US2283706A - Protective system and device - Google Patents

Description

y 1942- A. s. STIMSON 2,283,706 PROTECTIVE SYSTEM AND DEVICE Filed May 2'7, 1941 In vehbor: Allen 6. Stimson His Attorne y Patented May 19, 1942 2,283,706 I PROTECTIVE SYSTEM AND DEVICE Allen G. Stimson, Marblehead, Mass, assignor to General Electric Company, a corporation of New York Application May 27, 1941, Serial No. 395,430

11 Claims.

My invention relates to protective systems and devices and particularly to an alternating current overload protective system and a suitable relay therefor havin selective instantaneous and inverse time-current characteristics.

One object of my invention generally stated is to provide an alternating current overload relay arrangement which shall be'suitable for the protection of motors and other electric energy translating devices against overloads and consequent over-temperature conditions.

The principal object of my invention is to provide an alternating current overload relay arrangement which shall'have selective instantaneous and inverse time-current characteristics and which shall also be capable of giving a remote indication of the temperature of th protected apparatus.

Another object of my invention is to provide a new and improved overload relay which shall have instantaneous: operating. characteristics upon the sudden occurrence of an overload cur rent in excess of a predetermined value and which shall have. inverse time-current characteristics upon the occurrence of a continued overload current of less than said predetermined value.

To the attainment of the above and other objects which will hereinafter become apparent, the invention comprises a relay having an actuating winding connected in series'circuit relation with a body of resistance material having a marked negative temperature coeflicient of resistance in combination with a load responsive primary winding and. a short circuited secondary Winding arranged to be heated inductively by the primary winding and positioned in heat conducting relationship to the body of resistance material. In order to give a remote indication of the temperature of the protected apparatus, an electric indicating instrument calibrated directly in the desired temperature unit maybe connected in series circuit relation with the relay energizing winding and the resistance material.

My invention itself will be better understood, however, and its objects and advantages further appreciated by referringnow to the following detailed specification taken in connection with the accompanying drawing, the single figure of which represents a side view, partly in section, of an overload relay embodying my invention together with a schematic circuit diagram of connections of the relay to a source of energy and. to a pro-. tected electric energy translating device,

Referring now to the drawing, I have shown a preferred embodiment of my overload relay'constructed upon and including a laminated magnetic frame lilv which comprises a transformer portion H and a relay core portion I 2. As shown the transformer portion II is formed by'providing a pair of windows l3 and I4 in the frame laminations to. define a central transformer leg 15. Encircling the leg l5 are positioned a load responsive primary coil l6, a pair of short circuited secondary windings I1 and I8, and a potential coil l.9.. Preferably the primary coil I6 is positioned between the potential coil 19 and the short circuited windings l1 and [8 for maximum inductive effect. The relay core portion l2 of the frame comprises a single upstanding leg 20 adjacent one of the side legs of the transformer portion andfmagnetically connected to the side leg by the base portion of the frame. The upper end of the relay core 20 defines a pole face 2| positioned in normal spaced attractive relationship to a pivotally mounted magnetic armature member 25. In order to complete a magnetic circuit. for the relay portion of the magnetic frame, the pivoted end of the armature 25 is mounted upon the adjacent side leg of the transformer section, of the frame. A relay actuating winding 26 is mounted upon the. upstanding leg 20 of the relay core portion I2. Inorder to prevent chattering of the, armature 25 against the pole face 2|, the pole face is slotted and provided with a shading coil 21 of a typewell known to those skilledin the art.

For, instantaneous trip upon the occurrenceof an excessive overload the relay core 20 may, if desired, be provided with a series winding 26a. It will be understood that the winding 26a will be provided with a sufficiently small number of turns so that it will be efiective to operate the relay armature 25 only when an excessive overload current flows. v

I wish to have. it understood that, if desired, the relay core l2 and. the transformer core ll may be separate piece of apparatus and thus magnetically independent of each other. For convenience and simplicity of construction, however, the transformer and the relay may be built as a unit as shown.

The relay is provided with a pair of cooperating circuit controlling contacts 28 and 29. The contact 28 is stationary and is fixed to a strip of insulating material 38 fastened to the frame I!) and overhanging the relay armature 25. The contact 29 is supported upon a strip of resilient material 3l which is connected to the armature 25 and insulated therefrom by a shim 32 of insulating material. Th armature 25 is biased to a normal deenergized position spaced from the pole face 2| by means of a tension spring 33 connected between the armature and the overhanging bracket 30.

