US2748317A - Mutator system, more particularly a rectifying system, in the graetz arrangement, and to a method of controlling such a system - Google Patents

Description

y 29. 9 A. VAN DE WIEL 2,

MUTATOR SYSTEM, MORE: PARTICULARLY A RECTIFYING -SYSTEM, IN THE GRAETZ ARRANGEMENT, AND TO A METHOD OF CONTROLLING SUCH A SYSTEM 2 Sheets-Sheet Filed Jan. 4, 1951 IIIIA INVENTOR ALFRED VAN DE WIEL y 9, 1956 A. VAN DE WIEL 2,748,317

MUTATOR SYSTEM, MORE PARTICULARLY A RECTIFYING SYSTEM, IN THE GRAETZ ARRANGEMENT, AND TO A METHOD OF CONTROLLING SUCH A SYSTEM Filed Jan. 4, 1951 2 Sheets-Sheet 2 L 0A D i X 4m fizz? 5' /2' mun REM/AVE ol GEN, o- 4 IN VEN TOR.

133.6 ALFRED VAN DE WIEL United States Patent MUTATOR SYSTEM, MORE PARTICULARLY A RECTIFYING SYSTEM, IN THE GRAETZ AR, RANGEMENT, AND T9 A METHOD OF CON- TROLLING SUCH A. SYSTEM Alfred Van De Wiel, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Coma, as trustee Application January 4, 1951, Serial No. 204,298

Claims priority, application Netherlands January 26, 195i) 7 Claims. (Cl. 315-144) The invention relates to a mutator system, more particularly a rectifying system, in the Gratz arrangement and to a method of controlling such a system. By the use of controllable commutators, such as grid-controlled, gas or vapour-filled incandescent cathode discharge tubes the output voltage may be made continuously controllable between a maximum and minimum value.

Since in a Gratz circuit arrangement the current invariably passes through two discharge tubes at the same time, the control should be such that the tubes concerned actually strike simultaneously at the correct instant. When usingstriking voltages, which are applied to the tubes for a comparatively long period, this is directly obtainable. However, if very accurate control of the starting instant is required, it is known to be necessary to use striking voltages having a steep wave front, for example sharp voltage pulses. In such cases it has been found to be very difiicult to ignite both tubes concerned simultaneously at the correct instant, since this also required the peaked striking voltages to be produced exactly at the same instant. If one striking voltage is slightly in advance relative to the other, the first tube will ignite, but extinguish immediately thereon, since the current cannot yet pass through the second tube, which has not yet struck, so that the system does not operate. In such a case the object could, if desired, be realized by using rectangular ignition voltages.

However, if, as required in the case of comparatively high voltage, use is to be made of tubes comprising a cold liquid or solid cathode and an ignition electrode, it is futile to apply a rectangular voltage to the ignition electrode, since the ignition spark occurs at the instant only of applying the voltage. Even in this case satisfactory operation cannot generally be obtained, since, as stated above, it is very diflicult to apply the two voltages at exactly the same instant.

According to the invention, the disadvantage can be obviated by using controllable, gas or vapour-filled discharge tubes of the kind comprising a cold liquid or solid cathode, an ignition electrode and an auxiliary anode in a mutator system in the Gratz arrangement. The control-means are such that the output voltage is controllable in practice from the minimum to the maximum value obtainable, each of the auxiliary anodes being connected periodically to a positive auxiliary voltage source for more than 180, butless than 360 degrees of the electrical wave.

If the control of the rectifying system-is adjusted, for example, to a low output voltage, a tube in the Gr'zitz arrangement which has ignited and is then extinguished, will generally have to re-ignite, when the next following tube isignited, in order to allow the passage of the current of the latter tube. This is made possible by the measure according to the invention, since the discharge path of the ffirst tube, after the latter is extinguished, is maintained in the ionized condition by the auxiliary are between the auxiliary anode and the cathode, which,

2,748,317 Patented May 29, 1956 ice similarly to the main are between the main anode and the cathode is ignited by the ignition voltage, so that the first tube ignites automatically under the action of the positive anode voltage, when the second tube strikes. This second automatic ignition of the first tube is thus not initiated in a direct manner by the control-means, but by the ignition of the second tube so that the aforesaid stringent requirement of simultaneous ignition of the two tubes at exactly the same instant with the use of a control-voltage is done away with.

A second advantage of the invention is, as stated above, the possibility of causing the tubes to deliver their maximum output.

The auxiliary anodes must not be continuously con nected to the positive auxiliary voltage, since the controllability of the system would be affected.

Not only a rectifying system, but also an inverter system may be arranged in accordance with the invention, for example to feedback alternating current energy to the power lines when electrically braking a direct-current motor .opflrating as a generator.

As a rule, it will be found sufiicient for the positive voltage to be supplied for a maximum of 345 degrees to each of the auxiliary anodes, so as to ensure in practice the time of ii-ionization required for the controllability of each of the discharge tubes.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described in detail with reference to the accompanying drawing, in which the figures show diagrammatically one embodiment of the commutator system according to the invention.

