US3029579A - Selector switch mechanism - Google Patents

Description

4 Sheets-Sheet 1 H. BElRNE ETAL SELECTOR SWITCH MECHANISM Th l 83 vApril 17, 1962 Filed June 14, 1960 April 17, 1962 H. BEIRNE l-:TAL

SELECTOR swITcH MECHANISM 4 SheetsfSheet 2 Filed June 14, 1960 Rn. Y OPR E mm" Bt R E VYM Nrn T lne A MK WITNESSES W f L April 17, 1962 H. BEIRNE Erm. 3,029,579

SELECTOR swITcH MECHANISM Filed June 14, 1960 4 Sheets-Sheet 3 Fig.4

April 17, 1962 H. BEIRNE ETAL SELECTOR SWITCH MECHANISM 4 sheets-sheet 4 Filed June 14, 1960 Fig. 6

Unite States This invention relates generally to a selector switch mechanism, and relates specifically to a selector switch with safety interlock for controlling the electrical connection between a rectifier power unit and the individual sections of a two-section precipitator of the industrial type.

In the operation of a two-section industrial precipitator connected to a rectifier power unit, it is at times desirable to change from full wave operation of the two lsections to half wave operation on each section or to full wave operation on either section with the other section grounded or to ground both sections for the purpose of carrying out maintenance on either or both sections. Heretofore, these operations have been performed by means of three separate switches combined with complex and cumbersome mechanical interlocking mechanism.

It is a prime object of this invention to perform the foregoing operation by means of a single, double deck, selector switch.

It is a further object of this invention to perform the foregoing operation 'by means of a single, double deck switch in combination with simplified safety interlocking means.

Other objects will, in part, be obvious and will, in part, be explained hereinafter.

In practicing this invention in accordance with one of its embodiments, the switch operating mechanism is xedly attached to a large handhole cover on a housing in which is mounted a high voltage supply transformer, a full-wave rectifier assembly, and -a double deck selec-tor svsutch mechanism for selectively connecting the rectified output from the high voltage transformer to control the energization of the individual sections of a twosection precipitator, which precipitator may be mounted in a separate remote housing. The switch may be mounted upon and permanently connected to the rectifier assembly, while the switch may be connected to the switch operating mechanism by means of an insulating shaft having a universal slip joint engageable wi-th the switch. The unitary rectiienswitch combination may be connected to the high voltage transformer by means of manually releas-able connectors which can be easily disconnected and which are accessible when the large handhole cover and switch operating mechanism is removed from the housing. This structure provides for inspection and maintenance of the rectifier and switch with a minimum expenditure of time and labor and at the same time.

eliminates the necessity of disturbing the supply transformer or the draining of any fluid from the housing since the unitary rectifier switch may be readily removed lfrom the tank through the large handholev cover without dise turbing the transformer.

The switch operating mechanism comprises a handle movable to different positions with respect to an index plate and operable when moved to rotate a connecting shaft and thus effect the switching changes. An interlock mechanism is provided so fthat working personnel may safely work on grounded portions of the precipitator without danger of the switch being accidentally moved to energize the grounded section or sections. The interlock mechanism comprises three sets of two matching locks, each set being operated by a different corresponding key.

Three of `the locks, each from a different set, are xed to the operating handle in radial position around the connecting shaft. One of the matching locks is installed as ice 2 a breaker lock in the primary of `the high voltage transformer, while each of the remaining two matching locks is installed to lock or unlock one of the precipitator sections. The plungers of the three locks on the operating handle are at different distances from the center of rotation of the operating handle so that each plunger moves on its own circle of rotation about a common center concentric with the shaft. The indicating dial is fixed mmediately below the operating handle for indicating rthe five switch positions, and includes a number of apertures Vthrough which the plungers can descend when actuated.

The apertures are positioned so that only the plungers of the locks intended to be actuated on any given position of the switch can engage with the indexing apertures. The lock mechanisms are of a conventional type and are of such nature that the operating key cannot be removed until the key-operated plunger has extended its full length into the corresponding aperture. The key can then be removed and inserted in the corresponding matching lock in either the breaker or either section ofthe two section precipitator, as the case may be. In this manner, there is achieved positive, safe interlocking.

