US3028685A - High voltage electrostatic demonstration apparatus - Google Patents

Description

April 10, 1962 D. SILVERMAN 3,028,635

HIGH VOLTAGE ELECTROSTATIC DEMONSTRATION APPARATUS Filed Dec. 23, 1960' 2 Sheets-Sheet 1 IN VEN TOR.

A ril 10, 1962 D. SILVERMAN 3,028,685

HIGH VOLTAGE ELECTROSTATIC DEMONSTRATION APPARATUS Filed Dec. 25, 1960 2 Sheets-Sheet 2 IN V EN TOR.

1 3,028,685 HIGH VOLTAGE ELECTROSTATIC DEMON- STRATION APPARATUS Daniel Silverman, 5969 S. Birmingham, Tulsa, Okla.

Filed Dec. 23, 1960, Ser. No. 77,902 V 14 Claims. (Cl. 351-19) This invention relates to an apparatus for demonstrating the principles of electrostatics. More particularly, the invention relates to apparatus adaptable to the study of the character of static discharges from high voltage electrodes and the effect on such discharges of the radius of curvature of the discharge electrodes.

Studies of the character of electrical discharges in air from high potential electrodes are important in the work of protecting structures against lightning discharge, and in the design of lighting protection equipment. Instruments which clearly illustrate these phenomena can be useful in research and development, and especially in the training of operators of this type of equipment and in the instruction of students.

One means of effectively producing high voltage concentration of electrostatic electricity is by means of the Van de Graaif generator, well known in the science'teaching field. This invention provides a device for use in conjunction with such high voltage electrostatic generators for a studying and demonstrating electrostatic from, a spheroidal electrode mounted on the top of said column, a controllable conductor means within said insulating column adaptable to controllably ground said base with said electrode, a control means within said base and extending external of said base adaptable to control said conductor means whereby said electrode may be grounded to said base, and a movably afiixed extensible conductor rod positioned within an opening in said electrode adaptable for extension and retraction within said electrode whereby said electrode may be extended or retracted to demonstrate the effect on electrical discharge of the variation in the diameter of the electrode.

It is therefore an object of this invention to provide States Patent "ice 2 device showing means whereby the electrode is grounded to the base.

- FIGURE 4 is a partial view of the device of the invention showing an alternate embodiment of a means of grounding the electrode to the base.

FIGURE 5 is a top view of the spooling mechanism utilized in the grounding method of the alternate embodiment of FIGURE 4.

FIGURE 6 is a cross-sectional partial view of the electrode of the invention showing another embodiment whereby the radius of curvature of the electrode portion may be varied. 3

FIGURE 7 is a view of the device of the invention used in conjunction with a Van de Graafi electrostatic generator disclosing means whereby the device is used as a demonstration apparatus.

Referring now to the drawings, and first to FIGURE 1, one embodiment of this invention is shown. An electrostatic discharge device, indicated generally by the numeral 10, is composed of a base 11, an insulating tubular column 12 and a spherical or spheroidal electrode 13. The base 11 is preferably made of cast metal or molded plastic so as to have suflicient weight to stably support the column 12 and electrode 13. Rotatably supported in the wall of base 11 is a shaft 17, a knob 18, a collar 19 and pulley 20. An insulating cord 21 of nylon or 'some similar insulating material is fastened to and an improved apparatus for demonstrating the principles f of electrostatic discharge.

Another object of this invention is to provide a high voltage electrode system which can be grounded or in sulated at will while the device is in use. I

Another object of this invention is to provide an electrode system in which the minimum radius of curvature of the electrode can be varied at will while the device. is in use.

Another object of this invention is to provide anelectrode system for use in the demonstration of electrostatic discharge phenomena wherein a conductor of diminished radius may be extended or retracted into said electrode While the electrode is in use to demonstrate the effect of the variation of the curvature of the electrode.

