Patent GB-190809844-A (GB)
Title: Improvements in or relating to Automatic Cut Out Apparatus for Electrical Circuits.
Filed: 1908-05-06
Granted: 1909-05-06
Abstract: 9844. Felten & Guilleaume-Lahmeyerwerke Akt.-Ges. May 6, 1907, [date applied for under Section 91 of Patents &c. Act, 1907]. Distributing; switches ; out-outs.-In a protective arrangement for distribution systems, the trip coils of the cutouts are connected in an auxiliary circuit, which is controlled by two relays, one at each end of a line section, and is closed by one of the re'ays when the relative direction of the currents is disturbed. The operating-coils of reverse current relays r<1>, r<2>, Fig. 1, are connected in the lines l, and the permanent magnets m of these relays actuate switches c<1>, c<2> with two sets of contacts in the auxiliary circuit h. Under normal conditions, a current flows in one direction through the section 1, and the magnets m occupy similar positions. If a short circuit occurs along the section l, the current at one end will reverse in direction, and so operats one of the relays r<1>, r<2>, to close the auxiliary circuit through. the batteries b<1>, b<2> and the tripping-coils. Uircuitbreakers e<1>, e<2> at each end of the section are then operated. This action also occurs if the current ceases at one end of the section l. The arrangement can be applied to a three-phase system, by substituting for the relays r<1>, r<2> others which have a current coil and a pressure coil and are operated by a displacement of phase between the two coils. If balancing-machines u, Fig. 3, are used, only one relay is necessary. The two coils m<1>, m<2> are connected on one side of the machines u, as 'shown, and the coil m<3> is connected on the other side of the machines, When the current on one, side reverses, the relay closes the trip-coil circuit, and the circuit-breakers e<1>, e<2> are opened. The necessary connexions for an alternating-current line are shown in Fig. 4. The aotuatihg-coils of the relays are supplied through current transformers s<1> s<2>, &c., and are so connected that the coils m<1>, m<2> are supplied from the transformers s', s<1> respectively, at opposite ends of the line l. Under normal conditions, the current is always in the same direction in each of the transformers, and the relays r<1>, r' are in their ' off' positions. When a short circuit occurs in the section L. the currents at the two ends will be opposed to each other, and will therefore operate the relays to complete the trip-coil circuit. If a line l<1> is connected to take current from the line l, a current transformer s<3> is connected in circuit as shown. The arrangement shown in Fig. 4 may be modified by connecting the coils m<1>, m<2> in series with each other and with the secondaries of two current transformers, one at each end of the line. A modification applied to a three - phase transformer t is shown in Fig. 6. The switch c in the trip-coil circuit is operated by an arm z, controlled by electro-magnets connected to current transformers in the primary and secondary circuits. Normally, the switch c is open, but when a fault occurs, the rotating field of the relay is reversed, and the movement of the arm z closes the switch c. Two relays of the type shown in Fig. 6 may be used on a three-phase system, being placed one at each end of the line, and so arranged that every alternate coil on one relay is connected in series with a coil on the other relay and with transformer windings at each end of the line. Branch lines may also be connected to similar relays through transformers. Separate relays may be used for each end of each phase, as shown in Fig. 8. When a short circuit occurs in the section l, the currents in the electro-magnets n<1>, n<2>, &c. disappear, or change direction relatively to the others, thus reversing the direction of the rotary field and causing the relays to close the trip-coil circuit. The motion of the relay disks may be retarded by permanent magnets p, and may be limited by stoppins. The relays may act on the switch-releasing device through intermediate relays.