CA2097251A1 - Actuator - Google Patents

Abstract

ABSTRACT
An actuator for use in operating switches such as air break switches of the type used on overhead power systems. The actuator is based on an over-centre mechanism.
Movement of an operating arm indirectly drives a drive arm via the over-centre mechanism with the energy of a resilient member being used to regulate the opening of a switch connected to the drive.

Description

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This invention relates to actuators.

In parlicular, bul nol exclusively, this invenlion r~lates to an actuator for use in operating an ùr break switch o~ e lype used on overhead power distribution ~ystem~, and also relates to methods of operaling air break switches.

Common types of air break switches used on power distribution systems lor isolalinEs seclions or lhe diskibulion system comprise electrical contacls which are connecled together or separated by means of an actualing mechani6m. In general lhere are lhree sets of contacts for the three phases of the di~tribution system and these are acluated in unison.
The contacts usually comprise fixed contact6 which may be a f~rket type contact, and a movable contact which may be in the ~orm of a blate pivoted about one end so that the other ent may be moved into and out of contact with the fixed contact. Alr break switches may be broadly clsssified into side swing types where lhe movable contact swing~
sideways in a horizontal plane, and vertical types where the movable contact swing~ in a vertical plane. There are al60 single phase isolator typ~ switch~ which are ~en~rally singlc unlls lilled lo each phase and operated ~ndependently of each olher by a hot stlck.

The common method o~ operalion of standard verlical lype threc phase alr break swltches is to u6e a handle positioned near the basc ~f the power pole ar,ld pivoted about a support flxet t~ the power pole so ~s to have a throw of approximately 180 degrees in a,vertical plane. The handlc is llnked to a shaft of the air break switch which i~ located al lhe top o~ lhe power pole, by either a metal lube or woodcn (treated hardwood) rod. By pulllng the handle down or pushing up throug,h 180 . VA.~, -- 2 -- . .
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degrees, the movable contact~ of the air break switch are t~rned thr~ugh a predetermined angle thereby respectively opening or closing the contacts.

With side swing type air break switches, a similar operating method i~
provided except that the operating handle is generally rotated about a vertical axis through a predetermined angle.

In the case of single phase type isolalors, these are ~nerally opl!ratcd by hooking the end of a hot slick (insulated rod~ into a ring connected to ~
movable contact and pullillg or pushing on the ring to open or closc the contacts respectively.

A prob1em wtth these methods of operating air break switches is the difficully in obtaining uniform and optimum speed opening and closin~
of the contacts due to operator variabillty and difficully Or access. In th~
case of the verticàl and side swing type three phase air brcak switch, the open/cluw operativn generally requires the operator to change hant posltions on the handle half way through the operation, while in the c~se of the single phase air break switch there is the difflculty of smoothly pulllng or pushing un the hot sliclc, usually while standing on a latder.

Consequcntly, air break switches are generally llmited in thelr appllcation ~o the sv~itching of unloaded or very lightly loaded muns, ror isulatiun purposes, since if operated under loat, severe arcing across the contacts may occur if the opening rale is not fast enough. There ls also the possibility of arc jump across lhe phases with consequent phase shorting if the contacls are not opened ~miformly. These limitation6 are a ~napr draw back with air break switches, sinoe il is often inconvenient 20972~
to deload a dislributlon sy~tem before openin~ the air break switch.
Hence an operalor may have to operate a standard air break switch under a light load using extreme care to ensure a rapid and smooth opening of the ct~n~acts so as lO minimise problems of arcing.
Allernatively, in si~uations where load breaking is un~void~ble, special equipment such as arc quenching devices may be li~led to control the arc that inevitably occurs as a result of non-optimtJm non-uniform speed opening, tllereby givin~ the air break switch the~capacity to disconnect a mains carrying a heavier current. I~owever arc quen~hing devices involve additional costs and problems due to arc erosion of the contacts still exist.

An alternative method of ensuring positive and rapid opening of the contacts is to use a pneurnatic or solenoid operated mechanism. Systems of this type however are expensive and are generally only economic~lly feasible when used in combination with remote control systcms, for enabllng air break switches ~o be operated from a remote location.

Other attempts to assisl lhe operator in obtaining a uniform and positivc openlng and closing of an air break switch include ~ spring b~lance arrangement whereby the weight of the actuating rod is balanced in one dlrectlon of operation. However this mcthod only reduces the operating load on the operator and does not ensure a fast ant uniform opening of the contact6, 50 the that the problem of arang is still present ..
It is an ob~ect o~ the present Invenlion to provide an actuator which addresses the above problems and difficulties or at the very least offers useful choice.

