Rotary switch for gas-insulated substations

A rotary selector switch comprises a generally flat blade mounted for rotation in its own plane about an axis passing through it into and out of contact with one or more of several spaced terminal contacts.

BACKGROUND OF THE INVENTION 
This invention relates to gas-insulated substations and more specifically 
relates to a novel rotary switch for gas-insulated substations. 
In gas-insulated substations a variety of switching functions must be 
performed and, consequently, a variety of disconnect switch types have 
evolved. These would include, for example, horizontal switches, breaker 
switches, tap switches, ground switches and the like. Each of these 
switches is now made as a separate unitary device and several distinct 
switch devices are interconnected in any given substation assembly. Each 
of the distinct switch devices is relatively expensive and requires 
separate engineering drawings. In addition, each unitary switch takes up 
space, and limits the substation compactness that can be achieved, 
particularly at lower voltages. The individual switches must also be 
provided with respective controls and, frequently, with motor operators, 
gas monitoring systems, and the like. 
SUMMARY OF THE INVENTION 
The principal object of the present invention is to provide a novel 
selector switch that can fulfill the functions of at least two separate 
conventional switches in a gas-insulated substation, to permit greater 
economy and compactness. 
It is another object to provide a single switch assembly that can replace 
several types of switches in the conventional substation so as to reduce 
such costs as tooling, engineering, and documentation required in the 
manufacture of a plurality of different assemblies. 
It is a further object to provide a novel switch that permits use of a 
simpler control scheme, motor operators, etc., resulting in greater 
economy. 
To satisfy these objects, the present invention provides a rotary switch 
for a gas-insulated substation that can, for example, serve the functions 
performed conventionally by two breaker switches and a tap switch. In one 
preferred embodiment, the switch of the invention comprises a conductive 
blade having the form of a disc from which an angular section has been 
removed. It is mounted so that it can rotate about the axis of the disc. 
Three terminals are disposed relatively close together angularly about a 
portion of the disc's circumference. Each terminal is shaped to 
accommodate the blade between two sets of contact fingers while permitting 
it to rotate fairly freely. By rotating the blade to the proper angular 
position, any one, any two or all three of the terminals can be contacted 
by the blade, the center of which may be in electrical contact with a 
fourth conductor if voltage indication is desired. All three poles can be 
housed in a single gas-filled tank, permitting considerable economy.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows a typical conventional three-phase gas-insulated substation. A 
typical prior art gas-insulated substation is described, for example, in 
U.S. Pat. No. 4,130,850 dated Dec. 19, 1978. The three phase lines 2,3 and 
4 enter the substation via air to-gas bushings 5,6 and 7 and horizontal 
disconnect switches 5a,6a and 7a. Each line passes through a respective 
first disconnect switch 8,9 and 10 and enters a first respective circuit 
breaker 11,12 and 13. Leaving the circuit breakers 11,12 and 13, through 
respective second disconnect switches 14,15 and 16 each phase contains a 
respective tap switch 17,18 and 19 and a respective third disconnect 
switch 20,21 and 22 leading to a respective second circuit breaker 23,24 
and 25. Each of the three tap switches 17,18 and 19 permits connection to 
a respective pothead 26,27 and 28. Each of potheads 26,27 and 28 can 
receive test bushings. Each phase leaves the second breaker 23,24 and 25 
via a fourth respective disconnect switch 29,30 and 31, traverses a double 
tap switch 32,33 and 34 connected to respective poles 35a,35b and 35c of a 
power transformer 35. Tap switches 32,33 and 34 are also connected to 
respective poles of coupling capacitor voltage transformers 36a,37a and 
38a, respectively. Disconnect switches 29,30 and 31 are also connected to 
disconnect switches 36,37 and 38, respectively, of circuit breakers 39,40 
and 41, respectively. Breakers 39,40 and 41 are lastly connected to 
disconnect switches 43,44 and 45, respectively. 
