US3176089A

US3176089A - Load tap changers for transformers

Info

Publication number: US3176089A
Application number: US204029A
Authority: US
Inventors: Bleibtreu Alexander; Schunda Wilhelmine; Schunda Brunhilde
Original assignee: Maschinenfabrik Reinhausen Gebrueder Scheubeck GmbH and Co KG
Current assignee: Maschinenfabrik Reinhausen Gebrueder Scheubeck GmbH and Co KG
Priority date: 1961-06-22
Filing date: 1962-06-19
Publication date: 1965-03-30
Anticipated expiration: 1982-03-30
Also published as: NL279997A; GB953497A; BE619135A; DE1185715B; NL123797C; AT229436B; CH397073A

Description

March 30, 1965 A. BLEIBTREU ETAL 3,175,089

LOAD TAP CHANGERS FOR TRANSFORMERS Filed June 19, 19 62 5 Sheets-Sheet 1 Wyn/r0425.- WW WWW March 30, 1965 A. BLEIBTREU ETAL LOAD TAP CHANGERS FOR TRANSFORMERS 5 Sheets-Sheet 2 Filed June 19, 1962 41 f/A/mvroes 0mm WM 1, WWW b March 30, 1965 A. BLEIBTREU ETAL 3,176,089

LOAD TAP CHANGERS FOR TRANSFORMERS Filed June 19, 1962 5 SheetsSheet 3 /NVEN7'O,PS

EMMA Wm WM 4mm March 30, 1965 A. BLEIBTREU ETAL 3,176,089

LOAD TAP CHANGERS FOR TRANSFORMERS Filed June 19, 1962 5 Sheets-Sheet 4 lurzwrops WW Mm WMM m M VA/WW im W Mamh 1965 A. BLEIBTREU ETAL 3,175,039

LOAD TAP CHANGERS FOR TRANSFORMERS Filed June 19, 1962 5 Sheets-Sheet 5 WW1. MAM WM KW M. M WW XWW United States Patent LOAD TAP CHANGERS FOR TRANSFORMERS Alexander Bleibtreu, Regensburg, Germany, and Anton August Schunda, deceased, late of Regensburg, Germany, by Wilhelmine Schunda, Anton Schunda, and

Brunhilde Schunda, heirs, all of Regensburg, Germany,

assignors to Maschinenfabrik Reinhausen (lehruder Scheubeck K.G., Regensburg, Germany, a firm of Germany Filed June 19, 1962, Ser. No. 204,029 Claims priority, application Germany, June 22, 1961, M 49,421 8 Claims. (Cl. 200-18) This invention has reference to load tap changers for power transformers as applied, for instance, to maintain a constant secondary voltage with a variable primary voltage, to control the flow of reactive kva. between two generating systems, and to control the division of power between branches of loop circuits, etc.

It is a general object of this invention to provide improved load tap changers for polyphase transformers, in particular polyphase high voltage power transformers.

A further object of this invention is to provide load tap changers for polyphase high voltage power transformers which are considerably more compact, and involve considerably smaller manufacturing cost, than comparable prior art load tap changers.

Load tap changers include selector switches and transfer switches. The selector switches serve the purpose of selecting a particular tap on a tapped transformer winding intended to be connected into an electric circuit. Selector switches do not carry any load currents at the time a particular tap is selected, i.e. they are not required to interrupt or close on current-carrying circuits. This task is performed by the transfer switches. The latter perform all switching operations under load. Therefore all arcing is restricted to the transfer switches, the selector switches merely selecting the particular transformer tap to which the load is to be transferred.

Polyphase transformers require a selector switch and a co-operating transfer switch for each phase of the circuit. The selector switch and the transfer switch of each phase must be electrically insulated from the selector switch and the transfer switch of each other phase according to the full voltage between phases. For this reason it has become common practice to subdivide polyphase transformers into separate transformer units. Each such single phase unit comprises a separate tank, a separate single phase transformer, a separate load tap changer, and a separate drive for the latter. A plurality of such single phase units are integrated into a transformer bank. Transformer banks tend to be extremely bulky.

It is, therefore, another object of this invention to provide load tap changers which are less bulky than the load tap changers normally associated with transformer banks including a plurality of separate single phase transformer units.

It is frequently possible to reduce the aggregate size of a polyphase transformer including load tap changing means by arranging all the phases of such a transformer and the selector switches and the transfer switches of all the phases in a common tank. Where the voltage of a given polyphase transformer is high and its power large, the size of such transformers and of their associated load tap changing means tends to become intolerably large, and often exceeds the bulk limits required for transportation via rail, i.e. on railroad cars.

It is, therefore, another object of this invention to provide polyphase high voltage load tap changers which lend themselves to be combined with polyphase transformers whose various phase windings are arranged in a common "ice tank, i.e. built into the common tank, which load tap changers are extremely compact and add relatively little to the bulk of the composite transformer and load tap changer unit.

In the method of tap changing a current limiting device must be employed during each transition period from one tap position to the other. Such current limiting devices may either be center tapped reactors or resistors. This invention is particularly concerned with load tap changers wherein resistors are used as current limiting devices.