~urther objects and advantages of tlle present invention will now be discussed b~ way o~ example only in the followin~ descrip~ion. ~ :~

Accordin~ to one aspect of the present invention, there is provid~d an actuator comprising a frame assembly on which is mounted an operating means, a drive means and an overcentrc mechanism comprising a resilient member, the operating means and drive means being linked together indirectly by way of the overcentre mechanism in such a way thal movement of lhe operating means up to a centre point condilion of the overcentre mcchanism applies a load to the resilient member, and furlher movement past the centre point condition results in the load in the resilient member being applied to the drive means lhereby causin~ the drive means to move.

~urthermore, the present invention also relates to a method of operating an air break switch using tlle actuator as aforessid, which comprises the step of; moving the operating arm from a closed condition wherein the drive arm is holding an air break switch mechanism in a closed condition, to an open condition, whereby the drive arm operatcs under the urging of the resilient member lo cause the air break switch to open~ Thls movement may be achleved by manual operatlon of an arm of the operating means, or by operation of the electrically drlven actuator. Furthermore, when the second actuator is used, this may be controlled by a remote control system involving telephone or radio communication signals.

It may be seen from the above description, that an actuatc~r of the present invention when fitted ~o an clperating mc~hanisnt of an air br~ak switch, : .
provides a means of addressin~ the problems associated with ~ . " ~

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con-~entional types of clirectly opcrated a~r break swilches. This i~
because the switch mechanism is operated indirectly and independently by the energy of a loaded resilient member, so that by suitable design of the actuator components, and selection of thc resilient member it is possible to provide an actua~or which will produce uniform opening and closing of the contacts of the air break switch at a predetcrmined speed, independent of the manner of operating an operating means.
Fur~hermore, once ~he contacts o~ the air break switch have closet, thcy may be held in the closed condition by a force of the resilient mcmber.

~Iso, since the opera~ing means of the actuator is not directly linked to the drive means, forces re~ulting from rapid moven ent of the drive means due to unloading of the resilient member are not hlt by thc opcrator, thereby avoiding discomfort lo the operator, and obstruction to the operation of the trive means.

Tl~e actuator of the above description may be easily att~ched to a po~4er pole supporting an air break switch and connected to an operating device of the air break switch. Furthermore, by appropriate motlfication and deslgn, lt may be posslble to provide a lighl weight actuator according to ~he present Invcntion suitable for connection to, and oper~tion o~, a single phase type isolator~

In an cmbodiment of the present invenlion the fraJne assembly may consist of onc or more site plates provided with bearings for pivotal mounting of respective operating means and drive means. The side plate or plates may be prc~vided with mounting means for mounting on a pole or for conneclion to an air break switch mcchanisn~.

.... ... ........ . .....

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The operating means may comprise an operating arm fixedly attached to a pivot shaft whi~h is rotatably accommodated in one of the side platc bearings, and the drive means may comprise a drive arm fixedly atlached to another pivot shaft which is rota~ably accommodated in another of the side plate bearin~s.

In the case o~ lwo sidc plates, the bearing for the operating means may be provided on one of the side plates and Ihe bearing ror the d~ive means may be provided on the other side plale. The side plates may be connected logether by at~achment bolts, and held apart a predetermined distance with spacers so as to be subshnlially parallel to each other.

The overcentre mechanism may comprise a spring assembl~ with a helical compression spring forming the resilient member. The spring assembly rnay be connected at one end to the site p1ate and the other end may be linked to a pivot a~m which is pivotally mountet on the side plate. In the case of two side plates lhe connection of one end of the spring assembly may be to one of the side plate spacers, and the pivot arm may be pivotally mounled on both side plates.

The arrang~ment o~ the pivot arm and spring assembly may be such that pivotal movemcnt of the pivol arm aboul ils pivotal mounting rcsults ln the spring of the overcentre mechanism being loaded (compressed) up to a cerhin conditlon where an axis of the pivot arm aligns with an axis of the spring assembly. In this condition the spring is de~ormed to a maxlmum condition, and the condition is referred to as the centre point condition. Furlher pivotal movement o~ the pivol arm past this centre point conditlon results in the spring being unloaded. Alternatively, inslead of a compression sprin~, a tension spring may be used. In this 20972~
case pivotal movement of the pi~rot arm may cau~e the 5pring tO be tensioned instead of compressed up to the centre point condition.

