Patent GB-500877-A (GB)
Title: Improvements in or relating to the insulation of enclosed electrical conductors or apparatus
IPC: H01B3/16
Filed: 1937-08-14
Abstract: 500,877. Insulating conductors ; cable joints; two-part couplings; transformers ; switchgear structures. HEYROLLE & CO.,-Ltd., A., and DEAN, W. J., and CLOTHIER, M., [Representatives of CLOTHIER, H. W.], HARLE, J. A., and COATES, F. Aug. 14, 1937 Nos. 22387/37 and 21367/38. [Classes 36 and 38 (i)] [Also in Groups XXXV and XXXVI] Conductors or joints therein are insulated from a surrounding casing by solid pulverulent mineral insulating material which is maintained in an atmosphere of gas at superatmospheric pressure within the casing, but which is not otherwise impregnated. The conductors may form part of a switch gear installation or tho windings of a transformer. The gas may consist of compressed air, nitrogen, carbon dioxide, argon, a fluorinated chloro-paraffin, or a mixture of the lastnamed gas and air. The solid insulating material, which may consist of powdered magnesia, glass, alumina, silica, or crushed mica, may substantially wholly fill the space between the conducting part and the casing, the gas permeating the interstices between the insulating particles. Alternatively, the particles may be compacted preferably by mechanical pressure, into one or more masses around the conducting parts, the gas filling the remainder of the space within the casing serving to increase the breakdown voltage of the surface leakage paths. Figs. 1 and 2 show metal-clad switchgear of the draw-out type comprising bus-bar sections X, Y, Z, feeders H and circuit-breaker leads D<SP>1</SP>, D<SP>2</SP>, each in the form of a cable consisting of a conductor enclosed in a metal sheath and separated therefrom by highly compressed mineral insulating powder such as magnesia. The insulation at each cable end is disposed in a gas-tight chamber, which may or may not be packed with powdered insulating material, to which gas under pressure is admitted, the gas filling the and permeating the insulating material of the cable. The chambers for the ends of the cables D<SP>1</SP>, D<SP>2</SP> connected to the circuit-breaker contacts are formed by insulators D<SP>3</SP>, D<SP>4</SP> closed by plugs D<SP>5</SP>, and caps D6 which are secured to the top B<SP>3</SP> of the circuitbreaker tank and wiped to the sheaths of the cables. The chambers at the other ends of these cables and at the ends of bus-bar and feeder cables are formed in a similar manner. The feeder cables H each pass into a gas-tight casing .1 containing a current transformer and thence to a gas-tight dividing box K, the cables leaving the dividing box being connected to the current transformer by a short length of cable J<SP>5</SP> similar in construction to the cables D<SP>1</SP>, D<SP>2</SP> etc. The casing J and the dividing box K are filled with gas under pressure. The stationary portion of the switchgear carries a gas-filled container L which houses a potential transformer, current for the primary winding of which is supplied through cables M<SP>4</SP>, one end of each cable being connected to a feeder cable- H in the current transformer casing J and the other end terminating in a contact M disposed in a gas-filled chamber M<SP>2</SP>. The primary windings of the potential transformer terminate at contacts L<SP>7</SP> adapted to connect with the contacts M. The secondary windings L<SP>2</SP>, Fig. 6, of the potential transformer are wound on a three-limbed core L<SP>1</SP> and are insulated from the primary windings L4 surrounding them by tubes L<SP>3</SP> of agglomerated insulating powder. Similar tubes L<SP>5</SP> surround the primary windings, connections to the contacts L<SP>7</SP> being taken through holes in the tubes. The various gasfilled chambers and casings of the switchgear are interconnected by pipes N<SP>2</SP>-N<SP>14</SP>, gas being supplied to these pipes by a main pipe N<SP>1</SP> connected to a gas cylinder N. The insulation at the cable ends within the gas-filled chambers may be simply formed into a cone, or additional pulverulent insulation E<SP>3</SP>, Fig. 3, may be compressed against the cable end so as to expand the end of the sheath E<SP>1</SP>. Alternatively a bushing E<SP>5</SP>, Fig. 4, of agglomerated pulverulent insulation may be fitted over a projecting portion of the cable insulation E<SP>2</SP> from which the sheath has been removed. Specifications 496,731 and 500,878 are referred to.