US2398581A - High voltage electrostatic generator - Google Patents

Description

April 15, 4 J. G. DELCAU v 2,398,581

HIGH VOLTAGE. ELECTROSTATIC GENERATOR FiledDec. 27, 1944 ife-1.

lNVENTOR I6. 52 Cfll/ BY W ATTORN EY Patented Apr. 16, 1946 UNITED STATES PATENT, OFFICE HIGH VOLTAGE ELECTROSTATIC GENERATOR Joseph G. Delcau, Baltimore, MIL, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation oi. Pennsylvania Application December 27, 1944, Serial No. 569,979

6 Claims. (Cl. 171-329) The present invention relates to X-ray apparaspacing of the parts without impairing the emtus and particularly to a high voltage electrostatic ciency of its operation. generator for energizing X-ray tubes with a volt- Still further objects of the present invention age of the magnitude of 1000 kilovolts and higher. will become obvious to those skilled in the art by Apparatus of this general type is now well reference to the accompanying drawing wherein: known in the art and is shown, for example, in Figure 1 is an elevational view partly in section Patent No. 2,252,668, granted August 12, 1941, to along the line II of Fig. 2 and showing a high John G. Trump. As pointed out in such patent, voltage electrostatic generator constructed in acit is essential in apparatus of this kind that a cordance with the present invention; substantially uniform potential gradient be es- Figure 2 is a sectional view taken on the line tablished between the walls of a substantially uni- Ill-II of Fig. 1;

form field surrounding the carrier and the in- Figure 3 is a sectional view taken on the line sulating support for the high voltage terminal. IIIIII of Fig. 2; To this end a number of equipotential rings in the Figure 4 is an elevational view of an insulator form of thin shields, each of conductive metal employed in the apparatus of the present invenpreferably tubular in form to present rounded tion to space the equipotential rings; and

external surfaces, and spaced from each other in Figure 5 is a sectional view similar to Fig. 3 but the gap between the terminal and the walls of the showing in dotted lines the former parallel tank, are provided. mounting of the resistors together with the rela- It is also expedient to control the field due to tive increase in spacing due to the staggered belt charge by providing a series of conductors ex'- mounting of the present invention.

tending beyond the width of the belt and located R erring now to the drawings in detail, the

in the same plane as the equipotential rings and apparatus as shown in Fig. 1 comprises a metallic disposed on each side of the belt both in its ascent tank 5 preferably filled with gas under pressure and descent through these rings. To further of approximately twenty atmospheres. A metalmaintain a uniform potential gradient between 110 base plate 6 is supported from the walls of the the electrode and ground, the equipotential rings tank by suitable flanged brackets I. Extending have heretofore been connected together by reupwardly from this base plate 8 are a plurality sistances so as to divide the potential. of insulating rods 8 of high dielectric strength,

Although the construction as above noted and such as glass or the like, which form a ball and as shown in the Trump Patent 2,252,668 will cpsocket connection 9 with the base plate 6, and

erate satisfactoril for units quite large in size, at their top support a ring In of conducting madifficulties are encountered in the construction of terial, being fastened thereto through a tensioned apparatus as small and compact as required for screw and nut arrangement I2. A high potential commercial purposes. This is due to the fact that electrode terminal ii of conductive material, such in making an apparatus of commercially feasible as brass or the like, and of substantially hemissize, the parts must be spaced closer together pherical configuration, is in turn supported by the without impairment of satisfactory performance. metallic ring it) concentric with the wall or dome As as result the voltage gradient per inch between of the cylindrical tank 5, thus providing ample the ends of the resistors connecting the equipo- 4 clearance between the tank walls and h hi tential rings becomes greater, causing failure and potential terminal it carried by ring ID, with the attendant spark-over near the ends of the relatter being held in place by the insulating rods sistors where the potential difference is greatest, 8 and by the tension of the belt or charge carwhen the resistors connect each equipotential rier ll. ring at diametrically opposite joints. 5 As customary in this type oi apparatus, the Itis accordingly the primary object of the pre charge carrier is in the form of an endless belt ent invention to provide an X-ray generator of I4 01' insulating material, such as rubber fabric, the high voltage electrostatic type wherein the cotton or the like, which passes over a metallic potential gradient between the resistor ends is pulley l5 journaled below the base plate 8 and greatly reduced, thus enabling closer spacing of grounded as at It, with this pulley l5 being rothe various parts without impairing operation of tated by an electric motor (not shown). Jourthe apparatus. nalled above, but insulated from, the top ring l0, Another object of the pfesent invention is the is a similar pulley I! over which the carrier ll provision of an X-ray generator of the high voltpasses, thus providing a parallel ascent and age electrostatic type in which the resistors for indescent for such carrier. terconnecting the equipotential rings are stag- Through a multiple-needle electrode It, the gered so as to connect adjacent rings at opposite lower end of the carrier I4 is supplied with a pointsinparallel planes, thereby reducing the pohigh voltage electrical charge from a suitable tential gradient per inch between resistor ends source of electric energy, which may comprise and enabling a more compact generator by closer a transformer and a rectifier. A similar type ing a uniform potential gradient down the insulating column formed by the rods I between the grounded base plate and the high potential electrode terminal II, a series of closely spaced metallic rings 22 are provided. Such rings 22, as shown more clearly in Fig. 2, are of tubular form at their periphery and surround the rods I, as well as the x-ray tube andthe ascending and descending run of the carrier it. These equipotential rings 22 are suitably spaced and insulated from each other by annular insulators 28, as shown in Fig. 4,

