The use of single-core lead-covered and armoured cables for alternating currents

In a previous paper Miss Calderwood and the present author examined the losses in the lead sheath of a single-core cable when carrying an alternating current, and concluded that, provided the outgoing and return cables were laid within a certain limiting distance of one another, no difficulty would arise due to eddy currents in the sheaths at normal frequencies. In the present paper this work is extended to cover the case of single-core cables that are both lead-covered and armoured. A theoretical investigation of the reactances and losses is carried out and is checked against the actual test figures obtained by Harvey and Busby. It is shown :- 1. That the flux in the armour, the reactance due to that flux, and the appropriate hysteresis and eddy losses can all be approximately predetermined. 2. That for low-tension transmission, lead-covered and armoured cables are impracticable with armouring as at present constructed. 3. That the use of such cables for e.h.t. transmission is not precluded by the magnetic conditions introduced by the armour, and consequently such cables are practicable. There would, however, be some difficulties to be overcome due to large capacity currents when the transmission distance is great.