US2411351A - Overload relay - Google Patents

Description

Nov. 19, 194e.A

G. c. ARMSTRONG OVERLOAD RELAY Filed April 1, 1942 4 Sheets-Sheet 1 INVENTOR mmgmim y' 5 NOV. 19, 1946. G Q ARMSTRONG 2,411,35

OVERLOAD RELAY Filed April l. 1942 4 Sheets-Sheet 2 fig/f5.

7/ JH/(l @5 faz/.957.375

ATTORNEY Nov. 19, 1946.

-G. C. ARMSTRONG OVERLOAD RELAY Filed April l. 1942 /OZ- WlTNESSES:

4 Sheets-'Sheet 3 Nov, W, 1946.

G. C. ARMSTRONG OVERLOAD RELAY Filed April l. 1942 4 Sheeis-Sheet 4 /5 xr:- WITNEssEs; 3 ,7 ,95, 139577535, 3 INVENTOR /6 Lm leoc'acfmjf'rqoy:

BY F ATTORNEY f Patented Nov. 19, 1946 2,4ll,35l

OVERLOAD RELAY George C. Armstrong, Forest Hills, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 1, 1942, Serial No. 437,235

24 Claims. 1

My invention relates to shock resisting overload relays particularly those useful in protecting motors from excessive currents and which say, a given relay is, responsive to the moto-r current through selectively operable thermal and magnetic operating means.

More specically my invention relates to an overload relay having therein a tripping element unaffected by a shock of predetermined value, which involves, by way of example, a plurality of current carrying bimetals which, upon determined heating due to excessive currents passing therethrough, will actuate the tripping element to trip the relay, and a pair of armatures either of which in the event of excessively high currents will trip the relay.

An object of my invention is to provide a solidly constructed relay capable of withstanding heavy shock.

Another object of my invention is to provide a thermal overload relay which will not trip under heavy shock when carrying a large percentage of rated current.

Another object oi my invention is to provide a thermal overload relay which shall be compensated for ambient temperature.

A specic object of my invention is to provide a thermal overload relay solidly constructed on a steel frame and having a balanced tripping mechanism requiring a relatively great travel for tripping, thereby reducing the effect of mechanical shock.

Another object of my invention is to provide a thermal overload relay having therein a plurality of poles for protecting each phase of the system in which the relay is used,

A specic object of my invention is to provide a thermal overload relay having therein a plurality of poles for protecting each phase of the system in which the relay is used and having therein means for quickly tripping the relay in case of an open phase and after a predetermined time delay during normal overload conditions.

Another object of my invention is to provide a thermal overload relay having therein an inertia element or latch to prevent tripping of the relay when subjected to mechanical shock.

Another object of my invention is to provide an overload relay having therein tripping means responsive either to thermal or magnetic elects, both caused to operate by the motor armature current.

A specic object of my invention is to provide a thermal and magnetically actuated overload. relay solidly constructed on a steel frame, having therein a balanced tripping mechanism designed to reduce the effect of mechanical shock, a plurality of bimetallic elements heated by excessive currents which selectively actuate the tripping mechanism to quickly trip the relay in case of an open phase in the system which it protects. But the bimetallic elements also provide a predetermined time delay duringr normal overload conditions. Further tripping means magnetically controlled are provided to instantly trip the relay in the event of excessively high currents due to a short circuit, and means are included for automatically compensating for changes in ambient temperature as Well as means adjustably xing the rating of the relay above and below 100% of rated current.

Other objects and advantages will become more apparent from a study of the following specilication when considered in conjunction with the accompanying drawings, in which:

Figure l is an end view of an overload relay embodying the principles of my invention;

Fig. 2 is a view of the end opposite to that of Fig. 1;

Fig. 3 is a plan view of the overload relay;

Fig. l is a sectional View taken on the line IV-IV of Fig. 3;

Fig. 5 is a sectional view similar to Fig. 4, but with the tripping mechanism shown as tripped by one actuating bimetal;

Fig. 6 is a sectional view similar to Fig. 4 but with the tripping mechanism shown as tripped by both actuating bimetals;

Fig. 7 is a top view of the tripping mechanism as shown in the open phase tripped position in Fig. 5;

Fig. 8 is a sectional view taken on the line VIII-VIII of Fig. 3;

Fig. 9 is a plan View of a relay embodying certain principles of my invention having plane movement for its tripping action;

Fig. 10 is an end view of Fig. 9;

Fig. 11 is a plan View of a relay having plane movement of its tripping mechanism and an inertia latch for resisting shock;

Fig. l2 is an end view of Fig. 11;

Fig. 13 is a fragmentary plan view of the tripping mechanism shown in Figs. 9 and l0 having an inertia element i or resisting shock.

Fig, 14 is a plan view of the tripping mechanism shown in Figs. 1 8, inclusive, having an inertia element for resisting shock;

Fig. 15 is a modified form of tripping mechanism having rotary movement for tripping and an inertia latch `for resisting shock;

Fig. 19 is a perspective View of the magnetic tripping assembly.