Load tap changers utilizing resistors as current-limiting devices and fast operating transfer switches are known, or referred to, as Jansen type load tap changers. This type of load tap changers has important advantages over load tap changers of other kinds. In this type of load tap changers the current-limiting resistors are in parallel with respect to the load current and in series with respect to the circulating currents which flow during transition times between tap changes. This makes it possible to reduce the resistance of the current limiting resistors to relatively low ohmic values without giving rise to large circulating currents. In Jansen type tap changers the movable contacts of the transfer switches move at high speeds, or with a snap action, wiping over the fixed contacts to which the current limiting resistors are connected. As a result of this fast motion the transition periods during which the current limiting resistors must carry load currents are very short, say in the order of a few hundredths of a second. This has two significant advantages: The current limiting resistors can be made very small and the voltage fluctuation resulting from tap changes insignificant. The rapid operation of the transfer switches is produced by stored energy means, preferably wound up springs which are maintained in a pre-wound, or pre loaded, condition in readiness for the next tap changing operation. Load tap changers of the Jansen type are well known in the art and have been described in many printed publications such as, for instance, the book by H. P. Young, Electric Power Control Systems, London, England, Chapman 8: Hall Ltd, 1942, and reference may be had to such publications for a more complete description of Jansen type load tap changers, and the structural features and operating characteristics thereof.

It is another object of this invention to provide improved lansen type load tap changers for polyphase high voltage power transformers.

The foregoing and other general and special objects of the invention and advantages thereof will appear more clearly from the ensuing particular description of the invention as illustrated in the accompanying drawings, wherein:

FIGS. la and lb are substantially a vertical section of a high voltage polyphase load tap changer embodying the present invention and comprising a plurality of selector switches, a plurality of transfer switches cooperating with the selector switches and drive meaens for both the selector switches and the transfer switches, FIG. 1a showing the left portion of the structure and FIG. 1b showing the right portion of the structure, both FIGS. 1a and 1b being complementary, FIG. la showing at the right side thereof some structural detail which is also shown in FIG. lb to the left side thereof;

FIG. 2 is a top plan view of one of the selector switches and of one of the transfer switches of the structure of FIG. 1;

FIGS. Zia-3c are top-plan views of the three transfer switches of the structure of FIG. 1; and

FIG. 4 is a connection diagram of one phase of a polyphase transformer provided with a load tap changer embodying the present invention.

Referring now to the drawings, the structure shown in FIGS. 1 and 2 is intended to be accommodated within a en /spec transformer tank having a cover on the top thereof. Neither the transformer tank nor the tank cover have been shown in FIG. 1. The cover of the tank of the transformer defines an opening which is covered by a part which may be referred to as a sub-cover. Reference numeral 115 has been applied in FIG. 1 to indicate the aforementioned sub-cover. Sub-cover 19 supports a vessel 11 of insulating material including a bottom 12. The lateral walls of vessel 11 are formed by an insulating cylinder or tube as widely applied in high voltage engineering. Vessel 11 is filled with an appropriate insulating liquid such as insulating oil. The bottom 12 of vessel 11 is provided with an opening 13 normally closed by a screw for draining oil from vessel 11. Tubular switch support 14 is arranged inside of vessel 11 in coaxial relation thereto. Support 14 is made of insulating material and houses three

transfer switches

15, 16 and 17 which are arranged in coaxial relation to each other and to support 14 and vessel 11 and stacked one above the other. Transfer switches 15, 16, 17 are of the rotary type and are mounted on, and operated by, a common shaft 18 adapted to insulate each transfer switch from the others. As clearly shown in PEG. 2 each transfer switch comprises a set or group of movable contacts 19 adapted to cooperatively engage a set or group of circularly arranged fixed contacts 21. The set or group of contacts 19 is pivotally supported at 19a on a rotatable contact carrier 20. Contacts 19 are arranged along a sector of a circle whose center 19a is spaced from the axis of rotation of contact carrier 20. The fixed contacts 21 are supported on the inner surface of the aforementioned insulating cylinder or insulating tube 14. When contact carrier 20 and movable contacts 19 are operated, fixed contacts 21 are sequentially engaged by movable contacts 19, the latter performing a composite rotary and radial motion as set forth more in detail in US. Patent 2,680,790 to B. Jansen. The two movable contacts 19 on both ends of the sector of movable contacts 19 are main contacts, and the intermediate contacts of the sector of movable contacts 19 are switch-over contacts. In a like fashion the two contacts on both ends of the sector of fixed contacts (indicated in some of the figures by reference character 22) 21 are main contacts and the intermediate contacts of the sector of fixed contacts 21 are switch-over contacts (indicated in some of the figures by reference character 23). The aforementioned fixed main contacts 21 are conductively connected to the particular tap of the transformer winding which has been selected, while the aforementioned fixed switch-over contacts 21 are conductively connected to switch-over resistors or tap-changing resistors 24 in the fashion shown in FIG. 4.

Each

transfer switch

15, 16, 17 comprises in essence three sector-shaped spaces of which one is occupied by the set of movable contacts 19 and the two others 25 are occupied by the aforementioned switch-over or tap-changing resistors 24. The location of the latter has been clearly shown in FIG. 2 as well as in FIGS. Zia-3c.

The carriers 20 for the movable contacts 19 are secured to composite shaft 18. This shaft comprises tubular sections 26 of insulating material alternating with sections formed by metal rods 27. Each of the two sections formed by metal rods 27 is interposed between a pair of sections 26 of tubular insulatin material. The latter sections 26 separate and insulate each

transfer switch

15, 16, 17 from the transfer switch or transfer switches immediately adjacent thereto.

Reference character 28 has been applied to indicate annular members for controlling the voltage distribution, i.e. the distribution of the electric field, around transfer switches 15, 16, 17 along

parts

11 and 14. At least two such voltage control members 28 are anranged at each axial end of each

transfer switch

15, 16, 17. As shown in FIG. 1 some of the voltage distribution control 23 are arranged inside of insulating tubing 14 and su ported by the latter, and others are arranged outside of vessel 11 and are supported by the latter. All of th voltage distribution control rings 28 are arranged in coaxial relation to

parts

11, 14 and 18.

