US3446927A - Disk contacts and flat annular shield arrangement in gas filled switch - Google Patents

Description

1969 c L SHACKELFORD 3,446,927

LAT ANNULAR SHIELD ARRANGEMENT DISK CONTACTS Aim IF IN GAS FILLED SWITCH Filed Jan. 10, 1966 1 1. I I 40 49 71 27 -gal- 4? Z/ 26 ,1

INVENTOR fehaarLf/am aroep ATTORNEYS United States Patent DISK CONTACTS AND FLAT ANNULAR SHIELD ARRANGEMENT IN GAS FILLED SWITCH Charles L. Shackelford, Cedar Grove, N.J., assignor, by mesne assignments, to Wagner Electric Corporation, South Bend, Ind., a corporation of Delaware Filed Jan. 10, 1966, Ser. No. 519,589 Int. Cl. H01h 9/30, 33/14 US. Cl. 200-144 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to improvement-s in gas filled switches for breaking large alternating currents. The invention has particular reference to a switch for breaking currents with a minimum amplitude of transient disturbances.

When an ordinary knife switch is opened in air while carrying a large current, an arc is formed which causes erosion of the switch elements and produces a transient disturbance in the connected electrical system which may produce large resonant voltages and cause considerable damage. An improvement of the knife switch in air resides in a switch within an enclosure which is evacuated. Such an arrangement has been used but the current forms a metallic vapor arc and is often cut off too abruptly and the transients are even larger than those produced by a switch in air. The present invention is an enclosed switch provided with a shielding means which insures that there will be no spark over after the switch has been opened. The enclosure is gas-tight and contains a gas at a low pressure. The pressure of the gas within this enclosure is maintained by a titanium hydride reservoir with lead-in connectors and a heater for maintaining the temperature of the regulator at a predetermined value. Under these conditions, when the switch is opened, an arc is formed which reduces the current slowly until the alternating current approaches a zero value at the end of a half wave. This type of current reduction produces a transient wave which is low in current amplitude and does not cause any damage.

One of the objects of this invent-ion is to provide an improved switch which avoids one or more of the disadvantages and limitations of prior art switches.

Another object of the invention is to break a large current slowly but within the time duration of one-half cycle of the alternating current.

Another object of the invention is to reduce the transient current amplitude caused by a fast disruption of current flow.

3,446,927 Patented May 27, 1969 Another object of the invention is to prevent arc-over currents by providing a shielding means which reduces the electric field intensities when the switch is in its open position.

Another objection of the invention is to maintain the pressure within the switching unit at a constant predetermined value.

The invention comprises a gas-filled switch for breaking large alternating currents and includes a sealed envelope for housing all the switch components in hydrogen at a predetermined pressure. A stationary cont-act disk is conected to a lead-in conductor for forming one of switch contacts. A movable contact disk forms the other switch contact and is connected to another lead-in conductor. The movable contact disk is connected to flexible leads within the envelope and is secured to an expandable bellows for sealing the envelope. The movable contact disk is surrounded by an annular shield for reducing the electrical field intensity at the edge of the disk.

One feature of the invention includes a filling of hydrogen gas at a pressure which is below the pressure which support-s sustained electrical conduction.

Another feature of the invention includes the use of a hydrogen gas reservoir which may be constructed of titanium metal and its hydride. This reservoir also contains a heater with leads which may be connected to an external source of electrical power and acts as a regulator to maintain the hydrogen in the envelope at a predetermined pressure.

For a better understanding of the present invention, together with other and further objcts thereof, reference is made to the following description taken in connection with the accompanying drawings.

FIG. 1 is a cross sectional view taken along line 1-1 of FIG. 4 and shows all of the internal components in the switch envelope except the hydrogen reservoir.

FIG. 2 is a cross sectional view of the switch shown FIG. 1 and is taken along line 22 of that figure. FIG. 3 is another cross sectional view of the switch shown in FIG. 1 and is taken along line 33 of that figure.

FIG. 4 is an end view of the switch.

FIG. 5 is a graph commonly known as Paschens curve and is plotted with values of volts and spacing times pressure.

