Grounding Switch

Abstract

An improved grounding switch is provided capable of either an electrical drive, or manual actuation by means of a removable handle. The grounding is accomplished by the screw-driven linear motion of a cylindrical grounding contact, which moves into a stationary finger set attached to the main high-voltage conductor. The motor-driven grounding switch of the present application is particularly suitable for use with gas-insulated high-voltage transmission systems, and may, for example, be located at junction boxes provided at suitable locations.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS

Reference is made to a related patent application filed Mar. 27, 1972, Ser. No. 238,381, by Harvey Spindle, J. R. Meyer, and R. H. Hess, entitled "Improved Switch and Mechanism Therefor", and assigned to the assignee of the instant application.

BACKGROUND OF THE INVENTION

In recent years, there has come about a demand for a reduced-size substation, and this demand, on the part of public utilities, has been met by gas-insulated substation equipment, such as set forth in U.S. Pats: No. 3,378,731, - Whitehead; No. 3,348,001 - Upton et al; No. 3,356,798 - McKinnon; No. 3,610,858 - Gruber et al; No. 3,599,041 - Boersma et al; No. 3,562,460 - Koener.

The foregoing equipment significantly reduces the space required by the high-voltage side of substations rated, for example, 115 KV through 345 KV. The space reduction is accomplished by replacing the open-bus and air-type bushings with gas-insulated bus filled, for example, with a highly-insulating gas, such as sulfur-hexafluoride (SF.sub.6) gas, at a pressure say, for example, 45 p.s.i.g., and thereby permitting the movement of electrical equipment very closely together. This gas-insulated substation equipment has many advantages, among which are:

1. Significant reduction in space requirements both in land area and overall height.

2. Added system reliability by eliminating the possibility of phase-to-phase faults, lightning strokes within the system, or contamination of insulators.

3. Reduced maintenance because the closed system is isolated from its environment.

4. Added personnel safety because all live parts are covered by grounded shields.

5. The gas-insulated modular approach has the additional advantage, because it provides the user with lower installation costs, when compared with conventional, or other types of power systems.

The gas-insulated system, as briefly described above, has additional design strategies, inasmuch as the high-voltage equipment is compressed, so that both the space required, and the total length of bus is minimized. The power transformers may be located on outside corners so as to be capable of ready removal, and the location of cable potheads is flexible, with the result that the system may be readily connected to overhead lines.

As examples of the types of ratings for such gas-insulated transmission systems, reference may be made to the specification ratings, as set forth below:

115/138 kv Ratings General Ratings for MGT Systems SF.sub.6 at 45 psig Rated maximum voltage 145 BIL 650 60 HZ-one minute withstand 310 Chopped wave Not applicable Symmetrical 3 Second Current Rating 47 ka Momentary Current 76 ka Switching Current Ratings Circuit breaker (maximum rated interrupting current) 50 ka Magnetizing current switch 35 amps Isolator No load switching only Ground switch No load switching only Continuous Current Ratings Circuit breaker 2500 Amperes Load break switch 2500 Amperes Magnetizing current switch 2500 Amperes Isolator 2500 Amperes Ground Switch Not applicable Bus 3000 Amperes 230 kv Ratings General Ratings for MGT Systems SF.sub.6 at 45 psig Rated maximum voltage 242 BIL 900 60 HZ-one minute withstand 425 Chopped wave Not applicable Symmetrical 3 Second Current Rating 47 ka Momentary Current 76 ka Switching Current Ratings Circuit breaker (maximum rated interrupting current) 50 ka Magnetizing current switch 35 amps Isolator No load switching only Ground switch No load switching only Continuous Current Ratings Circuit breaker 2500 Amperes Load break switch 2500 Amperes Magnetizing current switch 2500 Amperes Isolator 2500 Amperes Ground switch Not applicable Bus 3000 Amperes 345 kv Ratings General Ratings for MGT Systems SF.sub.6 at 45 psig Rated maximum voltage 362 BIL 1050 60 HZ-one minute withstand 555 Chopped wave Not applicable Symmetrical 3 Second Current Rating 47 ka Momentary Current 76 ka Switching Current Ratings Circuit breaker (maximum rated interrupting current) 50 ka Magnetizing current switch 35 amps Isolator No load switching only Ground switch No load switching only Continuous Current Ratings Circuit breaker 2500 Amperes Load break switch 2500 Amperes Magnetizing current switch 2500 Amperes Isolator 2500 Amperes Ground switch Not applicable Bus 3000 Amperes

