US2662137A

US2662137A - Transformer protective switch

Info

Publication number: US2662137A
Application number: US271765A
Authority: US
Inventors: Jr Sidney R Smith
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1952-02-15
Filing date: 1952-02-15
Publication date: 1953-12-08
Anticipated expiration: 1970-12-08
Also published as: GB760107A

Description

Dec. 8, 1953 s. R. SMITH, JR

TRANSFORMER PROTECTIVE SWITCH Filed Feb. l5, 1952 Inventor Sidneg R. Smith HIS Atto-Teg Fi g4.

Patented Dec. 8, 1953 .TaANsFoRMEa PROTECTIVE sWIToH Sidney R. Smith, Jr., Pittseld, Mass., assignor to General Electric Company, a corporation of New York Application February 15, 1952, Serial No. 271,765

2 Claims.

This invention relates to a protective device for electrical apparatus having high voltage and low voltage windings, such as a transformer, and more particularly to means for interrupting the current flowing through the windings upon the occurrence of a predetermined condition of load on the transformer.

Broadly speaking, various arrangements have been provided in the past to accomplish this purpose. For example, a current responsive means such as a bimetallic element has been series connected in the secondary circuit to serve as an actuating means to separate a pair of interrupting contacts series connected in the primary circuit. In some cases, the current responsive actuating means as well as the interrupting contacts has also been series connected in the primary circuit. However, there have been certain defects or objections to all such arrangements known to applicant. Inasmuch as the actuating energy of the bimetallic elements, for example, usually has been transmitted more or less directly from the bimetallic element to movable interrupting contacts and since the movement of a bimetallic element is relatively limited, the movement or separation of the interrupting contacts has likewise been limited or has been smaller than desirable to interrupt high voltage currents. Moreover, the amount of energy available from bimetals is relatively small and is not suflicient to actuate simple mechanical contacts in a reclosing manner with suflicient travel of the contacts to repeatedly interrupt the short circuit current of the transformer. Furthermore, in the event of permanent faults in the secondary circuit, the v elements therein continued to open and close the interrupting switch in the primary an indefinite number of times until such time as the fault was removed from the system. Such continual action,

of course, resulted in a relatively short life of the L tively fragile and, since it must be produced by specialists in the electronics eld, is rather costly. For the same reason, the mechanical means usually employed to interconnect the actuating element in the secondary with the interrupting .switch in the primary, such as a snap acting (Cl. 20o-116) over-center togg1e, is relatively costly since it is very fussy to make and assemble, and must be intimately tied in with the calibration of the switch. Moreover, the trend in the power dis- -tribution field is to larger transformer sizes, which imposes a heavier interrupting duty than such a vacuum type switch will handle.

It is therefore an object of this invention to provide a new and improved circuit interrupting means.

It is also an object of this invention to provide an improved protective arrangement for a transformer in connection with which the operation of an interrupting switch in the primary circuit is controlled by a thermal means responsive to current in the secondary circuit, but is directly and independently actuated by a separate drive means.

It is a further object of this invention to provide an interrupting switch of the reclosing type, which will lock open following a predetermined number of openings and closings caused by a fault condition in the secondary circuit.

It is also an object of this invention to provide a reclosing type protective switch for a transformer, together with a combination indicating and resetting means to indicate, outside of the transformer, whether the switch is opened or closed and also permit resetting of thD switch from the outside of the transformer.

The invention will be better understood from the following description when taken with the accompanying drawing, and the scope of the invention will be pointed out in the appended .claims In the drawing, Fig. 1 is a side elevation view partly'in section of a transformer, generally showing the protective switch as positioned in relation to the windings therein; Fig. 2 is an enlarged perspective view of the entire switch with the exception of the main support base thereof and a cover or enclosure therefor; Fig, 3 is an end elevation view of the right-hand portion of the device as illustrated in Fig". 2; Fig. Li shows the combination resetting and indicator arm and the indicating dial therefor as viewed from the exterior of the transformer, and Fig. 5 is a schematic diagram illustrating the relationship of the switch to the transformer windings and circuits therein.l

Referring now to Fig. 1, there is illustrated an dielectric I3, such as oil or a halogena-ted hydro-` carbon. @Immersed within the insulating dielectric are the transformer core and windings generally designated by the numeral I4.

