1. FACTS Devices for Dynamic Reactive Power Compensation in Wind Farms
Piotr R. Wiczkowski
Sargent & Lundy LLC | Electrical Analytical Division
Abstract
Federal Regulatory Energy Commission (FERC) Order No. 827, which was issued in June 2016 and became effective in September 2016, requires wind farms to provide dynamic reactive power compensation. The ruling was initiated and justified based on the advancements in Type III and Type IV inverter-based wind turbine generator (WTG) dynamic reactive power supply capabilities. In addition to the WTG’s inherent reactive power capabilities, Flexible AC Transmission Systems (FACTS) devices such as Static VAR Compensators (SVCs) and Static Compensators (STATCOMs) can be utilized to supplement the wind farms to be in full compliance with the dynamic reactive power compensation requirements. Today, about 5 % of the FACTS market segment is for renewable projects, and the share is expected to increase in the near future with the FERC ruling. This poster explains key design considerations and performance requirements for the FACTS devices. Additionally it overviews prudent approaches for project developers and in preparing specifications, performing bid evaluations and executing procurement of Facts Devices.
Methodology
As part of our extensive electric power industry experience, Sargent & Lundy has significant wind energy experience. We have provided a full range of services to the wind energy industry, including site screenings, project feasibility studies, wind resource assessments, independent engineering, collector interconnection planning, conceptual engineering, contract development, detailed engineering, design reviews, construction monitoring, commissioning, and operations and maintenance (O&M) support. Sargent & Lundy has worked on wind farm projects for over 15 years. We participate in the AWEA Offshore Wind Working Group and the AWEA Wind Power O&M Working Group. We also actively participate in the IEEE Wind Plant Collector Design Working Group as well as the High Voltage Power Electronics Working Group.
FERC Order No. 827
New wind power generation must maintain a composite power delivery, at continuous rated power output, at the high-side of the generator substation at a power factor within the range of 0.95 leading to 0.95 lagging. The power factor range standard shall be dynamic and can be met using, for example, power electronics designed to supply this level of reactive capability (taking into account any limitations due to voltage level, real power output, etc.) or fixed and switched capacitors, or a combination of the two
Regional entities, such as ERCOT, may have stricter requirements. Requiring power factor, calculated at a units maximum power output, available at all MW output levels
What is a FACTS
A flexible alternating current transmission system (FACTS) is a system composed of static equipment used for the AC transmission of electrical energy. It is meant to enhance controllability and increase power transfer capability of the network. It is generally a power electronics-based system.
These devices, in conjunction with turbine capabilities, enhance dynamic VAR support
FACTs devices offer advantages outside required VAR support including fault recovery, voltage support, phase balancing, etc.
FACTS Devices
Static VAR Compensators (SVC)
A continuously adjustable (dynamic) admittance, capacitive through inductive. SCVs can respond quickly to network changes to counterbalance the variations of the load flow or occurrence of faults
SVCs are thyristor controlled shunt capacitors and/or reactors
More typically for higher voltage transmission applications
Produces Low Order Harmonics
Historically lower cost than STATCOMs
Static Synchronous compensator (STATCOM)
Voltage source convertor (VSC). Compromised of a voltage source (DC Capacitor) behind a reactor.
Advantages over SVCs include greater performance at low operating voltages, faster response time, and small form factor
Expensive at higher voltage levels, typically installed on the collector system
Historically more expensive than SVCs but reaching price parity
Can be designed with almost no harmonics
Most common for wind farms
Analysis Requirements
Typical Support Studies
Reactive Compensation / Sizing Study Assess VAR support need to meet regulator requirements
Load Flow / Voltage Drop Confirm network load flow conditions are with acceptable limits across all operating conditions
Harmonics FACTS devices can be a significant source of harmonics. This study is necessary to determine if the wind farm is operating within IEEE limits and if mitigation is required
Transient Stability FACTs devices can provide voltage support during transient events such as system faults
System Protection Protection must be coordinated to protect FACTS device while also ensuring operability through range of operation
Software Packages
ETAP, SKM, or PSS/E packages for reactive compensation, load flow, and protection studies
EMTP, PSCAD, and PSS/E for Harmonics and transient stability
Contact with equipment vendors vital to obtain critical model input parameters
Specification and Procurement
Functional vs. Detailed Functional vs. Detailed Specification
IEEE recommends the Detailed Functional route.
IEEE 1031 can be used, even though it is designed for transmission class SVCs.
IEEE is working on a STATCOM functional specification guide. Manufacturers are familiar with the IEEE guides and it touches on all the key aspects of specifying an SVC, but it will still give the manufacturer the flexibility to choose what they want. Will give the best in terms of pricing.
Smaller pre-engineered devices exist (S&C Purewave, ABB PCS6000) and these can be easier to work with. Tend to come in blocks of VAR capability (up to 15MVAR/35kV).
Bid Evaluation
Important to include cost categories within the specification to help judge manufacturers.
Bids received, especially for transmission class devices, may be specialized and highly customizable. Manufacturers will spend a decent amount of engineering time to prepare a proposal.
For a wind farm, depending on the dynamic range and response time needed, the best solution might include a dynamic device (containerized STATCOM) along with an external cap bank
Loss evaluation is critical. This will force manufacturers to make certain design choices. Need to balance upfront cost savings versus long term operating costs
S&L can provide support over the lifecycle of the project
Takeaways
FERC Rule 827 as well as recent ISO rule changes created stricter VAR support requirements for new wind generation projects increasing the need for FACTS devices
Two common types of FACTs devices available, SVCs and STATCOMs, with STATCOMs being the most common
FACTs devices require an array of analyses utilizing specialized software to support their deployment
Recommend a detailed functional specification
FACTS devices are often specially engineered to the specification and highly customizable
Piotr R. Wiczkowski is a Project Associate with Sargent & Lundy’s Electrical Analytical Division. His experience in the wind industry focuses on electrical analysis. These analyses include reactive power compensation, voltage drop/regulation, short circuit, transients, insulation coordination, and harmonics. Piotr holds B.S. and M.S. degrees in electrical engineering from the University of Illinois Urbana-Champaign. Piotr is a Licensed professional engineer in the State of Illinois.