The possibilities of transmission by underground cables at 100,000/150,000 volts

Abstract

The paper is primarily a plea for the use of single-phase cables. The effect of separating the cores is considered, both in its relation to easing the potential gradient and in relation to eddy currents induced in the lead sheathing. The gain effected by employing ?intersheaths? is pointed out, and the author's proposals for obviating the disadvantages of intersheaths by combining their employment with a six-phase transmission are considered. An actual transmission of 50,000 kW at 100,000 volts over a distance of 30 miles is worked out in detail and compared with a similar transmission at 30,000 volts. A saving of roughly £500,000 is shown. The principal conclusions arrived at are:? (1) Reliability under the six-phase/three-phase system very greatly increased, as compared with plain single-core cables (as at Gennevilliers), or with three-phase cables for equal-voltage. (2) The author's arrangements will permit of loads of poor power factor being taken up, with positive gain in efficiency and regulation. (3) The maximum voltage gradient being no greater with 100,000 volts than with 30,000 volts, such transmissions can be undertaken immediately the cable makers are in a position to guarantee the cables. (4) The investment in capital outlay proceeds, in the six-phase/three-phase scheme, in proportion to the development of the load. A start could thus be made with only 8,000 kW. (5) The reduction in line-charging current in the six-phase/three-phase scheme, and the improvement in ?regulation? are very considerable, as compared with those for any other proposals.