US1852868A - Electric circuit breaker and the like - Google Patents

Description

April 5 1932. w B WHITNEY ET AL ELECTRIC CIRCUIT BREAKER AND THE LIKE Filed July '7, 1924 Patented Apr. 5, 1932 UNITED STATES PATENT OFFICE WILLIS BEVAN WHITNEY AND EDMUND BASIL WEDMORE, OF WESTMINSTER, LONDON, ENGLAND, ASSIGNOR-S TO THE BRITISH ELECTRICAL AND ALLIED INDUSTRIES RESEARCH ASSOCIATION, OF LONDON, ENGLAND, A BRITISH ASSOCIATION ELECTRIC CIRCUIT BREAKER AND THE LIKE Application filed July 7, 1924, Serial No. 724,569, and in Great Britain September '7, 1923.

This invention relates to multi-pole circuit breakers for rupturing multi-phase alternating electric current circuits. The term circuit breakers employed in this specification and in the claims is intended to include switches and like means used for breaking alternating electric current circuits. The invention is directed more particularly to improvements in means by which a circuit is broken between contacts under oil or other fluid although it is not limited to this feature.

The term pair of contacts used hereinafter is to be understood as meaning two co-operable arcing contacts between which an arc is drawn when the circuit breaker operates to break the circuit, one of said contacts being usually fixed while its co-operating contact is movable (there may be other and heavier contacts in parallel with these which are so arranged that no arcs are drawn by them).

For the purpose of this specification, a pair of contacts separates or is separated or separation of a pair of contacts occurs immediately upon complete cessation of mechanical contact, i. e. when arcing would be presumed to commence, if a current were flowing through a pair of contacts. Such a pair of contacts, when separate, forms one break or point of breaking.

A circuit breaker element, of the circuit breaker is used herein to mean that part of the circuit breaker connected in series with one of the several conductors in the multiphase circuit in which the circuit breaker is used, each conductor connecting a separate terminal of the source with a separate terminal of the load, for example, a triple-pole or triple-element circuit breaker has three circuit breaker elements irrespective of the number of breaks or pairs of contacts that there may be in each or any circuit breaker element.

In multi-pole circuit breakers generally employed hitherto wherein the separation of two or more pairs of contacts takes place simultaneously or substantially simultaneously there is a great variation in the result of breaking the circuit, these variations depending, amongst other features, upon the instantaneous current value at the time of separation. The energy liberated in the circuit breaking device (in the form of heat generated by the are which occurs between the contacts with separation) may be negligible in amount or may be very large with identical external circuit conditions depending, as above stated, upon the instantaneous current value.

The object of the present invention is to reduce, in any particular case, the average amount of energy and also the maximum energy so liberated in the circuit breaking device, and thereby to increase the rupturing capacity of the device.

According to this invention a multi-pole circuit breaker for multi-phase alternating current electric circuits, comprises a circuit breaker element in each phase, a plurality of switch elements each of which comprises at least two pairs of contacts in series and operating means for separating the pairs of contacts, the contacts and operating means being so shaped and disposed that no two pairs of contacts separate simultaneously and one separation of a pair of contacts occurs on each element before separation of a second pair of contacts occurs on any element and the separations of the second pairs of contacts on the several elements occur in the same order of elements as the separations of the first pairs of contacts.

By the invention the advantage is obtained that when a fault occurs between two conductors of, for example, a three-phase system, the pairs of contacts of the two circuit breaker elements in series with the said conductors are all in series, and as the pairs of contacts separate in succession an increased rupturing capacity is obtained. In the case of a short circuit across all three conductors one switch element will rupture first and thereafter the current will traverse the remaining two breaks in series.

In order that the invention may be more clearly understood, a description of some preferred embodiments of circuit breaking devices will now be described with the aid of the accompanying drawings in which Figure 1 represents diagrammatically one form of the invention,

*igur-e 2 represents in a similar manner a second form of the invention,

Figure 3 is a view of the parts shown in Figure 2, seen from the left of that figure,

Figure 4 shows diagrammatically a circuit breaking element of a further alternative embodiment, and

Figure 5 shows on a lar er scale than Figure 1 the means for adjusting a contact piece.

Like reference numerals indicate like parts where they apply in the several figures of the drawings.

In Figure 1 a well-known type of circuit breaker is illustrated in each element of which a movable main brush contact member 10 is shown as co-operating with two fixed contact members 11. There is provided also as is well known, two pairs of sparking contacts 12 and 13 which constitute in this example the pairs of contacts connected in ries referred to above. The contacts 12 are movable with the brush contact 10 by means of a plunger rod 14 and a carrier frame member 15 which are resiliently pressed towards the contacts 13 as shown in Figures 1 and 5. The mounting of the contacts 12 on the member 15 is by means of bolts 18 which may be of varying lengths and of which the effective lengths may be adjusted by screwing them into and out of threaded holes in the contacts 12. Springs 19 urge the contacts 12 towards the contacts 13. The three plunger rods 1st of the three switch elements are connected together by means of a crossbar 17 so as to move together. For purposes of clarity the pairs of contacts are shown coplanar in Figure 1. It will be appreciated that in practice the three switch elements would normally be arranged parallel with one another, i. c. with the members 15 extending at right angles to the plane of the paper.

