US2214871A - Voltage generating apparatus - Google Patents

Description

Sept. 17, 1940.

w. F. WESTEN'DIORP 2,214,871

VOLTAGE GENERATING APPARATUS Filed Aug. 27, 1938 Sheets-Sheet l i A /m v v A Ce mm 06F07'E/1/77/1L CONDENSER VOL746 Cg J6,

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Willem F. Wescendorp,

H is Attorney.

p 1940- w. F. WESTENDORP 2,214,871

VOLTAGE GENERATING APPARATUS Filed Aug. 27, 193.8 2 Sheets-Sheet 2 Inventor: Wi I learn F. Westendorp,

i Attorney.

Patented Sept. 17, 19 40 UNITE STAi'Efi VOLTAGE GENERATING APPARATUS Willem F. Westendorp, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application August 27, 1938, Serial No. 227,223

8 Claims.

The present invention relates to static apparatus for generating unidirectional potentials.

It is an object of the invention to provide means whereby a constant potential of great magnitude can be derived from an alternating potential source of low intensity. The new apparatus involves the combination of a resonant oscillating circuit with means for causing voltages developed in the circuit to appear as a constant potential across appropriate terminals. The system provided has a substantial advantage over systems heretofore available in requiring relatively simple and inexpensive apparatus. It is particularly noteworthy that where the system is to be used for high voltage purposes, it can utilize a large number of relatively low tension elements each of which sustains only a proportionate share of the total load.

The novel features which I desire to protect herein are pointed out in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which Fig. 1 illustrates diagrammatically one embodiment of the invention; Fig. 2 is a vector diagram useful in explaining the invention; Figs. 3, 4a, 4b and 4c are graphical representations helpful in describing the operation of the invention; and Figs. 5, 6, '7 and 8 illustrate alternative applications thereof.

In Fig. 1 I have illustrated the application of my invention in connection with a multisection X-ray tube of known character. Referring particularly to the circuit elements which appear at the left hand side of the figure it will be seen that they comprise a pair of similar circuit branches each of which includes a plurality of elemental sub-groups. Each group in turn comprises a condenser and an inductance element which is adapted to resonate with the condenser at a particular frequency. The inductances, which may advantageously be of the iron core type, are numbered from 10 to 1'7 inclusive while the condensers are respectively numbered from 18 to 25.

The two circuit branches referred to are connected in a closed circuit so as to have two common terminals; one at the bottom (1') and one at the top (2'). As a means for exciting the circuit there is provided an alternating voltage source 30 which is coupled to the circuit by means of a transformer 3| having its secondary winding directly in circuit with the condenser and inductance elements. This arrangement is not essential, however, and it should be understood that any other known means of supplying exciting energy to the circuit may be employed. It is the function of the source 30 to supply the losses which occur in the resonant circuit and in the load apparatus associated therewith. In this connection the potential of the source 30 may be quite low and need have no special relationship to the total voltage desired to be generated by the apparatus as a whole.

With the circuit elements as so far described, and ignoring for the moment the remaining illustrated parts of the apparatus, the potential distribution may be as indicated by the vector diagram of Fig. 2. In this figure the letters employed correspond to the terminals which are identified by similar letters in Fig. 1. The diagram as a Whole is assumed to apply to the case where the circuit is energized at its resonant frequency. From a consideration of the diagram it will be seen that no point in the circuit attains a potential itith respect to any other point appreciably greater than the value of the vector ab. (Actually the vector z'b, which is not shown in the drawings, would represent the greatest A. C. potential difference attainable in the system.) This is due to the fact that the voltage across a given inductance and the successive condenser are practically out of phase.

The vectors ac, ce, etc., correspond to the components of voltage required to supply the power losses in the various circuit groups. These components, which are supplied by the transformer 31, may be quite small with relation to the reactive voltages developed. For example, assuming that twenty inductance elements and twenty condensers are provided and that the voltage developed across each element is 100 kilovolts (peak value) for a current of 100 milliamperes (peak value) then an input voltage of only 20,000 volts peak would be required to supply a loss in the circuit of 1,000 watts (i. e., 2,000 watts peak).

