EP0281622B1

EP0281622B1 - Circuit breaker

Info

Publication number: EP0281622B1
Application number: EP19870906398
Authority: EP
Inventors: Jan Windfeld; Lajos Marot
Original assignee: Holec Systemen en Componenten BV
Current assignee: Eaton Holding International I BV; Danfoss Power Solutions II BV
Priority date: 1986-09-19
Filing date: 1987-09-04
Publication date: 1993-11-24
Anticipated expiration: 2007-09-04
Also published as: EP0281622A1; FI882341A; DK450286A; FI882341A0; FI88084B; AU8073587A; DE3788277T2; FI88084C; ES2005325A6; WO1988002178A1; DE3788277D1; GR871434B; DK158422B; AU603616B2; DK158422C; DK450286D0

Abstract

Circuit breaker with a number of movable contact members (20) and a corresponding number of fixed contact members (25, 26) where at least one of the contact members comprises a spring-loaded set of contact rolls (20) with several rolls (21, 22, 23, 24) arranged in such a way as to contact plane side surfaces of two contact bars (25, 26) between the rolls, said rolls being able to glide or roll on said surfaces during the closing and opening of the circuit breaker. In order to limit the necessary travel of the movable contact members between the closing and the opening it is suggested to arrange the set of contact rolls (20) and the co-operating contact bars (25, 26) so that they form a stepped engagement. Thus the physical dimensions of the circuit breaker are reduced compared to the prior art, even with circuit breakers with several poles and for heavy currents.

Description

Technical Field

The invention relates to a circuit breaker with a number of movable contact members and a corresponding number of fixed contact members, where at least one of the contact members comprises a spring-loaded set of contact rolls with several rolls arranged in such a way as to contact plane side surfaces of two contact bars between the rolls, said rolls being able to glide or roll on said surfaces during the closing and opening of the circuit breaker.

Background Art

Several circuit breakers with contact rolls are known. Circuit breakers for heavy current are normally equipped with several rolls mounted in pairs for each phase so as to split the heavy current into several parallel currents through four, six, or more rolls. One of the consequences of such a splitting into several rolls is, however, that the travel of the movable contact member during opening and closing increases with the number of rolls employed. Thus the circuit breaker housing and the built-in mechanical parts become correspondingly larger. The set of rolls closest to the fixed contact in the open position is exposed to great wear, since this set of rolls alone carries the full current just after opening and just before closing, i.e. the current capacity as well as the breaking capacity of the circuit breaker is in reality limited to the ability of this one set of rolls. DE-A-32 23 669 describes an arrangement having two contact rolls for each contact bar.