The temperature sensitive element of my relay consists of a mass 35 of resistance material having a negative temperature coefficient of resistance and positioned between the short circuited rings l1 and I8 of electrically conducting material such as copper. structurally, the outer copper annulus I8 is of channel-shaped cross section, while the inner annulus I1 i of rectangular cross section. The annulus I1 is positioned within the channel-shaped annulus l8 in spaced relation to the inner surfaces of the annulus l8. Within th channel-shaped annular space between the rings I1 and I8 i located the mass 35 of resistance material. Thus the copper annuli I1 and I8 serve both as heaters for the resistance material 35 and as electrodes for making electrical connection to opposite sides of the material. The mass 35 of resistance material has a marked negative temperature coeflicient of resistance and is preferably of the type described in the copending application of Chester I. Hall, Serial No. 327,901, filed April 4, 1940, and assigned to the same assignee as the present application. As described in th copending application,'the mass 35 is preferably a, sintered granular resistance material comprising magnesium oxide, sodium silicate, and copper oxide.

The entire temperature sensitive element comprising the resistance material 35 and the copper annuli I1 and i8 is preferably encased by insulating material 36 and positioned to encircle the central leg 15 of the transformer section II in inductive relation to the primary winding Is.

In the embodiment shown in the drawing, the central transformer leg 15 also carries the potential winding l9 in whichvoltage is induced by the primary winding I6 and which is connected as a source of energization for the actuating coil 26 of the relay. I wish to have it understood, however, that while the energizing voltage for the relay actuating winding 26 may be generated by transformer action from the primary winding l6, as shown, the winding 26 may, if desired, be energized from any separate source of substantially constant potential, such as for example, the line conductors 31, 38.

The series connected relay circuit energized from the potential coil I9 includes not only the actuating winding 26 and the temperature sensitive resistance element 35, but also a milliammeter 39 by means of which a remote indication of the temperature of the protected apparatus may be had.

, For operation, the primary coil N of the transformer and the series coil 26a of the relay are connected in series in a power circuit including a load device such as a motor 45 to be protected. The motor 45 is shown energized from the line conductors 31, 38 through a contact 46 of a line contactor 41. An actuating coil 48 for the line contactor 41 is energized from the line conductors 31, 38 through the contacts of a normally open starting switch 49 and the normally closed relay contacts 28, 29. Upon actuation of the line contactor 41 by means of the starting switch 49, the contactor locks itself in around the switch 49 through a manually operable normally closed stop switch 50 and a pair of normally open interlock contacts 5| on the contactor 41. It will thus be evident that the relay contacts 28, 29 are included in both the pick-up and holding circuits of the line contactor 41.

In operation, under normal operating conditions, the temperature of the mass of resistance material 35 is such that its then relatively high resistance preclude the flow of sufficient current in the relay circuit to actuate the relay armature 25. Upon the occurrence of a continued moderate overload, however, excess current flowing in the primary coil I6 produces an increased induced current in the short circuited copper annuli I1 and I8 and heats these annuli by induction. The annuli I1 and H3, in turn, conduct heat to the sintered granular matrix 35 of resistance material. When the resistance of the material 35 has decreased to a predetermined point by the application of a suflicient amount of heat, it will permit the passage of suflicient current through the relay circuit to actuate the relay armature 25. It will be understood that upon moderate overloads the series coil 26a. is not sufiiciently energized to actuate the relay by itself.

It will be evident that the rate of heat generation in the copper annuli l1 and I8, and thus the rate of decrease of resistance of the body of resistance material, will depend upon the magnitude of the overload current flowing through the primary winding l6. Upon moderate overloads below a predetermined value, therefore, the relay will operate with an inverse time-current characteristic. Furthermore, the magnitude of the current flowing through the relay circuit, whether above or below the necessary relay actuating value, will depend upon the resistance of the body of material 35 and the induced voltage in the potential coil l9 and thus will always bear a predetermined relationship to the magnitude of the current in the primary coil l6. The milliammeter 39 may therefore be calibrated to give an indication at a remote point of the temperature of the motor 45. It should be pointed out, however', that the inverse time-current characteristic will be more pronounced and the calibration of the milliammeter 39 will be much more uniform where a separate source of substantially constant potential is used in place of the potential coil 19 to energize the relay circuit. Where a potential coil 19 is used to energize the relay circuit both the resistance of and the voltage applied to the relay circuit will be dependent upon the magnitudelgf the current flowing in the primary windmg While the use of an induced voltage for energizing the relay circuit is disadvantageous to some extent so far as the temperature indication is concerned, it produces a very favorable effect upon the operation of the relay as a whole. Because of the fact that the actuating coil 26 is energized by the induced voltage in the coil l9, it will be evident that there is some predetermined value of overload current in the primary winding l6 at which the induced voltage in the potential coil 19 will be sufliclent to force through the coil 26 a current sufliciently large to actuate the relay in combination with the current in the series coil 26a in spite of the fact that the resistance material 35 has not yet been heated and therefore retains its relatively high normal resistance. It is at this predetermined value of overload current that the inverse time-current characteristic of the relay changes discontinuously to an instantaneous characteristic. Thus my relay, when equipped with a potential coil l9, has the very advantageous property of acting with an inverse time-current characteristic upon the occurrence of continued moderate overload while it operates instantaneously upon the sudden occurrence of an excessive overloadabove a predetermined value. It will be understood of course that, though the necessary current will be greater, the relay will possess an instantaneous trip characteristic even if the series coil 26a is omitted. Similarly, where the actuating coil 26 is energized from .a separate source of constant potential, the series winding 25a may be used alone to obtain instantaneous trip at high overloads.