These and other objects and a better understanding of the inventon may be had from the following description and claims taken in conjunction with the attached draw- I ings in which:

i FIGURE 1 is a vertical section of one embodiment of FIGURE 2 is a section of a portion o-f'the base of the adapted to be wound up on pulley 20 by means of knob 18. Knob 18 is adaptable for manual rotation, Supported additionally in the wall of base 11 is a shaft 22, knob 23, collar 24, and pulley 26, on which is wound insulating cord 27.

The column 12 is made of an insulating plastic material (preferably transparent) such as Lucite. It is fastened to the base 11 by means such as the screws 28. The screw 28 that is placed in the back of the base 11 also supports a grounding strip 29 as shown in more detail in FIGURE 3. The upper end of the column 12 protrudes within opening 3t) in the lower portion of electrode 13, termed the lower hemisphere 31 and is fastened thereto by, means such as the screws 32. These screws 32 also support a frame 33 which carries means 34 to support spring 35, and also arms 36 to support roller 37. The helical spring 35, made of electrically conducting material such as steel, is supported from the frame 33 and is adapted to be of such length as to be entirelywithdrawn into the electrode 13, and to have sufficient extensibilty to be drawn down to contact the grounding strip 29 afiixed to base 11 and thus ground the spherical electrode 13 .to the base 11. This grounding is facilitated by a small conducting sphere 38 supported by the spring 35 and to which is tied the insulating'cord 27. When the spring 35 is fully extended the conducting sphere 38 contacts the grounding strip 29 which is fastened by screw 28 to the base 11.

As shown in FIGURE 2, there are two small openings 39 and 4th in the side wall of the lower hemisphere .31. One of these openings 39", serves to mount a leaf spring 41, which supports an arm 42, to which is fastened an extensible electrode or rod 43. Rod 43 can be part of a screw 4d fastened'to the arm 42. The end or forward surface of the rod 33 is shaped to be a hemispherical surface 46 of small radius of curvature. A multiplicity of rods 43 of this type can be provided, each with different radius of curvature of surface 26, one of which can be small enough to be essentially the point of a needle. The leaf spring 4-1 forces arm 42 against the inside of the opening 39 to expose the forward surface 46 of rod 43 outside of the spherical electrode 13. The arm 42 (and thus rod 43) can be retracted by means of insulating cord 2-1 which runs over roller 37 and down to pulley 20.

Thus by turning knob 18, the rod 43 can be extended or retracted through the wall of the electrode 13.

The character of the electrical discharge from an electrode is a function of voltage. For an electrode of a given minimum radius of curvature voltages of less than a certain value can be supported without discharge. As the'voltage rises above this critical value a corona discharge forms at the surface of minimuinradius of curvature, limiting the maximum voltage that can be supported to that value. If the voltage on the electrode is just under the maximum supportable value and the minimum radius of curvature is reduced, a situation will be reached Where a corona forms. By using several rods 43 of. different radii 4-6, it can be demonstrated that the voltage maxirna on the electrode 13 will be different for each value of radius 46, and will be higher the larger the radius.

The openings 39 and 40 are formed whereby the sharp edges (small radius of curvature) of the openings face inwardly, and are not exposed on the outside of the electrode 13. By this means, the large radius of curvature of the spherical electrode 13 is not effectively reduced by the openings 39 and 40. Of course, other ways of mounting leaf spring 41 and arm 42 can be used other than the screw 47. For example, the leaf spring 41 can be cemented to the inside wall ofthe electrode 13, or it can be supported by an extension of the frame 33.

The spherical electrode 13 can conveniently be made in two parts, a lower hemisphere 31, supported on the column 12, and an upper hemisphere 48, having downwardly projecting lip 49 to lock together the two hemispheres 31 and 48.