For a more complete understanding of the nature and Iscope of the invention, reference is made to the following detailed description, which may be read in conjunction with the drawings, in which;

FIGURE l is aside elevational view of the selector switch and operating mechanism;

FIG. 2 is a top plan view of the operating mechanism of FIG. 1;

FG. 3 is a plan View of rthe upper deck of the selector l switch, with 3 point contact, and outlining 2 point contact on lower deck;

FIG. 4 i-s a sectional view of the high voltage supply housing and the enclosed apparatus;

FIG. 5 is a schematic illustration of the manner in which the high voltage rectifier supply is connected t0 the individual section of the precipitator when the selector switch is in the position No. 1;

FIG. 6 is la schematic illustration of the manner in which the high voltage rectifier supply is connected to the individual sections of the precipitator when the selector switch is in position No. 2;

FIG. 7 is a schematic illustration of the manner in which the high voltage rectifier supply is connected to the individual sections of the precipitator when the selector switch is in position No. 3;

FIG. 8 is a schematic illustration of the manner in which the high voltage rectifier supply is connected to the individual sections of the precipitator when the selector switch is in position No. 4; and,

FlG. 9 is a schematic illustration of the manner in which the high voltage rectifier supply is connected to the individual sections of the precipitator when the selector switch is in position No. 5.

Referring now to FEGURE l of the drawings, there is disclosed a selector switch gene-rally indicated at 10 connected to respond to the operation of the selector switch operating mechanism general-ly indicated `at 11. The selector switch assembly 10 comprises a rectangular upper deck 12 land a rectangular llower deck 13 fixed in parallel spaced relationship by means of four parallel arranged upright members i4 fixed to the corners of the decks 13 and 1?, [by any suitable means, such as studs (not shown) extending through the members 14. The decks 12 and 13 and the uprights 14 are constructed of any suitable insulating material. The upper deck 12 includes a centralized aperture 15 for receiving contact operating means hereinafter described. The upper deck 12 serves as a mount for seven insulated copper studs 16, 17,18, 19, 20,

3 centralized aperture i5. Each stud extends through the deck 12 Iand includes a contact 26 on the upper end and a threaded portion 27 on the lower end. The lower deck 13 is identical to the upper deck 12,and includes a centralized aperture 2S for receiving the aforesaid contact operating means. The lower deck 13 serves as a mount for seven insulated copper studs 29, Sti, 3l, 32, 33, 34, and 35, which are equally spaced laround a circle on the periphery of the deck i3 which circle is concentric with the centralized aperture 2S. Each stud extends through the deck 13 and includes la `contact 36 on the lower end and a threaded portion 37 on the upper end.

A contact operating means comprising a tube 35 extends through the .aperture 15 in the upper deck and the aperture 28 in the lower deck to serve as a common mounting means for the moving contacts corresponding to each deck. The upper portion of the tube 38 includes a rst pair of parallel, dat- bottomed grooves 39, 39, arranged transversely of the tube 38, and a second pair of identi-cal parallel itat-bottomed grooves 4d, 40, on the tube opposing the iirst pair of grooves 39, 39. A pair or identical U-shaped contact mounts 41, 42, which may be constructed of any conventional insulating material, each includes a pair ot' legs 43, 43 and 4d, 44, respectively, received in a set-of the opposing grooves 3%, 46 to thus comprise fa pair of juxtaposed mounts. A flat elongated conducting arm 45 is fixed-ly mounted by any suitable means between the pair of juxtaposed contact mounts 41, 42 so as to extend across 'the legs 43, 43 and 44, 44 and outwardly from the tube 38 beyond the limits of the U-sh-aped mounts 41, 42'and so as to extend inwardly toward the tube in abutting relationship therewith so that the mounts 41, 42 are rigidly fixed on the tube through cooperation between the grooves 39, 39 and 40", 40 and the conducting member 45. A group of three resilient conducting members 46, 47, and 48, each carrying a contact 49, Sil, 51, respectively, on the outer end, are each attached at the inner end to the outer periphery of the conducting far-rn 45 in spaced relationship along the perniphery of the conducting arm d5 to thus provide simultaneous contact between each of the three contacts 49, 5t?, and 51 and the contacts on any three adjacent ones ot' the studs 16 through 22 as the tube 38 is rotated about its longitudinal axis.` A second pair of U-shaped contact mounts 52, 53, constructed of insulating material, are positioned at the lower end of tube 38 in vertical lalignment with .the previously described mounting members 41, 42, by means of -a iirst pair of transverse grooves 54, 54 vertically aligned `with the first-mentioned pair of grooves 39, 39, and an opposing set of grooves (not shown) whereby the mounts 52, 53 serve as mounting means for an elongated conducting arm 55 which is attached between the mounts 52, 53 in the same manner' as previously described with respect l'to the elongated conducting member 45 vas mounted between the first-mentioned pair of mounting means 41, 42. A pair of resilient conducting members 5.7, 57, having contact at the outer end `are each attached at the inner end to the outer periphery of the conducting arm 55, thus providing simultaneous contact between `any two adjacent bushings 29 through 35 on the lower deck 13 and the outer ends of the pair of conducting members S7 as` the tube 38 is rotated.