Fig. 1 is a schematic circuit diagram of a rectifying system in a three phase Gr'altz arrangement and Fig. 2 is a graph representing the associated voltages in the system of Fig. 1.

Fig. 3 is a graph .of a control-voltage for a second preferred embodiment of the invention.

Fig. 4 is a schematic circuit diagram of said second mbodirnent.

Fig. 5 is a graph showing the output voltage furnished by the circuit in Fig. 4.

A Fig. 6 is a schematic circuit diagram of the arrangement shown in Fig. l, in which solid-cathode gas-filled tubes are used instead of liquid-cathode vapor-filled tubes.

Referring to Fig. l, six .gasor vapour-filled discharge tubes 1 to 6 are connected in a normal Gratzarrangement to a three phase mains 7. Each of the tubes comprises a mercury cathode 8, an immersed ignition electrode 9, an anode l0 and an auxiliary anode 1 1. A load 12 is connected to the direct voltage line 13, 14. As shown solely in conjunction with tube 9, the ignition electrode 9 of eachtube is supplied with pulse-shaped ignition voltages produced by a source 36 whose output is shiftable in .phase As shown solely .in conjunction with discharge tubes 3 and 4, the ignition electrodes 9 .of these tubes are supplied with pulse-shaped ignition voltages 3" and 4 by pulse generators 38 and 39, respectively, whose outputs are-shiftable in phase. Any conventional pulse generat-or circuit may be used for this purpose. The auxiliaryanodes 11 of tubes 3 and 4 are supplied with a direct voltage 17 formore than but less than 360 .of the alternating current periodby the square-wave generators 40 and 41. A preferred form of the square-wave generator is shown in ,Fig. 4, which will be discussed indetail later inthe specification.

.Fig. 2 shows the anode voltages 4 to 6 of the tubes 4 to 6 and the cathode voltages 1' to 3' of the tubes 1to;3. The figure furthermore shows the control-voltage 4"for thetube 4, the control yoltage 3" for the tube 3 andt he control voltage for the tube 5 as pulse type voltages. These control-voltages are adapted to be shifted in phase, at least in the section of the positive anode voltage 4, provided that complete controllability of this arrangement from minimum to maximum direct voltage is desired.

If a comparatively low output voltage is desired ignition will have to take place comparatively late in the half-period, for example at the instant indicated by the ignition peak 4. The tube 4 then ignites with anode voltage 4. It is assumed that the current passing through this tube also makes its way through the tube 2. The tube 4 is alive until the instant 16, when the anode voltage becomes negative and the discharge between the anode 10 and the cathode 8 is consequently interrupted.

At the instant of the ignition voltage 3", the tube 3 is ignited with negative cathode voltage 3 (and consequently positive anode voltage). As a matter of course in a Gratz arrangement the current passing through this tube has to pass through a further tube and according to I the invention this is now directly possible, since a positive auxiliary voltage 17 (Fig. 2) is applied to the auxiliary anode 11 of the tube 4, which just has been extinguished. Dining the ignition of the tube 4 with the use of the ignition voltage 4", an auxiliary arc was also struck between the auxiliary anode 11 and the cathode 8, this auxiliary arc being maintained even after the instant 16, when the main are is interrupted, so long as the auxiliary voltage 1"! remains positive.

At the instant of ignition of the tube 3 by the pulselike voltage 3", the said auxiliary arc is also struck with the result that the discharge path of the discharge of the tube 4 just interrupted at the instant 16 remains in the ionized state, so that the tube 4 automatically re-starts, when, this tube, owing to the ignition of the tube 3, has a positive anode voltage relative to the cathode. This is known to be invariably the case, so long as the voltage 1 (the subsequent voltage of the voltage 4) of the tube 4 is more positive than the cathode voltage 3 of the tube 3. The two tubes then extinguish simultaneously at the instant 18.

Similarly, the tube 5 ignites at the instant 5", so that the tube 3 just extinguished is again forced to strike under the action of the positive anode voltage, provided that the auxiliary are between the auxiliary anode and the cathode is also ignited at the instant 3" owing to the presence of a positive auxiliary voltage, this auxiliary are maintaining the ionization of the tube 3 till the instant 5".

The period of time for which the auxiliary voltage is to be applied to the auxiliary anode 11 must exceed 180 degrees. Since in the present case, it is desired that the rectifier be controllable from the minimum to the maximum voltage, this implies that at the maximum voltage the control-voltage 4" for the tube 4 having the anode voltage 4' must occur at the instant 19. However, with phase-shifting devices it is very difiicult to adjust the control to be such that the ignition peak is exactly coincident with the instant 19. Consequently, in practice this necessitates the use of a margin of tolerances. If this margin is provided to the right of the point 19, ignition will invariably take place, but the maximum voltage is not invariably obtainable. lf the margin is provided on either side or to the left of the point 19, either ignition of the tube 4 will occur only occasionally or it will not occur at all because the ignition peaks which are produced to the left of the point 19 do not bring about ignition, since the anode voltage 4 to the left of point 19 is still negative in relation to the cathode. By starting the positive auxiliary voltage for the auxiliary anode 11 at the left of the point 19, an ignition peak at the left of point 19 will strike the auxiliary arc, after which, as soon as the point 19 has been passed by the main arc is automatically struck by the auxiliary are under the action of the higher anode voltage 4' at the right of point 19, whereas the ignition peak 4" proper has already vanished.

