US2749407A

US2749407A - Single phasing preventor

Info

Publication number: US2749407A
Application number: US386352A
Authority: US
Inventors: Walton James Rignell; Burke James Neil; Cure Arnold Walton
Original assignee: Electrical Apparatus Co Ltd
Current assignee: Electrical Apparatus Co Ltd
Priority date: 1953-10-15
Filing date: 1953-10-15
Publication date: 1956-06-05
Anticipated expiration: 1973-06-05

Description

J. R. WAL-row ET AL 2,749,4@7

SINGLE PHSING PREVENTOR June 5, i956 2 Sheets-Sheei l Filed Oct. l5, 1953 ATTORNEYS jm@ 5 E956 J. R. WALTON ETAL 2,7497

SINGLE PHASING PREVENTOR Filed Oct. l5, 1953 2 Sheets-Sheet 2 Fie? FIG ATTORNEYS SINGLE PHASNG PREVENTR lames Rignell Walton, Harpenden, .lames Neil Burke, Barnet, and Arnold Walton Cure, St. Albans, England, assignors to The Electrical Apparatus Company, Limited, St. Albans, England, a company of Great Britain Application Gctober 15, 1953, Serial No. 386,352

8 Claims. (Cl. Z130- 116) This invention relates generally to devices for protecting polyphase circuits.

Devices of the subject type are especially useful for protecting polyphase alternating current electrical apparatus, and particularly polyphase electric motors, and comprise a plurality of current-sensitive members each of which can respond to one of the currents between which unbalance is to be avoided, a switch, and a operative connection between the current-sensitive members and the switch for operating the latter to disconnect the apparatus by non-uniform movement of the member in the event of unbalance, Since the device is particularly useful in protecting polyphase motors against single phasing, it is described hereinafter as a single phasing preventor or more brielly, as a preventor. According to the practice of the prior art, a number of bimetal strips was employed to operate the preventor, these being heated in accordance with the currents in the respective phases of the circuit being protected, either by passing current through the bimetal itself or through a resistance element mounted with it. In either case, if it was desired to renew the heating elements, or to exchange them for others of different value, it was necessary to reassemble the bimetal strips, if not to exchange them for others, which involved re-adjusting the mechanism.

Therefore, it is the primary object of the present invention to provide for the replacement of the heating elements without interference with any mechanically operated parts, whereby to obviate the necessity for re-adjustment when the heating elements are replaced. in accordance with said object, it is a more specic object to provide for the replacement of the heating elements without disturbing the bimetal strips. Another object of the present invention is to make the means of attaching in place the heaters, or carriers, therefor such that positive location is obtained on interchange.

A further object is to provide a more efiicient improved and generally simplified single phasing preventor.

The above and other objects, features and advantages of the present invention will be more fully understood from the following description considered in connection with the accompanying illustrative drawings.

In the drawings:

Fig. 1 is a top plan View of a preventor, pursuant to the present invention, for protecting a three phase electric circuit against unbalance, two of the heaters being removed for purposes of illustration;

Fig. 2 is a view similar to Fig. l, with the cover of the device removed, two of the heaters being removed as in Fig. l;

Fig. 3 is a front elevation taken in the direction of arrow 3 in Fig. 1;

Fig. 4 is a sectional view taken on the line 4-4 of Patented June 5, i956 Figs. 7 and 8 illustrate one form of heater for the preventor; and

Figs. 9 and 10 illustrate another form of heater therefor.