FIGURES 4 and 5 disclose another embodiment in which the conductor, which is controlled so as to ground the spherical electrode 13 to the base 11 (not shown in FIGURES 4 and 5) is a conducting cord or wire 50 which is part of a continuous loop which passes around a number of idler pulleys 51 and the drive pulley 26 in the base 11. v

A frame 52 is mounted by brackets 53 and fasteners 32 and 54- to the upper end of the column 12. The frame 52 has three shafts 55, 56 and 57 journaled in the side members of the frame 52 and locked in place by collars 158. Each shaft 55, 56 and 57 has one 'or more idler pulleys 51 positioned from each other and from the frame 52 by means of spacers 59. A continuous loop of cordlike material 50 is threaded around the idler pulleys 51 and the pulley 26 on shaft 22 in the base 11. By turning the knob 23 on shaft 22 the loop is caused to run over the pulleys 51. Part of the loop is made of conducting material and part by a non-conducting material 60. The'conducting portion 50 is longer than V the distance from shaft 57 to shaft 22, so that when conducting part 50 is in proper position it will connect by conducting material from the upper sphere 13 to the base 11. The remaining portion of the loop being made of insulating or non-conducting cord 60, so that when the loop is transversed until conducting part Sills entirely looped between pulleys 51 on shafts and 56,

and non-conducting portion 60 is looped between pulleys on shafts 57 and 22, the spherical electrode 13 is fully insulated. Conducting portion 53 can be made of a non-conducting cord treated by a chemical or conducting paint. However, it is preferably made of a fine wire or braided conductor. By control of the shaft 22, the spherical electrode 13 can be grounded to or insulated from the base 11. I I

FIGURE6 discloses another embodiment which comprises a conducting surface of substantially spherical shape that can be varied in radius of curvature. It comprises essentially a variable radius assembly 61 having a case 62, a flexible rubberlike membrane 63 positioned over the end of the case 62 and fastened thereto by means such as a cord 64. The case 62 has an opening into which is fitted a small tube 65 of insulating material such as nylon or polyethylene. This tube 65 is long enough 75 earth, (the discharge electrode 13),

66 is filled with an insulating fluid e7 such as air or oil;

so that by compressing the bulb 63 to increase the pressure in the fluid 67 the membrane 63 can be caused to bulge out into contours 63, d9, 79, etc. which are 'e'ssem tially spherical surfaces of different radius of curvature. The higher the pressure, the greater the radius of curvature. 1

The variable radius assembly 61 canbe inserted into the opening 39 in the lower hemisphere 31, and can be held by a press fit. However, it is considered more reliable to use a frame 71, springs '72 and brackets 73 to hold assembly 61 in place.

The outer surface of the membrane es is covered with conducting paint or similar treatment to make its outer surface conducting. Thus by appropriate pressure created in the fluid 67 by force on the bulb 66 the radius of curvature of the conducting surface of membrane 63 can be made of any desired value.

Operation charge. Referring to FIGURE 7, a typical Van de Graafll electrostatic generator 74, of a type commonly used in the generation of electrostatic electricity, having an electrode portion with a spherically defined electrode, of a j diameter approximately equal to the diameter of the electrode 13 of the device of this invention, is utilized. The base 11 of the discharge electrode 10 of this invention is electrically connected to the ground terminal of the Van de Graalf generator by means of a conductor 75.

The discharge electrode 13 and the electrode of the genera- I tor 74 are spaced apart depending upon the intensity of the voltage to be generated before causation of an electrical discharge between the two electrodes.

By turning knob 23 the discharge electrode 13 is grounded to the base 11 and therefore to the base of the generator 74. With the generator 74 in operation electrostatic electricity will accumulate on the generator electrode to a point where a spark discharge occurs between the generator electrode and the discharge electrode 13 at frequent intervals. (The higher the generator voltage the" greater the possible spacing between the electrode spheres.) While a condition of frequent electrical dis charges occurs, knob l8 is turned allowing the rod 43 to extend out through the opening in the lower hemisphere of the discharge electrode 13 so as to be exposed to the outside. The radius of curvature of the rod 43 being of a much smaller diameter than the radius of the electrode 13 causes a disturbance in the electrostatic field between the two spherical electrodes so that a spontaneous continuous discharge, called corona, develops at the small radius portion of the rod 43. This corona discharge drains current from the generator 74 and holds down the voltage accumulation and thus prevents spark discharges from the generator 74 to the discharge electrode 13. This efiectively demonstrates the phenomena caused by the erection of a lightning rod on a building.