The low voltage or secondary winding of transformer IU is provided with a mid-tap so that three secondary terminal leads, I5, I6 and I1 5 (see Fig. are provided, I6 forming the midtap and being usually grounded. The transformer casingk Il is `provided With'a .cover I8 which supports a high voltage bushing I9. Preferably mounted within high voltage bushing I9 y10 is a suitable protective device such as a bushing fuse 20, only a portion of which is yshown.; Bushing fuse provides protection to a distribution line 2| to which the high; voltage winding may be connected as shown in-Fig.5,-and insures `15 'i continuity of service as far as the distribution line is concerned by disconnectingthe Itrans-,- former in the vent of an internal fault.

The circuit interrupting switch proper ofthe invention, best shown in Figs. 2 and 3, comprises 20 a lstationary contact- `22 .electrically connected 'to the transformer primary winding 23 as shown in.` Fig. 5 and a relatively .movable switch'armr24 `of conducting materialf. electricallyl connected i toy ground. Contact 22 is mountedon asupport base25I 25 of insulating material; shown onlyin fpart in Fig. 2 in the interest. of simplicity.. Support base 25 `is fixed inrany suitable manner vto 'theutransformercore I4 `so that aHtheelements of the device are immersed in the liquid die1ec-tricas30 illustrated. in Fig.Y 1. Switch arm` 241,r having a contact end26engageable withfixed contact 22 a and anielongated-slot l21. adjacent-'the opposite end thereof, is pivotally-mounted intermediates the ends on a shaft 2B solasto `bevfreely rotatable 35 with respectthereto.'V Shaft :28 `is rotatably mounted in shaft supports 2I-and130yivhich`may be an integral part of or fixedly mounted on support base .1251." Switch arm 24pm-,electrically connected to a terminal 3| meuntedonl support base 40 25 by a conductor 32 provided with sufficient slack to permit` free movement ofswitcharrnf24r- The l terminal 3I= and thus the-switchrarm-is invturn electrically connected'to ground as )by a vconductor 33 grounded toithettransformer casing` at 34,?r 45 Fig. l1.

Although switch armA 24' iswcontrolled Ajor ,rene dered operative only in response `to a faultvconditionin the.secondarycircuitzor inresponse ,to the temperature ofthefliquid dielectric I3 'in a.. manner which will bedescribed hereinafter, contacts 26 and 422'are positively :and directlywengaged andfdisengagedby an independentdrivemeansl comprising adrivinggshaftf35 rotatably mounted in a support 36in turnnxedly mounted on support base 25,:eand. a drivenshaft'31 also rortatably mounted 4in support-36, .support AStand an intermediate supportfiirlwhichr Ymaybe fan'in- Y tegral part of or xedlymounted on support plate" or base '25m Aftorsion or coiled spring 39-With 60 one end fixed to shaft35.and `the opposite end thereof xed to a pin Illle fixedlymountedfin the upwardly extending arms-of=support 361serves as an energy source, when woundvlrelatively tight, to drives-haft 35' ina counterclockwise direction 65 as viewed in Fig. `2. f As illustrated,` driving shaft 35 extends to the exteriorv of `the transformer casing through a stuffngbox,-not shown, or any other suitable means to prevent leakage ofthe dielectric liquid I3`and is provided with-a com- 70 bination resettingand-'indicator arm 4I flxedly mounted on the exterior-end' thereof.' Shaft'35ll also extends throughfan-opening in anindicator dial 42 mounted on the outer surface-ofthe cas-f` ing II. Driven-shaftfBlis driven-in=ac1ockwise= 75 direction by driving shaft 35 at a higher speed than shaft 35 by a pair of engageable spur gears 43 and 44 respectively mounted on and fixed or keyed to

shafts

35 and 31. A drive escapement disk 45 having a tooth 46 in the periphery thereof is keyed or otherwise suitably fixed to driven shaft 31 at the end thereof opposite to spur gear 44.v Disk 45 is provided with aswitch arm drive or crank pin 41 which projects laterally from a face of the disk and extends through slot 21 in switch arm 24 as illustrated. Crank pin 41 has a diameter slightly less than the width of slot opening 21 so that vit is freely slidable therein and will cause. oscillation of switch arm 24 to alternately-disengage, then engage, etc.

contacts

22 and 25 as disk 45 is rotated clockwise by spring 39.,.as Willbemore clearly understood by inspection ofA Fig. 3.

