US2875303A

US2875303A - Circuit interrupter

Info

Publication number: US2875303A
Application number: US463912A
Authority: US
Inventors: Ralph B Immel; Arthur S Nadrowski; Marshall P White
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1954-10-22
Filing date: 1954-10-22
Publication date: 1959-02-24
Anticipated expiration: 1976-02-24
Also published as: FR1137680A

Description

Feb. 24, 1959 R. B. IMMEL ET AL 2,875,303

CIRCUIT INTERRUPTER 2 Sheets-Sheet 1 Filed Oct. 22, 1954 INVENTORS WITNESSES dlph B. I,Arthur S.N0drowski shull P. White Imme and Mar ATTORNEY Feb. 24, 1959 R- B. IMMEL ET AL' 2,875,303

CIRCUIT INTERRUPTER 2 Sheets-Sheet 2 Filed Oct. 22, 1954 United States Patent CIRCUIT INTERRUPTER Ralph B. Immel, Williamsville, and Arthur S. Nadrowski and Marshall P. White, Buflalo, N. Y., assignors t0 Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 22, 1954, Serial No. 463,912 7 Claims. (Cl. 200-147) This invention relates generally to electric circuit interrupters and, in particular, to such apparatus embodying improved arc extinguishing arrangements.

With particular reference to electric switches, various means have been provided in prior art arrangements for extinguishing the arc which is drawn upon separation of the movable contact from the stationary contact. In a general sense these means may be divided into two categories, in the first of which the arc is drawn and extinguished by distortion of the arc magnetic field through the introduction of iron grid plates in the region of the arc magnetic field and in a second of which an external magnetic field linking the arc magnetic field is utilized to displace the arc and expedite its extinction.

The second of the two above-mentioned methods involves some means for producing a magnetic field. One arrangement employs a blowout coil which may be energized in dependence of arc current to produce a magnetic field directed lateral-1y of the arc and a second arrangement utilizes metallic permanent magnets as a substitute for the blowout coil. Each of these expediencies tends to increase the size and complexity of the arrangement and although satisfactory in certain respects in a functional sense, the increased cost and inherent manufacturing problems are factors to be minimized if not completely eliminated in view of the competitive nature of the apparatus.

More particularly, most conventional and commercially available contactors employ a strap or wire wound blowout coil assembly in conjunction with a single break contact. The current is carried through the blowout coil which must be insulated from the arc horns and terminals. The coil assembly usually comprises an iron core, the ends of which contact field plates, the latter of 'which are used to direct the magnetic blowout field across the arc interrupting chamber at the contact area. As the actual insulation between the blowout coil and the iron parts is rather small, it is usually necessary to provide considerable space or substantial insulation barriers between terminals and auxiliary contact parts of opposite polarity to obviate the possibility of switch failure after a period of use. Blowout coil windings are often the largest source of heat in a contactor and frequently contribute to contact overheating. In view of this high operating temperature it is usually necessary to braze all points in the blowout coil assembly to provide good electrical conductivity at these points and, therefore, minimize overheating of the joints. In arrangements such as described using single break contacts, a flexible connection between the moving contact and one of the switch terminals is employed. These flexible connections are frequently a source of mechanical trouble. For simplicity, they are usually connected to the armature; and the frame of the contactor. These arrangements make .it very diflicult to mount the contactor on anything except an insulating panel. The present invention is, directed'to improving and 2,875,303 Patented Feb. 24, 1959 simplifying arrangements of the type described and at the same time providing a contactor or switch usable on either alternating current or direct current service.

Accordingly, a general object of this invention is to 5 provide an improved circuit interrupting device which is small in physical size for its rating and low in cost.

More particularly, it is an object of this invention to provide an electric switch in which the electrical insulation problems are minimized.

Another object of this invention is to provide an electric switch having a simple are extinguishing arrangement.

It is also an object of this invention to provide an electric switch in which the arc extinguishing capacity over prior art devices of the same rating is increased.

Further to the preceding object, it is an object of this invention to provide an electric switch in which for a given rating the length of the arc path is increased.

A specific object of this invention is to provide a circuit interrupting device having an arc blowout arrangement embodying an arc chamber of electrical insulating heat resisting permanent magnet material.

Another specific object of this invention is to provide a circuit interrupting device which is usable on either alternating current or direct current within its rated capacity without modification of the switch construction in any way.

A further specific object of this invention is to provide a circuit interrupting device employing permanent magnet means for producing an arc blowout field in which the arc box structure and contact disposition therein is such that the device may 'be used on either alternating current or direct current service.