The fore-going structure provides for fixation of the upper movable contact mounts 41, 412 with respect to the lower movable contacts 52, 53, whereby rotation of the tube 38 about its central axis provides for simultaneous movement of the upper movable contacts and the lower movable contacts across the respective iixed contacts in the predetermined xed relationship as illustrated in FIG. 3.

The studs 16 through 22 on lthe upper deck 12 are electrically connected to the studs 29 through 35 on the lower deck 13 in the manner illustratedschematically in PIG. 5 so that asthe tube 38 is axially Irotated by the operating d mechanism, as hereinafter described in detail, the upper movable contact mounts 41, 42 and the lower movable contact mounts 53, 52 carry their corresponding movable contacts into engagement with the various studs in predetermined `arrangements to elect control of the energization ot' the individual sections of the precipitator as hereinafter described indetail.

The operating mechanism for the hereinbefore described switch mechanism comprises a shaft 59 connected at itslower endto the upper end of tube 38 by means of a universal slip joint 6%. The upper end of shaft 59 is journaled into the hub 61 of a handle 62 and is aiiixed to the hub by means of a transverse pin 63 extending through the hub 61 and the shaft 59. A boss 64 on the hub extends downwardly along the shaft to act as a spacer in a manner hereinafter described. The

hub 61 is substantially rectangular in form and is journaled on the shaft 59 substantially oil center whereby each of the four vertical sides of the hub are positioned at different distances lfrom the shaft 59. The hub 61 serves not only as a mount for the handle arn1'62, which extends laterally from one rectangular face of the hub 61 transversely of the shaft 59, but also serves as a mount for three key'operated lock mechanisms 65,66, and 67, each xedly mounted on one of the three remaining vertical rectangular sides of the hub 61. Each lock mechanism 65, 66, and 67 includes an extensible plunger 66, 69, and 7b, respectively, the plungers being reciprocably operable parallel to the axis of the shaft 59 for engagement with an indexing mechanism to be hereinafter described in detail. The lock mechanisms are each responsive to a different key, and, as previously mentioned, are of the type wherein a key cannot be removed until the plunger is fully extended as illustrated in FIG. l.

lt is seen that the plungers of the three locks on` the operating handle are positioned at different distancesV vides a basis for selective operation of the individual lock mechanisms in any combination. This is achieved through the provision of an indicating `dial 71 centrally sleeved on the boss 64 to rest adjacent the handle 62 and the lock mechanisms 65, 66 and 67. The indicating dial 71 includes the numeral l, 2, 3, 4, and 5 spaced radially about the upper surface of the dial to thus show the tive positions of the operating handle for elicoting the various switching movements of the switch mechanism as hereinafter described in detail. indexing between the handle portion 62 and the various numerals is achieved by Iway of aperture 72 in the handle 62, through which aperture the various numerals are vertically Viewed by the operator to establish the prime positions of the handle when moving the handie `from one switch position to another. The-indexing dial 71 also includes a group of holes 73 through S0, through which holes the lock plungers may extend when in the fully extended position. As is hereinafter described in detail, the individual holes are placed in predetermined positions on the dilerent circles of rotation of the different plungers so that for each position of the handle 62, only predetermined ones of the lock mechanisms 65, 66, and 67 may be operated.

