US3445615A

US3445615A - System for increasing the switching capacity of transfer switches for tap-changing transformers

Info

Publication number: US3445615A
Application number: US544142A
Authority: US
Inventors: Alexander Bleibtreu
Original assignee: Maschinenfabrik Reinhausen Gebrueder Scheubeck GmbH and Co KG
Current assignee: Maschinenfabrik Reinhausen Gebrueder Scheubeck GmbH and Co KG
Priority date: 1966-04-21
Filing date: 1966-04-21
Publication date: 1969-05-20
Anticipated expiration: 1986-05-20

Description

y 0, 1969 A. BLEIBTREU 3,445,615

SYSTEM FOR INCREASING THE SWITCHING CAPACITY OF TRANSFER SWITCHES FOR TAP-CHANGING TRANSFORMERS Filed April 21. 1966 ALEXANDER BLEIBTREU Y ATTY,

United States Patent U.S. Cl. 200-146 3 Claims ABSTRACT OF THE DISCLOSURE In a Jansen-type transfer switch system including switch-over resistors, pairs of auxiliary movable contacts are mechanically coupled by tie means, and different ohmic values are imparted to the switchover resistors whereby the recovery voltage appearing across the main contacts following a switching operation involving a load current is drastically limited, and whereby in case of a switching operation involving an overload current the gaps formed between the main contacts are shunted by resistors having a small ohmic value.

This invention relates to transfer switches for tapped regulating transformers including sequentially operable movable main contacts and movable auxiliary contacts and switch-over resistors operatively related to said main contacts and to said auxiliary contacts.

it is a general object of this invention to provide improved so-called Jansen-type transfer switches for the tapped regulating transformers.

Another object of this invention is to provide transfer switches of the aforementioned description having a relatively high interrupting capacity, i.e. a higher interrupting capacity than comparable prior art Jansen-type transfer switches.

Another object of this invention is to provide improved Jansen-type transfer switches wherein the switch-over resistors control the transient recovery voltage across the separated fixed and movable main contacts.

Still another object of this invention is to provide improved versions of the transfer switches disclosed and claimed in U .8. Patent 3,174,097 to Alexander Bleibtreu, issued Mar. 16, 1965 for Transfer Switch for Tap Changers for Regulating Transformers, assigned to the same assignee as the instant invention.

The above and additional objects and advantages of the invention will become more apparent from the ensuing description thereof When read in connection with the accompanying drawings wherein:

FIG. 1 is a diagrammatic representation of a transfer switch embodying this invention shown in a first operating position;

FIG. 2 shows the same structure as FIG. 1 in the same fashion as FIG. 1 but in another operating position; and

FIG. 3 shows the same structure as FIGS. 1 and 2 in the same fashion as FIGS. 1 and 2 but still in another operating position.

Referring now to the drawings, Tr has been applied to designate the winding of a regulating transformer having two taps A, B. Actually winding Tr has a larger number of taps than the two taps A, B shown in the drawing, but for the purpose of explaining the present invention it is sufiicient to consider but the aforementioned two taps A, B. Taps A, -B are connected by leads 12 to a transfer switch generally indicated by reference character T. Leads 12 include also a selector switch which is not shown in the drawing, since the presence of a selector switch is 3,445,615 Patented May 20, 1969 not essential to an understanding of the present invention, and since selector switches, and their mode of operation, and the way of connecting the same int-o electric circuits are well known in the art.

The transfer switch T comprises a pair of spaced fixed main contact means a, a. Each of said pair of main contact means includes two spaced fixed main contacts a and a. The contacts a and a shown to the left of the drawings may be bridged by a movable main contact 1 and the contacts a and a shown to the right of the drawings may be bridged by the movable main contact 6. In the position of the transfer switch T shown in FIG. 1 movable main contact, or cont-act bridge, 1 interconnects conductively the fixed main contacts a, a to the left, and the movable main contact, or contact bridge, 6 is separated from the fixed main contacts a and 11' shown to the right of the drawings. Movable main contact, or contact bridge, 1 may be moved out of engagement with fixed main contacts a and a, and movable main contact, or contact bridge, 6 may be moved into engagement with fixed main contacts a and a. Transfer switch T further includes two pairs of fixed auxiliary contact means arranged inside of a space bounded by the aforementioned pair of fixed main contact means a, a and a, a. Each fixed auxiliary contact means includes a pair of spaced fixed contacts b and b. The aforementioned fixed auxiliary contact means b, b cooperate with two pairs of movable auxiliary contacts, or contact bridges, to which