Referring now to the drawings in detail, the protector device of the present invention is provided with an insulating base 2l) on which the various component parts thereof are mounted. Provision is made for three laterally spaced conducting brackets or terminal elements 22, each provided with a terminal 24 for the incoming current, said brackets being suitably secured to the base 20, as by the securing elements 23 (Fig. 4). Three conducting brackets or terminal elements 26 are also secured to the base 20 as by the securing elements 27, said brackets extending through apertured portions 29 of the base and being each provided with a terminal Z8 for the outgoing current. Consequently, it will be understood that there is an input terminal 24 and an output terminal 23 for each current phase. The base 20 has defined therein three laterally spaced chambers 34 in each of which there is mounted a bimetal strip 39. More specifically, each strip is provided with a looped portion 32, an end portion 33 which is secured to the insulated base in the companion chamber, as by means of a clip 36, and with a free end 38 which extends from the chamber and engages in

slots

40 and 42 provided in the longitudinally extending slide members or

plates

44 and 46, respectively. The plates are disposed between the base 2G and a cover 48 which is ixed thereto, said base and cover dening a housing for the protector. Said plates are mounted for slidable movement in the direction of their longitudinal axis under the control of the birnetal strips. Adjacent one end thereof, the upper plate 44 carries a pivot 5t) on which there is pivotally mounted a bell crank lever 52. A pin 56 carried at one end of the lower plate 46 extends into and is connected with one arm 54 of the bell crank lever. The other arm 58 of the bell crank lever engages a hook contact 60, which constitutes one of the contacts of a switch 61, best illustrated in Fig. 6, the other switch contact being indicated at 68.

Switch 61 is of similar construction and operation to the switch illustrated and described in the British patent specification No. 553,154 and in No. 628,220. As illustrated and described therein, and as shown herein, the aforementioned hook contact of the switch extends vthrough an opening 62 provided in a fixed conducting bracket 64, which is provided with a terminal screw 65 (Fig. 5). One end of the companion contact 68 is hooked, as at 7i), into a contact bar 72 (Fig. 3) which is fixed to the device in a suitable manner and which is provided with a terminal 76. A spring '74 operates to move the contact 68 downwardly from the full line, to the broken line position thereof, as illustrated in Fig. 5, when the companion contact 60 is rocked in a clockwise direction, viewing said figure. In this connection it will be noted that the hook contact 60 has an extension portion 66 upwardly of the bracket 62, which extension is biased by a spring 67 in a direction to effect engagement of the opposite end of the hook contact 6i) with the companion contact 68. It will be understood that the

switch contacts

60 and 68 are connected in well known manner to control the supply of current to a suitable load, for example, and not by way of limitation, to a motor, and, when the switch is opened, protects the motor by cutting off the current supply thereof. In this connection, the switch may be connected in series with the operating coil of a suitable contacter (not illustrated) for controlling the supply of current to the apparatus, for example, a motor, which is being protected.

The aforementioned spring 67 serves to press the hook contact 6d against the bell crank lever 52, as best illustrated in Figs. 3 and 5. When the bell crank lever is in the position thereof illustrated in Fig. 3, the hook at the lower end of the hook contact 60 is in contact with and holds the companion switch Contact or arm 68 ot the switch 6l. FEhe Vpressure yexerted :by the spring 67 through the hook contact 66 on the bell crank 52, makes the latter thrust the plate d6 in the direction of the arrow 47 in Fig. 3, and relative to the companion plate d4, so tar as such movement is permitted by the engagement of the bimetal ends 33 in the slots of these plates. The relative position of the various parts being, as illustrated in Fig '5. Uniform hearing of the bimetal strips Sti will cause their tree e, 33 to move in the direction of the arrow d? by equal amounts, and it will be apparent that the plates lid and d() and the bell crank lever 52 will move in the direction of said arrow i7 with said free ends of tie heaters. The upper arm 53 of the bell crank lever, ag 'nst which the hook contact o@ presses, will slide under the latter without affecting the closed condition of the switch di. Hou# ever, should unequal heating ot the him-etal st s occur, so that one of them moves less than the others, this one will limit thc movement of the plate do in the direction ot the arrow d?, but the plate dd will continue to move in said direction under pressure from the other strips which are moving further than said one strip. Consequently, the plate will move in the direction of the arrow i7 over plate d6, carrying with it the pivot t? of the l crank lever 52, while the piu 5o which is hired to the ate de and which engages in the lower arm 54 of the l crank lever will prevent that lower arm from moving in the direction of the arrow 47. Consequently, the bell crank lever will pivot in a counter-clockwise direction, viewing Fig. 3, so that the arm 5S thereof moves upwardly from the position thereor" illustrated in said ligure. This arm forces the hook Contact dit upwardly, viewing Fig. 3, until it disengages the companion switch contact 68, permitting the latter to be moved to the open position thereof by spring 74, as illustrated in broken line in Fig. 5. Since, as previously indicated, the switch is connected to control the supply of current to a motor, it will be apparent that when opened the switch protects the motor by cutting oit the supply of current thereto. As previously indicated, the Contact arm d8 being pivoted at the hook portion 7@ and biased by the spring '7dto press firmly against the 'nook end of hook contact 7) iu the engaged condition thereof, when the lower portion ot the hook Contact di) is moved in the direction of the arrow 63 (Fig. 6) to disengage the hooked end there-of from the companion contact 68, as previously explained, the latter is moved downwardly by the spring 7d until it abuts an insulating nose 78, as illustrated in Fig. 5.