While I have described and illustrated only certain preferred embodiments of ,my invention by way of illustration, many other modifications will undoubtedly occur to those skilled in the art, and I therefore wish to have it understood that I 1 intend by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A protective system for an alternating current power circuit comprising a relay provided with an actuating winding and circuit controlling contacts actuable thereby, a resistor having a negative temperature coefiicient of resistance for controlling said actuating winding, said resistor being connected in electric circuit relation with said actuating winding, a primary winding arranged for energization in accordance with the load on said power circuit, and a short circuited annulus of electrically conducting material inductively associated with said primary winding for controlling the temperature of said resistor, said resistor being positioned in intimate heat conducting relation with said annulus.

2. A protective system for an alternating current power circuit comprising a relay provided with an actuating winding and circuit controlling contacts actuable thereby, a resistor having a negative temperature coefficient of resistance for controlling said actuating winding, said resistor being connected in series circuit relation with said actuating winding to a source of electric energy supply, a primary winding arranged for energization in accordance with the load on said power circuit, and a pair of closed annuli of electrically conducting material inductively associated with said primary winding, said resistor being positioned between said annuli in heat conducting relation therewith.

3. A protective device for an alternating current power circuit comprising a magnetic frame, a load responsive primary winding mounted upon said frame, a short circuited secondary winding mounted upon said frame in inductive relation to said primary winding, an actuating winding, and a resistor having a negative temperature coelficient of resistance positioned in heat conducting relationship with said secondary winding, said resistor being connected in circuit relation with said actuating winding to a source of electric energy supply.

4. A protective device for an alternating current power circuit comprising cooperating circuit controlling contacts, a magnetic frame having a transformer portion and a relay core portion, a movable armature operativel associated with one of said contacts and biased to a normal position spaced from said relay core portion, a

:primary winding mounted upon said transformer portion of said frameand arranged forenergiza tion in accordance with the current flowing .through saidpower circuit, a closed annulus of electrically conducting material mounted upon said transformer portion in inductive relationship with said primary winding, an actuating winding mounted upon said relay core portion and arranged for connection to a source of electric energy supply, and means for controlling the current in said actuating winding comprising a temperature sensitive resistor connected in circuit therewith, said resistor being positioned in heat conducting relationship with said annulus of electrically conducting material.

5. A protective relay for an alternating current power circuit comprising cooperating circuit controlling contacts, a magnetic frame structure having a multiple leg transformer portion and a relay core portion adjacent one of said legs, a movable armature for controlling one of said contacts, said armature being pivotally mounted upon said magnetic frame, spring means for normally biasing said armature to a deenergized position spaced from said relay core portion of said frame, an actuating winding mounted upon said relay core portion in magnetizing relation to said core and armature, a primary winding mounted upon said transformer portion, said primary winding being arranged for energization in accordance with the value of current flowing in said power circuit, a pair of closed annuli of electrically conducting material mounted upon said transformer portion in inductive relationship with said primary winding, and a body of temperature sensitive resistance material positioned between said annuli, said resistance material being connected in circuit with said actuating winding to a source of electric energy supply thereby to control the current in said actuating winding.

