US3475709A - Thermic flash-over current- and phaseinterrupting protective relay - Google Patents

Description

3,475,709 INTERRUPTING L 1969 T. s. BASSE THERMIC FLASH-OVER CURRENT- AND PHASE PROTECTIVE RELAY Filed June 16, 1967 FIG-.5

INVENTOR. TAGE sTENBERG BASSE ATTORNEY United States Patent THERMIC FLASH-OVER CURRENT- AND PHASE- INTERRUPTING PROTECTIVE RELAY- Tage Stenberg Basse, Nordborg, Denmark, assignor to Danfoss ved ing. M. Glausen, Nordborg, Denmark, a corporation of Denmark Filed June 1 6, 1967, Ser. No. 646,705 Int. Cl. H01h 61/01, 71/16 US. Cl. 337-44 Claims ABSTRACT OF THE DISCLOSURE A thermally actuated protective relay for a multiphase circuit comprises a plurality of approximately parallel bimetallic strips, a pair of slide rods actuated by the concerted action of the strips, a lever-swingable by the slide rods and a switch actuated by the lever. The point at which the lever is connected to the switch is selected so that it does not move materially when all of the strips and slide rods move together. However, when movement of one slide rod is selectively limited, the resulting relative movement of the slide rods produces angular movement of the lever to actuate the switch. The switch is also actuated in the event the current in one phase isinterrupted or is excessive. Preferably the switch is a snap switch having a first pivoted arm connected to the aforementioned lever, a second pivoted arm carrying a movable contact and a spring connecting the two arms- Movement of the movable contact is preferably limited by a back contact which can 'be selectively positioned to provide either one or two stable states for the movable contact as desired.

The present invention relates to protective relays and particularly to a relay for protecting a multiphase circuit both against overload and against current interruption or abnormal current in one phase.

In accordance with the invention, a single set of contacts is utilized to provide protection both against excess current and against failure in one phase. However, despite use of the same set of contacts, the two modes of protection are independent of one another.

The relay in accordance with the invention preferably comprises a snap-acting switch which is actuated by a relatively small movement of the actuating member. Moreover, the switch provides two modes of operation in one of which the relay automatically resets itself as soon as abnormal conditions in the circuit have ceased and in the other which the relay, when tripped must be manually reset. A member which is selectively positioned to select the mode of operation is also operable to reset the relay manually when it is operating in the non-automatic mode. A further feature of the invention is that the relay cannot be manually reset so long as the abnormal conditions which produced the tripping of the relay still persists.

The nature and advantages of the protective relay in accordance with the invention will be more fully understood from the following description of preferred embodiments shown by way of example in the accompanying drawings in which:

FIG. 1 is a schematic illustration of a relay in accordance with the invention for a 3-phase circuit, the relay being shown in cold condition,

FIG. 2 shows the relay during normal operation,

FIQ. 3 shows the relay being tripped 'by reason of excessive current,

FIG. 4 shows the relay being tripped by interruption of current in one phase and FIG. 5 is a schematic illustration of a snap switch arrangement incorporated in a relay of the kind shown in FIGS. 1 to 4.

The relay shown by Way of example in FIGS. 1 to 4 is for the protection of a 3-phase alternating current circuit, e.g., the three wire supply of a 3-phase motor. For this purpose, the relay comprises three bimetallic strips 1, 2 and 3 which are heated respectively by the current of the three phases. The respective thermal windings are not shown in the drawings but are connected in usual manner so that each of the bimetallic strips is heated in proportion to the current flowing in the respective line of the 3-phase circuit. The three bimetallic strips 1, 2 and 3 are suitably anchored on a suitable support as indicated at 1a, 2a and 3a. Free end portions of the bimetallic strips are movable laterally in proportion to the temperature to which the strips are heated by the respective thermal windings. As illustrated in the drawings, the free upper end portions of the strips move toward the left as the strips are heated.

The three bimetallic strips cooperate with two slide rods 4 and 5 which extend transversely of the strips and are longitudinally slidable in suitable supports 6 and 7. The two slide rods 4 and 5 are approximately parallel to one another and are spaced apart, the upper slide rod 5 being located near the upper ends of the bimetallic strips 1, 2 and 3 while the lower slide rod 4 is located at a position spaced from the upper ends of the strips by distance amounting, e.g., to about /3 to /6 the length of the strips. The lowest slide rod 4 is provided with shoulders 4a, 4b and 46 which are engageable respectively by the bimetallic strips 1, 2 and 3 when the strips move in the direction toward which they are flexed when heated. The upper slide rod 5 is provided with shoulders 5a, 5b and 5c which are engageable respectively with the opposite sides of the bimetallic strips.

The slide rods 4 and 5 are pivotally connected by links 8 and 9 with a lever 10 which extends downwardly toward the anchored ends of the bimetallic strips and is connected by a link 11 with the movable contact element 12a of a switch 12 having a stationary contact 12b. An adjustable stop shown in the form of a screw 13 is provided for selectively limiting the movement of one of the slide rods 5.

