US2725446A - Circuit interrupter - Google Patents

Description

2 Sheets-Sheet 1 Filed NOV. 18, 1950 n 0 I u m E 8 9 B16 H 5 k l 8 7 5 I 2 2 2w L 7% I I 7 7 w 4 4 M. 4 3 2 rhvfi m n 79 5 86 N 7 33 4 3 w l 5 y U 3 .1 4 6 o 2 2 l 4 ,4 3 3 4 n I w B a. m n s I w F n I Insulation To Hydroqen-- pp y m T N E V I Joseph Slepion. BYSZ/ 7 ATTORNE 1 2,725,446 CIRCUIT INTERRUPTER Joseph Slepian, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 18, 1950, Serial No. 196,435

6 Claims. (Cl. 200-147) This invention relates to circuit interrupters in general, and, more particularly, to arc-extinguishing structures therefor.

The general object of my invention is to provide an improved circuit interrupter, which will interruptthe circuit passing therethrough in a more effective manner than has heretofore been achieved.

A more specific object is to provide an improved circuit interrupter of high-interrupting capacity in which one or more permanent magnets are utilized to assist in extinguishing the arc, in a gas or fluid of such characteristic that the dimensions of the cooperating permanent magnets are within practical limits.

Another object is to provide an improved circuit interrupter in which an arc is established between cooperable contacts, at least one of the contacts being tubular and to dispose within the tubular contact a permanent magnet to create a radial magnetic field between the contacts to rotate the are drawn therebetween. Preferably the contact structure is disposed in a chamber containing hydrogen to minimize the strength of the magnetic field required to produce effective rotation of the arc, so that the dimensions of the required magnet will not be excessively large.

Further objects and advantages will readily become apparent upon a reading of the following specification taken in conjunction with the drawings, in which:

Figure l is a vertical sectional view taken through a circuit interrupter embodying my invention, the contacts being in the closed circuit position; I

Fig. 2 is a sectional view taken along the line IIII of Figure 1;

Fig. 3 is a perspective view of contact structure which may be employed in my invention;

Figs. 4, 5 and 6 are views of proposed contact structure and a suitable hysteresis loop;

Fig. 7 shows a proposed switching arrangement for producing a rectified current passing through a coil to produce a radial magnetic field; and

Fig. 8 shows curves which relate the radial magnetic field strength to the volts per centimeter interrupted, as a function of the medium in which interruption takes place.

It is known that by keeping an alternating-current are moving transversely to its length, through a fluid medium, at considerable velocity, its voltage-interrupting capacity is' considerably increased. A known convenient way of maintaining this velocity is by means of annular electrodes, as shown in Fig. 3, with a radial magnetic field. In Fig. 3 the reference numerals 1 and 2 designate cooperating tubular contacts between which an are 3 is established and rotated by a radial magnetic field, not shown, in a direction as indicated by the arrow 4.

This magnetic field has usually been obtained by means of a series coil, and when the device carries the commonly used alternating current, the magnetic field is alternating. The use of a series coil has the disadvantage in performance, in that for small currents, the field is weak, and the improvement in interrupting power for small currents is lost.

To use a magnetic field excited by direct current eliminates the foregoing disadvantage. However, this calls for a source of'direct current of considerable power, tens of kilowatts. If this source is outside the breaker, then means for bringing it into the breaker, such as leads of proper size, bushings, etc., must be provided, as well as proper relay or contact means for turning the source on States Patent G 2,725,446 Patented Nov. 29, 1955 at the time of a breaker operation. Also the proper insulation of this outside source from the electrodes of the breaker, which may be at high voltage, offers great difiiculties. Furthermore, the reliability of the breaker, now dependent on the integrity of an outside source, is greatly reduced.

If rectifiers are built into the breaker for supplying the direct current, it would necessitate rectifiers of considerable capacity. However, rectifiers at present available, of the required capacity, are bulky and costly. Furthermore, to take care of small currents, the rectifier would need to be shunt excited, and to take care of short circuits, where voltage is not available, the rectifier would need to be series excited. This calls for complicated switching arrangements within the breaker. We may use rectifiers in series, one series excited, and the other shunt excited, as in Fig. 7, but this also is a considerable complication.

I propose to obtain the equivalent of a direct-current field by means of permanent magnets. However, with such permanent magnet materials as are available, this does not seem possible at first sight within any reasonable dimensions. Since this invention proposes means for overcoming this diificulty with permanent magnets, We shall examine more closely here the difiiculties we run into.

What strength of radial magnetic field should be used? The answer is, enough to multiply the interrupting capacity of the are several fold, if air or oil is the fluid. If a gas, other than air, is used, then the multiplication of the interrupting capacity should be still greater, say, at least five fold, to justify the complication of the gas reservoir, valves, etc., which another gas would require.