It will be noted that the point i is separated from the point r (that is from ground) by the insulation of several condensers in series. Assuming that some means can be provided for giving each of the condensers a constant charge of proper polarity, the possibility exists of developing at the point i a constant potential of appreciable magnitude. Thus, 20 condensers, each with 100 kilovolts constant potential, would provide together 1,000 kilovolts constant potential. My invention provides means by which this result can actually be obtained.

Broadly, this is effected by the use of means connected to permit unidirectional charging of the condensers pertaining to those circuit groups across which a constant potential is desired to be developed. Various arrangements of asymmetrically conductive devices may be used for this purpose and several such arrangements are shown in the drawings.

Possibly the simplest connection is that shown in Fig. 1 wherein a series of rectifiers or unidirectionally conducting elements numbered 35 to 38 respectively are connected across the condensers l8, I9, 20, and 2!. The rectifiers employed may be of any one of various known types such as a contact rectifier or a vacuum or gas-filled discharge device. With the arrangement shown each condenser will draw a charging current until the anode of its associated rectifier no longer becomes appreciably positive with respect to the rectifier cathode during any portion of the cycle. When this condition is attained the voltage across the condenser is a D. C. voltage plus an A. C. voltage of the same magnitude. The A. C. voltage is still neutralized by the voltage of the associated inductance so that the overall voltage across each elemental circuit group is a constant potential without A. C. ripple. Furthermore, the voltage across the series of successive groups is a constant potential comprising the sum of the constituent voltages. The condensers in the left branch of the circuit, i. e., condensers 22, 23 24, and 25 will automatically assume the same charge distribution as the shunted condensers provided their leakage is equal.

The potential relationships referred to will be better understood by reference to Fig. 3 in which the curve A represents graphically the variations of the voltage of the point b with respect to point a. The curve B represents the similar variations of voltage of the point c iizith respect tob, that is to say of the voltage across the condenser l8. From these curves it will be seen that the inductance voltage varies symmetrically above and below the potential at a. However, due to the presence of the shunting rectifier 35 the upper plate of the condenser l8 can never become appreciably positive with respect to the lower plate. On the other hand, the upper plate can and will during certain periods become negative with respect to the lower plate and during certain other periods can and. will come to zero potential with respect to the lower plate. During the period that the two plates of the condenser l8 are at the same potential, the lower plate is at a relatively high negative potential with respect to point a due to the voltage existing across the inductance l0. Similarly, at the time the upper plate attains its highest negative potential with respect to the lower plate the latter is at its highest attainable positive potential with respect to point a, due again to the phase relation of the voltage across the inductance Ill. The net effect is that the upper plate of the conductor i8 is maintained at substantially constant negative potential with respect to point a, or, in other words, that the potential across the elemental circuit group comprising the inductance I0 and the condenser i8 is constant. To say the same thing in another way, the voltage across the condenser is a D-c voltage having superimposed thereon an alternating current voltage of the same magnitude as the D-c voltage. As far as the condenser and inductance in combination are concerned, the alternating current voltage across the condenser is neutralized by the oppositely phased voltage simultaneously developed across the inductance.

The resultant D--c potential with respect to ground appearing at the point 0 is represented by the horizontal line C of Fig. 3. The total unidirectional potential developed aoross the circuit as a whole is represented by the line C1 which represents the sum of the constituent voltages existing across the various condensers in series.

It will be seen that since the circuit in question is of the resonant type the total voltage produced is independent of the voltage of the supply source 30 or of the transformer 35. The total voltage is limited only by the resistance losses in the system and may reach a very great magnitude if these losses are supplied from an external source (i.e., the source 36) It is furthermore to be noted that each of the elemental circuit groups sustains only its proportionate share of the total voltage so that no great concentration of the voltage stress is produced across any one element. Consequently no individual element needs to be highly insulated.