However,-as previously pointed out, the rotation of the switch drive means including disk 45 and' `pin 41v is lcontrolled by zacurrent responsive means in the secondary circuit of the transformer@` and comprises ay pair -of bimetallic elements 46.

and49 electrically connected in series in secondaryl terminal leads I5=.andI1 respectively as illustrated in-Fig.,5. Each bimetallic element is-,f fixedly mounted to support base 25 at one end of I the element, `which endV is electrically `connected by a conductor I5'.or I1` to one yend ofthe second-- ary winding 5l),` for example, while the opposite end of each:bimetallicaelementis freely-movable andr electrically connected `lby a conductor vto a terminal which inturnisconnected by a leadito a f wall bushing terminal.` lor example; conductor I5 having sufficient slacksoas not to impair the movement of the free endof bimetallic element 48 i electrically connects this `end of the element with a terminal 5 I; whichiinturn is connected by conductor I5 to secondary wallbushingor terminal 52.1 The free fend cfleach bimetallc element carriesfan adjustable screw v53, each engageable withI an arm 54,preferablymade ofinsulating materialV and fixedly mounted at'opposite ends o rotatable shaft 28.- In addition-shaft y28 carries a 'drive brake means comprising a drive or escapement disk Aholding latch 55 :xedly mounted on the shaft and having afpair of arms 56 `and 51, the

endsof which-are' alternately fengageable with theftooth 46 :ondisk 45qupon rotation of arms 54 respectively in opposite directions.-

Under-;normal currentyconditions in the ,loadfv circuit connected to .the transformer secondary winding, the free .end'ofeach bimetallic element remains inv thexlowerfor yfull linexpositionillus-` Atratedin Fig. 3,. with the arms54v biased into engagementv withthe -adjustablei screws V53 fbyA a 1 spring 58, and Vwith the-.endfofxflatch armv 51: in; engagement'lwith toothlllti on :disk 45jV so.- thatV switch arm contact2will ,be maintained inengagement with stationary contact122'as `illustrated. However, upon theoccurrence of a pre-` determined` fault conditionsin the loe-.dccircuity thefree endof one or bothv'of the 'bimetallic elements will be flexed upwardly',` whereupon the adjustable screw lor screwswl` "will causeupward or counterclockwise rotationof arms 54, shaft 28,v and brake latch 55 to effect disengagement o1 latch arm 51y thereof from disktooth 46,"and permit torsion spring .33 to lefiectclockwise .ro-

tation of disk 45,'-counterclockwise rotation. of-

switch4 arm 24, and movement of Vthe disk-tooth'V latchfarm 56, therend of whichwas previously.

. moved into the path of the tooth travel. Engagement ofl arm 56 with tooth 4@ will maintain switch arm 24 in this position and the contacts 224 and 2S out of engagement until such time as the cooling of the bimetallic elements caused by interruption of the current in the primary winding results in flexing of the bimetallic elements downwardly to the illustrated full line position. Biasing spring 58 will, of course, cause arms 54 to follow, causing clockwise rotation of latch 55 and disengagement of latch arm 55 from tooth 4S, whereupon torsion spring 3s will effect engagement of contacts 22 and ES by rotating switch arm 24 clockwise to the illustrated full line position. In the event that the fault in the secondary circuit was only temporary and has been removed in some manner, engagement or latch arm 5l with tooth 46 on disk d5 will maintain the contacts in engagement. Ii, however, the fault is permanent, the bimetallic elements will again be heated and flexed upwardly, causing further openings and reclosines of the switch in the primary circuit in the manner described. However, following a predetermined number of such openings and closings, experience has shown that the fault is probably a permanent one and, other than early destruction of the contacts and failure of the switch mechanism, nothing will be accomplished by permitting the switch opening and closing operations to continue. Thus, I have provided a stop pin 59 mounted on and projecting laterally from the face of the spur gear d3 a sumcient distance so that, upon counterclockwise rotation of gear 42, it will eventually engage the vertical edge of one of the upstanding legs of support 36 when

contacts

22 and 25 have been separated, following the third reclosing operation of the switch. Thus, further movement of the switch drive will be prevented and the switch will be locked in the open position to isolate the faulted load circuit from the balance of the distribution system until such time as the fault has been removed. The switch may then be reset by turning the resetting and indicator arm c! in a clockwise direction until the pointed end thereto operate the switch upon the occurrence of i.,

subsequent faults.

