US3407275A

US3407275A - Transfer switch means for tapped transformers including a voltage limiting device

Info

Publication number: US3407275A
Application number: US589646A
Authority: US
Inventors: Breuer Wolfgang
Original assignee: Maschinenfabrik Reinhausen Gebrueder Scheubeck GmbH and Co KG
Current assignee: Maschinenfabrik Reinhausen Gebrueder Scheubeck GmbH and Co KG
Priority date: 1965-11-04
Filing date: 1966-10-26
Publication date: 1968-10-22
Anticipated expiration: 1985-10-22
Also published as: DE1538023B2; BE689265A; GB1103017A; NL130955C; SE322834B; NL6615343A; FR1498240A; AT265442B; CH448256A; DE1538023A1

Description

Oct. 22, 1968 w. BREUER 3,407,275

TRANSFER SWITCH MEANS FOR TAPPED TRANSFORMERS INCLUDING A VOLTAGE LIMITING DEVICE Filed on. 26, 1966 2 Sheets-Sheet 1 l/wmraP:

" mm. m

3,407,Z 75 NSFORMERS INCLUDING A Oct. 22, 1968 w. BREUE TRANSFER SWITCH MEANS FOR TAPPED T VOLTAGE LIMITING DEVICE 2 Sheets-Sheet 2 Filed Oct. 26, 1966 W n/r0? Bum w w 2%, w

Insulatingly Supported by Contact Bridge Carriers, issued United States Patent 3 12 Claims. (Cl. 200-11) 0 ABSTRACT OF THE DISCLOSURE Described below is a transformer and load-tap changer assembly wherein physical switch-over impedances such as, for instance, switch-over resistors, are dispensed with, and wherein the current-limiting action normally performed by such impedances is performed by the arc voltage of an electric are drawn in the transfer switch. The circuitry includes a surge voltage discharge means such as, for instance, a spark gap, that is connected in series with a portion of the tapped transformer winding and any electric are formed upon parting of the contacts of the transfer switch. The aforementioned surge voltage discharge means is being short-circuited when the transfer switch completes its tap-changing stroke, or completes its travel from one of its limit positions to the other of its limit positions.

This invention refers to load tap-changers for regulating transformers, and more particularly to so-called Jansen type load tap-changers for such transformers, and to transfer switches required for'such transformers.

Such systems and the constituent parts thereof are disclosed in numerous US. patents assigned to the same assignee as the present invention, e.g., U.S. Patent 3,218,400 to A. Bleibtreu, Transfer Switches for Tap-Changing Regulating Transformers Having Squirrel-Cage-Shaped Support for the Fixed Contacts Thereof, issued Nov. 16, 1965, and US. Patent 3,238,820 to A. Bleibtreu, Transfer Switch for Tap Changers for Regulating Transformers Including a Cylindrical Insulating Housing, a Squirrel- Cage-Contact-Supporting Structure and Contact Bridges Mar. 1, 1966, or to US. Patent 3,250,864 to A. Bleibtreu et al., Regulating Transformers Having a Large Number of Taps, issued May 10, 1966.

In all these prior art systems the transfer switches are associated with ohmic resistors which are sequentially inserted into the circuit when changing from one tap of the tapped transformer winding to the tap immediately adjacent thereto.

The presence of such ohmic resistors, often referred to as switch-over resistors, or tap-changing resistors, greatly increases the bulk and the cost of load tap-changers of the Jansen type.

It is, therefore, one object of this invention to provide I ansen type load tap-changers which do not require bulky and costly switch-over resistors, or tap-changing resistors.

Another object of this invention is to provide load tapchangers of the Jansen type wherein arc resistance is used as an effective substitute for the costly and bulky switch-over resistors, or tapchanging resistors.