Furthermore, a lea~ spring may be used as Ihe resilient me~ns with one end fixedly attachcd to the frame assembly and the pivot arm slitingly engaged with another end portion, so that the spring may be loaded with pivotal movement of the pivot arm up to the centre point condition where the spring is deformed by a maximum amount, ~fter whi~h the spring may be unloaded with further pivolal movement of the pivot arm past the centre point condition. Alternalively any othcr suihble arrangement of spring device and pi~,rot arm may be possible.

Althougl~ in the above the resilient means has been described as variou~
~orms of spring devices, any oll er form of resilient means or any combination of resilient means may be possible depending on the application and operating conditions. For example a means utilizing a bellows or cylinder filled with a compressible fluid may be suitabk.

The pivot arm of the above embodimenl m~y be linked to the oper~tinE~
mcans by a link arm havin~ one end portion pivotally connectet to the plvc)t arm, and another end portion pivohlly connected to an operating arm of the operating means. The plvotal connections of the link arm to the pivot arm and the operatlng arm may comprise a pin on e~ch of the <~perating arm and the link arm which flts in a hole or slot on the link ann. Thc length and location of the slol or slots in the link arm may be such that movement of the operating arm resulls in a turnin~ force being applied to tlle pivot arm up the centre point condition, after which the pivot arm is fre~ to move a predetermined ~mount pa6t the centre point condition wilhout further movement of the oper~ting arm.

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Similarly the pivot arm may be linked to the drivc means by another link arm having onc end pivotally connected to ~he pi~?ot arm and an~ther end pivotally connected to a drive arm of ~d~e drivc means, with pins engaged in a hole or slot in a similar manner to the conncction of the operating arm and the pivot arm. Similarly the lenglh and iocation of the slot or slots in the link arm may be such that the the pivot arm may be turned abouL its pivotal mounting up until ~he centre point condition wilhout movcment of the drive arm, after which the pivot arm is able to exert a Çorce on thc drive arn~ so thal thc drive arm moves together with the pivot arm.

With thc actua~or as described above it may be preferable from the point of view of compactness of design and inlerchangability of components to have the mounting bearings for the operaling arm and the drive arm arranged in line on opposite side plates. In this configuration the first link means may comprise a bushing welded lo or cast integrally with a pivot arm and rotatably fitted over the pivot shaft of the operating arm so as to engage with a pin passing through and substantially perpendicular to a cenlral longitudlnal axis of the pivot shaft ant extendlng out e~ther side thereof. lllis pin may be a roll pin which i5 resnovablc from lhe shaft for assembly and disassembly purposes. The bushin~ may be engaged with the pin by means of recesse~ formed on either side of its end hce which accommodate the ends of the pin and allow a predetermined amount of ro~tation of lhe bushing abollt the ~xis of the pivot shaft. With a first link means of this construction, the pivot arm may be pivotally mounted on ihe pivot shaft ant tumed by turning of the opcrating arm up to the centre point condi~ion, after whicl~ it is :

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free to turn a predetermined amount past tlle centre pnint condition without furlher turning of the operating arm.

A ~imilar arrangemenL of components may be provided for the dri-ve arm and second link means. In this case the drive arm, pivo~ shaft, roll pin, bushing ànd pivot arm^may be made identical to or mirror images of the above mentioned components. Alternatively the pivot arm may be welded to or cast in~egrally with the bushing oÇ the first link means and said bushing may have similar recesses fonned in either side of its oppositc ends. The pivot shaft of the drive arnt may be rotatably mounted in Lhe mountin~ bearing opposite the operating arm mounting bearing on the opposite plate. The pivot arm may be rotatabl~!
mounted thereon in a similar fashion to lhe pivot arm mount~d on the pivot shaft of the operating arm. An opposite end portion of the pivot arm may be connectcd to an identical opposite end portion of the operating arm pivol arm by a link pin which also serves as a means for connection of the pivot arms to an end of a spring assembly disposet between the side plates and supporl:ed at an opposite end by one of the above mentioned spaccrs.