. The system described may be employed to energize any kind of load device which requires constant undirectional potential. In the present case I have illustrated as a load device a multi-section X-ray tube Ml comprising a cathode M and a target or anode 42. There are also provided a number of intermediate electrodes d3, 84, and 65 which serve to maintain a desired distribution of voltage along the axis of the tube. Assuming that the various elemental sub-groups of the resonant circuit are of similar character the intermediate electrodes is, M, and 45 may appropriately be energized by connection to the terminals provided for these sub-groups as illustrated.

In operation the current which is caused to flow through the X-ray tube (it by means of the potential applied to its terminals finds a continuous return path which may be traced through the rectifier 33, the inductance i3, rectifier 3 inductance l2, rectifier 36, inductance ll, rectifier 35, inductance it and transformer 35 to ground. The system shown may be indefinitely extended as long as the circuit connections provide a continuous path for the unidirectional load current and for the charging current of the various condenser elements.

The operation of the invention in connection with a load device is illustrated graphically in Figs. 4a, 4b, and 4c. The first of these represents the load current, which may be assumed to be substantially constant after it is once initiated. As a result of the loss of charge by the condensers during the period of operation of the load device, a substantial ripple may appear in the unidirectional potential existing across the system. This is illustrated in Fig. 4c wherein theregions of negative slope correspond to the discharge periods of the condensers. The loss of charge is automatically supplied, however, during a portion of each cycle of the oscillation of the resonant circuit by the passage of current through the rectifiers 35, 35, 3? and 38. The nature of this restorative current is illustrated in Fig. 4b. It will be understood that the total integrated area of the current curves of Fig. 4b will be the same as the area underlying the load current curve of Fig. 4a.

The amount of ripple or variation occurring in the unidirectional potential is a function of the capacity of the condensers utilized and may be limited to a desired value by an appropriate choice of condensers. The magnitude of the ripple may also be decreased and its frequency doubled by supplying additional rectifying devices in shunt to the condensers 22, 23, 24, and 25WhiCh are provided in the left hand branch of the resonant circuit. As previously pointed out, the system described may be extended by cascading a large number of elemental circuit groups, so as to produce a very high unidirectional voltage. In order properly to insulate the high potential terminal of the system from ground the apparatus as a whole may be enclosed in a suitable casing and immersed in a high strength dielectric medium such as insulating oil or gas.

Assuming that the circuit elements employed in the two circuit branches are identical, precisely the same unidirectional voltage distribution will be maintained along each branch. This is true especially if the leakage factors of the condensers employed in the left branch are equal. When this condition is fulfilled, it is apparent that corresponding points in the two branches are at the same potential. Consequently, in connection with the inductance elements it is possible to utilize a common iron core member for two corresponding elements. This arrangement is illustrated in Fig. 5 wherein parts corresponding to those already described in connection with Fig. 1 are similarly numbered. It will be seen that in this case the inductance coils i8 and it are paired so as to share a common iron core, identified in the drawings by the numeral 56. Similarly, commcn cores 5! and 52 are provided for the remaining inductance windings. This feature adds to the economy of the system in that it permits the use of a light and inexpensive construction. If desired, a common magnetic circuit may be used for all the inductance elements provided proper insulation is provided between the various parts of such circuit.

As a further consequence of the symmetry which exists between the two branches of the resonant circuit it is possible to use the further alternative arrangement shown in Fig. 6 wherein only alternate condensers of each branch are shunted by rectifiers. More specifically, in the right hand branch only the condensers l9 and 2| are shunted, while in the other branch shunting rectifiers 53 and 5d are provided for condensers 22 and 24. In order to provide a continuous circuit for the current which is to be drawn from the system by a load device, equipotential points of the two circuit branches are interconnected by choke coils 55, 56, and 5". as shown. By this means a path for direct current is provided between the terminals 1' and i by means of the various inductance elements and rectifiers taken in connection with the choke coils. The relatively high impedance of the choke coils for alternating currents of the frequency assumed to be developed in the resonant circuit prevents any short-circuiting effect as to such currents. The operation of the circuit of Fig. 6 is substantially identical with that of Fig. 1 except for the fact that the ripple appearing in the unidirectional potential developed between the terminals r and i will be of double frequency. This is due to the fact that the rectifiers in the two branches pass current during alternate half-cycles.

