Patent GB-190761-A (GB)
Title: Improved devices for balancing the currents in parallel-connected conductors for heavy alternating-currents
IPC: H02H7/26
Filed: 1921-08-30
Abstract: 190,761. Field, A. B., and Metropolitan-Vickers Electrical Co., Ltd. Aug. 30, 1921. Transformers. - The current distribution among a number of parallel-connected conductors forming a composite conductor carrying a large alternating current is equalized or proportioned by introducing compensating balancing voltages mutually induced between the component-conductors, by means of differential transformer devices. The method is applicable to parallel-connected conductors or the sections of a composite conductor forming the windings of transformers and it may be combined with known methods of reducing eddy losses in composite conductors by transposing the components as the conductor passes from slot to slot in a generator or like winding. Figs. 1 and 4 show the application to an alternator coil having one conductor per slot composed of two sections 2, 3, each of which may be laminated and transposed in known manner. These sections are lightly insulated from each other and are connected in parallel at the ends of the winding. Before connection at one end, they are passed through laminated transformer cores 6 and in the case shown, where the section 2 has half the area of the. section 3, the former has twice as many turns around the transformer as the latter to equalize the currents in the two sections. Any difference of volts induced in the two parallel sections by a parasitic or other flux causes a local current in the loop, the flux of which, in turn, generates electromotive forces in the transformer tending to neutralize the current difference in the sections. The. relative current densities in the sections may be controlled by varying the numbers of their turns in the transformer. Fig. 5 shows the use of three transformers 6, 6a, 6b, for a composite conductor having three parallel sections 7, 8, 9 threaded through the, transformers in symmetrical pairs. Alternatively, two of the sections 7, 9, Fig. 6. may be first equalized in a core 6a before paralleling at 10, their resultant current being then equalized at 11 in a second core 6c by two turns of the remaining section 8. The trans. formers may be combined into a single multi-leg unit and instead of having the conductor sections actually passed through them they may have separate windings which are connected to the sections anywhere in their circuits. A part of the magnetic core of a single electrical apparatus may be used instead of the transformers, as shown in Fig. 9, in which the stator winding of a dynamo is star-wound in two parts 12, 13, the respective terminale of which ,are brought out at the two ends of the machine. The two parts are connected by pairs of leads 2a, 3a, 2b, 3b, 2c, 3c of corresponding phases which pass through tunnels 14 in the stator to the machine terminals. Instead of the terminal ends of the windings, the star-point ends may be carried through the tunnels, thereby reducing the risk of a fault to earth in the tunnels. Alternative forms are shown in which two-part stator windings pass through stator tunnels and outside the stator to a star-point and in which leads from all three phases pass through four tunnels. A two-phase stator winding with three balancing tunnels is also shown. The leads in the tunnels may be of concentric or multi-core conductor. Fig. 13 shows a balancing arrangement for a bus-bar made of two parallel sections 20, 21 which, by means of U-shaped members 22, 23, are passed through a laminated compensating transformer 6.