The above mentioned embodim~nts of the acLuator of thc present invention may be mounted on a power pole of an electrical distribution sy~tem having an air break switch. An operating rod for the air brcak swltch may be connected to the operating arm, and a drive rod may be connected between the drive arm and t~le air break switch operating mechanism. The actuator may be preferably mounted on the power pole dose to the air break switch so that the weighl and length of the drive arm is minimized enabling a more positive action during switching of the air brcak swi~ch~

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Furthcrmore the actuator may be mounted so that pivot ~hafts of both the operating arm and drive arm are arran~ed substantially pe~pendicular to the longitudinal ~xis of the power pole in any orientation from tan~3ential to a peripheral surface or the power pole to normal to said peripheral surface. The orientation of other component~
such a: ~he re~ilient member and pivot arms is also optional. Also by suitable construction of the connecting means ie: by suitable o}ientation of the pins passing Lllrough lhe operating arm and drive arm pivot sh~ft~ the operating arm and drive arm may be arranged so as to lie in subslan~ially tlle ~anl~ ori~ntations in the closed and open conditions or to lie at different orientations to each other to sui~ mounting conditions and enhance ergonomic operation ol the actuator and air break switch.

The actuator may also be mounted so that the pivoL shafts of both ~he operating arm and drive arm are arranged subslanlially parallel to the longitudinal axis of the power polc. This configuration may be particularly suitable for side swing ~ype air break switches. In this case the operating arm m~y bc connected lo a crank mechanlsm so th~t rotary actlon of the crank shaft may be transmitted lo lhe pivol sh~ft of the operatin~ arm. AlLerna~ively a shaft extending lo the base of the pole may be connected as an ex~ension of the pivot sha~l and a crank attached to the base end thereof.

Alternalively ~he actuator may be allached directly to a single phase isolator type air break switch with the drive arm eilher connected ~o the contact opera~ing mechanism of forming a part of the mechanism. The operatinl3 arm may be provided with a suitable hot ~tick connection ~97~1 means such as an aperture so that the operating arm may be turned by pulling or pushing on a hot stick.

A biasing means may also be provided for biasing ~he movemenl of the operating arm or the drive arm in one direction. In ~his way, the force applied by the actuator to open the air break switch may be made different to the force applied in closing the air break switch. Thus a more optimum opcning and ~losing operation of the air break switch may be possible. The biasing means may comprise for examp1e a spring member atlached between tlle drive arm and the aclua~ing rod to lhe air break switcl1. I~y suitable location of attachment pc~ints, the loading produced by the spring may assist movement of the drive arm in one direction and res~rict movement o~ lhe drive arm in an opposite direction. Alternatively, a c021 ~prin~ may be ~itled~ for example, concen~ric with a piYot shaft of the drive arm, and connecled belween lhe drive arm and the body of the actuator so as lo assisl movement of the drive arm in one direction and reslricl movement in the other dlrection, Of course any other suitable means whicl achieves the e~fec~
of biasing the 1oading on lhe drive arm or ~pcrating arm may be pos6ible, Opcralion of lhe ac~ualors o~ lhe above embodiments may also be possible by means of an electric motor connecled Ihroug}~ a reduction gear to Ihe plvot shaft of an operatlng means, or by a solenoid linked to the operatiny~ arm, lhereby offering the facility for remote control and operation. In the case of an electric motor, this may be incorporated in a linear actuator device connected between the operating arm and a m~unl:ing on the power po1e.

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Aspects of the present invention will now be discussed by way of example only with reference to the accompanying drawings in which:-Fig~re la: is a plan view of a possible embodiment of an actuator of thepresent inventioll in a closed condition, and I;igure lb: is a side view of a seclion on A-A of Fig. la, and Flgure 2a: is a plan view o f pivot arms and a bushirlg o~ the actuator, and Figure 2b: is a side view of the pivot arms and bushing of Fig. 2a, and Figure 3a: is a plan view of the actualor of Fi~s la, lb in a closed condltion, and Figure 3b: is a side view of a section on B B of Fig. 3a Flgure 4: is a schematic view showing a possible biasing spring arrangement according lo an embodiment of the present invcntion.

Flgure 5: is a schematic view of a remote control installation accorting lo an embodiment of the present invention With respect to Figs la, lb there is provided an actu~tor ~ener~lly indicaled by arrow I according to the present invention comprising left and ri~ht side plates Ia, lb of a generally rectangular shape in side view wlth either integral or separate base plates for mountin~ on ~ pol~ along a base ~Ide. The side plates la, lb are connected together by thrce assembly bolts "a", "b", ~cn and held in parallel relalion to each other by spacers fitted over t2~e assembly bolts between inner faces of the sid¢
plales la, Ib. Tl~e side plales la, lb act as a support me~ns for pivot bearings 2a, 2b which are fixedly connected to ou~er sides of the 20972~

respec~ive side plates la, Ib with axes in line and substantially perpendicular to respective planes of tlle side plates la, lb. Apertures are formed in the respective side plates 1~, lb having diameters slightly larger than internal diameters of the bearings 2a, 2b so as to allow respective pivot shafts 3a, 3b to be rotatably fiued in the respective bearings ~a, 2b and extend out Ol1 either side of the bearings 2a, 2b.

