Passive mitigation of stray magnetic fields generated by underground power lines

This paper focuses on magnetic fields created by joint bays. For technical reasons, within a joint bay cables have to be arranged in flat configuration. Due to the larger gap between cables a higher magnetic field generation occurs with respect to the trefoil arrangement. Joint bays are usually mitigated by means of passive shields. The literature covers comparisons of flat metallic shields, passive loops and passive loops with improved magnetic coupling (called HMCPL). In the renewal of the high voltage electrical network of Torino, from 2010 to 2014 sixteen new 220 kV lines were laid. The total length is about 50 km. The cables were provided from three different manufacturers. Seventy joint bays were installed and twenty of them required a mitigation system. In 14 joint bays HMCPL system has been used whereas in the others 6 the classical passive loops system has been installed. This paper summarises the performance of these existing systems comparing its performance. Very satisfactory results are obtained regarding HCMPL, furthermore, it is confirmed that the site assembly of HMCPL is faster and more flexible than any other shielding solution.