The point of connection 11 of the actuating lever 10 with the movable element 12a of the switch 12 is selected in relation to the length of the bimetallic strips and the distance between the slide rods 4 and 5 so that the connection 11 remains substantially stationary when the three bimetallic strips 1, 2 and 3 bend together by approximately the same amount and the shoulders 4a, 4b and 4c of slide rod A and shoulders 5a, 5b and 5c of slide rod 5 remain in contact with the respective strips. This is seen by comparison of FIG. 1 which shows the relay in cold condition with FIG. 2 where the relay is shown in normal operating condition with all of the strips having flexed toward the left. It will be seen that the point of connection 11 of the actuating lever 10 with the switch 12 has remained in essentially the same position. It has been found that the desired relationship is obtained by the formula where x is the length of the lever 10 a is the distance between the slide rods 4 and 5 L is the length of the bimetallic strips The positon of the screw 13 is adjusted so as approximately to engage the upper slide rod 5 when the bimetallic strips 1, 2 and 3 are heated by normal current 3 I flowing in the 3-phase circuit. This condition is illustrated in FIG. 2. If the current is increased above its normal value, the resulting additional heating effect tends to flex the strips 1, 2 and 3 farther toward the left. However, since the upper slide rod is held stationary by engagement with the screw 13, only the lower slide rod 4 can move. The resulting relative movement between the slide rods produces angular movement of the lever about the link 8 as a fulcrum so as to open the switch 12 as illustrated in FIG. 3. It will be understood that by adjustment of the screw 13, it is possible to select the point at which the relay will trip. Once the slide rod 5 has engaged the screw 13, tripping of the relay is effected by only a short additional movement of the slide rod 4 by the bimetallic strips.

FIG. 4 illustrates the condition which arises in the event the current in one phase is interrupted or materially decreased. By way of example, it is assumed that there is no current in phase 2 while the current in phases 1 and 3 is normal. Since the bimetallic strip 2 is not heated and hence not flexed, engagement of strip 2 with the shoulder 5d of slide rod 5 holds the silde rod against movement toward the left. However, slide rod 4 is moved toward the left by the flexing of bimetallic strips 1 and 3 by normal heating current. The resulting relatively movement of the slide rods 4 and 5 produces angular movement of the actuating lever 10 so as to open the switch 12 as is illustrated in FIG. 4. In this manner, tripping of the relay is effected by any material unbalance between the three phases. The relay is sensitive in that opening of the switch 12 is effected by relatively slight relative movement of the slide rods 4 and 5. Moreover, tripping of the relay by reason of unbalance of the phases is completely independent of the adjustment of the relay for overload current by means of the screw 13.

In FIG. 5, the switch is shown as a snap switch which is operated by the actuating lever 10. The switch comprises a first lever arm 14 pivotally mounted at 15 and a second lever arm 17 pivotally mounted at 18. The two lever arms 14 and 17 are connected by a tension spring 19. The actuating lever 10 of the relay is connected to the first operating arm 14 of the snap switch through a pivotal connection 11. The second operating arm 17 of the snap switch carries a contact which is engageable with a fixed contact 21 when the switch is in closed position as illustrated in FIG. 5. When the first lever arm 14 is moved to the left by the actu'ating lever 10 so that the lower end of the arm to which spring 19 is attached moves to the left of the pivot 18, the spring 19 causes the second lever arm 17 to move to the left with a snap action. Movement of the second lever arm toward the left is limited by a back contact 22 carried by a leaf spring 23.

Means is provided for selectively positioning the back contact 22 in a first position as shown in solid lines in FIG. 5 and a second position 22' as indicated in dotted lines. When the back contact 22 is in the position shown in solid lines, the lever arm 17 carrying contact 20 has twostable positions with the contact 20 engaging contact 21 and 22 respectively. When the back contact 22 is in the dotted line position 22', the lever arm 17 has only one stable position with the contact 20 engaging contact 21 and will return to that position as soon as the actuating force exerted by lever 10- is removed. Hence in the latter case, the relay automatically resets itself upon termination of the disturbance which caused tripping of the relay while in the former case, the switch remains in tripped condition and must be reset, e.g., manual-1y.

The means for selectively positioning the back contact 22 is shown by way of example in FIG. 5 as a slide bar 24 having an inclined end engageable with an inclined end portion of the spring 23 which carries the back contact 22. A spring tends to hold the slide bar 24 in retracted position as shown in the drawing. When the slide bar 24 is pushed inwardly against the force of spring 25, the inclined inner end 24a of the bar 24 engages the inclined end portion on leaf spring 23 to move the spring and the back contact 22 to the dotted line position 22'. The slide bar 24 can, if desired, be latched in its inner position by a sliding bolt 26 engageable with a aperture 24b in the slide bar.

