US2816990A - Circuit breaker - Google Patents

Description

Dec. 17, 1957 F. GELZHEISER 2,316,990

CIRCUIT BREAKER Filed Sept. 24, 1954 Fig. I.

Silicone Silicone 1 Fig. 4. a i l3 sniconc WITNESSES INVENTOR f Francis L. Gelzheiser Q I BY 1 g Y lwToRmz United States Patent CIRCUIT BREAKER Francis L. Gelzheiser, Beaver, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 24, 1954, Serial No. 458,210

7 Claims. (Cl. 200-144) This invention relates to circuit breakers, and, more particularly, to insulating housing members for enclosing and supporting circuit breaker mechanisms.

The insulating housing and support members for enclosing and supporting circuit breaker structures are usually made from a general purpose phenolic molding compound and are subjected to the heat of the are drawn upon separation of the circuit breaker contacts. This is particularly true when the circuit breaker is not equipped with an arc extinguishing structure. It is well known that when repeatedly subjected to arcs, such insulating members become carbonized and their insulating properties are destroyed or greatly reduced. The carbon formed on the surfaces of the insulating parts thus provides a path along which the are may track across the surface of the insulation from line to load. This further decreases and may destroy the insulating property of the insulating housing parts.

The insulating housing parts of circuit breakers have heretofore been coated with various preparations for the purpose of protecting them from the heat of the are, but the coating materials previously used for this purpose themselves become carbonized when repeatedly subjected to arcs and dielectric breakdown results.

Small circuit breaker structures are usually enclosed in two-part insulating housings formed from a general purpose phenolic molding compound and are sometimes mounted on metal panels or plates in panelboards and load centers. The two-part housing members sometimes form imperfect or loose seams or joints which provide creepage or flashover paths from the live parts within the circuit breaker housing to the grounded metal mounting plate.

I have discovered that the tracking of the are along the surfaces of the insulating parts of a circuit breaker is prevented by applying a selected silicone coating to the affected area of the housing parts. The silicone coating is capable of withstanding temperatures in the neighborhood of 600 F. and when subjected to higher temperatures the silicone decomposes into silicon dioxide which has high insulating properties.

By applying a selected silicone coating to the interior of the insulating housing parts, specifically in the areas afiected by the arc, the insulating properties of the parts are increased to the extent that the arc extinguishing structure usually provided in conventional circuit breakers can be omitted, thus effecting a considerable reduction in the cost of the circuit breaker.

It has been further discovered that a silicone coating applied to the joints and overlapping portions of the circuit breaker housing members seals the cracks or joints and prevents creepage or fiashover therethrough to ground.

An object of the invention is to prevent tracking of the arc across the inner surfaces of insulating housing members of a circuit breaker by applying certain silicone coatings to the affected areas.

Another object of the invention is to prevent creepage from the live parts of a circuit breaker to ground through 2,816,990 Patented Dec. 17, 1957 the seams of abutting insulating housing members by applying a silicone coating to the adjoining or overlapping portions of the members before they are assembled.

The invention both as to structure and operation, to-

gether with additional objects and advantages thereof,

will be best understood from the following detailed description thereof when read in conjunction with the accompanying drawing.

In said drawing:

Figure 1 is a side elevational view with the cover removed of a circuit breaker embodying the principles of the invention;

Fig. 2 is an elevational view showing the inside of the cover with the silicone coating applied;

Fig. 3 is an elevational view of a part of the circuit breaker shown in Fig. 1 but provided with an are extinguisher structure; and

Fig. 4 is an enlarged fragmentary sectional view taken substantially on line IV-IV of Fig. 3.

Several silicone compositions may be used to coat the housing parts, such for instance, as silicone gels, silicone emulsions, silicone varnish and silicone greases. For the purpose of this invention silicones having methyl and ethyl substituents on silicon are suitable. Silicones are often designated as siloxanes or organopolysiloxanes.

Silicones suitable for providing coatings having nontracking properties are methyl silicones and ethyl silicones having an average of from 1.1 to 1.9 of the methyl or ethyl groups, or combinations of both, per silicon atom. These silicones are resinous or of gel-like characteristics. They may be dissolved or emulsified in a volatile liquid solvent or carrier to produce liquid compositions and when such compositions are sprayed, brushed or otherwise applied, the solvent or liquid carrier evaporates leaving an adherent coating on the surface to which it is applied.

