US3153175A - Two stage system for initiating an electric arc - Google Patents

Description

Oct. 13, 1964 J. w. WINZELER TWO STAGE SYSTEM FOR INITIATING AN ELECTRIC ARC Filed June 29. 1960 IN V EN TOR. J qia HAW/72BX9- 3,153,175 TWO STAGE SYSTEM FOR TIATIN G AN ELECTRIC ARC John W. Winzeler, Santa Ana, Caliii, assignor, by memo assignments, to Giannini Scientific Corporation, Long Island, N.Y., a corporation of Delaware FiledJune 29, 1965, Ser. No. 39,709 1 Claim. (Cl. 315-411) This invention relates to a spark-generating or igniter means. More specifically, the invention relates to means the electrodes of such circuit.

Another object is to provide an arc-starting circuit which is extremely economical to construct and maintain.

These and other objects and advantages of the invention will be more fully set forth in the following specification and claim, considered in conjunction with the single-figure drawing associated therewith.

Referring to the drawing, the circuit will be described as associated with an electrical plasma-jet torch having a nozzle electrode 11 and a back electrode 12, the latter being coaxial with the opening 13 in the nozzle electrode.

Formed between the electrodes is a cylindrical gas chamber 14 into which gas is introduced continuously from a suitable source 15 through a passage means 17. The opening from passage means "17 into chamber 14 is tangential to the chamber, so the gas flows vortically in the chamber and then discharges out the opening 13 in the form of high-temperature plasma. The main arc circuit includes a suitable source 18 of low-voltage high-current DC power, such source being connected through leads 19 and 20 with the back and nozzle electrodes, respectively.

The back and nozzle electrodes are separated byrsuitable insulation means 22 into which a metallic electrode sleeve 23 is inserted inorder to form an explosion chamber 24. An electrode 25 is mounted axially of the sleeve 23 and is insulated therefrom by an insulating tube 27, the result being that a spark may be generated in the explosion chamber between the tip of electrode 25 and the wall of sleeve 23. Such spark effects formation of plasma in the explosion chamber 24, which plasma jets into the gas chamber 14 to result in initiation of the main are between the nozzle and back electrodes 11 and 12 For a more complete description of a representative torch and starting-electrode means, reference is made to co-pending application Serial No. 790,692, filed February 2, 1959, for Apparatus and Method for Initiating an Electrical Discharge, inventor Adriano C. Ducati, now Patent No. 3,007,630. Such application is assigned to the same assignee as the present one.

Stated generally, the arc-starting circuit of the invention comprises a relatively large capacitor 29 and a relatively small capacitor 31, means to charge such capacitors in parallel-circuit relationship, and means to effect discharging of the small capacitor 31 in such manner as to form a low power high-frequency spark in explosion chamber 24 and thereby trigger discharge of the large capacitor 29 to create a higher-power spark in such explosion chamber.

The means to charge the capacitors 29 and 31 in parallel-circuit relationship is illustrated to comprise a suit- United States Patent 0.

3,153,175 Patented Oct. 13, 1964 "ice able source 32 of -volt power, such source being connected through a pushbutton switch 33 with the primary of a one-to-one isolation transformer 34. Since the isolation transformer is one-to-one, it will be understood that the large capacitor is only charged to a low voltage on the order of 110 volts. The secondary of such transformer is connected through a current-limiting resistor 35 and a rectifier 37 to the large capacitor 29 for charging thereof. Leads 38 and 39 are connected from opposite sides of large capacitor 29 to opposite sides of the series combina-v tion of small capacitor 31 and the primary of a stepup autotransformer 42, there being a resistor 40 interposed in lead 39 to effect relative isolation between the capacitors 29 and 31 when discharging.

Such series combination of capacitor 31 and the autotransformer primary is connected to the contacts 44 of a normallyblosed relay 45 having a coil 46 in the circuit between transformer 34 and power source 32. A potentiometer winding 47 is connected across small capacitor 31, and a portion of such winding is connected across a suitable neon tube 48, the relationship being such that the tube will light when capacitor 31 is fully charged.

The secondary winding of the step-up autotransformer 42 is connected in parallel with an extremely small capacitor '51. The parallel combination of such secondary and capacitor 51 is connected through a spark gap 52 to a lead 53 which extends between rectifier 37 and electrode 25. A second lead 54 is connected between electrode sleeve 23 and the opposite side of capacitor 29 from rectifier 37, that is to say to the lead 38 and the lower end of the secondary winding of isolation transformer 34. It is an important feature of the invention that an isolation inductor 56 is interposed in lead 53 between the connection thereof with spark gap 52 and the connection thereof with resistor 40. Such inductor 56, spark gap 52, capacitor 51, transformer 42, relay 45 and resistor 40 (together with certain other elements) form the above-indicated circuit for effecting discharge first of capacitor 31 and then of capacitor 29 to result in sparking in explosion chamber 24.