6. An overload protective relay for an alternating current power circuit comprising cooperating circuit controlling contacts, a magnetic framemember having a multiple leg transformer portion and a relay core portion adjacent one of said legs, a magnetic armature pivotally mounted upon said one leg of said transformer portion, said armature being movable toward and away from said relay core portion to control said contacts, spring means for normally biasing said armature to a deenergized position spaced from said'core portion, an actuating winding mounted upon said relay core'portion in magnetizing relation to said core and armature, a primary winding mounted upon said transformer portion, said primary winding being connected in series circuit relation with said power circuit, a channelshaped ring of electricall conducting material mounted upon said transformer portion of said frame in inductive relationship to said primary winding, a second ring of electrically conducting material arranged within said channel-shaped ring in spaced relation thereto, and a body of resistance material having a negative temperature coefficient of resistance arranged to fill the space between said rings, said rings serving to heat said resistance material by inductive action from said primary winding and acting also as terminal electrodes for connection of said resistance material in current controlling relation to a relay circuit, said relay circuit comprising said resistance material and said actuating winding connected in series circuit relation to a source of electric energy supply,

7. An instantaneous and inverse time overload relay for an alternating current electric power circuit comprising a magnetic frame, a load responsive primary winding mounted upon said frame, a short circuited secondary winding mounted upon said frame in inductive relation to said primary winding, an actuating winding for said relay, a source of potential for energizing said actuating winding comprising a potential winding mounted upon said frame in inductive relation to said primary winding, and means for controlling the current in said actuating winding comprising a body of temperature sensitive resistance material mounted in heat conducting relationship with said secondary winding and connected in circuit with said actuating winding.

8. An instantaneous and inverse time-current overload relay for an alternating current power circuit comprising cooperating circuit controlling contacts, a movable armature operatively associated with one of said contacts, a magnetic frame structure, a primary winding mounted upon said frame structure and connected to be'energized in accordance with current flowing in said power circuit, a first actuating winding arranged in magnetizing relation to said armature, a second actuating winding mounted upon said frame in magnetizing relation to said armature and connected in series with said power circuit, a potential winding mounted upon said frame structure in inductive relation to said primary winding, said potential winding being connected to supply electric energy to said first actuating winding, a pair of closed annuli of electrically conducting material mounted upon said frame in inductive relation to said primary winding, said annuli being adapted to be inductively heated upon the flow of excessive current through said primary winding, and a body of temperature sensitive resistance material positioned between said annuli in heat conducting relation therewith, said annuli serving as electrodes for connection of said resistance material in series circuit relation with said first actuating winding.

9. A protective device for an alternating current power circuit comprising cooperating switch contacts, a magnetic frame member having a multiple leg transformer portion and a relay core portion adjacent one of said legs, a movable armature operatively associated with one of said contacts, said armature being pivotally mounted upon said one leg of said transformer portion and biased to a normal position spaced from said relay core portion, an actuating winding for said relay mounted upon said relay core portion in magnetizing relation to said armature, a primary winding mounted upon said transformer portion and arranged to be energized in accordance with the current flowing in said power circuit, a source of electric energy for said actuating coil comprising a potential winding mounted upon said transformer portion in inductive relation to said primary winding, a channel-shaped ring of electrically conducting material mounted upon said transformer portion in inductive relation to said primary winding, a second ring of conducting material arranged within said channel-shaped ring in spaced relation thereto, and a body of resistance material having a negative temperature coefficient of resistance arranged to fill the space between said rings, said rings serving as electrodes for connection of said resistance material in series circuit relation with said actuating winding to control the current in said actuating winding.

10. An overload protective and indicating device for an alternating current power circuit comprising a magnetic frame member, a load responsive primary winding mounted upon said frame member, a short circuited secondary winding mounted upon said frame member in inductive relation with said primary winding, a relay actuating circuit comprising an actuating winding for said relay connected to a source of electric energy supply, means for controlling the current in said relay circuit comprising a body of temperature sensitive resistance material arranged to be heated by induction from said primary winding, and an electric indicating instrument connected in said relay circuit thereby to be energized in accordance with the current controlled by said resistance material and to give an indication at a remote point of the load upon said power circuit.

11. A protective and indicating device for an alternating current electric power circuit comprising a magnetic frame member, a primary winding mounted upon said frame member and connected to be energized in accordance with the current flowing in said power circuit, a pair of circuit controlling contacts, a movable mag: netic armature pivotally mounted upon said frame member and operatively associated with one of said contacts, an actuating winding mounted upon said frame in magnetizing relation to said armature, a short circuited secondary winding mounted upon said frame in inductive relation to said primary winding, a body of resistance material having a negative temperature coefficient of resistance positioned in heat conducting relation to said secondary winding, said resistance material being connected in series circuit relation with said actuating winding to a source of electric energy supply, and an electric indicating instrument responsive to the current flowing in said actuating winding thereby to indicate at a remote point the magnitude of the load upon said power circuit.

ALLEN G. STIMSON.

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