Since

contacts

19 and 21 of transfer switches 15, 16, 17 part while carrying load currents arcs are kindled between these contacts incident to parting thereof, and these arcs form hot, ionized products of arcing. In order to avoid discharge of hot products of arcing formed in lower transfer switches to the arcing zones of the transfer switches arranged at a relatively higher stack level, transfer switches 15, 16, 17 are angularly displaced. In three phase transformers comprising three

transfer switches

15, 16, 17-one for each phase-the angular displacement of the three transfer switches is degrees. This has been shown in FIGS. 3a3c of which each figure is a horizontal section at right angles to shaft 18 and of which each figure shows in top-plan view one of the three

transfer switches

15, 16, 17.

Transfer switches 15, 16, 17 are operatively related to rotary selector switches 30, 31 and 32, i.e. transfer switch 15 is operatively related to selector switch 39, transfer switch 16 is operatively related to selector switch 31 and transfer switch 17 is operatively related to selector switch 32. Selector switches 30, 31 and 32 are stacked substantially in the same fashion as transfer switches 15, 16 and 17. Transfer switch 15 and selector switch 36 are arranged substantially at the same level, transfer switch 16 and selector switch 31 are arranged substantially at the same level, and transfer switch 17 and selector switch 32 are arranged substantially at the same level. The three

selector switches

30, 31 and 32 are mounted on a common tubular insulating shaft 29.

Switches

15 and 30 are arranged in the same phase of a three phase circuit, e.g. phase U. In a

similar fashion switches

16 and 31 are arranged in the same phase of a three phase circuit, e.g. phase S. Finally switches 17 and 32 are arranged in the third phase or phase T of a three phase circuit.

Switches

15 and 39 are interconnected by relatively short, substantially horizontal leads 33, switches 16 and 31 are interconnected by relatively short, substantially horizontal leads 34 and switches 17 and 32 are interconnected by relatively short and substantially horizontal leads 35.

Each

selector switch

30, 31, 32 comprises a plurality of fixed radially outer contacts 36 of which each is secured to an insulating rib 37. Fixed contacts 36 are adapted to be cooperatively engaged by the two bridge elements or bridge contacts 38 which may be turned about the center of a circle along which fixed contacts 36 are positioned. The current-carrying bridge elements or bridge contacts 38 are mounted on insulating tube 29. Insulating tubes 39 extend parallel to insulating tube 29i.e. both are vertical-and the latter support slip rings 49 clearly shown in FIG. 2 for connecting fixed leads to rotary bridge contacts 33. As shown in FIG. 1 annular members or rings 41 are arranged above each fixed contact 36 of each

selector switch

30, 31, 32 for controlling the voltage distribution in the region of contacts 36. Annular metal members or rings 28 for the control of the voltage distribution in axial direction are also arranged on the top and at the bottom of the stack formed by the three

selector switches

30, 31, 32.

Insulating tubes 39 integral with the stack of selector switches 30, 31, 32 are operable by means of a Geneva gear 42 shown in FIG. 1 arranged above the stack of selector switches 30, 31, 32. Geneva gears are widely applied in the art for operating selector switches of load tap changers and, therefore, Geneva gear 4-2 provided at the top of the stack of selector switches 311, 31, 32 does not call for a detailed description. Gear train 43 arranged above Geneva gear 42 is provided for operating the latter. Gear train 43 is operated from a shaft 45 by the intermediary of a transmission which may include a clutch or coupling 44. Shaft 45 is driven by an electric motor (not shown) which drives also the three

transfer switches

15, 16, 17 shown to the left of FIG. 1. This is achieved by means of gear 46 and an eccentric 47 operating a link or rod 48 loading a spring 49 upon rotation of shaft 45. Reference numeral 50 has been applied to indicate a tripping latch for releasing spring 49 when the particular taps intended to be inserted into the load circuit have been selected by means of the three selector switches 31 31 and 32. Operation of the latch 50 results in an instantaneous movement of the current carrying contacts 38 of the three

transfer switches

15, 16, 17 from their original positions to their pre-selected positions. Operation of the three

transfer switches

15, 16, 17 by spring 49 is effected by the intermediary of an eccentric to which reference character 51 has been applied. The aforementioned drive comprising spring 49 and the transmission means for loading the same and for tripping the same are arranged within a gear housing 52 which is mounted on top of horizontal plate or cover on the top of the transformer tank. Gear housing 52 is provided on the upper side thereof with an opening or window 53 making it possible to readily determine the particular position of the stack of transfer switches 15, 16, 17 and to inspect the constituent parts or elements of the drive housed within gear housing 52.

Referring now more particularly to FIG. 4, this figure shows to the left thereof three windings 100 of a polyphase transformer. All three windings 100 pertain to the same phase-say phase U-and only the center winding 100 is tapped. The center winding 1% has ten taps of which each is connected to one of the ten fixed contacts 36 of one of the selector switches, say selector switch 30. In order to make it clear that the center windings of the other phases S, T are also tapped and also connected to selector switches in the same fashion as the center winding of phase U, the

reference characters

31 and 32 have been added in parentheses in FIG. 4 after reference character 30. The FIGURES 1 to 10 at the left of FIG. 4 have been applied to distinguish between the ten fixed contacts 36 of selector switch 30. Transfer switch has been shown to the right of the selector switch and

reference characters

16 and 17 have been added in parentheses after reference character 15 to indicate that the transfer switches 16 and 17 are related in the same fashion to selector switches 31 and 32 as transfer switch 15 is related to selector switch 30. Each

transfer switch

15, 16, 17 is provided with six fixed contacts 21 of which each of the four inner contacts 21 is connected to one of four tap changing resistors 24. The latter are, in turn, connected to the rotary contacts 38 of selector switches 30, 31, 32 by the intermediary of

leads

33, 34, 35.

