US1748060A - Electric high-tension switching system and apparatus - Google Patents

Description

rll. fili G. A.,BURNHAM Filed Dec.vl3. 1927 2 Sheets-Sheet l ELECTRIC HIGH TENSION SWITCHING SYSTEM AND APPARATUS l l l Feb. 25, 1930.

Feb. 25, 1930. G, A, BURNHAM y 1,748,060

`:IIJEGTRIC HIGH TENSION SWITCHING SYSTEM AND APPARATUS Filed D90. 15. 192'? 2 Sheets-Sheet 2 Patented l Feb. 25, 1930 uNrrlsD STATES PATENT OFFICE GEORGE A. BURNHAM, F SAUGUS, MASSACHUSETTS, ASSIGNOR T0 CONDIT ELECTRI- CAL MANUFACTURING CORPORATION, OF SOUTH BOSTON, MASSACHUSETTS, A COR- PORATIOISIl OF MASSACHUSETTS ELECTRIC HIGH-TENSION SWITCHING- SYSTEM AND APPARATUS Application led December 13, 1927. Serial No. 239,790.

This invention relates to electric high tension switching systems and apparatus wherein the high tension buses, usually extended di rectly from the generators, are contained 1n 5 ducts and are extended immediately above or beside oil immersed switches which are con nected with the buses and also with branch lines which they control. When oil switches are opened under heavy .loads or under a short circuit, heated oil and flame are frequently expelled from the switch casings. If the heated vapor or flame comes in contact with the high tension buses it forms a sutilciently low conducting path between them tol cause a disastrous arc to form. Since the buses usually are directly connected with the generators without interposed overload circuit breakers therein there is no way of quenching the are and removing the short circuit from the buses. The arc can thereupon continue indefinitely and cause great damage to the station and cause a loss of service extending over many hours. As a consequence, the buses are usually enclosed in the aforesaid ducts to shield them from contact with conducting gases that may be expelled from the switches.

There are a number of types of bus enclosing systems. In one type, the duct in which the bus is contained is filled with oil which serves not only to shield the bus from contact with gases butalso to provide the insulation for the bus. With this system, however, the duct must be made and kept absolutely oil l tight, otherwise the oil will leak out and remove the insulation from the`bus so that a flash over will occur from the bus to the duct, which usuall is made of metal. Danger from fire, due to tlvxe ignition of the oil in the duct from aL possible flash over, is always present. When 'a flash over occurs large volumes of explosive gases and vapors and free carbon may e generated; andthese may explode and do great damage. e

In another type of .bus structure the oil is replaced by ain insulating compound .which is pouredinto the ductwhile hot and liquid and cools and solidiies about the bus and thus forms a hard and brittle insulating compound. Danger of leakage of the insulating conductingwalls of the duct.

valso removed therefrom,

compound is thus obviated but the fire hazard is not greatly reduced. Since the compound is brittle, it has a tendency to crack when subjected to strains and thus open up a path for a flash-over arc. The arc sets fire to the compound and it burns, with disastrous results.

In yet another system of bus structure, tl1e\ bus is contained within a duct which contains no especial insulating material,y and the duct is made suiiciently large inI cross section to prevent flash over between the bus and the With this type of structure, it has been found that hot gases discharged from the switch will be forced into the duct through seemingly minute crevices and channels between the walls thereof and cause the formation of an arc between the bus and the dpct. In some instances, it has'- been found that the interior walls of the duct andthe insulators on which the bus is mounted become coated with carbon expelled from the oil switch and that the carbon provided aconducting path which caused a flash over and I the failure of theswitching system.

` present invention to It is an object of the provide a switching system of the type above set forth with a bus structure yat the oil switches so arranged that gas expelled from the switch can not vcome in contact with the bus; and also so arranged that the troubles ,B0 and defects of the above enumerated present systems are absent. It is a further object of the invention to rovide an electrical switchi lng system and a us structure therefor wherein the bus is enclosed in an insulating body 85 that is not affected by arcs, will not burn or i give'oilt' gases, and is mobile so that it can conform itself to changes in shape or dimensions vof the bus and enclosing structures due to expansion, distortion and the like and o0 also so that it can be poured or otherwise placed readily inthe bus-enclosing duct and and, while being freely mobile, yet has such characteristics that only the material immediately at large openings in the duct will escape, while none i will escape through small openings. I

It is a further object of the 'invention to provide an electrical switching system composed of oil immersed electric switches and an .100

sion circuit. A. platen or carriage 14 is verf enclosed bus structure associated with the switches, with a loose, solid filler in the bus ducts which is composed of discrete, solid, electrically-insulating particles which surround and enclose the bus and prevent the gases discharged from the oil switches vfrom penetrating the filler sufficiently to come in contact with the bus and cause trouble.

