US2253388A - Protective relay - Google Patents

Description

Aug. 19, 1941. P. MQSHANE PROTECTIVE RELAY Filed Dec. 14, 1938 WITNESSES:

Patented Aug. 19, 1941 2.25am PROTECTIVE RELAY Pheian McShane, Wilkinsburg, Pa assignor to Westinghouse Electric a Manufacturing Company, East Pittsburgh, Pa a corporation of Pennsylvania ApplicaticnDecember 14, 1938, Serial No. 243,665

7 Claims.

The present invention relates to protective relays, and more particularly to a thermo-responsive device for protecting electrical equipment,

against overload current conditions.

It is common practice in the art to employ overload relays which are responsive to the curthermo-responsive device is itself traversed by the circuit current, the effect is to add undesirable resistance in the circuit which prevents the proper functioning of fuses and circuitbreakers in the circuit, and there is always the possibility that the heater or thermo-responsive element may burn out or fuse.

It is an object of the present invention to provide a thermal overload responsive relay avoiding the difficulties above set forth, in which the moving parts are hermetically sealed and in which the theme-responsive element is heated indirectly by electrical induction.

It is a further object of the invention to proerably of copper although other electrically conducting material may be used, is loosely carried by the stud O. The member III is of substantial mass compared to the element I and is provided with a heavy peripheral flange which directly engages the surface of the thermal element I. A helicalsprlng l2 secured to the stud 8 resiliently biases the member Ill into such engagement and is of such dimensions that the member It will be in engagement with the thermal element 6 in both limiting positions thereof.

The thermal element 6 is provided with contact buttons it which cooperate with contact member it carried by the supporting disc 4, and

a pin i I projecting from supporting plate 4 I through a hole in element 6, insures against rovide such a relay with means whereby it may be adjusted to respond to currents of various magnitudes so that a relay of a standardized size may be employed in circuits traversed by currents of various values.

Other objects of the invention will be apparent from the following description and from the accompanying drawing, in which:

Figure l is a view in section of a relay in accordance with the invention, and

Fig. 2 is a view in section taken on the line II-II of Fig. 1.

Referring to the drawing, the relay comprises a casing 2 of non-metallic material in which is provided a supporting disc & tightly fitting the inner contour of the casing and sealed in place by a suitable material.

A thermo-responsive element 6 which may be a composite disc of two dissimilar metals is supported axially'upon. a stud 5 secured to the supporting disc 4; Preferably, the thermo-responsive element 6 is of the snap-acting type which moves suddenly from one limiting position to another when heated to a predetermined degree. of temperature, and a conducting member Iii, preiof force generated by the winding, when con-- tation of the latter so that contact buttons and members will be maintained in alignment. In the position shown in Fig. l, the thermal element 8 with its contact elements bridges the contacts I8 to establish a circuit therebetween. Upon a predetermined change-in temperature, the element 8 will snap to a dished position opposite to that shown in Fig. 1, thereby opening the circuit between the contact members it. This type of thermal element. is well known in the art and need not be described in further detail. With the construction described, and alter circuit connections have been made to the terminals 01 contact members it as by conductors i8, the casing is sealed with an insulating material which will not runor soften when subjected to the temperature of the coil in which it rnay be immersed, or to atmospheric conditions to be encountered in service.

It is intended that the thermal element 8 and tively from outside the casing 2 and to this end there is provided a winding 20 which closely surrounds the casing 2 in a position where the lines nected to a source of alternating current, will cut the member Ill and element 6 to induce currents therein to heat them. Although it is possible to dispense with the member iii and have the inductive heating occur in the thermal element 8 only, it is preferred for most applications to take advantage of the greater amount of heat which can be developed in the member In by reason of its lower electrical resistance compared with that of the usual metals employed in the thermal elements.

In practice, the winding 20, which is energized in accordance with the alternating current traversing the circuit to be protected, will be mounted in astationary position, as by the clamp 22, for example. In order to adjust the response of the thermal element 8 with respect to the current traversing the winding 20, the casing 2 slidably fits within the winding 20 and by means of the adjustment 24 may be'moved with respect to the winding 20, as should be obvious from Fig. 1.

Also, it is desirable that the winding and conducting member ID shall be more or less in the position shown in which the member ID is spaced to one side of the center of the winding so that when the winding is energized there will be a force produced tending to expel the member away from the winding into more intimate contact with the thermal element thereby supplementing the infiuence'of the spring H.

The casing 2 being non-metallic, the flux may pass freely through it, and it inherently would be of poor thermal conductivity so that variations in the temperature of .the medium surrounding it will not seriously affect the operating time of thermal element 6. Also, if the device is designed to operate at a relatively high temperature the eflect of ambient temperature variations will be minimized.

In accordance with the construction disclosed; an unusually simple and efiicient relay has been provided which is sealed against the entrance of dust and corrosive gases oil-proof and adjustable in its operation to take care of various installation conditions to which relays of this character are subjected.

Obviously changes may be made in the con struction shown within the scope of invention and it is intended that no limitation shall be placed on the invention except as set forth in the appended claims.

I claim as my invention:

1. A thermo-responsive device comprising an operating element movable in response to a change in temperature, an electrical conducting member and means for biasing it into contact with said operating element, and means for inducing an electric current in said conducting member to heat it.

2. A thermo-responsive device comprising an operating element movable in response to a change in temperature, an electrical conducting member and means for biasing it into contact with said operating element, means for inducing an electric current in said conducting member to heat it comprising a current carrying winding and means for mounting said conducting member in the field induced by said winding.

3. A thermo-responsive device comprising an operating element. movable in response to a change in temperature, an electrical conducting member and means for biasing it into contact with said operating element, means for inducing an electric current in said conducting member to heat it comprising a current'carrying winding,

means for mounting said conducting member in the field induced by said winding, and means for adjusting the position of said member in said field to vary the magnitude of the current induced in the member.

4. In a thermo-responsive device comprising an operating element movable from one limiting position to another in response to a change in temperature, a conducting member in engagement with said element, means for resiliently biasing said member into such engagement, a casing of non-metallic material for enclosing said element, member and biasing means, means for hermetically sealing said casing, and means outside said casing for inducing a heating current in said conducting member.

5. In a thermo-responsive device comprising an operating element movable in responsive to a change in temperature from one limiting position to another, a conducting member in engagement with said element, means for resiliently biasing said member into such engagement, a casing of non-metallic material for enclosing said element. member and biasing means, means for hermetically sealing said casing, and means outside said casing for inducing a heating current in said conducting member comprising a current carrying conductor surrounding said casting in such position that said conducting member is within the field induced by said coiled conductor.

6. In a thermo-responsive device comprising an operating element movable in response to a change in temperature from one limiting position to another, a conducting member in engagement with said element, means for resiliently biasing said member into such engagement, a casing of non-metallic material for enclosing said element, member and biasing means, means for hermetically sealing said casing, means outside said casing for inducing a heating current in said conducting member comprising a current carrying conductor surrounding said casing in such position that said conducting member is within the field induced by said coiled conductor, and means for adjusting the relative positions of said conducting member and coiled conductor to vary the magnitude of the current induced in said member.

7. In a thermo-responsive device, a conducting winding, a thermo-responsive element of the snap-acting type which suddenly moves from one limiting position to another, a conducting member and means for slidably mounting it adjacent to said element, resilient means for biasing said member toward said element into contact therewith in both limiting positions thereof, a current carrying winding for producing a magnetic field, and means for mounting it in a position to induce a current in said member to both heat it and magnetically bias it into contact with said element.

PHELAN MCSHANE.

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