The foregoing statements are merely illustrative of the various aims and objects of this invention. Other objects and advantages will become apparent from a study of the following specification when considered in conjunction with the accompanying drawings, in which:

Figure l is a perspective view, fragmentarily in section, illustrating an electric switch representing one embodiment of this invention;

Fig. 2 is a perspective view, fragmentarily in section, illustrating an electric switch or circuit interrupting device representing a second embodiment of this invention, and

Figs. 3 and 4 are, respectively, perspective views illustrating the elementary parts of the circuit interrupting devices of Figs. 1 and 2.

Referring to Figs. 1 and 3, the embodiment of theinvention illustrated therein comprises a double break horizontally disposed contact arrangement including a movable contact bridge generally designated 1, having mounted thereon at longitudinally spaced points respective contacts 3 and 5. This movable contact bridge is provided with oppositely disposed slots at its central portion which receive the legs of a yoke 7 which is mounted upon a strap 9 carried by a movable support 11 which may be actuated in any suitable manner. For example, the support 11 may be made of electrical insulating material and mounted upon the armature of an electromagnet, the magnetic field of which is utilized to move the armature. Such an armature is usually spring loaded to provide positive bias to a given position upon deenergization of the electromagnet. This and other conventional expediencies may be practiced in actuating the support 11. The movable contact bridge is spring loaded against stops provided at the end of the yoke, by means of a compression spring 14.

Contacts 3 and 5 of the movable contact bridge are arranged in confronting arrangement with a pair of correspondingly spaced horizontally disposed stationary contacts generally designated 13 and 15. These stationary contacts are mounted on the unsupported ends of a pair of strap conductors, repectively designated 17 and 19, which are of generally J-shaped configuration. These conductors in turn are secured to the vertical leg 21 of an L-shaped base 23 of electrical insulating material. The vertical legs of the J-shaped conductors extend to a point adjacent the upper end of the vertical leg 21 of the base and provided with suitable holes 25 providing means for making electrical connections therewith. With this arrangement, a double break in the circuit between the J-shaped conductors is provided at the respective pairs of cooperating contactsS, 13' and 15, eliminating all need for flexible shunts or other equivalent expedients as is required in arrangements embodying only a single break contact construction. Base member 23 includes a central insulating barrier 27 which may be integrally formed with the vertical leg 21 and the horizontal leg 29 and which is disposed between the respective stationary contacts and strap conductors connected therewith to provide an electrical insulating barrier therebetween.

The switch structure is enclosedby means of an arc box structure or assembly 31 which may comprise any suitable type of cold molded material or ceramic material such as those conventionally used in switch manufacture and is provided with permanent magnet inserts 3'3 and 35, both of which appear in Fig. 3. These inseits' may be disposed internally or externally of the arc box sidewalls and while they may be made of conventional metallic permanent magnet material, are preferably made of electrical insulating ceramic permanent magnet material which may be a magnetic mixed oxide compound selected from the group consisting of BaO-6Fe O PbO-6Fe O and SnO-6Fe O 'Thes'emagnetic inserts provide a very uniform and strong magnetic field for blowing out the arc which is initiated when the contacts separate.

As no space is required for a blowout coil, this space Y can be effectively utilized to increase the length of the arc horns, in this case, the J-shaped strap conductors. These are horns are much more effective in are interruption over the more conventional L-shaped arrangements because the dip at the bottom of the J-shaped configuration may be such as to stretch the are approximately 50 to 75% further than with conventional L-shaped arrangements. Elimination of the blowout coil thus makes it possible to utilize space more economically;

Ceramic permanent magnet plates, such as 33 and 35, identified by any one of the groups hereinabove referred to, have an electrical insulation resistance approximately of the order of ohms per cubic centimeter and do not require additional insulation between terminals and other energized parts. These magnets can be readily cemented into suitable openings or recesses in the arc box with commercially available ceramic cements. Another desirable feature is that the cost of a ceramic permanent magnet is many times less than that of a comparable metallic magnet of an alloy of aluminum, nickel and cobalt. A further desirable property of this material in switch applications is its high resistance to heat, making it feasible to mount the permanent magnet plates of this material in close proximity to the contact gaps which more effectively concentrates the magnetic field in the region of the arcs struck upon contact separation'thereby more effectively deflecting the arcs and expediting their extinction.