Transfer switches wherein arc resistance takes the place of the conventional switch-over resistors, or tap-changing resistors, require normally very high contact moving speeds. Thus the time required for the movable contact of a transfer switch to move from one of its limit position to the other of its limit positions may be in the order "ice of milliseconds. This condition imposes requirements on the drive mechanism which can only be met with difiiculty and at great cost. The aforementioned difii'culty increases in proportion with the magnitude of the load currents and/ or the magnitude of the overload currents which the transfer switches are supposed to carry and to interrupt. This is primarily due to the fact that the size and the weight of the movable contacts of transfer switches increases in proportion to the magnitude of the load currents and/ or the magnitude of the overload currents which such switches must carry and interrupt.

It is therefore, another object of this invention to provide load tap-changing systems including transfer switches predicated on the use of arc-resistance rather than the use of physical ohmic resistors for performing tap-changing operations, but not subject to the aforementioned limitations, and particularly not requiring a complex or critical drive or operating mechanisms for operating the movable contact, or contacts, of the transfer switches.

The above and additional objects and advantages of the invention will become more apparent from the ensuing descritpion of the invention, and specific embodiments thereof, when read in connection with the accompanying drawings.

Load tap-changing regulating transformers include selector switches and transfer switches. The former serve the purpose of selecting any desired tap among the many taps present along a tapped transformer winding which is intended to be connected into an electric circuit. Selector switches are not required to interrupt current-carrying circuits, or to close on current-carrying circuits. This task is assigned exclusively to the transfer switches. These perform all switching operations under load. For a full understanding of the present invention the presence and function of selector switches is immaterial and such switches are, therefore, not included in the accompanying drawings.

Referring now to the accompanying drawings:

FIG. 1 shows diagrammatically a tapped transformer winding and transfer switch circuitry embodying the present invention, the transfer switch being directly connected to the taps of a tapped trasformer winding, i.e., without interposition of a selector switch;

FIG. 2 shows the same elements and the same circuitry as shown in FIG. 1 in a position preparatory to performing a tap-changing operation of the transfer switch;

FIG. 3 shows the same elements and the same circuitry as shown in FIGS. land 2 during the first phase of a tap-changing operation of the transfer switch from the one of two taps of the tapped transformer winding to the other of the two taps thereof;

FIG. 4 is the same as FIG. 3 but shows a second or subsequent phase of the tap-changing operation of FIG. 3;

FIG. 5 shows the same elements and the same circuitry as FIGS. 1-4, inclusive, upon completion of the tapchanging operation from one of the two taps of the transformer winding to the other of the two taps of said winding;

FIG. 6 shows substantially the same elements and the same circuitry as FIGS. 1-6, except that a double break, or multibreak, transfer switch has been substituted in FIG. 6 for the single break transfer switch of FIGS. l-S, inclusive, the position of the transfer switch shown in FIG. 6 corresponding to the position of the transfer switch shown in FIG. 3;

FIG. 7 shows a side elevation of the transfer switch diagrammatically shown in FIG. 6;

FIG. 8 is a section along VIII-VIII of FIG. 7; and

FIG. 9 is a section along IX-IX of FIG. 7.

Referring now to the drawings, and more particularly toFIGS. "1-5 thereof, rerr'eaiie character T has been applied to indicate a tapped-transformer winding having two taps A and B. The transformer whose winding T is shown in FIGS. 1-5 may include other-windings, not shown in these figures, or it may be an auto-transformer. While FIGS. 1-5 show but two taps A, B of winding T,., the number of taps will generally be considerably larger. But two taps A and B have been shown in FIGS. '1-5 since, assuming'the presence of but two taps, is sufficient and adequate to explain this invention and the mode of operation thereof. Reference character S has been applied to generally indicate a transfer switch for effecting tap changing operationsfrorn tap A to tap B, and vice versa. Transfer switch S includes a. pair of fixed contacts 10, 11 and a movable contact 12 supported by a lever 12' pivot'able about fulcrum 17. Pivotal motion of contact 12 about fulcrum 17 results-in disengagement of contact 12 from contact and in engagement-of contact 11 by contact 12 when effected in clockwise direction, as seen in FIGS. 1-5, inclusive. Pivotal motion of contact 12 aboutfulcrum 17 -in opposite direction results in disengagement'of contact 12 from contact 11 and engagement of contact 10 by contact 12. The circuitry of FIGS. 1-5 includes an auxiliary switch generally indicated by reference numeral 16, including 'a pivotable contact arm adapted to engage selectively either left fixed contact 16 or right fixed contact 16".