Experiments show that to get such improvements in interrupting capacity, in general, fields of several thousand gausses are necessary. For example, with oil, in one set of experiments, 2000 gausses were necessary to get an interruption of 2000 volts/cm., and less than this performance would probably not be worthwhile, since simple oil structures, which move the arc laterally by magnetic means into a restricted slot, without using an external magnetic field, can give similar performance.

In air 60 volts/cm. were obtained in an apparatus with zero radial field, and when 2000 gausses were used this was raised to about 200 volts/cm, barely high enough to justify the complication.

Thus it would seem, in general, that a field greater than 2000 gausses would be necessary to justify the use of a radial field. But now, if one attempts to construct a permanent magnet to give such a field with electrodes of reasonable dimensions, one runs into great difiiculties. For example, suppose the field is to be produced by permanent magnets within hollow electrodes as in Fig. 4. This arrangement has the advantage of shielding the magnet from the effect of the current carried by the breaker.

One of the best permanent magnet steels has a hysteresis loop like Fig. 5. We may have a B of 3500, with H =200. If the radial field is 2000, then with S=5 cm., as shown in Fig. 4, the total flux outward from the poles would be 2000 1r D 5=10,0001. D maxwells.

Assuming B=3500, the total flux from the two pole faces would be Hence l7501r D =l0,0001r D or D=5.7 cm.=2.25 in.

This would be the minimum size electrodes which could be used with 1 inch separation. The effective M. M. F. for the external field will be approximately 2000 D=ll,500 counting only the region in the vicinity of the contacts, and neglecting the M. M. F. elsewhere.

3 This would require. a magnet length. ofv at least g=57.5 em. =22.e inches Since each magnet will need to be of this length, this begins to be excessive.

For larger separation of electrodes, the magnets would need to be proportionally larger, in diameter as well as in length.

If one examines the various available gases, one finds that all seem to require radial fields of more than 2000 gausses, and, therefore, excessively large dimensioned permanent magnets. However, I have found that there is apparently one exception, namely, hydrogen. For hydrogen, the magnet dimensions come down to attractively small dimensions, and so this invention proposes the use of hydrogen in a breaker with the magnetic field for moving the arc, produced by permanent magnets. The outstanding advantage of hydrogen is shown in Fig. 8 giving test results obtained with a particular structure.

We see that with hydrogen we get particularly attractive performance with radial magnetic fields, even as low as 200 gausses. This makes an enormous difference in the size of the permanent magnet which may be used successfully. Thus, if we again make the calculation for Fig. 4, but now use the radial field strength required as 200, We get 17501.- D =10007r D or D=.57 cm. or 0.22 inch, or practically no lower limit to the size of the electrode.

Take S=2.5 cm., D=2.5 cm., as shown in Fig. 6, as a practical example. The total radial outward flux at H=200 will be 2.5 1r 2.5 200=12501r maxwells.

If we assume half the magnetic flux from the permanent magnet goes outwards, we get for the inner diameter of the magnet 1r(2.5 x 3500=12501r, or x=2.4 cm., or the magnet thickness needs to be less than one millimeter. As for the magnet length, taking the effective length of the flux path in air, as 2.5 cm., this gives a magnetomotive force of 2.5 200=500, and with H in the magnet equal to 200, the magnet length equals 2.5 cm. or 1 inch. According to the curve of Fig. 8, with such small electrodes and magnets, we should be able to interrupt about 2000 volts A. C. at the 1 inch separation.

We see then that by using hydrogen, a switch using permanent magnets as means for moving the arc becomes practical.

It is known generally that hydrogen has superior arcinterrupting properties to those of other gases. However, what I propose here is not the mere substitution of hydrogen for another gas for the sake of improving a switch which could utilize other gases. What is proposed here is a wholly new kind of switch, which cannot be made in practical dimensions with any gas other than hydrogen, namely, a switch where arc motion is produced by permanent magnets.

In other forms of switches the superior performance of hydrogen is due to its higher thermal conductivity. The switch of this invention uses in addition other unique properties of hydrogen, namely, its low density and vis cosity. Because of these qualities, a relatively small magnetic field acting upon an arc of given current is able to give it the high velocity necessary for a large increase in interrupting ability.

In the practical embodiment of this invention, it is probable that for lower voltages, contacts with associated magnets would be placed in hermetically sealed containers filled with hydrogen, with the contacts operated through sylphon bellows.

For higher voltages it will probably be desirable to go to higher pressures of hydrogen, perhaps ten atmospheres. A chamber, built to withstand this pressure would be connected through a reducing valve to a commercial tank of hydrogen at 3000 lbs. per square inch. Because of the increased pressure a higher interrupting power would be obtained. A field considerably greater than 200 gausses will be necessary, but as the calculations have shown there is still a good deal of latitude left to increase this field without exceeding practical dimensions. It seems conservative to estimate that an interrupting power of more than 5000 volts per inch will be reached in this way.