Referring more particularly to Figures"1,`2and 3 of the drawings, numeral I denotes a U-shaped frame member to which are fastened the rtransformer cores 3 and mounting brackets 5 by means of screws 'l extending through the brackets, transformer cores and the side walls of the YU- frame I to thread into tapped holes in the strengthening strip S and one leg iI of U- member I3, all of which are mounted against the inner wall of the fra-me l, to clamp the assembly rigidly in position. The outwardly bent bottom portion I5 of the brackets 5 having holes drilled therethrough, provide means for mounting the relay.

The transformer cores 3 are of laminated construction and are assembled in two pieces. The lower sections Il are secured to the frame I by the screws l' while the upper section I9 are of the form of straight bars and seat upon the ends of upwardly extending portions of the lower core sections H. Clamping screws ZI threading through tapped holes in the inwardly bent top portion 23 of the brackets 5 clamp the upper sections Il of the transformer cores 3 in position. :u

This construction facilitates the assembly of the primary coils V25 and the secondary coils 2-1 about the lupper sections I9, said assembly being yaccomplished by positioning the coils in-their respective positions and sliding the *upper core sections through openings in the centers of the coils. Once in place the upper core sections I9 are held in accurate location -by seating the screws 2I in the slots 29.

An internally thermally and electrically insulated shielding member 3I open at its ends is fastened to the frame I. At one end of said shielding member is the leg 33 of U-member I3 to the right top side of which leg as seen in Fig. 2 is insulatedly secured at its open end a hairpin shaped Vor Vbifurcated current carrying bimetal 35. To the lower left side of said leg is insulatedly secured a second bimetal 3l similar tothe first. Both bimetals are of sufiicient length to extend through the shield 3l and engage cooperating parts of the tripping mechanism indicated -generally at 39 which they actuate A Vpair of leads or connections 4I extending from each of the secondary coils are fastened to the open ends of the bimetals thus completing a current Vpath from a secondary coil through a bimetal and back again to the coil. 'The primary coils are connected to the motor circuit.

A third bimeta-l 13 is fastened to an angle 45 insulatedly mounted on the bottom of a, laminated cross member All which bridges the frame I and is fastened in position on turned out portions i9 of Vframe I by 'screws 5I and 53. The bimetal eX- tends longitudinally of the relay similarly to the hairpin bimetals and is of suflicient length to intercept a cooperating part of the tripping mechanism. As viewed in'Fig. 2 this bimetal is disposed directly above the shield 3l through which the current carrying bifurcated bimetals pass and is protected from heat 'transfer from vsaid bimetals by said shield, the inner walls of which are coated with a heat resisting material 55, and thermally insulated from the frame by the insulating element 5l of the laminated cross member e1. Ambient temperature changes produce deflections in bimetal 43 in the same direction relative to rotation of the tripping element as produced in the bifurcated bimetals.

The shield 3! serves several purposes. It decreases loss of heat from the activating bimetal elements, thereby decreasing the power input required .to operate the device. It decreases heat transfer to the compensating bimetal; inasmuch Aas the .eifective .tripping temperature of the actuating lbimetals Ais the difference between their temperature rise and the temperature rise due to Aheat Itransfer to the compensating or ambient temperature bimetal, such heat transfer reduces the sensitivity and affects the tripping time characteristics. So shielding the actuating bimetals from the compensating bimetal increases the tripping time on small overloads. The shield also acts to increase the tripping time at small overloads in another way. Restrictions of ventilation about the bimetals results in the gradual heating of the air so enclosed within the shield. It restricts circulation of air to the adjacent surfaces of the coils andthe frame. Consequently upon the relatively rapid heating of the 'bimetals due to internal heating is superimposed, rst the reactive heating due to the increase of air temperature within the shield, second Vthe reactive heating due to internal heat absorption of the shield and iinally reactive heating due t0 .the more gradual heating of the coils andthe frame. The compensating bimeta-l is so ventilated and its mounting so insulated as to isolate it as much as possible from these secondary temperature changes. The cross section of the transformer iron and the resistance of the secondary .circuits are carefully vselected to cause va certain degree of magnetic saturation at high overloads. All of these effects are utilized to give the relayhighly advantageous time characteristics, namely a long tripping time at small Aoverloads which the protected motor can carry for an hour or more without attaining an excessively high temperature and a tripping time at current equivalent to locked-rotor currents which are sufficiently long to allow the motor to accelerate high inertia loads yet short enough to protect the motor if it fails to start. The tripping time at high overloads can be easily modified to meet special requirements by changing the number of laminations in the transformers removable core assembly.