It isa yet further object of the invention to provide an electrical vswitching apparatus wherein the buses are enclosed incompartments and'wherein the compartments contain sand. in which the buses are submerged.

A further object of the invention is generally to improve the construction and operation of high tension electric switching systems.

Fig. 1 is a front elevation of a switching system embodying the present invention.

Fig. 2 is a sectional view taken along line 2-2 of Fig. 1.

Fig. 3 is a sectional detail of the contact structure between the switch terminals Vand the bus terminals.

Fig. 4 is a perspective view of a bus duct embodying the invention.

Fig. 5 -1s a longitudinal sectional elevation through a bus duct embodying the invention.

Fig. 6 is a perspective detail showing a modied form of bus duct.

Fig. 7 is a sectional detail illustrating the manner in which the sand filler is retained in the duct about an opening therein.

Figs. 1 and 2 `illustrate my invention applied to a three phase switching apparatus. As shown in these figures, the ap aratus includes a frame having theJ base or door 10 and the -laterally-spaced vertical side walls 12 which form thr'ee cell enclosures a, b, c, respectively, for the three phases'of a high tentically movable between and is guided by the walls 12 of e'ach cell on a vertically screw threaded shaft 16 which' is operated by suit- Iable mechanism 18 from a control shaft 20 to raise and lower the carriage or platen. I An oil immersed electric switch 22 of any suitable type is received in an opening in each platen and is supported thereon by the feet 24., The platen can be raised to elevate the switch into an'operating. position as shown in Fig. 2 and it can also be lowered to lower the switch so thatit is supported byits .wheels 26 on the floor 10 of the cell and thus can be moved out of the cell and away from the platen for inspection or otherwise.

The terminals 28 of the switch extend vertically thereabove and are provided with vertical contact blades 30 for engagement with the bus terminals hereinafter to be described. insulating cups 32 surround said terminals and upstand thereabove and are intimately connected mechanically therewith and are'` adapted to contain oil in which the contact blades and also the terminals of the buses are adapted to be immersed, thereby to shield the live partsl of thecontact structurefrom access by the hot gases expelled from the' switch. The cups 32 are provided with depending annular iianges 34 which surround the upper ends of the insulators of/the switch l terminals for the same reason.

Brackets 36 are carried by and upstand i lshelves 38. The enclosing ducts or compartments can have any suitable construction but, as here shown, are formed of side and bottom walls 54 secured to longitudinally eX- tended corner angles V56. Each duct is provided with a cover 58 which is removable for access to the interior of the duct. No especial care is taken to make the ducts absolutely iuid tight. The ends of the ducts are provided with outstanding ianges 59 by which horizontally aligned ducts of adjacent switching systems can be attached thereto. The buses are mounted in the middle of the ducts on suitable insulators 60 which are carried by the bottom walls of the ducts. Each of the buses is provided with branch'leads 42a, 44a, and 46a which are extended through the middle of openings 62 in the front` :walls of theV ducts land into vertical branch ducts 48a, 50a, and 52a which are disposed in front of the main ducts and abovethe switches. The

branch ducts are constructed in the same manner as the main ducts and have removable top walls or` covers and openings' in their rear walls which register with the openings in the main ducts; and said openings are practically the full height of the main ducts. Insulating bushings 64 are extended through the bottom walls of the branch ducts, in the middle thereof, and have their upper ends connected with the branch busesand have spring pressed contactvjaws 6 6 at their lower ends which are adapted to be engaged by the contact blades 30 of the switch terminals thereby to connect the switches electrically with the buses. Small compartments or pot heads 68 which may be similarly constructed .to the bus ducts are located immediately underthe line 4of bus ducts and in the rear and in line with the branch ducts and above the rear switch terminals. Insulating bushings 70 are extended through the middle of the bottom walls of said potV heads and are. adapted to be connected iso electrically with the rear terminals of the switches.

