IEC 61400-11:2002/AMD1:2006

Overview

IEC 61400-11:2002/AMD1:2006 is an important amendment to the international standard governing acoustic noise measurement techniques for wind turbine generator systems. Developed by IEC Technical Committee 88, this amendment addresses specific measurement scenarios, including cases where wind turbines reach 95% of rated power at wind speeds below 10 m/s and sites where such wind speeds are rare. It also provides clarifications on regression analysis methods and A-weighting frequency techniques used in noise measurement.

This amendment ensures precise, consistent, and reliable acoustic noise data crucial for wind turbine manufacturers, developers, regulators, and stakeholders. By refining measurement methods, the standard supports compliance verification with declared noise levels and enhances environmental noise impact assessments.

Key Topics

• Special Cases for Power Output and Wind Speeds
  Incorporates procedures when 95% rated power is achieved below 10 m/s wind speed, including guidance for sites with rare 10 m/s wind occurrences.

• Wind Speed Measurement Methods

  • Introduction of nacelle anemometer wind speed (Vₙ) as a key parameter.
  • Recommendations for using the nacelle anemometer or alternative anemometers mounted on the nacelle, especially for turbines with hub heights below 30 m.
  • Clarification that nacelle anemometer data, calibrated in situ, should not be used for background noise but can be sourced from turbine control systems.

• Verification Measurement Procedures
  Specifies wind speed ranges for verification: annual average wind speed at 10 m height ±1 m/s minimum, including three consecutive integer wind speeds plus 8 m/s.

• Noise Measurement and Analysis Techniques

  • Use of narrow band measurements requiring minimum two-minute A-weighted wind turbine and background noise recordings near integer wind speeds.
  • Conversion from linear spectra to A-weighted spectra per IEC 61672-1:2002 if direct A-weighting is unavailable.
  • Use of fourth-order regression for sound pressure level estimation when correlation coefficients exceed 0.8, otherwise bin analysis with linear regression within 1 m/s wind speed bins.

• Wind Speed Data Processing
  Two preferred methods for determining wind speeds above 95% rated power:

  • Nacelle Anemometer Method: Linear regression correlating nacelle wind speeds and corrected hub height wind speeds.
  • κ-Factor Method: Applies a ratio between standardized and measured wind speeds to adjust the wind data.

• Additional Measurement Recommendations
  Suggests measuring and reporting rotor speed and pitch angle from the wind turbine controller to support comprehensive acoustic characterization.

• Uncertainty Considerations
  Highlights the importance of accounting for uncertainties in measured or derived wind speeds, including calibration, site effects, and power curve variances-especially significant above 95% rated power.

Applications

This amendment is essential for professionals involved in:

• Wind Turbine Acoustic Compliance Testing
  Ensures that wind turbine noise emissions meet regulatory and contractual requirements by providing robust measurement protocols.

• Environmental Impact Assessments
  Supports accurate noise assessment for project approvals and community impact studies, factoring in site-specific wind conditions and turbine operational parameters.

• Wind Turbine Design and Performance Optimization
  Enables manufacturers and engineers to analyze noise behavior under diverse wind regimes and improve turbine design for noise reduction.

• Wind Farm Development and Operation
  Assists in selecting appropriate measurement techniques for verifying noise levels at various wind speeds, supporting operational noise management and stakeholder communication.

Related Standards

• IEC 61400 Series

  • IEC 61400-1: Design requirements for wind turbines.
  • IEC 61400-12: Power performance measurement of electricity-producing wind turbines.

• IEC 61672-1:2002

  • Electroacoustics – Sound level meters – Part 1: Specifications, referenced for A-weighting conversion and sound measurement accuracy.

• Site-Specific Standards and Local Codes
  May require adjustments to wind speed measurement ranges or additional noise assessment procedures beyond those outlined in IEC 61400-11 amendment.

By applying IEC 61400-11:2002/AMD1:2006, stakeholders ensure reliable and industry-recognized procedures for acoustic noise measurement in wind turbine systems. This amendment enhances the precision of noise data critical for sustainable wind energy deployment and community acceptance worldwide.