The assembly is further provided with an arc cup 37 which is disposed beneath and which straddles the stationary and movable contact assemblies. The stationary contacts and the movable contact bridge which cooperates therewith are mounted within and spaced from the sides and bottom of this are cup. The are cup is made of magnetic material and tends to confine and restrict an are which is directed thereinto by the magneti'c'field and by its action reduces the are magnetic field in the cup area which tends to prevent the are from spreading from the cup. The function of such an arcing cup is well known in that it tends to divide the arc into series sections, one between the movable contact bridge and the bottom of the cup and the second between the bottom of the cup and the stationary contact and/or are horn at that point. This series division ofjthe arc introduces a multiple number of arc terminals which requires a higher voltage to maintain the arc and, hence, hastens its extinction. Further the arc cup provides additional cooling surface area which helps to keep the assembly cooler and hasten arc extinction.

The ceramic permanent magnet plates-33 and .35 are poled in series magnetic relation soas to produce a unidirectional magnetic field therebetween which is directed from one end of the movable contact bridge to the otheracross the two contact gaps. For the purposes of this discussion, assume thatthe strap conductor 17 is positive and the strap conductor 19 is negative. The current flow in the are which will be struck at contact separation will flow from stationary contact 13- to movable contact 3 through the movable contact bridge from left to right, as viewed, and thereafter from contact 5 to stationary contact 15 to strap conductor 19. Assuming further that the magnetic field, due to the permanent magnet plates, is from left to right, as viewed, it will be appreciated that the are appearing between

contacts

3 and 13 will be directed upwardly into the arc box and that the arc struck between contacts 5 and 15 will be directed downwardly into the are cup. The are struck between

contacts

3 and 13 while being drawn upwardly, due to the magnetic field force acting thereon, will also be drawn rearwardly over the J-shaped strap conductor 17 tending to move upwardly on the vertical leg thereof which is secured to the vertical leg of the base. 'A suitable opening 39 is provided in the arc box in its upper face adjacent the

respective straps

17 and 19 to provide venting of the arc gases at that point and to permit arc travel upwardly along this portion of the strap conductors. The downwardly deflected arc between contacts 5 and 15 is drawn downwardly intothe arc cup as described and is then drawn rearwardly below the J-shaped conductor 19 which hastens its extinction. The length of the are along the lower face of strap conductor 19 is measurably increased by providing suitable vent holes 41 therethrough which permits the escape of. are gases minimizing pressure therebeneath. A similar set of holes is provided in the strap conductor 19. If the polarity of the strap conductors is now reversed, it will be appreciated that the arc struck between contacts 5 and 15 will be blown upwardly into the arc box and the arc struck between

contacts

3 and 13 will be blown downwardly into the arc cup. In view of this described symmetry in arc interrupting capacity, it will be appreciated that the switch is well suited to alternating current service, the arc configuration at contact separation depending upon the instant polarity of the conductors at theinstant of contact separation.

The configuration of the arc box structure may be con ventional being provided with suitable slots such astne slot 43 extending through its top and front facesfor venting the gas pressure, resulting from the arcs, to the atmosphere. The box is conveniently mounted in suitable grooves 45 provided in the horizontal portion 29 of base 23 which receive the lower side edges of the arc box structure. The back end of the arc box is left open for venting purposes and the sides of the arc box straddle the vertical leg 21 of the base. Any suitable meanstnot shown) may be utilized to secure the arc box to the base.

The embodiment of this invention shown in Figs. 2 and 4 is a simplified assembly using the same interrupting principle. In view of the similarity in structure and. in principle of this device with respect to. Fig. 1, ,partsin Fig. 2 corresponding to those in. Fig. I bear like reference characters. In Fig. 2 only one permanent magnet 47 is required for the blowout field and the steel arcing cup 37 in Fig. 1 is not required. This may be explained as follows: With the two magnets as in Figs. 1 and 3 the field between the magnets is quite uniform and the flux lines are straight. The field is quite strong and in a compact switch design not much arcing space is available for arcs driven downwardly. Hence, in such an arrangement the steel arcing cup 37 helps to control the arc. With'one magnet the field has a different shape. The field at the magnet is in the same general direction as with the two magnets, but loops from one magnet face around to the other. Hence, if the magnet is set too high or too far away from the stationary contacts, the field will be reversed from the desired direction. In the arrangement shown the lower edge of the magnet is positioned in the most favorable position with respect to the stationary contacts to provide the best control of the lower are. For this reason the steel arcing cup may be eliminated and the major circuit interruption is done with the are driven upwardly.

In addition to reducing the number of parts with the arrangement of Fig. 2, the size of the switch can also be reduced. With the assembly illustrated in Fig. l, the permanent magnets must always be assembled in series, that is north to south, etc. If this is not done the magnets are opposed to each other and .both arcs will either go up or down depending upon the magnetic polarity. Because of the thermal rise of hot gases and venting of the are box 31 it is generally more desirable to direct one of the arcs in an upward direction.

