US1946973A

US1946973A - Rectifier control system

Info

Publication number: US1946973A
Application number: US586543A
Authority: US
Inventors: Keller Hans
Original assignee: BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Germany; BBC Brown Boveri France SA
Priority date: 1931-01-07
Filing date: 1932-01-14
Publication date: 1934-02-13
Anticipated expiration: 1951-02-13

Description

2 Sheets-Sheet l H. KELLER RECTIFIER CONTROL SYSTEM Filed Jan. 14, 1932 E) M z-wYo'z Feb. 13, 1934.

2 Sheets-Sheet 2 H. KELLER RECTIFIER CONTROL SYSTEM Filed Jan. 14, 1952 Feb. 13, 1934.

Patented Feb. 13, 1934 UNITED STATES PATENT OFFI CE' RECTIFIER CONTROL SYSTEM Hans Keller, Baden, Switzerland, assignor to Aktiengesellsehaft Brown Boveri & Cie., Baden, Switzerland, a joint-stock company of Switzerland 8 Claims.

This invention relates to improvements in electric current rectifying systems employing an electric current rectifier of the metallic vapor arcing type and particularly to means in con-- nection with such systems for controlling the operation thereof by controlling the arcing within the rectifier.

The voltage of the output direct current of an electric current rectifier of the metallic vapor arcing type may be controlled by the use of control electrodes associated with the anodes of the rectifier. The picking up of the arc by the anodes of the rectifier is controlled by controlling the impression of a potential on the control electrodes. Such potential may be either alternating or direct and may be of the same frequency as the potential impressed on the anodes of the rectifier. When an alternating potential is impressed on the control electrodes and is displaced relative to the anode potential,

the picking up of the are by the anodes is delayed and the direct potential delivered by the rectifier decreases. A control electrode will then have a potential impressed thereon for a longer Q5 period of time than the potential is impressed on the associated anode. The control electrode will, therefore, still be in operative condition as an anode i. e. will be positive when the associated anode is already strongly negative, both considered relative to the cathode potential.

Under such circumstances back-fires or short circuits are likely to occur because the contents of the space about the anodes are still ionized by the space charge due to the potential impressed on the control electrode. It has been proposed that the above disadvantage be avoided by displacing the neutral point of the transformer supplying the control electrodes in a negative direction relative to the cathode potential by means of a variable direct current potential superimposed on the alternating potential supplied by the transformer. The ignition point i. e. the point at which the arc will be picked up by the control electrodes and the anodes may then be displaced in either direction by variation of the direct current potential superimposed on the alternating current potential impressed on the grids. The use of such superimposed direct current potential has the advantage that charging of the control electrodes will coincide in polarity with that of the anodes relative to the cathode potential. The use of such superimposed direct current potential, however, still presents the disadvantage that the anodes will pick up the arc at different times rather than at regular intervals so that the direct current potential obtained is not uniform and the anodes are not equally loaded.

It is therefore among the objects of the present invention to provide means in connection with an electric current rectifying system employing an electric current rectifier of the metallic vapor type by which the ignition periods of the anodes oi the rectifier may be controlled.

Another object of the present invention is to provide means in connection with an electric current rectifying system employing an electric current rectifier of the metallic vapor type provided with control electrodes associated with the anodes by which the polarity of the potential impressed on the control electrodes and on the anodes of the rectifier may be made to coincide relative to the cathode potential.

Another object of the present invention is to provide means in connection with an electric 76 current rectifying system employing an electric current rectifier of the metallic vapor type by which a potential of higher frequency is impressed on the control electrodes of the rectifierv in addition to the potential of the lower frequency 80 impressed thereon for the purpose of securing coincident charging and operating of the anodes and the control electrodes of the rectifier.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawings, in which:

Figure l diagrammatically illustrates an electric current rectifying system employing an electric current rectifier of the metallic vapor arcing type having electrodes to control the arc within the rectifier and means for impressing a potential on such electrodes;

Figure 2 diagrammatically illustrates an embodiment of the invention in which the means for impressing a potential on the control electrodes is modified relative to that shown in Figure 1;

Figure 3 diagrammatically illustrates a further modified embodiment of the means for impressing a potential on the control electrodes of a rectifier; and

Figure 4 shows a plurality of curves illustrating the potential relations of the anodes, the control electrodes associated with the anodes and the cathode of a rectifier taken relative to the potential of the neutral point of the transformer secondary winding supplying an alternating potential to the control electrodes in a 110 33 and the direct current source 41.

system such as is illustrated in Figs. 1 to 3, inclusive.

Referring more particularly to the drawings by characters of reference, the reference numeral 6 designates an alternating current line which is connected with the primary winding '7 of a transformer, of which the secondary winding is divided into two star connected systems 8 and 8c. The several coils of the transformer secondary winding are severally connected with the anodes 9 to 14, inclusive, of an electric current rectifier of the metallic vapor type, generally indicated at 16 and having a cathode 17 formed of a vaporizabie material such as mercury. The neutral points of the transformer secondary windings 8 and 8a are interconnected by an interphase transformer 21, the midpoint of which is tapped by a conductor 22 forming the negative bus bar of a direct current circuit. The positive bus bar of the direct current circuit which is supplied by the rectifier 16 is formed by a conductor 23 connected with the cathode 17, the circuit supplying direct current consuming devices such as indicated at 24.