An operating ~rm 4, is fixedly attaclled to an outer end of the left pivot shafl 3a and a drive arm 5 is fixedly attacl~ed lo an outer end of the right pivot shaft 3b in a like manner to thc left pivol shaft 3a attachment. The op~rating arm ~ and the drive arm S are lhus able to pivot about the bearings 2a, 2b throu~h an angle of approximately 100 degrees defined by the location of assembly bolts "a" and "b", which act as limit stops.

As shown more clearly in FiE~s. 2a, ~b, a bush 7 on which are fixedly mounted left and ri~ht pivot arms 6a, 6b is slidably mounted on inner ends of the pivot shafts 3a, 3b respeclively so as to ~e rotatable thereaboul. Link pin holes 8a, 8b are drilled in lhe ends of the pivot arms 6a, 6b opposite to the bush 7 hr taking the load of a sprin~ to be m~ntioncd lat~r. Outer end faces 9a, 9b of the bush 7 are machined so as to form recesses 10a, 10b on either side of a cenlral axiS of the bus~ 7.
The recesses 10a, 10b are iden~ical in shape and have bottom hces substantially parallel to planes of the respective arms 6a, 6b with end walls substantially perpendicular thereto, and are for accommodating roll pins 11a, 11b (see ~igs. la, lb? fitted to the pivol shafts 3a, 3b, passingthrough central axes thereof and substantially perycndicular ~hereto at a predetermlned angle in relation to the axis of the operating arm 4 or the drive arm S respectivcly.

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A spring assembly ~enerally indicated by arrow 12 is provided belween thc end of the pivt)t arms 6a, 6b and the assembly bolt "c" of the side plales la, lb. The spring assembly 12 comprises a tension plate 13 having an elongated hole 14 at one end thereof and a load pin hole 15 and link pin holc 16 at the other end thereof. The elongaLed hole 14 is of such a size as to slidably accommodate a spacer 17a on the assembly bolt "c". A
spring 17 Hlted ~ver the tension plate 13 is held under nominal compression between Ihe spacer 17a and a load pin 18 fitted in the load pir~ hole 15.

Thc spring assembly 12 is held in position in Ihe actuator 1 by means of the attachment bolt "c" passing throu~h lhe tube spacer 17a ~nd securely clamping the two side plates la, lb together, and a link pin 16a passing through the link pin holes 8a, 8b on the ends of the pivot arms 6a, 6b respectively. Wlth the spring assembly 12 fitted, lhe pivot arms 6a, 6b are positioned as sl~own in Fig,.lb with upper surfaces in contact with a spacer fitted over the attachment bolt "a"~ Rotation of the pivot anns 6a, 6b aboul Lheir respective pivot shafts 3a, 3b in a clockwise direc~ion is prevenled by ~he altachment bolt "a", while rotation in an anti-clockwise direction is resisted by the compresslve force of thc sprin~ 17.

An acIualor constructed as above m~y be moun~et on a power pole to which a manually opéra~ed air brake swi~ch is Qlted, at an intermediate position between the air brake switch and a manual operating lever.
Prcferably the nlowltings posilion would be close to the air brake switch so lhaI an acluatin~ rod connecting the actuator drive arm 5 by a holc 5a o the air brake swilch may be kept short. This would reduce the weight to be moved by the actuator and al~o minimise problcms related to bending and distortion inherent wilh a long actuating rod. The operating arm 4 may be connecLed by means of a hole 4a to another rod which is linked lo the operating lever at the bottom of the pole By pulling on the opcrating lever lhe operating arm 4 may be turncd about the left pivot bearing 2a and in so doing the pin 11~ bears against the edge of the recess 10a In the bush 7 so that the bush 7 ant the left and right pivot arms 6a, 6b turn aboul their respective bearings 2a, 2b Due to thc ends of the pivot arms 6a,.6b being connectet to the spring assembly 12 by means of the link pin ~6a, the spring 17 of the sprinE~
assembly 12 is comprcssed During the inltlal turning of the operatin~ arm 4 tl e pivot arrns 6a, 6b turn about respective pivot bearings 2a, 2b and t}~e spring 17 is compressed until a point is reached where the longitudinal axis of the ~prlng assembly 12 coincides with a line through th~ centre of the link pin 16a and lhe piYot shafts 3a, 3b This condilion is referred to as the centre point condition ant In this condition ~he spring 17 is fully compresset Up until this condition the lurning of the bush 7 has not been Iransmitted to the right pivot shaft 3b since lhe pin 11b has been free ~o move In the recess lOb in lh~ bush 7 Howev~r thc timensions of the recess 10b ~re such that any ~urther turning o~ lhe bush 7 results in the perpendlcular wall of the recess 10b conlacling the pin 11b fitted to the ri~ht pivot shaft 3b so that the ri~hl pivot shaft 3b turns toE ether with the bush 7 thereby causing the drive arm 5 lo swlng downward Furthermore once the before mentioned in line condition of the spring assembly 12 and pivot anns 6a, 6b has been reached, the spring 17 is in its fu~ly loaded state, and any further turning of the operating arm 4 results in the in line condition passing to over centre so that the spring 17 . -- 16 --begins to extend and drive the drive arm 5 From this condition on, the dri~re arm 5 is turned by a ~orce rrom ~he spring 17 which can be sel ~o a predelermined value by suitable selection Or Ille spring, and the bush 7 is free lo lurn about the pivot shaft 3a withou~ causing further rolation c)Ç
the pivot shaft 3a, due to the dimension of the recess 10a wllicll allows lhe pin 11a lo move therein relati~re to the recess 10a.

