Patent GB-283185-A (GB)
Title: An improved device for feeding low tension measuring instruments from high tension systems
IPC: H01F38/26
Filed: 1928-01-06
Abstract: 283,185. Tr³b, Tauber, & Co., and Imhof, A. Jan. 6, 1927, [Convention date]. Current and pressure meters; power meters; meters with alternating-current transformers; wire resistances, cored; resistances with specially related inductance; inductances. - Low-tension measuring-instruments are fed from high-tension systems by connecting between the high-tension conductor and earth a series of choking coils, arranged on separate iron cores and wound with wire of high specific resistance in series with the earthed primary winding of a current transformer, to the secondary winding of which the low-tension instrument is connected. In the construction shown in Fig. 1, a number of choking coils are wound with very fine wire having a high specific resistance and a low temperature coefficient. The ohmic resistance is preferably at least 50 per cent of the inductive resistance when the phase displacement is less than 60 degrees. These choking coils are mounted on iron cores 1 - - 4 supported vertically above a current transformer 5. An insulating casing 6 is fitted at its lower end into a base 9 and is closed at its upper end by a cap 8. The casing is filled with oil or with a. compound which can be cast or run therein. For measuring the voltage to earth the apparatus is connected between the line and earth, a voltmeter being connected to the secondary winding of the transformer. Two current transformers may be connected in series to give an increased secondary output. For measuring the: voltage between the lines, each line wire is connected to earth through a resistance and transformer primary winding, the secondary windings being connected in opposition in series with a voltmeter. A second transformer or secondary winding may be provided for each line to read the voltage to earth. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the following subject-matter :-The pressure coils of wattmeters and energy meters may be similarly energized. The electrical mid-point of each group of coils is electrically connected to the iron core. In a modification shown in Fig. 1 (Cancelled), the chohin"- coils 1 are arranged on insulating spacing tubes 2, a number of the coils 1 forming a constructive unit between insulating discs 4, so that each group can be protected against corona effects by a metallic screen. A. cylindrical casing 6 of insulating material is filled for cooling and insulating with transformer oil, or with a compound which can be poured and which will afterwards solidify. Tubes 3, which may be of metal to screen the coils against corona effects, have rows of holes at the top and bottom to promote oil circulation. At the lower end is a-current transformer 7 carried by a metal base 8 making an oil-tight joint with the casing 6. Fixed to the transformer 7 by a tubular spigot is a central insulating tube 5. A float 11 and indicator 12 form an oil-level indicator. The upper end of the casing 6 is closed by a cap 9 carrying the high tension terminal 10. When used in outdoor stations the insulating cylinder is either made of porcelain or is covered with a porcelain mantle fitted with rain shields. This subject-matter does not appear in the Specification as accepted.