Patent GB-347616-A (GB)
Title: Means for and methods of protecting conductors in 4-phase and 2-phase circuits
IPC: H02H3/33
Filed: 1929-12-19
Abstract: 347,616. Protective cut-out arrangements. TAYLOR, A. M., Inkford House, Wythall, near Birmingham. Dec. 19, 1929, Nos. 38879/29, 689/30, 1518,/30, and 26499/30. [Class 38 (v).] Relates to a 4-phase transmission system in which 3-phase current from the generator bus-bars is converted by Scott transformers or the like into high-tension 4-phase current with a neutral and similarly re-converted to 3-phase at the receiving end as described in Specification 317,099, [Class 38 (iv), Electric supply and transmission systems &c.]. The four phases are indicated at AA<1>, BB<1>, CC<1> and DD<1> and the neutral at 0<1>, 01<SP>1>. Protection is effected by means of a pair of current transformers CTa, CT<b> (in two phases AA<1> and BB<1> of opposite polarity) connected for circulating current, the operating windings OC1. OC2 of the tripping relays being connected across the respective transformers. These relays according to the invention are of the non-polarized (or non-directional) type. A similar system employing polarized relays is described in Specification 327,799, [Class 38 (v), Electric switches &c.]. The current transformers are connected together as shown with intervening resistances R1, R2 to increase the potential at the terminals of the transformer in the faulty line. A third current transformer CTo derives current from the neutral and its secondary is connected with the secondaries of the other transformers and in series (or, as shown, in parallel) with two auxiliary operating coils SC1, SC2 on the relays. The whole arrangement described for the sending ends is duplicated at the far ends and is applied also to the transmission lines CC<1>, DD<1>. With a fault at F on the line AA<1> the increased current in CTa causes operation of the relay Q, and the consequent opening of the main switch on the line AA<1>. An increased current appears also in the auxiliary coil SC1 which opposes OC1, but this is inadequate to prevent the operation. With AA<1> out of action and the consequent reversal of the current in the neutral 0, 0<1>, the current in the auxiliary coil SC2 is reversed and instead of aiding the operating coil opposes it and prevents operation of the sound phase BB<1>. At the far end, the circuit-breaker OS<1>a is brought out after OSa, by the auxiliary coil SC<1>, excited by the fault current in the neutral wire, and the relay Q<1>2 in the sound line is held out of action as before. Circuits are provided as in Specification 327,799 (but not shown in the present Figure) whereby it is ensured that when one phase is cut out on fault (for example AA<1>) the phase in quadrature CC<1> is cut out also, the remaining conductors, together with the neutral, thereupon providing the transmission as a threewire, two-phase system (the " Quarter-phase " system of Specification 236,759, [Class 38 (iv, Electric supply and transmission systems &c.]. In a modification (Fig. 2, not shown) auxiliary conductors are used in the manner of pilot wires to ensure that the far-end circuit-breakers come out at once with the near end breakers thereby preventing damage which may arise due to the delay inherent in the sequential action above described. In this form the current transformers may be inserted between the neutral point and the phase winding at each end of the system so as to take care of transformer faults also. The impedance R1' R2 may be replaced by a restraining coil acting on the relays with a force proportional to the current and serving to prevent faulty action on through faults.