Reference numeral 54 has been applied to indicate a reversing switch of the kind widely applied in connection with load tap changers. Reversing switch 54 comprises a fixed center contact K and four additional fixed contacts A, A, B, B. Lead 101 connects the lower terminal of the upper transformer winding 160 to the fixed contact A of the reversing switch 54 and lead 102 connects the upper terminal of the lower transformer winding 100 to the fixed contact B of the reversing switch 54. Fixed contacts A and B of reversing switch 54 are connected by leads 103 and 103a to the upper terminal of transformer center winding 10%. Fixed center contact K of reversing switch 54 is connected by lead 104 to the support 20 of movable contacts 19 of the transfer switch 15. In the position of the reversing switch 54 shown in FIG. 4, the fixed contacts A and A are conductively interconnected by movable contacts C and the fixed contacts K and B' are conductively interconnected by the movable contact D. The current path of phase U shown in FIG. 4 is as follows: upper transfer winding 100, lead 101, fixed contact A, movable contact C, fixed contact A, lead 103, center winding 10!), fixed contact of selector switch 39 at tap number seven, bridge contact 38, slip ring 40, lead 33, lead 105, upper fixed contact 6 21 of transfer switch 15, movable contact 19 of transfer switch 15 engaging the aforementioned fixed contact 21 thereof, contact support 20, lead 104, fixed contact K of reversing switch 54, movable contact D, fixed contact B, lead 102, lower transformer winding 190.

In the embodiment of the invention shown in FIGS. 1, 2 and 3a, 3b, 30 each transfer switch comprises but one single substantially sector-shaped set of movable contact fingers 19 and one single set of fixed circularly arranged contacts 21 cooperating with contact fingers 19. Where prevailing current intensities are very large it may be necessary, or desirable, to provide each

transfer switch

15, 16, 17 with more than one substantially sector-shaped set of movable finger contacts 19, and with an equal number of sets of fixed circularly arranged contacts 21. The aforementioned sets of movable and fixed contacts are connected in parallel into each phase of a polyphase circuit, thus limiting the current carrying duty which must be assigned to each single set of contacts. In such a plural contact set arrangement there is less room within the space occupied by the transfer switches 15, 16, 17 for accommodating tap changing resistors 24.

According to FIG. 4 tap number seven is included in the circuit of the transformer and the load tap changer thereof. Assuming now that it is desired to change from tap number seven to tap number eight. Such a change involves the following steps to be carried out in the following sequence: Contact 38 which, heretofore, has been in engagement with the fixed selector switch contact number six is moved from the latter position into engagement with fixed selector switch contact number eight. This change of position of one of contacts 38 of each

selector switch

30, 31, 32 does not involve the flow of any circulating currents. Nor does it involve any change in regard to the active windings of the transformer. Concomitant with the aforementioned change of the position one of contacts 38 of each of the selector switches 30, 31, 32 the spring 49 for instantaneous or snap-action operation of transfer switches 15, 16, 17 is loaded, and thus readied to effect an instantaneous operation of said transfer switches. Upon tripping of latch 50 the movable set of contacts 19 of each

selector switch

15, 16, 17 perform a composite or rolling motion thereby sequentially engaging the fixed contacts 21 thereof. As a result of this motion the following switching operations are performed sequentially. The upper tap changing resistor 24 of FIG. 4 is inserted into the circuit, the two upper tap-changing resistors 24 of FIG. 4 are inserted into the circuit, the two tap changing resistors arranged in the center of FIG. 4 shunt the part of center winding 1% situated between taps number seven and number eight for a very short period of time, the two lower tap-changing resistors 24 of FIG. 4 are inserted into the circuit, but the lowest tapchanging resistor of FIG. 4 is inserted into the circuit, and finally only the lowest of movable contact 19 engages the lowest fixed contact 21 providing a direct current path not including any of the tap-changing resistors 24. At this point of the tap changing operation contact 38 engaging fixed contact 36 of tap number seven does not carry any current any longer, all the current being carried by the other contact 38 in engagement with fixed contact 36 of tap number eight.

The next operation of the load tap changer may either consist in a return of the constituent parts thereof to their original positions indicated in FIG. 4, which is a reversal of the operation which has been previously described in detail, or the next operation of the load tap changer may consist in a switching operation from taps number eight of selector switches 3t 31, 32 to taps number nine thereof. The last mentioned operation is a duplication of the switching operation which has been described above, i.e. a switching operation from taps number seven of selector switches 31), 31, 32 to taps number eight thereof.

Provision of reversal switch 54 makes it possible to reduce the number of taps of center winding 1% for a given or predetermined control duty since it makes it possible to use the voltage in the tapped center winding 1% selectively either for the purpose of boosting or for the purpose of bucking.