If the relay is tripped when the slide bar 24 is in the retracted position shown in solid lines in FIG. 5, the force exerted on lever arm 14 by the actuating lever 10 causes the lever arm 14 and also the lever arm 17 to swing to the left to break the contact between contacts 20 and 21 and to bring the movable contact 20 into engagement with the back contact 22. Only slight movement of the lever 10 is required to trip the relay. If the disturbing force which caused tripping of the relay is now removed, contact 20 remains in engagement with contact 22 so that the relay is not self resetting. Resetting of the relay can be effected by moving the slide bar 24 inwardly and thereby moving the back contact 22 to the dotted line position 22' whereupon the spring 19 will elfect further movement of the lever arm 17 to bring contact 20 into engagement with fixed contact 21. If, however, the disturbance which caused tripping of the relay has not been removed, a force will still be exerted on lever arm 14 by the actuating lever 10 and hence the contact 20 will remain in engagement with back contact 22 even when in the dotted line position 22'. Hence the relay cannot be manually reset so long as a disturbance continues.

If the relay is tripped when the slide "bar 24 is held in its inner position by the bolt 26, the force exerted on the lever arm 14 by the actuating lever 10 will cause the lever arm 17 to swing to the left until contact 20 engages the back contacting position 22' As soon as disturbance which caused tripping of the relay is removed, the lever arm 17 will return to the position shown in FIG. 5 with contact 20 in engagement with contact 21. The relay in this condition is thus automatically resetting.

It will thus be seen that the member 24 serves not only to select the mode of operation of the relay so as to automatically resetting or non-automatic as is desired but serves also to reset the relay when in its non-automatic mode of operation.

While preferred embodiments of the invention have been illustrated by way of example in the drawings, it will be understood that many alterations can be carried out without deviating from the fundamental concept of the invention. For example, the adjustment member illustrated schematically as the screw 13 may be a sliding rod positioned by a bimetallic strip exposed to ambient tem perature so as to compensate for the effect of variation of room temperature on the operation of the actuating bimetallic strips 1, 2 and 3. When the slide rods 4 and 5 are connected by means of a spring, the pivotal connections 8 and 9 between the slide rods and the actuating lever 10 can be formed as recesses or notches in the slide rods engaging suitable fulcrum edges on the actuating lever. Still other variations and modifications will be apparent to those skilled in the art.

What I claim is:

1. A thermal protective relay for a multiphase circuit comprising a plurality of approximately parallel bimetallic strips each heated by current of one phase of said circuit, each of said strips being anchored at one portion and having a portion that is movable upon heating of the strip, two approximately parallel slide rods. spaced from one another and mounted for longitudinal movement transversely of said movable portions of said strips, one of said slide rods being disposed closely spaced to a point of anchorage of each rod and the other rod being disposed spaced from each point of anchorage about /6 to about /3 the axial length of said strips, one of said slide rods having abutments engageable with one side of each of said strips respectively and the other of said slide rods having abutments engageable with the opposite side of each of said strips respectively, whereby said slide rods are movable longitudinally by said strips, a lever extending transversely of said slide rods and flexibly connected thereto, a switch actuatable by said lever, said lever having a portion extending approximately parallel to said strips and in a direction generally toward the anchored portions of said strips, means connecting said extending portion of said lever with said switch, said connecting means being located at a point on said lever which remains approximately stationary when said strips and slide rods move together, and means selectively limiting movement of one of said slide rods to cause relative movement of said slide rods when said limit is reached and thereby produce angular movement of said lever to actuate said switch.

2. A relay according to claim 1, in which said switch is a snap-acting comprising a first pivoted arm connected with said lever, a second pivoted arm approximately in line with said first arm and carrying a movable contact and a tension spring connecting said arms.

3. A relay according to claim 2, in which said switch further comprises a fixed contact, and a back contact engageable by said movable contact and means for selectively positioning said back contact in a first position providing two stable positions for said movable contact in engagement with said fixed contact and back contact respectively and a secured position providing only one stable position for said movable contact in engagement with said fixed contact. I

4. A relay according to claim 3, in which said means for selectively positioning said back contact comprises means for manually resetting said relay.

5. A thermal protective relay for a multiphase circuit comprising a plurality of approximately parallel bimetallic strips each heated by current of one phase of said circuit, each of said strips being anchored at one portion and having a portion that is movable upon heating of the strip, two approximately parallel slide rods spaced from one another and mounted for longitudinal movement transversely of said movable portions of said strips, one

of said slide rods having abutments engageable with one side of each of said strips respectively and the other of said slide rods having abutments engageable with the opposite side of each of said strips respectively, whereby said slide rods are movable longitudinally by said strips, a lever extending transversely of said slide rods and flexibly connected thereto, a switch actuatable by said lever, said lever having a portion extending approximately parallel to said strips and in a direction generally toward the anchored portions of said strips, means connecting said extending portion of said lever with said switch, said connecting means being located at a point on said lever which remains approximately stationary when said strips and slide rods move together, means selectively limiting movement of one of said slide rods to cause relative movement of said slide rods when said limit is reached and thereby produce angular movement of said lever to actuate said switch and said slide rods being spaced from each other axially along the strips and said lever has a determined length by the formula:

a 2.La

where x is the length of the lever a is the distance between the slide rods, and L is the length of the bimetallic strips References Cited UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner R. L. COHRS, Assistant Examiner US. Cl. X.R. 20067; 33749

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