Patent GB-364021-A (GB)
Title: Improvements in or relating to electrical power transmission systems
IPC: H02H7/08
Filed: 1930-09-25
Abstract: 364,021. Protective cut-out arrangements; automatic circuit breakers. WESTINGHOUSE ELECTRIC & MANUFACTURING CO., East Pittsburg, U.S.A.- (Assignees of Evans, R. D. ; 1125, Milton Street, Swissvale, Pennsylvania, Fortescue, C. Le G. ; 1013, Herberton Avenue, Pittsburg, Crichton, L. N. ; 61, South Munn Avenue, East Orange, New Jersey, MacNeill, J. B. ; 1359, Marlboro Avenue, Wilkinsburg, Pennsylvania, Griscom, S. B. ; 930, Milton Street, and Wagner, C. F. ; 1303, Macon Street, both in Swissvale, Pennsylvania, U.S.A.) Sept. 25, 1930, No. 28721. Convention date, Oct. 30, 1929. [Class 38 (v).] In the protection of super-power, extra-hightension polyphase transmission systems of complex form involving parallel connected long distance transmission lines of considerable reactance, very high-speed circuit-breakers (and high-speed relay systems for operating the circuit-breakers) are used for selectively opening a faulty section (and that only) at both ends simultaneously in the event of a fault within 7 to 15 cycles of the commencement of a fault (on a 60 cycle circuit). This time of action is so small that none of the numerous parallel - connected and synchronously - running generators connected on the system falls out of step. The quick-response system constituting the invention may be supplemented by the known quick response excitation system whereby a condition of artificial stability may be set up by changing the excitation voltages at a high rate, quicker than the rate at which the machines drift out of step. It is stated that, in order to meet the requirements of a normal transmission system of the kind to which the invention relates, the fault must be cleared in a time less than approximately a quarter of a second and this will enable the system to deal successfully with a double single-phase fault and with a complete three-phase fault and will enable a greater load to be carried by the line without danger of instability on fault. The protective lay-out is shown in Fig. 4 for one end only of one (23a) of two parallel connected transmission lines extending from the bus-bars 181, 191 of one generating station. The transmission line shown forms one half of a section of a complex system which includes twelve synchronouslyrunning generators electrically connected on to the system through step-up transformers as described with reference to Fig. 1 (not shown). The necessary speeds of action are based on experimental data which is furnished in the form of curves. In Fig. 4 the protection is effected by two sets of instantaneously-acting impedance-measuring relays 50a, 50b, 50c and 50A, 50B, 50C for interphase faults and faults to earth, respectively, connected through current transformers 60 and potential transformers 61. The primaries of the potential transformers are connected with the line through bushing-type condenser insulators 62. The instantaneouslyacting relays are set to a predetermined minimum for the section ; they operate within one cycle of the commencement of the fault and, in order to avoid incorrect operation due to the asymmetrical component which is very strong during the first half-wave, a transient shunt 64 (consisting of resistance and reactance in the same proportion as these occur in the section of line when under fault) is connected across the current responsive actuating coils of the relays. Rapid-acting directional relays 67, 68, 69, each one serving for two of the impedance relays, are employed to prevent faulty relay operation in sound lines and the polarizing windings (those on the central limb in the Figure) are supplied from a constant-direction source. As shown, they are supplied through phase-adjusting impedances 75 from the potential transformer 61 the voltage of the polarizing coils being upheld (in tines of fault) by a small synchronous motor shunted across the three phases. The relay contacts are connected in parallel to operate a quickacting tripping relay 58, the contacts of which complete the local tripping circuit of the very rapid circuit-breakers 20, 21. The apparatus described is provided at both ends of the section; on closure of relay 58 an auxiliary relay 59 closes and, by means of a pilot wire 85, carrier-current connection, high-frequency currents or impulses or an A.C. pilot wire with repeaters the circuitbreakers at the far end are brought out. With one line tripped out, a fault due to a flash-over produced by a lightning discharge may be cleared by rapid tripping and rapid reconnecting, the whole cycle taking place in “ sec. before any serious instability develops. The reclosure is effected, as shown, by a reclosing-relay 87 which is closed by back contacts on the circuit-breaker 21 when the latter is tripped open and serves to apply to the line a testing voltage from a normally idle running small generator 89. If the line is not faulty, all the under-current relays 91A, 91B, 91C remain closed and complete (through the relay 87) the closing circuit of a relay 94 which, in turn, completes the closing circuit of the circuitbreaker. A pilot connection 100 may ensure simultaneous reclosure at both ends. Automatic circuit-breakers. The high-speed circuit-breaker, which operates within approximately 1/5 sec., has a high-speed tripping action with trip-free mechanism so that the contacts, detached from the actuating mechanism, can be rapidly accelerated. It also has means for retaining oil in the arc path to ensure rapid extinguishing of the arc and may be of multiple-break construction with four serially-connected breaks per pole and electrostatic shields for improving the voltage distribution in the arc path at the zero of the A.C. cycle. One construction is shown in Figs. 5, 7 and 8 in which fixed contacts 107 have adjacent to them arc-quenching means consisting of bundles of V-slotted insulating plates 112 interspersed with magnetizable plates having slots lined with insulating material. The movable, bridging contact-member 109 passes through the slots into engagement with the fixed contacts and, when the arc is drawn at break, it is caused to move along the slot by the magnetic field and to vaporize fresh oil which quickly deionizes the arc space. The distribution of voltage across each break is controlled by conducting electrostatic shields 116, 117 which prevent excessive potential gradients. Circuit-breaker actuation and tripping. An electromagnet 97, Fig. 7, serves to close the circuitbreaker and another 80 to trip it. The rod 122, which is linked with the switch rod 110, in rising causes the rod 110 to fall. The upward movement of the rod 122 is produced by a powerful spring 124 acting through the lever 125. This lever is latched in the position shown, corresponding to the closed position of the circuit-breaker, by the linkage 137,133, the lever 133 being pivoted at 126 to the closing armature and at the other end engaged under a latch 134 pivotally carried by the downwardly-extending ends of a double-armed lever 127 with a fixed pivot at 128, a pivotal connection with the closing armature at 126 and its other end retained under a latch 129 carried by a fixed pivot. When the coil 80 is energized, the latch 134 is tripped and the lever 133 released. This frees the lever 125 which, under the action of the spring 124, raises the rod 122 rapidly. At the same time, the upper upturned end of the lever 133 turns somewhat to the left and knocks out the latch 129 thereby freeing the lever 127 which, under the action of the spring 130, turns in a clockwise direction following up the movement of the lever 125 and, when the lever 127 has caught up the opening mechanism, the right-hand end of the lever 133 is forced down into engagement with its latch 134 so that the parts are in a reset condition for reclosing when the coil 97 is energized. If the fault persists, the circuit-breaker is immediately reopened as soon as preliminary contact is made. In a modification, Figs. 9 to 12 (not shown), the circuit-breaker contact-member is trip free inside the pole unit instead of being trip free at the closing-coil mechanism. Moreover, the stack of insulating and magnetic plates with top and bottom conducting plate, as already described, is associated with a resistor connected between the top and bottom plates and with the magnetizable plates to carry a leakage current and serve as a voltage distributer and electrostatic shield.