It will be apparent from the foregoing that a polyphase load tap changer embodying the present invention comprises a plurality of substantially identical transfer switches 15, 16, 17 each connected into one phase of a polyphase circuit and superimposed in substantially coaxial relation to form a transfer switch stack. The transfer switches comprised in said stack are angularly displaced a number of degrees equal to 360 divided by the number of the phases of the polyphase transformer. As a result of this angular displacement the hot products of arcing formed at load current switching operations of the transfer switches which are arranged at relatively low levels of the aforementioned stack are substantially kept away from the arcing zones of the transfer switches which are arranged at relatively high levels of the aforementioned stack. The particular embodiment of the invention described above is a load tap changer for a three phase transformer and its transfer switch stack comprises three transfer switches. The three transfer switches are angnlarly displaced 360:3:120 degrees, as best shown in FIGS. 3a, 3b and 3c. The aforementioned an gular displacement of the constituent transfer switches 15, 16, 17 of the transfer switch stack is generally sufifici ently effective to provide for a rapid dielectric recovery of the ionized gaps formed between the parting contacts of transfer switches 15, 16, 17. If desired baffles may be provided between the various levels of a stack of transfer switches to keep the hot products of arcing of one transfer switch away from the arcing zone of the other transfer switches and to control the upward fiow of products of arcing in a predetermined desired fashion.

The aforementioned angular displacement of transfer switches 15, 16, 17, i.e. of the sets of fixed contacts 21 and the sets of movable contacts 19 thereof makes it necessary to angularly displace the tap-changing resistors 24 in the same fashion. This has been clearly shown in FIGS. 3a-3c in which structure the tap-changing resistors 24 of transfer switches 15, 16, 17 are angularly displaced 120 degrees.

It appears further from the foregoing that each of the transfer switches 15, 16, 17 of polyphase load tap changers embodying the present invention includes a plurality of fixed circularly arranged contacts 21, a set of movable contacts 19 and current-limiting tap change resistors 24 within the cylindrical space defined by said circularly arranged fixed contacts 21.

The present invention contemplates the use of transfer switches of the general type disclosed and claimed in United States Patent 2,680,790 to B. Jansen, Load Changeover Switch for Tapped Transformers Using a Combination of Contact Movements, June 8, 1954 and United States Patent 2,833,873 to B. Jansen, Multi-Pole Tap Switch for Changing Transformer Taps Under Load, May 6, 1958, and reference may be had to the two aforementioned patents as to further details in regard to the transfer switches intended to be used for carrying the present invention into effect.

Load tap changers embodying the present invention further comprise insulating means for insulating the constituent transfer switches 15, 16, 17 of the transfer switch stack in accordance with the voltage prevailing between phases. The aforementioned insulating means include the body of oil inside of vessel 11 in which the transfer switches 15, 16, 17 are immersed, and the aforemen tioned insulating means further include the common shaft 13 for jointly operating the constituent transfer switches 15, 1d, 17 of the transfer switch stack which shaft is at least in part of insulating material.

it appears also from the foregoing that load tap secutive or contiguous taps.

changers embodying the present invention comprise a plurality of substantially identical selector switches 39, 31, 32 each connected into one phase of a polyphase circuit and superimposed in substantially coaxial relation to form a selector switch stack arranged in proximity of, or immediately adjacent to, the aforementioned transfer switch stack. The vertical spacing of the constituent transfer switches of the transfer switch stack and the vertical spacing of the constituent selector switches of the selector switch stack is substantially equal. Hence each transfer switch and each selector switch pertaining to the same phase are situated at substantially the same level, and each transfer switch is operatively related to one of the selector switches by

leads

33, 34, 35 which are substantially horizontal or, in other words, do not extend beyond the two horizontal planes which form the upper and the lower boundary of a pair of associated and cooperatively related transfer switches and selector switches. These leads are, therefore, arranged in equipotential spaces, i.e. spaces throughout which there is substantially the same potential. To be more specific, the required insulation of the

leads

33, 34, 35 between cooperating transfer switches and selector switches is but that called for by the difference in voltage between con- This is a minimum of insulation requirement. The tap change resistors 24 for limiting the flow of circulating currents incident to changing from one tap to another are preferably arranged within the above equipotential areas, forming integral parts of the transfer switches 15, to, 17 to which they are operatively related. The gear means for operating the transfer switches 15, 16, 17 and for operating the selector switches 39, 31, 32 are arranged on top of the transfer switch stack and on top of the selector switch stack.

It will also be apparent from the foregoing that the leads 33, 34, 35 operatively relating the transfer switch and the selector switch pertaining to the same phase do not cross with like leads operatively relating transfer switches and selector switches of other phases.

It is a feature inherent in the above described structure that the constituent switches 15, 16, 17 of the transfer switch stack and the constituent switches 39, 31, 32 of the selector switch stack may jointly be insulated against ground, which results in much more economical and compact structures than where cooperating pairs of transfer switches and selector switches are separately insulated against ground. Since the impulse strength of insulation against ground must be relatively high, this feature is one which is of considerable importance.

The common drive means for all transfer switches 15, 16, 17 and for all selector switches 30, 31, 32 of the load tap changer is a feature greatly reducing prime cost and space requirements. Since the volume of oil involved for insulating load tap changers embodying this invention is relatively small, and since inspection of the aforementioned common drive and of the switches integrated into the transfer switch stack and of the switches integrated into the selector switch stack is relatively simple, the cost of maintenance of load tap changers embodying the present invention are minimized.

Load tap chargers embodying this invention lend themselves to manual as well as to automatic supervisory control.

It will be understood that although but one embodiment of the invention has been illustrated and described in detail, the invention is not limited thereto. It will also be understood that the structure illustrated may be modified without departing from the spirit and scope of the invention as set forth in the accompanying claims.