Contacts

10 and 16 are conductively connected by leads a to tap A and contacts 11 and 16" are conductively connected by leads b to tap B. Reference numeral 13 has been applied to generally indicate a surge voltage discharge means being normally an electric insulator and turning into a good conductor of electricity when a predetermined voltage level across discharge means 13 is exceeded. In other words, discharge means 13 is a device which is characterized by the occurrence of an electric breakdown when a predetermined critical voltage level across it is exceeded. Spark gaps pertain to this type of devices, and device 13 is preferably a spark gap including two spaced

electrodes

14, 15 separated. by a gaseous gap which breaks down when a predetermined voltage is being applied across spark gap 13. The upper electrode 14 of spark gap 13 may be connected selectively to tap A and contact 16', or to tap B and contact 16", depending upon the position of auxiliary changeover switch 16. Contact 12 is conductively connected to fulcrum 17, as by its supporting arm or lever 12, and the lower electrode 15 of spark gap 13 is conductively connected to fulcrum 17 by means of lead 0. The

electrodes

14, 15 of spark gap 13 have preferably relatively large, parallel, equidistantly spaced surfaces bounding the electric discharge gap formed between

electrodes

14, 15.

Depending upon the design of the transformer a predetermined voltage prevails between the taps A and B of the winding T, thereof. The breakdown of surge voltage discharge device or arc gap 13 is in excess of the voltage normally prevailing between contiguous taps A and B of transformer winding T,.

An arc is formed between

contacts

10 and 12 upon separation thereof. The same applies as to contacts 11 and 12 upon separation thereof. It may be necessary, or desirable, to control the rate of rise of the arc voltage of any are or arcs formed between contacts 10', 12 and '11, 12, respectively. This may be achieved by any conventional means suitable for the purpose in hand, e.g., subjecting the arcs to de-ionizing blasts of fluids such as,

for instance, oil, or subjecting the arcs to the action of magnetic fields in the presence of arc chutes. Reference character F has been applied in the drawings to indicate a pair of nozzles for establishing fluid blasts across the arcs formed between

contacts

10, 12 and 11, .12 upon separation thereof. In FIG. 3 reference numeral 18 has been applied to indicate the arc formed upon separation of

contacts

10, 12 and an arrow drawn adjacent left nozzle F indicates a cross-blast of fluid emanating from the left noizle F for ebarbmn' therateof rise of the voltage across are 18.

Preparatory to separating

contacts

10, 12 switch 16 is moved from its position shown in FIG. 1 to its position shown in FIG. 2. Thereuponarm 12' is pivoted in clockwise direction by conventional drive means, e.g., a spring motor (not shown) and thus contact 12 is moved to its position shown in FIG: 3 'wherein are 18 extendsbetween and-conductively interconnects contacts 10 and 1-2'. The rate of rise of the arc voltage across contacts 10- and 12 may be controlled'in any "desired fashion as, for instance, a fluid blast ejected from nozzleF. At acertain position of contact 12 or, in other words, when the gap formed between

contact

10 and 12 reaches a certain critical magnitude, the voltage across spark-gap 13 exceeds the breakdown voltage of spark gap. 13, many electrical equivalent of spark gap 13. Since the separation between contacts '10 and 12 and the voltage of the arc across contacts'10 and 1-2 keep on increasing, arc 18 extinguishes'soon'after the breakdown of spark gap 13. Final extinction of arc 18 may readily be achieved after the first zero of the current wave, or not later than after the second zero thereof. Thus arcing time and arc energy may be drastically reduced when considering comparable load tap-changing circuitry. This, in turn, results in drastic limitation of contact erosion. These significant achievements-"are not conditioned on the presence of abnormahexpensive and critical contact-operating motor means capable of separating the contacts on the-transfer switch at extremely high velocities.

