Abstract: This invention relates to a sealing composition for a mineral insulated electric cable termination. The sealing composition includes an inert filler such as silica flour, a low vapor pressure organic material such as a polyphenyl ether and an aerosil. This composition has improved slump resistance at high temperatures with little run out and no tendency to crack at 250.degree. C.

Abstract: A traction power supply system in which one, two or three single-phase traction loads are supplied from a 3-phase high voltage system. Balancing of the load in each phase of the high voltage system and reduction of reactive currents in that high voltage system is achieved by simulating any further single-phase load or loads necessary to make the number up to three and providing individual controllable balancing circuits for all of the single phase circuits together with individual harmonic filters designed to include accommodation of the harmonic currents generated by the balancing circuits.

Abstract: A selector mechanism, especially for actuating a switch and capable of selectively operating in two different modes utilizing the same operation of a common actuator, comprises a pair of links each connected at one end to an actuating member and carrying at the other end a projection engaging in a respective slot in an operating member, each of which slots has a recess into which the respective projection rests in a neutral position of the operating member, and a selector device operable to cause a surface thereof to engage one or other of the projections and retain it within the respective recess, so as to cause movement of the respective link to be transmitted to the operating member and move it in a direction determined by the link, while leaving the projection associated with the other link free to move along its respective slot.

Abstract: A permanent split-phase capacitor induction motor having a capacitor (7) connected in series with an auxiliary winding (5) via an electronic switch (9) which is operated by a control circuit (11, 13) so as to obtain a higher starting torque than if the switch were permanently closed.The control circuit suitably comprises an integrating (21 to 31) responsive to the voltage appearing across the switch (9) and trigger circuit (19) which closes the switch when the output of the integrating circuit exceeds a threshold value, the integrating circuit resetting when the switch closes, and the switch reopening at the next current zero.

Abstract: A D.C. excited rotor winding arrangement for a dynamoelectric machine comprises at least one closed loop (1,2,3) of three or more series-connected winding sections (10,11,12,13,16,17,18,19,20,21,22,23) with at least three current-supply terminals (ABCD) at their interconnections. At least one pair of adjacent winding sections (10,13; 11,12) generate opposite magnetic poles when fed in parallel with current from their common supply terminal (such terminals are designated "odd", as opposed to "even" terminals which are each associated with two poles of the same sense) and the pole number is varied by switching the current supply from "odd" to "even" terminals or vice versa. Preferably the winding arrangement comprises a plurality of series-connected closed loops (1) of four winding sections interconnected at two odd (B5, D5) and two even (A5, C5) terminals. Preferably the winding arrangement is fed with current from one of a plurality of rotating rectifiers (4,6,7) according to the pole number required.

Abstract: A D.C. current transformer (used for measuring D.C.) comprising a common primary winding and a pair of saturable magnetic cores on which respective secondary windings are wound and connected in opposite series in series to a source of alternating e.m.f., is provided with phase-sensitive device for determining the sense of the unknown D.C. in the primary winding. The phase sensitive device periodically senses and integrates the voltage (whose waveform is the -45.degree. to +45.degree. portion of a sine wave) across at least one of the secondary windings. The sense of the integrated waveform depends on whether said voltage is initially positive or negative, and is determined by the sense of the unknown D.C. in the primary winding. Preferably said voltage is sensed at each half cycle of said alternating e.m.f.

Abstract: A multi-loop control system for convertors of the kind used in h.v.d.c. transmission and industrial applications. The invention consists in a control circuit which effects transfer between two or more control loops, e.g. a constant-current loop and a constant .alpha. loop, in a smooth and precise manner, without extra smoothing lags, even in the presence of ripple in the controlled quantities.

Abstract: A multi-phase inverter comprising a bridged array of thyristors periodically fired in sequence by a source of firing pulses has a circuit arrangement for controlling each extinction angle (.gamma.) of the thyristors individually. Said circuit arrangement comprises an adder for summing .gamma. signals and adder for differencing said sums to generate an error signal and, said error signal being applied to said source of firing pulses at appropriate phase angles to appropriate thyristors so as to tend to equalize said sums, the number of pairs of differenced sums being equal to the number of thyristors in the array. Preferably each error signal acts as a constant multiplier of a correction signal which is a harmonic of the A.C. output frequency of the inverter. The arrangement improves the efficiency by enabling each .gamma. to be minimized individually without risk of commutation failure.

Abstract: A self-starting single phase induction motor wherein the required quasi-second phase for starting is provided by controlling the phase of the voltage applied to one stator winding (91) of the motor relative to the phase of the voltage applied to another stator winding (87) of the motor by means of an electronic switching arrangement (93) and an associated control circuit (95).

Abstract: In a mineral insulated electric cable the powdered insulating material is impregnated with a quantity of a hydrophobic material, for example a silicone, which has been introduced into the powder in liquid form. The added hydrophobic material serves as a barrier against the ingress of moisture, and liquid dimethylpolysiloxane has been found particularly effective, the pressure of even a small quantity of this preventing any significant degree of moisture penetration into the cable.

Abstract: A polyphase static reactive compensator comprising a main saturated reactor (SR1) connected in series with a number of smaller saturated reactors (SR2-4) of graded voltage rating. The smaller reactors are shunted by respective thyristor switches (TV2-TV4) so that selected combinations of reactors can be obtained to provide control of the overall operating voltage. The slope of the overall characteristic can be controlled by switching through successive reactor combinations. Further refinement of the overall characteristic can be obtained by phase control of the smallest reactor (SR4) thyristor switches (TV3) or, in an alternative form of the invention, by the use of a single reactor (SR1) having a primary winding, a closed mesh secondary winding (19) and a phase-controlled auxiliary reactor (AR, ACR) constituting a load on the closed mesh winding. The two forms of the invention may be combined in one equipment.