- which it into recesses provided in the surface of the rings so as to prevent displacement oi the insulators. Accordingly, upon tightening of the tensioned screw and nut arrangement I2, the entire assembly forms a rigid column.

To control the field due to carrier charge a series of aluminum conducting rods 24 are secured to about every fourth equipotential ring 22 and extend beyond the width of the carrier If in the equipotential plane and spaced a short distance from the latter on each side of the ascending and descending run of the carrier H. In addition, the same equipotential rings 22 carrying the aluminum voltage gradientcontrol rods 2i, also carry insulating rods 2|, such as glass or the like; positioned between the rods 24 and the car'-. net It and serve as guides so as to maintain the carrier ll spaced substantially a uniform distance from the voltage gradient control rods. Each equipotential ring 22 is provided with a metallic projection 26, thus reducing the spacing between the rings 2: at such projection and forming a spark-gap of a definite breakdown potential which enables distribution of the potential from one ring to that next adjacent, should the potential build up too high.

Inasmuch as the operation of the structure thus far described diflers substantially in no way from that of the above-noted Patent No. 2,252,668, it is believed unnecessary to herein reiterate the same, since reference may be had to such patent. However, this prior patent discloses that, to divide the potential on the high potential terminal above ground uniformly between the equipotential rings, it is desirable to connect such rings with each other by suitable resistors.

In the prior art such resistors have extendedfrom a point on the periphery of one equipotential ring to a point diametrically opposite on the next adjacent ring, with the next resistor in the series extending from a diametrically opposite point on the same ring to a point diametrically opposite on the next, so that no end of any resistor is connected to the same point on the same equipotential ring and the resistors are thus parallel to each other. Although this arrangement operates satisfactorily, as before mentioned, it results in a very large and cumbersome apparatus because of the spacing required between the parts.

In accordance with the present invention, the

resistances which connect each equipotential ring 16 are staggered, enabling a reduction in the spacing formerly required between the parts resulting in a more compact and commercially practical apparatus.- Such construction is shown more clearly in Fig. 3 wherein resistors 21 connect the equipotential rings 22 in a staggered relation, as above mentioned. By this is meant that while one resistor 21 connects a point of one equipotential ring 22 with a-point diametrically opposite on the next adjacent equipotential ring 22, the next resistor connects this latter ring at substantially the same point with the next adjacent ring at a diametrically opposite point, thus making a staggered or V-shaped arrangement of the resistors 21 as shown in Fig. 3, in contrast with the parallel arrangement previously employed in apparatus of this type.

By this staggered or V-shaped arrangement of theresistors 21 in accordance with the present invention, the voltage gradient per inch between resistor ends carrying a potential difference is reatly reduced by as much as approximately fifty per cent. This follows despite theiact that even though the spacing between resistor ends having a potential difierence is doubled, the voltage therebewteen is also doubled. This may be better appreciated when it is considered that the potential gradient E between two flat parallel planes is equal to the voltage V therebetween, divided by the distance D, or

If new the voltage and spacing between such parallel planes are doubled, the same relationship or proportionality follows, or

However, with parallel rings, or ends of the resistors 21 as shown and even when disposed in parallel relation as in the prior art (see Fig. 5), the above noted formula does not hold or and by the same token nor does any rule of proportionality follow. In other words, whatever the value of the potential gradient E with a given spacing between parallel rings or resistor ends, doubling of the spacing and voltage does not give the same value for E, but on the contrary the potential gradient per inch is reduced with an increase in spacing even when the potential is increased in proportion to the increase in spacing. This may be better appreciated by reference to Fig. 5 wherein the parallel spacing is shown in dotted lines and the staggered arrangement of the present invention in full lines. The resistors 21 are one inch in diameter'with a spacing between centers of one and one-quarter (1%) inches at their point of connection with the equipotential rings 22. The spacing at the point of greatest potential stress (a-Fig. 5) is accordingly one-quarter /4) inch. Assuming a 50,000 volt potential difference therebetween, the above formula, gives resistors 21, as shown in Fig. 3 and the full lines of Fig. 5, their spacing on centers is doubled to two and one-half (2 inches and the spacing between points of greatest potential stress "--Fig. 5) now becomes one and one-half (1 /2) inches with a potential difference therebetween or 100,000 volts. Again applying the above formula which gives a potential gradient of 67,000 volts per inch instead of the'200,000 volts .per inch of the prior parallel arrangement.