It is desirable to provide an improved grounding switch, which will permit the grounding of the high-voltage conductor, or bus, either at times when it is desirable to work upon the gas-insulated high-voltage system, or to deliberately create a grounding fault and to trip remote circuit breakers. It is desirable, in addition, to provide an improved switch of the foregoing type, which may ground, for example, a 50 KVA fault for three seconds without damage to the grounding switch.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention, a motor-driven grounding switch is provided to cause an extension and retraction of a movable grounding contact into and out of engagement with the stationary grounding contact structure, associated with the high-voltage conductor, or high-voltage bus. Preferably, it is desirable to provide a motor-driven actuation of the grounding switch, and for emergency use, a portable collapsible handle may be provided to enable manual grounding of the device.

Accordingly, it is a general object of the present invention to provide an improved motor-driven grounding switch.

A more specific object of the present invention is the provision of an improved motor-driven grounding switch particularly adaptable for use with a gas-insulated high-voltage transmission system.

Another object of the present invention is the provision of an improved motor-driven grounding switch, which also causes operation of auxiliary switches, and a proper indication of a position-indicator, such that the position-indicator will be in a neutral position, other than when the grounding switch is either in the fully-open or fully-closed positions.

Another object of the present invention is the provision of an improved motor-driven grounding switch, in which the same gear drive, which actuates the movable grounding contact, also actuates a screw-driven guide-block, which, through a cam actuator, effects a proper indication of an externally-visible position-indicator.

Still a further object of the present invention is the provision of an improved grounding switch for a gas-insulated transmission system, in which the dielectric gas, such as sulfur-hexafluoride (SF.sub.6) gas, that is used in the main conduit system, is also used in the guide chamber for the linearly-driven movable grounding contact, and surrounding the gas-insulated guide chamber is an outer chamber, preferably having atmospheric air therein.

Another object is the provision of an improved grounding switch, as set forth in the immediately preceding paragraph, in which suitable heating means are provided to prevent condensation within the surrounding air chamber.

Still a further object of the present invention is the provision of an improved grounding switch for a gas-insulated transmission system of compact dimensions, of rugged construction, and capable of fool-proof operation, with the ultimate in safety provided for the maintenance man.

Still a further object of the present invention is the provision of an improved grounding switch of the foregoing type, in which a removable collapsible handle is provided, close to the housing, for the grounding switch, and capable of being used in place of the motor-driven drive for emergency use.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a somewhat diagrammatic view of a gas-insulated substation, showing the general environment for one application of the improved grounding switch of the present invention;

FIG. 2 is a one-line diagram for the gas-insulated substation of FIG. 1;

FIG. 3 illustrates a junction box in section and a portion of the grounding switch;

FIG. 4 is an enlarged sectional view taken along the same plane as FIG. 3;

FIG. 5 is a vertical sectional view, partially in side elevation, of the improved grounding switch of the present invention, taken in application with a gas-insulated transmission line, the view showing a transfer section across the gas-insulated line, and the movable grounding contact being shown in its open position;

FIG. 6 is an enlarged vertical sectional view taken substantially along the line VI--VI of FIG. 9;

FIG. 7 is an inverted plan view, in section, taken substantially along the line VII--VII of FIG. 6;

FIG. 8 is a fragmentary vertical elevational view taken substantially along the line VIII--VIII of FIG. 6;

FIG. 9 is an inverted plan view taken substantially along the line IX-IX of FIG. 8, illustrating the collapsed and storage position of the collapsible handle;

FIG. 10 is a view, somewhat similar to that of FIG. 6, but showing the collapsible handle extended, and in position to manually effect movement of the grounding switch; and,

FIG. 11 is a view of the collapsible handle in its extended position, ready for insertion into the handle-storage compartment of the grounding-switch housing.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention has particular application to a new line of equipment 1 involving gas-insulated substations having gas-insulated components, and somewhat diagrammatically illustrated in FIGS. 1 and 2 of the drawings.