The rating of the relay is adjustable within predetermined limits above and below rating, said adjustment being accomplished as shown in Fig. 3. A pointer 59 shown in the 190% rating position is pivoted about the screw 5I extending through a slot el through one end of the cross member ft'i and threadedly engaging a turned out portion i9 of the frame l. A pin 53 rigidly fastened in the pointer rotatably en- 1 gages the cross member il in the slot Gia. The

entire assembly is locked in any of its positions by tightening the screw 5l. If the pointer 59 is rotated clockwise it will be seen that the pin 63 will rotate the cross member l counterclockwise about screw E3 within limits imposed by the slot 6i. With the bimetal 63 fastened to said cross members as hereinbefore described, ccuntercloclrwiseV rotation of its mounting will move the free end of the bimetal to the left thereby increasing. the travel of the tripping mechanism before tripping takes place and increasing the rating of the relay. Rotation of the pointer counterclockwise will move the free end of the bimetal 43 to the right to decrease the rating of the relay.

Referring now to Figs. 4 to 8, inclusive, of the drawings, in which the tripping mechanism has been particularly shown, said tripping mechanism is denoted generally at 39 and is pivotally mounted in a sleeve bearing 95 secured in a metal plate 61 of the laminated plate assembly 69V secured to outwardly bent portions of the frame I, by a plurality of screws 1|. Said laminated plate assembly comprises the metal plate 61 and a pair of insulating plates 13 and 15. The

outerinsulating plate 15 has holes drilled therel through and countersunk in its inner face to receive screws 11 of a corresponding shape in a manner to present a flush surface on its inner face. To its outer face is fastened by means of said screws a pair of stationary contacts 19 and 8|. insulating plate 13 forms an insulating barrier between the screws 11 and the frame An insulating disc 83 having tted on its periphery a metal ring 85 which is secured thereon by pressed over portions 81 forms a movable contact 88 which bridges the stationary contact elements 19 and 8|.

In Fig. 8, I have shown a sectional view through the center line of the tripping mechanism 39. A shaft 89 having riveted to its one end a latch element 9| and its other end reduced in diameter and threaded to receive a nut 93 is pivotally and slidably mounted within the sleeve bearing 05. A catch element 95 which cooperates with the latch 9| is pivotally mounted about the sleeve bearing 65 and prevented from traveling axially by the shoulder 91 on the one side and washers 99 disposed between the catch element and the plate 61 on the other. A torsion spring |0| positioned about the end of the sleeve bearing 65 has one end secured about a pin |03 in the latch element 9| and its other end secured to a pin |95 in the catch element 95 which will, as seen in Fig. 4, bias the latch element 9| clockwise and the catch element 95 counterclockwise to contact the pins |04 and |05 against one side of the ends of the bifurcated or hairpin bimetals 35 and 31 and the projections I 06 and |01 of the latch element against the other side when the movable Contact 88 is in engagement with the stationary contacts 19 and 8|.

As may be seen in Figs. 4, 5 and 6, the latch 9| and catch element 95 of the tripping mechanism are positioned and balanced about the same axis of rotation. The torsion spring |0| biases the latch element 9| away from tripping position. As a result, reaction forces on these elements due to heavy vibrations of the relay will be equally distributed about their axis of rotation thereby greatly reducing the possibilities of tripping from this source.

Open phase protection If one phase of the motor circuit is open so that only one of the actuating or bifurcated bi-V metals 35 and 31 is heated, the other actuating bimetal being cold and therefore stationary will so bias the catch element 95 of the tripping mechanism 39 as to prevent its moving. It will,

Aof said latch element counterclockwise.

ating bimetal 35 is in circuit with a phase of a motor which is closed, it will be apparent that excess-currents passing through the bimetal will cause heating which heating will dei-lect said bimetal to the left against the projection |06 ofthe latch element 9| to begin rotation During this time, however, the lower actuating bimetal 31 being in circuit with a phase which is open is not heated and remains stationary, and by its contactwith pin |05 prevents the catch element from rotating with the latch element. As a result the pins |02 and |03 immediately clear the edges of the notches |08 and |99 in the catch element allowing the shaft 39 to be thrust axially to the right (Fig. 8) by the compression spring unseating the movable contact from the stationary contacts as shown in Fig. 7. The movable contact is biased by the compression spring I|2 against the stationary contacts when the relay is closed and against a washer H4 of insulating material locked between a shoulder on shaft 89 and the nut 93 when the relay is open. This slidable mounting provides suicient resilience that the movable contact may properly seat itself on the stationary contacts.

The small travel of the latch element 9| for single or open phase tripping is an important feature for the following reasons.

With any multipole relay in which the several poles act on a single tripping mechanism the current required to trip the relay with one pole only is greater than with all poles heating and acting because only one bimetal supplies the force necessary for tripping. Therefore the load on said bimetal is increased. In addition there is the absence of heat transfer between the poles which would ordinarily cause each to reach a higher temperature than if heated alone.

