US2875302A - Circuit interrupter - Google Patents

Description

1959 R. B. IMMEL ET AL 5,

CIRCUIT INTERRUPTER Filed Feb. 8. 1954 ATTORNEY WITNESSES United States Patent CIRCUIT INTERRUPTER Ralph B. Immel and Arthur S. Nadrowski, Buiialo, N. Y., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 8, H54, Serial No. 408,910

6 Claims. (Cl. Nil-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 are 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 energi zed in dependence of arc current to produce a magnetic field directed laterally of the arc and a second arrangement utilizes permanent magnets as a substitute for the blowout coil. Each of these expedients tends to increase the size and the 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 or the apparatus.

More particularly, most conventional and commercially available direct current 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 connect with field plates, the latter or" 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 may contribute to contact overheating. In view of this high operating temperature, it is usually necessary to braze all joints 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 cont act 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. This arrangement makes it very difiicult to mount the contactor on anything except an insulating panel.

Accordingly, a general object of this invention is to 2,875,302 Patented Feb. 24, 1959 provide an improved circuit interrupting device which is small in size for its rating and low in cost.

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

Another object of this invention is to provide an elec tric switch having a simple arc extinguishing arrangement.

It is also an object of this invention to provide an electric switch in which the arc extingushing 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 permanent magnet material.

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

Figure l is a perspective view fragmentarily in section of an electric switch embodying the principles of this invention, and

Fig. 2 is a perspective view illustrating the elementary parts of the circuit interrupting arrangement.

Referring to the drawing, the illustrations show a double break switch ararngement embodying a pair of stationary contacts 2 and 4, disposed one above the other, and a movable contact bridging member 6 adapted for movement between positions engaging and bridging stationary contacts 2 and 4 and disengaging the stationary contacts.

An arc box- 8 straddles and encloses the contact assembly and is equipped with permanent magnet inserts liland 12 which are utilized to produce a magnetic field across the gaps between the stationary contacts and the movable contact bridge. The contact assembly and the arc box structure is mounted upon a suitable base of electrical insulating material, generally designated 14. Base 14 supports a contact strap 16 which is connected to and which supports the upper stationary contact 2. The base also mounts and supports a terminal 18 connected by a screw 20 to the lower stationary contact 4.

The movable contact bridge 6 is slidably mounted in a yoke 22 and spring loaded by a compression spring 24 which is disposed between one end of the yoke and the central portion of bridging member 6. Yoke 22 is secured to the upper end of a metal strap 26, the lower end of which is mounted on an actuator 28 of insulating material. In the interest of simplicity, the means for operating the actuator 28 have not been shown. Such means may be manual or, may involve any one of numerous conventional electro magnetic arrangements.

The are box structure, generally designated 8, may

comprise any suitable type of cold molded material or ceramic material such as those conventionally used in switch manufacture. However, the magnetic inserts 10 and 12 are made of electrical insulating ceramic permanent magnet material which may be a magnetic mixed oxide compound selected from the group consisting of BaO.6Fe D PbO.6Fe O and SrO.6Fe O These inserts provide a very uniform and strong magnetic field for blowing out a direct current are when the contacts are opened.

As no space is required for a blowout coil this space can be effectively utilized to increase the length of. the strap 15 which functions as the upper are born. This are horn, which is of J-shaped configuration, is much more effective in arc interruption overv the more conventional L-shaped arrangement because the dip in the are born or strap at 34) may be such as to stretch the are approximately 50 to 75% further than with the conventional arrangement. Elimination of the blowout coil thus makes it possible to utilize space more economically. Ceramic permanent magnet plates, such as it} and 12, identified by the formula BaO.6Fe O have an insulation resistance 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 several times less than that of a comparable magnet of an alloy of aluminum, nickel and cobalt.

The lower stationary contact 4 and the lower portion of the movable contact bridge which cooperates there- With are mounted within and spaced from the sides and bottom of an arcing cup 32 of magnetic material. This arcing cup being of magnetic material confines and restricts the lower arc between its side walls and bottom and reduces the magnetic field in this area which prevents the arc from spreading from the cup. The function of such an arcing cup is well known in that it tends to divide the are into two sections, one between the lower portion of the movable contact bridge and the bottom of the cup and the second between the bottom of the cup and the lower stationary contact. This series division of the arc tends to reduce the strength of the arc and hastens its extinction.

In Figure 2, with the magnet plates 1% and 12 oriented to provide a magnetic field flux in the direction shown and with the'upper terminal or strap 16 connected to the positive side of the circuit controlled by the switch, "the arc betweencontact' 2 and the upper portion of the movable contact bridge is blown upwardly and the arc drawn between the lower stationary contact 4 and the lower portion of the movable contact bridge is blown downwardly into the arcing cup 32. The lower contact and arcing cup structure holds and restrains the lower arc while the upper arc is stretched out to interrupt the circuit.

Due to the arc division which takes place in the cup, this portion of the arc circuit also assists in the interruption. During a current interruption the upper arc actually runs down the outer face of support 26 of the movable contact bridge. The are conditions illustrated by the zigzag lines merely approximately illustrate one instant of arc development.