It will be seen that the bolts 18 upon which the contacts 12 are carried are of different lengths so that the several pairs of contacts 12 and 13 will not separate simultaneously but successively. According to the invention advantage is taken of the fact that, for ex ample, on a triple element circuit breaker for a three-phase circuit such as that shown in Figure 1 the contacts on at least two elements of the circuit breaker are involved in every short circuit between phases. By adjusting the contacts so that those of the two elements do not open simultaneously, a reduction in the amount of energy liberated by the arc is obtained.

Any two of the three poles may be involved in a short circuit between phases and good results are obtained by adjusting the contacts so that the pair of contacts in each pole separate with an interval of ths of a cycle and the first contact to break on each pole separates with an interval of /glL-ll of a cycle in advance of the adjacent pole, thus the contacts on the three poles separate all of them consecutively with th period interval with a total interval of ths of a period between the opening of the first and the last.

As the speed and contact movement of the circuit breaker has not a definite value for all constructions and makes, it will be understood that the invention is not confined to the precise dimensions described above.

In order to make provision for possible variations, it is found best in commercial practice to adjust the interval between contact separations for the least speed of contact movement likely to be met, and it is found where several breaks are employed that there is less loss by extending the interval somewhat beyond the optimum value than by reducing itby the same amount.

In applying this device to a triple pole double break circuit breaker for a 50 cycle circult and having a speed of break of 50 inches per second, which is a representative figure, the above periods or cycles are represented in fractions of an inch, th of a period bein th of an inch and the contacts being ad justed with a maximum difference in (ll-- mensional adjustment of %thS of an inch.

These dimensions become larger on circuit breakers with accelerating springs or other means giving hi her speed of break.

In Figures 2 and 3 the invention is illus trated in its application to a circuit breaker having plunger contacts. In this example again the main fixed contacts are denoted by the reference numerals 11 and the auxiliary contacts by the reference numerals 12 and 13. The pairs of the latter are arranged, as will be readily seen, to separate in succession not simultaneously, the three pairs of contacts on the left of Figure 2 separating first in the order from the nearest to the furthest and the three pairs of contacts on the right of the figure separating subsequently also in the order from the nearest to the furthest.

In both examples illustrated respectively in Figure 1 and Figures 2 and 3, the circuit is finally broken at the auxiliary contacts 12 and 13. In some cases, however, it is possible to dispense with the auxiliary contacts and to separate the main contacts in such a manner that one portion of it, for example, one of the contacts 11 and its co-operating face of the contact 10, is separated before the other pair of engaging surfaces 10 and 11.

In Figure 4 is illustrated a well known type of multiple break circuit breaking element in which the main contact members 11 are situated outside the auxiliary members and the latter are carried, both fixed and movable members on insulating supports 16. The auxiliary contacts are so arranged that when the bridge 15 with the movable contact member 10 is lowered to separate the main contacts, the auxiliary contacts subsequently separate in succession. It will be appreciated that the circuit breaker comprises one or more fur ther contact elements similar to that shown, the moving parts of all the elements being connected so as to move together. The adjustment of the length of the auxiliary contacts is exaggerated in the drawings to make this feature quite clear, and it will be seen that the separation of the auxiliary contacts in the elements shown occurs in succession from right to left. T he lengths of the ant;- iliary contacts in the other switch elements will be such that a separation on each of these elements is interposed between two consecutive separations on the elements shown.

We claim 1. A multi-pole circuit breaker "for multiphase alternating current comprising a plurality of switch elements each of which comprises at least two pairs of contacts in series and operating means for separating the pairs of contacts, the contacts and operating means being so shaped and disposed that no two pairs of contacts separate simultaneously and one separation or" a pair of contacts occurs on each element before separation of sec ond pair of contacts occurs on any element and the separations of the second pairs of contacts on the several elements occur in the same order of elements as the separations of the first pairs of contacts.

2. A multi-pole circuit breaker for multi phase alternating current comprising a plurality of switch elements each of which comprises at least two pairs of contacts in series and operating means for separating the pairs of contacts, the contacts and operating means being so shaped and disposed that the separations of the several pairs of contacts occur at substantially equal intervals of time and separation of one pair of contacts on each element occurs before the separation of a second pair of contacts on any element, and the separations of the second pairs of contacts on the several elements occur in the same order of elements as the separations of the first pairs of contacts.

3. A three-pole circuit breaker for threephase alternating current comprising threeswitch elements each of which comprises two pairs of contacts in series, and operating means for separating the pairs of contacts, the contacts and operating means being so shaped and disposed that the several pairs of contacts separate substantially at intervals of one eighth of a cycle, and separation of one pair of contacts on each element occurs before the separation of a second pair of contacts on any element, and the separations of the second pairs of contacts on the several elements occur in the same order of elements as the separations of the first pairs of contacts.

4. A multi-pole circuit breaker for multiphase alternating current comprising a plurality of switch elements, carriage means for moving all the movable contacts together and at least two pairs of contacts in series in each switch element so shaped and mounted on the carriage means that the separations of the several pairs of contacts occur at different positions of the carriage means in the opening movement, and between the positions of the carriage corresponding to successive separations in any one element there are positions oi the carriage corresponding to a separation in each of the other elements. In testimony whereof we have signed our names to this specification.

WILLIS BEVAN WHITNEY. EDMUND BASIL WEDMORE.

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