US2581882A - Device for protecting polyphase circuits - Google Patents

Description

Jan. 8, 1952 c. E. RANDALL 2,581,832

DEVICE FOR PROTECTING POLYPHASE CIRCUITS Filed Feb. 10, 1949 2 Si-IEETS-SHEET 1 Inventor CYRIL. E.RAND'4 L.

B I /r y Arro%y Jan. 8, 1952 Q RANDALL 2,581,882

DEVICE FOR PROTECTING POLYPHASE CIRCUITS Filed Feb. 10, 1949 2 SHEETS-SHEET 2 3 4/ 39 y k p g 37 H 42 24- 26 42 v3 I 3 f 2/ L1:

9 lln 23 [5 Inventor CYRIL E. RANDALL Art 091/ Patented Jan. 8, 1952 DEVICE FOR PROTECTING POLYPHASE CIRCUITS Cyril E. Randall, Bedford, England, assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application February 10, 1949, Serial No. 75,613 In Great Britain July 27, 1948 This invention relates to devices for protecting polyphase circuits. The object of the invention is the provision of improvements in such devices and the invention consists broadly of a device for protecting polyphase circuits against phase unbalance, comprising a plurality of elements together forming, in a mechanical series, a force-transmission means for retaining the device at a normal or non-tripped position, said elements being adapted to be individually positioned in a sense transversely to the direction of the force transmission, according to the current in the respective phases, and the mechanical correlation of said elements being such that, upon the transverse positioning of any neighboring pair relative to each other, departing, to more than a given extent, from the normal, the force transmission gives way so as to permit the device to move to the tripped position.

In order that the invention may be the more clearly understood a device in accordance therewith, together with a modification of said device. will now be described, reference being made to the accompanying drawings in which:

Fig. 1 is a somewhat diagrammatic perspective view of said device.

Fig. 2 is a similar view of the left hand end of said device showing the modification.

Referring first to Fig. 1, the circuit to be protected is a three phase circuit, and said circuit is interrupted upon disengagement of a moving contact I from a fixed contact 2. Said contacts iand 2 may for example be connected in series with the winding of a three pole contactor controlling said three phase circuit.

-Said moving contact I is carried at the upper end of an upright leaf spring 3 and said moving contact is controlled by means of an upright pressure plate 4 which is mounted so as to be horizontally slidable. Said pressure plate 4 has a short horizontal projection 5 which engages said leaf spring, and when said pressure plate is slid to the right (according to the drawing) it presses said leaf spring to the right so that the moving contact I engages with the fixed contact 2. When said pressure plate is released said leaf spring presses said pressure plate to the left and simultaneously disengages said moving contact from said fixed contact.

For guiding said pressure plate 4 to move horizontally as stated, the upper end of said pressure plate is slidable between horizontal guide members 6 and its lower end is slidable between horizontal guide members I. To restrain said pressure plate against vertical movement, it has transverse upper and lower pins 8 and 9 project ing from it, the upper pin 8 engaging the under surface of the guide members 6 and the lower pin 9 engaging the upper surface of the guide members I.

7 Claims. (Cl. 200-113) Normally said pressure plate 4 is held at its right hand position so that the contacts I and 2 are in engagement, but, upon the occurrence of either overload or voltage failure in one or two of the phases, said pressure plate is released, enabling the contact i to leave the contact 2, and

causing the controlled circuit to be interrupted.

To this end three vertical sliding plates l0, ii and I2 are provided whose upper ends slide between the upper guide members 6 and whose lower ends slide between the lower guide members I. These sliding plates are able to move not only horizontally, but also vertically, between the guide members. The sliding plates are controlled as to their vertical positions by means of respective bi-metal elements l3, l4 and 15 whose temperatures vary according to the current in the three phases. These elements 13, M and I5 are fixed at one end to fixed metal mountings l6, and their other ends are adapted to rise and fall according to their temperatures, that is according to the current value in the respective phases. These movable ends engage in horizontal slots I! in the respective sliding plates, and thus, as the ends of the bimetal elements rise and fall, said sliding plates also rise and fall. At the same time the slots I! are sufficiently long to enable said sliding plates to make their horizontal components of movement independently of the bimetal elements.

The sliding plate ID has two projections l8 extending horizontally from its right-hand edge and engaging the left hand edge of the pressure plate 4. Said sliding plate l0 also has two projections l9 extending horizontally from its left hand edge, and, when said sliding plate I0 is at the same horizontal level'as the sliding plate ll, these projections I9 abut, end to end, with two similar projections 20 extending horizontally from the right hand edge of the sliding plate I I. Said sliding plate II has also two projections 2| extending horizontally from its left hand edge, and. when said sliding plate II is at the same horizontal level as the sliding p ate l2, these projections 2| abut, end to end, with two similar projections 22 extending horizontally from the ri ht hand ed e of said sliding plate l2. Finallv said sliding plate l2 has two projections 23 extending horizontally from its left hand edge and abutting a a nst the right hand edge of a fixed vertical member 24.

Above the sliding plate I2 is provided a p n 7'5 which is ca able of being adjusted vertically to a po it on which accords to the degree of overload at which it is desired to have the dev ce trip.