Description of the Invention

It is the object of this invention to provide a circuit breaker arrangement for heavy currents, e.g. 63 A or 125 A, said arrangement enabling a decrease in size of circuit breakers and their housings for such currents compared to known ones by means of shortening the travel of the contact rolls between the open and the closed position.
This object is solved by the features of the claims.
According to the invention it is suggested that the set of contact rolls and the contact bars co-operating with the set are arranged to form a stepped engagement. Such a stepped engagement results in a more or less simultaneous closing or opening of the different contact rolls, i.e. if one roll is in the open position, all rolls are in the open position, so that the travel of the movable contact member is reduced. Although the set of contacts comprises three pairs of rolls the travel may be limited to the travel necessary to open a single pair of rolls. The short travel results in reduced space requirements per phase so that the overall dimensions of the circuit breaker are considerably reduced, although there are e.g. four or more parallel rolls. Another advantageous consequence of the short travel is an immediate splitting of the current through the parallel rolls and thus an increase of the current capacity of the circuit breaker as well as a decrease of the repelling forces during the closing operation (repelling forces are the electromagnetic forces arising when a heavy current is initiated between two contacts brought in touch with each other).
The circuit breaker is preferably provided with an even number of contact rolls two and two alike, thus forming pairs with one or more stepwise increasing dimensions. Typically four rolls are used, two large ones and two small ones, their absolute size depending on the current the circuit breaker is to be dimensioned to.
It is known to mount the movable contact means of a multi-pole circuit breaker on a translatorally displaceable contact bridge. According to an embodiment of the invention the length of the displacement is almost equal to the distance between the centre axes of two successive contact rolls, said length of the displacement being necessary to transfer the contact bridge from an open position - where the contact rolls and the contact bars are spaced by an air gap large enough to ensure the breaking of a current and to avoid voltage breakdowns - to a closed position - where all contact rolls are in contact with the contact bars. Since the distance the contact bridge has to travel is shorter than previously known, the circuit breaker and thus its housing may be reduced in size. The mechanism transferring the rotational movement of a handle to a translatory displacement of the contact bridge is also simplified.
According to an embodiment of the invention it is suggested to provide a circuit breaker with contact rolls in such a way that all contact rolls in a set of contact rolls have the same diameter, but each pair has a different length and that the two shortest rolls are placed closest to the contact bars, and that the longests rolls are placed furthest away from the contact bars, and that the contact bars on the edges facing the set of contact rolls are stepped with a pitch of each step corresponding to the difference in length of the contact rolls, and that distances between opposite steps are so much longer than the corresponding roll contacts that there is an air gap everywhere between contact rolls and contact bars in the open position.With a set of connected contact rolls and contact bars of the above type the set of contact rolls is displaced by a travel corresponding to the distance between the centre axes of two adjacent rolls in each pair. Care has to be taken, however, that the above air gap is large enough to prevent voltage breakdowns in the circuit breaker.
In another embodiment the distance between the individual contact rolls measured in the direction perpendicular to the side surfaces of the contact bars decreases stepwise so that the two rolls closest to the contact bars they cooperate with have the largest distance from each other, while the two rolls farthest away have the smallest distance from each other, and that the contact bars correspondingly have a narrow bar part along the edge facing the set of contact rolls, said bar part being of a thickness corresponding to the distance between the farthest pair of contact rolls and increasing in thickness from there stepwise corresponding to the distance between the contact rolls. In this embodiment all contact rolls have the same length. The contact surfaces obtained between the contact rolls and the contact bars are larger compared to the aforementioned solution. The main object of the invention, the short travel, is also achieved, Means must, however, be provided to prevent the generally spring-loaded contact rolls from being pressed into contact with the bars in the open position of the circuit breaker. In this embodiment it is also important that the set of contact rolls and the contact bars are formed in such a way as to co-operate by direct contact in the closed position, whereas there must be an air gap everywhere between rolls and bars in the open position, said gap being large enough to avoid voltage breakdowns.
To further increase the power handling capacity of the circuit breaker, the division into several pairs of rolls may be extended to include a division into a main contact and a spark contact. With such a division one or two rolls are selected to be spark contacts and this spark contact is always to be closed first and opened last. This is achieved by adjusting the position of the contact rolls or by adjusting the length or thickness of the step(s) in question on the contact bar. It will be appreciated that also this embodiment possesses the characteristic part of the present invention, i.e. that the rolls open approximately simultaneously, and the advantages connected thereto, especially the very short travel. Preferably the smallest or the two smallest contact rolls are chosen as spark contacts, but the largest and thus most robust rolls may also be selected. The choice depends i.a. on the service possibilities available where the circuit breaker is mounted.
In an especially preferred embodiment a number of standard sizes are predetermined for the contact rolls, said standard sizes corresponding to typical standard dimensions of circuit breakers. Thus a given size of contact rolls may be used as largest contact roll in one circuit breaker for a given current and as a "smaller" contact roll in another circuit breaker for a somewhat heavier current. Thus the number of different sizes for contact rolls to be kept in stock is reduced.

Brief Description of the Drawings

The invention is explained further in the following and with references to the accompanying drawings in which

Fig. 1 shows, in a lateral, diagramatic view of a first embodiment for a set of contact rolls and two fixed current bars in an open position,
Fig. 2 shows a section through an example of the embodiment of the set of contacts of Fig. 1 along the line II-II,
Fig. 2a shows an exploded view of the set of contact rolls of Fig. 2,
Fig. 3 shows the same embodiment as Fig. 1 but in closed position,
Fig. 4 shows a diagramatic view of an embodiment with four pairs of contact rolls,
Fig. 5 shows a diagramatic view of another embodiment of a contact set and current bars in open position,
Fig. 6 shows another variation of the embodiment of Fig. 5
Fig. 7 shows a diagramatic view of a third embodiment of a contact set with the contact bar in an open position,
Fig. 8 shows the embodiment of Fig. 7 in a closed position,
Fig. 9 shows an example of a retainer in a spring-loaded set of contact rolls,
Fig. 10 shows an example of an alternative spring arrangement,
Fig. 11 shows a sketch of the basic arrangement of a known circuit breaker with contact rolls, and
Fig. 12 shows another example of a similar, known circuit breaker arrangement.