Accordingly, as will be noted particularly from Fig. 3, the ends of resistors 21 carrying a potential difference are spaced apart so they are connected to substantially a common point on every other equipotential ring 22. This accordingly doubles the spacing previously mployed in the art between resistor ends carrying a potential difference therebetween. At the same time since they connect at a point on every other equipotential ring 22 such potential difference is also approximately doubled. However, the potential gradient per inch between such resistor ends is greatly reduced for the reasons above noted over what it is per inch when the resistors are disposed in parallel with each other and connect adjacent equipotential rings at diametrically opposite points. The various parts of the apparatus can accordingly be spaced closer together for the same given potential as a prior art device without in any way impairing the efficient and successful operation of the generator.

It thus becomes obvious to those skilled in the art that a high voltage electrostatic generator is herein provided which is of compact design because of closer spacing between the various parts due to a staggered arrangement of the resistors connecting the equipotential rings.

Although one specific embodiment of the present invention has been shown and described, it is to be understood that further modifications thereof can be made without departing from the spirit and scope of the appended claims.

I claim:

1. A high voltage electrostatic apparatus comprising a high voltage terminal, insulating supporting means for said terminal, a movable endless belt-like charge carrier for transmitting charges between said terminal and ground, a plurality of equipotential conductive surfaces insulatingly spaced from each other closely adjacent said carrier and disposed transversely of the latter, and resistors in staggered relation to each other and connecting said equipotential conductive surfaces to maintain a controlled potential difference therebetween.

2. A high voltage electrostatic apparatus comprising a high voltage terminal, insulating supporting means for said terminal, a movable endless belt-like charge carrier for transmitting charges between said terminal and ground, a plurality of equipotential conductive surfaces insulatingly spaced from. each other closely adjacent said carrier and disposed transversely of the latter, and resistors connected to a substantially common point on one of said equipotential surfaces and connected to a diametrically opposite point on each next adjacent equipotential surface to maintain a controlled potential difference therebetween.

3. A high voltage electrostatic apparatus com-- prising a high voltage terminal, insulating supporting means for said terminal, a movable endless belt-like charge carrier for transmitting charges between said terminal and ground, a plurality of equipotential. conductive surfaces insulatingly spaced from each other closely adjacent said carrier and disposed transversely of the latter, and resistors connected from a substantially common point on every equipotential surface to a diametrically opposite point on each next adjacent equipotential surface to maintain a controlled potential difference therebetween.

4. A high voltage electrostatic apparatus comprising a high voltage terminal, insulating supporting-means for said terminal, a movable endless belt-like charge carrier for transmittin charges between said terminal and ground, a plurality of equipotential conductive surfaces insulatingly spaced from each other closely adjacent said carrier and disposed transversely of the latter, a conductor disposed parallel to and supported by at least one of said conductive surfaces on each side of the ascending and descending path of said carrier in closely spaced relation thereto and of greater length than the width of said carrier to control the electrostatic field due to carrier charge, and resistors connected from a substantially common point on every equipotential surface to a diametrically opposite point on each next adjacent equipotential surface to maintain a controlled potential difference therebetween.

5. A high voltage electrostatic apparatus comprising a high voltage terminal, insulating supporting means for said terminal, a movable endless belt-like charge carrier for transmitting charges between said terminal and ground, a plurality of equipotential conductive surfaces insulatingly spaced from each other closely adjacent said carrier and disposed transversely of the latter, a series of spaced conductors supported by said equipotential conductive surfaces adjacent the ascending and descending path of said movable carrier and of greater length than the width of said carrier to control the field due to carrier charge, and resistors connected from one equipotential conductive surface to a point diametrically opposite on each next a jacent equipotential conductive surface with the resistor ends lying in a common vertical plane on every other equipotential conductive surface to maintain a controlled potential difference between equipotential conductive surfaces.

6. A high voltage electrostatic apparatus comprising a high voltage terminal, insulating supporting means for said terminal, a movable endless belt-like charge carrier for transmitting charges between said terminal and ground, a pin-- rality of equipotential conductive surfaces insulatingly spaced from each other closely adjacent said carrier having a tubular periphery and. disposed in a transverse plane about said carrier, a series of spaced conductors supported by said equipotential" conductive surfaces adjacent the ascending and descending path of said movable carrier and of greater length than the width of said carrier to control the field due to carrier charge, and resistors connected from a substantially common point on the tubular periphery of each equipotential conductive surface to a diametrically opposite point on the tubular periphery of each next adiacent'equipotential surface to maintain a controlled potential difference therebetween."

- JOSEPH G. DEICAU.

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