Abstract: A dynamic braking system for a D.C. traction motor which is driven from an asymmetric bridge rectifier having freewheel diodes to permit circulation of motor generated current. The system employs field reversal to ensure a generated (braking) current direction the same as for motoring and this facility permits injection current braking by phasing up the supply bridges when the motor is braking with full excitation. The brake resistance is in two parts one of which forms an uncontrolled arm of the bridge, this part of the resistance being shunted by a thyristor. Part way through an injection braking process the supply bridge is phased down, the resistance bridge arm shorted out and the supply bridge phased up again. Lower losses and greater braking efficiency result.

Abstract: In the manufacture of a glass optical fibre preform by forming a coating of oxide material on the interior surface of a substrate tube, in particular a coating of silica and one or more dopant oxides on a vitreous silica tube, by causing a reaction to take place between oxygen and the vapor or vapors of one or more compounds such as halides, the reactant vapors are introduced into a perforated tube supported coaxially within the heated substrate tube and pass through the perforations into the annular space between the perforated and substrate tubes, while oxygen, and optionally an additional carrier gas, is passed either into the perforated tube or directly into said space. The coating-forming reaction is caused to take place in said space by generating energy in the space, in the form of a plasma, or a laser beam, and/or heat, and/or gas combustion, whereby the coating is formed simultaneously on the whole heated length of the substrate tube.

Abstract: A length of filament, such as wire or optical fiber, is loosely coiled on a flat carrier, in the form of a figure of eight coil, the lobes of which are laid respectively in clockwise and anticlockwise directions, by feeding the filament downwards through a gimbal mounted guide member attached to reciprocating means whereby the guide member is oscillated about two horizontal axes at right angles, corresponding to the transverse and longitudinal axes of the figure of eight coil produced. The guide member preferably incorporates a compressed air injection gun, to assist in maintaining the downward travel of the filament at a desired constant speed, the relationship between the filament travel speed and the oscillation frequencies being controlled to produce a figure of eight coil of a desired size.

Abstract: A synchronization arrangement for delaying excitation of the field winding (5) of a brushless synchronous motor until the motor rotor has run up approximately to synchronous speed in which the appropriate moment for applying the field excitation is determined by monitoring two signals respectively representative of the currents in two rectifying devices (11, 15) separately connected, oppositely poled, across the motor field winding.

Abstract: In apparatus for the manufacture of mineral insulated cable by a continuous process in which the tubular sheath is formed by bending and seam welding travelling metal strip, and insulating powder is fed through a powder delivery tube into the sheath while the latter is travelling vertically downwards, the conductor wires are introduced into the sheath down the outside of the powder delivery tube through guide means which may include, for a wire adjacent to the seam, a tube having an aperture in its wall adjacent to the weld area. Excess heat is removed from the weld area by either a wire or an air gap adjacent to the weld. When the sheath is formed of an oxidizable metal such as copper, means are provided for delivering a continuous stream of rare gas to the underside of the weld area. Various configurations of the powder/wire delivery system are described.

Abstract: A continuous elongate strength member for reinforcing an optical fibre cable consists of an assembly of aromatic polyamide filaments impregnated with a synthetic resin, in which the filaments are individually coated with the resin, and the filaments of at least an outer layer of the assembly are helically stranded. The impregnation is carried out by separating the filaments and immersing them in a low viscosity dispersion of the resin in a liquid medium; the filaments are then stranded, and the resin is cured. Apparatus for manufacturing the strength member and various forms of cable incorporating one or more strength members, are described.

Abstract: A stand for supporting and rotating shafts in fractions of a revolution, for example for assembling armature slot conductors. Conventional arrangements use multiple rollers conforming to the shaft, one of which is motorized by way of gearing. This tends to be cumbersome, expensive and complex. According to this invention a shaft is supported on the walls of a channel between roller stops. A lever within the channel is jacked up to tilt the shaft against one roller and the lever is pushed longitudinally, allowing the shaft to remain in position but rolled around against the stop by an amount corresponding to the linear lever movement. The lever is then lowered and retracted.

Abstract: An actuating mechanism for a vacuum interrupter incorporates a pivotable bell crank mechanism and a displacement structure for imparting movement of the bell crank mechanism to a coupling structure which is connectable to a contact stem carrying the movable contact of the interrupter for moving the contact into and out of engagement with another contact of the interrupter. After movement of the coupling structure for a sufficient distance in a direction which causes closure of the contacts the displacement structure is capable of being moved for a further distance to disengage it from a cooperating surface of the coupling structure. On the return movement the displacement structure is traveling at high velocity when it re-engages the cooperating surface of the coupling structure which produces a rapid acceleration of the latter and hence, in use, of the movable contact of the interrupter to the open position.

Abstract: A saturated reactor adapted for direct connection to an EHV line and thus constituting a combined reactor and transformer. A problem arises in that earthing of the primary winding star point would normally short circuit the 3rd harmonic. The invention overcomes this by series connection of primary coils coupled to three limbs whose fluxes are spaced at 40.degree.. 3rd harmonic voltages therefore cancel in the series primary windings. The series primary windings may be obtained as separate coils on individual limbs or as one coil (per phase) embracing three limbs. Elimination of the 3rd harmonic enables the ninth harmonic to be short circuited in a mesh winding.