US 3740499 A
A high voltage oil filled stepping switch connects a plurality of DC voltage sources to a common output terminal. The rotor and housing is formed of plastic and contains appropriate grooves and flutes to increase electrical resistance to voltage breakdown while increasing the oil storage space. A flexible self-aligning shaft incrementally positions the rotor contacts with the housing contacts.
Claims available in
Description (OCR text may contain errors)
ilnited States Patent  Standing OIL FILLED STEPPING SWITCH Arthur F. Standing, Rockville, Md.
Communications Satellite Corporation, Washington, DC.
Apr. 6, 1971 Inventor:
US. Cl 200/ 8 R, 200/8 A, 200/11 TC Int. Cl. I-I0lh 19/56, HOlh 21/76 Field of Search ZOO/8 A, 8 R, 11 TC References Cited UNITED STATES PATENTS 3/1966 Voss 200/8 R X 6/1964 'Ausfeld... 200/8 A June 19, 1973 3,226,496 12/1965 Seabury, Jr. 200/8 R X 3,564,168 2/1971 Bigg 200/8 R Primary Examiner-4. R. Scott Att0rney-Sughrue, Rothwell, Mion, Zinn & MacPeak [5 7] ABSTRACT A high voltage oil filled stepping switch connects a plurality of DC voltage sources to a common output terminal. The rotor and housing is formed of plastic and contains appropriate grooves and flutes to increase electrical resistance to voltage breakdown while increasing the oil storage space. A flexible self-aligning shaft incrementally positions the rotor contacts with the housing contacts.
11 Claims, 2 Drawing Figures Patented June 19, 1973 ATTORNEYS OIL FILLED STEPPING SWITCH BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to an oil filled stepping switch that provides a plurality of high-voltage DC current sources to a common output terminal. More particularly, the present invention relates to an oil filled, break-before-make, stepping switch which can selectively connect one of a plurality of high voltage DC sources to a common output terminal for providing a variable source of voltage to a modulating anode of a high power transmitter tube.
2. Brief Description of the Prior Art The higher voltage stepping switches generally available have failed to meet the requirements of the high power TWT (traveling wave tube or other tubes) utilized in high. power transmitting stations such as those which communicate via a satellite. Generally the tubes must be provided with a source of adjustable voltage to the modulation anode to thereby control both RF power output and DC power consumption. Attempts have been made to utilize both low voltage switches and elaborate three-phase on-off switches in modulating the anodes of the tubes. These attempts have included providing a completely separate power supply and a relay system with incremental units of resistance. However, the problems associated with turning the high power units off and on, rather than just their voltage and in providing a sufficiently high voltage range, have proved beyond the capacities of the prior art stepping switches.
Thus the prior art devices have left the high power tubes extremely vulnerable to the damaging effect upon the tubes and the corresponding circuitry when the switch arcs upon the application of increments of high voltage.
SUMMARY OF THE INVENTION The present invention provides a relatively inexpensive and effective means of protecting the tubes from overload, while at the same time permitting a reasonable current to be carried'over a long life. The present switch is quite capable of providing incremental voltage steps from zero to kilovolts while at the same time maintaining a compact structure that is both cheap and relatively easy to assemble.
These features of the invention are accomplished by providing a cylindrical stator housing having a plurality of input terminal contacts positioned in a common plane around the inside surface of the housing. A selfaligning shaft is rotatable within and concentric to the cylindrical housing while a sleeve rotatably by the shaft includes a single contact element for selectively engaging one of the input terminals. The contact element is securely fastened to the sleeve. The shaft is flexible due to both the elasticity of the nylon rotor shaft and its two part construction utilizing an adaptor. The flexibility improves boththe operation of the switch and facilitatesits initial construction. A pin connects the shaft and adaptor. An appropriate conductive ring is connected to the contact element for providing an electrical path through a brush member in sliding contact with the conductive ring and an output terminal. A stepping motor is utilized for the appropriate incremental movement of the alignment shaft. The interior of the housing and the rotor are provided with grooves and flutes to increase both the oil capacity of the housing for long life and to provide an extra electrical length to prevent electrical breakdown. Likewise the exterior of the housing has appropriately placed grooves to increase the resistance to voltage breakdown. A noninflammable oil such as ASKAREL is utilized to reduce arcing between the input terminals and the rotatable brush element and for providing a rotational damping and lubricating function. By utilizing this particular arrangement of parts and be carefully choosing the appropriate material to construct the various elements of the stepping switch the device of the present invention has the particular advantages of high voltage isolation between each of the input terminals as well as with the indexing mechanism while remaining relatively simple and inexpensive to construct. Generally, nylon is favored as the constructional material for electrically isolating the switch terminals.
