US1980461A - Arcing frequency changing system - Google Patents

Description

Nov. 13, 1934. s, WI DMER ARCING FREQUENCY CHANGING SYSTEM Filed June 15, 1952 Patented Nov. 13, 1934 Ul'TED STATES ATENT ()F'FECE Aktiengesellschaft Brown Boveri Cie, Baden, Switzerland, a joint-stool: company of Switzerland Application June 15, 1932, Serial No. 617,400 In Germany June 15, 1931 Claims.

This invention relates to improvements in systems for converting alternating current of On frequency into alternating current of another frequency by the use of electric current valves of the 5 metallic vapor arcing type provided with means by which the arcing within such valves may be controlled.

In frequency changing systems of the character a ove indicated, it is necessary that short cirlO cults be avoided in the connections between the several valves by preventing operation of the anodes of such connected valves at the same time. It is also desirable that a potential having a substantially sine curve wave shape be delivered to the load circuit. Both of the above requirements can be met if control electrodes are provided for each of the anodes for the purpose of controlling the point in the cycle of the alternating current supply potential at which the several anodes will pick up the arc by controlling he impression of a positive potential on the several control electrodes serially associated with the anodes. It s, however, necessary to control the impression of a positive potential on such control electrodes very exactly and to vary the point in the alternating current supply potential cycle at which the D tive potential is applied to obtain proper sequential operation of the anodes and of the valves and to vary the time at which the several anodes will operate in such a manner as to vary the amplitude of the potential produced by such operations so that the load circuit potential half Waves composed of the several potentials of the anodes of one rectifier may approximate a sine curve.

It is, therefore, an object or" the present invention to provide a frequency changing system employing electric current valves or" the metallic vapor arcing type for obtaining a sequential but non-uniform operation of the anodes of the valves.

Another object of the invention is to provide a frequency changing system employing electric current valves of the metallic vapor arcing type in which means are provided for permitting operation of the anodes of the valves at Varying points in the cycle of the alternating current potential supply to the valve to secure a substantially sine shaped potential delivered by the valves.

Another object of the invention is to provide a frequency changing system employing electric current valves of the metallic vapor arcing type having main anodes and electrodes controlling the operation of the main anodes, the control elec- 55 trodes having a potential impressed thereon dependent on the position, the spacing and the 0 length or the contacts of a distributor connecting such control electrodes with a source of potential.

Another object of the invention is to provide a frequency changing system employing electric current valves of the metallic vapor arcing type having main anodes and electrodes controlling the operation or" the anodes connected with a source or" potential, the potential impressed on the control electrodes from the source being so controlled by a distributor having contacts of different lengths arranged at varying spacings and in varying positions to control the movement in the alternating current supply potential cycle which the several anodes operate in sequence as to obtain a substantially sine shape potential wave therefrom.

Qcjects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawing which diagrammatically illustrates one embodiment of the present invention in which a plurality of electric valves of the metallic vapor arcing type are connected with a source of alternating current supply at one quency and are controlled by such means and in such manner as to obtain the delivery therefrom to a load circuit of alternating current of a frequency other than that of the supply.

Referring more particularly to the drawing by characters of reference, the reference numeral 5 designates a polyphase electric transmission line supplied from a suitable source or electric current (not shown) at any desired frequency. A transformer comprising a primary winding 6 and the secondary windings 7 and 8 is connected with the line 5. The secondary windings are each star connected and the several phase sections thereof are connected with the anodes of electric current valves 10 and 11, respectively. The anodes of the valve 10 are designated by the numerals 14, 15, 16, 17, 18, and 19 and the anodes of the valve 11 are designated by the numerals 24 25, 26, 27, 28, and 29. Each of the rectifiers are provided with a cathode 31 and 32, respectively, which cathodes are pools of vaporizable material preferably a metal such as mercury. It will be understood that each of the valves is provided with suitable means for striking and for maintaining an arc therein such as is well known in the electric current rectifying art. The cathode of each of the valves is connected with the neutral point of the transformer secondary winding supplying potential to the anodes of the other valve, thus forming a circuit which has generally the form of the numeral eight in a horizontal position. The cathodes are connected with a load herein shown as a resistance 36, a reactance 3'7 and a capacitance 38 for the purpose of illustrating the fact that any type of load may be supplied with the current delivered from the cathodes 31 and 32. The load circuit is supplied at a potential difierent from that of the line 5 as will be described.