It is claimed:

1. A load tap changer for polyphase transformers comprising in combination with a plurality of tapped phase windings of a polyphase transformer:

(a) a horizontal cover plate;

(b) an oil filled cylindrical vessel attached to said plate ranged fixed contacts engageable by said pair of and projecting from the lower surface thereof; rotary contacts, each of said plurality of fixed con- (c) a plurality of stacked transfer switches each artacts of each of said plurality of selector switches ranged within said vessel in coaxial relation thereto, being conductively connected to one tap of one of each of said plurality of transfer switches including 5 said plurality of .phase windings, and said pair of fixed contacts and movable contacts cooperating with rotary contacts of each of said pair of selector said fixed contacts in a predetermined sequence; switches being conductively connected to said second (d) a shaft coextensive with the axis of said vessel end of said constituent resistors of one of said pluprojecting transversely through said cover plate for rality of groups of resistors. joint operation of said plurality of transfer switch s; 19 3. A load ta-p changer for polyphase transformers com- (e) a plurality of groups of resistors arranged Within prising in combination with a plurality of tapped phase said vessel each at substantially the same level as one windings of a polyphase transformer: of said plurality of transfer switches, the constituent (a) a plurality of stacked transfer switches each inresistors of each of said plurality of groups of recluding fixed contacts and movable contacts cosistors having a first end conductively connected operating with said fixed contacts in a predetermined to some of said fixed contacts of one of said pluralsequence; ity of transfer switches and the constituent resistors (1;) a ti l haft for gang-operating id l lit of each of Said plurality 6f groups of resistors 113V" of transfer switches including insulating means for ing a second end; insulating said plurality of transfer switches from (f) a plurality of stack selector switches each arranged 20 h th at substantially the same level as one of said plurality a plurality of stacked groups of resistor h of transfer wit d One Of Said plurality of ranged at substantially the same level as one of said groups of resistors, each of Said plurality of Selector plurality of transfer switches, the constituent resis- SWllIClli-ZS including 21 pair Of rotary contacts, and each tors f each of said plurality of groups of resistors of Said plurality of Selector Switches including 3 p 25 having a first end conductively connected to some il 0f circularly arranged fixed ccflmcts engageable of said fixed contacts of one of said plurality of y Said P of TOtaYY Contacts, each of Said plurality transfer switches and the constituent resistors of each of fixed contacts of each of said plurality of selector f said prurarity f gmups f resistors having a switches being conductively connected to one tap of d d; 0116 Of Said plurality of Phase windings, and Said (d) a plurality of stacked selector switches each ar- P of rotary Contacts of each 0f Said P of 5615C- ranged at substantially the same level as one of said tor switches being conductively connected to said plurality f t n f r i h and one of id 1 second end of said constituent resistors of one of said m f groups f resistors, h f i 1 1i g plurality of groups f TeSiStOYS; selector switches including a pair of rotary contacts, (8) an insulating column Parallel to Said Shaft P and each of said plurality of selector switches infulcra for said pair Of I'OtZlIy contracts Of Each a plurality of circularly arranged fixed on of said plurality of selfictof Switches; and tacts engageable by said pair of rotary contacts, each (h) drive means for said plurality of transfer switches f Said m m f fixgd Contacts of h of i and for Said plurality of Selector Switches PP plurality of selector switches being conductively cony Said Cover Plate, Said drive maans including a 4" nected to one tap of one of said plurality of phase loaded Operating Spring arranged abflve Said Cover windings, and said pair of rotary contacts of each Plate for Operating Said first Shaft and a Geneva gear of said pair of selector switches being conductively dIiW for gang Opfifatifig Said P of rotary Contacts connected to said second end of said constituent reof each of Said p y of Selector SWilChQS- sistors of one of said plurality of groups of resistors; A 10215 p Changer for P yp transfflfmers C0111" (e) a vertical insulating column in the center of said p in Combination With a plurality of pp Phase a plurality of selector switches providing fulcra for windings Of 51 1 311 transformer: said pair of rotary contacts of each of said plurality (a) an oil filled substantially cylindrical vessel; f glegtor it h an insulating Cylinder arranged inside Said vessel (3) additional vertical insulating columns providing in coaxial relati n h 'w; 5O mechanical ties between each of said pair of rotary a plurality of Stacked transfer Switchfis each contacts of each of said plurality of selector switches;

ranged within said vessel in coaxial relation thereto, and each of said plurality of transfer switches including a Geneva gear d i arranged above id l lit fixed contacts and movable contacts cooperating with f salector i h tiv ly engaging b upper said fiXcd Contacts in a predetermined Sequence, 55 ends of said additional insulating columns for gang said fixed contacts of each of said plurality of transoperating said plurality of selector switches.

fer switches being supported by said insulating cylinder;

(d) a plurality of groups of current-limiting resistors arranged within the space bounded by said insulating 4. A load tap changer for polyphase transformers comprising in combination with a plurality of tapped phase windings of a polyphase transformer:

69 (a) a plurality of stacked, jointly operable rotary seleccylinder each arranged at substantially the same level as, one of said plurality of transfer switches, the constituent resistors of each of said plurality of groups of resistors having a first end conductively connected to some of said fixed contacts of one of tor switches electrically insulated from each other, each being at a predetermined potential, each of said plurality of selector switches including a plurality of circularly arranged fixed contacts each connected to one of the taps of one of said plurality of tapped said plurality of transfer switches and the constituent Phase windings of said transformer and each of said resistors each of Said plurality of groups of plurality of selector switches further including a pair SiStOIS having a Second and or" movable contacts each cooperating with said (e) a plurality of stacked rotary selector switches each plurality of fixed contacts;