The new circuit breaker is developed for the use in circuit breakers with three or four poles, e.g. of the known type of Figs. 11 and 12, i.e. circuit breakers with several current bars, especially three or four current bars R, S, T and O with circuit breaker functions in the three phases, and possibly also at the O-terminal, as suggested in Figs. 11 and 12. The four current bars may be situated in mutually parallel planes, as shown in Fig. 11, or parallel in the same plane, as shown in Fig. 12. Via movable contact rolls 20 on a displaceable contact bridge 60 the four current bars R, S, T and O are electrically connected with four corresponding current bars designated R', S', T' and O' on the other side of the contact bridge. The contact bridge 60 may be shaped in many different ways and in the drawing it is only suggested with a "dot and dash" line and a double arrow indicating the displacement direction. The moving mechanism is not shown but may be realised in many ways as well known to those skilled in the art, and may be a manually initiated circuit breaking effectuated by turning or rocking of a handle, the movement of the switch being transferred to a translatory displacement of the contact bridge 60 via the moving mechanism. The circuit breaker may also be provided for automatic opening and closing.
For clarity's sake only two contact rolls are shown in the front of each current bar in the drawing, since it is considered obvious for those skilled in the art that there are, of course, also two corresponding rolls in the back of the current bar. Depending on the denominated current flow there may be a different number pairs of contact rolls. During the opening and closing of a circuit breaker the travel of the contact bridge has to be so long that all contact rolls are disconnected from the contact bar. As a consequence the circuit breaker housing has to be large enough to allow space for the necessary travel. A long travel associated with many contact rolls entails a more complicated moving mechanism and increases the time passing between an inititated opening or closing respectively and its completion.
In the following a new type of contact roll set for the above described multipole circuit breaker is disclosed and the following Figures illustrate examples of different embodiments of a set of contact rolls and its bars. It will, however, be appreciated that the new type of contact rolls may, of course, also be used in a circuit breaker with one or two poles.
In the first embodiment of Figs. 1-3 a set of contact rolls 20 with four rolls 21, 22, 23, 24 is employed, said rolls forming pairs two and two and all of them possessing the same diameter but different lengths L, l, with the two rolls 21, 22 closest to the fixed contacts 25 and 26, said rolls being shorter than the two other rolls and forming a pair. Correspondingly the fixed contacts 25 and 26 are provided with a recess for the smallest pair of contact rolls 21, 22 to fit this recess without touching the fixed contacts until the large contact rolls 23, 24 are in contact with the fixed contacts. As shown in Fig. 1 the recess is made exactly as deep as necessary to allow the two contact pairs to come into contact with the fixed contact approximately simultaneously. It is an important advantage of the present invention that all contact rolls connect approximately simultaneously. In this case simultaneousness is understood to be within approx. 5 msec, i.e. within the same quarter wave period at 50 Hz. As is obvious for those skilled in the art, a wholly exact simultaneousness is impossible and it is thus in the above embodiment impossible to decide immediately which contact roll is the first to make or break the circuit. In a variation of the embodiment of Figs. 1-3 it is therefore suggested to reduce the shown recess slightly in size so that the smallest contact pair 21, 22 comes into contact first and breaks the contact last. This contact pair thus forms a spark contact while the contact pair 23, 24 forms a so-called main contact. In this embodiment it is advantageous to make the two spark contacts 21, 22 and possibly the part of the fixed contact in connection with the spark contact of a more resistant material than ordinary copper and/or subject this contact to a special surface treatment thus rendering it more resistant towards the burns a spark contact is exposed to. In an alternative embodiment the described recess is slightly deeper so that the contact pair 23, 24 is to constitute the spark contact. It is to be stressed in this connection that the difference between the closing moments is minimal in the proposed embodiment, in principle it still applies that the described contact rolls close approximately simultaneously. Fig. 3 shows the position of the contacts in the closed position. Comparing Fig. 1 and Fig. 3, it is evident that the travel of the set of contacts from the open position to the closed position corresponds to the length of the arrow of Fig. 1. The travel corresponds on the whole to the travel required to close the contact of a single roll and this applies regardless of the number of rolls.
The contact rolls shown may be mounted in several, known ways, e.g. as shown in the Danish Patent Specification 142.254, or as illustrated in Figs. 5, 6 and 7 in a retainer 50 with one or more springs F, pressing the contact rolls together in order to ensure a suitable contact pressure when the contact rolls slide in on each side of a corresponding, fixed contact bar. By selecting suitably strong springs a sufficient contact pressure is ensured. It may be advantageous to adjust the force of the spring according to the dimensions of the contact roll in question.