It is not necessary that the rectifying elements be applied directly across the condenser elements as long as a continuous path for unidirectional current is provided which will permit unidirectional charging of the condensers. An alternative arrangement for accomplishing this result is illustrated in Fig. '7 wherein are provided a plurality of rectifying devices $5, 65, B7 and 68 connected between the two circuit branches. It will be noted that each rectifier is connected from the bottom plate of a condenser in one branch of the circuit to the upper plate of the corresponding condenser in the other branch of the circuit. Consequently, a continuous though zig-zag path for unidirectional charging current for the various condensers may be traced through the various rectifiers and'the inductance elements in circuit therewith. The operation of the circuit will, therefore, be generally similar to that of the arrangements previously described.

By referring again to curve B of Fig. 3 it will be realized that the peak voltage developed across each condenser is twice the unidirectional voltage developed across the elemental circuit group with which that condenser is associated. This means that a 200 k. v. condenser will contribute only 100 k. v. to the overall constant potential. In order to permit better utilization it is desirable to improve this ratio. Fig. 8 shows one arrangement by which this object may be accomplished. (In this figure, the resistors 69 to "H are of high value and serve merely to equalize the potential distributions along the two branches of the circuit.)

In Fig. 8, for reasons shortly to be explained, the peak alternating voltage across the condenser and inductance elements is much smaller than the constant potential developed across each elemental circuit group. A a particular example I may refer to the case in which the A. C. voltage attains a magnitude of only 30 k. v. peak whereas the direct current voltage attains a value of 100 k. v. For this case the condenser rating need be only 136 kvp, since this is the maximum stress which will be encountered. In order to charge the condensers to 100 k. v. average under these conditions, each of the reactors I0 to It is provided with a booster winding (numbered it to 53 inclusive). The booster winding is assumed to be inductively coupled to the main inductance winding so as to produce a step-up effect by transformer action. The ratio of the windings should be such that a voltage of 30 k. v. in the main inductance winding will correspond to '70 k. v. in the booster winding. Each of the booster windings is in series with a rectifier connected in shunt to a condenser as in the arrangements previously described.

Since the action of the circuit in the absence of the booster winding would be to charge the condensers to a peak potential of 60 k. v., the addition of the booster windings necessarily serves to increase the peak charging of each condenser to 130 k. v. Since this peak potential is decreased by only 60 k. v. (2X30 k. v.), at each swing of the oscillating circuit, it will be seen that an average charge of 100 k. v. is maintained on the condenser. A comparison of the peak charge (130 k. v.) with the average charge (100 k. v.) shows that a high degree of utilization of the condenser capacity is thus achieved.

Fig. 8 also illustrates an arrangement by which .it is possible to energize the cathodes of the various rectifying devices by abstracting power from the main resonant circuit. This is accomplished by providing in addition to the booster windings Ill, ll, I2 and I3, additional windings ID" to It" inclusive. These are inductively coupled to the other windings referred to so as to be excited thereby. Regulation of the cathode heating may be accomplished in each case by the provision of control resistors numbered 12 to H5 inclusive. These may be controlled by means of a common control shaft I6 indicated in dotted outline.

In similar fashion the cathode 4! of the load device 4|] may be energized by being inductively coupled to; the resonant circuit. For effecting such coupling there is shown a transformer 18 having its primary in the resonant circuit and its secondary in series with the cathode 4|. A regulating resistor 79 and a control element 80 therefor are also illustrated.

While I have described my invention in connection with particular embodiments thereof it will be understood that numerous modifications may be made by those skilled in the art without departing from the invention. 1, therefore, aim in the appended claims to cover all such equivalent variations as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a resonant circuit containing two similar branches each made up of a succession of alternately arranged condensers and inductance elements, the two branches being connested in a closed circuit so as to have common terminals at their ends, means including rectifiers associated with the condensers for providing a continuous path for unidirectional current flowing between said terminals, the said path being conductive in one direction only whereby unidirectional charging of said condensers is permitted, means for exciting the circuit at its resonant frequency, and means for connecting a direct current load device to the said circuit terminals.