In op ration. assum ng the current in the controlled three phase circuit is switched oif. all three of the bimetal elements l3, II and i5 will be ecually cold and the three plates l0, H and I2 will accordingly be at the same level. Therefore the projections i9 and 28 will be in engagement, and so will the projections 2| and 22. The dimensions are such that, under these circumstances the pressure plate 6 is held sufiiciently far to the right to cause the contact i to engage the contact 2.

If now the current is switched on, and assuming that there is no voltage unbalance, the three bimetal elements will heat up equally and the three plates II], II, l2 will rise together remaining at the same level. The projections i9 and 20 will remain in engagement, and so will the projections 2| and 22. The projections ill will slide up the left-hand edge of the pressure plate 5, and the projections 23 will slide up the right hand edge of the fixed member 24. The pressure plate 4 will remain unmoved and the contacts i and 2 will remain closed.

If now the current increases above the predetermined safe value, these three plates it, i i and I2 will continue to rise until the upper edge of the plate l2 engages the pin 25. This prevents any further upward movement of said plate l2, but the plates II and ID will continue to rise, until the projections 2i cease to register with the projections 22, whereupon the pressure plate d together with the sliding plates is and ii are free to move to the left until the projections 2i engage the right hand edge of the sliding plate i 2, and/or the left hand edge of the sliding plate ii engages the prolection 22. This movement is sumcient to enable the contact i to disengage the contact 2.

If instead of overload there has been a voltage failure in one or two phases, or some other voltage unbalance had taken place, a difference of level between certain of the plates ID, i l l2 would have eventuated so that either the projections 2i 22 or the proiections i9, 22 would have ceased to register. Once again therefore the pressure plate 4 would have been free to move to the left, and the contact I would have disengaged.

In any event, for resetting the device after the bimetal elements have again become cold, a reset plate 26 is provided. This plate is mounted so as to be horizontally slidable in a plane parallel to the common plane of the four plates i, i8, ii, i 2, and it carries transverse pegs 27 which pass through apertures 28 in the sliding plate i9, and also transverse pegs 29 which pass through apertures 30 in the sliding plate ll. Said reset plate 26 is biased by means of a spring (not seen) to a left hand limit as illustrated, and when it is pushed to the right i by means of a finger knob 3i mounted on it) the pegs 2i engage the right hand edges of the aperture 28 and press the plate ill to the right, and the pegs 29 engage the right hand edges of the apertures 3t and press the plate H to the right. The pegs are so placed that the plate i is moved sumciently in advance of the plate Ii to enable the projections is and 20 once more to comeinto line (if they had disengaged) so that they will again abut against each other when the reset plate 28 is released. Equally the plate ii is moved in advance of the plate i2 so that the projections 2i and 22 (if they had disengaged) will abut against each other when the reset plate is released.

The reset plate 26 may also carry transverse pegs 31 which pass through apertures 38 in the pressure plate 4. When the reset plate is pushed to the right these pegs 3'! engage the right hand edges of the apertures 38 before the pegs 27 engage the right hand edges of the apertures 29. Thus the pressure plate 4 is kept clear of the pro- 4 jections l8 during the resetting operation. thereby making it easier for the bimetal elements to return the sliding plates vertically to their correct levels.

In construction the guide members 6 are shown as forming the upper member, and the guide members I the lower member, of a rectangular frame one of whose end members is constituted by the aforesaid member 24. The other end member of said frame, which is designated by the reference 32, serves as the support on which the contact 2 and also the leaf spring 3 are mounted.

The heating of the bimetal elements l3, l4 and it may be eilfected either by connecting them directly in the phases of the circuit to be protected, or by means of heating coils (not shown) connected in said phases.

The pin 25 is shown as mounted on an arm 33 which is pivoted at 34, so that, by moving said arm about its pivot, the raising and lowering of said pin 25 is effected. The extremity of said arm moves over, and reads against, a scale 35 which may be calibrated in terms of the current value at which it is desired to have the de vice trip.

The whole structure is mounted on a suitable base 38.

Referring now to Fig. 2 this allows a modification in which, instead of providing the pin 2| for checking the upward movement of the plate I! on overload so that the plates H and I0 continue to rise until they are free to move to the left relative to said plate i2, an additional vertical sliding plate 31 is provided between the plate" and the vertical member 24. This plate 31 has projections 38 extending horizontally from its right hand edge which normally abut end to end with the projections 23 of the plate i 2. Said plate 311 is normally stationary during the operation of the device, and the projections 38 are 01: considerable vertical depth as shown.

In operation, when the current is switched on, and assuming no voltage unbalance, the three plates l0, ii, i2 will rise together at the same level and the projections 23 will slide up the ends of the projections 38, and the pressure plate 4 will remain unmoved and the contacts I and 2 will remain closed. If, however, the current increases above the predetermined sai'e value, the projections 23 will slide clear of the projections 38, and the pressure plate 4, together with all these sliding plates iii, ii and i2, will be free to move to the left and enable the contact I to disengage the contact 2.