By the substitution of rods 43 having various radius of curvature it can be demonstrated that the smaller the radius of curvature the lower the corona voltage and thus the less chance of a spark discharge occurring, It can easily be demonstrated that the radius of curvature of the rod being a point, that is a minimum radius of curvature, and is most effective in reducing the chance 'ofa discharge between the electrodes and thus the reason'for lightning extending upward from the earths surface (the small diameter rod 43), and thereby illustrates the action of the lightning rod in preventing lightning discharge.

Another type of experiment which can be conducted by using the discharge electrode device of this invention is by ungrounding the electrode 13 from base 11, utilizing the embodiment of FIGURE 1 or that of FIGURES 4 and 5. With the discharge electrode 13 ungrounded the discharge from the generator electrode will cease. With the discharge electrode ungrounded the discharge device of this invention may be placed so that the discharge electrode 13 is in contact with the generator electrode. Another grounded sphere (not shown) may be placed at a proper distance away. In this arrangement sparks will occur between the ungrounded electrode 13, which will then have a electrostatic voltage potential equal to the electrode of the generator 74, and the grounded electrode.-

With sparks occurring at frequent intervals, the extension of the rod 43 from the ungrounded electrode 13 (now at the high potential of the generator electrode), again sets up .a corona and stops the sparking. This serves to demonstrate that the radius of curvature of either the generator 74 electrode or the discharge electrode 13 is determinative of the extent of accumulation of electric-a1 charge and therefore the intensity of discharge which Will occur between two bodies.

Many other experiments and demonstrations will readily suggest themselves utilizing the features of. this invention.

Many changesmay be made in the details of construction, the arrangement of components and the application of the device of this invention. For instance, if a grounded electrode is to be required inthe application of the invention at all times, the column 12 may be of a conducting'material eliminating the other embodiments wherein the electrode may be grounded or ungrounded. Many other changes may be made in the construction of the invention without departing from the spirit and scope of this disclosure, as defined in the appended claims.

I claim:

1. A high voltage electrostatic demonstration apparatus of the type described comprising a base, an insulating column supported uprightly from-said base, a spheroidal electrode affixed at the top of said column, an adjustable conductor means within said insulating column adaptable to oontrollably ground said base with said electrode and a control means within said base and extending external of said base adaptable to control said conductor means to ground said spheroidal electrode to said base as required.

2. An apparatus according to claim 1 wherein said adjustable conductor means includes a spring means attached at one end to said electrode, a non-conducting cord affixed to the other end of said spring and extending to said base, and wherein said control means includes a shaft rotatably supported in said base and partially extending exterior of said base, a pulley affixed to said shaft adaptable to wind-ably receive said non-conducting cord, and a knob affixed to said shaft whereby said knob may be rotated to extend said spring to contact said base and thereby ground said electrode to said base.

3. A demonstration apparatus as in claim 1 in which said adjustable conductor includes a flexible metallic conductor of length greater than the spacing between said electrode and said base, a length of insulating cord attached to said metallic conductor, said insulating cord of approximately twice the length of said metallic conductor, said conductor and said insulating cord attached to form an endless belt, a multiplicity of idler pulleys rotatably positioned in said electrode, a shaft rotatably positioned in said base, a driver pulley mounted rigidly to said shaft, said endless belt looped over said idler and said driver pulleys whereby when said shaft is rotated said belt will traverse over said pulleys until said metallic conductor portion extends between said electrode and said base, thereby grounding said electrode to said base.

4. A high voltage electrostatic demonstration apparatus of the type described comprising, a base, an insulating column fastened to said base and extending uprightly therefrom, a spheroidal electrode mounted on top of said column, said electrode having an opening therein, control means positioned in said base, an extensible electrode pivotably positioned in said electrode adaptable to extend in part through said opening and exterior of said electrode, said extensible electrode pivotably operable by said control means whereby said extensible electrode can be extended by operation of said control means to project outside said electrode.