FIG. 4 shows the operating condition of the circuitry following extinction of the arc kindled between

contact

10 and 12, while spark gap 13 is still in breakdown condition and carrying current.

When contact 12 engages contact 11, spark gap 13 is shunted, or short-circuited, by-contacts 11 and 12, and thus the gap discharge across spark gap 13 extinguished. This operating condition is shown in FIG. 5. I

Spark gap 13 includes preferably means (not shown) for varying the spacing between the discharge-gap-bounding surfaces thereof. This makes it possible to compensate for erosion of the electrodes 14, -15 of spark gap 13, and to use a standard spark gap for situations involving different voltages between contiguous taps A, B of tapped transformer windings T It will beunderstood that the spark gap 13 breaks down when the voltage of arc 18 reaches its peak value. Breakdown of the spark gap 13 results in the flow ofv a current from tap B to point 17 of the circuit which happens to be the fulcrum of contact-carrying lever 0 arm 12.

Preparatory to switching contact-carrying arm 12' in counterclockwise direction the movable contact of switch 16 is separated from fixed contact 16 and caused to engage fixed contact 16'. This might be achieved manually, but is preferably achieved by automatic motor means (not shown).

In connection with load-tap changers involving relatively high power levels it may be desirable to establish multibreaks by the transfer switch rather than single breaks as shown'in FIGS. 1-5, inclusive. FIGS. 6-9 refer to load tap-changing circuitry including .a multibreak or dual break transfer switch generally indicated by the reference letter S. Transfer switch S comprises a first pair of fixed contacts 20, 20' and a second pairof fixed

contacts

21, 21. The two subcontacts 20, 20" are electrically insulated from each other and take the place of contact 10 of FIGS. 1-5. The two subcontacts 21, 21' are electrically insulated from each other and take the place of contact 11 of FIGS. 15. Movable contact 23 is intended to selectively engage fixed subcontact 20, 20' and separate from fixed

subcontacts

20, 20. In like fashion, movable contact 24 is intended to selectively engage fixed subcontacts 21, 21' and separate from fixed subcontacts 20, 21'.

Contacts

23, 24 are supported by a common support 22 of insulating material insulating contacts 23,- 24 frorn eachother. Support 22 is, in turn, supported by a pivotable arm25 having its fulcrum at 26. Tap Ais conductively connected by lead a to subcontact 20 and tap Bis conductively connected by lead b to subcontact 21. Lead 41" conductively connects subcontact 20' to point 17 and lead b" conductively connects subcontact 21' to point 17. The changeover switch 16 comprises a pivotable contact conductively connected to electrode 14 of spark gap 13. The pivotable contact of changeover switch 16 has two limit positions. In one of these limit positions it engages. fixed contact 167 conductively connected to tap A of winding T,, and in the other of these limit positions it engages fixed contact 16'. conductively connected to tap B of winding T Electrode of spark gap 13 is conductively connected to point 17 by means of lead c'. l v