55, 56, 57, 58, and 59, are associated with the anodes of the valves 10 and fll, respectively. The control electrodes of the valve 10 are severally connected through resistances 61 and 62 with the negative terminal of a source of direct current potential such as the battery 65. An intermediate point of battery 65 is connected with the cathode 31 and the positive terminal of the battery 65 is connected with the distributor brush 64. 1 The brush is preferably rotated by a synchronous motor 66 connected with the line 5 and having a resistance in the excitation circuit thereof for the purpose of permitting control of the operation of the motor. The control electrodes of valve 11 are connected in a similar manner to those of valve 10, that is, through resistance 71 and 72 and a distributor comprising a series of contacts 73 and a brush 74 with a source of direct current potential having an intermediate point thereof connected With the cathode 32. The negative terminal of the source of current such as the battery '75 is connected with the contacts of the distributor and the positive terminal of the battery is connected with-the brushes thereof. The brush 74 of the distributor is operated in a man ner similar to that described for the brush 64 by means of a synchronous motor 76. It will be seen from the drawing that nine contacts are provided in each of the series of contacts 63 and '73 so that the first three control electrodes operating in each series are severally connected with the first three and with the last three contacts in their respective series of contacts.

In changing from the frequency of line 5 to that desired in the load circuit, it is necessary that short circuits be avoided in the figure eight circuit and that the potential of the load circuit approach as nearly as possible sinusoidal wave form. Current can, therefore, be allowed to pass only through one of the valves at a time and the potentials of the anodes combined to obtain the output to the load circuit must be of such ampli-- tudes as to produce a substantially sinusoidal potential wave form in such load circuit. The above result is obtained by the particular construction of the distributors and the arrangements of the connections as shown. The contacts of each of the distributors are arranged over less than 180 degrees of such distributor and the first contacts of the distributors are arranged at least 180 degrees away from each other. Even though the brushes 64 and '74 are rotated in synchronism, their angular positioning is such that a positive potential can be impressed only on the control electrodes of one valve at the same time thus preventing possibility of short circuits by allowing the anodes of both valves to operate simultaneously. The shape of the voltage wave delivered to the diiferent frequency load circuit is dependent on the spacing and on the length of the contacts in each series and is materially improved by increasing the number of anode firing periods per half wave of the output voltage to the load circuit and by controlling the amplitudes of the potentials delivered by the several anodes by control of the points in the cycle of the supply potential at which the arc will be picked up by the anodes.

In operation, assuming that the motors 66 and 76 are operating in synchronisrn and that the brushes 64 and '74 are in the position shown, a positive potential relative to the cathode potential will be impressed in sequence on the control electrodes of valve 10 and the anodes thereof Will Control electrodes44, 45, 46, 4'7, 43, 49, and 54,

pick up the arc in the following order-14, 15, 16, 1'7, 18, 19, 14, 15, 16-due to connection of the rst and the last three of the contacts 63 with the anodes 14, 15, and 16. By the time the anodes have all operated in the above order, brush 64 will have passed beyond the last of the contacts 63 and a negative potential will be impressed on all the control electrodes of valve 10 fromthe negative terminal of battery 65 through resistances 61 and 62. The contacts are so spaced and are so arranged relative to the alternating current potential supply cycle that a positive potential is impressed on the control electrodes at diiferent points in the cycle thus varying the amplitudes of the potentials impressed on the anodes at the time such anodes are firing and producing substantially a sine half wave potential in the load circuit. By the time brush 64 has passed beyond the last of the contacts 63 and the current on anode 16 firing last in the above series has dropped to zero, brush 74 will have reached the first of contacts 73 and a positive potential relative to the cathode potential is impressed in sequence on the control electrodes of valve 11 thus permitting the anodes thereof to pick up the arc in the following order-25, 26, 27, 28, 29, 24, 25, 26, 27. Valve 11 thus supplies a potential half wave of substantially sine curve shape to the load circuit and of opposite direction to that supplied from the valve 10. After brush '74 has passed beyond the last of contacts 73 and the current on anode 27 has dropped to zero a negative potential is impressed on the control electrodes of valve 11 and brush 64 has again reached the first of the contacts 63. The above cycle of operation is then again repeated for each cycle of the potential supplied to the load circuit.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

, It is claimed and desired to secure by Letters Patent:

1. Li a system for converting alternating current of one frequency into alternating current of another frequency, electric current rectifying means comprising a plurality of groups anodes, and a plurality of control electrodes severally associated with said anodes, an alternating current output circuit connected with said means to be supplied with load current therefrom, an alternating current input circuit connected with said anodes and supplying load current through said means to said output circuit, means connected with and operable to impart to each of said control electrodes potential of such sign and. magnitude as to prevent initiation of flow of current through the associated anodes from said input circuit to said output circuit, and means connected with and operable to sequentially and continually impress potential momentarily on each of said control electrodes associated with the anodes of each said group-thereof alternately of such sign and magnitude and at such recurring periods as to permit such sequential initiation of flow of current through said anodes from said input circuit as to supply substantially sine Wave alternating current through said means to said output circuit at a predetermined frequency.