Once the switch 'Si is opened in the described manner, it remains open even though the hook Contact dit moves back in the direction opposite the arrow o3. However, alter the hook Contact has returned to the position thereof illustrated in Fig. v5 or 6, the companion switch contact (itt may be re-enoaged therewith by moving upwardly upon the nose as illustrated in Fig. 5, to move the contact back into engagement with the hook Contact all to reset the switch.

lrovision is made for a bracket titi which is pivoted at d2 which carries a bimetal strip S4. Provision is also made for a lever do which is pivotally mounted, as at S3, and which is provided with a pointer (Fig. 3), which pointer moves relative to notches @l provided on the base Zit as the lever 86 is rotated on its pivot. As best seen iu 2, the lover 36 is provided with a projection SM which limita the rotation of 'the bracket tit), it being noted that the latter is provided with a part 3l which is adapted to engage the projection 34, said projection being disposed in the path of movement of the part til. As best seen in Fig. 3, the bimetal strip tid extends from the bracket 8 into the path of movement of the lower plate 16 in the direction of the arrow 47 to limit the movement of said plate in said direction.

En view of the foregoing, it will be apparent that the extent ct' the movement ofthe plate d6 in the direction of the arrow t7 may be predetermined by the setting of the pointer 9) at a particular ,notch 92., the setting of said pointer determining the position of the lever 86 and thereby ,limiting the clockwise rotation of the bracket 80, viewing Fig. 2, which in turn determines the setting of the bimetal 8d which, as indicated, predetermines the extent of the movement of the plate 46 in the direction of the arrow 67. Under conditions of uniform heating of the various bimetal strips 39, the

plates

44 and 46 move in the direction of the arrow 47, viewing Fig. 3, as previously d bed, until movement of the plate 46 is stopped by its engagement with the bimetal strip tid. Further heating of the strips 3) will cause the companion plate 44 to move in the direction of the arrow 47, relative to the plate 46, to result in the pivotal movement of the bell crank lever in a direction to open the switch 6l, as previously described, and thereby discontinue the supply of current to the apparatus, 'for example a three phase motor which is being protected. Therefore, it will be apparent that the preventor device herein described provides protection gaiust ordinary overload of the ap aratus as well as protef ion against unhalanee in the various current phases thereof. ,Ev a suitable design or construction of the bimetal strip Se, so that .for a given change of ambient temperature its delection is the .same as that of the bimetal strips 3h, the uniform overload which will trip the switch 67, caused to be made independent of ambient temperature.

The base Ztl and the cover 48, which constitute the housing, are extended to overlap the free ends 38 of the birnetal strips Sti to hold a transparent front window plate (Fig. 2). The base and the cover may also be extended at each side of the device to overlap the strip and associated parts, and to hold transparent side window plates and liftil. Consequently, the various operating parts are clearly visible and yet they are protected. in this connection, it will be understood that it is particularly useful to be able to observe the movement of the free ends 33 of the various strips 3l) in order to see if they are moving together, as when the three leads of the circuit being protect-ed are equally loaded, or if one or more of the ends is lagging, as when imbalance exists between the three leads of rthe circuit being protected.