5. A demonstration apparatus as in claim 4 in which said extensible electrode has a substantially hemispherical surface, said extensible electrode being adapted to be extended outwardly through said opening in said electrode to expose said hemispherical surface outside the surface of said electrode.

6. Demonstration apparatus as in claim 4 in which said extensible electrode comprises a length of conducting rod one end of which is formed into a substantially hemispherical surface of desired radius, a leaf spring affixed to the interior surface of said electrode, said extensible electrode supported to said leaf spring and pivotable by flexing of said spring to extend through said opening in said electrode, and insulating operating means attached between said control means in said base and said leaf spring whereby when said control means is operated said extensible electrode is extended through said opening of said electrode exposing said hemispherical surface on the outside of said electrode.

7. A high voltage electrostatic demonstration apparatus of the type described comprising, a base, an elongated insulating support means fastened to said base and extending uprightly therefrom, a spheroidal electrode mounted on top of said support means, control means positioned in said base, extensible conductor means positioned in said electrode, and insulating operating means connected between said control means and said conductor means, whereby said conductor means can be extended outside of said electrode by operation of said control means to project outside said electrode.

8. A high voltage electrostatic demonstration apparatus as in claim 4 in which said opening in said electrode through which said extensible electrode is adapted to extend, is substantially in the center of a re-entrant portion of the surface of said electrode.

9. A high voltage electrostatic demonstration device of the type described comprising a base, an insulating column supported uprightly from said base, a spheroidal electrode atfixed at the top of said column, said electrode having an opening therein, an adjustable conductor means within said insulating column adaptable to controllably ground said base with said electrode, a first control means within said base and extending external of said base adaptable to control said conductor means to ground said spheroidal electrode to said base as required, a second control means positioned in said base, an extensible electrode pivotably positioned in said electrode adaptable to extend in part through said opening and exterior of said electrode, said extensible electrode pivotably operable by said second control means whereby said extensible electrode may be extended by operation of said second control means to project outside said spheroidal electrode.

10. A high voltage electrostatic demonstration apparatus as in claim 7 in which said extensible conductor means comprises conducting spring means attached at one end to said electrode and said insulating operating means comprises insulating cord means attached at one end to said control means and at its other end to the extensible end of said spring means.

11. A high voltage electrostatic demonstration apparaapeaaae tus as in claim 7 in which said spheroidal electrode has at least one opening in its wall, and said extensible conductor means comprises a conductor adapted to project through said opening to the outside of said electrode.

12. A high voltage electrostatic demonstration apparatus as in claim 11 in which said extensible conductor means comprises at least one of a plurality of hemispherically tipped conducting rods each of different diameter and radius of curvature adapted selectively to project through said at least one opening to the outside of said electrode.

13. A high voltage electrostatic demonstration apparatus as in claim 11 in which said extensible conductor means comprises the conducting coating on the surface of a thin Walled extensible bulb mounted inside of said electrode adjacent said opening, a flexible container positioned in said base, insulating tubing means connecting said flexible container with said extensible bulb, said bulb, said tubing, and said container filled with insulating fluid, whereby pressure on said container causes the con- Q Q ducting surface of said bulb to expand and project out side of said electrode, and greater pressure causes said surface conductor to conform to a greater radius of curvature.

14. A high voltage electrostatic demonstration apparatus as in claim 11 including means by which the conductor adapted to project through said opening can be varied in radius of curvature.

References Cited in the file of this patent UNITED STATES PATENTS 622,210 Dodd et a1. Apr. 4, 1899 700,536 7 Moore et al May 20, 1902 1,991,236 Van de Graaff Feb. 12, 1935 2,070,972 Lindenblad Feb. 16, 1937 2,811,674 Smith Oct. 29, 1957 FOREIGN PATENTS 308,358 Switzerland Sept. 16, 1955

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