A particular aid in the construction and operation of the oil filled stepping switch of the present invention is the self-aligning feature of the rotor shaft. The stator housing itself contains interior flutes which simply increase the length of the electrical leakage path between the electrical contacts. These flutes serve a further advantage by providing a reservoir for theoil and a convenient positioning or locating reference during the assembly of the switch. Circumferential grooves on the rotor both above and below the brush contact point further help increase the relative length of the electrical leakage path and thus protect against voltage breakdown. Similar grooves on the outside body of the switch also increase the length of the relative electrical leakage path. Generally, the switch is preferably sealed to make it air-tight and the maximum grounding effect possible is provided.
DESCRIPTION OF THE DRAWINGS OF THE PREFERRED EMBODIMENT FIG. 1 is a sectional side elevational view of the present invention.
FIG. 2 is a plan view of the switch of the present invention with the cover removed.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 the housing or stepping switch body 10 is appropriately connected for example by four connecting members (not shown) to the cover l2. Both the cover 12 and the stator housing 10 can be made from nylon. Appropriate sealing means can be provided to insure an air tight seal. An outer terminal 14 located on the cover or closure 12 comprises a threaded stud 16 that terminates in a stud contact portion 22 with a washer 18 and a locating bolt 20 for firmly attaching the threaded stud 16 in position. The stud 16 can be brass or copper and the washer 18 a plastic such as Teflon. The cylindrical walls 24 of the stepping switch housing 10 are fluted on the interior with flutes 28 and have circumferential grooves 26 on the exterior. The flutes 28 and circumferential grooves 26 both increase the relative electrical leakage path to help prevent electrical breakdown of the stepping switch. It has been found that circular fluted cuts and semi-circular radial grooves are advantageous shapes respectively for the flutes 28 and circumferential grooves 26. The base member 30 of the stepping switch body 10 has a stepped cylindrical portion 31 with an axial bore for receiving the flexible drive shaft means which comprises the rotor drive shaft 34 and theadaptor 36. Both the base 30, the cylindrical portion of the base' 31 and the rotor drive shaft 34 are preferably constructed of nylon. The rotor drive shaft 34 is fastened to adaptor 36 by pin 35. The adaptor 36 is preferably constructed of an aluminum alloy and includes a lower stud member 37 for connecting the input of incremental motion from a stepping motor 54. Appropriate seals 39 and are utilized to position and seal the adaptor 36. The lower adaptor portion 37 is preferably of an oval cross-sectional shape. A base plate 32 which can be made from Plexiglass is appropriately connected to the stepping switch base 30. The cover 12 is appropriately recessed to permit a rotor connecting plate 38 and washer 40 to be located within the recessof the cover 12 and connected to the rotor 42. A fastener'41 holds the rotor connecting plate 38 on the rotor drive shaft 34. The rotor 42 is connected to the rotor connecting plate 38 by four circumferentially spaced screw members 60. The connection of the rotor 42 with the flexi ble shaft 34 is only through the rotor connecting plate 38, thus permitting a torsion bar spring flexing of the shaft 34 to aid in alignment and assembly of the switch. The rotor 42 is provided with, in the preferred embodiment; 12 longitudinal grooves 43 on the interior adjacent the cylindrical portion 31 of the base 30. These grooves serve the purpose of providing lubrication and damping to the rotor movement.
The rotor body is stepped in its upper portion and provides a seat for a slip ring 44 preferably made from copper. The slip ring 44 is a cylindrical ring which provides a contact with the stud contact 22 of the terminal 14. Slip ring 44 is connected to the rotor body 42 by four circumferentially spaced 'screw members 62 as shown in FIG. 2. A connecting member 52 extends from the slip ring 44 to provide an electrical connection with a threaded brush member 50 which extends radially through the rotor body 42. The brush member 50 can be brass and it contacts the contact plates or members 46, likewise of brass, appropriately positioned in an internal flute28.