Also in case of an open phase the increase in current of a three phase motor running single phase in many cases is not greatly in excess of the minimum tripping current of the relay and unless the'relay is accurately adjusted and applied it may fail to protect the motor. Further, in order to avoid tripping during starting, relays are often designed to have a tripping time which is as long as safety will permit if the load should jam and lock the rotor from turning. This is permissible because such occurrences are extremely unusual and is necessary to allow the Inotor to start heavy inertia loads without the relay opening. However, an open phase, due to an open fuse or connection, is much more usual, and in some cases the currents within the motor may be increased by a much greater percent from normal than the line currents. It is, therefore, more important for the relay to trip in case of single phase than for balanced operation. As a two pole relay, my inventive relay trips much more quickly in two out of the three possible phase openings in a three phase system, and in any case in a two phase system.

Normal tripping In Fig. 6, I have shown the tripping mechanism 39 in its normally tripped position. During normal overload conditions both actuating bimetals 35 and 31 carry excess currents. The resulting heating deflects the upper bimetal 35 to the left and the lower bimetal 31 to the right against the projections |09 and |01 rotating the latch element 9| counterclockwise as here viewed.

In this instance the catch member 95 is rotated therewith by the torsion spring I0 l, and by the friction of the pins |02 and |03, there now being no obstruction to resist such rotation until the pin I I3 in the catch element `'95 is intercepted in its travel by the ambient temperature bimetal 413. The latch element continues to rotate until the pins I Q2 and |03 clear the notches |98 and |59 in the catch plate at which time tripping takes place as'hereinbefore described 'for open `phase protection. The ambient temperature bimetal 43 corrects for surrounding temperature changes. As the temperature changes the bimetal d3 is deiiected in the same relative rotational direction and in proportion to deilections in the actuating bimetals 35 and Si as produced by temperature variations and which will rotate the tripping mechanism accordingly. A uniform tripping travel for normal overload conditions is, therefore, maintained. This feature, of course, has no effect upon open phase tripping since the 'ambient temperature bimetal i3 plays no part in that action.

The relay can be modified `to eliminate ambient temperature compensation by substituting a solid metallic `strip for the compensating bimetal. In this case the element i3 can be made non-temperature-responsive.

For open phase protection my inventive overload relay may be of the form as shown in Figs. 9 and 10 wherein plane movement instead of rotational movement for tripping is used.

In this application the bimetals I l5 and III do Y not carry current, although they may be readily so designed, but are heated by the heater elements IIS and |2i. I-Iere again either bimetal may actuate a latch member |23 to eiect tripping. Assuming upward deflection of the upper bimetal IE5 as caused by overheating due to an open phase, the actuating rod |25 being moved upwardly moves with it the latch |23 until a reduced end portion thereof |29 is adjacent a win- -dow or. opemng ISI in the catch element |33 at which time vsaid latch quickly releases the catch |33 since the lbottom bimetal being cold restrains 4the slidabiy mounted Vcatch element |33 Ifrom moving upward under the inuence of the compression spring A|35. Releasing or" the catch permits Vits free end iii-i normally biased to engage `the contact IISSi completing a circuit through a relay lcoil to open the motor circuit (not shown). Undernormal overload conditions both bimetals Ill-5 and ili .mounted catch element |33 is moved upwardly with the bimetals and latch by the compression spring M35 until a projection iti on said slidable catch element engages a stop M3, adjustable for changing the re'lays rating, thus stopping the catch. Continued movement of the bimetals will i then release .the catch |33 and complete the relay ycircuit as before described.

As may be readily seen the type of relay shown in Figs. 9 and 10 lis not 'necessarily limited to two poles but may have any number of poles Vthat may be required by the system which it protects. With this embodiment of my invention,a bimetallic element may be provided for each phase in a system thus providing quick single phase 4protection in any case.

Relays of the type shown in Figs. 9-12 are not inherently shock resisting. In order that this type may no-t trip during periods .in which it is subjected to mechanical shock an inertia. type of latch |455 has been added. This latch is pivotally mounted at It? to the relay base and projects through a window or opening |49 in the trip latch |5I. The end projecting through the window is .ben-t upwardly at right angles a sumcient distance deflect upwardly. The slidably that its upper end projects above the opening Il|9 in the trip latch. As may bev seen in the drawings; the latch is rst bent upwardly at an angle then nally at a right angle to the portion of the latch extending through the window. During normal tripping when the trip latch is deflected to the left, the lower surface of the inertia latch |65 follows the window edge upon which it rests dropping the upwardly extending portion of the latch down until it will clear the window andno longer obstruct travel of the trip latch to the tripping position. If, however, the relay were subjected to sudden shock from such a direction that the trip latch |5| wouldsuddenly be deflected to the left, the inertia latch in this instance due to the instantaneously high velocity of trip latch movement will not .move a substantial distance from its normal horizontal position and its up- Wardly extending edge will not clear the upper window edge in the trip latch thus preventing the trip latch from reaching its trip position. In this embodiment of my invention quick single phase protection is not to be had because the cat-ch element is not slidably mounted. The distance the trip latch must travel before tripping takes placeis, therefore, fixed for both single phase and normal overload tripping. Quick single phase tripping could be accomplished if, as shown in Fig. 13, the inertia latch M5 were pivotally mounted at |68 to a slidably mounted catch member |33 similar to that of Figs. 9 and 10. The inertia latch `Ii in that case would move with the catch member |33 and the trip latch |23 and thereby maintain a xed position with respect to the trip latch.

