US1939019A - Contact protection circuit - Google Patents

Description

bec z; 1939. R oURlEFF 1,939,019

CONTACT PROTECTION CIRCUIT Filed Sept. 6, 1952 Patented Dec. 12, 1933 1,939,019 PATENT OFFICE CONTACT PROTECTION CIRCUIT Paul Ouriefl, Los Angeles, Calif., trainer to Clem S. Clarke, Long Beach, Calif.

Application September 6, 1932. Serial No. 831,836

4 Claims.

This invention relates broadly to electrical protective devices and mostparticularly to contact protective circuits for preventing destructive arcing when contacts are broken in a high potential circuit.

A broad object of the invention is to provide a simple, inexpensive, and effective method of preventing destructive arcing at contact points in electrical circuits.

Another object is to provide a potential limitingdevice of simple and inexpensive nature for at all times limiting the possible potential existent in a circuit to a predetermined maximum value, thereby preventing excessive electrostatic stresses on the insulation of the electrical equipment and reducing the lire risk and risk tolife resulting from insulation break-downs. I

In many circuits, of which neon sign circuits are typical, a load is energized from a source of current having a relatively high internal impedance as compared to the impedance of the load. As a result, the potential of the source is much higher when the load is disconnected therefrom than when it is drawing current from the source, and when an attempt is made to break the circuit there is serious arcing at the switch points.

In accordance with the present invention, I greatly reduce such arcing by bridging a gaseous discharge device such as a neon tube across the source. As is well .v known, such discharge devices have extremely high resistances until the gas therewithin is ionized by a potential of predetermined value depending upon the kind of gas, the pressure of the gas, and the length of the electrical path therethrough; thereafter the "device .has a much lower resistance and readily conducts relatively large currents.

The gaseous discharge device'bridged across the source in accordance with my invention is such as to require an ionizing potential in excess of the potential of the source when the latter is connected to the load but less than the open-circuit potential of the source; therefore, it draws no current while the load is connected to the source. However, when the load circuit is disconnected, the potential of the source begins to rise; thereupon the gaseous discharge device is ionized and its resistance reduced sumciently to draw current from the source and prevent any further increase in the potential thereof. when the load is again connected to the source, the potential of the latter is reduced below the ionizing potential of the protective tube, which then ceases to draw current. A gaseous discharge tube used as described may be considered as a safety valve which has no effect on the op;- eration of the circuit to which it is connected as long as the potential in the circuit does not exceed a safe or a desired value, but breaks down widely used.

in the potential of the circuit when the normal load is disconnected.

Two specific embodiments of my invention will now be described with reference to the drawing in which- Figure 1 is a neon sign circuit employing a aseous discharge protective tube in accordance with my invention, and

Figure 2 is a similar circuit in which the gaseous discharge protective tube is used as a part of the sign.

Referring to Figurefl, I have shown two neon lamps 1 and 2, each of which is formed from glass tubing of relatively small diameter bent into the form of a letter. Each tube has metallic terminals in contact with the gas within the tube which are connected by leads sealed through the ends of the tubes to metallic terminals 3, 4, 5, and 6.

Tubes 1 and 2 are energized from a transformer 7 having a primary winding 8 and a secondary winding 9. One end of the secondary winding 9 is connected by a conductor 10 to terminals 4 and 6 on tubes 1 and 2 respectively. The other end of. the secondary winding 9 is connected by conductor 11 to the armature 12 of a relay 13. Relay 13 has a front contact 14and a back contact 15 cooperating therewith and the front contact 14 is connected by a conductor 16 to terminal 5 on lamp 2 while the back contact 15 is connected by a conductor 17 to terminal 3 on lamp 1. The relay is is provided with an energizing winding adapted to be actuated through conductors 18 from any desired control circuit.

The circuit so far described is old and has been It is open to the objection that the transformer 7 usually has relatively poor regulation and also has more or less leakage reactance. As a result, when the relay 13 is energized or deenergized to switch the current from one or the'other of the tubes 1 and 2, serious arcing takes place at the contacts 14 and 15. Furthermore, should one or both of the tubes 1 and 2 become inoperative or become disconnected, the potential across the secondary winding 9 of transformer 7 would rise to a very high value, which might break down the insulation of the leads and cause flre or endanger life.

In accordance with my invention, I therefore modify the circuit described by shunting a gaseous discharge protective tube 19 across the secondary winding 9 of transformer 7. The protective tube 19 may be similar in dimensions and characteristics tothe tubes 1 and 2-or it may be a shorter tube having a dillerent gas pressure.

tected is connected. 7 The protective tube 19 is so designed as to have a higher ionizing potential than either of the tubes 1 or 2 forming the load circuit. This higher ionizing potential may be obtained in several ways, the most common ways of varying the ionizing potential being to vary the length of the tube between the terminals and to vary the pressure of the gas within the tube. Both of these methods of varying the ionizing potential are old and well known and do not form a part of my invention.