The auxiliary voltage must consequently start at the left of point 1). The end of the duration of the auxiliary voltage must be substantially to the right of point 18, since for obtaining the minimum direct voltage, an ignition has to take place near the end of the half period 3' of the tube 3, immediately to the left of point 18. However, this also means that at this instant the main are of the tube 4, as the subsequent tube, must still be able to start automatically with the use of the auxiliary are, which has ignited immediately before point 16 (near the end of the half period 4-). Since the course 20 between 18 and 19 is degrees, the auxiliary voltage must be applied to a greater course, that is to say, exceeding 180 degrees, as is indicated by the auxiliary Voltage 17.

However, before in the subsequent cycle at the point 21 it is again the turn of tube 3, the auxiliary arc must be extinguished, since otherwise the main arc would reignite under the action of the anode voltage 4' immediately at the right of point 21, while it is precisely an ignition immediately before point 22 near the end of the half period which is desired. Consequently, the auxiliary voltage must be applied to a course shorter than 360 degrees, i. e. the course 20+23, that, is to say, so much shorter that the tie-ionization time till point 24, where the auxiliary voltage is re-applied, is sufiicient.

In order to provide sufficient time for the tube 4 to de-ionize before the point 21, it is generally advisable to provide for the duration of the period 17 of the positive auxiliary voltage not to exceed 345 degrees.

The positive auxiliary voltage may be applied to the auxiliary anodes in various ways for example, by temporary connection to a direct voltage source 37 with the use of mechanical contacts 38.

An improved method consists in the application of a direct voltage having superposed thereon an alternating voltage, as is shown in Fig. 3. The zero-voltage line is designated 25, the direct voltage 26 and the alternating voltages 27. During the course 28 of approximately 300 degrees, the auxiliary volta e is positive and during the course 2? of about 60 degrees it is negative in order to bring about the de-ionization.

Fig. 4 illustrates a preferred method of producing the required auxiliary voltage with the use of a normal three phase-transformer connected to an alternating current line and of two small rectifiers. Two windings 30 and 31 of the secondary star-connected winding of a line transformer (not shown for the sake of simplicity) are each connected in series with a dry rectifier 32 and 33 to each other and, by way of a load resistance 34, to the auxiliary anode 11. The star point is connected to the cathode 8. The third winding 35 is not connected.

The voltage of this arrangement is similar to that shown in Fig. 5, the course 36 with positive voltage being again 300 and the course 37 with negative voltage being 60 degrees.

The circuit of Fig. 6 operates similarly to that of Fig. 1, described above.

What I claim is:

1. In a mutator system for an alternating voltage wherein discharge tubes are connected in a Gratz arrangement, said tubes each having a cathode, an ignition electrode, an auxiliary anode and a main anode, control apparatus for said system comprising means to apply an igniting voltage to the ignition electrode of each tube at a desired instant with respect to the cycle of alternating voltage, and means to connect periodically an auxiliary voltage to said auxiliary anode in each tube for more than 180 degrees but less than 360 degrees of said cycle, the value of said auxiliary voltage being sufficient to maintain auxiliary arcs following extinguishment of the main arcs in said tubes.

2. In a system, as set forth in claim 1, wherein said tube is a vapour-filled tube and said cathode is a cold liquid cathode.

3. In a system, as set forth in claim 1, wherein said tube is a gaseous tube and said cathode is a solid cathode.

4. Apparatus, as set forth in claim 1, wherein said auxiliary voltage is supplied to each auxiliary anode for not more than 345 degrees,

5. Apparatus, as set forth in claim 1, wherein said auxiliary voltage is produced by a source including a three phase transformer, having three windings with a common end terminal therefor, a first rectifier connecting the other end terminal of one of said windings to the auxiliary anode of a tube, a second rectifier connecting the other end terminal of a second winding to said auxiliary anode, and means connecting the common terminal to said cathode.

6. In a mutator system for an alternating voltage wherein vapour-filled discharge tubes are connected in a Gritz arrangement, said tubes each having a cathode, an ignition electrode, an auxiliary anode and a main anode, control apparatus for said system to vary its output from the minimum to the maximum value obtainable comprising means to apply igniting pulses to the ignition electrode of said tube, said pulse means being adjustable in phase, and means to connect periodically an auxiliary voltage to said auxiliary anode in each tube for more than 180 degrees but less than 360 degrees with respect to the cycle of said alternating voltage, the value of said auxiliary voltage being sufficient to maintain auxiliary arcs following extinguishment of the main arcs in said tubes.

7. Apparatus, as set forth in claim 6, wherein the beginning of the positive auxiliary voltage is before the point at which ignition of the tube is possible with the use of the igniting pulse for obtaining the maximum value of the output voltage.

References Cited in the file of this patent UNITED STATES PATENTS 20 2,248,625 Herskind July 8, 1941 2,291,092 Cox et a1. July 28, 1942 2,549,831 Longini Apr. 24, 1951

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