Should the resistance to shock of the particular embodiments of my invention as illustrated in Figs. lto '8 be insuicient, Aa shock absorbing weight or inertia element |53 as shown in Fig. 14 may be used as an additional safeguard. It is pivotally mounted to the catch element 95 by the screw |55 `and supported on its opposite side by its projection |51 which rests upon pin HB3 on the latch element 9|. Forces exerted by the inertia element through the above mechanical couple Will rotate the catch element counterclockwise and the latch element clockwise. In other words torques will be developed about the rotation axis of the latch and catch elements opposite to those necessary for tripping. Clearance in the hole I59`around |55 is offset so that movement of the inertia element |53 by shock to the left rotates catch element 95 counterclockwise away from tripping position by reason of its couple with vthe catch `element at |55. Shock from any direction which will move the inertia element lto the right will rotate the inertia element counterclockwise about its pivot axis |55 engaging projection |5| of the inertia element with pin ||3 on the ycatch element to rotate said catch element counterclockwise about its pivot axis whichv rotation is opposite Yto tripping rotation. VFrom the foregoing it may be seen that regardless of the direction of shock forces to which the vrelay may be subjected torques will be developed about the pivot axis of the latch and catch elements by the inertia element opposite to torques necessary for tripping.

In Fig. 15 an inertia latch I of the type used in the relay which employs plane movement of the tripping elements is applied to a relay having rotational movement of its tripping elements. y

In this instance, the inertia latch is pivotally mounted at |67 to the trip latch lISS) and is carried therewith during its rotative movement.

Said inertia latch |65 is provided with a substantially L-shaped slot |1| which surrounds a pin |13 in the disc |15 and spaces the trip latch |69 from the disc |15 when the trip elements are in the closed position as shown. Said pin supports the inertia latch |65 in a substantially horizontal position.

The function of the tripping elements in this modification of my invention is identical with that shown in Figs. 1-8, inclusive. The bimetallic elements disposed between the projections on the trip latch and pins secured to the disc actuate the trip latch in single or open phase and normal overload conditions in a manner identical with that of the previously described embodiment. The ambient temperature bimetal also performs the same function as before by automatically maintaining a xed distance between the projection |63 therefrom and the pin I|3 in the disc with which it cooperates during normal overload tripping.

Assuming rotative movement of the trip latch either by normal overload or single phase tripping it is readily seen that the right-hand end of the inertia latch |55 will drop downwardly when the edge i12 of the slot |13 passes beyond the pin allowing the trip latch |59 to be rotated through an angle sufficient for tripping before the rotative movement is checked by the pin contacting the end of the slot. Ii, however, the relay is subjected to forces due to shock which are of a nature to cause rotation in the direction of tripping of the trip latch the inertia latch |165 due to the instantaneously high angular velocity of the trip latch will be maintained in the position shown. The length of the slot |1| in this instance being of insufficient length to permit full tripping travel of the trip latch will, therefore, prevent tripping.

In the embodiment of my invention as shown in Figs. 16 to 19, the type of thermal overload relay shown inFigs. 1 to 8 has been modified to provide instantaneous tripping in response to short circuit currents.

With contactors now available capable of interrupting short circuit currents to extremely high values for use in controllers for power house auxiliaries, and for other applications in which the motors are located close to a supply source of high capacity, it is necessary to have a relay which will trip instantaneously on such currents, to deenergize the contacter magnet. An overload relay to protect the motor from excessive loading or from stalled currents is also necessary. This embodiment of my invention combines these functions, thereby reducing cost, siZe and complications. The usual thermal overload relay must have its heating elements protected by quick acting fuses or back-up breaker and, for circuits capable of delivering more than 5,000 amperes, must also have same means of limiting the current which flows through the heaters, such as saturating transformers or shunts. This device uses saturating transformers as integral parts of the relay, so that the heating elements are automatically protected, even with the relatively long opening time of a contactor.

The/thermal tripping operation is identical to that of the hereinbefore described relay but the contacts are modified to substitute for one of the stationary contacts a sliding contact |11 normally latched in position to contact the ring or movable contact 88. The movable contact 85 is normally latched by the tripping mechanism (not shown) to form a bridge circuit between the sliding contact 11 and the stationary contact |19. The movable butt contact 85 is thermally tripped while the sliding contact |11 is magnetically tripped. 5 The two transformers, having primary coils 25 energized by the current to the protected motor, and secondary coils 21 connected to the relay bimetallic elements are designed to have appreciable magnetic iiux at locked rotor currents. At higher currents magnetic leakage flux rapidly increases, and actuates the magnetic armatures E19, there being one for each pole, at l2 to 15 times the thermal rating. Movement of either armature will trip the sliding contact.