One example of a possible embodiment of a set of contact rolls is shown in Figs. 2 and 2a. This set of contact rolls comprises an approximately T-shaped piece of iron 27, a spring washer 28a with a corresponding counterpart 28b, four contact rolls 21, 22, 23, 24 partially resting against the spring washers 28a and 28b and partially held together by the clamps 29a and 29b. Between the rolls 21, 24 and 22, 23 and their clamps 29a and 29b is a spacer 19 with a thickness corresponding to the thickness of the contact bar. The parts 28a, 29a, 19, 29b and 28b are all provided with a longitudinal slot for the passage of the leg of the T-shaped piece of iron 27. Above the last spring washer 28b there is a helical spring and the whole arrangement is held together by a locking plate 17 provided to be pressed down on the T-shaped leg and then being turned approx. 90° . The central spacer 19 is furthermore provided with extensions 19a co-operating with means on a displaceable contact bridge provided for this purpose in order to lock the set of contact rolls to the contact bridge with the help of tools provided for this purpose (prior art). A set of contact rolls may be arranged in many different ways and the above is just one example of an embodiment.
Fig. 4 shows a contact set arranged according to the same principle but with four pairs of contact rolls and four steps. As evident from the Figure such a contact type may be provided with more or fewer rolls according to requirements. Also in the case of four pairs of rolls the necessary travel of the contact bridge from the closing to the opening position corresponds only to the travel of one contact set with a single roll or two rolls. In this embodiment it is also possible to choose to let one of the rolls act as a spark contact.
In another embodiment the rolls have different diameters, as illustrated in Fig. 5. In this embodiment the rolls may have the same but also stepped length. The rolls 31 and 32 have a small diameter d, whereas the rolls 33 and 34 have a larger diameter D. Correspondingly the fixed contact is comparatively narrow along the outer edge close to the movable contact members so that the small contact rolls 31 and 32 slide in across the close, narrow part 35 of the fixed contact without touching it, whereupon the small contact rolls 31 and 32 are connected with the wide part 37 approximately simultaneously with the narrow part 35, said part being connected to the two large contact rolls 33, 34. In this embodiment it is also possible to choose to let one pair of contacts act as a spark pair and to adapt the dimensions in such a way as to let this contact pair make the contact first and break it last. In this case it is, however, only a question of small changes in dimensions so that is still applies that the contacts connect approximately simultaneously.
In the example of Fig. 6 the smallest contact rolls 31' and 32' are provided to come into contact with the thin parts 35 of the bars, whereas the large contact rolls 33' and 34' are in contact with the thick parts 37 of the bars. Since the electromagnetic forces between the contact rolls arranged in parallel in one pair of contacts, e.g. 31 and 32, are proportional to the length of the contact rolls and inversely proportional to their mutual distance (corresponding to the length and width of the air gap), it may be advantageous to use individual spring loads for each pair of contact rolls, as suggested in Fig. 6, or for each contact roll, as suggested in Fig. 5. In the embodiment of Fig. 6 the thick parts 37 of the bars may be coated with a more resistant material thus making the bars resistant to spark formation. In this case the rolls 33' and 34' are equally made of a correspondingly spark-proof material.
In Figs. 7 and 8 a variation is shown where the contact rolls used have the same diameter but are mounted with different mutual distances. Thus the same effect as the one in the arrangements of Figs. 5 and 6 is in principle obtained. The rolls 41 and 42 possess a larger distance from each other than the rolls 43 and 44 and the correspondingly fixed contact 46 is provided with a set of steps so that the four contact rolls open simultaneously when they are drawn away from the fixed contact. Also in this case it is possible to designate one or two rolls to be spark contacts and to have them and possibly the corresponding part of the bar made of an especially spark-proof material. It is obvious that the arrangement shown may be extended to hold six, eight or more rolls.
In the embodiments of Figs. 5, 6 and 7 it is important that the retainer 50 is shaped as to maintain a predetermined, minimum distance between the contact rolls of each pair of contact rolls in the open position. It is evident for those skilled in the art that this is realized in many different ways. One example of a possible embodiment is illustrated in Fig. 9, showing a section through a retainer, where there is provided a guidance shaped like an elongated hole 51 for the contact rolls as well as support surfaces and possibly guidances for pressure springs pressing the rolls against each other.
It has to be stressed that it is also within the scope of this invention to provide a retainer with tension springs, e.g. as suggested in Fig. 10, where the two springs 53 and 56 pull the roll 21 down and the two tension springs 54 and 55 pull the roll 22 up. 57 and 58 are separating walls provided with an elongated guidance for the contact rolls, as shown in Fig. 9.
The invention may be varied in many ways. It is thus within the scope of the invention to vary one or more of the parameters, the length of the roll, diameter, distance as well as spring pressure within the same set of contact rolls.

