GB630674A - Improvements in and relating to electric circuit breakers - Google Patents

Abstract

630,674. Automatic circuit - breakers. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 23, 1945. Convention date, Nov. 2, 1944. [Class 38(v)] A D.C. circuit-breaker, particularly for use in aircraft, is opened when a reverse current in a conductor-bar 3 sets up a flux in a yoke 47 in opposition to that due to a permanent magnet 40, and enables a stressed spring blade 33 to snap an armature 32 away from a pair of pole-pieces 43. A spring 28 thereupon rotates a latch support 25 about a pivot pin 26 so as to disengage a latch 21, pivoted to the support at 24, from a roller 22 carried by an operating member 16, which is then rotated clockwise by a spring 37 to open main-contacts 9 and arcing-contacts 12. The member 16 is pivoted at 18, and connected by a togglelink 17 to a U-shaped bridging member 7, which is slidable between guides 10 and carries the contacts 9, the contacts 12 being carried by a bridging-member 11, resiliently supported between a pin 13 and the base 8 of the member 7 by a spring-blade 14, so that the contacts 12 close before, and open after, the contacts 9. The pivot 18 is engageable with a slot 39 in the member 16, so that the spring 37 itself urges the contacts into engagement, and the friction at the pivot is thereby reduced. When the member 16 reaches the end of its opening travel, the roller 22 engages an arm 34 of the spring-blade 33 and returns the armature 32 to the attracted position. The armature is centrally, loosely attached to blade 33 by a short rivet 36, a guide member 36<SP>1</SP> being also provided. The breaker is manually re-closed by thumbing the part 56 of the member 16, the roller 22 deflecting the latch 21 against the action of a spring 27, which returns the latch 21 against the pivot 26. The sensitivity of the breaker may be varied by a screw 49, 50 which passes through the ends 48, 51 of the yoke 47, and the pole-pieces 43, 44, to provide an adjustable-gap between the pole piece 44 and the yoke-end 51, Fig. 4. To prevent the breaker being tripped by small reverse-current pulses of short duration, a time-delay may be introduced by fitting copperrings around the legs of the pole-pieces and the yoke, Fig. 6 (not shown). The yoke 47 is arranged to saturate with heavy currents, so as to avoid demagnetisation of the magnet 40 with heavy forward-currents, and to ensure that heavy reverse-currents will not raise the armature-flux to a sufficiently high value in the reverse direction, to stop the armature tripping. The armature and its co-operating pole-faces are preferably chromiumplated.