Patent GB-646994-A (GB)
Title: Improvements in or relating to mechanically driven mercury rectifiers and similar devices
IPC: H02M1/30
Filed: 1947-11-21
Abstract: 646,994. Commutator switching arrangements. SOC. ANON. DES ATELIERS DE SECHERON. Nov. 21, 1947, Nos. 30975 and 30976. Convention dates, Nov. 21, 1946 and Oct. 30, 1947. [Class 38 (ii)] [Also in Group XXXVII] A rectifier or frequencychanger comprises an enclosed container of conducting-liquid such as mercury whirled around an axis and so mounted that the mercury also moves relatively to the container, by which latter movement the circuit is continuously made and broken between parts of the mercury. The centrifugal force acting on the mercury due to the whirling is considerably greater than the gravitational force acting on it and makes possible the necessary rapid movement of the mercury relatively to the container. A cylindrical cage 4 rotated by a vertical shaft 2 at a speed equal to the A.C. frequency has mercury containers 12, 12<SP>1</SP> secured to spindles 7, 8 rotatably supported in the ends 1, 3 of the cage. Armatures 18, 18<SP>1</SP> on the containers co-operate with a fixed semicircular electromagnet 19 whereby the containers are pivoted clockwise on the spindles 7, 8 against the action of torsion springs 22, and are held in that position throughout every half-revolution of the cage. The extreme positions of the containers are determined by stops, not shown. During that half of a revolution in which an armature as 18 is not influenced by the magnet 19, the circuit between cavities 13, 14 of the container is completed by the mercury 15 which is driven centrifugally against the outer wall of the container, whereas during the other half of the revolution when the armature is attracted by the magnet, the mercury, as shown in container 12<SP>1</SP>, separates; the cavities 131, 141, however, remain filled. Connection to the electrodes 16, 17, 16<SP>1</SP>, 17<SP>1</SP> is made through slip rings, not shown. The spindles 7, 8 may oscillate instead in a horizontal plane (Figs. 3, 4, not shown). More than a pair of containers connected in parallel may be used so as to proportionately reduce the speed of the cage. The centrifugal force acting on the mercury hinders its vaporization and also causes a clean break to be made at a specific spot in the containers thereby permitting accurate control of the timing of the commutation when employing a plurality of containers. In Fig. 5, a drum 33 rotated at the A.C. frequency about a stationary shaft 34 and pinion 35, pivotally supports shafts 37, 37<SP>1</SP> having pinions 36, 361 meshing with the similar pinion 35. Annular mercury containers 39, 39<SP>1</SP> fixed to the shafts 37, 371 have a pair of electrode cavities 40, 40<SP>1</SP> (only one shown) and thus by making two revolutions on the shafts 37, 371 for each revolution of the drum 33 each container makes and breaks the circuit once. One electrode of each container is earthed to the drum, whilst the current from the other electrode 40 or 40<SP>1</SP> is lead away through frictional contacts and brushes 44, 45, &c. In a modification (Fig. 6, not shown), the annular containers are replaced by tubes mounted coaxially in housings in the shafts 37, 371 and the circuit is made and broken between a pair of axially-aligned electrode cavities in the tubes. In another modification of Fig. 5 the shaft 34 is driven in the same direction as, and at twice the speed of, the drum 33, whereby the shafts 37, 37<SP>1</SP> do not rotate relatively to their own axes and the connections from the containers 39, 39<SP>1</SP> are lead away through flexibly supported tubes, thus eliminating the frictional contacts and brushes (Fig. 7, not shown). In a 3-phase rectifier, Figs. 8, 9, six mercury containers 67, spaced 60 degrees apart, are pivoted on pins 86 in a drum 68 rotated on shafts 71, 72 at the A.C. frequency. Slotted arms 84 on the containers embrace the offset portion 79 of a shaft 80, 81 freely supported within the drum shafts 71, 72 whereby an angular displacement α varying sinusoidally with the angle of rotation # is imparted to the containers to make and break the circuit, the arrangement being such that the circuit is made when the ratio dα/d# is high so as to prevent evaporation of the mercury. The angular position of the offset portion 79 is adjustable by moving an arm 80a, fixed to the shaft 80, along an arcuate guideway in a member 80c. Slip rings 73, 74 serve for the A.C. supply and the rectified current, respectively. Since the moments of making and breaking the circuit in the containers must both be controllable within fine limits, the containers may be duplicated and work together in pairs connected in parallel, and the periods of operation of the containers of each pair are such that they overlap, whereby only the closing moment of one container and the opening moment of the other container have to be accurately adjusted. In Fig. 14, a shaft 106 rotates a plate 105 carrying containers 100, 