If hvwever the ~ilualion arises wherein lhe sprirlg force is not sufficient to operate the dri~re arm 5, it is possible to continue to apply a turning force to the pivot arms 6a, 6b and bush 7 by continuing to turn the operaling arm 4 therel)y continuin~ to transmil a turning force through lhe lell pin 11a to the bush 7~ When evenlually lhe ~orce to o~erate the drive arm S decreases, such as when any welding or sticking of tl e contacls ol lhe air break switch has been broken, the drive arm S then becomes frce to move rapidly under tl-e driving force ol lhe spring 17 lhereby insuring that the air break switch is opened in a su~ficiently short time to prevent problems such as arcing.

Although in the above description the bush 7 engages with the right pi~rol shaft 3b at thf~ centre point condition, il is possible by suitaible orienlalion ol lhe pinC 11a, 11b to have ~he bush 7 eng~;e with the ri~ht plvot shaft 3a al some predelermined posilion b~fore or after the centre point condition.

Ihe closing c)f an i~ir brake switch tv which the actuator I is connecled is achieved by an o~?eratlon in reverse of the above mentioned operation.
rigures 3a and 3b depict the actuator 1 in an open condition with both the operatin~ arm 4 and the drive arm 5 turned down, the spring asscmbly 12 deflected towards the base side of the side plales la, lb, and ~972~

~he pivol arm 6b resling ag,ainst the attachment bolt "b". To ciose the air break switch, the operating arm 4 is pushed upwards by means of an operating handle (not shown) so that the pin 11a bears against an end of tlle recess 10a thereby causing the bush 7 and pi~rot arms 6a, 6b to turn to~elher with the pivot shaft 3a. The turning of lhe pivot arms 6a, 6b resulls jn compression of the spring 17 as the axes of lhe pivot arms 6a, 6b and the spring assembl~ 12 move into alignment.

During lhis ~ime the bush 7 is free ~o lurn relalive ~o lhe right pivot . shaft 31) and the pin 11b moves in the recess 10b. Al llle poinl where the axis of the piv-)l arms 6a, 6b line up with the axis of the spring assembly 12, the right pin 11b comes into contact with the end wall of the recess 10b so that further rvtation of the pivot arms 6a, 6b results in rola~ion of the right pivot shaft 3b. In this condltion the spxing force is such lhal i can lurn the right pivot shaft 3b and move the drive arm 5, thereby transmittlng a force to the air break switch (not shown) and closing the contacts of the air break switch.

Since the closing of the air brake switch i~ achi~ved solely by the tr~nsmi~6ion of a predelermined force from thc spring 17, a unilorm closing rate cdn be obtalned wlth suilable selec~ion of the spring and de~;ign of the linkage mechanisms. While the drive arm S is beinE~
rotated under the action of the spring force, the left pivot arm 6a is able to turn on thc pivot shaft 3a and the pin 11a moves relative to the bush 7 in6ide the recess 10a so ~hat the action of the spring force is not transmitted to .tl~e operating arm 4, and hence is not felt by the op~rator, th~reby avoiding any discomfort, and obstruction to movement of the drive arm 5.