FIG. 2 is a one-line diagram of the equipment 1 illustrated in FIG. 1. It will be noted, from a consideration of FIGS. 1 and 2, that the high-voltage equipment 1 is arranged so that both the space required, and the total length of the gas-insulated bus 3 is minimized. The power transformer 4 is located on an outside corner, preferably, so that it can be easily removed. The gas-insulated bus 3 is attached directly to the transformer bushing minimizing area and height required. The location of the cable pothead is flexible. In the gas-insulated system 1, as illustrated in FIGS. 1 and 2, it is chosen to minimize the length of the SF.sub.6 bus 3. If a lightning arrester 5 is located at each pothead 7, an arrester 5 is not required at the transformer 4.

It will be noted that the gas-insulated system 1 of FIG. 1 can be connected to overhead lines. However, the air clearances, required by incoming lines, will somewhat enlarge the total area required by the system 1, and will require additional SF.sub.6 bus 3.

The gas-insulated transmission system 1 illustrated in FIG. 1 is a line of equipment, which will significantly reduce the space required by the high-voltage side of substations rated 115 KV through 345 KV. The space reduction is accomplished by replacing the open bus and air bushings, commonly used, with gas-insulated bus 3 filled with sulfur-hexafluoride (SF.sub.6) gas, for example, at 45 psig (at 70.degree.F.), and moving the electrical equipment as close together as possible.

The use of gas-insulated transmission systems 1 offer many advantages. The use of the system offers several advantages to the user, some of these are:

1. Significant reduction in space requirement both in land area and overall height.

2. Added system reliability by eliminating the possibility of phase-to-phase faults, lightning strokes within the system, or contamination of environment.

3. Reduced maintenance because of the closed system is isolated from its environment.

4. Added personnel safety because all live parts are covered by grounded shields.

5. The modular approach, described in the following section, was chosen because it could provide the user with lower installation costs when compared with conventional or other gas-insulated systems.

6. The system can be overbuilt to permit multiple use of land.

Generally, the equipment 1 includes a plurality of bus assemblies determined by the length that can generally be shipped. The typical bus length 3 will be, for example, 40 feet, and may consist of two 20-feet lengths, with an epoxy spacer in each length. The ends of the bus 3 can be connected to additional lengths of bus, or any functional member of the system. Expansion joints are located in each 20-foot bus section 3 to absorb the maximum of 0.4 inches of expansion expected. As stated, sulfur-hexafluroide (SF.sub.6) gas at 45 p.s.i.g., for example, fills both sheath 11 and bus conductor 3, and is free to move throughout the entire bus. The 45 p.s.i.g. pressure provides approximately the highest dielectric strength possible down to -40.degree.C without liquefaction, eliminating the need for auxiliary heat. The 45 p.s.i.g. pressure also eliminates the possibility of stable corona existing within the system 1.

The present invention is particularly concerned with the motor-driven grounding switch 13, illustrated in FIGS. 3-6 of the drawings. With reference to these figures, it will be noted that there is provided a gas-insulated bus, or high-voltage metallic conductor, designated by the reference numeral 3.

