BS EN 61400-21:2008

BS EN 61400-21:2008 Wind turbines. Measurement and assessment of power quality characteristics of grid connected wind turbines

BS EN 61400-21 is the European standard for testing of wind turbines, though it contains information that may also be useful for testing of wind farms.

BS EN 61400-21 of IEC 61400 includes:

• Definition and specification of the quantities to be determined for characterizing the power quality of a grid connected wind turbine
• Measurement procedures for quantifying the characteristics
• Procedures for assessing compliance with power quality requirements, including estimation of the power quality expected from the wind turbine type when deployed at a specific site, possibly in groups.

The measurement procedures are valid for single wind turbines with a three-phase grid connection. The measurement procedures are valid for any size of wind turbine, though this part of IEC 61400 only requires wind turbine types intended for PCC (Point of Common Coupling) at MV or HV to be tested and characterized as specified in this part of IEC 61400.

The measured characteristics are valid for the specific configuration and operational mode of the assessed wind turbine type only. Other configurations, including altered control parameters that cause the wind turbine to behave differently with respect to power quality, require separate assessment.

The measurement procedures are designed to be as non-site-specific as possible, so that power quality characteristics measured at for example a test site can be considered valid also at other sites.

The procedures for assessing compliance with power quality requirements are valid for wind turbines with PCC at MV or HV in power systems with fixed frequency within ±1 Hz, and sufficient active and reactive power regulation capabilities. In other cases, the principles for assessing compliance with power quality requirements may still be used as a guidance.

This part of IEC 61400 uses the following terms for system voltage:

• Low voltage (LV) refers to Un ≤ 1 kV
• Medium voltage (MV) refers to 1 kV < Un ≤ 35 kV
• High voltage (HV) refers to Un > 35 kV

The purpose of BS EN 61400-21 is to provide a uniform methodology that will ensure consistency and accuracy in the presentation, testing and assessment of power quality characteristics of grid connected wind turbines (WTs). The power quality characteristics here include wind turbine specifications, voltage quality (emissions of flicker and harmonics), voltage drop response, power control (control of active and reactive power), grid protection and reconnection time.

BS EN 61400-21 can be applied by:

• The WT manufacturer striving to meet well-defined power quality characteristics
• The WT purchaser in specifying such power quality characteristics
• The WT operator who may be required to verify that stated, or required power quality characteristics are met
• The WT planner or regulator who has to be able to accurately and fairly determine the impact of a WT on the voltage quality to ensure that the installation is designed so that voltage quality requirements are respected
• The WT certification authority or component testing organization in evaluating the power quality characteristics of the wind turbine type
• The planner or regulator of the electric network who has to be able to determine the grid connection required for a WT.

BS EN 61400-21 provides recommendations for preparing the measurements and assessment of power quality characteristics of grid connected WTs. BS EN 61400-21 will benefit anyone involved in the manufacture, installation planning, obtaining of permission, operation, utilization, testing and regulation of WTs. The measurement and analysis techniques recommended in this part of IEC 61400 should be applied by all parties to ensure that the continuing development and operation of WTs are carried out in an atmosphere of consistent and accurate communication.

BS EN 61400-21 presents measurement and analysis procedures expected to provide consistent results that can be replicated by others.

Contents of BS EN 61400-21 include:

• Scope
• Normative references
• Terms and definitions
• Symbols and units
• Abbreviations
• Wind turbine power quality characteristic parameters
• Wind turbine specification
• Voltage fluctuations
• Continuous operation
• Switching operations
• Current harmonics, interharmonics and higher frequency components
• Response to voltage drops
• Active power
• Maximum measured power
• Ramp rate limitation
• Set-point control
• Reactive power
• Reactive power capability
• Set-point control
• Grid protection
• Reconnection time
• Test procedures
• Wind turbine specification
• Voltage fluctuations
• Fictitious grid
• Current harmonics, interharmonics and higher frequency components
• Response to temporary voltage drop
• Active power
• Maximum measured power
• Ramp rate limitation
• Set point control
• Reactive power
• Reactive power capability
• Set point control
• Grid protection
• Reconnection time
• Assessment of power quality
• Current harmonics, interharmonics and higher frequency components
• Sample report format
• Voltage fluctuations and flicker
• Measurement of active power, reactive power and voltage
• Bibliography
• Adjustment of active power set-point

This European standard supersedes EN 61400-21:2002 which has been withdrawn.

BS EN 61400-21:2008 includes additional information:

• Interharmonics and current distortions (< 9 kHz)
• Response to voltage dips
• Active power ramp rate limitation and set-point control
• Reactive power capabilities and set-point control
• Grid protection and reconnection time after grid faults.