Claims

Circuit breaker with a number of movable contact members (20) and a corresponding number of fixed contact members (25, 26) where at least one of the contact members comprises a spring-loaded set of contact rolls (20) with several rolls (21, 22, 23, 24) arranged in such a way as to contact plane side surfaces of two contact bars (25, 26) between the rolls, said rolls being able to glide or roll on said surfaces during the closing and opening of the circuit breaker characterised in, that each of the contact bars (25, 26) has a stepwise configuration having at each step at least one contact surface being engageable with a respective roll of the set of contact rolls (20).
Circuit breaker according to claim 1 and of the kind where the movable contact members are mounted on a translatorally displaceable contact bridge (60), characterised in that the length of the displacement is almost equal to the distance between the centre axes of two successive contact rolls, said length of the displacement being necessary to transfer the contact bridge from an open position - where the contact rolls and the contact bars are spaced by an air gap large enough to ensure the breaking of a current and to avoid voltage breakdowns - to a closed position - where all contact rolls are in contact with the contact bars.
Circuit breaker according to claim 1 or 2, characterised in that all contact rolls (21, 22, 23, 24) in a set of contact rolls (20) have the same diameter but each pair has a different length (L, l), and that the two shortest rolls are placed closest to the contact bars (25, 26), and that the longests rolls are placed furthest away from the contact bars (25, 26), and that the contact bars on the edges facing the set of contact rolls are stepped with a pitch of each step corresponding to the difference in length of the contact rolls, and that distances between opposite steps are so much longer than the corresponding roll contacts that there is an air gap everywhere between contact rolls and contact bars in the open position.
Circuit breaker according to claims 1 or 2, characterised in that the distance between the individual contact rolls measured in the direction perpendicular to the side surfaces of the contact bars decreases stepwise so that the two rolls (31, 32, and 41, 42) closest to the contact bars (37, 46) they co-operate with have the largest distance from each other, while the two rolls farthest away have the smallest distance from each other, and that the contact bars correspondingly have a narrow bar part (35, 45) along the edge facing the set of contact rolls, said bar part being of a thickness corresponding to the distance between the farthest pair of contact rolls (33, 34, 43, 44) and increasing in thickness from there stepwise corresponding to the distance between the contact rolls.
Circuit breaker according to claim 4, characterised in that the diameters of the contact rolls decrease stepwise in pairs.
Circuit breaker according to claim 5, characterised in that all contact rolls have the same length.
Circuit breaker according to any of claims 1-6 characterised in that the stepped engagement is supplemented with an individually or pairwise stepped spring load for each roll or pair of rolls.
Circuit breaker according to any of claims 1-7, characterised in that the contact set is divided into at least one main contact and at least one spark contact, and that the spark contact and/or the corresponding part of the contact bar is either made of a material especially resistant to burns after spark formation or is surface-treated with a resistant coating.