The effect of trees on calculation of electric fields near 400 kV transmission lines

摘要

In a previous study on electric fields near 400 kV transmission lines it was noticed that the differences in calculations and measurements were caused by trees dampening the electric field. This caused the need for further investigation and dampening measurements. The aim of this study is to model single trees and forest, in the calculation of electric fields using the Finite Element Method (FEM). International Commission on Non-Ionizing Radiation Protection (ICNIRP) has published guidelines for public and occupational exposure to 50 Hz electric fields caused by power transmission lines. They are 5 kV/m and 10 kV/m, respectively. There are some spans, where guideline for public exposure may be exceeded. Thus it is important to find ways to reduce these fields. The 2D-FEM-model created in a previous study consisted of 20-meter-high forest and conductors but it was noticed that the effect of single trees on electric fields should also be considered. Single spruce tree, one-meter-high grass and 20-meter-high spruce forest were created for the example spans. Results of numerical calculation were compared to measurement results. The maximum value of measurement was 4.38 kV/m and the maximum value of numerical calculation was 5.02 kV/m. The major difficulty is to find adequate material properties for the mathematical model. Therefore the determination of permittivity and resistivity of living organisms is necessary, which depend on several environmental factors.