The indicating dial 71 is ixedly attached atop a pair of vertical support arms Si, S2 on a support plate S3 which is centrally aperturcd to receive the shaft 59 and to abut the lower end of boss 64 which acts as a spacer between the bottom of the hub 61 and the support plate S3. l The support plate 83 is, in turn, fixed toa on the high voltage powerv supply and switch housing 86, as shown in PEG. 4, the indexing plate 71 is tixed` with respect to the fixed contacts of the switch 10, while the handle 6-2 may be rotated to any position to rotate shaft 59 and tube 38 to effect switching, as desired, in accordance with the individual numerals on the indexing dial 71.

Referring now to FIGS. through 9, there is shown a group of schematic illustrations showing the relationship between the various switch positions and the corresponding position of the switch mechanism for each of thefive switch positions. in FlG. 5, there is yshown a high voltage transformer 87 having a circuit breaker A66 operable to be locked to the open position and unlocked to the closed position only'by the key corresponding to lock 66 in the operating mechanism. The locks 65', y66', and 67', are identical to their respective matching locks 65, 66, and `67, respectively, and are operable to retain the' operating key until the locks are in the fully locked condition. The output of the transformer is electrically connected to a full wave rectifier element 88 which may be comprised of four or more silicon diode stacks 89, 90, 91, and 92. A -first pair of diode stacks S9 and 90 are connected'in forward relationship between ground and terminal 18 on the upper deck 12. The other pair of diode stacks 91, 9-2, are connected in forward relationship between groundand terminal 17 on the upper deck 12. Section No. 1 of the precipitator is series connected with a lock switch 67', operable only in response to the key relating to corresponding matching lock 67 in the operating mechanism'. The locky67' and section No. l of the precipitator are connected between terminal 31 on theiower deck 13 and ground." Section No. 2 of the precipitator is series connected with a lockswitch 65' operable only in response to the key corresponding to matching lock 65 in the operating mechanism 11. Section l2 of the precipitator and the series connected lock 65' arefconnected between terminal 29 on lower deck 13 and ground.

Vlf it is' desired to move the operating handle 62 from any one position to another, it is necessary that allrtbree locks 65, 66, and `67 on the hub 61 be in the unlocked position so that all the corresponding plungers 68, 69 and 70 are in the fully retracted position and the keys may not be removed. At the same time, the breaker lock 66' and the precipitator lock switches 65' and 67' must be locked open, otherwise the keys could not have been removed therefrom to unlock the operating handle 62 as described immediately above.

Position No. `1 of the operating handle, as shown in FIG. 5, operates the switch 10 to apply full wave direct current on both section No. l and section No. 2 of the precipitator. When the operating handle is indexed over numeral l on the index panel, lock 66 is locked by the operator to effect extension of corresponding plunger 69 into corresponding hole 7-4 on the index plate 7:1, thus locking the operating mechanism 11 in switch 10. The key is then removed from lock 66 and inserted in matching lock 66' to unlock the breaker lock 66', thus effecting 'energization of the transformer 87 and rectifier V88. When the upper end of the transformer secondary is positive, section No. A1 of the precipitator is energized from the transformer through rectifier 89, ground, lock switch 67', precipitator section No. l, studs 31, 19, and 22, conductingv arm 45, stud 17, and through rectifier 92 to the lower end of transformer 87. At the same time, precipitator section No. 2 is energized through rectifier 89, ground, lock switch65, section No. 2 of the precipitator, studs 29, 33 and 16, conducting arm 45, stud 17 and through rectifier 92 to the lower end of the secondary oftransformer 87. When the lower end ofv transformer 87 is positive on the next half cycle, precipitator section No. l is energized through rectifier 91, ground, lock switch 67', section No. l, stud 31, conducting arm 55, studs 32, 18, rectifier 90, to the upper end of transformer 87. At 'the same time, precipitator'section No. 2 is energized through rectifier 9,1, ground, lock switch`65, section No.