It will be noted that the high-voltage central conductor, or high-voltage bus 3, is spaced coaxially along an outer metallic grounded sheath, or cylinder 11 (FIG. 1) by a plurality of suitably-spaced insulating spacers (not shown). As will be obvious to those skilled in the art, it may, at times, be necessary to sectionalize the gas-insulated transmission system 1, and it may be desired to ground the central high-voltage bus-conductor 3. Spaced at suitable intervals along the gas-insulated conduit system are a plurality of junction boxes 15, illustrated more clearly in FIGS. 3 and 4 of the drawings. These junction boxes 15 constitute a suitable point for connections of additional components in the gas-insulated system 1. The outer case 17 of the junction box 15 is solidly bolted to the outer case of the adjacent device. Inside the junction box 15 is a set of shielded finger contacts 19, which are mounted upon a tubular insulator 21. The inner high-voltage conductor 3 is free to move due to thermal expansion in finger contacts 19 mounted within the contact shield.

The junction box 15 is equipped to handle two bus runs 3 and a portable ground. The junction box 15 can have up to six useful sides, which can be used for a portable ground entrance, isolator switch entrance, or for up to five runs of bus 3.

The junction box 15 offers several advantages to both the designer and the user. From the designer's viewpoint, it offers a great deal of flexibility, and permits a modular approach to a system design. From the user's viewpoint, its compact design keeps the space requirements down, and eases field erection.

The junction box 15 has a pair of spaced finger assemblies 19, which provide expansion of the inner high-voltage bus 3. When initially installing the bus 3 in the system, the bus 3 is free to move through the center of the junction box 15. When the bus 3 is mounted at both ends, the keeper plate 23 is inserted, fixing the bus 3 in position. FIG. 4 illustrates the construction more clearly.

The present invention is particularly concerned with a motor-driven grounding switch 13 to provide an effective ground for the gas-insulated transmission system 1, in the presence of the maximum asymmetric fault currents that the system 1 can provide. A gear-motor 25 and screw-mechanism 27 drive the grounding contact 29 in both directions at about 0.6 inches per second for a total operating time of ten seconds. A visible position-indicator 31 and auxiliary-switch system 33 are driven by a gear 35 and screwdriver 36, that is independent of the motor-drive system. The position-indicator 31 has three distinct positions. An intermediate position-indication is shown for all other positions than fully-open or fully-closed. This has been accomplished by a cam-drive system 38 (FIG. 8), so that a positive indication is provided. In addition, a manual operating crank 40 is stored in the mechanism housing 42, and can be provided with a padlock to positively lock the switch 13 in the closed position.

FIG. 6 more clearly illustrates the construction of the screw-operated mechanism 27. The electrical driving motor, designated by the reference numeral 44, may be of the type ordinarily used in hand-drills, and may, for example, have a rotating speed of 500 RPM. The driving shaft 46 of the motor 44 is pinned to a driving gear 48, which meshes with a driven gear 50, which is pinned at 51 to the rotatable driving screw shaft 52. The motor pin is such that binding of any part of the ground switch mechanism will cause the motor gear pin to shear. Thus, no false status indication can result. In addition, the driving gear 48 also meshes with another driven gear 35, which is pinned to an indicator-shaft 54, which effects linear motion of a threaded guide-block 56. The guide-block 56 is interiorly threaded, and moves back and forth in accordance with rotation of the screw-shaft 54, which rotates in stationary bearings 59 and 60 (FIG. 6), one of the bearings 59 being supported in the mounting flange plate 62, and the other bearing 60 being provided by a mounting plate 64, in turn bolted to a support plate 66.

Consequently, when the driving motor 44 is energized, the three meshed gears 35, 50 and 48 rotate to effect linear opening and closing motions of the tubular grounding contact 29 by a driven nut 68, which is securely fastened to the movable grounding contact 29, and is threaded upon the threaded portion of the driving-screw shaft 52.

It will be noted that the grounding switch 13 comprises two compartments 70, 71, the inner one 70 of which is in gas communication with the insulating gas 72 utilized in the transmission system 1, namely, sulfur-hexafluoride (SF.sub.6) gas, at a pressure say, for example, 45 p.s.i.

Externally of the guide chamber 73, constituted by the guide casting 75, is an outer air chamber 71 which is encased by an external mechanism housing 42 having an accessopening 77 therein. A cover plate 79 (FIG. 9) covers the access opening 77, and, at times, permits the insertion of a removable collapsible manually-operable handle 40, illustrated in FIG. 11, and capable of emergency use.

