Document Z8J7NK3QvNLZx1kzQRGL7ED4p

United States Patent [i9] Hayes im 4,082,931 [45] Apr. 4,1978 [54] ARCCHUTE [75] Inventor: Matthew N. Hayes, Amherst, N.Y, [73] Assignee: WestinghooseElectric Corporation, Pittsburgh, Pa. [21] Appl. No.: 676,181 [22] Filed: Apr. 12,1976 [51] Int. ..... ........................... ............H01H 33/08 [52] UJS. CL .................................................. 200/144 C [58] Field of Search........................ 200/144 C, 149 A [56] References Cited U.S. PATENT DOCUMENTS 2,270,723 1/1942 Boehne.............................. 200/144 C 2,279,040 4/1942 Grosse............................. 200/144 C 2,822,448 2,911,505 3,009,041 2/1958 Wegmann......................... 200/144 C 11/1959 Legg et al........................... 200/144 C 11/1961 Zlupko............................... 200/144 C Primary, Examiner--Robert S. Macon Attorney, Agent, or Firm--L. P. Johns [57] ABSTRACT An arc . chute for a circuit breaker characterized by a pair of spaced side walls for an interior arc extinguish ing chamber, the surfaces of the walls forming the chamber being covered with a coating of an arc resis tant ceramic material, such as aluminum oxide, zirco nium oxide, chromic oxide, magnesium oxide, and cal cium oxide. 1 Claim, 2 Drawing Figures SC-ELEC-07150 U.S. Patent April 4, 1978 Sheet 1 of 2 4,082,931 FIG.I U.S. Patent April 4, 1978 Sheet 2 of 2 4,082,931 43 FIG.2 4.082.931 12 contacts .13,15, the conductor structure 19, a shunt 25, ARC CHUTE a shunt connector 27, and a load terminal 29. BACKGROUND OF THE INVENTION When the contacts 13,15 separate under load, an arc 1. Reid of the Invention 31 develops between them. The arc blowout unit and This invention relates to an arc chute of heat resistant 5 the arc chute 11 are provided to extinguish the arc 31 material having a surface coating of an arc resistant and minimize its effect upon the contacts. The arc chute ceramic material. ' - 11 is a housing comprising a heat resistant, electrically 2. Description of the Prior Art : insulating material, such as material filled melamine-for Arc chutes or arc shields are commonly used to con maldehyde resin. Other materials for the arc chute may fine and extinguish electric arc drawn between electri- 10 include a mixture of Portland cement with (asbestos) cal contacts of circuit breakers. An arc chute is gener zircon, glass polyester, or the like. A very satisfactory ally comprised of a pair of slightly spaced walls of heat composition for the material of the arc chute 11 com resistant, electrically insulating material that confine prises a mixture of melamine-formaldehyde resin with and extinguish an arc by cooling the arc to extinguish (asbestos.) ' ing temperatures. An example of an arc shield is shown IS The arc chute 11 preferably comprises two half por and described in U.S. Pat No. 2,270,723, issued Jan. 20, tions 33, 35 (FIG. 2) having inner wall surfaces 37, 39 1942, in the name of Eugene W. Boehne. which surfaces are oppositely disposed or facing sur A difficulty with some arc chutes of prior construc faces and provide an elongated narrow arc chamber 41. tion has been that the walls of the arc chute become As shown in FIGS. 1 and 2 the arc 31 is more readily heated during an arc lifetime to cause out-gassing of 20 transferred from the contacts 13,15 to the arc chute 11 certain materials from the body of the arc chute walls. by providing a line arc horn or conductor 43 and a load As a result the out-gas contributes to continuation ofthe arc horn or conductor 45 which extend from the zone arc rather than its extinguishment Various attempts adjacent the contacts to divergent locations 43a 45a have been made to overcome the out-gassing problem within the arc chute. The arc 31 progresses from posi but none have been commercially successful. One at- 23 tion 31a to positions 316, 31a 314 31e through the tempt has included heating of the arc chute during elongated narrow arc chamber 41 and is extinguished production for a sufficient time to drive out the gas. under normal conditions. Such a heating process however is not economically In accordance with this invention, in order to mini feasible on a production basis. mize or eliminate any prior existing conditions which SUMMARY OF THE INVENTION 30 contribute to the continuation ofan arc in the arc chute, such as the existence of vapor occurring due to thermal In accordance with this invention, it has been found decomposition of melamine to provide formaldehyde that the foregoing problem may be overcome by pro and ammonia which are more electrically conductive viding an arc chute or arc shield comprising a pair of than air, the surfaces 37,39 are covered