The description of construction and operation is as follows. A pair of latch bars |3| (see Fig. 19) are biased upwardly by the coil springs |83. Their upper ends are notched to receive the extremities of the cross arm |81 which has pivotally mounted at its center |89 a reset member |9| slidably mounted in the laminated plate assembly 99 and which serves to support and actuate the movable or sliding contact |11, thus providing independent tripping for either pole. The tripping details are assembled on a pair of plates |95, one mounted on either side of the relay, replacing the stiffening strips adjacent to the primary coils 25, and secured by the two screws 1 holding the transformer to the frame. The steel arma- :lo tures |19 are pivoted about the pins |91 and biased clockwise away from the primary coils by the coil springs |99. The catches 253| are pivoted at 203 and carry pins 295 which engage slots in the upper ends of the armatures. N otches 2M in the catches Zei normally engage lugs 26S on the latch bars lili when the latter are in their downward position, with the contacts closed. When the magnetic force in either pole is suiicient to overcome the bias of either of springs |99, an armature |19 will rotate counterclockwise about its pivot disengaging the latch bar and tripping the sliding contact |11. Resetting after tripping magnetically is accomplished by pressing upon the button 2li formed on the top end of the sliding contact carrying or reset member |9| which action by means of the cross-arm |81 forces the latch bars I8! down against the bias of the coil springs |83 until the lugs projecting therefrom are reengaged by the notches in the catches 29|. The sliding contact carrying member |9| is grooved to slide in a guiding slot in the insulating front plate of the relay.

Because the magnetic force does not attain effective magnitude until the transformer saturates, no adjustment is necessary, the springs being designed to trip at l2 to 15 times coil thermal trip rating. The instantaneous trip rating is changed simultaneously with the thermal rating by changing the primary coils.

The shielding effect of the frame and the properly limited size of the armature, prevent the development of magnetic forces above the strength of the parts. The light masses and strong tripping springs give very high speed action 65 at high currents.

I am, of course, aware that others, particularly after having had the benefit of the teachings of my invention, may devise other devices embodying my invention and I, therefore, do not wish to 70 be limited by the specic showing made in the drawings or the descriptive disclosure hereinbefore made, but wish to be limited only by the scope of the appended claims.

I claim as my invention:

l. A thermally responsive device comprising, in

combination, a pair of thermally responsive elements which deflect when heated, pivotally mounted tripping means actuated by the deflections of said thermally responsive elements, movable contacting means slidably disposed about the pivot axis of said tripping means, spring means disposed about said pivot axis between said movable contact and said tripping means for eecting snap-action of said movable contact, and a bimetallic element exclusively responsive to ambient temperature for effecting uniform tripping travel oi the tripping means during surrounding temperature changes.

2. Apparatus as recited in claim l, together' with means for adjustably supporting said bimetallic element responsive to ambient temperature to provide an adjustment of its fixed positi Within predetermined limits to effect predetermined variation of the travel of the tripping means necessary for tripping.

8. A thermal overload device comprising, in combination, a pair of bimetallic elements oi the form of bifurcated strips, means for passing electric current therethrough for heating the same, pivotallyA mounted trippingT means balanced about its pivot axis and spring means for biasing the same away from tripping position thereby reducing the relative effect of vibrations or mechanical shock due to impact of large magnitude imposed upon the relay, said tripping means being actuated by deflections or" said bimetallic elements being heated, resiliently mounted movable Contact means slidably disposed about the pivot axis of said tripping means, spring means disposed about said pivot axis between said movable contacting means and saidv tripping means for eifecting snap action of said movable contact, a bimetallic element or" the form of a flat strip exclusively responsive to ambient temperature for effecting uniform tripping travel of the tripping means during surrounding temperature changes.

4. A thermally and magnetically responsivedevice comprising, in combination., a plurality of imetallic elements, transformer means for heatingV the same, tripping means, a movable contact operated by said tripping means in response tov deflections of said bimetallic elements being heated by said transformer means, separate -tripping means responsive to/magnetic effects operableupon magnetic saturation of said transformenand a sliding contact engageable with said movable contact and actuated by said magnetically responsive tripping means.

5,.V A thermally and magnetically responsive device comprising, in combination, a pair of bimetallic elements, a pair of poles, each pole comprising primary and secondary coils, thus forming, in effect, on each pole, a transformer, one oi said secondary coils being in circuit with one of said pair of bimetallic elements, the other of said secondary coils being in circuit with the other of said pair of bimetallicelements, for heating the same, tripping. means actuated by said bimetallic elements being heated, movable contacting means actuated by said tripping means, a bimetallic element responsive to surrounding temperature changes for effecting uniform tripping travel'of the trippingmeans during surrounding temperature changes, separate tripping means responsive to the magnetic field surrounding said poles, and a sliding contact engageable with said movable contacting means and actuated by said magnetically responsive tripping means.