arranged at substantially the same level as one of said 70 (b) a m m of smacked jointly opgmble namfer plurality 0f transfer Switches and one 0f said P switches electrically insulated from each other, each ity of groups of current-limiting resistors, each of b i t a predecermined potential, each of said plusaid plurality of selector switches including a pair rality of transfer switches having a plurality of cirof rotary contacts, and each of said plurality of seleccularly arranged fixed contacts including outer main tor switches including a plurality of circularly ar 7 contacts and inner auxiliary contacts and each of said plurality of transfer switches further having a plurality of movable contacts each cooperating in a predetermined sequence with one of said plurality of fixed contacts, each of said plurality of transfer switches being arranged at substantially the same level as one of said plurality of selector switches being at the same potential; and

c a luralit of rou s of switchin resistors the constituent resistors of each of said plurality of groups of switching resistors having a first end and having a second end and being connected with said first end. thereoi to said pair of movable contacts of one of said plurality of selector switches, and being connected with :said second end thereof to said fixed auxiliary contacts of one of said plurality of transfer switches, and each of said plurality of groups of switching resistors being arranged at substantially the same level as one of said plurality of selector switches and one of said plurality of transfer switches.

comprising in combination with a plurality of tapped phase windings of a three phase transformer:

(a) a plurality of stacked jointly operable rotary se- V lector switches electrically insulated from each other and at different potentials, each of said plurality of selector switches having circularly arranged fixed contacts conductively connected to the taps of one of Said plurality of phase windings of said transformer and a pair of movable contacts cooperating with said fixed contacts;

(b) a plurality of groups of stacked switching resistors having a spacing substantially equal to the spacing of said plurality of selector switches, the constituent resistors of each of said plurality of groups of switching resistors having a first end and having a second end and being conductively connected with said first end thereof to said pair of movable contacts of one of said plurality of selector switches; and

(c) a plurality of stacked jointly operable rotary trans- 5. A load tap changer for polyphase transformers corne prising in combination with a plurality of tapped phase windings of a polyphase ransformer:

(a) a plurality of stacked jointly operable rotary selecfer switches electrically insulated from each other and at different potentials, each of said plurality of transfer switches having a plurality of circularly artor switches electrically insulated from each other and at different potentials, each of said plurality of selector switches having a plurality of circularly arranged fixed contacts each connected to one of the taps of one of said plurality of phase win-dings of said transformer and each of said plurality of searranged fixed contacts including outer main contacts and inner auxiliary contacts and each of said plurality of transfer switches further having a plurality of movable contacts cooperating in a predetermined sequcnce with one of said plurality of fixed contacts, each of said plurality of transfer switches being arranged at substantially the same level as one. of said plurality of selector switches;

(d) means for controlling the voltage distribution along the stack formed by said plurality of transfer switches ranged fixed contacts including outer main contacts and inner auxiliary contacts and each having an equal number of movable contacts cooperating in a predetermined sequence with said fixed contacts, said plurality of transfer switches having a spacing substantially equal to the spacing of said plurality of selector switches and said fixed auxiliary contacts of lectof hailing P movabla com'acts each of said plurality of transfer switches being cone'ach wlth Sam plurality of fixed Comm; ductively connected to said second end of said constit- (b) means for controlling the voltage distribution along uent resistors of one of Said plurality of groups of Stack foamed by Said plurality of semen switches switching resistors, said plurality of fixed contacts tending to @Smabush of equitlolemial Zoms and said movable contacts of each of said plurality eallh Occupied by Om of Sand mummy of Selector of transfer switches being angularly displaced 120 Swltchfls; degrees and encompassing an angle of less than 180 (c) plumhty 1 stacked iomtly Can-Mable transfer degrees, each of said plurality of groups of switching switches electrically 1nsulated from each other each resistors bang arranged immediately adjacent Said being at a different pawl-M131 each of Sand i t lurality of fixed contacts and immediately adiacent of transfer switches having a plurality of circularly 49 g said movable contacts of one of Said plural'ity of transfer switches and angularly displaced 120 degrees.

7. A load tap changer as specified in claim 6 comprising a common vertical shaft for jointly operating said plurality of transfer switches, said shaft comprising insulating sections alternating with metallic sections, each of said insulating sections being arranged between contiguous of said plurality of transfer switches and each of said metallic sections being substantially coextensive with 50 the hei ht of one of said luralit of transfer switches. wndmg egtabhsh plulr'ahty o'fpeqmplotemmal Zonfis 8. A load tap changer fofpolypli ase transformers coml g i Led one of smd pummy of {mm/fen. prising in combination with a plurality of tapped phase f windings of a polyphase transformer:

(e) a i p gmd'ps Of i i i' (a) a plurality of stacked jointly operable rotary selecsmd mummy Of glllpsofswlichmg reslsltors banig tor switches electrically insulated from each other i at i 2 i of d and at different potentials, each of said plurality of phlarhty P i regsselector switches having circularly arranged fixed of each of Sald plurality of gsqups of Switching contacts conductively connected to the taps of one resistors h ving a first end and having a seE-ond end of Said plurality of phqse windings of said trans t v 1 p S U L, r v I c L c I i Q befmg i f Qald first .i e Of.to former and a pair of movable contacts cooperating ua fiked l contacts of ahty with sa d fixed contacts of transfer switchesand b a luraht of rou s of current-limitm 1m ed- (f) of i l g i i g i g zinces each if said plufality of groups of imiedaiices pairs o ea s,eac o sat puraty o pair's o ea s b in If n ed t bt H c s the same level as one conductively connecting said pair 01. movable con- 7, e a g a an m taots of one of said plurality of selector switches 4:0 giggigg g gi i g g g 2 5 ;5 1:2 2; said second end of the constituent resistors of one impndances having a first end ,md gi a second of mad mummy i l f g i end and being conductively connected with said first and each 531d f pjaus end thereof to said pair of movable contacts of one arnauged in one of said plurality of equipotential of Said plurality of selactor switches;