Said plate 3'! has projections 39 from its left band edge which abut slidably against the right hand edge of the vertical member 24, and said plate 31 is vertically adjustable, and it will be seen that its vertical adjustment determines the degree of overload at which the projections 23 clear the projections 38. The vertical adjustment may be effected by pivotally connecting at $0 the *upper end of said plate M to the aforesaid arm 33. Thus the adjustment of said arm 33 determines the vertical adjustment of said plate 31, and said arm 33 indicates, as before, on the scale 35 the degree of overload to which the device is set.

The device functions exactly as before on phase unbalance. It will be seen that. for resetting the device, it will now be necessary to provide the reset plate 26 with additional transverse pegs M which pass through additional apertures 42 in the plate 02. Thus when the reset plate 2! is pressed to the right for resetting, the pegs 4| will engage the right hand edges of the apertures 42 and press the plate 12 to the right. The pegs 4| are of course so placed that the plate ll moves suiliciently far in advance of the plate ii to permit the projections 2| and 22 to re-engage if they have been disengaged by phase unbalance, and at the same time the plate 12 is moved sufllciently far to the right to enable the projections 23 and 38 to re-engage if they have been disengaged by overload.

I claim:

1. In a protective device for electric circuits wherein a relay is used to control the circuit controllin switch in accordance with the condition of a plurality of thermal responsive elements, each of which elements is adapted to be heated in accordance with the current in a separate conductor 01! the protect d circuit. tripping means for said relay com rising a plurality of sl de members. one for each thermal responsive element, guide means for holding said members in coplanar relationship and for permitting them to move only longitudinally and laterally, a plurality of ,Dl'OjectiOlls extending laterallv from adjacent edges of said movable members to prov de increased s acing between said members when the projections on adjacent members are in alignment with each other, means for connecting said mo able m mbe s to said thermal responsive elements to efiect longit dinal m v ment of said members in accordance with the value of current in their respective con uctors, and means for biasing said re ay to tripped position, said movable members being normally positioned with their coo erating proj ctions in alignment to hold said relay in normal position against the force of said biasing means. whereby upon an unbalance of curr nt in the conductors of the controlled circuit which causes the proiections to be moved out of alignment at least one of sa d members wi l be moved laterally to permit trip ing of said relay.

2. A releasing device for an electric switch comprisin in comb nation, means for normally biasing said switch to o en position. a plurality of movable members guided to move in a common plane and free for movement in said plane relative to each other. said members each havin laterally extending projections arran ed for end-to-end en a ement w th similar projections on adjacent members, said members being' positioned to ho d said s itch in closed position a ainst the force of said biasin means when said pro ections are in enga ement, and a pluralitv of c rrent res onsive elements individually connected to said movable members to effect movement thereof in parallel directions in accordance with the value of current controlling each element, whereby u on an unbalance in said values of current the proiections on at least two adiacent movable members will move out oi en a ement to ermit transverse movement of at least one of said members under the force oi said biasing means to o en said switch.

3. The combination with a switch having a movable element, of a fixed member, a group of slide members interposed between said fixed member and said movable switch element. said slide members bearing one a ainst another and being of contour form such that the group is expansible or contractable for exerting or relieving pressure on said switch element by sliding any one of said slide members relative to an adjacent slide member and current responsive means for effecting sliding of said slide members individually and selectively according to unbalanced current conditions of said means.

4. The combination as in claim 3, wherein said movable switch element has stability during sliding of said slide members together, and including means for restricting the range of movement of one of said slide members to permit sliding of another relative thereto under predetermined current conditions.

5. A relay for polyphase alternating current circuits comprising the combination with thermal elements for association with different phases of the polyphase circuit of a switch having a movable element, a fixed member, a. group of slide members interposed between said fixed member and said movable switch element, said slide members bearing one against another and being of a contour form such that the group is expansible or contractable for exerting or relieving pressure on said movable switch element by sliding any one of said slide members relative to an adjacent slide member, said thermal elements each having connection with an associated slide member for effecting sliding 01' said slide members individually and selectively according to unbalanced current conditions in the different phases of the polyphase circuits.

6. A protective device for polyphase electric circuits comprising. in combination, a switch. means for biasing said switch to a given position, force transmission means for holding said switch in another position against the force 0! said biasing means, said i'orce transmission means comprising a plurality of slide members in end to end engagement and which upon a predetermined sliding movement of any one relative to the member enga ed thereby eilects a change in the force transmission means to permit said switch to move to said given position, and current responsive means for sliding said slide members independently of one another for relative movement thereof when they are subjected to unbalanced current, said slide members havin laterally extending pro ections arranged for end to end engagement with similar projections on adjacent members for eiteciing a reduction in the effective length of said force transmission means upon movement of said projections out oi engagement with each other.

'7. A device according to claim 6, wherein a resetting member is provided for engagin each 01 the slide members after the first and movin them in the direction of force transmission, said slide members having apertures formed therein,

engagement being effected bv transverse proiections on said resetting member which pass throu h said apertures in said slide members for engagement with the walls 01' said apertures. whereby each member is moved suiiiciently far in advance of the preceding one to enable them to return to normal relative positions.

CYRIL E. RANDALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Besag May '1, 1940

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