Cover 425, when mounted on the base 2l), closes the top of the various chambers 34. The heaters MEZ are disposed in each of the chambers 34 when the protector device is in use. Pursuant to the present invention, as best shown in Fig. 4, each heater M92 is fixed to a companion incoming terminal bracket 22 by a securing portion lii which extends transversely of the bimetal loop outwardly of the associated chamber, through the medium ot the screw 1194 and is iixed to a companion outgoing terminal bracket 26 by a securing portion 105 which extends transversely of said loop outwardly ofthe associated chamber, through the medium of a screw 106. Consequently, it will be apparent that at both ends thereof, the heater is secured outwardly of the housing. It will be noted from the left hand. chamber, viewing Fig. 2, that the heater lies within and adjacent to the loop 32 of the associated birnetal strip 3@ in close spaced thermal relation therewith to obtain maximum heat transfer. Referring now to Fig. 4, it will be noted that the housing cover d3 is cut away, as at 198, to permit the heater to be readily removed or replaced through the cover, without the necessity of removing the latter, by merely removing the screw ldd and by backing up or slackening the screw 106. Each heater 102 has attached to itself, or made a part thereof, a plate llt) which serves to close the opening 108 provided in the cover 48 when the heater is in position in the device. Fig. 2 illustrates only one ot the heaters in position, the heater in the left hand chamber, viewing said tigure, being shown in section at the level of the companion bimetal strip 30, the heaters in the center and the right hand chambers having been removed for purposes of illustration. The center and right hand heaters have also been removed from Fig. 1 and in addition the screws 104 which hold the heaters to the brackets 22 have also been removed so as to reveal the openings 108 in the top cover 48.

The heater 102 shown in position in the protector device is formed of sheet metal and is suitably shaped for disposition within the loop 32 of the associated bimetal strip and to provide the

terminal connecting portions

103 and 105 thereof. Thicker or thinner sheet metal is employed for larger or smaller currents respectively, provided however that the heater is not made of such thin material as to be readily liable to accidental deformation.

For smaller currents, a heater 102A, as illustrated in Figs. 7 and 8 may be used. Said heater is made of spirally wound wire, being provided with the apertured end portion 112, apertured as at 112A, for connection by screw 104 to the terminal brackets 22 and with the U-shaped end or peripherally interrupted portion 114 for connection by screw 106 to the terminal bracket 26. For still smaller currents, a heater 102B, as illustrated in Figs. 9 and l0 may be used. Said heater is formed of a relatively thin or ne wire which is spirally wound on an insulating former or mounting member 116. The heater 102B is provided with an apertured end 118, apertured as at 118A, for connection by screw 104 with the terminal bracket 22 and with a slotted end 120 for connection by screw 106 to the terminal bracket 26. It will be understood that the heater 102 is also apertured in the connecting portion 103 thereof, and is slotted in the connecting portion 105 thereof in the same manner, as at 120 in Fig. 9. lt will be noted in addition, that the U-shaped opening 114 in Fig. 7, is substantially in the form of an open ended slot as in Fig. 9. Therefore, in view of the slotted ends of each of the heaters, in removing or replacing a heater, the screw 106 which engages in said slotted ends needs to be slackened back only. However, the screw 104 must be entirely removed, but being at the top of the device, as will be apparent from Fig. 1, this is readily effected, and, in order to facilitate the removal of the screw 104, the latter is provided with a long hexagon head to provide a suitable iinger grip. Once the screw 104 is entirely withdrawn, and the screw 106 is partially withdrawn, the heater may be readily removed through the opening 108 in the cover 48 without the necessity of removing the cover. If the heaters are not inherently suiiiciently rigid, strict interchangeability may be secured by mounting the heater on a carrier which may be of ceramic or other heat resisting material; moreover all the heaters may be mounted on one carrier, or the carriers of different phases mounted together to form one unit. In any event, the attaching means for the heaters, or carriers if used, as previously described, provide for positive location of the various heaters upon interchange or replacement thereof.

