Patent GB-191404742-A (GB)
Title: Improvements in Electric Furnaces.
Inventor: DIXON JOSEPH LAWTON
IPC: F27D11/00
Filed: 1914-02-24
Granted: 1915-01-21
Abstract: 4742. Dixon, J. L. Feb. 24. [Cognate Applications, 8513/14, 16,263/14, and 17,909/14.] Electrode furnaces.-Circuit connexions are arranged so that current through hearth or analogous electrodes can be regulated without unbalancing a polyphase supply circuit. This regulation may be effected by adjusting the upper electrodes, one or more of which may even be rendered inoperative; by reversing one or more phases, or otherwise varying the phase relationships in the electrode circuits; and by transforming different phases to different and variable pressures. The last method is applicable to a simple three-phase furnace with three star-connected upper electrodes and a single lower one connected to the common point of the star; further regulation is obtainable by phase reversal. Fig. 6 shows a furnace supplied with two-phase current transformed from threephase by two transformers, the secondaries of which are connected at their ends to four upper electrodes, and at one or both of their midpoints to one hearth electrode; the current through this may be regulated by adjusting the upper electrodes. A similar arrangement may be used with six upper electrodes supplied with three-phase current by three transformers having their primaries either star or mesh connected. To allow of larger currents through the bottom electrode, one or more of the transformers in the two last arrangements may be each replaced by two, Fig. 26, having their primary windings connected in parallel through switches k, l, m, n such that one or both is capable of reversal in phase; each secondary of the pair is connected at one end to an upper electrode C<1>, C<2> and at the other to a common bottom electrode. The connexions of the midpoints of the other transformers to the bottom electrode may then be omitted. In a threephase furnace, a further modification consists, as shown, in linking the secondaries star-wise and connecting each outer terminal of the single transformers a, b to two electrodes. Fig. 12 shows a system allowing variation of phase relationships. Three-phase current is transformed to two-phase by two pairs of transformers a ... d, each pair being connected on the three-wire system to two upper electrodes and a common bottom one. With a switch k closed, the primary circuits of the second pair c, d are similar to those of the first pair, but inverted, so that the secondary currents of all four are four-phase and symmetrical. With the switch k open and a switch l closed, the connexions of the second pair of transformers are displaced with regard to the first, as shown diagrammatically in Fig. 16. In addition, with either switch closed, one or more single transformers may be inverted in phase. An analogous arrangement for six upper electrodes comprises three similar pairs of Scott transformers; denoting the supply mains by 1, 2, 3, the connexions of similar points of the pairs are respectively 1, 2, 3; 2, 3, 1; and, according to the positions of switches, either 3, 1, 2 or 1, 2, 3, the undivided transformer of this pair having its connexions inverted with regard to the supply main and the other transformer in the latter case, while in the former case the electrode currents are balanced. Another system for six electrodes and two pairs of Scott transformers is shown in Fig. 23, one phase being reversible by switches k, l. Either of two of the transformers a, b may be replaced by a pair. A furnace with any even number of upper electrodes may be fed from the same number of transformers supplying two-phase currents in pairs; one or more pairs may be replaced by single larger transformers. If the number of upper electrodes is odd, some may be supplied with two-phase and others with three-phase current. A three-phase furnace with six electrodes may be fed by six transformers arranged in two sets which have their primaries respectively star-connected and mesh-connected. The single hearth electrode may be replaced by two or three separate ones; for instance one hearth electrode may be connected to terminals of the transformers a, c shown in Fig. 12, and another to terminals of the transformers b, d; or a separate hearth electrode may be connected to the mid-point of each transformer secondary in Fig. 6. A hearth electrode may be of carbon, graphite, or metal, or may consist of the hearth itself, connexion being made to the metal casing. An upper electrode may supplement or replace a hearth electrode.