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20972~1 Although in Lhe presenl embodimenL a single compression sprin~3 17 has been used as a resilient member for driving the me~l1anism, it may be possible to use more Ihan one compression spring arranged either side by side or one inside the other to obtain different sprin~ charac~eristics to suil the application, ~n the case of one spring being arranged inside llle other, the springs would preferably be wound in opposite directions to avoid scctions bccoming caught between each olher, Als~, depcnding on the required operating forces, and configura~ion and size limitations of the actuator it may be more suitable to use a tension spring or leaf sprin~ in place of lhe compression spring, This may be the case where lhe aclualor is lo be used wilh single phase isolator type switches where il is envisioned ~hat a compacl actuator may be constructed in~egral with the switch mechanism.

~urthermore, although in the present embodiment the left and righl pivot shafts 3a, 3b have been mounted so as to be in line with each other, tho m~chanism is not limited to tl-is arrangemenl. For example, it may be posslble to have th~ pivot arm 6b mounted on a separat~ bushing on the pivot sllaft 3b. Furthermore it may be posslble lo have lhe pivot shaft 3b pivotally supportcd at some other location, and the pivot arm 6b col~nected by a suihble linkage to the link pin 16a.

Fi~ure 4 S]IOWS a schematic view of a possible biasing spring arrangemenl according lo an embodimcnt of the present invention. In thls figure component previously described are idenlified with the sam¢
numeral and description is omitted for brevily. The actuator 1 is shown w~th ~he drive arm 5 in an upward position. The drive arm 5 differs from the previously described drive arm 5 in that the end of the drive 2 0 9 7 2 5 ~
arm 5 is elongated past the hole 5a to provide a connection point 20 ~or a biasing spring 21. Another connecLion poinl 22 is also provided on the driv~ .lrn~ S inw.lrd of the hole 5a. The bias spring 21 is connected by an attachment 23 to an actuating rod 35 which is connected bctween the hole Sa of the drive arm 5 and standard air break switch mounled on top of a power pole to which the actuator 1 is mountet (not shown in the fi~ure). With this arrangement upward movemenl of the drive arm S
(clnFkwise in the figure) is assisted by the tension ~orce in lhe spring 21 so tllat the closing force on the air break switch may be increased.
Furthermore, with downward movement of the drive arm 5 (anti-clockwise in lhe fi~ure~, this movement is reslricled by the increasing tension ln the spring 21 so that the opening force applied lo the air break switch is reduced. In this way, the opening and closing forces applied to the air break switch may be varied to enable optimum condilions. The connection point of thc spring 21 lo the drive arm 5 may be changed from the poinl 20 to the point 22. In tllis case lhe biasing produced by the spring 21 k in the oppositc direction. Hence, an increased opening force on ~he air break switcll may be achieved as required.

Flgurc S shows a schcmatlc view of a rcmole control installation accordin~ to an embodimenl of the present invention. In thls figure components previously described are idenli~ied with thc same numeral and description is omitted for brevily. l~e actualor 1 is mounted on a power pole 25 In a vertical orientatlon such that pivot shafts of both Ille operating arm 4 and drive arm S are arranged subslantially perpendicular to the longitudinal axis of ~he power pole, and subs~anlially langenlial lo a peripheral surface thereof. The oper~ting arm 4 is connecled lo an operatin~ end of an eleclrically driven actua~or .. . ... . . _ . . ....... .

20972~

30. The lower moun~ end of the actuator 3û is connected to an 1-pper end of an operating rod 31 which is mounted at its lower end on a slandard air break switch crank mechanism generally indicated by arrow 32. The crank mechanism 32 comprises a manual operating handle 33 which may be swun~ upwards or downwards aboul a pivot mounting and locked in either an up or down position. Tllc drive arm 5 of the aclualor 1 is connected by an actuating rod 35 to a standard air break switch moun~ed on ~op o~ lhe pole 25. With such ~n ~rrangemenl, the air break switch may be operated manually by pulling up or down on the handle 33 to cause the actuator 1 to operate as dcscribed beforehand.
Allerna~ively, the handle 33 may be locked in the up or down position, and ~he actuator 1 may be operated by supplylng an eleclrical current to the llnear aclualor 30 lo cause il lo either exlend or relract. The linear acluator 30 ls controlled by means of a control box 36. The control box 36 incorporates a re-chargable battery, and a switching dcvice wh{ch may be operated by radio frequency transmission received by an aerial 37. The ballery supply is kept charged by a 601ar panel 38 mounted on a side of the control box 36. Limit switches 39 are mounted on the actuator 1 lo swilch the lincar actuator 30 off at predetermined positions determined by l~e op~rating r~nge of the actu~tor 1. The control box 36 incorporates electrical circuitry so that depending upon the signal received by the aerial, the actuator may be driven in either direction to cause the air break switch to be opened or closed as required.