2. In combination, a resonant circuit having two similar branches each of which comprises a series of elemental groups made up of alternately arranged condenser and inductance elements so correlated as to be mutually resonant, the branches being sequentially connected in a closed circuit so as to have two common terminals, rectifiers shunting the condensers of one group so as to permit unidirectional charging thereof and thereby to develop a continuous potential across each of said elemental groups, and means for connecting a load device to the said common terminals of the two circuit branches so as to subject the device to the total continuous potential developed across such branches.

3. In combination, a resonant circuit containing two similar branches each made up of a succession of condenser and iron-core inductance elements, the two branches being connected in a closed circuit so as to have common terminals at their ends and the corresponding inductance elements of each branch being paired, a plurality of ferromagnetic core elements, each forming a common core for one pair of inductance elements, means for exciting the circuit at its resonant frequency, means including rectifiers associated with the circuit elements to provide a continuous path for unidirectional current flowing between the said terminals, the path being conductive in one direction only whereby unidirectional charging of said condensers is effected, and means for connecting a direct current load device to the said circuit terminals.

4. In combination, a resonant circuit containing two similar branches each of which comprises a succssion of alternately arranged condenser and inductance elements, the branches being connected in a closed circuit so as to have common terminals at their ends, rectifiers shunting certain condensers in each branch, means conductive to low frequency currents only for interconnecting the two branches at appropriate intermediate points so as to provide in combination with the rectifiers a continuous path for unidirectional current between the said common terminals, the said path being conductive in one direction only whereby unidirectional charging of said condensers is permitted, means for exciting the circuit at its resonant frequency, and means for connecting a direct current load device to the said circuit terminals.

5. In combination, a resonant circuit including at least two serially connected elemental groups, each of which includes a condenser and an inductance element adapted to resonate with the condenser at a particular frequency, means for exciting the circuit at such frequency, a rectifier shunting at least one of the condensers to permit unidirectional charging thereof, step-up means in series with the said rectifier to cause the average potential maintained across the shunted condenser to exceed that which it would attain as a result of the circuit oscillations alone, and connections for impressing on a load device the unidirectional potential developed across the elemental group with which the said shunted condenser is associated.

6. In combination, a resonant circuit including at least twoserially connected elemental groups each of which includes a condenser and an inductance element adapted to resonate with the condenser at a particular frequency, means for exciting the circuit at such frequency, a rectifier shunting at least one of the condensers to permit unidirectional charging thereof, a step-up winding coupled to the inductance element associated with the shunted condenser, means connecting the step-up winding in series with the said rectifier thereby to cause the average potential maintained across the shunted condenser to exceed the value which it would attain as a result of the circuit oscillations alone, and connections for impressing on a load device the unidirectional potential thus developed across the elemental group with which the said shunted condenser is associated.

7. In combination, a series resonant system comprising a succession of elemental circuit groups each of which includes a condenser and an inductance adapted to resonate with the condenser at a particular frequency, means for exciting the system at such frequency, asymmetrically conducting means connected to permit unidirectional charging of the condensers thereby to develop a continuous potential across each of said groups, and means completing a series circuit between the terminals of said resonant system, said last-named means being conductive as to alternating current but non-conconductive as to direct current, whereby the potential appearing between the said terminals of the resonant system comprises the sum of the continuous potentials developed across the various elemental circuit groups.

8. In combination, a series resonant system comprising a succession of elemental circuit groups each of which includes a condenser and an inductance adapted to resonate with the condenser at a particular frequency, means for exciting the system at such frequency, rectifiers shunting the condensers to permit unidirectional charging thereof, and means completing a series circuit between the terminals of said resonant system, said last-named means being conductive as to alternating current but non-conductive as to direct current, whereby the potential appearing across the said terminals of the resonant system comprises the sum of the continuous potentials developed across the various elemental circuit groups.

WILLEM F. WESTENDORP.

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