US1235935A - Rectifying spark-gap for high-tension alternating electrical currents. - Google Patents

Description

A. SHAW.

RECTIFYING SPARK GAP FOR HIGH TENSION ALTERNATING-ELECTRICAL CURRENTS.

APPLICATION FILED OCT. 28. 19M.

Patented Aug. 7, 1917.

ARCHIBALD SHAW, OF RANDWICK, NEAR SYDNEY, NEW SOUTH WALES, AUSTRALIA.

RECTIFYING SPARK-GAP FOR HIGH-TENSION ALTERNATING ELECTRICAL CURRENTS.

Specification of Letters Patent.

atented Aug. 7, 1917.

Original application filed June 29, 1912, Serial No. 706,638. Divided and this application filed October 28, 1914. Serial No. 869,111.

To all vi /mm it may concern.

Be it known that I, Anouumno SuAw, a subject of the King of Great Britain and Ireland, residing at Dutrue street, Randwick, near Sydney, New South Wales, Aus tralia, have invented new and useful Improvements in llectifying S):lI'l(-( ifl|)S for High-Tension Alternating Electrical Currents, of which the following is a specification.

This invention relates to means, usable primarily in connection with wireless teleraph transmitters, for controlling powerful liigh tension high frequency alternating electric currents in circuits containing lI1- 'ductance and capacity, and it has for its object to cause said currents to pulse in one direction and to inhibit pulse of same in the reverse direction in such circuits.

When the condenser charge breaks down in a circuit carrying powerful alternating currents and containing a spark gap of which one electrode is a substantially flat surface and the other electrode is a rod with a tapered or rounded end, the discharge across the gap is a plain alternating current are resembling in appearance a candle flame,

rovided that the secondary circuit containmg the spark gapis in resonance with the primary power circuit which charges t throl'igh an inductive coupling. In the primary circuit and the secondary circult are not in resonance, the discharge across the gap takes the form of irregular stringy white sparks. In the former case the gap becomes conductive and current oscillates across it in the same frequency as that of the primary circuit; such oscillations are too low in frequency to be utilized for exciting a Hertzian radiator. In the latter case, oscillations of current occur in the circuit and internal losses are sustained, diminishing the efficiency of the circuit.

If, however, in accordance with my invention, the rod electrode is pierced axially with a fine hole through which gas is forced so as to impinge with considerable velocity upon the opposed face of the other electrode, and the primary and secondary circuits are in resonance, an arc is no longer formed, but the discharge immediately takes the form of a bluish white incandescent blaze of tapered form extending across the gap, and a pulsa- .voltages approximately 28000.

tory discharge having a very high frequency passes in one direction only.

In practice, a blast of suitable gas under pressure such as air is used in the gap, the axial jet is made about one sixty-fourth of an inch (more or less) in diameter at the nozzle thereof, and the pressure used is from to 150 lbs. on the square inch. \Vith a substantially flat faced electrode of two inches or more in dian'ieter, and a rod electrode of about an inch in diameter formed at the head as a blunt nosed cone, and a gap measuring about three-eighths to half an inch between the electrodes, as much as 20 kw. can be passed under a pressure of about 28000 volts. These proportions are therefore eminently suitable for the purposes ofa high power wireless transmitter. For this purpose air pressure at about 110 lbs. per square inch has been found to give very satisfactory results. The length of the gap that is the distance between the electrodes is varied according to the voltage and the pressure of air used; for a voltage approximately 28000 and an air pressure of 110 lbs. per square inch, the correct distance is from three-eighths of an inch to one-half an inch. The air pressure should be increased with the voltage, about 110 lbs. per sq. in. being correct for 28000 volts. for wireless transmitters are obtained with Such high voltage, with quantity of current necessary for long distance wireless transmission, cannot be used with quenching gaps of the Lepel type; nor can heavy currents be rectified, as may currents o miniature quantity though high voltage, in pointandplate gaps such as are frequently used with influence machines. Experimentally, dis charges having a voltage about 00,000 have been passed through gaps constructed according to this invention, and the length of the gap has been extended to as much as two inches. Substantial flatness of the opposed electrode is desirable, the best economy being attained with a flat disk upon the face of which the air jet impinges perpendicularly. The electrodes are preferably made of copper or silver; zinc is undesirable as it shows a tendency to pit at the place of impact of the jet. The diameter of the jet should be increased with the power used in The best results i the circuit, a diameter of one sixty-fourth of an inch being correct for 2 kw. and slightly more for heavier currents. If an air pressure of about 150 lbs. or more per between the electrodes andv symmetrical in form, and the pulsatory current is substantially uniform in voltage and quantity. Not only so, but when the adjustments are perfected, so that the secondary circuit discharges once in every half cycle of the primary circuit and the length of the gap and the ,air pressure are approximately correct, the secondary circuit containing the gap operates only as an exciting circuit in'relation to a radiator coupled thereto electrostatically, and the radiator emits one highly damped wave only for .each impulse delivered to it, this wave having a frequency determined by the radiator constants and unaffected by the secondary circuit values. A second wave of different period may be detected when the adjustments are disturbed, but when they are correctly arranged as already stated one wave length only is found by observation with the usual instruments. The wave train frequency is determined by the primary circuit frequency, while the individual wave frequency is determined by the radiator constants. v

In the drawings, Figure 1 is a sectional elevation of the spark gap apparatus as used by me, Fig. 2 an enlarged scale sectional elevation of the electrodes, and Fig. 3 face end views of the electrodes. Fig. 4 is a diagram of a wireless telegraph transmitter in which my spark gap is used.