reference characters

2, 3, 4 and 5 have been applied. In the position of the parts shown in FIG. 1 movable auxiliary contacts, or auxiliary contact bridges, 2, 3 are in engagement with their fixed contacts b, b', and movable auxiliary contacts, or auxiliary contact bridges 4, 5 are out of engagement with their cooperating fixed contacts b and b, Hereinafter the fixed auxiliary contacts b, b adjacent fixed main contacts a, a will be referred to as first fixed auxiliary contact means, and the fixed auxiliary contacts b, b remote from the fixed main contacts a, a will be referred to as second fixed auxiliary contact means. The movable

auxiliary contacts

2, 3 form parallel current paths and are mechanically coupled, or tied together, for joint movement into, and out of, engagement with their cooperating fixed auxiliary contacts b, b. In a similar fashion movable auxiliary contacts, or contact bridges, 4, 5 form parallel current paths and are mechanically coupled, or tied together, for joint movement into, and out of, engagement with fixed auxiliary contacts b, b'. The mechanical coupling between movable auxiliary contacts, or contact bridges, 2, 3 has been indicated by reference character 9, and the mechanical coupling between movable auxiliary contacts, or contact bridges, 4, 5 has been indicated by reference character 10. All fixed auxiliary contacts b are conductively interconnected as indicated at 13, and leads 13 are conductively connected to the neutral point of the system indicated by character Y.

Fixed main contacts a, a and fixed auxiliary contacts b, b may be arranged on the inside of a cylinder of insulating material and supported by the radially inner surface thereof. The movable contacts, or

contact bridges

1, 2, 3, 4, 5 and 6 may be arranged inside the aforementioned cylinder and may be movable radially outwardly into engagement with their cooperating fixed contacts a, a and b, b. Mechanisms or linkages for effecting the aforementioned radial movement of movable contacts, or contact bridges, 1, 2, 3, 4, 5 and 6 are well known in the art and, therefore, do not need to be described in this context. Such mechanisms or linkages have been disclosed, for instance, in the aforementioned U.S. Patent 3,174,097 to which reference may be had for additional information in regard to appropriate contact operating means with which the structure according to the instant invention is intended to be associated.

The transfer switch T further comprises two pairs of switch-over resistors to which reference characters R R have been applied. Resistors R which may be referred to as first switch-over resistors have a relatively small ohmic value in comparison to switch-over resistors R which may be referred to as second switch-over resistors. Conductor means 14 are conductively connected to taps A and B, respectively, and each conductor means 14 establishes a series connection of first switch-over resistor R with first fixed auxiliary contact means b, b and with first movable auxiliary contacts, or contact bridges, 2, 5. Conductor means 15 establish a series connectionof second switch-over resistors R second fixed auxiliary contact means b, b and second movable auxiliary contacts, or contact bridges, 3, 4. Reference characters 7 and 8 have been applied to indicate conductor means serially connecting each of the aforementioned pair of movable main contacts, or contact bridges, 1 and 6 with the fixed auxiliary contact means b, b immediately adjacent thereto and with the first movable auxiliary contacts, or contact bridges, 2 and cooperating with these fixed auxiliary contact means.

It will be apparent from the foregoing that each of the movable contacts, or contact bridges, 1, 2, 3, 4, 5 and 6 establishes a pair of series breaks when separated from its cooperating fixed contacts a, a and b, b. This is the preferred embodiment of the invention. The structure shown in the drawings might, however, be modified by substituting for each pair of fixed contacts a, a; b, b cooperating with a movable contact, or contact bridge,

, 1, 6; 2, 3, 4, 5 a single pair of cooperating contacts of which one is fixed and the other movable. Such a modification would entail the substitution of one single point of break for each double break occurring in the structure illustrated in the patent drawings.

Movable contacts, or contact bridges, 1, 2, 3, 4, 5 and 6 are arcing contacts since they separate while carrying current. As a result, the aforementioned movable contacts, or contact =bridges, must be made of a metal or an alloy which has a sufiiciently high resistance against contact erosion and, consequently, a relatively limited current-carrying capacity. If the transfer switch shown in the drawings is intended to carry relatively large currents as, for instance, in the order of several hundred amps, then it is advisable to provide the structure with two additional pairs of current-carrying contacts of which one is arranged to shunt movable current-carrying contact, or contact bridge, 1 when the latter is in the closed position thereof, and the other is arranged to shunt the movable main contact, or contact bridge, 6, when the latter is in the closed position thereof. Since the provision of additional current-carrying contacts is well known in the art, and since their presence is not mandatory in structures embodying the present invention, current-carrying contacts have not been shown in the drawings.