6 2 studs 29, 33, and 16, conducting arm 45, studs 22, 19, and 31, Vconducting arm 55, stud 32, and 18, rectifier 90, to the upper end of the secondary of transformer 87.

lPosition No. 2 of the operating mechanism 11, as shownv in FIG. 6, operates switch 14! to apply full wave direct current on precipitator section No. 2 while at the Y same time grounding section'No. l of the precipitator. To move the handle 62 from position 1 to position 2 and to effect the new operation, previously unlocked breaker lock 66' is locked to open the breaker and deenergize the rectifier 88,' the key is removed therefrom and inserted to unlock the lock 66 thus releasing the operating mechanism, whereafter the operating mechanism is indexed to position No. 2. The lock mechanism 67 is locked, thus effecting extension of plunger 70 into corresponding hole 75 in the indexing plate 71, the key is removed from lock 67 and is utilized to unlock matching lock 67', lock `66 is locked effecting extension of plunger 69 into the corresponding hole 76, and finally the key is removed from lock 67 and is utilized to lock breaker lock 67' to thus effect reenergization of the rectifier S8. When the upper end of the secondary of transformer 87 is positive, precipitator section No. 2 is energized through rectifier 89, ground, lock switch 65', studs 29, 33, and 16, conducting arm 4S, stud 17, rectifier 92 to the lower end of the secondary of transformer 87. When the lower end of the secondary of transformer 87 is positive, section No. 2 of the precipitator is energized through rectifier 91, ground, studs 29, 33 and 16, conducting arm 45, stud 18, rectifier 90 to the upper end of transformer 87. Section No. l of the precipitator is not energized on either half cycle because of the open condition of lock switch 67. At the same time, precipitator section No. 1 is connected to ground through stud 31, conducting arm 55 and stud 30.

Position 3 of the operating mechanism 11, as shown in FIG. 7, loperates switch 10 to apply full wave direct current on section No. l of the precipitator while at the same time grounding section No. 2 of the precipitator. To move the handle 62 from position 2 to position 3 and effect the new operation, lock 66' is locked to open the breaker and deenergize the circuit, the key is removed from lock 66' and utilized to unlock lock 66, lock 67 is locked, lock 67 is unlocked, the handle 62 is indexed to position 3, lock 65 is locked, lock 65' is unlocked, lock 66 is locked, and lock 66' is finally unlocked to close the breaker effecting reenergization of the circuit. Position No. 3 of switch mechanism 10 provides full wave direct current to section No. l of the precipitator while grounding section 2 of the precipitator through the circuitry clearly indicated in FIG. 7.

Position 4 of the operating switch 11, as shown in IFIG. S, operates the switch 10 to apply half wave direct current to each of section No. l and section No. 2 of thev precipitator. To move the handle from position 3 to position 4 to effect the new operation, lock 66' is locked to deenergize the circuit, lock 66 is unlocked, lock 65' is locked, the handle is indexed to position No. 4, lock 66 is locked, and lock 66' is unlocked to reenergize the circuit.. Each of the precipitator sections No. l and No. 2 are thus energized by half Wave direct current through the circuitry clearly illustrated in FIG. 8.

Position No. 5 of the operating mechanism 11, as shown in FIG. 9, operates switch 1i) to groundboth section No. 1 and section No. 2 of the precipitator. To move the handle 62 from position 4 to position 5, lock 66 is unlocked to deenergize the circuit, lock 66 is locked, both locks 67 and 65 are locked, and matching locks 67 and 65', respectively, are unlocked. Both section 1 and section 2 of the yprecipitator are grounded through the circuitry clearly illustrated in FIG. 9. Inasrnuch as lock 66 cannot be operated in this opsition, the key may not be removed to operate breaker lock 66', therefore, the circuit cannot be energized.

