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Oft Overlooked Innovations
Within Van de Graaff`s
Original Patent of 1935

A feebly conductive coating on the supporting column overcomes corona leakage at opening of sphere, & possibility of replacing charge transport belt with pumped insulating fluid

"A generator system operative to produce voltages of the order of several million volts is illustrated in Fig. 2. For convenience of description, it will be assumed that a maximum voltage of about 10,000,000 volts is to be produced between the spherical electrodes 40, i. e., a potential difference of about 5,000,000 volts between each electrode and ground."

Diagram 2 from VDG Patent

"The electrodes take the form of a thin conducting shell 40 that is supported by an interior framework 41, the conducting shell being free from surface irregularities or projections and having a diameter of about 10 feet. The insulator columns 42 which support the electrodes 40 on the movable bases 43 may be tubular sleeves of non-conducting material, for example, paper or wood veneer impregnated with shellac or an artificial resin. Adequate insulation will be provided when the insulator columns have a length of about fifteen feet.

To insure most efficient operation it is highly desirable to maintain a uniform potential gradient between the electrode and ground along the supporting column 42. This condition will obtain when the insulating support presents high conductivity in horizontal planes and a controlled resistance in vertical planes along the column. By providing a conductive coating upon the surface of the column, the coating being of substantially constant but relatively low conductivity, the leakage flow of current will establish a uniform potential gradient along the column and, since the potential will be substantially constant over any horizontal plane, the lines of force in the space within the column will be substantially linear and parallel to the axis of the column."

Diagram 3 from VDG patent

"This leakage coating may take the form of a paint or varnish layer 42a, of low conductivity, as shown in Fig. 3 and at the left of Fig. 2, or it may comprise a cord or thread 42b that is rendered slightly conductive by treatment with graphite or India ink, and is wound spirally around the column 42, as shown at the right of Fig. 2.

The gradual potential gradient down the insulating column tends likewise to produce a lowering of the electric field at points on the spherical electrode adjacent the entering portion of the column 42, thus resulting in the location of the most concentrated electric field at a region of the electrode remote from the supporting column."

Diagrams 5 & 6 from VDG Patent

"As shown in Figs. 5 and 6, the charge carrier is a fluid medium, such as oil, circulated through the endless pipe line 64 by a pump 65. The fluid medium is charged, at the lower portion of the system, by a discharge point 66 which extends into the conduit 64 and terminates adjacent the larger and rounded electrode 67. Condenser plates 68 are arranged within a portion of the conduit 64 which lies within the hollow electrode 69, and washers or baffles 70 compel the moving column of oil to flow between the condenser plates. The condenser is charged by a current source of low voltage, such as a battery 71 of the low current drain type commonly used with vacuum tubes as a plate battery, the battery being connected between one condenser plate and the electrode 69, while the other plate is connected directly to the electrode.

With this arrangement, the moving column of a fluid non-conducting medium receives electrical charges as it passes the pointed electrode 66, and the charges are removed and transferred to the electrode as the medium passes between the condenser plates. If desired, the fluid medium may have fine particles suspended therein to act as the charge carriers, but this is not generally necessary as the charges may be applied directly to the non-conducting fluid. The fluid may be a liquid or a gas or vapor, or a mixture."

From Patent 1991236 R.J.Van de Graaff 1935

A convential re-entrant, belt Van de Graaff generator

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