Patent GB-107272-A (GB)
Title: Improvements in and relating to the Protection of Electric Transmission Systems.
IPC: H02H3/13
Filed: 1916-07-14
Abstract: 107,272. British Thomson-Houston Co., (General Electric Co.). July 14, 1916. Protective arrangements; electro-magnetic switches.-In polyphase electric transmission systems a protective device is used which, upon the occurrence of a broken line wire, indicates the phase of the broken line wire and opens the circuit of the faulty feeder. As applied to a three-phase system, three wattmeter elements-one for each phase-comprising current coils 10, 11, 12, Figs. 3 and 5, and voltage coils 13, 14, 15 are arranged to act on a three-armed common armature 22, which is maintained in a state of balance, when conditions are normal in the three-line wires 1, 2, 3. Assuming that one of the line wires breaks with or without grounding so that the current or potential in that wire falls practically to zero, the corresponding wattmeter element will be overcome by the other two elements and the common armature will be inclined and bring one of the arms against a spring-carried contact 26, 27, or 28. A local circuit is thus completed including an annunciator or drop indicator 31, 32, or 33, an indicator 37 common to all three of the contacts 26, 27, and 28 and a relay 38 for an oil switch 40 in the feeder. The particular indicator 31, 32 or 33 which is actuated shows which line wire is broken. If the broken line wire is broken so that a heavy current flow takes place in that wire, the corresponding wattmeter element will pull down one of the arms of the common armature 22 against the action of the other two elements and close a local circuit through one of the contacts 41, 42, or 43 including one of three indicators 44, 45, or 46, the common indicator 37, and the relay 38, showing on which line the fault occurs; the other two arms will close the circuits through two upper contacts and actuate the corresponding indicators, but no notice is taken of the indicators 31-33 when one of the indicators 44-46 acts. When the feeder connects two stations A, B, a protective device is used at each end of the feeder, and both devices act on a break If the break is near the station B and only the end near B is grounded as shown in line 1 at 76, the power factor in phase 1 will fall to zero and the corresponding watt meter 10, 13 will cease to act on the common armature, causing actuation as described above. In order that the device will act at the same percentage disturbance between the phases at all loads, the common armature is connected by adjustable springs 48 to a three-armed extension of a core 49 which is acted on by three current coils 50, 51, and 52. When the protective device is applied to a grounded neutral system as shown in Fig. 5, an additional protective arrangement is used responsive to unbalancing between the feeder and the ground; this comprises a transformer 55 in the earthing wire and connected to a relay 54 in parallel with the relay 38. An adjustable condenser 60 and spark-gap 61 are placed across this circuit to allow only currents of the normal frequency of the feeder to act on the relay 54. This additional protective device is used when only one feeder is used between stations when several are used, a switch 57 is opened to disconnect this additional protective means. With a transmission system where the neutral is not grounded, as shown in Fig. 6. an additional protective device is used consisting of a threearmed pivoted member 62 acted on by three double-solenoids 65 which are connected to the secondaries of transformers 66, the primaries of which are placed in a circuit between each phase and ground The armatures 64 of the solenoids are mounted by means of knife edges on the arms of the member 62. When the solenoids 65 are unbalanced and the member 62 is inclined, a relay 73 in parallel with the relav 38 is actuated to cause opening of the oil switch 40.