6. Apparatus as recitedA in claim 5, inv which said tripping means responsivev to magnetic ef- Iii) l2 fects comprises a pair of armatures disposed' in proximity to said poles, spring means for biasing said armatures away from said poles, catch meansfcontrolled by either of said pair of armatures, latch means, said latch means being releasably engaged by said catch means, spring means for biasing said latch means to tripped position, said slidingv contact being actuated by said latch means for disengaging the sliding, contact from said movable contacting means.

2. Apparatus as recited in claim 5, in which said tripping, means responsive to magnetic effects comprises a pair of armatures, a pair of springs for biasing each of said armatures into normal or latched position, a pair of catches, each engaging one of said pair of arma-tures to be controlled by movements thereof, a pair of latches, each of said catches releasably engaging one of said pair of latches, a cross-arm or bridging member engaged at its ends in cooperating notches in said pair of latches, said sliding contact being pivotally mounted centrally of said bridging member and guided for travel in a fixed line for effecting disengagement thereof with said movable contacting means upon release of either of said latches when one of said armatures is actuated andl upon release of both of said latches when both of said armatures are actuated.

8. n a relay, a stationary contact, a movable contact mounted for movement back and forth between positions engaging and disengaging said stationary contact, and having a bias to one of said positions, tripping means for holding said movable contact against movement under its bias comprising a pair of members movable relative to each other to tripping position for releasing said movable contactv for movement under its bias, and a pair of temperature responsive elements, each of said elements having a connection to both of said members for effecting simultaneous movement thereof without movement therebetween when both elements are heated, one of said elements beingy effective to anchor one of said members and the other being effective to move the other of said members to tripping position when only one of said elements is heated.

9. In a relay, a stationary contact, a movable contact mounted for movement back and forth between positions engaging and disengaging said stationary contact, and having a bias to one of said positions, tripping means for holding said movable contact against movement under its bias comprising a pair of members movable relative to eachr other to tripping position for releasing said movable contact for movement under itsy bias, and a pair of temperature responsive elements, each of said elements having a connection to both of said members for eecting simultaneous movement thereof without movement therebetween when both elements are heated, a stop engageable with one of said members for arresting movement thereof after a predetermined movement of both of said members, each of said: elements through said connections functioning as a stop when only one of said elements isheated, operation of said stop or one of said elements as a stop beingeffective to cause relative. movement between said members to trip said tripping means.

1). In a relay, a stationary Contact, a movable contact mounted for movement back and forth between positions engaging and disengaging said stationary contact, and having ar bias to; one of said positions, tripping means for holding said movable` contactagainst movement under its bias tripping means for biasing said comprising a latch member and a catch member, said members being mounted for movement in the same direction and for relative movement with respect to each other to tripping position, a pair of temperature responsive elements, each of said elements having a connection with said members for eiecting movement thereof in the same direction when both of said elements are heated, a stop engageable with one of said members for arresting movement thereof after a predetermined movement of both of said members, each of said elements functioning as a stop through said connections when only one of said elements is heated.

11. In a thermal overload relay, a pair of contacts movable to and from engaged and disengaged positions, and means for operating said contacts to one of said positions comprising a pair of thermostats respectively comprising a temperature responsive element, and means intermediate said elements and contacts for operating said contacts upon a predetermined movement of said thermostats when both of said elements are heated7 and upon a smaller movement of said thermostats when only one of said elements is heated.

12. In a thermal overload relay, a pair of contacts movable to and from engaged and disengaged positions, and means for operating said contacts to one of said positions comprising a pair of thermostats respectively comprising a temperature responsive element, and means intermediate said elements and contacts operative upon travel thereof a predetermined distance in response to heating of both of said elements for operating said contacts, and operative upon a travel thereof a shorter distance'in response to heating of only one of said elements for operating said contacts.

13. In a thermally and magnetically operated overload relay, the combination of, a contact assembly including a pair of movable contacts, movement of either of said movable contacts being effective to open the contact assembly, core members, inductively related windings on each of the core members, tripping means for one of said movable contacts; thermally responsive means electrically associated with the inductively related windings for operating the tripping means, an inertia member forming a part of the tripping means against movement to tripping position, second tripping means for operating the other of said movable contacts, and a magnetically operated member adjacent each of said co-re members for operating said second tripping means.

14. In a thermally and magnetically operated overload relay, the combination of, a stationary contact, a slidably mounted Contact, a movable Contact for bridging the stationary and slidably mounted contacts, a pair of core members, a primary and a secondary winding on each of said core members, a bimetallic element connected across each of said secondary windings, tripping means for operating said movable contact, said bimetals engaging cooperating parts of said tripping means for operating the tripping means, an inertia latch forming a part of the tripping means for preventing tripping of said tripping means as a result of mechanical shock, tripping meansI for operating the sliding contact, and a magnetically operated member disposed in proximity to each of said core members for operating said second mentioned tripping means.