As shown in FIG. 1, tap A is conductively connected to the neutral point of the system Y and the current path of the current then flowing includes the two contact bridges 1 and 2.

The tap-changing operation from tap A to tap B includes a number of steps which must be performed sequentially. These steps are opening of bridge 1; closing of bridges 4, 5; opening of

bridges

2, 3 and closing of bridge 6. Thus the first step consists in the separation of movable main contact, or contact bridge, 1 from its cooperating fixed contacts a, a.

In case that the current under interruption is of load current proportions rather than of overload current proportions the normal transient recovery voltage occurs after the series arcs kindled at the two breaks formed at movable main contact, or bridge, 1 are extinguished 4 and prior to engagement of movable auxiliary contacts 4, 5 and their cooperating fixed contacts b, b (FIG. 2). In that instance the transient recovery voltage U is determined by the equation wherein I is the current flowing through the aggregate resistance determined by the resistances R R of the aforementioned switch-over resistors R and R In case of relatively onerous circuit interrupting conditions as, for instance, interruption of relatively high overload currents, the series arcs formed at movable main contact, or contact bridge, 1 may not be extinguished at the time when the movable auxiliary contacts, or contact bridges, 4, 5 engage their cooperating fixed contacts b, b (FIG. 2). In such instances the switch-over resistor R shunts the two series breaks at movable main contact, or contact bridge, 1 upon separation of auxiliary contacts, or contact bridges, 2, 3 from their cooperating fixed contacts b, b. The two series breaks formed by auxiliary contact, or contact bridge, 2 are then connected in series with the two breaks formed at movable main contact, or contact bridge, 1. The series arcs formed at main contact, or contact bridge, 1 and at auxiliary contact, or contact bridge, 2 will extinguish at the first zero of the current wave, and thereafter there will be a tendency of reignition of the series arcs. As a result of the mode of operation of the transfer switch, the arc gaps adjacent contact bridge 2 will be shorter than the arc gaps adjacent contact bridge 1; hence, if there is a reignition of arcs following a zero of the current wave, such reignition will occur at the breaks formed adjacent contact bridge 2 rather than at the breaks formed adjacent contact bridge 1. The portion of the transient recovery voltage then prevailing across the series breaks formed adjacent contact bridge 1 is determined by the voltage drop across switch-over resistor R having the relatively smaller ohmic value. Accordingly, that portion of the transient recovery voltage is relatively small.

Since the total switch-over resistances required for performing a tap-changing operation are subdivided into two parallel resistances R and R it is possible, without changing the aforementioned total resistances, to assign to the partial resistance R a sufficiently small value to effectively limit the transient recovery voltage at the breaks formed adjacent contact bridge 1. By so doing, the dangerof reignition of an arc formed between contact bridge 1 and its cooperating fixed contacts a, a may be entirely eliminated. This, in turn, makes it possible to increase significantly the interrupting capacity of the transfer switch.

As shown in FIG. 3 contact bridge 6 has engaged its cooperating fixed contacts a, a, thus substituting tap B of transformer winding Tr for tap A.

As a result of the fact of the subdivision of the switchover resistances into two partial resistances R R which are connected in parallel,

contact bridges

2, 3, 4, 5 do not carry currents of the same magnitude during tapchanging operations. The total current carried by

contact bridges

2, 3 and 4, 5, respectively, is subdivided in accordance with the ratio of the resistances of resistors R R

Auxiliary contacts

2, 5 and auxiliary contacts 3, 4 must have different parameters to conform to the specific requirements imposed by the difference of their switching duties.

It will be apparent from the foregoing to those skilled in the art that various changes and modifications may be made without departing from the spirit of the invention as set forth in the appended claims.

I claim as my invention:

1. In a transfer switch for tapped regulating transformers including sequentially operable movable main contacts and auxiliary contacts and switch-over resistors operatively related to said main contacts and to said auxiliary contacts the combination of:

(a) a pair of spaced fixed main contacts means;

(b) a pair of movable main contacts, each of said pair of movable main contacts being movable into and out of engagement with one of said pair of fixed main contact means;

(c) two pairs of fixed auxiliary contact means arranged inside of a space bounded by said pair of fixed main contact means, each of said two pairs of fixed auxiliary contact means including a first fixed auxiliary contact means and a second fixed auxiliary contact means;