In addition to being responsive to a predetermined current in the load circuits, the thermal means comprising bimetallic elements it and 49 are also responsive to the temperature of the transformer oil or liquid dielectric i3. Under certain conditions, even when the load current in the secondary is of a relatively small value, the oil temperature might be excessively high either due to high ambient temperature or from previous loading or from both in which event the biinetallic elements will be ilexed sufciently to effect disengagement of the contacts in the primary circuit thus allowing maximum safe loading of the transformer under all conditions.

Thus a transformer protective switch has been provided which is controlled in response to a fault in the secondary circuit but is positively actuated by an independent drive means. lvloreover, I have provided a reclosing type transformer protective switch which will interrupt the transformer primary circuit four times in case of a permanent fault, and then lock open until manually reset. Furthermore by the employment of an independent switch drive driven by a spring 6 means, sufcient energy is available for operating the interrupting contacts without resorting to the more expensive vacuum type switch which is capable of interrupting an appreciable but nevertheless limited amount of power with small movement of its contacts.

While I have, in accordance with the patent statutes, shown and described a particular embodiment of my invention, it will be obvious that changes and modifications can be made without departing from the invention in its broader aspects and I, therefore, aim in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A protective device for electric apparatus comprising a relatively stationary contact and a rotatably mounted switch arm, said switch arm having a contact end engageable with said stationary contact and an elongated slot adjacent the opposite end thereof, switch drive means mcluding a driving shaft and a driven shaft mounted in a support structure, said drive shaft having an indicator arm xedly mounted on an end thereof, a driving gear Xedly mounted on said driving shaft, a driven gear xedly mounted on driven shaft and engageable with said driving gear, an escapement disk having a single tooth in the periphery thereof xedly mounted en said driven shaft, a pin projecting transversely from a face of said disk and engageable with said slot in said switch arm, a torsion spring biasing said shafts, said indicator arm and said escapement disk for rotation in one direction to cause oscillation of said switch arm and alternate disengagement and engagement of said contact end with said stationary contact, a drive holding latch xedly mounted for rotational movement on a shaft, a latch operating arm idxedly mounted for rotational movement on said latch shaft, said drive holding latch having a pair of arms alternately engageable with said tooth upon rotation of said holding latch and said operating arm respectively in opposite directions, a bimetallic element xedly mounted at one end and the opposite end of said element being engageable with said latch operating arm and movable in response to a fault condition in said electrical apparatus to cause disengagement of one of said latch arms from said tooth to permit movement of said drive means and disengagement of said contacts and to simultaneously cause movement of the other of said arms for engagement with said tooth to limit the movement of said drive means and maintain said contacts out of engagement, and a spring biasing said latch operating arm for movement in a direction opposite the movement thereof caused by said birnetallic element, said last-mentioned spring being eiective upon disengagement of said element with said operating arm to cause disengagement of other latch arm with said tooth to permit movement of said drive means and engagement of said contacts, said switch arm mounted on said latch shaft, and a stop pin projecting from a face of said driving gear and engaging said support to cause said contacts to be locked in a disengaged position following a predetermined number of disengagements and engagements of said contacts, said torsion spring being rewindable by rotation of said indicator arm.

2. A protective device for electrical apparatus comprising, a ,stationary1v Contact,v a switch arm, rotatably Y, mounted-,on` a .rotatable shaft, one .end 'j of; said switch armtbeing a contact .endand the other end 101 saidswitch armhavng anelongated slot-therein,- a` rotatableescapement discV having a single tooth thereonsaid1dischaving.

a pin'thereon projecting laterally therefrominto .saidv slot; rotation. `ofsaid disc causing vsaid .-contact endtof said switch armftoengage-and disengagezsaid stationary contact, arvholding4 latch on-said `shaft havingl two-arms. each ,alternately engageable. with said tooth vtao-hold -sadcontact end in an engaged and disengagedy position with respect to said` stationary contact, arifactuating,Av arm on said shaft for rotating said shaft to cause said latch-armste alternately engage and disengage said ftootha spring; and 'an' element `rel References- ,oitatmta nie `0f this patent UNITED STATES Number f Number Nanie-"I- Datei"Y MacGahan`-` Jury# 1,-19192- Allutt Augsj- 219212 Daley Feb?13.5"1934F=` Frarxkl Sept.-1, l1936?y Cooneyf Sept18-1v936ff Hodnette" Jams," Y193'?-l Putman Dee. 3,"f 19'4o1* Putman-etais o't. 65194221 Jonas Aug-r11, 19431` MayA May '23] 1944 smith Nv:v 251948 smith: Dec.r `13;"1949-VSL FOREIGN-PATENTS .was