Wind turbines are just one (albeit an important) component of bulk wind plants. With individual turbine sizes now exceeding 1 MW, nameplate ratings for single wind plants of many tens to hundreds of MW are common. The geographic extent of the wind plant must be large enough to not only accommodate the dozens to a hundred or more turbines, but also allow optimal spacing and utilization of local terrain features that will maximize energy production. The infrastructure for connecting a large number of widely distributed turbines to a single point of interconnection with the transmission system has important influence over the electrical characteristics of the wind plant.
Design and Configuration
Realizing the benefits of enhanced capabilities of wind turbines will depend in large part on the overall wind plant design, since the actions of a large number of relatively small wind turbines must be coordinated to have positive impacts on the overall power system. The installed and proposed utility-scale wind plants in the U.S. have some common design characteristics that offer potential simplifications for constructing aggregated models for transmission system studies. These commonalities stem from practicalities and optimizations regarding the local wind regime, micro-siting of individual turbines, electric system design, and operations and maintenance economies.
- Reactive Power Management and Dispatch
Because of the fast pace at which the wind industry has emerged and grown over the last decade, the reactive power characteristics of a wind plant are more often than not an “outcome” rather than a design requirement.
- Communications and Control
The communications and control infrastructure of even present-day wind plants is quite sophisticated, with high-speed SCADA to each turbine and other critical devices or points within the collector system.
- Wind Plant Production Forecasting
While the fast fluctuations in wind plant output can create problems with respect to voltage flicker and reactive power management, somewhat longer term fluctuations in wind plant production appear to be of the most consequence for control area operators.
Models that capture the aggregated behavior of all components in a wind plant as seen from the interconnection point to the transmission network are the most useful and sometimes practically required for large power system studies. These components contributed to behavior of the wind plant as a single entity connected to the transmission network for steady-state and dynamic conditions.
The WECC generic models are reduced-order, positive-sequence models suitable for transmission planning studies involving a large network, and thousands of generators, loads and other dynamic components. The objective of dynamic simulation is to assess dynamic stability following large-signal disturbances such as transmission-level faults with integration time steps in the order of 1 to 5 milliseconds. The WECC generic models are intended to address NERC and WECC modeling requirements. As the generic models continue to be refined over time, they will eventually be used for generator interconnection studies as well, consistent with power system industry practice. At the discretion of the Transmission Planner, manufacturer-specific models may be used in the context of interconnection studies; however, such practice has a number of technical and process drawbacks.