(d) two pairs of movable auxiliary contacts, each pair of said two pairs of movable auxiliary contacts including a first movable contact and a second movable contact forming parallel current paths and being mechanically coupled for joint movement into and out of engagement with one of said pairs of fixed auxiliary contact means;

(e) two pairs of switchover resistors, each of said two pairs of switch-over resistors including a first switchover resistor having a relatively small ohmic value and a second switch-over resistor having a relatively large ohmic value;

(f) conductor means serially connecting said first switch-over resistor of each of said two pairs of switch-over resistors with said first fixed contact means of one of said two pairs of fixed auxiliary contact means and with said first movable auxiliary contact of one of said two pairs of movable auxiliary contacts;

(g) conductor means serially connecting said second switch-over resistor of each of said two pairs of switch-over resistors with said second fixed auxiliary contact means of one of said two pairs of fixed auxiliary contact means and with said second movable contact of one of said two pairs of movable auxiliary contacts; and

(h) conductor means serially connecting each of said pair of movable main contacts with said first fixed auxiliary contact means of one of said two pairs of fixed auxiliary contact means and with said first movable auxiliary contact of one of said two pairs of movable auxiliary contacts.

2. A transfer switch as specified in claim 1 wherein each of said movable main contacts and each of said movable auxiliary contacts is formed by a movable contact bridge having two spaced points of contact, and wherein each of said fixed main contact means and each of said fixed auxiliary contact means includes two spaced fixed contacts having the same spacing as said two spaced points of contact.

3. In a transfer switch for tapped regulating transformers including sequentially operable movable main contacts and auxiliary contacts and switch-over resistors operatively related to said main contacts and to said auxiliary contacts the combination of:

(a) two pairs of fixed main contacts;

(b) a pair of parallel main contact bridges each movable into engagement with and out of engagement with one pair of said two pairs of fixed main contacts;

(0) four pairs of fixed auxiliary contacts arranged inside of an area bounded on one side by a straight line interconnecting one pair of said two pairs of fixed =main contacts and bounded on the other side by a straight line interconnecting the other pair of said two pairs of fixed main contacts, said four pairs of fixed auxiliary contacts including two pairs of fixed auxiliary contacts each arranged relatively close to one of said pair of main contact bridges, and said four pairs of fixed auxiliary contacts further including two pairs of fixed auxiliary contacts each arranged relatively remote from one of said pair of main contact bridges;

(d) conductor means permanently short-circuiting one of the fixed auxiliary contacts of each of said four pairs of fixed auxiliary contacts;

(e) two pairs of parallel auxiliary contact bridges, one auxiliary contact bridge of each of said two pairs of auxiliary contact bridges being arranged relatively close to, and the other contact bridge of each of said two pairs of auxiliary contact bridges being arranged relatively remote from one of said pair of main contact bridges, each auxiliary contact bridge of said two pairs of auxiliary contact bridges being movable into engagement with and out of engagement with one pair of said four pairs of fixed auxiliary contacts;

(f) a pair of mechanical coupling means each coupling one auxiliary contact bridge arranged relatively close to and one auxiliary contact bridge arranged relatively remote from one of said pair of main contact bridges for joint movement in engagement direction and in out of engagement direction;

(g) a pair of resistors each having a relatively large ohmic value and each being arranged to be connected in series with one of said auxiliary contact bridges arranged relatively remote from one of said pair of main contact bridges; and

(h) a pair of resistors each having a relatively small ohmic value and each being arranged to be connected in series with one of said auxiliary contact bridges arranged relatively close to one of said pair of main contact bridges, each of said pair of resistors having a relatively small ohmic value being conductively connected at the ends thereof to one pair of said two pairs of fixed main contacts to shunt one of said pair of main contact bridges when in substantially engaged position thereof by a relatively small resistance, and each of said pair of resistors having a relatively large ohmic value and each of said pair of resistors having, a relatively small ohmic value having a common end each conductively connected to one contact of said two pairs of fixed main contacts.

References Cited UNITED STATES PATENTS 3,014,999 12/1961 Pensis.

FOREIGN PATENTS 1,354,591 1/1964 France.

ROBERT S. MACON, Primary Examiner.

US. Cl. X.R.

PO'WFJO UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 {a}? Dated Ma 2Q 1252 Inven ofls) Alexander Bleibtreu It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

{an Column l,- insert after line 8 laims priority, application Germany, April 24, 1965,

Sit: all Aim QEALH) JAN 6 "1970 (SEAL) Meat:

Edward M. Fletcher, 1:. WILLIAM E. PSOHUYIER, J'R.

00 n1 Attesting OfflCCl m1 atents