A transformer 31 is connected in parallel with one of the windings of interphase transformer 21, the secondary winding of the transformer 31 being connected with the neutral point of a star connected primary winding 32 of a control electrode supply transformer. The terminals of the primary winding 32 are connected with the three anodes connected with the secondary winding 8a of the rectifier supply transformer. If desired primary winding 32 may be connected with an auxiliary source of alternating current at a suitable potential, rather than with the anode connections as shown. The secondary winding 33 of the control electrode supply transformer is connected in star and the terminals of the several coils thereof are severally connected through current limiting resistances with control electrodes 34 to 39, inclusive, associated severally with the anodes. The neutral point of the control electrode supply transformer secondary winding 33 is adjustably connected with a source of direct potential such as the battery 41, the positive pole of which is connected with the positive bus bar 23 for the purpose of superimposing a direct potential bias on the transformer which is negative relative to the cathode potential.

In operation, a combined alternating and direct potential are impressed on the control electrodes 34, etc. from the supply transformer 32,

The alternating potential supplied is a combination of the fundamental taken from the secondary winding 8a of the anode supply transformer and the third harmonic taken from the interphase transformer 21 by the auxiliary transformer 31.

If desired, the

supply transformer

32, 33 may be so constructed as to shift the phase of the potential supplied therefrom to the control electrodes. The direct potential superimposed on the control electrode transformer potential from the direct current source 41 is biased in a negative direction relative to the cathode potential of the rectifier for the purpose of obtaining ignition of the control electrodes on the steepest portion of the composite potential curve reignition point may be displaced to any desired portion of the curve and the ignition of the control electrodes will then be forced to occur in the same cycle.

Figure 2 illustraates an embodiment of the invention which is similar to that shown in Figure 1 and described above except that a plurality of excitation anodes 43, 44 and 45 are shown supplied from the secondary winding 47 of a transformer, the primary winding 48 of which is connected with the secondary winding 8a of the anode supply transformer. The

excitation transformer

47, 48 may, of course, be connected with another source of alternating potential, if desired, rather than with the anode supply transformer. The neutral point of the excitation transformer secondary winding 47 is connected through a resistance 49 with the direct current positive bus bar 23 and the neutral point of the anode supply trans-former secondary winding 8a is connected through a current transformer 51 with the neutral point of the control electrode supply transformer primary winding 32. The control

electrode supply transformer

32, 33 is preferably then constructed as a phase shifting transformer. In the embodiment shown in Fig. 2, an alternating potential of the same frequency as the frequency of the potential of the anode supply transformer is supplied to the

control electrode transformer

32, 33 and a third harmonic potential is superimposed on such fundamental frequency potential from the

excitation transformer

47, 48 through the current transformer 51 in addition to the direct potential impressed thereon from the source 41.

Fig. 3 illustrates a modified form of the invention in which a phase shifting transformer having a primary winding 53, connected with the anode supply transformer secondary winding 8a, and a secondary winding 54 is connected with and supplies an alternating potential at the fundamental frequency of the line 6 to the

control electrode transformer

32, 33. The third harmonic frequency for the control electrodes may be secured by constructing the control electrode transformer with a four-legged core which is saturated. The direct potential is obtained from the source 41 as shown and described with re spect to Figs. 1 and 2 of the drawings.

The potential relations of the several portions of the system may be seen in Fig. 4 in which curve a represents the potentials of the anodes 9 etc. relative to the line b representing the potential of the cathode 17; the line 0 represents the potential of the neutral point of the control electrode transformer secondary winding 33, and the curve d represents potentials of the supply frequency impressed on the control electrodes 34, etc. from windings 8a. The curve e represents potentials of the third harmonic frequency, relative to the frequency of the potentials of the supply source 6 impressed on the control electrodes from the several sources above described and the curve I represents the resultant or combined potentials of the curves d and e. The curves d, e, and 1, indicate the potentials impressed on the control electrodes relative to the neutral point potential represented by the line 0. Assuming that it represents the potential, above the cathode potential, which must be impressed on a control electrode to permit picking up of the are by the anode associated therewith and that y is the voltage drop from the control electrode to the cathode; when the phase of the alternating current potential on the control electrode is retarded by the amount w and a direct current potential is impressed on the control electrode, the control electrode will permit picking up of the arc by the anode, at the point k located by'the intersection of the line limiting the value u with the curve f. The are will continue to flow from each anode until the potential thereon drops below the point 1 which is the value indicated by the intersection of the line limiting the value y with the curves a and f. Thus the quenching of the are on the anodes and change of the potential impressed on the grids and on the anodes at different times with the resulting non-uniformity of the direct current output voltage of the rectifier and the unequal loading on the anodes is avoided by producing a steeper wave front than would otherwise be obtained. Such wave front is obtained by the use of the third harmonic voltage e which, in combination with the fundamental voltage d, produces the resultant f. The control electrodes and theassociated anodes, therefore, ignite at different times, relative to each other, than heretofore, but the quenching of the arcs takes place at the time shown by the intersection of the line limiting the value of y with the curves a and f. The potentials on both the control electrodes and the anodes are thus at such valueas to permit the anodes to operate only for such length of time as the control electrodes are positive relative to the cathode potential.

