US1867293A - Electric circuit breaker - Google Patents

Description

July 12, 1932. E. B. WEDMORE ET AL ELECTRIC CIRCUIT BREAKER Filed May 22, 1929 2 Sheets-Sheet 1 mum I w/ud July 12, 1932. E. B. WEDMORE ET- AL ELECTRIC C IRCUIT BREAKER Filed May 22, 1929 2 Sheets-Sheet 2 5 Jaw 2 Patented July 12, 1932 UNITED STATES PATENT OFFICE EDMUND BASIL WEDMORE AND WILLIS BEVAN WHITNEY, OF LONDON, ENGLAND, ASSIGNORS TO THE BRITISH ELECTRICAL AND ALLIED INDUSTRIES RESEARCH ASSOCIATION, OF LONDON, ENGLAND, A BRITISH ASSOCIATION ELECTRIC CIRCUIT BREAKER 'Application filed May 22, 1929, Serial No. 365,081, and in Great Britain June 8, 1928.

This invention consists in improvements in or relating to circuit-breakers for use in circuits carrying. electric power, and is particularly, although not exclusively, applicable to circuits wherein the electrical pressure is relatively high, say of the order of 10,000 or more line volts, more especially to circuits of the higher voltages.

It is now generally appreciated that it is important, in the case, for example, of power circuits, so to arrange conditions that in the breaking of the circuit the arc will not reform. after the current has reached zero value. In highly inductive circuits, however, the full electrical pressure of the circuit may come upon the contacts of the circuit-breaker almost immediately after the current has reached the zero value, thus causing the arc to reform. In the neighbourhood of the arcroot on the contacts when the breaker is operating, the temperature is likely to be high, thus facilitating ionization (corona formation) and breakdown in this part at the time of zero current, while at the same time the tendency to breakdown of the different parts of the gap between the contacts varies with the gaseous content, temperature, pressure, and previous history of the arc.

It is generally recognized that it is advantageous to reduce'the amount of energy produced in the breaker itself during the operation of breaking cireuit; and with this in view, the general object of the present invention is so to improve circuit-breakers for use in power circuits, that they will be more reliable in operation than breakers heretofore constructed and will operate with less production of energy within them in making and breaking of the circuit.

It is known that the density of an electrostatic field on the surface of a charged body depends, amongst-other factors, on the shape of that surface, the density being greatest at the most abrupt or pointed portions of that surface. The use of corona shields around the fixed contact for preventing corona under normal running conditions is known, see, for example, prior British Patent No. 19583/11. In such designs, when the moving contact leaves the fixed contact, no

attempt has been made to prevent formation of corona on the moving contact. It will be understood that corona on the moving contact will cease after the circuit has been broken and the gap filled with oil so that its existence is only momentary and this has been considered satisfactory in the past.

We find, however, that it is of great advantage to suppress the formation of all corona in the arc gap while the circuit is being broken, and according to our invention, corona shields are provided for each contact so designed as to suppress or prevent the formation of corona on the contacts at both ends of the gap. One result obtaining by means of our invention is the approximate adjustment of the field gradient to'the strength of the different parts of the gap so as to withstand maximum voltage across a given ap. The guard or shield device is applica le on occasions to both the main and the arcing contacts. The invention is applicable to circuitbreaking apparatus having separable contacts or separated contacts includin such of the latter as are connected by a fus1ble link.

In the case of a multiple-break circuitbreaking apparatus having a plurality of pairs of separable or separated contacts, the contacts of each pair are provided with corona shields.

For a given voltage, we are thus able to use a much shorter gap especially on very high voltages with a consequent reduction in are energy and burning of contacts.

Preferably, one or each shield is movable relatively to its own contact in the direction of separation, and in one preferred form of the invention, each such moving shield iscombined with a spring or equivalent means which serves to urge the shield towards the companion shield. Thus, as the contacts are closed, the movable shield jor shields may be I pressed back to allow such closure and, when the contacts separate, the shield or shields are moved forward again to a position in front of or beyond the ends of their respective contacts. It is not essential that after said contacts have separated the shield or, shields should move forward beyond the contact or contacts which they guard, as we fin breaker so that said moving contact or contacts move through or towards or level with an aperture in said shield or shields, being electrically connected with said shield or shields by flexible or other suitable connections.

In a modified form of apparatus according to this invention, one shield may be of smaller diameter than the other so that it may enter inside the companion shield when the breaker contacts are closed, thus avoiding the necessity for having one or both shields relatively movable in relation to their respective contacts. Where the shield or shields are within or .near the arcing zone, it is desirable to insulate their exposed surfaceswith solid insulating material so that the arc cannot come into contact with the conducting material of which they are formed.

In order that the invention maybe more clearly understood, one construction will now be described with the aid of the accompanying drawings, in which Figure -1 illustrates more or less diagrammatically a section through a pair of contacts of a circuit-breaker, the section being taken in a plane containing the axis of the arc path,

Figure 2 is a section on the line 2-2 of Figure 1 and Figure 3 is a view similar to Figure 1 of a modified construction.

Like reference numerals indicate like parts in both figures of the drawings.

