Laboratory Validation of Calculations of Magnetic Field Mitigation Underneath Transmission Lines Using Passive and Active Shield Wires

Abstract

This paper is aimed at reporting experimental measurements and calculations of how the magnetic field underneath overhead transmission lines is mitigated using passive and active shield wires. The magnetic field values were compared to those calculated using the current simulation technique (CST). A laboratory transmission line model representing the Egyptian 500 kV EHV line was built with dimensions scaled down in the ratio 10:1. The flat single circuit of the line was modeled in the laboratory by phase separation of 1.2 m and conductor diameter of 2.76 mm at height of 1.9 m. The shield wires were spaced 4.3 m at a height of 1.45 m. Magnetic field measurements were carried out for load currents of 5.7 and 10 A. The field was measured at 0.3 m above ground level with and without passive and active shield wires for several different lateral positions. The measured and calculated field values generally agreed reasonably with an error ranging between 2.5 and 20 % within the ROW. The maximum reduction of magnetic field from the passive shield wires is 10% at the edge of right of way. With active shield wires carrying a current of 5 A (one half of the conductor current), the reduction of magnetic field reached 17% at the edge of ROW.