UNE-EN IEC 61400-12-6:2024

50 This part of IEC 61400-12 specifies a procedure for measuring the nacelle transfer function of

51 a single electricity-producing, horizontal axis wind turbine, which is not considered to be a small

52 wind turbine per IEC 61400-2. It is expected that this standard shall be used when a valid

53 Nacelle Transfer Function is needed to execute a power performance measurement according

54 to the IEC 61400-12-2 standard.

55

56 A wind speed measured on the nacelle or hub of a wind turbine will be affected by the turbine

57 rotor (i.e. speeded up or slowed down wind speed). Therefore, the nacelle-measured wind

58 speed shall be corrected for this flow distortion effect. Procedures for determining that

59 correction will be included in the methodology. In IEC 61400-12-1, an anemometer is located

60 on a meteorological tower that is located between two and four rotor diameters upwind of the

61 test turbine. This location allows direct measurement of the free wind with minimum

62 interference from the test turbine s rotor. In this IEC 61400-12-6 procedure, the anemometer is

63 located on or near the test turbine s nacelle. In this location, the anemometer is measuring a

64 wind speed that is strongly affected by the test turbine s rotor and the nacelle. The procedure

65 in this standard includes methods for determining and applying appropriate corrections for this

66 interference. However, it must be noted that these corrections inherently increase the

67 measurement uncertainty compared to a properly-configured test conducted in accordance with

68 IEC 61400-12-1.

69

70 This IEC 61400-12-6 standard describes how to characterise a wind turbine s nacelle transfer

71 function. The nacelle transfer function is determined by collecting simultaneous measurements

72 of nacelle-measured wind speed and free stream wind speed (as measured on a meteorological

73 mast) for a period that is long enough to establish a statistically significant database over a

74 range of wind speeds and under varying wind and atmospheric conditions. The procedure also

75 provides guidance on determination of measurement uncertainty including assessment of

76 uncertainty sources and recommendations for combining them.