Patent GB-396759-A (GB)
Title: Improvements in electric power transmission
IPC: H02J3/04
Filed: 1931-11-11
Abstract: 396,759. Transmission line arrangements; protective cutout systems. ECONOMIC TRANSMISSIONS, Ltd., Lancaster House, Newhall Street, Birming- ham, and TAYLOR, A. M., Inkford House, Wythall, near Birmingham. Nov. 11, 1931, Nos. 31204/31, 32342/31, 35239/31, 5323/32, 9479/32, and 15045/32. [Class 38 (iv).] Systems depending upon static transformers.- A 3 - phase/4 - phase/3 - phase overhead line transmission system in which the 4-phase high tension current is carried by at least four conductors and a ground wire, includes protective arrangements incorporating a "balanced beam " relay whereby, on a fault occurring on a line, that line and the line carrying the " quarterphase " associated with it are disconnected and earthed, the system then operating as a 3- phase/2-phase 3 wire/3-phase system. If a spare pair of conductors is available they may replace the broken down conductor and associated line. At the generating station the system comprises two 3-phase/2-phase (i.e. " quarter-phase ") step up transformers the two " quarter-phase " systems being of opposite phase with respect to each other and the neutral points O of each transformer secondary 1, 2 ; 3, 4 being connected together the windings 1, 2 forming one " quarter-phase " system and 3, 4 the other. At the substation similar transformers change the current to 3-phase low tension current and the neutral points O, O<1> at the main and sub-stations may be directly connected together by a ground wire G which may be earthed directly or through a spark gap 40 in parallel with a switch 41. Each line is provided with isolating switches such as 5, 6, 33, 36 opened by trip relays such as 7, 8 energized from a battery such as 17, 45, on the operation of balanced beam relays 11, one per " quarter-phase " at each end of the line. The relays 11 are balanced by quadrature currents from two current transformers such as 9, 10, 31, 32 on each of the two lines in the " quarter-phase " system. An additional conract such as 27 or a push switch such as 26 operates relays such as 24, 28 at each end of each line to connect the line to neutral when it has been disconnected from the supply. Overload current transformers such as 18, 19, 35, 43 are also provided at each end of each line. Assuming a fault at F on a line B, the armature 13 A of relay 11 is pulled down and energizes the coil 8 to open the switch 6. This de-energizes the line B and the relay 11 is oscillated in the opposite direction. This reverse operation is delayed for about 2 seconds to allow the substation relays to operate but eventually opens the switch 5. During the interval the substation relay is tilted to isolate the lines A, B. The earthing relays 24, 28 are also operated to connect both lines to neutral. The reverse movement of the relay 11 may be delayed by an auxiliary contact which energizes a magnet through a meter type relay to hold down the lever arm 11 for the requisite time. Opening of any one of the switches 36, 33 at the substation end of the system energizes a coil 42 to connect the ground wire directly to the substation neutral O<1>. To prevent relays on the sound " quarter-phase " system from being operated the battery 45 may be used to lock these relays at both ends of the line. In Figs. 4 to 7 (not shown) arrangements of the conductors on towers and methods of conversion of existing 3-phase lines to the present system are shown. Lightning-protection arrangements.-On the approach of a thunderstorm .the conductors of one " quarter-phase," e.g. A. and B, may be isolated from the line and connected to earth and vice versa at the masts by trip switches energized from the substation, ground wires being used for the transmission of the energizing current. Where one ground wire is available the opening and closing relays have different speeds of operation but with two ground wires one is used for the earthing operation and the other for the reverse operation. The relays are energized from current transformers on the ground wires. The following arrangements may be used for different line systems. (1) Eight conductors on two parallel lines of towers. The four outermost conductors constitute the conductors A .. D of the system in Fig. 1, A and B being the upper outers and C and D the lower outers. The two lower inner conductors are connected through isolating and reversing switches to a spare 2-phase transformer energized in phase with that con- ,nected to conductors A, B or through switches to earth. The upper inner conductors are connected through earthing switches to earth or may alternatively be connected to another spare 2-phase transformer. When lightning is threatened the two upper inner conductors are earthed and the lower inner conductors are connected to the spare transformer so that on breakdown of either A or B, they can take up the load, A and B being now earthed. (2) Six conductors on two parallel lines of towers. In one arrangement, Fig. 9, A and B form the upper outers and C and D the lower outers. S1 and S2 are spares and may be connected to a spare 2-phase transformer or earthed. In another arrangement A and B are interchanged in position with S1, S2, Fig. 9. The conductors are in all cases arranged so that maximum protection from lightning is obtained, faulty earthed conductors and stand-by earthed conductors acting as shields for sound conductors, and in the extreme case, the system functioning as an emergency 2-phase three-wire system. . Lodgment of ice and snow on conductors is prevented by transmitting all the load through one quarter-phase only and connecting the other two conductors at the generating end to a 2-phase booster transformer the other end of the conductors being earthed and the booster neutral being connected to the neutral of the working transformer so as to heat up the conductors, Fig. 11 (not shown). A similar booster transformer may be connected at the substation end of the system but here a variable reactance is provided on the 3-phase side to vary the voltage of the booster transformer. When light the whole load may be supplied through booster transformers. Interference with telephone lines is prevented by the provision of short-circuited spark gaps at the masts connecting the ground wires to earth through relay windings which open the short circuit on the occurrence of earth current due to a fault. A consumer supplied from the " through " line, Fig. 13, is provided with two 2-phase to 3-phase transformers 1, 2, the connection between each line and the transformer winding being made through a no-volts release circuit breaker. On the occurrence of fault in one " quarter-phase " system, that system is disconnected and supply is continued through one of the 2-phase to 3-phase transformers. The output may be either 2-phase or 3-phase. Specifications 317,099, 337,022, [both in Class 38 (iv), Electric supply and transmission systems &c.], and 346,265 are referred to.