ZQHES P- {me f said plurality f (c) cylindrical contact supporting means of insulating switches and in one of said plurality of equipotentlal i l; and

limes p' y One of Said Plumli'iy 01f mimfel (d) a plurality of stacked jointly operable rotary transswitches. fer switches electrically insulated from each other 6. A load tap changer for three phase transformers and at different potentials, each of said plurality of rel transfer switches having a plurality of circularly arranged fixed contacts including outer main contacts and inner auxiliary contacts supported by said cylindrical contact supporting means and each having movable contacts cooperating in a predetermined sequence with said fixed contacts, each of said plurality of transfer switches being arranged at substantially the same level as one of said plurality of selector switches and one of said plurality of groups of irnpedances, said fixed auxiliary contacts of each of said plurality of transfer switches being conductively connected to said second end of said constituent impedances of one of said plurality of groups of impedances, said plurality of transfer switches being angularly displaced a number of degrees substantially equal to 360 divided by the number of phases of said polyphase transformer.

References Cited in the file of this patent UNITED STATES PATENTS Von Zweigbergk Sept. 20, Sessions Sept. 26, Koontz Feb. 13, Jansen Jan. 1, Le Count Aug. 19, Jansen June 8, Jansen Oct. 5, Jansen Nov. 8, Jansen May 6,

FOREIGN PATENTS France Apr. 24,

Claims

1. A LOAD TAP CHANGER FOR POLYPHASE TRANSFORMERS COMPRISING IN COMBINATION WITH A PLURALITY OF TAPPED PHASE WIDNINGS OF A POLYPHASE TRANSFORMER: (A) A HORIZONTAL COVER PLATE: (B) AN OIL FILLED CYLINDRICAL VESSEL ATTACHED TO SAID PLATE AND PROJECTING FROM THE LOWER SURFACE THEREOF; (C) A PLURALITY OF STACKED TRANSFER SWITCHES EACH ARRANGED WITHIN SAID VESSEL IN COAXIAL RELATION THERETO, EACH OF SAID PLURALITY OF TRANSFER SWITCHES INCLUDING FIXED CONTACTS AND MOVABLE CONTACTS COOPERTING WITH SAID FIXED CONTACTS IN A PREDETERMINED SEQUENCE; (D) A SHAFT COEXTENSIVE WITH THE AXIS OF SAID VESSEL PROJECTING TRANSVERSELY THROUGH SAID COVER PLATE FOR JOINT OPERATION OF SAID PLURALITY OF TRANSFER SWITCHES; (E) A PLURALITY OF GROUPS OF RESISTORS ARRANGED WITHIN SAID VESSEL EACH AT SUBSTANTIALLY THE SAME LEVEL AS ONE OF SAID PLURALITY OF TRANSFER SWITCHES, THE CONSTITUENT RESTORS OF EACH OF SAID PLURLITY OF GROUPS OF RESITORS HAVING A FIRST END CONDUCTIVELY CONNECTED TO SOME OF SAID FIXED CONTACTS OF ONE OF SAID PLURALITY OF TRANSFER SWITCHES AND THE CONSTITUENT RESISTORS OF EACH OF SAID PLURLAITY OF GROUPS OF RESITORS HAVING A SECOND END; (F) A PLURLAITY OF STACK SELECTOR SWITCHES EACH ARRANGED AT SUBSTANTIALLY THE SAME LEVEL AS ONE OF SAID PLURALITY OF TRANSFER SWITCHES AND ONE OF SAID PLURALITY OF SELECTOR GROUPS OF RESISTORS, EACH OF SAID PLURALITY OF SELECTOR SWITCHES INCLUDING A PAIR OF ROTARY CONTACTS, AND EACH OF SAID PLURLAITY OF SELECTOR SWITCHES INCLUDING A PLURALITY OF CIRCULARLY ARRANGED FIXED CONTACTS ENGAGEABLY BY SAID PAIR OF ROTARY CONTACTS, EACH OF SAID PLURALITY OF FIXED CONTACTS OF EACH OF SAID PLURALITY OF SELECTOR SWITCHES BEING CONDUCTIVELY CONNECTED TO ONE TAP OF ONE OF SAID PLURALITY OF PHASE OF WINDINGS, AND SAID PAIR OF ROTARY CONTACTS OF EACH OF SAID PAIR OF ELECTOR SWITCHES BEING CONDUCTIVELY CONNECTED TO SAID SECOND END OF SAID CONSTITUENT RESISTORS OF ONE OF SAID PLURALITY OF GROUPS OF RESISTORS; (G) AN INSULATING COLUMN PARALLEL TO SAID SHAFT PROVIDING FULCRA FOR SAID PAIR OF ROATARY CONTACTS OF EACH OF SAID PLURLAITY OF SELECTOR SWITCHES; AND (H) DRIVE MEANS FOR SAID PLURLAITY OF TRANSFER SWITCHES AND FOR SAID PLURALITY OF SELECTOR SWITCHES SUPPORTED BY SAID COVER PLATE, SAID DRIVE MEANS INCLUDING A LOADED OPERATING SPRING ARRANGED ABOVE SAID COVER PLATE FOR OPERATING SAID FIRST SHAFT AND A GENEVA GEAR DRIVE FOR GANG OPERATING SAID PAIR OF ROTARY CONTACTS OF EACH OF SAID PLURALITY OF SELECTOR SWITCHES.