. As .shown in FIGS. 7 and 8 contact 24 is preferably U- shaped, defining a groove or recess 24a between the flanges thereof. A barrier 27 of insulating material projects into recess 24a. Contact 23 is shaped in substantially the same fashion,.defin ing a groove or recess for receiving insulating barrier27.. a v c In the structure of FIGS. 7-9 the subcontacts 20, 20' and subcontacts 21, 21' of FIG. 6 are arranged to opposite sides. of insulating barrier 27 as clearly shown in FIG. 9 in regard to subcontacts 21, 21'. Fixed subcontacts 20, 2t]? and 21, 21 are sandwiched between a.pair of fiat insulating barriers 28 parallel to insulating barrier 27. This, has been clearly shown in FIG. 9 with regard to subcontacts 21, 21'. Insulating barriers 28 further

sandwich pivotable contacts

23, 24. In FIG, ,7 one of the bar'riers28 has been removed to expose to view subcontacts 20,21, the flange portions of

contacts

23, 24 situated in front of barrier 27 and the front of barrier 27. Thus the pair of series arcs drawn between the two flanges of movable contact 23 and fixed subcontacts 20, 20' are separated from each other by insulating barrier 27 and separated from the outside space by the insulating barriers 28. In a like fashion, the pair of series arcs drawn between pivotable contact 24 and fixed

subcontacts

21, 21 are separated from each other by insulating barrier 27 and separated from the outside space by insulating barriers 28. c I

It will be apparent from the foregoing that FIG. 6 shows the same phase in the tap changing process as FIG. 3, i.e., the point of time of arc inception and are elongation preceding the point of time of breakdown of the spark gap 13. The principal distinction of the structure of FIG. 6 from that of FIGS. l-5 resides in the fact that a pair of serially related arcs 18 is formed in the latter at each tap-changing operation of transfer switch S.

FIG. 6 may be considered as, and is, a diagrammatic representation of the structure of FIGS. 7-9 including other circuit elements required to perform a tap-changing operation in accordance with the principle underlying this invention.

The change-over switch 16 may be deleted if the circuitry is provided with two separate spark gaps 13 rather than a single spark gap, but the structures of FIGS. 1-5 and 6 including one single spark gap 13 and a changeover switch 16 are preferable.

It will be apparent from the above that a transformer and load-tap changer assembly according to this invention includes a transformer winding having a pair of taps A and B and a transfer switch S having a pair of contacts 10, 11 each conductively connected to one of said pair of taps A, B of said winding T Winding T includes a portion situated between taps A and B. The transfer switch S further includes an additional contact 12 selectively engageable with and separable from each of said pair of contacts 10, 11. A transformer and load-tap changer embodying this invention further includes a surge voltage discharge means 13 being normally an electric insulator and turning into an electric conductor when a predetermined voltage across said discharge means is exceeded. The circuitry according to this invention further includes means for serially connecting said surge voltage discharge means 13, said portion of said winding situated between said pair of taps A, B and any electric arc 18 formed upon separation of said additional contact 12 from one of said pair of contacts 10, 11 and for shortcircuiting said surge voltage discharge means 13 upon engagement of said additional contact 12 and the other of said pair of contacts 10, 11. c a

It will also be apparent that

parts

10, 11, 12, 12' form a first change-over switch and that

parts

16, 16, 16." form a second changeover switch. I

While there has been described what are at present considered preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications maybe madetherein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In combination:

(a) a tapped transformer winding havinga pair of taps, said winding including a portion situated between said pair of taps;

(b) a transfer switch having a pair of contacts each conductively connected to one of said pair of taps of said winding and an additional contact selectively engageable with and separable from each of said pair of contacts;

(0) a surge voltage discharge means being normally an electric insulator and turning into an electric conductor when a predetermined voltage across said discharge means is exceeded; and

(d) meansfor serially connecting said surge voltage discharge means, said portion of said winding situated between said pair of taps and any electric are formed upon separation of said additional contact from one of said pair of contacts and for short-circuiting said surge voltage discharge means upon engagement of said additional contact and the other of said pair of contacts.

2. A combination as specified in claim 1, wherein said pair of contacts is fixed and said additional contact is pivotable about a fulcrum arranged between said pair of contacts.

3. A combination as specified in claim 1 wherein said surge voltage discharge means is a spark gap.

4. A combination as specified in claim 1 wherein said surge voltage discharge means is a spark gap including a pair of electrodes having parallel equidistantly spaced surfaces bounding a gap formed between said electrodes.