Referring now to FIGS. 1 through 4, the gas-filled switch includes two conductive panels 10 and 11 which also serve as the switch terminals. Each panel contains several mounting holes 13 for securing the panels to some form of non-conductive mounting means or to buss bars. Connections from the panels 10 and 11 may be made by means of wire terminals 14 and 15, each secured to one of the panels by bolts 16 and 17. Other means of connection may be used.

The switch elements are disposed within an envelope which includes a hollow cylindrical insulator 18 which may be made of either glass or ceramic. The ends of the insulator are brazed to annular conductive members 20 and 21 and these members are Welded respectively to an end disk 22 at one end and a conductive washer 23 at the other end. End pieces 22 and 23 are soldered or welded to terminal portions 24 and 25, these portions containing threaded holes for accommodating a plurality of machine screws 26 which anchor the switch envelope to the two end panels 10 and 11.

The cylindrical insulator 18 may be formed in a single cylindrical piece but it has been found that better shielding means may be obtained by the installation of a floating electrode shield 27 This shield may have an annular flange 28 which separates the cylindrical insulator into two portions. While the shield 27 is generally left floating and thereby assumes a voltage which lies somewhere between the potentials of the two end portions, some applications may require connection of flange 28 to a voltage divider connected between the two end panels or to some other potential.

Inside the envelope a contact disk 30 is supported on another disk 31, the edges of which are turned over to provide an annular shield 32. These two elements 3 and 31 are also secured to a heavier piece of metal 33 which may be made of copper and which acts as a heat sink. This array of electrodes is supported on a hollow metal cylinder 34 which in turn is secured to conductive panels 22 and 24. Cylinder 34 is provided with several holes 35 so that the gas in the envelope may move through them when the envelope is exhausted. A tubular conduit 36 is welded to disk 22 and is used as an exhausting and filling means. It is sealed by crimping in the well known manner and is protected by a cap 37 which surrounds the end of conduit 36 and which is secured to end panel 10. Current is lead into the interior of the envelope by means of clamping screws 26, disks 24 and 25, conductive members 20 and 21, and conductive cylinders 34 and 44.

The other contact member is a movable disk 40 secured to a cylindrical piece of copper 41 which acts as a conductive element and a heat sink. Secured to the cylinder 41 are four flexible leads 42 which carry the current from cylinder 41 and disk 40 to another washer 43 secured to a stationary cylindrical conductor 44. Conductor 44 surrounds a bellows 45 and is secured to conductive washer 23 and supporting means 25. Washer 23 is connected directly to end panel 11 by four screws 26.

The flexible leads 42 are composed of a plurality of fine copper wires which may be braided or otherwise joined to form a conductive and flexible current carrying means. The stationary ends of these conductors are soldered to tubes 46 which are an integral part of a washer 47 and ring 43. The washer 47 is welded to the inner end of the bellows 45 while the outer end of the bellows is welded to another washer 48, secured to an axial rod 50. Washer 47 is also connected to a cylindrical conductive shield 49 lying within shield 47. Rod 50 is connected to cylinder 41 by any conventional means such as a screw thread and in addition is connected to an exterior rod 51 which may be coupled to a handle for manual operation or to a circuit breaker actuating mechanism which separates contact portions 30 and 40 whenever certain conditions arise which call for the opening of the switch.

FIG. 2 shows a hydrogen reservoir 52 having lead-in conductors 53 and 54. These lead-in conductors pass through washer 23 and the annular support 25 so that an electrical source of power may be connected to them and heat up the reservoir to a predetermined temperature. Only one lead-in conductor is necessary, the other heater terminal may be connected to washer 23. The reservoir 52 may be made of many materials but it has been found that a cylinder of titanium is the most efficient reservoir material. As is well known, the titanium metal combines with hydrogen to form titanium hydride, the extent of such combination being dependent upon the temperature of the reservoir. By applying the right amount of heat to the reservoir, a definite pressure of hydrogen may be maintained within the envelope. Other isotopes of hydrogen such as deuterium or tritium may be used, these forms having different Paschen curves.