Operation Assuming that all parts are initially in the positions illustrated in the drawing, the gas source 15 is operated in a manner effecting introduction of gas into chamber 14, and the power source 18 is operated to apply a voltage between the nozzle and back electrodes 11 and 12. The operator then presses the push-button switch 33 to complete a circuit from 1-10-Volt source 32 through the primary of isolation transformer 34 and also through the relay coil 46. The large capacitor 29 is thus charged, to a low voltage, through a circuit including the secondary of transformer 34, and also including the current-limiting resistor 35 and the rectifier 37. The small capacitor 31 is also charged through a circuit which may be traced as follows: secondary of transformer 34, resistor 35, rectifier 37, lead 39 including resistor 40 therein, capacitor 3 1, the primary of transformer 42, and lead 38 back to the secondary of transformer 34. Because of the above-indicated energization of coil 46 of relay 45, contacts 44 thereof are maintained open to prevent discharge of capacitor 31. It is pointed out that capacitor 29 will not discharge through the spark gap between electrodes 23 and 25, until such gap "is ionized, because of the low voltage to which the capacitor 29 is charged. Also, capacitor 29 will not discharge through the secondary of transformer 34 since such discharge is blocked by rectifier 37.

The push-button switch 33 is maintained closed until lighting of neon tube 48 indicates that capacitor 31 is fully charged. The operator then releases the switch 33 to dc-energize transformer 34 and effect closing of the contacts '44 of relay 45. The relatively small capacitor 31 then discharges through contacts 44 and through the prision chamber 24. The circuit through which this highfrequency low-power current flows may be traced as follows: secondary of transformer 42, spark gap 52, lead 53, electrode 25, electrode sleeve 23, lead 54, and lead 38 back to the secondary of transformer 42 It is emphasized that (because of the low amount of power) such current is not harmful or dangerous in any way, despite the step- ,up nature of transformer 42.

As soon as the above-indicated,high-frequency but'lowpower discharge is for-med in explosion chamber 24, discharge of the relatively large capacitor 29 is triggered through a circuit which may be traced as follows: upper side of capacitor 29, inductor 55, lead 53, electrode 25,

electrode sleeve 23, and lead 54 back to the capacitor 29.

This last-mentioned capacitor discharge results in generation in explosion chamber 24 of a spark discharge having sufiicient power to form high-temperature plasma therein, such plasma jetting into the gas chamber 14 and providing an ionization path between main electrodes 11 and 12. The main are between electrodes 1'1 and 12 then strikes, resulting in formation of a plasma jet which streams out through opening 13.

It is emphasized that the inductor 56, which has a relatively low inductance, is nevertheless sufficient to prevent the high frequency current from capacitor 51 and spark gap 52 from feeding into the circuit including resistor 40, capacitor 29, etc. Such inductor is not, however, eifective to materially impede discharge of capacitor 29 after the spark gap between electrodes 25 and 23 is triggerexl.

The resistor 40 also performs an important function, namely maintaining .the discharges of capacitors 29 and 31 relatively separate. Capacitor 31 is thus caused to discharge substantially entirely through the primary of transformer 42, and capaict-or 29 is caused to discharge substantially entirely through the spark gap in explosion chamber 24, without undesirable interaction.

Specific Example Capacitor 31 may :be a 150 volt D.C. capacitor having a capacitance of 150 nt. Capacitor 51 may be a kv.

capacitor having a capacitance of 0.0005 mf. The inductor 56 may comprise three turns of insulated wire disposed in a tight helix and having a diameter on the order of four inches. The transformer may be a PF 3 trigger transformer having a 15 kv. peak in the primary and a 1500 kv. peak in the secondary.

Various embodiments of the present invention, in addition to what has been illustrated and described in detail, may be employed without departing from the scope of the accompanying claim.

I claim:

An automatically-starting plasma torch system, which comprises an electrical plasma torch system having a front electrode and a back electrode adapted to have a highcurrent main are maintained therebetween, power-supply means to impress a voltage between said front and back electrodes, said power-supply means being adapted in response to ionization of the space between said front and back electrodes to initiate a high-current main are therebetween, means to effect a continuous flow of gas between said front and back electrodes and in such relation to said main are that said gas is heated thereby, at least one starting electrode additional to said front and back electrodes and disposed in the vicinity thereof, said starting electrode being so related to said front and back electrodes'that passing of a high-power low-voltage spark from said starting electrode to another electrode will effect sufiicient ionization of said space between said front and back electrodes to result in initiation of said main are by said power supply means, a large capacitor, means to charge said large capacitor to a relatively low voltage insufficiently high to generate a spark from said starting electrode to said other electrode in the absence of ionization of the space therebetween, circuit means to.connect said large capacitor to said starting electrode and said other electrode, and extremely low-power means electrically connected to said starting electrode and other electrode to generate a low-power spark therebetween and thus efiect ionization of said space thereb etween, said low-power spark causing generation of said high-power low-voltage spark in said space by said large capacitor and thereby resulting in initiation of said main arc between said front and back electrodes.

References tlited in the file of this patent UNlTED STATES PATENTS 1,962,342 'Fahnoe et al. June 12, 1934 2,508,954 Latour May 23, 1950 2,700,120 Germeshausen Jan. 18, 1955 2,738,443 Danziger Mar. 13, 1956 2,837,698 Segall June 3, 1958 2,873,409 Most Feb. 10, 1959 2,919,370 Giannini Dec. 29, 1959 2,953,721 Chauvineau Sept. 20, 1960

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