15. In a thermally and magnetically operated relay, the combination of, a contact assembly in-V cluding a pair of movable contacts, movement of either of said contacts opening said contact assembly, tripping means for one of said movable contacts, a plurality of bimetallic elements having connections to cooperati g parts of the tripping means for operating the tripping means, a plurality of pole assemblies including inductively related windings, each of said bimetallic elements being electrically associated with a winding of one of said pole assemblies, a bimetallic element exclusively responsive to ambient temperature changes for regulating operation of the tripping means, an inertia latch forming a part of the tripping means for biasing said tripping means against movement to tripping position as a result of mechanical shock, second tripping means for operating the other of said movable contacts, and means associated with each of said pol'e assemblies and responsive to the magnetic field about each oi said pole assemblies for operating the second tripping means.

15. Tn an overload relay, the combination of a plurality of transformers each forming a pole assembly of the relay, a contact assembly comprising' a pair of movable contacts each constructed and arranged to open the contact assembly upon movement thereof, thermally responsive tripping means controlled by the electrical outputs or each of said transformers, for operating one of said movable contacts; an inertia latch forming a part of the thermally responsive tripping means for biasing said tripping against movement to tripping position as a result of mechanicalshock, and magnetically responsive tripping meansy controlled by the magnetic fields about each of the transformers for operating the other of said movable contacts.

1 7. In an overload relay, the combination of, a plurality of transformers each forming a pole assembly of the relay, a contact assembly comprising a pair of movable contacts each constructed and arranged to open the contact assembly upon movement thereof, thermally responsive tripping means controlled by the electrical outputs of each of said transformers, for operating one of said movable contacts; and magnetically responsive tripping means controlled by the magnetic fields about each of said transformers for operating the other of said movable contacts.

18. In a thermally operated tripping mechanism, the combination of, a latch member, a catch member, and a plurality of thermally responsive elements which deilect when heated, each of said elements being disposed in operative relation with respect to both said members, for eiecting simultaneous movement of said members without movement therebetween when both said elements deilect, one of said elements being effective to anchor one of said members and the other of said elements being effective to move the other of said members to tripping position when only one of said elements deiiects.

19. In a thermally operated tripping mechanism, the combination of, a pair of movable tripping members, each operatively related to the other and adapted for simultaneous movement without movement therebetween and relative movement to tripping position, means for limiting the movement of one of said members, and means including a plurality of thermostatic elements which deect when heated, each being operatively related to both said members for electing simultaneous movement of both said memantigeen bers when both'` 'said' elementsdeflect, V one of said elements. being operative toanchor one' of said'- members-andvthe other of said-elements being operativeV to/move theother of! said members when only. one ofsaid elements d'eect's.

20.. In a thermally operatedtripping mechanism, the combination of,av pair of rictionally` engaged movablev tripping members constructed' and arrangedV for simultaneous-movement withoutmovement therebetween and relative movement to tripping position, a pair of independently movable control elements disposed between said members, and a control device constructed and arranged to engage but oneof said members.

22. A thermally responsive device comprising, in combination, tripping means comprising a catch element and a latch element each rotatably mountedrabcut the same axis, means for axially biasingr the latch and catch elements together, spacingmeans disposed between-the latch and catch elements for providing a predetermined axial spacing of said elements throughout a limited range of relative rotational movement thereof and thereafter permitting relative axial movementor said elements under the iniluence of the axial biasing means, thermally responsive means for rotatably-actuating said latch element, means for limiting the rotational movements' of the catch element, and means responsive to relative axial movement of the latch and catch elements.

23. A thermally responsive device comprising, in combination, tripping means comprising a ivf-6;'- catchl element andi a latch element each rotatably` mounted about the'f sameY axis,vspring means for rotatably' biasing said elements together, means for axially biasingi the latch and catch' elements v together,t spacing: means disposed between the latch and catch elements for providing apredetermined axial spacing' ofv said elements throughout a limited range of relativerotational movement-,thereof and thereafter permittingrelative' axiaLmoVeme'r-it of said elements under theiniiuenceA of the axial: biasing means,` thermally responsive means for rotatably actuating said latch element, means for limitingthe rotational movements of the catch element, and means-respcnsive to relative'. axial movement of thelatch and catch elements 24.. A' thermally responsive device comprising,l in combination, tripping meanscomprising ar catch element and a latch element each rotatably' mounted abouti the same axis, spring' means for rotatably' biasing said elements together; meansi for axially biasing the-latch and catch elements together, spacing means disposed between the latchv and catch elements for providing a predetermined axial spacing of said elements throughout a limited range of relative rotational movement there'offand thereafter permitting relative axial movement ofv said elements under the? in'uence of the axial biasing means', thermally responsive means for rotatably` actuatingf said-y latch element, means for limiting the rotational movements of the catch element, aninertia-element pivotally connected to/said catch element and having projections thereon for engaging cooperating parts of saidlatch and catch elements, said inertia element rotatably biasing said latch and catch elements together, and means'responsive to'relative axialmovement of the latch and catch elements.

GEORGE C. ARMSTRONG.

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