In the assembly shown in Fig. 2, it makes no difference how the magnet, with reference to its polarity, is assembled in the base 23. As shown, the permanent magnet 47 is mounted in a suitable cavity formed in the barrier 27a disposed between the

respectivestrap conductors

17 and 19. If the visible face of the magnet in Fig. 2 which is marked N is considered a north pole, then the magnetic field will be directed from left to right of the assembly which, if strap conductor 17 is positive and strap conductor 19 is negative, results in arc deflection which directs the are between the

contacts

13 and 3 upwardly and that between contacts Sand 15 downwardly as was the situation for the magnetic polarities described in Fig. 1. However, if the magnet 47 were reversed in polarity from that indicated in Fig. 2, the magnetic field for the instant polarity of the

strap conductors

17 and 19, described above, would be reversed, deflecting the are between contacts 5 and 15 upwardly and that between

contacts

3 and 13 downwardly. Because of this symmetrical arrangement of the switch it makes no difference which are goes up and which are goes down. Therefore, it is of no consequence from the standpoint of switch operation which polarity the magnet happens to be when it is assembled in the switch.

While a permanent magnet of ceramic magnetic material according to any one of the groups hereinabove reerred to is contemplated in this construction, which minimizes the thermal and electrical insulating problems existing in switches of conventional design, it will be appreciated that a properly insulated metallic magnet may also be'employed in this configuration with effective results.

' Extensive interrupting tests have been conducted on 50 ampere single pole models of both of the embodiments of this invention illustrated herein employing the ceramic permanent magnets. Of the two embodiments shown, equal functional ratings may be construed. However, the arrangement illustrated in Fig. 2 involving fewer parts is the more attractive from a manufacturing viewpoint. As a matter of practical interest, the physical dimensions of a contactor arcing structure constructed accord- 7 ing to the principles illustrated in Fig. 2 are given below for comparison with conventional contactor arcing structures of comparable rating. The arcing structure on a 50 ampere rated model is approximately 2 inches wide, 2 inches high, and 3 inches deep. This is considerably smaller than comparable 50 ampere contactors which are presently commercially available. In addition to being physically smaller, the external arcing clearance to parts of opposite polarity has been reduced to approximately 25% of that required for a conventional single break direct current contactor.

Typical interrupting characteristics of a contactor constructed according to Fig. 2 are as follows:

Although this disclosure, with particular reference to Fig. 1, illustrates an arc box construction involving permanent magnet inserts of ceramic permanent magnet material, it will be appreciated that the entire arc box may be made of this material without departing from the spirit and scope hereof. In such a construction one side of the arc box would be magnetized as a south pole and the other side of the arc box magnetized as a north pole to produce a magnetic field thereacross of the order described in connection with Fig. l.

The ceramic permanent magnet material may be coated with a vitreous or refractory enamel and fired without damage to the material. After all work on the magnet is completed it can be magnetized similar to any other type of permanent magnet. The resistance of the magnet to direct arcing is improved by this treatment.

The arrangements herein described substantially simplify apparatus of the type disclosed. For example, this switch in direct current applications accomplishes the functions of a switch equipped with a blowout coil but eliminates the space and cost requirements of such a coil, its core and insulation tube and washers, together with the iron field plates connected with the core. Moreover, overheating problems are reduced when the blowout coil is eliminated. In addition, insulation problems and space wasting insulation separations and barriers in and around the grounded coil and iron parts do not exist. Still further, the disadvantage inherent with a coil, of blowout field strength which varies directly with the current, is eliminated. With a blowout coil at low currents the interruption is usually poor as the field is very weak. With the present arrangement the blowout field strength is independent of the current which eliminates the mentioned fault.

The advantages which the use of ceramic permanent magnets afford over prior metallic permanent magnet arrangements are equally important. Being current conductors, the metallic magnets also present insulation problems.

In each of the above instances, this invention eliminates the need for separate magnetic field producing means by providing an arc box construction or more generally a switch construction including the ceramic permanent magnet material.

It will be appreciated that the present invention represents a novel approach to the problem of simplifying electric switch construction and increasing arc extinguishing capacity through the expedient of utilizing magnet arrangements of the class described. This simplifies the design and manufacturing problems and at the same time for a given rating, reduces the size and complexity of the arc extinguishing arrangement.

