GB434114A - Improvements in and relating to electric circuit breakers - Google Patents

Abstract

434,114. Automatic circuit-breakers. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of McNairy, J. W. ; 1019, Washington Place, Erie, Pennsylvania, U.S.A.) Dec. 27, 1933, No. 36424. Convention date, Dec. 29, 1932. [Class 38 (v)] Circuit-breakers are calibrated by means of a coil having a large number of turns as compared with the trip coil and located and energized so as to produce an m.m.f. equal to and in the same direction as that of the trip coil for given values of load current. A chart is provided showing values of calibrating-coil current required to produce the m.m.f. corresponding to various load currents in the trip coil. In the high-speed breaker shown, the fixed contact 11 co-operates with a contact 10 on an arm which is pivoted to a magnetic member 12, and the parts 10, 12 are together moved by a coil 25 and arm 31 to the closed position, in which they are maintained by a winding 17 on the magnet 16 against the action of an adjustable spring 14. A bucking bar 18 as described in Specification 125,279, [Class 38 (v)], serves as a series trip coil and is shunted by a resistance 30. Coil 25 is energized by the closure of contacts of a coil 26 in series with a manual switch 27, coil 26 being shorted by back contacts 28 in the closed position of the breaker. In Fig. 2, a calibrating coil 35 is wound on a spool 36 and slid inside the coil 18 with intervening insulation 37, this coil 35 being connected in series with a source 40, ammeter 41, and rheostat 42, Fig. 1. Calibration is effected, preferably at the factory, by adjusting the breaker so as to be released at a given current flowing in coil 18. The coil 35 is then switched in and its current adjusted until its m.m.f. is sufficient to cause release. This current is read on the ammeter 41 and the process repeated, whereby a table of related current values can be drawn up and attached as at 45, Fig. 2. To adjust the breaker after it has been in operation a while, the coil 35 is switched in and its current adjusted to produce the m.m.f. required for its original setting, and the spring-tension adjusted. When the contacts of a breaker of the type shown are worn, increase of tension is necessary.