Patent GB-679468-A (GB)
Title: Improvements in or relating to restoration and maintenance of conductivity in electrical systems
IPC: H02H7/00
Filed: 1947-12-15
Abstract: 679,468. Electric couplings; increasing conductivity. SHERMAN, R. Dec. 15, 1947 [Dec. 31, 1946; Dec. 31, 1946], Nos. 32985/47 and 32986/47. Class 38 (i). [Also in Group XXXVII] A system for maintaining conductivity between normally bodily contacting elements of an electrical circuit, comprises means for applying across the elements a conductivity restoring voltage or impulses thereof exceeding the voltage which normally exists across the surfaces of the elements to rupture any non- conducting layer which may have formed between the elements whilst preventing the flow of current from the restoring voltage through parts of the circuit which might be adversely affected thereby. In Fig. 3, a D.C. conductivity restoring potential derived from a battery 566 is applied to the circuit of a voltmeter 562 measuring the voltage drop between the electrode 3 and its holder 2 of an A.C. furnace whilst the measuring circuit is in use. In this example, a choke 573 prevents the indication of the voltmeter 562 from being affected by the shunt circuit formed by the " restoring circuit " and a rectifier 564 ensures that the direct current from the restoring circuit flows through the connections 6, 7 on the electrode and holder and not through the voltmeter. Modifications of this arrangement are illustrated in Figs. 4, 5 and 6 (not shown) in which a high-frequency A.C. restoring potential is applied to the connections of a voltmeter at the junction of normal frequency A.C. bus-bars, Fig. 4, an A.C. restoring potential is applied to the connections of an ammeter at a D.C. shunt, Fig. 5 (not shown), and a D.C. restoring potential of opposite polarity is applied to the connections of a voltmeter at the junction of D.C. bus-bars. In a further arrangement, Fig. 8, an A.C. measuring circuit is used to check the conductivity of the junction of D.C. bus-bars and a D.C. restoring circuit is used. The voltmeter 1909 measures the voltage drop across the junction of the bus-bars 401, 402 created by the alternating current from the transformer 404. The D.C. restoring potential from the battery 1911 is applied across the voltmeter connections 1901, 1927 on the bus-bars. Either of, or both of, a transformer 1904 and a rectifier 1903 isolate the voltmeter 1909 from the D.C. working and the D.C. restoring currents. A choke 1919 prevents the restoring circuit from shunting the A.C. measuring current and a rectifier 1918 may be provided to protect the restoring circuit from the effects of an unduly high voltage drop at the junction of the bus-bars derived from the D.C. working current. Modifications of this arrangement are also described in which an A.C. restoring circuit is used in conjunction with the D.C. measuring circuit for the junction of A.C. bus-bars, Fig. 7 (not shown), and a highfrequency restoring circuit is used in conjunction with the low-frequency measuring circuit for the junction of high-frequency bus-bars, Fig. 9 (not shown). Figs. 1 and 2 (not shown) illustrate arrangements. in which multi-position controllers are used to apply the restoring potential to various parts of measuring circuits whilst open circuiting the measuring instrument to protect it from damage by the restoring potential. In any of the above arrangements, the restoration of conductivity by the restoring voltage may be facilitated by mechanical means moving one contacting element with respect to the cooperating element, and Fig. 10 (not shown) illustrates an arrangement in which a motor with suitable gearing causes one element to make short turns in alternate directions, whilst Fig. 11 (not shown) illustrates an arrangement in which one element is reciprocated with respect to the other. Specification 654,287 is referred to. The Specification as open to inspection under Sect. 91 includes the two Figures of Specification 654,287. It also describes and illustrates an arrangement in which a D.C. restoring circuit is used for the connections of the shunt field of a self-excited D.C. generator, the restoring circuit also serving as a means for initially exciting the generator in the event of insufficient residual magnetism being present. In a further arrangement described and illustrated, a lamp and a switch are connected in parallel with a voltmeter, the lamp, when switched on, serving to increase the current through the connections for the voltmeter. This subject-matter does not appear in the Specification as accepted and printed.