Patent GB-269924-A (GB)
Title: Improvements in or relating to the protection of electric line sections on fault
IPC: H02H3/04
Filed: 1927-04-22
Abstract: 269,924. Siemens & Halske Akt.- Ges. April 24, 1926, [Convention date]. Cut-out arrangements; electromagnetic switches. -In order to afford selective protection of line sections and to obtain an indication in the event of fault, a quotient relay F actuated in accordance with the resistance of the protected circuit is adapted to close a circuit whereby a relay A - - D of the instrument type is caused to make a contact through its pointer and. according to the resistance indicated to close the tripping circuits of the section circuit-breakers after a shorter or longer time. The relay F is of the induction type with split dial to prevent mutual interaction of the series coil 55 energized from the current transformer 47 and the voltage coil 62 energized from the potential transformer 56 across the section S.T. The relay is of robust construction and, when the resistance of the section falls below a certain minimum on fault, contact is firmly made between 41 and 42. This supplies current to a winding 44 which attracts its core 25 and swings down a stepped frame 21 against the action of a spring 23 so as to depress the contact pointer 9 of the more delicate resistance, measuring relay A - - D on to one or other of contacts 13 which are connected with devices indicating the position of the fault and on to pivoted flaps 16. 72, 73 which remain down and give a visual indication. The actuating elements of the relay A are in three parts, (i) the upper element A with a magnetic system energized from the current transformer 47 and a short thick moving element with heavy energization from a transformer 52 in the magnetizing circuit, (ii) a Ferraris disc relay B energized by current, and (iii) a second Feraris disc relay C energized by current and voltage. The first element develops a torque proportional to the square of the current, and the third a torque proportional to the product of the current and potential. In consequence the pointer takes up a position depending on the resistance of the section; the second element is employed for damping the action. If the fault is on the protected section, the pointer 9 assumes a position to the extreme right so that the frame which at this portion is cut away most swings down a maximum amount before it is stopped by engagement with the pointer and the base 14 on which the contacts are mounted. During this swinging movement produced, by the solenoid 44, a detent 36 on the rod 24 is withdrawn from a gear-wheel 30 which rotates slowly under the action of an independent clockwork drive to carry a contact 32 on it towards a companion contact 29 on the gear-wheel 27. When these contacts come together the tripping coil 63 of the circuit-breaker is energized and the time before this takes place depends upon the distance to be covered before the contact 29 is reached. With fault on the section, as described, a maximum movement of the frame takes place, and through the rack 26 the contact 29 is immediately brought almost into juxtaposition with contact 32 so that the time delay is a minimum.