100<SP>1</SP> pivoted about horizontal axes 104, 104<SP>1</SP> and located in tubes 146 having ball-ended arms 147 co-operating with recesses 144 in a plate 131 rotated by upstanding pins 132 on the plate 105. A shaft 120 rotatably supported in the shaft 106 and in a fixed plate 117, carries a spherical seating 124 slidably engaging rings 125, 126 whereby the bearing forming by parts 127-131 can oscillate through an angle #; hence for each revolution of the shaft 106, the containers 100, 1001 oscillate twice through an angle twice α to make and break the circuit. The angles α, # may be varied by a lever 133 connected to the bearing 127-131 and having a slot 134 engaged by a pin 135 on a screwed rod 136 which is longitudinally movable by a nut 139 in arm 142 fixed to the shaft 120; alternatively, the'shaft 120 is moved axially by a screw 148 fixed to the shaft end by a ring 150 and cooperating with a fixed bush 149. The phase of the moments of making and breaking is adjustable by rotating a toothed segment 152 secured to the shaft 120 and moved by a pinion 153 having an adjusting head. In Fig. 15, a drum 154 rotated by a shaft 152 carries mercury containers 166, 166<SP>1</SP> pivoted on axes 167, 167<SP>1</SP> and having ball-ended arms 165, 165<SP>1</SP> engaging a peripheral groove 163 in a plate 162. The plate is locked in the desired inclination on a spherical body 160 fixed on a shaft 156 pivoted .in the base 151 of the drum, the shaft 156 being driven by a motor 158, 159 having its casing 155 supported by the top plate 153. For each rotation of the shaft 156 relative to shaft 152 each container makes one complete oscillation, the frequency of oscillation being adjustable by varying the speed of motor 158, 159, whilst the rotational speed of the containers is adjustable by varying the speed of shaft 152. In Fig. 16, a circular plate 168 pivotally connected to arms 181, 181<SP>1</SP> of containers 174, 174<SP>1</SP> mounted on a plate 172 driven by a shaft 172<SP>1</SP>, is supported by a universal joint 170 on a shaft 171 on the plate 172 whereby the plate 168 rotates at the speed of shaft 172<SP>1</SP>, and oscillation of the plate is produced by three 120 degrees spaced electromagnets 175, 176 (only two shown) supplied with 3-phase current so as to produce a rotating field and co-operating with armatures 177 on the plate underside. In this arrangement, the frequency of making and breaking the circuit within the containers 174, 174<SP>1</SP> depends solely upon the supply frequency. Springs 180 compressed between tubular members 178, 179 produce a return force on the plate 168. Alternatively (Figs. 17, 18, not shown), six containers may be mounted on the plate 168 itself. In Fig. 19, a shaft 192 rotates a drum 193 and, by means of a universal joint 202, a plate 200 carrying mercury containers 201. A shaft 199 on the plate 200 is received in a bearing 198 located in an oblique eccentric hole 197 in an element 196 rotatable by the shaft 195 of a motor 194 supported by the drum 193. If shaft 192 is rotated at twice'the speed of shaft 195, any point on the plate 200 describes the double ellipse 203, Fig. 20, the dotted circle 202<SP>1</SP> representing movement of the point when motor 194 is not driven and the shaft 192 rotated, and the curve 204 representing movement of the point when shaft 192 is stationary and the motor 194 driven. This compound movement of the plate 200 due to relative rotation of the shafts 192, 195 causes the circuit to be made and broken in the containers 201. For satisfactory operation, shaft 192 is rotated much faster than shaft 195. In an alternative construction (Fig. 21, not shown), each container is independently and non- rotatably mounted on a driven cranked shaft supported in diametrically-opposite bearings in the periphery of a rotatable plate. The containers may be fitted with electromagnet blow-out devices (Figs. 22, 23, not shown) comprising a horseshoe magnet, the air-gap of which embraces that part of the container where the breaking and making of the circuit occurs. In Fig. 24 (not shown), a container has a pivoted soft-iron casing and is surrounded by a coil supplied with alternating current. Permanent or electromagnets are positioned adjacent each end of the soft-iron casing whereby the container oscillates at the frequency of the current in the coil. Alternatively, the casing may be polarized and a pair of U-shape A.C. magnets arranged along the axis of the casing cause oscillation of the latter (Fig. 26, not shown). Fig. 28 shows an evacuated metallic container comprising a steel tube 242 to which are welded ends 243, 244 and insulators 250, 251, the latter enclosing metal sleeves 254, 255 surrounding the conductors 248, 249. As the container is oscillated about the axis 256, the mercury reaches the position denoted by line 261 and the circuit between the conductors 248, 249 is broken; in practice, however, the container is oscillated further so that the mercury finally assumes the position denoted by line 260. The. container