Active shielding of overhead line magnetic field: Design and applications

• Active shielding of the magnetic field of overhead lines has been successfully applied.
• Two plants have been built and are in operation and are the sole operating systems worldwide.
• A solution has been applied which avoid to install measuring devices on the line wires.
• A geometric solution has been found which can be practically applied to standard lines with acceptable costs and results.
• The solution is successful on both the technical and economical perspective.

The paper presents the successful field application of active shielding of the magnetic field of HV overhead lines. Two plants have been deployed and are being operated since some years on a 132-kV and a 400-kV line. The solutions adopted minimize the impact on the line structure. Also the configuration of the control systems has been studied in order to avoid any impact on the normal operation of the line. Two different solutions were used; the first is based on a current sensor and a radio transmitter–receiver system, the second relies on the mutual effect between the line and the shield wires thus not requiring any device installed on the power conductors.Both systems have been continuously operated for some years and have assured to keep the magnetic field at the sensitive targets below the desired limits.