Although but a few embodiments of the present invention have 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. In an electric current rectifying system including an alternating current supply line connected with a transformer for supplying alternating current to the anodes of an electric current rectifier of the metallic vapor arcing type having control electrodes associated with the anodes to control the establishment of arcs thereto and having a cathode, a transformer supplying a potential of fundamental frequency to the control electrodes, means for impressing a harmonic potential on said control electrodes, the harmonic potential being in constant phase relation with the fundamental frequency impressed on the control electrodes, and means for impressing a direct current potential on said control electrodes.

2. In an electric current rectifying system including an alternating current supply line connected with a transformer for supplying alternating current to the anodes of an electric current rectifier of the metallic vapor arcing type having control electrodes associated with the anodes to control establishment of arcs thereto and having a cathode, a transformer supplying a potential of fundamental frequency to the control electrodes, means for impressing a harmonic potential on said control electrodes, the harmonic potential being in constant phase relation with the fundamental frequency impressed on the control electrodes, and means for impressing on said control electrodes a direct current potential of a value negative relative to the cathode potential.

3. In an electric current rectifying system including an alternating current supply line connected with a transformer for supplying alternating current to the anodes of an electric current rectifier of the metallic vapor arcing type having control electrodes associated with the anodes to control establishment of arcs thereto and having a cathode, a transformer supplying a potential of fundamental frequency to the control electrodes, an auxiliary transformer for impressing a harmonic potential on said control electrodes, the harmonic potential being in constant phase relation with the fundamental frequency impressed on the control electrodes, and means fol-impressing a direct current potential on said control electrodes.

4. In an electric current rectifying system including an alternating current supply line connected with a transformer for supplying alternating current to the anodes of an electric current rectifier of the metallic vapor arcing type having control electrodes associated with the anodes to control establishment of arcs thereto and having a cathode, a transformer supplying a potential of fundamental frequency on the grids, an auxiliary transformer connected with the primary winding of said transformer supplying the control electrodes for impressing a harmonic potential thereon, the harmonic potential being in constant phase relation with the fundamental fretrol electrodes, an auxiliary transformer connect- 3 ed with the primary winding of said transformer supplying the control electrodes for impressing a harmonic potential thereon, the harmonic potential being. in constant phase relation with the fundamental frequency impressed on the control electrodes, said auxiliary transformer being connected with the transformer supplying the anodes, and means for impressing a direct current potential on the said control electrodes.

6. In an electric current rectifying system 3.1

including an alternating current supply line connected with a transformer for supplying alternating current to the anodes of an electric current rectifier of the metallic vapor arcing type having control electrodes associated with the anodes to control establishment of arcs thereto and having a cathode, a transformer supplying a potential of fundamental frequency to the control electrodes, an auxiliary transformer connected with the primary winding of said transformer supplying the 35,

control electrode for impressing a harmonic thereon, the harmonic potential being in constant phase relation with the fundamental frequency impressed on the control electrodes, a current transformer connecting said auxiliary trans- 3 z.

former with said transformer supplying thecontrol electrodes, and means for impressing a direct current potential on said transformer.

7. In an electric current rectifying system including an alternating current supply line connected with a transformer for supplying alternating current to the anodes of an electric current rectifier of the metallic vapor arcing type having control electrodes associated with the anodes to control establishment of arcs thereto and having a cathode, a transformer supplying a. potential of fundamental frequency to the control electrodes, said transformer having a fourlegged core and being highly saturated to impress a harmonic potential on the control electrodes in addition to the fundamental potential impressed thereon, the harmonic potential being in constant phase relation with the fundamental frequency impressed on the control electrodes; and means for impressing a direct current potential on said transformer.

8. In an electric current rectifying system including an alternating current supply line connected with a transformer for supplying alternating current to the anodes of an electric current rectifier of the metallic vapor arcing type having control electrodes associated with the anodes to control the establishment of arcs thereon and having a cathode, a transformer supplying a potential of fundamental frequency to the control electrodes, an auxiliary transformer connected with the primary winding of said transformer supplying fundamental frequency potential to the control electrodes, said auxiliary transformer being connected with the transformer supplying the anodes and impressing an uneven numbered harmonic potential on the control electrodes, the harmonic potential being in constant phase relation with the control electrodes, and means for impressing a direct current potential on the control electrodes.

HANS KELLER.