Patent GB-378006-A (GB)
Title: Improvements in or relating to protective arrangements for alternating current polyphase power transmission systems
IPC: H02H7/26
Filed: 1931-05-01
Abstract: 378,006. Protective cut-out systems. KAPP, R.. O., 25, Randolph Crescent, CARROTHERS, C. G., 5, Richmond Park Road, East Sheen, and GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, all in London. May 1, 1931, Nos. 12912 and 22605. [Class 38 (v).] Protection of a section of a polyphase transmission system, which may be an overhead-conductor ring-main system, is effected with the aid of separate single-phase directional and overload elements at each end of the section, each element exerting a control over a channel of communication extending to the far end. In Fig. 1, the section 1 has breakers 2 at each end, each controlled by normallyopen contacts 33 of overload elements 30 and normally-closed contacts 29 of overload relays the operating coils of which are respectively energized by closure of contacts 27, 34 of directional elements, which latter contacts are engageable by movable contacts 28 depending on whether current is flowing, respectively, into or out of the section at that end. The relay groups 24, 25, 26 are associated with the respective phases and the several contacts 29 are in series whereas those 30 are in parallel. When one of the latter closes on an overload passing from left to right and through the section, the relay 19 at the left-hand end closes, being energized by a battery 35, and moves its member 18 from contacts 13 to contacts 14 thereby establishing a circuit from battery 15 over the lower half of a differential relay 9 and resistance 11. The relay 9 does not operate, however, as its upper half also is traversed by an equal current over the pilot 6 to the relay 9 at the far end, the relay 19 of which does not operate as power is flowing out of the section. Moreover the appropriate relay contact 29 at the right-hand end opens so that, although the contact 17 at that end is closed by the contact 10, the circuit of the trip coil 5 is not made. If, however, a fault occurs within the section, the appropriate contacts 28 at both ends close the contacts 27 and hence the appropriate contacts 30 are closed and both relays 19 operate. As the batteries 15 are in opposition, no current flows over the pilot wire 6 and therefore only the lower halves of relays 9 are energized. Both contacts 17 are closed by closure of contacts 10 and, as contacts 29 remain closed, both trip coils 5 are energized. If the fault in the section is fed from one end only, the contacts 29 at the other (say right-hand) end remain closed and when the contact 17 at that end closes, the trip coil 5 is energized and also a pilot relay 8 which opens the pilot circuit. The relay 9 at the lefthand end therefore becomes unbalanced and causes tripping of the breaker at that end, thus completely isolating the section. The proper functioning of the system is ensured by making the elements 30 close with either a timelag, or higher setting, or both, as compared with the opening of the elements 29, and the latter are further arranged to close with a time-lag. In a modification, Fig. 2 (not shown), a modified arrangement of directional and overload relays is employed, the latter operating independently of the former, and a further relay of the balanced-beam type operates to open the trip circuit and prevent inadvertent interruption of a sound section on clearance of a fault in another section. In a further modification, Fig. 3 (not shown), the overload and directional overload elements of one phase are replaced by earth leakage elements, one of which is directional. Fig. 4 shows a section 61 with adjacent parts of neighbouring sections 64, 65, the equipment of section 61 being shown at 72, 73 and of the adjacent ends of 64, 65 at 74, 75, respectively. Control by means of carrier currents is used in each section, transmitters 68 at one end being adapted on closure of contacts 67 to transmit to a receiver 70 at the other end, thus actuating a preventive relay to open its contacts 71. Means are provided also to prevent a receiver being operated at the same time as the transmitter at the adjacent end. Directional overload relays 77, 78 having directional contacts 79 and overload contacts 80 are located in two phases and close when energy is flowing out of the section at that end, and a directional earth leakage relay 82 closes instantly when leakage current of a given value flows out of the section. Overload relays 83, 84 are associated with the same phases as relays 77, 78. The earth leakage relay 81 opens its contacts instantly at the same current value as that at which the contacts 82 close, and a further earth leakage relay 85 closes with a small time-lag at a slightly larger current value than that at which the relay 82 closes. The trip circuit extends through either of contacts 83, 84, 85, contact 71 and a contact 87, the coil 86 of which is energized over a circuit 71, 88, and relays 77, 81 or 78, 81 or relay 82. The operation of the relay 86 actuates the contact 67 also and so actuates the preventive relay at the far end, but only if the fault is a through one. Should a breaker fail to open on a fault in its own section, a relay 89 across its trip coil 5 operates with a time-lag to open at 88 the circuit of the neighbouring coil 86, whereby the adjacent circuit-breaker of the next section is opened in response to the fault conditions. The earth leakage relays of Fig. 4 could all be replaced by corresponding directional and overload elements.