As stated, the guide-block 56 moves a cam plate 81, more clearly shown in FIG. 8, to move the position-indicator lever 83 in a clockwise direction, until the flat portion 81a of the cam plate 81 moves over the roller 85.

In more detail the rightward closing movement of the cam-plate 81 will force the roller 85, affixed to the free end of the internal position-indicator lever 83, toward the right, to the dotted-line position, as shown in FIG. 8, at which time the roller 85 is maintained in this position by its engagement with the underside flat surface 81a of the cam-plate 81, until the vertical surface 81b of the cam-plate 81 positively engages the roller 85, at which time the grounding contacts 22, 29 are closed. Further closing movement of the movable grounding contact 29 will positively drive the roller 85 in a clockwise direction, as viewed in FIG. 8, thereby moving the external visible indicator lever 31 in a clockwise direction to indicate the grounded position of the device 13.

It will, accordingly, be noted that the position-indicator lever 31 is in its neutral position, as indicated by the dotted lines 88 of FIG. 8, until positive engagement by the vertical camming surface 81b of the cam-plate 81 with the roller 85.

A torsion spring 90 (FIG. 7) biases the indicator lever 31 toward the open position at all times. The indicator lever 31 is mounted upon a stub shaft 92, which extends through a Nylon sleeve 94 (FIG. 6), which prevents binding should snow or ice come between the metal bushing 96 and the stub shaft 92. The coefficient of friction between the Nylon sleeve 94 and the steel bushing 96 is such that no binding occurs, even though snow and ice would tend to gather within the small clearance spaces therein.

Heaters 98 are provided within the outer air chamber 71 to prevent internal condensation of moisture within the outer air chamber 71. It is, or course, only necessary to maintain the temperature within the air chamber 71 slightly above that of the outside atmosphere to prevent such internal condensation. The wires to the heater 98 may be attached to one of three terminal blocks, designated by the reference numeral 100, and shown more clearly in FIG. 7 of the drawings.

FIG. 7 also illustrates more clearly the meshing of the three spur gears 35, 48, 50 and also the storage compartment 102 for the collapsible manually-operable handle 40, illustrated in its collapsed position in FIG. 11 of the drawings.

FIG. 7 also shows a conduit entrance 104, through which wiring from remote sources may extend. This wiring, of course, attaches to terminal blocks 100, which, in turn, carry the wiring to the driving motor 44, heaters 98, and also to the auxiliary switch, designated by the reference numeral 106, and illustrated more clearly in FIG. 8 of the drawings.

Auxiliary Switch Operation

The auxiliary switch, illustrated in FIGS. 7 and 8 of the drawings, is actuated by a lever 107, which is engaged by adjustable studs 109, 110 carried by the movable guide-block 56. As mentioned before, the guide-block 56 is threaded on a rotatable screw shaft 54, which is driven by the lower driven gear 35 of FIG. 6. The auxiliary switch 106 is such that its operating lever 107 is biased to a neutral position, as indicated by the dotted lines 111 of FIG. 8. It is forcibly moved to either the opened or closed positions by positive engagement with the adjustable studs 109, 110 carried by the movable guide-block 56. The auxiliary switch 106 may control various electrical circuits, as well known by those skilled in the art.

It will be noted that a suitable seal 112 (FIG. 6) is provided extending out the shaft opening 113 of the interiorly-located guide chamber 73; and a plurality of Teflon washers 114 are maintained in compression by a helical spring 115, disposed within the annular recess 116 provided in the guide-block 75. In addition, a split guide-sleeve 117 (FIG. 6) is inserted within the bore 118 of the guide-block 75, and serves as a further guide for the linear movement of the movable tubular grounding contact 29.