A suitable silicone grease or gel comprising a fluid dimethyl silicone combined with a substantial proportion of a finely divided filler may be used. One such silicone gel consists of 88% by weight of a dimethyl silicone oil combined with an inert, refractory, nonconducting filler such as 12% silica aerogel.

An emulsion consisting of 25% methyl or ethyl silicone gel or resin suspended in water may also be used to coat the housing parts.

Silicone varnishes for use in coating the housing parts may comprise a methyl or ethyl silicone resin dissolved in a suitable solvent. The silicone resins are thermosettable polymers containing an R to Si ratio of 1.1 to 1.9. Where R represents methyl and ethyl groups, a suitable silicone resin may have an R to Si ratio of 1.5. Suitable solvents are toluene and xylene. Butyl titanate may be present to enable hardening of the applied resin at room temperatures. The methyl silicone resin above mentioned forms a suitable varnish when dissolved in 3 parts by weight of toluene for each part of resin.

I prefer to use a silicone liquid consisting of a silicone dissolved in a volatile liquid solvent which is readily sprayed on the housing parts. Spraying the parts with such a liquid silicone is quickly done and saves considerable time compared to brushing or otherwise applying the coating. Another advantage of spraying the silicone coating is that the volatile solvent quickly dries at room temperature, hence, no special drying apparatus is required. When the solvent dries it leaves a hardened, adherent coating, whereas the silicone gels and greases remain greasy or tacky and are thus less desirable, though usable.

Figure 1 of the drawing illustrates a conventional circuit breaker'which comprises generally an open-sided housing member 11 for receiving and supporting the several parts stationary contact 15, a movable contact 17, an operating mechanism 19 and a trip device 21.

The stationary contact is rigidly secured to the inner end of a conducting member 22 integral with a plug-in connector member 23 supported in the housing 11 and in the cover 13. At the opposite end of the housing 11 is disposed a conducting strip 29 which at its inner end is connected to the trip device 21, and is provided with a terminal connecting means, such as a screw 31, at its outer end for connecting the circuit breaker in an electric circuit.

The movable contact 17 is rigidly secured on the free end of a U-shaped switch member 37 having its legs 57 supported in recesses in the legs 55 of a U-shaped operating lever of molded insulating material. The operating lever 35 is pivotally supported by trunnions 3-6 molded integral therewith and mounted in suitable companion openings in the housing member 11 and in the cover 13. An overcenter operating spring 39 is connected under tension between the bight of the switch member 37 and a releasable carrier 33 pivoted on a pin 41 supported in the housing 11 and in the cover 13.

The operating lever 35 is provided with a handle 49 molded integral therewith and extending outwardly through an opening 51 in the housing 11. The operating lever 35 is also provided with an arcuate portion 53 Which cooperates with the housing 11 and the cover 13 to substantially close the opening 51 in all positions of the handle. The switch member 37 is conductively connected by a flexible conductor 59 to one end of a bimetal element forming a part of the trip device .21 which is suitably secured to and supported by the inner end of the conductor strip 29.

The switch arm 37 is operated to manuallyopen and close the contacts by operation of the lever 35 which is effected by manipulation of the-handle 49. Movement of the handle 49 ina clockwise direction forms the position shown in Fig. 1, carries the pivoted ends of the legs 57 of the switch member 37 across to the left of the line of action of the operating spring 39 which then biases the switch member 37 to .the open positionand causes movement of the switch member to the open position with a snap action.

The contacts are manually closed'by reverse movement of the operating lever 35. Counterclockwise movement of the lever 35 from the open position-to the closed position moves the upper pivoted ends of the legs 57 of the switch member 37 across to the right of the line of action of the spring 39 which then acts to close the contacts with a snap action.

The circuit breaker is tripped open after a time delay in response to overload currents below a;predetermined value, and instantaneously in responseto overload currents above the predetermined value, or in response to shortcircuit currents, by means of the trip device 21. Operation of the trip device 21 causes release of the carrier 33 whereupon the operating spring 39 moves the carrier 33 clockwise about its pivot 4-1 until it is arrested by a projection 61 molded integral with the housing part 11 and a matching projection 61a (-Fig. 2) on the cover 13. Theclockwise movementof the carrier 33 moves theline of action of the spring 39 across to the right-ofthe center line of the switch arrs.37 and the spring 39 thenracts tomove the switch member-to theopen position .with'a snapaaction.