In view of the foregoing, it will be readily apparent that there is no direct mechanical connection, nor any electrical connection whatsoever, between the heaters and the adjacent bimetal strips 30. On removing only one screw, namely the screw 104, and on slackening or backing up another screw, namely the screw 106, a heater may be removed and may be replaced by another heater without disturbing any of the operating mechanism of the device or the associated bimetal strip.

While we have shown and described the preferred embodiments of our invention, it will be understood that various changes may be made in the idea or principles of the invention within the scope of the appended claims.

Having thus described our invention, what we claim and desire to secure by Letters Patent is:

l. In a protective device for electric circuits, operating mechanism for said device including a circuit controlling switch, a plurality of thermally responsive elements and means for operating said switch in response to the condition of said elements; heaters for said elements, respectively, energized by the currents in said circuits, respectively, and means for removably mounting said heaters in said device independently of said operating mechanism, whereby said heaters are replaceable without interference with said operating mechanism, said thermally responsive elements being flexible bimetal members, and said heaters each being mounted in spaced thermal relation with an associated bimetal member and independently thereof, said bimetal members each having a loop defined therein and each heater being mounted within the loop of its associated bimetal member.

2. In a protective device for electric circuits, operating mechanism for said device including a circuit controlling switch, a plurality of thermally responsive elements and means for operating said switch in response to the condition of said elements; heaters for said elements, respectively, energized by the currents in said circuits, respectively, and means for removably mounting said heaters in said device independently of said operating mechanism, whereby said heaters are replaceable without interference with said operating mechanism, said thermally responsive elements being flexible bimetal members, and said heaters each being mounted in spaced thermal relation with an associated bimetal member and independently thereof, said bimetal members each having a loop dened therein and each heater being mounted within the loop of its associated bimetal member, said mounting means including spaced terminal elements for each circuit and each heater having securing portions extending outwardly of its associated loop for removable securement to the associated terminal elements.

3. In a protective device for electric circuits, operating mechanism for said device including a circuit controlling switch, a plurality of thermally responsive eiernents and means for operating said switch in response to the condition of said elements; heaters for said elements, respectively, energized by the currents in said circuits, respectively, and means for removably mounting said heaters in said device independently of said operating mechanism, whereby said heaters are replaceable without interference with said operating mechanism, said thermally responsive elements being flexible bimetal members, and said heaters each being mounted in spaced thermal relation with an associated bimetal member and independently thereof, said bimetal members each having a loop dened therein and each heater being mounted within the loop of its associated bimetal member, said mounting means including spaced terminal elements for each circuit and each heater having securing portions extending outwardly of its associated loop for removable securement to the associated terminal elements, and securing members threadedly engageable in said terminal elements for releasably securing said heater portions thereto, respectively, one of said heater portions being peripherally interrupted, whereby said one heater portion can be disconnected from its associated terminal element without disengaging the associated securing member from said latter terminal element.

4. A protective device for electric circuits comprising a housing for said device, a plurality of chambers defined in said housing, operating mechanism in said housing responsive to unbalance in said circuits and including thermally responsive elements for said circuits, respectively, said elements being mounted in said chambers, respectively, and heaters for said elements disposed within said chambers, respectively, in spaced thermal relation therewith and being removably mounted in operative disposition outwardly of said chambers, and means for mounting said heaters externally of said housing, said means comprising spaced terminal elements for each circuit provided with portions disposed outwardly of said housing, said heaters interconnecting the associated terminal elements by releasable securement to said portions thereof, said device being further characterized in that the heaters are sheet metal members provided with secur- ,uy ing portions extending outwardly of said housing, and securing elements interconnecting associated terminal and heater portions, one of said portions in each heater being peripherally interrupted, whereby to facilitate the disconnection of said one heater portion from its associated terminal portion without removing the securing elcment from the latter.