with coatings or spaced side walls ofheat resistant, electrically insulating 33 layers 47,49, respectively. The coatings 47,49 comprise material forming an arc chamber, the walls having op ceramic material that is arc resistant and refractory. posed surfaces defining the chamber, and each wall Examples of the ceramic material include aluminum having a coating of an arc resistant ceramic material oxide (AI2O3), calcium oxide (CaO), chromic oxide selected from the group consisting of aluminum oxide, (Cr2p3), magnesium oxide (MgO), and zirconium oxide zirconium oxide, chromic oxide, magnesium oxide, and 40 (Z1O2). The preferred coatings 47,49 are comprised of calcium oxide. A1203 or ZrOj, because they are not only effective but The advantage ofthe device ofthis invention is an arc comparatively inexpensive. The primary purpose of the chute having an improved arc interruption and quench coating 47,49 is to minimize and eliminate the out-gass ing property. ing ofvapors into the arc chamber 41 from the arc'chute BRIEF DESCRIPTION OF THE DRAWING 45 portions 33,35, by sealing the surfaces 37,39. The coat ings 47,49 may be applied to either at least a portion or FIG. 1 is a vertical sectional view through a magnetic all of each surface 37, 39. contactor having an arc chute mounted thereon; and The method by which the coatings 47,49 are applied FIG. 2 is a vertical sectional view taken on the line comprises basically a two-step procedure as follows: H--Hof FIG. 1. 30 1. Sandblasting the surfaces 37,39 to provide a rough DESCRIPTION OF THE PREFERRED EMBODIMENT ened texture with a non-metallic grit; and 2. Spraying the surfaces 37, 39 to apply the high temperature, insulating material onto the surfaces. In FIG. 1 a magnetic contactor is generally indicated The first step of roughening the surfaces, such as by at 1 and it comprises a base plate 3, electro-magnetic S3 sandblasting, is preferably performed with a non-metal- means or electromagnet 5, an electrically insulating lic grit to avoid the deposit of any conducting material housing 7, arc blowout unit 9, and an arc chute 11. The embedded in the surface that would otherwise result contactor 1 also comprises a stationary contact 13 and a where a metallic grit is used. The second step of apply movable contact 15 which are mounted on conductor ing or spraying a high temperature and electrically structures 17,19, respectively. The movable contact 15 60 insulating or non-conductive material onto the surfaces is movable between open and closed positions, the latter is preferably performed by flame spraying or plasma of which is indicated by the broken line position 15a spraying of a powder of refractory or ceramic material, The contactor of this invention is generally described such as certain metal oxides including A1203, CaO, or in U.S. Pat No. 3,311,950, for which reason the descrip ZiOj, at elevated temperatures. A1203, CaO, Cr203, tion of the contactor per se is limited heron to the fore- 65 MgO, and Zr02melt at 2045* C, 2590 C, 2280* C, 2800 going basic structure. Suffice it to say, an electric circuit C, and 2715 C, respectively. The oxides are applied as through the contactor 1 includes a line terminal 21, a powders to a .thickness of from about 0.001 to about blowout coil 23, the contact support structures 25,17, 0.020 inch. A preferred thickness of the coatings 47,49 4,082,931 34 is about 0.005 inch. A coating of 0.018 inch was tried and found to be too brittle. Thus, thinner coatings are preferred so long as they seal the surfaces 37,39 against spray equipment supplied by Metco, Inc. of Westbury, N.Y. , Accordingly, the application of a high temperature and arc resistant ceramic coating to an electrically insu out-gassing of vapors into the arc chamber 41. Metallic 5 lating surface improves the arc interruption and oxide coatings are preferred because of their high tem perature melting points and will therefore not decom pose under prevailing arc chamber temperature opera quenching properties of an arc shield surface such as the surface of an arc chamber of an arc chute. What is claimed is: l. An arc chute comprising a heat resistant electri tion. It was found that metallic carbonates decompose 10 cally insulating material comprising a melamine-for at such temperatures and are therefore not satisfactory. The ceramic coatings or layers 47, 49 are preferably applied by flame spray with an oxy-acetylene heat maldehyde resin, at least a portion of the surface being covered with a coating of an arc resistant ceramic mate rial selected from the group consisting of calcium oxide and chromic oxide. source, or by plasma flame such as provided by flame 15 20 25 30 35 40 45 50 55 60 65