US3053955A - Electrical contactors or circuit breakers - Google Patents

Description

Sept. 11, 1962 H. T. BALDWIN ELECTRICAL CONTACTORS OR CIRCUIT BREAKERS 2 Sheets-Sheet 1 Filed May 18, 1959 INVENTOR --FIG. 2--

ATTORNEYS p 1962 H. T. BALDWIN 3,053,955

ELECTRICAL CONTACTORS OR CIRCUIT BREAKERS Filed May 1959 2 Sheets-Sheet 2 I N v E N TOR $4 010 Zmaey 3420M W rlz'im v ATTORNEY5 United States Patent U 3,053,955 ELECTRICAL CONTACTORS OR CIRCUIT BREAKERS Harold Townley Baldwin, Eyre St., Sheffield, England Filed May 18, 1959, Ser. No. 814,045 Claims priority, application Great Britain Mar. 14, 1959 1 Claim. (Cl. 200--147) This invention relates to improvements in contactors or circuit breakers of the type in which the contacts are mounted within but out of contact with a shroud protecting the contacts from the entry of air during the breaking of the contacts.

As it is well known upon the breaking of electrical contacts an are or electron discharge occurs between the two contacts. The are occurs with explosive suddenness and the accompanying flame may propagate itself to great length and cross sectional area compared with the are core proper, and consequently the flame itself must be effectively controlled by means of additional to the mechanism for are rupture in order to break the circuit with maximum efficiency.

Attempts have been made in prior art circuit breakers to house or confine the flame by walls or barriers to prevent damage to adjacent parts and to prevent the flame from bridging metal parts causing a short circuit in the contacts and the flame must therefore be dealt with concurrently with the are proper.

The invention comprises a shroud formed of substantially semi-circular or D shape exposed to the atmosphere and closed at both ends by end plates with a stationary contact mounted in one end plate to project near to but out of contact with a ring or plate of magnetic material mounted intermediate the ends of the shroud, and a moving contact projecting into the chamber enclosed by the shroud and mounted on a slide for movement vertically into and out of engagement with the stationary contact, the ring or plate producing a circular magnetic field which prevents the arc from spreading sideways and promotes efficient arc control.

Where the surface area of the contact is large the normal requirements of electrical clearance will result in a chamber of large volume and the etfiective volume of air contained in the shroud chamber may be reduced by the employment of an inner shroud of substantially semi-circular or D shape, carried by the closed end of the outer shroud, and projecting from the closed end to adjacent the ring or plate.

For a double break contactor or circuit breaker a common slide carrying both movable contacts is mounted between the substantially semi-circular or D-shaped shrouds mounted in casings bolted together to sandwich the slide therebetween.

Two or more shrouds may be mounted side by side in the casing for simultaneously breaking single or multiphase circuits.

The invention will be described with reference to the accompanying drawings:

FIGURE 1 is a perspective exploded view of a three phase double pole contactor or circuit breaker showing the upper and lower end plates and the intermediate slide carrying the moving contacts;

FIGURE 2 is an elevation partly in section showing one shroud chamber;

FIGURE 3 is a horizontal section through the casing and slide on line 3-3, FIGURE 4;

FIGURE 4 is a vertical section at right angles to FIG- URE 3, and

FIGURE 5 is an elevation of one shroud chamber showing an inner shroud therein;

FIGURE 6 is a section on line 66, FIGURE 5;

Patented Sept. 11, 1962 FIGURE 7 is a plan view from below of a modification.

The drawings as shown in FIGURES 1 to 4 illustrate the invention applied to a three phase circiut breaker in which the contactor or circuit breaker comprises a casing formed in two sections, 1, 2 and bolted together by bolts passing through holes 3 therein between which is mounted a slid-e 4 carrying moving contacts 5. Each section '1 or 2 is divided by partition walls 6 into compartments, the partition walls 6 extending inwardly of the casing to engage grooves 7 in the slide 4 to form interphase barriers therefor.

A shroud 8 of magnetic or non-magnetic material substantially semi-circular or D shape with flanges 10 to enter recesses in the casing is mounted in each compartment of the casing and is enclosed at each end by end plates 16, 17, the outer periphery of the shroud being exposed to the atmosphere. A stationary contact 9 is mounted in the end plate 16 of the casing to project into the chamber A enclosed by the shroud and the slide and at the ends by end plates 16, 17. Intermediate the ends of the chamber A a disc or plate 11 of magnetic material of the same contour as the shroud is secured therein as shown or it may enter a groove in the shroud. The stationary contact 9 extends in close proximity to the disc or plate but out of contact therewith. The contact 9 may be provided with a shoulder to engage a recess in the casing and is formed with a screwed or other shank to receive a nut for attachment of the lead thereto.

The shroud is shown as being of metal to provide good heat conductivity so that, as the outer surface is exposed to atmosphere, heat is readily transferred thereto and the shroud is cooled, but the shroud may be formed of insulating material provided this material will withstand the heat generated by the arc.