For purposes of clarity, a line diagram of FIG. 1 is shown in FIG. 1a 
wherein the numerals of the pole containing line 4 have been used. 
Either or both tap switches 17-19, 32-34 can be replaced by the novel 
rotary selector switch of the invention for each respective phase. As 
described below, the selector switch of the invention would replace not 
only a tap switch but the two disconnect switches adjacent it as well, 
resulting in considerable economy of space and of maintenance costs. 
FIG. 2 shows a view of a portion of one pole of a substation like that of 
FIG. 1, employing the novel rotary selector switch of the invention. This 
switch, contained in schematically shown housing 46 performs the functions 
of tap switch 34 and of the adjacent disconnect switches 31 and 38 in the 
structure of FIGS. 1 and 1a. FIG. 3 shows schematically the switching 
functions of the rotary switch of the invention as employed in the single 
phase of the substation arrangement of FIG. 2. 
Switches 31, 34 and 38 in FIGS. 2 and 3 can be opened in any desired 
combination to isolate breakers 25 and 41 from one another or to connect 
either of the lines to the transformer 35. Details of the novel unitary 
switch 46 are shown in the following Figures. 
In FIG. 4, gas-filled bus housings 53, 54 and 45 contain conductors 55, 56 
and 57, respectively supported in bus housings 53, 54 and 45 by 
conventional insulative supports 58. Conductor 57, mounted in housing 47, 
is provided at its upper end, which extends into switch housing 46, with a 
terminal contact 59. The end of conductor 55 extends into the interior of 
housing 46 and is provided with a conductive arm 60 that extends downward 
into housing 46 toward terminal contact 59, at an angle of generally 
45.degree. from the horizontal. The lower end of the arm 60 is provided 
with a second terminal contact 61. Bus conductor 56 has a corresponding 
arm 62 and terminal contact 63. Blade 64, having the form of a disc of a 
conductive material from which a pie slice has been removed, is mounted in 
housing 46 for rotation about its center and is in electrical contact with 
one end of a fourth bus conductor 65. The blade 64 is so located and fills 
an angle about its center of such size that, by rotating the blade about 
its central contact 66, it is possible to put the blade 64 into contact 
with any desired combination of contacts 59, 61, 63, or to remove it from 
contact with them altogether. Contacts 59, 61 and 63, correspond to 
contacts of switches 34, 31 and 38, respectively, in FIG. 3. 
FIG. 5 shows a further embodiment of the blade 64a and the various 
positions into which it can be moved in order to connect any combination 
of contacts 59, 61, and 63. In this embodiment, the blade 64a has the form 
of a semicircle mounted for rotation about the midpoint 67 of its 
diameter, and having a section removed from the circular part of its 
circumference. The perimeter of blade 64a thus consists of: a straight 
diameter; a long arcuate portion 68 extending from one end A of the 
diameter of the blade 64a and subtending an angle of somewhat over 
90.degree.; an arcuate indentation 69, between points B and C in FIG. 5c, 
subtending most of the rest of the straight angle defined by the diameter 
of the blade 31a; and a short arcuate portion 70 from point C to the 
second end of the diameter. As can be seen from FIG. 5a, the long arcute 
part 68 of the perimeter of blade 64 is sufficiently long to permit it to 
be in complete electrical contact with all three terminal contacts 59, 61, 
and 63 simultaneously. The distance across the indentation 69, that is the 
distance between cusps B and C (see FIG. 5c), is small enough that blade 
64a can be in complete electrical contact with both contacts 61 and 63 
while the indentation 69 is located adjacent contact 59 so that contact 59 
does not touch the blade 64a (see FIG. 5c). 
