Patent GB-1364368-A (GB)
Title: Coated arc chute for an electric circuit breaker and method of making same
IPC: H01H33/72
Filed: 1972-07-12
Abstract: 1364368 Fused silica coating GENERAL ELECTRIC CO 12 July 1972 [14 July 1971 18 Oct 1971] 32553/72 Heading B2E [Also in Division H1] A fused silica coating is applied to a substrate of refractory non-metallic material by (a) providing an arc plasma spray gun comprising an arc chamber in which an electric arc is established, means for feeding gas into the arcing chamber to develop a high temperature arc plasma, a nozzle through which the arc plasma is exhausted from the gun and means through which particles of coating material can be fed into the arc plasma to melt the particles and entrain them in the arc plasma exhausted from the gun, (b) developing hightemgerature arc plasma within the gun and projecting the arc plasma from the gun on to a surface of the refractory non-metallic substrate, (c) feeding into the arc plasma particles of crystalline silica, which particles are melted by the high temperature arc plasma and entrained in the arc plasma, (d) holding the nozzle close enough to the substrate during the time that arc plasma containing molten silica particles is being projected thereon to effect melting of the surface that the molten silica particles are impinging against. The substrate may be the refractory non-metallic material of an arc chute for an electric circuit braker which chute comprises insulating side walls and plates of refractory non-metallic insulating material that extend transversely of the side walls and have edges for engaging the arc as it moves into the chute. The side-walls and the transverse plates of the chute may be made of phospho-asbestos material containing a filler. The edges and preferably also the side walls of the plates are coated with the fused silica. As shown in Fig. 1, the circuit breaker comprises a pair of terminal. bushings 1 and 2, the bushing 2 comprising a downwardly extending conductive stud 3 at the lower end of which a moveable conductive switch blade 4 is mounted by means of fixed pivot 5. At its outer end blade 4 carries circuit controlling contacts such as a main current carrying contact 6 and an arcing contact 7. Bushing 1 comprises a conductive stud la to which a downwardly extending conductive member 8 is electrically connected. Attached to conductive member 8 is a curved contact 'retaining member 9 which coacts with member 8 to form a pocket for receiving the anchored ends of main stationary current carrying contact fingers 10. These fingers are pivotally mounted on a curved portion 12 of the conducting member 8 and are biased for limited rotative wiping movement in a closing direction by means of compression springs 9a. The moveable arcing contact 7 cooperates with stationery arcing contact 13 which is mechanically and electrically connected to the conducting member 8 by clamping means 14. When the switch blade 4 is in its closed position as shown in Fig. 1 most of the circuit current flows through the current carrying contacts. When the switch blade 4 is driven counter-clockwise to open the breaker the arcing contacts part and draw a circuit interrupting arc therebetween which is driven into an arc chute 15 and there lengthened, cooled and extinguished. A reciprocable operating rod 16 pivotally joined to the switch 'blade at point 17 acts to move the switch blade 4 counter-clockwise to effect circuit interruption. The arc chute 15 comprises a pair of side walls 18 and 19 as shown in Fig. 3 clamped together with spaced apart relationship by clamping strips 20 and 21 and bolts 20a. Each side wall is provided with a plurality of plates or fins 22 interleaving with corresponding projecting fins on the other side wall. Disposed between the fins 22 are ribs 11 disposed in alignment with the fins on the opposite side wall. The forward edges of the interleaving fins 2 taper towards the arcinitiation region at the right-hand end of the chute. A pair of conductive arc runners 24 and 25 are provided along opposite edges of the chute for facilitating movement of the arc into the arc chute. The side walls 18 and 19 extend between these runners 24 and 25. In the throat region 50 of the arc chute there are two separate throat pieces 60 each constituting a side wall with short fins or ribs 62 integrally formed therewith. There is no interleaving of the ribs 62. Probes 51 project from upper runner 24 to accelerate transfer of the upper arc terminal to the upper arc runner 24. The arc chute further comprises a first group of blowout electromagnets 26, 27 and 28 mounted adjacent the upper arc runner 24 and a second group of blow-out electromagnets 29, 30 and 31 mounted adjacent the lower arc runner 25 to propel the arc and accelerate its movement along the runners into the interior of the arc chute. As the arc terminals move along the runners into the chute a column of the arc moves freely into the chute until it encounters the intersecting forward edges of the interleaving fins 22. Thereafter further penetration of the arc chute causes the arc column to assume a zig-zag form as it bends round the overlapping edges of the fins 22. The arc chute portions 18, 19 and 22 are formed of a refractory material made by reacting a concentrated ortho-phosphoric acid and chrysotile asbestos, and also includes a zircon filler. The plasma stream containing molten silica particles is projected on to the upper surface of the side walls 18, 19. The arc plasma gun is moved perpendicular to the longitudinal dimension of the ribs and fins 11, 22 and the whole area sprayed by a number of successive passes. The plasma spraying operations may be used both to flame-treat the base material and to apply the desired coating. At the rear or exhaust end of the arc chute a region 77 as shown in Fig. 1 is left uncoated so that its walls are capable of evolving gases which serve to block arc motion past the region of the boundary line 78 and also to effectively cool the arcing products exhausted through the rear of the chute. The surfaces of the fins 22 may be only partially coated to enable some gases to be evolved by the arc from the underlying base material of the fins, such gases providing a cooling effect. The fused silica coating effectively limits the amount of gas generated by the arc during the crucial high current interval and renders 'the arc chute highly resistant to arc erosion, and inhibits electrical current from flowing across the chute immediately after arcing thus further aiding in interruption.