The upper or female contact 10 is intended to be fixed, and the lower or male contact 11 is movable, and for this purpose is carried, in the example illustrated, by a cross-bar 12, at the other end of which there is another similar movable contact to be associated with a fixed contact for a double-break circuitbreaker. Alternatively, the contacts shown may be considered as those of a single-break circuit-breaker, and the cross-bar 11 can be considered as any moving carrier by which the movable contact is supported.

Surrounding the two contacts 10 and 11 are shields 13 and 14 respectively, each covered with insulating material indicated at 15. The shields are respectively in the form of rings supported by arms 16 and 17. The arms 16 of the shield 13 are bolted to a collar 18 that is fixed invelect-rical connection with the contact 10. The arms 17 are bolted to a collar 19 which is a sliding fit on the movable contact 11 and is maintained in 00d electrical connection with that contact y means of a conducting strip 20.

It will be seen that the ring 13 is retained at a position beyond the extremity of its associated contact 10 and, when the contacts are open, as shown in Figure 1, the shield 14 is retained in a similar manner beyond the end of its contact 11 by means of a coiled compression spring 21. When the contacts are to be closed, however, the insulation covering the shield 14 will contact with that covering the shield 13 so that the shield 14 is pressed back against the spring 21 to permit the contact 11 to enter the contact 10.

The shield 13, in one modification, may be similarly slidably mounted on or in association with the fixed contact 10 so that both shields may be pressed backwardly to some extent during the close of the contacts. In the modified construction shown in Figure 3, the diameter of the shield 14 is smaller than the internal diameter of the shield 13 so as to allow the shield 14 to enter within the latter, and the shield 14 is carried in fixed ple wood, which is soaked with oil or other 'moinsulating liquid.

Figure 1, which represents the shields and contacts in the course of contact separation, is an example of one type of shielding device suitable for guarding contacts on a switch handling about 10,000 R. M. S. volts per break or for mounting on a triple pole, 33,000 volt switch having a total of six breaks, the mean diameter of the upper guard ring in Figure 1 would in this case be about 5" but mention of this dimension does not preclude use of other sizes or dimensions.

We claim 1. Circuit-breaking apparatus comprising in combination relatively movable contacts affording at least one gap between which an arc may form, a guard of conducting material for and electrically connected to each arcing contact for modifying the distribution of potential in the gap between the contacts, one at least of the guards being movable relatively to its own contact in the direction of relative movement of the contacts.

2. Circuit-breaking apparatus comprising in combination relatively movable contacts afiording at least one gap between which an arc may form, a guard of conducting material for and electrically connected to each arcing contact for modifying the distribu tion of potential in the gap between the contacts, one at least of the guards being movable relatively to its own contact in the direction of relative movement between the contacts, and means associated with said movable guard serving to urge the latter towards its companion guard and, when the contacts have been separated, to move the guard beyond the extremity of its own contact considered in the direction towards the adjacent contact.

3. Circuit-braking apparatus comprising in combination relatively movable contacts afiording at least one gap between which an arc may form, a guard of conducting material for and electrically connected to each arcing contact for modifying the distribution of potential in the gap between the contacts, one at least of said guards being movable relatively to its own contact in'the direction of relative movement of the contacts, said movable guard being carried on and movable with its associated contact.

4. Circuit-breaking apparatus comprising in combination relatively movable contacts affording at least one gap between which an arc may form, a guard of conducting material for and electrically connected to each. arcing contact for modifying the distribution of potential in the gap between the contacts, one at least of said guards being movably carried on its own contact so as to be movable therewith and relatively movable thereto in the direction of movement of the contacts, and means associated with said movable guard serving to .urge the latter towards its companion guard and, when the contacts contact being itself movable relatively to its own contact in the direction of relative movement between the said two contacts.

6. Circuit breaking apparatus for the rupture of electric power circuits on load comprising in combination a fixed contact and a movable contact between which an arc may form and at least one guard of conducting material for and electrically connected to each arcing contact for modifying the distribution of potential in said gap, the guard for the fixed contact being mounted on a fixed part and the guard for the movable contact being movable with said contact, one at least ofsaid guards being movable relatively to its own contact in the direction of relative movement between the contacts, means associated with said movable guard servingto urge the latter towards 1ts companion guard and a separating member of insulating material on at least one of said guards serving to prevent electrlcal contact between said guards."

7. Circuit breaking apparatus for the rupture of electric power circuits on load comprising in combination a fixed contact and a movable contact between which an arc may form and at least one guard of conductm material for, electrically connected to an carried by each arcing contact for modifying the distribution of potential in said gap, one at least of said guards being movable relatively to its own contact in the direction of relative movement between the contacts, means associated with said relatively movable guard serving to urge the latter towards 1ts companion guards and a separating member of insulating material on at least one of sand guards serving to prevent electrical contact between said guards, the parts being arranged, so that when the contacts are closed the relatively movable guard is situated behind the tip of its contact but in front of 1t when they are separated.

In testimony whereof we have signed our names to this specification.

EDMUND BASIL WEDMORE. WILLIS BEVAN ,WHITNEY.

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