FIG. is a graph showing the Paschen curve for conduction within an evacuated envelope. This curve is well known and has been described and illustrated in many .4 publications. The curve 56 r epresents a mirror values of voltage and electrode spacing times gas pressure where a spark starts without benefit of prior gas ionization.

The operation of this device is as follows: let it be assumed that disk 40 is in contact with disk 30. This permits current to pass from connector 14 to connector 15 with substantially no loss of power. At this time the reservoir 52 is heated to a temperature which provides hydrogen at a predetermined low pressure in the envelope. Now let it be assumed that the switch is to be opened for any reason. Rod 51 is moved to the position shown in FIG. 1 and disk 40 is moved away from disk 30. An arc is formed between the two disks but because of the low pressure within the envelope there is a minimum of sputtering and the electrodes are not damaged. The two disks 30 and 40 are separated by an amount indicated by the distance 57. When the contacts are separated, the condition is represented by the arrow 58 which moves from a zero spacing condition to a point 60 where the arc is extinguished. If the switch is opened at a time when the voltage of the AC. power has a substantial positive or negative value, an arc is formed which continues until the voltage reaches a zero value between positive and negative waves. At this time the arc is extinguished and cannot be re-formed because point 60 is in the non-conducting area.

The above described action may take several milliseconds or the existence of the are between disks 30 and 40 may be quite short. In any event, the arc is extinguished when the current wave passes through zero and, because of this, the transient wave set-up, due to the disruption of current, has a minimum amplitude.

After the switch has been opened and the transient wave has disappeared, the two conductive end portions 10 and 11 are insulated from each other by the hollow insulator cylinder 18. The tendency to are over between these two contact portions 30 and 40 is reduced by an annular washer type shield 61 which lies flush with the surface of the movable electrode 40 when the switch is in its opened position. Washer 61 is connected to electrode 40 by means of shield 49 and washer 47 and the electric field between washer 61 and electrode 30 is the same as the field between electrodes 40 and 30. However, there are no sharp points nor corners to intensify the-electric field and, in addition, the floating electrode 27 divides the electric field into two equal parts in the annular space surrounding the switch components.

It should be noted that there are two gas pressures within a large voltage range wherein the combination of voltage and electrode spacing lie in a non-conductive region. It has been found that operating in the region indicated in FIG. 5 produces the best results. There is no large are when passing through the conductive region and the arc can be suppressed much faster.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

I claim:

1. A gas filled switch for breaking alternating currents comprising; a sealed envelope for housing all the switch components in a gas at reduced pressure; said envelope containing a stationary contact disk connected to a leadin conductor for forming a stationary switch contact, a movable contact disk connected to a lead-in conductor for forminga movable switch contact, said movable disk connected to flexible leads within the envelope and to an expandable bellows for sealing the interior of the envelope from the atmosphere a flat annular shield surrounding said movable contact disk for reducing the electrical field intensity, said annular shield mounted coplanar with the contact surface of the movable disk when in its open position, said gas pressure less than the pressure necessary to produce conduction at the voltage and spacing between the contacts when open but large enough to support a temporary are when the disks are being separated.

3,446,927 5 6 2. A switch as claimed in claim 1 wherein the station- References Cited ary disk and the annular shield are each connected respectively to cylindrical conductive shields positioned in UNITED STATES PATENTS axial alignment with the disks. 92,912 6/ 1959 Greenwood et al.

3. A switch as claimed in claim 1 wherein the envelope 3,156,803 11/1964 Scully et al.

contains a titanium reservoir for maintaining the gas pres- 5 3,189,715 6/ 1965 Jennings.

sure in the envelope at a value where sustained gaseous 3,261,954 7/1966 Yonkers.

conduction is impossible at the spacing between the open 3,328,545 6/ 1967 Holliday.

disks.

4. A switch as claimed in claim 1 wherein the gas in ROBERT S, MACON, Primary Examiner. the envelope is selected from the group whichconsists of 10 hydrogen, deuterium, and tritium.

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