In FIG. 5a, the blade 64a is shown with its longest arc 68 touching all 
three contacts 59, 61, 63. In FIG. 5b the blade 64a has been rotated 
counter-clockwise to align the indentation 69 with contact 61, so that 
only contacts 59 and 63 touch the blade 64a. In FIG. 5c, the blade 64a has 
been rotated further in the counter-clockwise direction so that the 
indentation 69 is aligned with contact 59 and the blade 64 touches 
contacts 61 and 63 only. In FIG. 5d, a further rotation has been made, 
aligning the indentation 69 with contact 63, so that only contact 59 
touches the blade 64a. By a further small rotation in the 
counter-clockwise direction, it would be possible to make the smaller arc 
70 of the blade 64a touch contact 63, leaving contacts 61 and 59 
disconnected from the blade 64a. By yet a further rotation in the 
counter-clockwise direction, as shown in FIG. 5e, it is possible to move 
the blade 64a so that it does not touch any of the three contacts 59, 61, 
63. By a further small rotation it would be possible to bring point A of 
the blade 64a into contact with terminal contact 61. Yet a further 
rotation, as shown in FIG. 5f, will bring the larger arc 68 of the blade 
64a into contact with contacts 61 and 59. A further rotation in the same 
direction, shown in FIG. 5g, returns the blade 64a to its original 
position. The corresponding switch positions of a conventional substation 
arrangement are shown schematically in FIG. 6. 
It is a central feature of the invention that the rotary selector switch, 
performing the functions of a plurality of conventional unitary switches, 
can be operated by a single control system (or by one motor operator), 
resulting in considerable economy. 
It should be noted that, although the rotary selector switch of the 
invention does not have the coaxial geometry associated with conventional 
disconnect switches, the intrinsic dielectric strength of SF.sub.6, if 
that gas is used for insulation, is so high that considerable 
non-uniformity in the electric field can be tolerated. A 145 kV unitary 
switch could be housed in a 22-inch diameter tank approximately 16 inches 
in length. The spherical corona shield on the switch jaws would be 
approximately 4 inches in diameter. In contrast, a conventional 145 kV 
disconnect switch requires a housing tank 16 inches in diameter and 
approximately 4 feet long. Furthermore, with the rotary switch of the 
invention, all three poles can be accommodated in one housing. 
FIG. 7 shows in detail a typical contact which can be used in the rotary 
selector switch of the present invention. The blade 64 of the switch 
housed in housing 46 is shown at the left. At the right is the flattened 
end 57a of bus conductor 57. Contact finger 72 is disposed underneath and 
in contact with the bus conductor section 57a, and contact finger 71 is 
similarly disposed above and in contact with the bus conductor section 
57a. These contacts are held in place by brackets 73, one of which is 
provided with a spring 74 to urge the lower contact finger 72 upwards 
against the bus conductor contact 57a and the blade 64. Because each 
bracket 73 is hooked over the top of upper contact finger 71, spring 74 
also has the effect of urging upper contact finger 71 against the blade 
64. Washers 75 and 76 are disposed between the contact fingers 71, 72 and 
the bus conductor 57. Each contact finger 71, 72 is provided with an 
arcuate section 77, 78 at each end. One arcuate section 77 of each contact 
finger 71, 72 makes high pressure electrical contact with the bus 
conductor section 57a, and the corresponding arcuate section 78 at the 
other end of the contacts 71, 72 makes the actual connection with the 
switch blade 64. The end of the bus 57 extends into housing 46 which 
covers the contacts. Annular corona shields 90 and 91 cover contacts 61, 
59 and 63, and discshaped corona shields 93 and 94 cover the edges of 
contact 64 and next into shields 91 and 92. The shields 91 to 94 are 
supported in any desired manner. 
FIG. 8 shows that a plurality of contacts 71e and 72a to 72d can be used in 
place of single contact fingers. 
Although several preferred embodiments of the present invention have been 
described above in detail, many variations and modifications thereof will 
now be apparent to one skilled in the art. Accordingly, the scope of the 
present invention is to be limited not by the details of the above 
detailed description, but only by the terms of the appended claims.