2. In a system for converting alternating current of one frequency into alternating current of another frequency, electric current rectifying means comprising a plurality of groups of anodes, and a plurality of control electrodes severally associated with said anodes, an alternating current output circuit connected with said means to be supplied with load current therefrom, an alternating current input circuit connected with said anodes and supplying load current through said means to said output circuit, means connected with and operable to continuously impart to each of said control electrodes potential of such sign and magnitude as to prevent initiation of flow of current through the associated anodes from said input circuit to said output circuit, and means connected with and operable to sequentially and continually impress potential momentarily on the said control electrodes associated with the said anodes of each said group thereof alternately of such sign and magnitude and at such recurring periods relative to the voltage frequency of said input circuit as to permit such sequential initiation of flow of current through said anodes from said input circuit as to supply substantially sine wave alternating current through said means to said output circuit at a predetermined frequency relative to the voltage frequency of said input circuit.

3. In a system for converting alternating current of one frequency into alternating current of another frequency, electric current rectifying means comprising a plurality of groups of anodes, and a plurality of control electrodes severally associated with said anodes, an alternating current output circuit connected with said means to be supplied with load current therefrom, a polyphase alternating current input circuit connected with said anodes and supplying load current through said means to said output circuit, means connected with and operable to impart to each of said control electrodes potential of such sign and magnitude as to prevent initiation of flow of current through the associated anodes from said input circuit to said output circuit, and means operable to sequentially and continually impress potential momentarily on each of said control electrodes associated with the anodes of each said group thereof alternately of such sign and magnitude and at such recurring periods relative to the respective phase voltages of said input circuit as to permit such sequential initiation of flow of current through said anodes from said input circuit as to supply substantially sine wave single phase alternating current of a predetermined frequency through said means to said output circuit.

4. In a system for converting alternating current of one frequency into alternating current of another frequency, electric current rectifying means comprising a plurality of groups of anodes, and a plurality of control electrodes severally associated with said anodes, an alternating current output circuit connected with said means to be supplied with load current therefrom, an alternating current input circuit connected with said anodes and supplying load current through said means to said output circuit, means connected with and operable to continuously impart to each of said control electrodes potential of such sign and magnitude as to prevent initiation of flow of current through the associated anodes from said input circuit to said output circuit, distributor switch means having connections with sources of control potential and being operable to sequentially impress the potential thereof momentarily on the control electrodes of each said group of anodes alternately of such sign and magnitude as to permit sequential initiation of flow of current from said input circuit through said anodes of each said group thereof alternately to thereby supply alternating current from said input circuit to said output circuit, and means for operating the said distributor switch means to cause the last said potential to be continually impressed on the said control electrodes at such recurring varied periods as to cause supply of substantially sine wave alternating current through said rectifying means to said output circuit at a predetermined frequency.

5. In a system for converting alternating current of one frequency into alternating current of another frequency, a pair of alternating current rectifiers each comprising a cathode, a plurality of anodes, and a plurality of control electrodes severally associated with the said anodes thereof, an alternating current input circuit, an alternating current output circuit, transformer means comprising a pair of secondary windings each divided into a plurality of star-point connected phase-displaced sections, the phase-displaced sections of each said winding being severally connected with the anodes of a different one of said rectifiers and the star-point connection thereof being connected with the said cathode of the other of said rectifiers and with said output circuit, source of control current connected with and imparting to said control electrodes of each said rectifier potential of sign and magnitude more negative than the potential of the cathode thereof, distributor switch means having connections with and being operable to sequentially and continually impress potential of said sources of control current momentarily on the control electrodes of each said rectifier alternately of sign and magnitude more positive than the cathode thereof and at such varied recurring periods as to permit such recurring sequential initiation of flow of current through said anodes as to supply substantially sine wave alternating current of predetermined frequency to said output circuit relative to the voltage frequency of said input circuit.

STEFAN WIDMER.

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