Wlth thls embodimen~, the air break switch on power distribution systems may be operaled remotely by transmillin~ the appropriate signal to the conlrol system. Of course, instead of a radio transmission system 20972~

the control box may be connected ~o a telephone link so that control may be effected by appropriate telephone signals.

We believe the advantag~s ~f our invention to be as follows, however itshould be appreciatcd that all such advantages may not be realised on all embodiments of the invenlion and the following list is given by Wly of example only as being indicative of potential advantagcs of the present inven~ion. Fur~hermore, it is not intended thal lhe advanlages of the presenl invenlion be restricted to those of the lisls which ~ollows~

. Positive operaLion Or an air break switch is possiblc at an optimum contact breakin8 speed (at least 7 ft per second).

2. Consislenl unlform operation independenl of operator variablcs.

3. Weld breaking of switch contacb by manual operation is possible in lhe vicinity of the overcenlre (cenlre point) condition.

4. The air brake switch may be held closed by a nominal compression force by the resilient member.

S. Iluman error in switch operation is elimjnatcd in both the opening and closin~ op¢rations.
6. Unirorm operation resulls in reduoed switch contact darnage and hence less maintcnancc.

7. Uni~orm operation enables increased load current breaklng ~:
capabilily (most switcl~es are never normally opened at their ratet current due to the possibility of non-optimum operation).

2 0 9 7 2 ~

8. Operalion aL hi~her currents is possible due to fast uniÇorm and positive action.

9. Can be easily fitted to existing air break switches using opcrating rods with minimum modification.
10. Installation method is standard and different switches and ratings can be accommodated by suitable selection of the sprin~.
I~urihermore a biasin~ spring may be fitted lo bias operation in tlle open or close direction.

~1. The actuator is designed for long life with no maintenance.

12. The acluator may be adapted or remote conlrol operalion.

13. llle actuator may be easily mod)fied and reduced in size for use on single phnse isol~lors wilh a hot stick operation m~ans.

14. The actuator may be adapted for other types of manually operated switches.

15. The design enables v~riation in orientation of the operating handlc to given enhanced ergonomic opcration.

Aspects of the present inven~ion have been described by way of example only and it should be aypreciated that modifications and additions may be made ther~to without departin~ from the scope thereof as described in the appcndcd clain~s.

Claims (6)

1. An actuator comprising a frame on which is mounted an operating arm, a drive arm and an overcentre mechanism including a resilient member, the operating arm and the drive arm being linked together indirectly by way of the overcentre mechanism such that movement of the operating arm up to a centre point condition of the overcentre mechanism applies a load to the resilient member, and further movement past the centre point condition results on the load in the resilient member being applied to the drive arm thereby causing the drive arm to move.

2. An actuator according to claim 1, wherein the overcentre mechanism comprises a pair of axially aligned bearings mounted with respect to the frame a split shaft supported by said bearings, a bush mounted on the split shaft and pivot arm extending from said bush mounted on the split shaft and being connected to said resilient member, free ends of said split shaft being connected to the operating and drive arms, the arrangement being such that pivotal movement of the pivot arms in one direction results in loading of the resilient member up to the centre point condition and continued movement past the centre point condition results in unloading of the resilient member, the operating arm being arranged so as to be engageable with the pivot arm during movement up to the centre point condition and the drive arm being arranged so as lo be engageable with the pivot arm during movement from the centre point condition.

3. An actuator according to claim 2, wherein the bush is provided with recesses on end faces thereof and each split shaft is provided with a contacting pin, the arrangement being such that rotation of the operating arm or it will cause contact to occur between the contacting pins and adjacent edges of the recesses at predetermined times resulting in movement of the bush and pivot arm against or with the bias of the resilient member.

4. An actuator according to claims 1, wherein the resilient member is a spring.

5. An actuator according to claim 1, wherein said drive arm or the operating arm includes a biasing element whereby movement of said drive arms or operating arm may be resiliently restricted or assisted in one direction.

6. A method of opening an air-break switch comprising the steps of:

(i) applying a pulling force on an operating arm connected to an over centre actuator so that a resilient member of said actuator is progressively loaded and a mounting element, of said resilient member is moved towards a centre condition with increased loading of said resilient member, and (ii) continuing to apply said pulling force on said operating arm so that said mounting element moves past said centre condition, and (iii) allowing the force of said resilient member to act on a lever connected to said air-break switch to open the contacts of said switch.