Further the switch configuration and are box arrangement provides an assembly usablewithout alterationon either-alternating current or direct current service.

While two embodiments of thisinvention have been herein illustrated, it will be appreciated by those skilled in the art that other materials having suitable electrical and magnetic properties may be substituted for those herein described and moreover that other arrangements and configurations of the arc extinguishing apparatus maybe utilized without departing from the spirit and said base, a movable contact bridge movable between positions engaging and disengaging said stationary contacts, at least a portion of each of said conductors adjacent the associated stationary contact being substantially aligned with the contact gap between the associated stationary contact and the cooperating part of said movable contact bridge and functioning as an arc horn, andmeans of ceramic permanent magnet material disposed adjacent said contacts to produce an arc deflecting magnetic field substantially longitudinally of said movable contact bridge.

2. An electric switch comprising, a base of electrical insulating material, a pair of conductors mounted on said base and having a pair of spaced unsupported ends horizontally disposed above said base, a pair of stationary contacts respectively mounted onthe unsupported ends of said conductors, a movable contact bridge movable between positions engaging and disengaging said stationary contacts, at least a portion of each of said conductors adjacent the corresponding stationary contact functioning as an arc horn, and means of ceramic permanent magnet material disposed adjacent said contacts to produce an arc deflecting magnetic field directed substantially longitudinally of said movable contact bridge.

3. An electric switch comprising, a base of electrical insulating material, a pair of conductors mounted on said base and having a pair of spaced unsupported ends horizontally disposed above said base, a pair of stationary contacts respectively mounted on the unsupported ends of said conductors, a movable contact bridge movable between positions engaging and disengaging said stationary contacts, at leasta portion of each of said conductors adjacent the corresponding stationary contact functioning as an arc horn, an arc box structure disposed to receive arcs struck at said contacts, and cerarnic permanent magnet means disposed internally of said are box structure and producing a magnetic field substantially longitudinally of said movable contact bridge.

4. An electric switch comprising, a base of electrical insulating material, apair of conductors mounted on said baseand having a pair of spaced unsupported ends horizontally disposed above said base, a pair of stationary contacts respectively mounted on the unsupported-ends of'said conductors, a movable contact bridge movable between positions engaging and disengaging both said stationary contacts, at least a portion of each of said conductors adjacent the. corresponding stationary contact functioning as an, arc horn, an arc box structurestraddling said stationary, contacts and conductors, and ceramic permanentmagnet plates supported by said are box on opposite sides of said stationary contacts and conductors and poled to produce a magnetic field across said stationary contacts ina directionsubstantially longitudinally of said movable contact bridge.

5. An' electric switch comprising, a base of electrical insulating material, a pair of conductors mounted on said base and having a pair of spaced unsupported ends horizontally disposed above said base, a pair of stationary contacts respectively mounted on the unsupported ends of said conductors, a. movable contact bridge movable between positions engaging and disengaging both said stationary contacts, at least a portion of each of said conductors adjacent the corresponding stationary contact functioning, ,as an arc horn, an arc box structure straddling said, stationary contacts and conductors, .and ceramic permanent magnet plates supported on opposite walls of said are box on opposite sides of said conductors and stationary contacts and poled to produce avmagnetic field thereacross disposed substantially longitudinally of said movable contact bridge. a

6. An electric switch comprising, a base of electrical insulating material, a-pair of conductors mounted on said base and having a pair o'f spaced unsupported ends horizontally disposed above said base, a pair of stationary contactssrespectively mounted on the unsupported ends of said conductors, a movable contact bridge movable between positions engaging and disengaging both said stationary contacts, at least a portion of each of said conductors adjacent the corresponding stationary contact functioning as an arc horn, an arc box structure straddling said stationary contacts and conductors, and a single ceramic permanent magnet plate disposed in said are box in a plane between said conductors and poled to produce 'a magnetic field across said contacts in a direction substantially longitudinally of said movable contact bridge.

7. An electric switch comprising, a base of electrical insulating material, a pair of conductors. mounted on said base and having a pair of spaced unsupported ends horizontally disposed above said base, a pair of stationary contacts respectively mounted on the unsupported ends of said conductors, amovable contact bridge movable between positions engaging anddisengaging both said stationary. contacts, at least a portion of each of said conductors adjacentthe corresponding stationary contact functioning as an arc horn, an arc box structure straddling said stationary contacts and conductors, and a single ceramic permanent magnet plate mounted between said conductors in said are box and poled to produce a magnetic field across said contacts in a direction substantially longitudinally of said movable contact bridge,

References Cited in the file of this patent STATES PATENTS.