Assume that the protective tube 19 is so designed as to have an ionizing potential definitely higher than the ionizing potentials of lamps 1 and 2 and that the transformer I is energized by connecting its primary winding 8 to a suitable source of energizing current such as the usual 69 cycle, 110 volt, alternating current main. With relay 13 deenergized so that armature rests against back' contact 13, the secondary winding 9 of transformer 7 will be connected to lamp 1 and the gas in lamp 1 will be ionized and the tube will glow. The protective tube 19 however will conduct substantially no current because its ionizing potential is higher'than the ionizing potential of lamp 1 and the latter will offer sumciently low resistance to prevent the potential of the secondary winding 9 from rising much above the ionizing potential of tube 1.

Assume that it is desired to alternately flash lamps 1 and 2 by periodically energizing the relay. 13 over conductors 18. when relay 13 is energized the armature 12 will be attracted causing it to move from the back contact 15 and thereafter sage of armature 12 between contacts 15 and 14,

it is disconnected from both of them and the potential of thesecondary winding 9 of the transformer 7 tends to rise to a much higher value. This rising potential tends to maintain an are between armature 12 and contact 15. Any great rise in potential of secondary winding 9 is prevented, however, for the reason that immediately upon the potential increasing to the ionizing potential of protective tube 19, the latter becomes conductive and passes suihcient current to prevent the potential of winding 9 from rising nearly as high as it otherwise would.

When armature 12 closes on contact 14, lamp 2 immediately becomes conductive and since its break-down potential is less than that of the protective tube 19, the potential across the terminals of winding 9 is reduced below the ionizing potential of the protective tube 19, the latter therefore ceases to draw current until the circuit through contact 14 is next broken. It will be observed that in the normal operation of the circuit in Figure 1 lamps 1 and 2 light alternately and during the short periods when both of these lamps are disconnected from the energizing circuit the protective tube 19 passes current and prevents the potential of the circuit rising mate'- rially above the ionizing potential of that tube.

In Figure 1, the protective tube 19 is used solely for protective purposes and would normally be concealed in the case housing the transformer "I and the relay 13. However, if desired, tube 19 may be utilized to produce useful illumination. A circuit for this purpose is shown in Figure 2 in which all of the elements are numbered similarly to the elements of Figure 1 with the suihx (1" added. The operation of the two circuits is identical. It will be observed, however, that the protective tube 19a has been shaped to be used for display purposes by bending it around the lamps in and 2a toform an encircling frame therefor. In operation, the lamps 1a and 2a flash alternately and the protective tube 19a, flashes for an instant between the lighting of tubes 1 and2.

It is understood that although I have shown a gaseous discharge tube as a protective device for preventing excessive potentials in a circuit that other devices having similar conductive characteri'stics may be used in place thereof.

1 claim:

1. A circuit of the type described comprising a source of current having considerable impedance whereby its potential varies with the current drawn therefrom, a load and a switching means connected in series withsaid source, and a gaseous discharge device connected in shunt to said source, said device having an ionizing potential less than the open circuit potential of said source but greater than the potential of said source when said load is connected thereto, and comprising a sealed container having a pair of electrodes and containing a gas at low pressure capable of supporting a continuous are for a substantial period f time without excessive heating and having substantial impedance at all potentials impressed thereon by said source, whereby said source is not short circuited in response to operation of said device. 4

2. In combination, an electrically actuated device normally operating below a predetermined voltage limit and means for protecting said de-' vice against potentials of excessive value comprising a cold electrode gaseous discharge tube connected in shunt to said device said tube having an ionizing potential in excess of said predetermined value, and comprising a sealed con-- tainer having a pair of electrodes and containing a gas at low pressure capable ofsupporting a continuous are for a substantial period of time without excessive heating and having substantial impedance at all potentials impressed thereon by said source, whereby said source is not short circuited in response to operation of said device.

3. A circuit of the type described comprising a source of current having considerable impedance whereby its potential varies with the current 4 drawn therefrom, a neon lamp and a switching means connected in series with said source and a gaseous discharge tube connected in shunt to said source, said tube having an ionizing potential less than the open circuit potential of said source but greater than the ionizing potential of said neon lamp, and comprising a sealed container having a pair of electrodes and containing a gas at low pressure capable of supporting a continuous are for a substantial period of time without excessive heating and having substantial impedance at all potentials impressed thereon by said source, whereby said source is not short circuited in response to operation of said device.

4. Means as described in claim 3 in which said gaseous discharge tube itself is combined with said neon lamp to constitute an illuminated sign.

PAUL ounmrr. 1

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