Abstract. During the assessment of the electromagnetic emissions of wind turbines
(WTs), the aspects of measurement uncertainty must be taken into account.
Therefore, this work focuses on the measurement uncertainty which arises
through distance errors of the measuring positions around a WT. The measurement distance given by the corresponding standard is 30 m with
respect to the WT tower. However, this determined distance will always
differ e.g. due to unevenness of the surrounding ground, leading to
measurement uncertainties. These uncertainties can be estimated with the
knowledge of the electromagnetic field distribution. It is assumed in
standard measurements, that the electromagnetic field present is a pure
transversal electromagnetic field (far field). Simulations of a simplified
WT model with a hub height of 100 m shows that this assumption is not
effective for the whole frequency range from 150 kHz to 1 GHz. For
frequencies below 3 MHz the field distribution is monotonically decreasing
with the distance from the WT since it behaves like an electrical small
radiator. Whereas for frequencies above 3 MHz, where the investigated model
forms an electrical large radiator, the field distribution becomes more
complex and the measurement uncertainty of the field strength at the
observation point increases. Therefore, this work focuses on investigations
where the near field becomes a far field. Based on the simulation results, a
method for minimizing the uncertainty contribution caused by distance errors
is presented. Therefore, advanced measurement uncertainty during in situ
test of WTs can be reduced.
Near-field and far-field analysis of an azimuthally polarized slow Bloch mode microlaser