The slide 4 is provided with the grooves 7 on both surfaces to receive the partition walls 6 which act as interphase barriers. The moving contacts 5 for a double break contactor or circuit breaker are mounted on the ends of a bar 12 supported on a member 13 spring mounted in the slide 4 with the bar 12 projecting at each side of the slide to extend into the chamber A in line with the stationary contacts 9. The bottom of the slide 4 is provided with a member 14 by which slide 4 is actuated to make or break the contacts.

On the breaking of the contacts the are thereby produced is controlled by the magnetic field which is produced in the disc or plate 1 1 which is of the general shape shown, the break taking place in the vicinity of the disc or plate 11. The heat generated by the arc passes to the shroud and is dissipated thereby. It has been found that the volume of air in the chamber A should be kept to a minimum consistent with a clearance between the contacts and the shroud and that after repeated operations removal of metal from the contacts is minimised thereby increasing the life of the contacts nor does erosion or other high temperature effects take place on the casing and end plates.

A limited volume of air can enter the chamber A along the bars 12 but no air will enter during the formation of an are on breaking of the contacts since the heat generated by the arc causes the air in the chamber A to expand and accordingly the pressure in the chamber A rises to more than atmospheric.

Where the contacts have to carry a high current the surface area of the contacts is increased and this increase in the surface area of the contacts necessitates a corresponding increase in the diameter of the shroud thereby increasing the volume of air in the chamber A. In order to reduce the effective volume of air at the moment of break a second shroud 15, FIGURES 5 and 6, is arranged inside the shroud 8, the shroud 15 being mounted on the end wall of the casing remote from the stationary contact 9 and extending adjacent to the stationary contact, the end of the shroud 15 adjacent the stationary contact being open. An annular air cushion B (FIGURE 6) is provided between the two shrouds 8, 15, which does not participate in the breaking operation. The shroud 15 is preferably metal and provided with an end plate of similar material to withstand the heat generated by the are but it may be of insulating material provided this latter will withstand the temperature.

Where a single break contactor or circuit breaker is required the casing is moulded to accommodate a single shroud 8 and the slide 4 moves in the casing and carries a single movable contact 5.

The movement of the moving contacts 5 in each chamber A will substantially change the air in each chamber between each break.

An alternative form of shroud (FIGURE 7) comprises metal laminates 18 of magnetic or non-magnetic material of U or ring form insulated from each other by laminates of insulating material 19 and projecting into the arc chamher to a less extent than the metal laminates 18. In this way the insulation material 19 is kept at a safe distance from the high temperature arc, and the projecting metal laminates 18 forming the shroud reduce the volume of air in the arc chamber.

For breaking of low current circuits all these laminates 18 forming the shroud may be of U shape, but for the breaking of higher currents one or more of these laminates 18a should be of magnetic material and of ring form, and of the general shape shown in FIGURE 7, to control the magnet field and thus the arc movement and operate as described in connection with the plate 11.

I claim:

In an electrical contact making and breaking device having a stationary contact and a movable contact engageable with said stationary contact and substantially aligned therewith long a longitudinal axis, a fixed housing defining a substantially enclosed chamber wherein said stationary and movable contacts are disposed and engage, said stationary contact being disposed near one end of said chamber and having an engagement surface extending radially with respect to said longitudinal axis and facing toward the opposite end of said chamber, a member extending into said chamber and mounting said movable contact in a position facing said stationary contact, displacement means mounted on said housing but exteriorly of said chamber for displacing said member together with said movable contact along said longitudinal axis, said movable contact being displaceable by said displacement means between a first position in electrical contact with said surface of said stationary contact and a second position spaced therefrom along said longitudinal axis but within said chamber, said housing comprising opposed end walls spaced apart along said longitudinal axis in transverse relationship thereto and delimiting the opposite ends of said chamber with one of said end walls fixedly mounting said stationary contact, and a curved side wall portion in at least semi-encircling relationship to said stationary and movable contacts and extending between said end walls and delimiting said chamber to control and protectively enclose an are formed between said contacts, said side wall portion comprising a plurality of stacked abutting layers of alternating members of electrically insulating material and of magnetic material with each of said layers extending transversely with respect to said longitudinal axis, said members of magnetic material being free of engagement with said contacts but projecting transversely inwardly into said chamber by a further distance than said insulating members to reduce the effective volume of said chamber and to enable said insulating members to be spaced at a sufficiently safe distance from said arc for withstanding the heat generated thereby.

References Cited in the file of this patent UNITED STATES PATENTS 2,058,656 Anderson Oct. 27, 1936 2,227,134 Hara Dec. 31, 1940 2,240,623 Lindstrom May 6, 1941 2,650,971 Dawe Sept. 1, 1953 2,692,318 Few et al Oct. 19, 1954 2,794,093 Morschel May 28, 1957 2,794,882 Russell June 4, 1957 2,874,245 Moyer Feb. 17, 1959 FOREIGN PATENTS 1,180,131 France Dec. 29, 1958

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