Harnessing the natural power of air in motion, wind turbines generate electricity. In all, U.S. wind turbines operated at a cumulative capacity of 105,853 MW in 2019 and generate over 7% of the nation’s electricity, making it the leader among renewable energy. Thanks to the federal Production Tax Credit (PTC) and the Investment Tax Credit (ITC), as well as an interest to combat climate change, the wind power industry is due to expand greatly, doubling by 2030.
These standards—mostly in the IEC 61400 series—support the safe, efficient work of the 114,000 people involved with the United States wind energy industry and its growth.
Installation, Design, and Maintenance of Wind Turbines
Clustered throughout the United States, 60,000 electricity-generating wind turbines are in operation. As the wind energy industry burgeons throughout the first half of the 21st Century, it is inherent that more windmills will need to be designed, constructed, and maintained.
IEC 61400-1 Ed. 4.0 en:2019 – Wind Energy Generation Systems – Part 1: Design Requirements specifies essential design requirements to ensure the structural integrity of wind turbines. Concerned with all subsystems of wind turbines—control and protection functions, internal electrical systems, mechanical systems, and support structures—this international standard provides an appropriate level of protection against damage from all hazards during the wind turbine’s planned lifetime.
Those making use of this international standard should note that its requirements apply to turbines of all sizes; however, for small wind turbines (SWTs), IEC 61400-2 Ed. 3.0 b:2013 details requirements. Similarly, IEC 61400-3-1 Ed. 1.0 b:2019 covers requirements for offshore wind turbines. While there currently is only one offshore wind farm in the United States, more are predicted to sprout up in the years ahead. In fact, the shores on both seas possess a power potential of more than 2,000 GW—this is nearly double the nation’s current electricity use.
When it comes to worker safety, construction and demolition operations for wind turbines present unique challenges. As wind farms in America are typically concentrated in areas like plains, mountains, and other remote areas, planning for safety involves confronting the lack of emergency response, unreliable communication, and environmental and other issues.
An American National Standard, ANSI/ASSP A10.21-2018, keeps this in mind while establishing recommended best practices to assure the safety and health of personnel involved in construction and demolition operations for utility-scale land-based wind generation/turbine facilities.
Regardless of location, personnel need to reach various sections of the turbine during construction and maintenance operations. The power output of any wind turbine is largely dependent on two primary factors: the wind speed and the height of the turbine. However, the greater the height, the more expansive the challenges in maintenance. To combat this, ASME A17.8-2016/CSA B44.8-2016: Standard For Wind Turbine Tower Elevators acts as the code for wind turbine tower elevators. Such elevators are unique, as they cannot contain the same welds as regular elevators, and being inside structures exposed to high winds, they are subject to extreme temperatures, humidity variations, and substantial horizontal motions. As part of the ASME A17 (or CSA B44) series, ASME A17.8-2016/CSA B44.8-2016 is a fully harmonized binational standard.
Environmental Effects on Wind Turbines
Due to the extreme climatic effects inflicted onto wind farms, it is essential for turbines to be adequately prepared. First and foremost, windmills need to handle, of course, wind. As stated in the Introduction of IEC 61400-13 Ed. 1.0 b:2015 – Wind Turbines – Part 13: Measurement Of Mechanical Loads:
“In the process of structural design of a wind turbine, thorough understanding about, and accurate quantification of, the loading is of utmost importance.
IEC 61400-13 Ed. 1.0 b:2015, which is another document in the international series of standards focused on which turbines, describes the measurement of fundamental structural loads on wind turbines for load simulation model validation. Specifically, this standard outlines requirements and recommendations for site selection, signal selection, data acquisition, calibration, data verification, measurement load cases, capture matrix, post-processing, uncertainty determination and reporting.
As for the standard’s applicability, it is noted that:
“These methods are intended for onshore electricity-generating, horizontal-axis wind turbines (HAWTs) with rotor swept areas of larger than 200 m2. However, the methods described may be applicable to other wind turbines.”
While wind farms are constructed with the effects of wind in mind, weather can be mercurial and subjugate the turbines to various natural forces. For instance, since wind turbines operate as some of the tallest structures in their immediate vicinity and contain metals, lightning protection is a crucial concern.
For this, IEC 61400-24 Ed. 2.0 en:2019 – Wind Energy Generation Systems – Part 24: Lightning Protection defines the lightning environment for wind turbines and risk assessment for wind turbines in that environment. This standard details requirements and test methods for protection of blades, other structural components, and electrical and control systems. It also covers guidance on lightning protection, personal safety, and damage statistics and reporting.
As you increase altitude, there is another atmospheric hazard that emerges. As temperatures lower at greater heights, taller wind turbines, and certainly those in farms in colder climates, become more prone to icing. An international standard, ISO 12494:2017 – Atmospheric Icing Of Structures, describes the general principles of determining ice load on structures. As mentioned in its clause, this standard is applicable to wind turbines.
Generating Electricity with Wind Turbines
The key interest when it comes to windmills is their effectiveness in generating electricity. Wind speed is a key element of power performance, and, in accordance with IEC 61400-12-1 Ed. 2.0 b:2017 – Wind Energy Generation Systems – Part 12-1: Power Performance Measurements Of Electricity Producing Wind Turbines, it is a key component of power performance testing. This international standard prescribes the use of cup or sonic anemometers or remote sensing devices (RSD) in conjunction with anemometers to measure wind. Ultimately, this standard, in offering guidance in measuring, analyzing, and reporting power performance testing for wind turbines, provides a uniform methodology to ensure consistency, accuracy, and reproducibility in the measurement and analysis of power performance by wind turbines. In fact, this standard is meant for a range of groups of users, including wind turbine manufacturers, wind turbine purchasers, wind turbine operators, and wind turbine planners or regulators.
A notable stipulation made in this standard is what actually defines wind speed. In accordance with this IEC 61400-12-1 Ed. 2.0 b:2017, wind speed can be supplemented with Rotor Equivalent Wind Speed (REWS), which is defined by an arithmetic combination of simultaneous measurements of wind speed at a number of heights spanning the complete rotor diameter between lower tip and upper tip.
When functioning, gearboxes enhance wind turbine speed and thereby increase the power rating. However, gearboxes operate differently than most other gear applications. Providing guidance in this area, ANSI/AGMA 6006-B20: Standard For Design And Specifications Of Gearboxes For Wind Turbines serves as a tool for wind turbine and gearbox manufacturers to communicate and understand each other’s needs in developing a gearbox specification for wind turbine applications.