Referring now to FIG. 4, there is shown the general organization of the individual apparatus elements previously described in detail. Specifically, there is provided a tank 86 having a cover 85 removably secured thereto in any suitable manner such as by bolts, not shown. The tank may contain any suitable insulating fluid such as oil. A large handhole cover S4 is removably secured on the cover 85. A small handhole cover 84A is removably secured on the large handhole cover 84 and is positioned in side-by-sideV relationship with the switch operating mecha- Y to a different one of two opposing internal walls of the tank `86. The selector switch mechanism 10 is removably attached as by a pair of brackets 99, 99 (only one shown) to the upper portion of support plate 95 immediately above the rectifier mechanism 88 and immediately below the operating mechanism 11 so that shaft 59 of the operating mechanism 11 engages pin 60 (FIG. l) on the upper end of selector switch shaft 38.

The transformer `87 is mounted within the tank 86 adjacent to the rectiero and switch 10 by means of the end framing members of a frame assembly 100 attached to the walls of the tank 86 in any suitable manner.

A pair of low voltage bushings 101, 101 are provided in the side of the tank 86 for connecting a primary supply to the transformer S7. A pair of filter choke coils 102, Y

102 (only one shown) are mounted by suitable bracket means 103, 10G in side-by-side relationship on the transformer support framing member 100 and serve to filter the direct-current output from the rectifier 83 through the selector switch mechanism 10i. A pair of high voltage bushings 104, 104 (only one shown) are provided in Sideby-side relationship on the cover'85 adjacent the large handhole cover 84 to serve as means for connecting the direct-current filter output leads to the two sections of the precipitator (not shown) positioned externally of the tank 86.

The electrical connections between the transformer 87, the rectifier 88, the selector switch 10, as shown schematically in FIGS. 5 through 9 are physically carried out within the tank y86 by means of a terminal board 105 mounted on the transformer framing member` 100 so as to be positioned between the transformer on the one side of the tank and the rectifier-switch assembly on the other side of the tank. The terminal connections are made by self-locking bayonet type connections which can be easily disconnected. This permits the rectifier and connector switch assembly to be removed from the tank for an inspection, through the handhole in the cover, without disturbing the other component parts of the apparatus.

The electrical connections between the component parts of FIG. 4 are Yobvious in view of the teachings of FIGS. 5 through 9 and in view of the foregoing description. Accordingly, the actual electrical connections have been omitted from FIG. 4 in the interest of drawing simplicity.

Since certain changes may be made in the above-described construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the above description and shown in the accompanying drawings should be considered as illustrative and not in a limiting sense.

We claim as our invention:

l. -In control apparatus: selector switch means including fixed contacts and movable contact means; shaft means for selectively positioning the movable contacts with respect to the fixed contacts; a handle fixed to the shaft and operable to selectively position the shaft at any one of a number 'of prdiermned positions; a plurality of key 8 l operated lock means on the handle; each lock means having an extensible member movable from a retracted position when unlocked to an extended position when locked; an indexing plate fixed with respect to the fixed-contacts and operable to prevent movement of the extensible member to the locked position; indexing means on said plate comprising apertures engageable with different predetermined ones of said movable members at'each different operating position of the handle relative to the plate to lock the handle in position and to permit extension of said movable members to the lock position; a plurality of keyoperated lock switch means connecting the fixed contacts to different electrical apparatus; each lock switch adapted for operation only bythe key of a predetermined one of said lock means.

`ln Va switching apparatus: a selector switch; a shaft axially rotatable and connected for selectively operating the selector switch to different operating positions; a handle having one end fixed to said shaft to effect, said axial rotation; a plurality ofkey operated locks liixed to the handle at said one end; each lock having a member extensible in response to a locking operation of the key and retractable in response to an unlocking Yoperation of the key; a plurality of electrical apparatus; lock operated circuit interrupter means connected to the switch for connecting and disconnecting corresponding'apparatus to the switch; each said lock operated switches operable to close the corresponding switch when locked and to open the corresponding switch when unlocked; each lock on each circuit interrupter corresponding to one of said locks on the handle to comprise a matching set adapted for individual operation by a common key, each said key being removable from each lock of the corresponding Set only when the lock is in the fully locked position; an indexing plate adjacent the handlelfor preventing extension of said extensible members; a plurality of apertures arranged in said plate in predetermined relationship to permit extension of different predetermined ones of the extensible members through the plate at each different operating position of the handle. Y

