Firstly, the maximum noise dispersed by WT is identified, and then its intensity level variation is calculated depending on the distance to the object. Data given in Table 2 reveal that in case when the difference of noises is higher than 10 dB(A), a bigger noise prevails, since the impact of smaller noise on the total noise level does not exceed 0.41 dB(A) value. Measurements of WT noise, taking into account the hygiene requirements [29], are carried out at 1.5 m height from the earth surface.
2.2. Experimental study and measurement technique of the WT noise propagation
Experimental research study was performed for the analysis of WT generated noise and influence of background noise on this process. Enercon E-40 type WT of JSC “Intuva” of Prozariškiai WT-1 power plant was used for the investigation. The WT was low-capacity (up to 250 kW), which was installed in Kaišiadoriai region further from residential areas; the tower height of WT was 65 m, and it was surrounded by agricultural land. There are no big trees or a bush nearby WT. Research was carried out at different wind speeds. Hand-held analyzer type 2250 Bruel and Kjaer was used for the measurement of noise. Frequency analysis software BZ-7223 was used for the analysis of measuring data.
Measurements of acoustic noise were carried out in the wind direction, against the wind direction and perpendicularly to the wind direction at different distances to WT tower (Fig. 2). Distance x from WT tower was changed every 25 m, i.e., it was chosen 0, 25, 50 m, etc. The duration of each measurement at 1.5 m in height from the earth surface continued approx. 5 min. Data were collected in analyzer׳s memory with the help of BZ 5503 software. Frequency analysis software enabled to use 1/1 octave and 1/3 octave and broadband sound measurements at one time.