From the foregoing description, it will be apparent that an improved grounding switch 13 is provided, driven by a reversible motor 44, and correlated with a screw-mechanism 27 to positively actuate auxiliary-switch operations and an externally-visible position-indicator devcie 31. The structure is such that the external position-indicator 31 is maintained in a neutral position until the grounding contacts 22, 29 are actually either in the closed position, or in the almost fully-open position. This is brought about by the configuration of the cam-plate 81 carried by the screw-driven guide-block 56.

Also, the auxiliary switch 106, being biased to its neutral position, is only opened or closed upon positive contact with the adjustable stud-bolts 109, 110 carried by the guide-block 56.

MANUAL OPERATION

The collapsible handle 40, illustrated more clearly in FIGS. 10 and 11, may be utilized for emergency use. Normally, it is carried in a storage compartment 102, illustrated more clearly in FIG. 9 of the drawings. When it is to be used, a wing-nut 119 (FIG. 9) is removed, and a small cover plate 79 is laterally displaced to permit removal of the collapsible handle 40. It is inserted through the access-opening 77, as illustrated in FIG. 10, and upon manual operation, may effect rotation of the central screw-mechanism 27. This will, of course, effect opening and closing motions of the grounding contact 29 in a manner similar to that brought about by energization of the driving motor 44.

Although there has been illustrated and described a specific structure, it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

Claims

I claim as my invention:

1. A grounding switching comprising, in combination, a movable grounding contact, a screw-shaft, means for rotating said screw-shaft by an electrical motor, a nut fixedly secured adjacent one end of the grounding contact, the screw-shaft effecting linear opening and closing motions of the grounding contact by threaded engagement with said nut, said electrical motor actuating a driving gear, a central gear fixedly secured to the said screw-shaft, an auxiliary switch, and an auxiliary gear, said auxiliary gear being fixedly secured to a screw-shaft for effecting operation of the auxiliary switch.

2. The combination according to claim 1, wherein a guide-block is threaded onto the auxiliary screw-shaft and is moved thereby in accordance with movement of the grounding contact, a cam-plate fixedly secured to and movable with the movable guide-block, an indicator positioning device, and the cam-plate actuating the indicator positioning device.

3. A motor-driven grounding switch adaptable for use with a gas-insulated transmission system comprising, in combination, means defining a guide-chamber having a linearly-movable tubular grounding contact disposed therein, a driving screw-shaft disposed interiorly of said tubular grounding contact, a driving motor, said motor driving said screw-shaft to effect opening and closing motions of the movable tubular grounding contact, a position indicator, and an additional auxiliary screw-shaft rotates with rotation of the first-mentioned screw-shaft and effects operation of the position-indicator.

4. The combination according to claim 3, wherein a movable guide-block is threaded to said auxiliary screw-shaft and carries a cam-plate therewith, said cam-plate positively effecting indicating motion of the externally-mounted position-indicator, and the position-indicator being biased to the open position.

5. A motor-driven grounding switch adaptable for use with a gas-insulated transmission system comprising, in combination, a support plate (62) adaptable to close an opening in said system, means defining a hollow guide chamber (73) secured to said support plate, a tubular movable grounding contact (29) longitudinally movable within said hollow guide chamber, a nut (68) secured to said movable grounding contact, means preventing rotation of said nut, the region (70) interiorly of said hollow guide chamber communicating with the gaseous region within said gas-insulated transmission system, means (42) defining a second region externally of said hollow guide chamber (73) in communication with the atmospheric air, a motor disposed within said second region (71), gear-means disposed within said second region (71) and operatively connected with said nut (68) for causing the longitudinal motion thereof to effect thereby opening and closing motions of the movable grounding contact.

6. The combination of claim 5, wherein a heater is provided within the second region (71) to prevent condensation therein.

7. The combination according to claim 5, wherein a second screw-shaft is connected to said gear means and serves to operate a position-indicator.

8. The combination according to claim 7, wherein a cam-plate moves with said second screw-shaft and effects the operation of an auxiliary switch.

9. The combination according to claim 5, wherein said preventing means includes a longitudinal slot in the bore of said hollow guide chamber 73).