GB455860A - Improvements in and relating to high speed electric controlling devices - Google Patents

Abstract

455,860. Protective cut-out systems. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London. April 26, 1935, No. 12564. Convention date, April 27, 1934. [Class 38 (v)] A rotary converter 12 is connected to supply lines 10, 11 by means of a high-speed breaker 18 of the kind disclosed in Specifications 125,279 and 187,993, [both in Class 38 (v)], the flux-shifting winding 26 of which is energized on closure of either of the contacts 40, 78 of identical relays 38, 39, responsive to reverse current and normal overload, respectively. The movable contact 40 is biassed " open " by a spring 42 and carries an armature 41 co-operating with poles 50, 51 extending from a closed magnetic circuit 45, which is normally energized to saturation-point by the coil 46 with only a little leakage flux effective on the armature. With a reverse current flow the rapidly-rising current causes the m.m.f. of coil 54 to oppose that of 46, whereby the flux is shifted from leg 55 to the poles to attract the armature and close the trip circuit. The contact-separation in the open position is between one-sixth and one-thirty-second of an inch, and the time of operation between one-and-a-half and two-thousandths of a second, and with a breaker time of operation of six thousandths, the total time taken to clear the fault is eight thousandths of a second, which is short enough to protect the converter from flashover. Opening of the breaker may de-energize the coil 46 so as to assist the relay 38 to reset. The shunt 19 across which 54 is connected has an inductance valve relatively high compared to its resistance, and the shunt 14 supplying the trip coil 72 of relay 39 has an inductance value which is less in proportion to the resistance than is 19, so that the rapidly-rising current due to a reversal will affect 38 much more quickly than a slowlyrising overload, and shunt 14 is less sensitive to a rapidly-rising overload but more sensitive to slowly-rising overloads than shunt 19. The relays are therefore selective. To further speed up operation, the time-constant of coil 26 is kept low by means of a high resistance in the coil or as shown at 84, and a highvoltage source is provided, the circuit being broken at contacts 30 when 18 opens.