By going to hydrogen at high pressures, the explosive hazard is practically eliminated. At ten atmospheres even if a full atmospheric pressure of air leaked in, an explosive mixture would not result.

Another advantage of the use of hydrogen is that oxidation of the contacts would be eliminated. Therefore, contacts can be rated at higher currents, since the higher contact temperatures will produce no adverse results.

With the foregoing theory in mind, reference may be had to Figs. 1 and 2, which show one embodiment of my invention.

Referring more particularly to Figure 1, the reference numerals 5, 6 designate the two halves of the tank structure. Each half of the tank structure may have a flange 7 integrally formed therewith, the flanges being rigidly held together by bolts 8 and nuts 9. Within the tank structure 11 is a tank liner formed in this instance by the cooperation of two insulating cylindrical members 12, 13.

An insulating bushing 14 passes through an opening 15 formed at the lower end of the half 5 and has passing therethrough a terminal stud 16. The upper end of the terminal stud 16 is threaded and secured by a nut 17 to a tubular stationary contact 18. Cooperating with the tubular stationary contact 18 is a movable tubular contact 19 having two or more studs 20 threadedly secured at its upper end. A plate 22 is supported by the studs 20, and is rigidly secured thereto by nuts 23. Flexible conductors 24 electrically connect the movable tubular contact 19 with a current distribution ring 25. The ring 25 is supported by an insulator 26 and an insulating bushing 27, which passes through an opening 28 provided at the upper end of the chamber 11. A terminal stud 29 passes through the bushing 27 and makes electrical contact with the ring 25 at 30. The stud 29 is threaded at its lower end, and is secured by means of a nut 31 to an insulating ring-shaped plate 32. A stud 33 fixed in place to the lower end of the insulator 26 cooperates with a nut 34 and a sleeve 35 to assist in maintaining the ring-shaped plate 32 in position.

Disposed within the stationary contact 18 is a tubularshaped permanent magnet 36. Also disposed Within the movable tubular contact 19 is a second tubular-shaped permanent magnet 37. The permanent magnets 36, 37 have their north poles opposing one another, so that in the open circuit position of the contacts 18, 19, a radial magnetic field passes outwardly across the annular gap formed between the separated contacts 18, 19, to effect a rotation of the are drawn between the contacts 18, 19 around their peripheries.

Disposed about the permanent magnet 36 is a tubular copper cylinder 38. Also disposed about the tubular permanent magnet 37 is a tubular copper cylinder 39, the purpose for which will appear more clearly hereinafter. The terminal stud 16 and the nut 17 cooperate in holding in position a ring-shaped insulating member 40. Also supporting the insulating member 40 is a stud 41 and nut 42, the stud 41 being secured at the upper end of an insulator 43. A conduit 44 connects the chamber 11 with a suitable external source of hydrogen, which may be at high pressure.

At the upper end of the magnet 36 is a soft iron pole piece 45. Also at the lower end of the magnet 37 is a soft iron pole piece 46.

An insulator 55 is secured at its lower end to the plate 22 and at its upper end to the lower end of sylphon bellows'56 having their upper end secured to the upper wall of the chamber 11. An aperture 57 may be provided to eliminate back-pressure formed within the bellows 56. Operating means for the movable contact 19 in this instance comprises an elongated member 58, extending through an opening 59 of the chamber 11 and having a latch portion 60 which may be latched in place by lever 61, pivoted at 62 and operated by a solenoid 63, the winding of which may be connected to an overload current transformer suitably connected in the circuit passing through the interrupter.

The operation of this embodiment of my invention will now be explained. In the closed circuit position of the interrupter, as shown in Figure l, the electrical circuit therethrough comprises terminal stud 16, tubular stationary contact 18, tubular movable contact 19, studs 20, conductors 24, current distributing ring 25, to terminal stud 29. The circuit may then pass through the primary winding of an overload current transformer, the secondary winding of which may be connected in series with the winding through the solenoid 63.

Hydrogen under pressure is maintained within the chamber 11, and the pressure of the hydrogen tends to force a collapse of the bellows 56 and to effect a separation between the contacts 18, 19. However, the lever 61 latches the member 58, to thereby hold the contacts 18, 19 in their closed circuit position. However, if an overload occurs to actuate the solenoid 63, the lever 61 will be rotated in a counterclockwise direction to unlatch the member 58, and to permit the pressure of the hydrogen gas within the chamber 11 to force a collapse of the bellows 56 and effect thereby a separation of the movable contact 19 from the stationary contact 18. The are, not shown, drawn between the contacts 18, 19 will be rotated about the opposed inner peripheries of the contacts 18, 19 by the radial magnetic field set up across the contact gap by the permanent magnets 36, 37.