5. A combination as specified in claim 1 wherein a predetermined voltage prevails between continguous taps of said winding and wherein said surge voltage discharge means have a breakdown voltage in excess of said predetermined voltage.

6. A combination as specified in claim 1 including a change-over switch for selectively connecting said surge voltage discharge means to different contiguous taps of said winding.

7. A combination as specified in claim 1 including means for controlling the rate of rise of the arc voltage of arcs formed between one of said pair of contacts and said additional contact.

8. A combination as specified in claim 1 wherein each of said pair of contacts comprises separate subcontacts electrically insulated from each other and wherein said additional contact has a point of engagement with each of said subcontacts of each of said pair of contacts to form series arcs upon separation of said additional contact from said two subcontacts of each of said pair of contacts.

9. A combination as specified in claim 1 wherein each of said pair of contacts comprises two separate subcontacts electrically insulated from said other by a flat insulating barrier and sandwiched between a pair of flat insulating barriers parallel to said insulating barrier, and wherein said additional contact includes two substantially U-shaped portions receiving said insulating barrier between the flanges thereof and sandwiched between said pair of insulating barriers, =bth flanges of each of said U-shaped portions being jointly engageable with and jointly separable from said two subcontacts of each pair of contacts.

10. In combination (a) a transformer winding having a portion situated between a pair of taps including a first tap and a second tap;

(b) a transfer switch having a pair of contacts including a first contact conductively connected to said first tap and a second contact conductively connected to said second tap, said transfer switch further having an additional contact selectively engageable with and separable from each said first contact and said second contact;

(0) a surge voltage discharge means being normally an electric insulator and turning into an electric conductor when a predetermined voltage across said surge voltage discharge means is exceeded, said surge voltage discharge means having two terminals;

(d) switch means for selectively connecting one terminal of said surge voltage discharge means to said first tap and to said second tap; and

(e) conductor means conductively connecting the other terminal of said surge voltage discharge means to said additional contact of said transfer switch.

11. In combination (a) a tapped transformer winding having a pair of taps and establishing a predetermined difference in voltage between said pair of taps;

(b) a first change-over switch having a pair of contacts each conductively connected to one of said pair of taps of said winding and an additional contact selectively engageable with and separable from each contact of said pair of contacts;

(c) a second change-over switch having a pair of contacts each conductively connected to one of said pair of taps of said winding and an additional contact selectively engageable with and separable from each contact of said pair of contacts; and

(d) conductor means including a spark gap having a breakdown voltage in excess of said predetermined voltage between said pair of taps connecting said additional contact of said first change-over switch and said additional contact of said second changeover switch.

12. In combination (a) a tapped transformer winding having a first tap and a second tap, the portion of said winding between said first tap and said secondtap' having a predetermined difference in voltage;

(b) a change-over switch having a first contact conductively connected to said first tap and a second contact conductively connected to said second tap, said change-over switch further having an additional contact movable relative to said first contact and to said second contact to selectively part from said first contact and, engage said second contact and part from said second contactandengage said first contact;

(c) a current-carrying lead conductively connected to said additional contact of said change-over switch;

(d) a surge voltage discharge device having a breakdown voltage in excess of said predetermined diiference in voltage, said surge voltage discharge device having a pair of terminals;

(e) means for selectively connecting one of said pair of terminals of said surge voltage discharge device to said first tap and to said second tap of said winding; and I (f) conductor means conductively connecting the other of said pair of terminals of said surge voltage discharge means to said current-carrying lead conductively connected to said additional contact of said changeover switch.

References Cited UNITED STATES PATENTS 3,211,956 10/1965 Dornbush 317-69 XR 3,329,869 7/1967 Obenhaus 317-13 LEWIS H. MYERS, Primary Examiner.

I. R. SCOTT, Assistant Examiner.