In preferred embodiment six incremental inputs of varying voltage from ground to a negative 20,000 volts are provided 60 apart through the cylindrical walls 24. The contact plates 46 have a half cylindrical shape and are positioned in six of the twelve flutes 28 of the cylindrical walls 24. Thus, the flutes 28 serve'as positioning means for the bronze contact plates or members 46 as well as oil reservoirs.
On the outside of the cylindrical walls 24 are provided stand-off studs 48 defining input terminals which are made preferably of nylon to permit an electrical connection with the incremental voltage source. A screw member 58 threaded at it end is connected through a bore in the stand off studs 48 and cylindrical walls 24 to a threaded bore in bronze contact plate 46. Screw member 58 is made-of an electrically conductive material such as bronze or copper to allow electric current to flow from the incremental voltage source to the contact plate 46. The rotor 42 is provided with semicircular circumferential grooves both above and below the threaded brush member 50 for the purpose of increasing the reservoir capacity of the stepping switch and for increasing the electrical leakage path to prevent voltage breakdown. The rotor is covered with a non-flammable oil to insure high voltage isolation between each of the input terminals as well as to provide a lubricating and damping function. An oil that has been highly successful is ASKAREL. This oil insures against a voltage arching between the various input terminals. It is clear that other forms of insulating liquid can replace the oil if it has the same electrical and nonflammable characteristics. The cover 12 and the cylindrical walls 24 are preferably sealed and air-tight to prevent deterioration and contamination of the oil.
In a preferred operation, the stepping switch is electrically connected to a high power tube with the output terminal 14 providing the input to the modulating anode which controls the voltage and current flow to a cathode. The stepping motor 54 revolves the selfaligning rotor shaft assembly to make the appropriate connections with the input terminal through the contact plates or members 46, the threaded brush member 50, the metal connecting member 52, the cylindrical slip ring 44 and the stud contact 22 of the terminal 14. The input terminals generally run in increments from ground to a minus 20,000 volts. The insulating aspects of the stepping switch provide both an increased electrical leakage path to prevent high voltage leakage and non-conducting insulating bodies comprised mainly of nylon with a non-flammable oil to isolate the appropriate voltage paths for each input terminal. While preferred material have been specified (for various components) it should be clear that substitutes are readily available that provide the electrical characteristics and ease of machining required in the present invention.
" What is claimed is:
l. A rotary stepping switch comprising:
a cylindrical housing having end closure means;
at least one output terminal mounted on said end closure means and a plurality of input terminals mounted on said cylindrical housing a flexible insulated shaft means concentrically positioned for rotation in the housing;
a rotor positioned concentrically within the housing means connecting said rotor to said flexible shaft means;
a plurality of stationary contact members secured to the interior of the housing in circumferentially spaced relation and electrically connected to the input terminals;
a slidable electrical connection means providing electrical contact between the rotor and the output terminal; and
contact means on the rotor electrically connected to the sliding electrical contact means and adapted to contact the stationary contact means on the interior of the housing upon rotation of the shaft and rotor in proper angular relation relative to the housing.
2. A switch as in claim 1 further including a body of oil substantially covering the rotor.
3. A switch as in claim 2 where the flexible shaft means include a flexible shaft and an adaptor, the adaptor rotatably connected to the housing and the shaft, the shaft connected to the rotor.
4. A switch as in claim 2 where the sliding electrical contact means includes a slip ring mounted on the rotor and a stationary brush mounted on said end closure means.
5. A switch as claim 3 where the flexible shaft is plastic and the rotor is connected only at the end of the shaft farthest from the adaptor.
6. A switch as in claim 4 where the flexible shaft means includes a flexible shaft rotatably connected to the housing at one end and connected to the rotor only at the other end, the interior periphery of the housing being fluted.
7. A switch as in claim 6 where the rotor has a circumferential groove to increase the electrical leakage resistance of the rotor. I
8. A switch as .in claim 6 where the exterior of the housing has a circumferential groove to increase the electrical leakage resistance of the housing.
9. A switch as in claim 6 where the stationary contact axial bore and the rotor having an axial bore positioned around the cylindrical member.
11. A switch as in claim 10 where the axial bore of the rotor has longitudinal grooves for lubricating and damping the relative movement of the rotor and the cylindrical member of the housing.