The flux for the magnet 36 will pass radially outwardly across the contact gap returning through the air to the south pole of the magnet 36. Also the flux through the upper magnet 37 will pass radially outwardly across the contact gap, through the air to the south pole of the mag net 37. The radial magnetic field thus set up by the magnets 36, 37 serves to rotate the are around the faces of the contacts 18, 19 to effect the extinction thereof.

Should the pressure of the hydrogen gas within the chamber 11 fall to a low value, the compression spring 64 will prevent an opening of the contact structure even though the lever 61 is rotated by the solenoid 63 and unlatches the member 58. The bafile members 47 serve to maintain the arc in position preventing it from bowing outwardly.

Mounting the magnet- s 36, 37 inside the tubular contacts 18, 19 reduces to a minimum the demagnetizing effect of current flowing in the contacts 18, 19, since, if the current is uniformly distributed, there will be no magnetic field within the contacts 18, 19. However, at points where the current enters and leaves the contacts 18, 19, the current concentrates, and does produce some demagnetizing elfect. To minimize these eifects the soft iron pole pieces 45, 46 are placed at the ends of the magnets 36, 37, and the copper cylinders 38, 39 are placed about the magnets 36, 37. Changes in flux due to the current in the contacts 18, 19 will induce opposite currents in the tubes 38, 39 tending to keep the induced magnetic flux out of the magnets 36, 37. The internal pressure acting on the bellows 56 provides the energy for opening the contacts. A relatively weak compression spring 64 keeps the contacts 18, 19 closed it the breaker has accidentally lost its gas pressure.

Following a circuit opening operation the pressure of the hydrogen gas within the chamber 11 will maintain the contacts 18, 19 in their separated position. To close the circuit through the interrupter suitable means, not shown, may be employed to effect a downward movement of the member 58 to force the contacts 18, 19 into engagement, the lever 61 latching over the latch portion 60 of the member 58. The circuit is then completed through the interrupter.

From the foregoing description of my invention it is apparent that I have provided a novel circuit interrupter of compact design and suitable for high-voltage service. By employing hydrogen as the arc-extinguishing medium the dimensions of the permanent magnets required to produce an effective radial magnetic field strength are greatly reduced, and the construction becomes of practical importance. Furthermore, I have disclosed how the structure may be arranged to minimize the demagnetizing eltects produced by the alternating current passing through the cooperable contact structure.

Although I have shown and described a specific structure, it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. In a circuit interrupter, a chamber containing hydrogen, means for establishing an arc within the chamber, and means comprising one or more permanent magnets for establishing a radial magnetic field in proximity to the arc to cause rotation of the arc to etiect the extinction thereof.

2. In a circuit interrupter, a chamber containing hydrogen, a pair of contacts disposed within the chamber cooperable to establish an arc therebetween, at least one of the contacts being tubular, and a permanent magnet disposed within the tubular contact to establish a radial magnetic field between the contacts when they are separated.

3. In a circuit interrupter, a chamber containing hydrogen, a pair of contacts disposed within the chamber cooperable to establish an arc therebetween, both of the contacts being tubular and having ring-shaped arcing portions, and a permanent magnet disposed within each contact and shielded thereby to avoid arcing thereto, the poles of the two permanent magnets opposing each other to establish a radial magnetic field between the contacts when they are separated.

4. In a circuit interrupter, a pair of contacts cooperable to establish an arc therebetween, at least one of the contacts being tubular and having a ring-shaped contact surface, and a permanent magnet disposed within the tubular contact and shielded thereby to avoid arcing thereto to establish a radial magnetic field between the contacts when they are separated.

5. In a circuit interrupter, a pair of contacts cooperable to establish an arc therebetween, both of the contacts being tubular, and a permanent magnet disposed within each contact, the poles of the two permanent magnets opposing each other to establish a radial magnetic field between the contacts when they are separated.

6. In a circuit interrupter, a pair of contacts cooperable to establish an arc therebetween, at least one of the contacts being tubular, a permanent magnet disposed within the tubular contact to establish a radial magnetic field between the contacts when they are separated, and a non-magnetic conducting sleeve about the permanent magnet and within the tubular contact for helping to prevent demagnetization of the permanent magnet by the current passing through the interrupter.

References Cited in the file of this patent UNITED STATES PATENTS 1,558,277 Phelan et al Oct. 20, 1925 2,355,482 Suits Aug. 8, 1944 2,367,934 Flurscheim Jan. 23, 1945 2,389,592 Bucklen, Ir., et a1 Nov. 27, 1945 2,411,892 Peters Dec. 3, 1946 2,485,783 Shaw, Jr Oct. 25, 1949 2,506,991 Brown May 9, 1950 2,522,596 Bevin-s Sept. 19, 1950 FOREIGN PATENTS 691,727 Germany June 4, 1940

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