To illustrate the improvements afiorded by the present invention the following test data is given. This applies to a 50 ampere model interrupting device which had an arc box with a width of approximately 1 inch, aheight of 2 inches and a depth of 3% inches/ It will be appreciated that this is considerably smaller than ducted on are interruption time for 250 volt D. C. circuits and inductive loads representative of motors.

Although this disclosure illustrates an arc box construction involving permanent magnet inserts of the 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.

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. Resistance 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 function of a switch equipped with a blowout coil, but eliminates the cost and space requirements of such a coil, its core and insulation tubeand washers, and 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.

The advantages which the present invention affords over prior metallic permanent magnet arrangements are equally important. Being current conductors, the metallic magnets presented insulation problems paralleling those of the blowout coil assemblies.

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

It will be appreciated that the. present invention repre- 'sents a novel approach to the problem of simplifying electric switch construction and increasing arc extinguishing capacity through the expedient of utilizing 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. 7

While one embodiment of this invention has been I herein illustrated, it will be appreciated by those skilled a comparable 50 ampere conventional switch. In addition to being physically smaller, the arcing clearance for the new model was less. The double break contact and 7 longer upper arc horn arrangement minimized the amount of arcing outside the box. This makes feasible a much smaller enclosure for the switch.

Cycles arcing time for contactor 1 cycles=1 second.

The data presented aboveis a result of 'tests'coninthe 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 may be utilized without departing from the spirit and scope of this invention. Accordingly, it is intended that the foregoing disclosure and the showings made in the drawing shall be considered only as illustrative of the principles herein set forth and not construed in a limiting sense.

We claim as our invention:

1. An electric switch comprising, a pair of spaced stationary contacts, a movable contact bridge movable between positions engaging and disengaging said stationary contacts, an arc box of electrical insulating material disposed about said stationary and movable contacts,

and permanent magnet inserts of ceramic electrical insulating material inserted in the face of said are box on opposite sides of said contacts to produce a magnetic ffield laterally of the path of movement of said movable contact.

2. An electric switch comprising, a contact assembly including a pair of stationary contacts, one disposed above the other, and a movable contact bridge movable between positions engaging and disengaging said stationary "contacts; a metal arcing cup disposed to receive the lower stationary contact and the corresponding contact portion ofsaid movable contact bridge, and a permanent magnet, electrical insulating, arc box straddling said con- "tact assembly and producing a magnetic field laterally of the path of movement of said movable contact bridge.

3. A direct current electric switch comprising, a contact assembly including a pair of stationary contacts, one stationary contact being disposed above the other, and a movable contact bridge movable between positions engaging and bridging said stationary contacts and disengaging said stationary contacts; an arcing cup receiving the lower stationary contact and the lower portion of said movable contact bridge, and an arc box structure comprising electrical insulating permanent magnet material disposed to produce a magnetic field across the path of movement of said movable contact bridge, the polarity of said magnetic field with respect to are current When said switch is being opened, blowing the are between the upper stationary contact and the upper portion of said contact bridge upwardly and blowing the are between the lower stationary contact and the lower portion of said contact bridge downwardly into said arcing cup.

4. A direct current electric switch comprising, a contact assembly including a pair of stationary contacts, one stationary contact being U-shaped and being disposed above the other, and a movable contact bridge movable between positions engaging and bridging said stationary contacts and disengaging said stationary contacts; an arcing cup receiving the lower stationary contact and the lower portion of said movable contact bridge, an arc box structure straddling said contact assembly, said are box structure including a pair of electrical insulating permanent magnets producing a magnetic field across the path of movement of said movable contact bridge, the polarity of said magnetic field with respect to are current blowing an are at the upper stationary contact upwardly and blowing an are at the lower stationary contact downwardly into said arcing cup.

5. A direct current electric switch comprising, a contact assembly including a pair of stationary contacts, one stationary contact being disposed above the other being U-shaped downwardly beyond the contact engaging region, and a movable contact bridge movable between positions engaging and bridging said stationary contacts and disengaging said stationary contacts; an arcing cup receiving the lower stationary contact and the lower portion of said movable contact bridge, an arc box structure straddling said contact assembly, and permanent magnet inserts in said are box structure, said inserts being disposed in opposite sides of said are box and producing a magnetic field laterally of the path of movement of said movable contact bridge, said inserts being of at least one magnetic mixed oxide compound selected from the group consisting of BaO.6Fe O PbO.6Fe O and SrO.6Fe O 6. A direct current electric switch comprising, a contact assembly including a pair of stationary contacts, one stationary contact being disposed above the other, and a movable contact bridge movable between positions engaging and bridging said stationary contacts and disengaging said stationary contacts; an arcing cup receiving the lower stationary contact and the lower portion of said movable contact bridge, an arc box structure straddling said contact assembly, and permanent magnet inserts in opposite sides of said are box structure producing a magnetic field laterally of the path of movement of said movable contact bridge, said inserts being of a permanent magnet material identified as References Cited in the file of this patent UNITED STATES PATENTS 2,101,665 Arey et a1. Dec. 7, 1937 2,332,446 Heinrich Oct. 19, 1943 2,337,949 Walle Dec. 28, 1943 2,524,287 Ellis Oct. 3, 1950 2,575,060 Matthias Nov. 13, 1951 2,626,331 Basnett Jan. 20, 1953

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