The trip device .2! comprises thebimetal element as connected tothe movable switch member by the flexible condnctor59 and electromagnetic means includingamagnetic member orarrnature 63 rigidly mounted on the bimetal element tifiand a magnet yoke 65movably supported in a recess 69 (Fig. 1) in. thehousing 11 and a companion recess 79 (Fig. 2) Vin.the:c,over 13. The-conducting strip 29 extends-along an end wall of-the housing 11 and is rigidly secured thereto byrascrew71, the bimetal element at one. end being rigidly. secured'by suitable means, such .as welding, totheupper inner end of the conductor strip 29.

The armature 63 is rigidly secured to the bimetal element 45 by a rivet 73 which also rigidly fastens a latch member 67 to bimetal element 45. The latch member 67 normally engages and releasably restrains the carrier 33 in operative position.

The recesses 69 and 70 (Figs. 1 and 2) in which the magnet yoke 65 is disposed, are wider at the bottom than they are at the top to permit pivotal movement of the magnet yoke in the direction of thermal bending of the bimetal element 4-5, the magnet yoke 65 being biased by a light compression spring 79 to the position shown to provide a normal air gap between the magnet yoke 65 and the armature 63. This arrangement permits maximum deflection of the bimetal element when it is hot and prevents it from taking a permanent set as it would if its deflection were opposed by any substantial force such as engaging a fixed magnet yoke.

Means is provided for calibrating the trip device. The calibrating means comprises a screw threaded through a fixed nut 8'7 disposed in a recess 89 in the adjacent end wall of the housing 11. The inner end of the screw 85 engages the upper end of the conductor strip 29 on which the bimetal element 45 is mounted and applies a pressure thereto. An access opening 91 is provided in the end wall through which the screw 85 may be rotated to vary t. e pressure on the conducting strip after which theopening 9.1 may be sealed to prevent tampering. Turning the screw 85 varies the pressure on the conductor 29 and causes movement of the upper end of the conductor according to the direction in which the screw is rotated. This varies the position of the bimetal element 45 and consequently varies the thermal tripping point of the breaker.

Upon the occurrence of a low persistent overload current below a predetermined value of, for example, ten times normal rated current, the bimetal element 45 becomes heated, and when heated a predetermined amount bends toward the right causing the latch67 to release the carrier 33 which effects opening movement of the switch member 37 in the manner previously described.

When an overloadcurrent above ten times normal rated current or a short circuit current occurs, the electromagnetic trip means is energized and the armature 63 is attracted toward the magnet yoke 65 bending the bimetal element 45 and causing the latch member 67 to instantaneously release the carrier 33 and open the contacts.

The releasable carrier 33 is reset and relatched and the contacts closed following an automatic opening operation by first moving the handle 49 clockwise to the oil position and then counterclockwise to the on position. Movement of the handle to the OE position causes the legs 55 of the operating lever to engage a pin 80 in the carrier 33 and move the carrier counterclockwise about its pivot 41. Near the end of this movement, the free or;latching end of the carrier 33 wipes by the latch 67, slightly bending the bimetal element which then resumes its normal latching position.

An arc chamber 93 is formed by the projection 61, the bottom wall 95 of the housing 11 and a projection 97 on the housing Hand by cooperating projections 61a, 97a and a bottom wall 95a (Fig. 2) on the cover 13. The are gases are vented through a passage 99 formed by the bottom wall 95 (Fig. 1) of the housing 11 and the matching bottom wall 95a (Fig. 2) of the cover 13, and by matching ribs .161 and Mia formed respectively on the base Ii and the cover 13.

As shown in Figs. 1 and 2 the silicone coating is applied to the base 11 and to the cover 13 in the area within the are chamber 93 and the area immediately surrounding the arc chamber substantially as indicated respectively at 1493 and 103a (Figs. 1 andZ). The silicone coat ing prevents the formation of carbon on the housing parts it and and thus prevents tracking of the are drawn between the breaker contacts. The silicone coating when subjected to the heat of the arc decomposes into silicon dioxide which is itself an insulator and does not cause dielectric break down or electrical creepage. By use of the silicone coatings of this invention, general purpose molding materials of the phenolic or other inexpensive types may be used, and thus save the expense of using molding materials with better dielectric and arc-resisting properties. Also, the cost of providing a special arc chute or are extinguishing structure may be saved.

As shown in Fig. l the breaker parts are assembled in the open sided base 11 after which the cover 13 is rigidly secured in place preferably by means of rivets 105 in a well known manner. A plurality of circuit breakers are usually mounted in a load center or panelboard on a grounded metal plate 107 by means of a hook or clip 1129 formed on one end of the plate and engaging a recess at the end of the breaker housing. The plug-in connector 23 at the other end of the breaker is forced into engagement with a stab connector 111 integral with a conductor 113 which is mounted on an insulating memher 115 supported on the plate 107.