5. A protective device for electric circuits comprising a housing for said device, a plurality of chambers dened in said housing, operating mechanism in said housing responsive to unbalance in said circuits and including thermally responsive elements tor said circuits, respectively, said elements being mounted in said chambers, respectively, and heaters for said elements disposed Within said chambers, respectively, in spaced thermal relation therewith and being removably mounted in operative disposition outwardly of said chambers, and means for mounting said heaters externally ot said housing, said means vcomprising spaced terminal elements for each circuit provided with portions disposed outwardly of said housing, said heaters interconnecting the associated terminal elements by releasable securement to said portions thereof, said device being further characterized in that the heaters are spirally wound elements provided with securing portions extending outwardly of said housing, and securing elements interconnecting associated terminal and heater portions, one ot said portions in each heater being 5.5- shaped, whereby to facilitate the disconnection of said one heater portion from its associated terminal portion without removing securing element from the latter.

6. A protective device for electric circuits comprising a housing .for said device, a plurality of chambers defined in said housing, operating mechanism in said housing responsive to unbalance in said circuits and including thermally responsive elements for said circuits, respectively, said elements being mounted in said chambers, respectiveiy, and heaters for said elements disposed within said chambers, respectiveiy, in spaced thermal relation therewith and being removably mounted in operative disposition outwardly of said chambers, and means for mounting said heaters externally of said housing, said means comprising spaced terminal elements for each circuit provided with portions disposed outwardly of said housing, said heaters interconnecting the associated terminal elements by releaseable securement to said portions thereof, said device being further characterized in that the heaters are spirally wound elements provided with securing portions extending outwardly of said housing and securing elements interconnecting associated terminal and heater portions, one of said portions in each heater being an open ended slot deined therein, whereby to facilitate the disconnection of said one heater portion from its associated terminal portion without removing the securing element from the latter.

7, A protective device for electric circuits comprising a housing for said device, a plurality of chambers defined in said housing, operating mechanism in said housing responsive to unbalance in said circuits and including a circuit controlling switch, a plurality of bimetal strips for said circuits, respectively, and means for operating said switch in response to the condition of said strips, said means including a pair of members mounted for relative movement, said members having slots defined therein, said strips being disposed in said chambers and having free end portions extending therefrom and through said slots for eiecting movement of said members upon ilexing of said strips respectively, and heaters for said strips, disposed within said chambers, respectively, in spaced thermal relation with said strips, said heaters extending from the respective chambers and being removably mounted outwardly of said chambers.

8. A protective device for electric circuits comprising a housing for said device, a plurality of chambers deued in said housing, operating mechanism in said housing responsive to unbalance in said circuits and including a circuit controlling switch, a plurality of bimetai strips tor said circuits, respectively, and means for operating said switch in response to the condition of said strips, said means inciuding a pair of members mounted for relative movement, said members having slots defined therein, said strips being disposed in said chambers and having tree end portions extending therefrom and through said slots for effecting movement of said members upon tlexing ot' said strips respectively, and heaters for said strips, disposed within said chambers, respectively, in spaced thermal relation with said strips, said heaters extending from the respective chambers and being removably mounted outwardly of said chambers, and a transparent window provided in said housing through which the tree ends of said bimetal strips are visible.

References Cited in the tile of this patent UNITED STATES PATENTS 1,910,494 OKeete May 23, 1933 2,'r99,477 Besag May 7, 1940 2,495,608 Schleicher Jan. 24, 1950 2,506,796 Krieger May 9, 1950 2,58l,882 Randall Ian. 8, 1952 2,584,673 Cole Feb. 5, 1952 FOREIGN PATENTS 482,822 Great Britain Apr. 4, 1938 553,l54 Great Britain May 10, 1943