POWERING DOWNHOLE DEVICES

A well installation comprising downhole power delivery apparatus for delivering electrical power from a surface power source S to a downhole tool T. The well installation comprises downhole metallic structure 2 running down into a borehole. The apparatus comprises an electrical cable 3 for carrying electrical power from the surface power source S, a power transfer arrangement 4 and a power pick up arrangement 5. The cable 3 runs down into the borehole together with the metallic structure 2 to the power transfer arrangement 4 which is provided at a first downhole location for transferring electrical power carried by the electrical cable 3 onto the downhole metallic structure 2 for onward conduction. The power pick up arrangement 5 is provided at a second downhole location, spaced from the first, for picking up electrical power from the downhole metallic structure 2 for supply to the downhole tool T.