As shown in Fig. 4, when the base 11 and cover 13 are fitted together, a portion of the bottom wall 95a of the cover overlaps a portion of the bottom wall 95 of the base 11 as indicated at 117 (Fig. 4). Since the seam or joint formed thereby is not sealed it has been found that, even with an arc extinguisher 119 as shown in Fig. 3, creepage may occur therethrough from the live parts within the breaker housing to the grounded plate 107. By coating the edges of the bottom wall 95 of the base 11 and the bottom wall 95a of the cover with a silicone coating before the parts of the housing are assembled, the seam is completely sealed upon assembling the parts of the housing thereby preventing dielectric breakdown to ground through the seam.

Tests have been made on circuit breakers of the type illustrated both with and without the silicone coating. The tests consisted of applying voltages to the terminal of the breakers following the interruption of a short circuit. The results of the tests show that in the case of the circuit breakers without the silicone coating dielectric breakdown occurred with an applied voltage as low as 120 volts, whereas with the silicone coating applied in accordance with the invention, between 2600 volts and 3000 volts were applied before dielectric failure occurred.

1 claim as my invention:

1. In a circuit breaker comprising a housing of molded insulating material, terminals at opposite ends of said housing, operating means disposed in said housing comprising separable contacts for drawing an arc, and a coating of a non-tracking silicone of a consistency ranging from a fluid to a gel applied to the insulating material of said housing after said housing is molded at least in the area where the arc is drawn.

2. In a circuit breaker comprising a housing of molded insulating material, terminals supported by said housing, operating means disposed in said housing comprising separable contacts for drawing an arc, and a coating of a non-tracking hydrocarbon silicone having as hydrocarbon substituents on the silicon atom thereof, groups selected from at least one of the class consisting of methyl and ethyl radicals, said coating being applied to said housing of insulating material after said housing is molded and improving the insulating properties thereof.

3. In a circuit breaker comprising a housing of molded insulating material, terminals supported by said housing, operating means disposed in said housing comprising separable contacts for drawing an arc, and a coating of dimethyl silicone fluid combined with a substantial proportion of a finely divided filler applied to said housing at least in the area where the arc is drawn after said housing is molded.

4. In a circuit breaker comprising a housing of molded insulating material, terminals at opposite ends of said housing, operating means disposed in said housing comprising separable contacts for drawing an arc, and a coating of a hydrocarbon silicone having an average of from 1.1 to 1.9 hydrocarbon groups per silicon atom, the hydrocarbon groups being selected from the group consisting of methyl and ethyl radicals, the silicone being gel-like or resinous in consistency when applied, said coating being applied to said housing at least in the area where the arc is drawn after said housing is molded and then drying at room temperatures to form a hardened coating.

5. In a circuit breaker comprising a housing of insulating material, terminals supported by said housing, operating means disposed in said housing comprising separable contacts for drawing an arc, and a coating of a non-tracking silicone fluid having a volatile liquid solvent, said fluid drying at room temperatures and being in the form of a hardened coating on a portion of said housing.

6. In a circuit breaker comprising a housing having two parts of molded insulating material, said two parts being secured together, terminals supported by said housing, operating means disposed in said housing comprising separable contacts for drawing an arc, and a hydrocarbon silicone having as hydrocarbon substituents on the silicon atom thereof, groups selected from at least one of the class consisting of methyl and ethyl radicals, said silicone being applied to the joint between the two parts of the housing after said housing parts are molded.

7. In a circuit breaker comprising .a housing of insulating material, terminals supported by said housing, operating means disposed in said housing comprising separable contacts for drawing an arc, and a hydrocarbon silicone having as hydrocarbon substituents on the silicon atom thereof, groups selected from at least one of the class consisting of methyl and ethyl radicals, said silicone being a liquid solution in a volatile solvent spray coated and air hardened on said housing of insulating material.

References Cited in the file of this patent UNITED STATES PATENTS 1,915,969 Barringer June 27, 1933 2,236,580 Sandin et al. Apr. 1, 1941 2,428,608 Bass Oct. 7, 1947 2,639,346 Yonkers May 19, 1953 2,640,128 Fahnoe et a1 May 26, 1953 2,645,693 Cole et .al. July 14, 1953

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