Wind Plants”
Summarizes the most important issues with respect to harmonics and resonances within wind power plants. An introduction is given to provide an overview of the various power quality related issues encountered when designing, commissioning, or operating a wind power plant, as well as typical characteristics of the components associated with wind power plants. The many variables which influence harmonics and resonance in wind power plants will be described with respect to analysis methods, avoidance, mitigation, and compliance with IEEE Std 519-1992 recommended practices.
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