3. In aA switching apparatus: a selector switch; a shaft axially rotatable and connected for selectively operating the selector switch to different operating positions; a handle having one end fixed to said shaft to effect said axial rotation; a plurality of key operated locks fixed to the handle at said one end; each lock having a member extensible axially of said shaft in response to a locking operation of the key and retract-able in response to an unlocking operation of the key; a plurality Vof electrical apparatus; lock operated circuit interrupter means connected to the switch for connecting and disconnecting corresponding apparatus to the swtich; each said lock operated switches operable to close the corresponding switch when locked andV to open the corresponding switch when unlocked; each lock on each circuit interrupter corresponding to one of said locks on the handle to comprise ak plurality of apertures arranged in said. plate in predeter-l mined relationship to permit extension of different predetermined ones of said extensible members through the plate at each different operating position of the handle 4. IIn a switching apparatus: a selector switch; a shaft axially rotatable and connected for selectively operating the selector switch to different operation positions; a handle having one end fixed to said shaft to effect said axialY rotation; a plurality of key operated locks fixed to the handle at said one end; each lock having a member extensiole axially of said Shaft in response to a locking operation of the'key and retractable in response to an unv locking operation of the key; aV plurality of electrically responsive apparatus; lock operated circuit interruptor 9 means connected to the switch for connecting and disconnecting corresponding apparatus to the switch; each said lock operated switch operable to close the corresponding switch when locked and to open the corresponding switch when unlocked; each lock on each circuit interrupter corresponding to one of said locks on the handle to comprise a matching set adapted for individual operation by a common key, each said key being removable from each lock set only when the individual locks are in the lfully locked position; an indexing plate adjacent the handle for lpreventing extension of said extensible members; a

plurality of apertures arranged in said plate in predeter-l mined relationship to permit extension of diterent predetermined ones of the extensible members through the plate at each diierent operating position of the handle; each aperture operable to tightly receive only one of said extensible members.

5. In combination: a precipitator comprised of a pair of independent sections; a high VVoltage transformer; rectiiier means comprising a first diode means connected in series aiding relationship, and second diode means connected -in forward relationship; means connecting the forward end of each diode means to ground; a selector switch having an upper deck and a lower deck; seven iixed contacts arranged in numerical sequence on each deck; the first contact on the lower deck connected to ground; the second contact on the lower deck connected to one of the sections of the precipitator, to the fth contact on the lower deck, and to the fifth contact on the upper deck; the third contact on the lower deck connected to the sixth contact on the upper deck; the fourth on the lower deck connected to ground and to the third contact on the upper deck; the sixth contact on the lower deck connected to the seventh contact on the upper deck; the seventh contact on the lower deck connected to the iirst contact on the upper deck; the sixth contact on the upper deck connected to the rearward end of said second pair of diodes; conductor means connecting the seventh contact on the upper deck to the rearward end of said rst pair of diodes; contact bridging means on the upper deck movable across the xed contacts and engageable with any three consecutive fixed contacts on the upper deck; movable contact bridging means on the lower deck engageable with any two consecutive fixed contacts on the lower deck; switch operating means including means tixing the movable contact bridging means together for simultaneous movement vacross the corresponding fixed contact whereby the positioning of the upper bridging contact member on any three consecutive iixed contacts effects positioning of the lower movable contact bridging member on a lower fixed contact corresponding to the highest numbered iixed contact on the upper deck engaged by the movable contact member on the upper deck and the next highest corresponding contact on the lower deck.

References Cited in the le of this patent UNITED STATES PATENTS 728,590 Linn May 19, 1903 2,576,836 Hulsinger Nov. 27, 1951 2,811,594 Papouschek Oct. 29, 1957 FOREIGN PATENTS 557,336 Great Britain Nov. 16, 1943

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