A is a case constructed of micanite or other suitable insulating material and fitted with a lift lid B; it is supported on insulators O, and fitted with leading-in insulators D and D, the detail construction of which is unimportant. E and F are portions of the exciting circuit, their terminals being connected to the stems G and H of the electrodes K and L. The electrode L .is fitted with a solidstem H which should be screwed to work in a nut in the leadingin insulator D to. enable the operator to electrode K is coned externally. P is an axial hole in the electrode K. The two electrodes K and L are arranged in axial alinement so that the gas jet impinges perpendicularly on the face of the flat electr'ode L. Q is an inclosing box of wood, supported on heavy insulating feet, R. I and J are leading in insulators in the box Q. The spent air or gas finds exit through the joints in the case A and the box-Q. The noise of the break is dampened by these inclosures.

The break is kept cool as a result of the. absorption of heat b the expanding gas, but the rectifying. e ect is not caused-by the'mere cooling of the gap.

An essential feature of the invention is the employment of a gas blast at a pressure varying between about 50 pounds and 140 pounds per square inch and preferably about 110 pounds per square inch, more or less, directed through a fine axial hole in a tubular electrode a ainst the face of a solid electrode across t e spark ap, the tubular electrode being conical and lunt nosed, and the solid electrode referably formed with an approximately at face.

Heretofore spark gap electrodes have been proposed one of which has the form of a point orpencil directed toward the other, which latter is made with a plane surface, with the object of obtaining a unidirectional flow of sparks and preventing oscillatory How of current across the gap; and it has been a common practice to play a jet of air on a spark gap, to efiect cooling and to prevent arcing. These methods do not produce a blaze or torrential flash of rectified currentsuch as is produced when the electrodes are formed as a blunt nosed cone and a flat plate with a needle jet of gas at a pressure of lbs. per square inch more or less passing through the cone electrode and directed axially from the point thereof onto the opposed electrode. In the case of the arrangement used by me a very large volume of energy passes over a short gap, which offers, other things being equal, minimum reslstance.

A practical instance of the utilization of a spark gap constructed as hereinbefore described is shown in Fig. 4 of the drawings, which represents diagrammatically a wireless telegraph transmitter in which Z is an alternator delivering current at about 500 cycles per second, Y, an inductance, W cir cuit closing key, and V the primary of a step up transformer. The primary charging circuit includes these four elements in series, and the secondary circuit is charged inductively through the transformer V V. In the secondary circuit K and L are electrodes of the spark gap, M a pipe connected to the tubular electrode K through an insulating coupling, and m a source of air under pressure. U is a variable inductance.

t is a condenser. T is an aerial, t a variable inductance in the aerial, and X a connection to earth or a counter capacity. The values in the secondary circuit are proportioned so that the condenser 6 will break down once in every half cycle of the primary current. The radiator T is constructed to radiate freely in the frequency required for transmission, tuning being effected by adjusting the condenser capacity, the length of spark gap and the variable loading inductance t. Discharge occurring on the breakdown of the condenser crosses the gap KL in one direction only, and feeds the radiator T with impulses of great rapidity. The wave train period of the radiator is determined by the frequency of the breaking down of the condenser t which is identical with the period of the alternator Z, but the wave oscillation frequency is determined by the capacity and inductance values in the radiator circuit. The high self induction of the transformer secondary V inhibits passage through it of the high frequency discharge which follows on the breaking down of the condenser 25.

What I claim as my invention and desire to secure by Letters Patent is 1. A spark gap comprising two fixed electrodes spaced apart, one of said electrodes being a metallic surface and the other electrode being a blunt nosed cone of metal axially directed toward the first mentioned electrode, and having a fine hole pierced axially through it, in combinationv with means for discharging a stream of gas under high pressure through said bore against the first mentioned electrode.

2. A spark gap whereof the electrodes are respectively a substantially flat metallic surface and a tubular metallic blunt nosed cone axially supported relatively thereto with its smaller end nearer to and spaced from said flat electrode, the passageway through said second electrode being connected rearwardly with a source of gas under pressure of between about fifty and one hundred forty pounds per square inch.

3. A rectifying spark gap comprising a metal blunt nosed cone which forms one electrode of said gap, a substantially flat member spaced axially from the smaller end of said cone and forming the other electrode, said cone having a small longitudinal bore, and means for discharging gas at high velocity through said bore.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

ARCHIBALD SHAW.

Witnesses:

W. J. DAVIS, M. RILEY.

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