Branch line cables 7 2 extend upwardly from the rear of the switching frame and have their lead sheaths secured in a fluid tight manner to the depending and rearwardly extended necks 69 of said pot heads while the insulated portion of the cable extends into the middle of the pot heads and is electrically connected to the upper ends of the bushings therein.

In accordance with this invention, the electric conductors are located in the middle of the ducts or enclosing compartments and the distance between the conductors and the side walls of the ducts which are made of metal is adapted to be sufliciently great to provide a suitably high factor of safety against flashover when the ducts are filled with air.

As above stated when the oil immersed switches open under severe overload or on short circuit, they sometimes expel into the surrounding atmosphere hot oil, vapors, gases, fume and flame which if allowed to come in contact with the high tension buses or conductors will cause a flash over between the buses and the casings and the enclosing ducts and thereby often cause Great damage and extended loss of service. onsequently, and in accordance with this invention, I ll the ducts with a loose, electricall reproof body 80 which complete y surrounds the ducts and provides an effective barrier against access of heated gases and conducting particles expelled from the switch thereto. Also, in accordance with this invention, the above 'described body is composed of sand which is the best material known to me at present. Sand has properties which are of particular value in connection with this invention. Sand is lreproof, and will not burn as oil does. The sand occupies the ducts as a loose body 80, and can be easily removed from the duct if it is desired to replace the bus with one of different current carrying section, or for other reasons. The sand can also be put into the ducts when the covers thereof are removed without any especial tools or without the exercise of any especial care exce t to see that the ducts are full. The branch ucts and pot heads are also filled with sand so that all bare high tension conductors are completely submerged in the sand. It is not necessary to exercise extreme diligence in sealing the ducts against small cracks or crevices as is the case with oil because the sand will not leak out of small crevices since it bridges them over and forms an arch which prevents the sand from falling out. Even though the crevices or openings are unduly large or a hole isburned in the bottom wall of a duct b some extraneous arc, the damage is slight fbr, because of the relatively steep angle of res ose of the sand, thesand on each side of t e opening,

as the opening 82 of Fig. 7, will assume the slope 84so that only the sand immediately above the opening will be lost while the remainder of the sandin the duet will remain in place. The sand is effective in. preventing hot gases from reaching the bus for the sand cools the gases as they flow therethrough so that they are cooled below a point at which they are deleteriously conducting before they have penetrated the sand body to any harmful distance. Furthermore, the sand body ol'ers great resistance to the flow of gas thereinto, and so also prevents access of gas to the bus. If oil or carbon is blown into the duct through small crevices or channels the oil and the carbon are entrapped in the voids between the small discrete particles of sand at the outermost surfaces of the sand body and so can not penetrate to the interior of the sand body. Sand is a good electrical insulator. It also provides mechanical support for the bus at all points along its length so that fewer insulating supports for the bus are needed and the bus is restrained by the sand from being forced out of its original position by strong magnetic forces acting lupon it as is often the case. Should an abnormally high potential be impressed upon the bus and an arc occur through the sand to the wall of the duct, no permanent damage lwill be done since the sand particles can move in to close any void formed by the arc; although experiments have failed to disclose the presence of an void. The sand also acts as a cooling medlum and tends to cool the arc and quench it so that the arc has a strong tendency to go out when the voltage of the bus is lowered. The presence of sand also prevents the formation of corona in the space between the bus and the duct at a value of potential4 that would cause corona in air. This is due to the greater dielectric capacity of the sand over that of air so that the electr'ostatic flux passes through the sand particles rather than in the a1r filled voids between them.

Preferably, the sand is a quartz sand and free from conducting particles, or metallic compounds, as an iron compound, although it appears that sand containing some amounts of iron oxide or other iron compounds usually found in sand gives satisfactory results. Sand taken; from many sources, and sand of various grades of iineness, beach sand and sand approximating in size line gravel, seem toperformvabout-equallywell. Preferably,the sand should be free from silt or decayed vegetable matter and foreign substances. The dimensions ofthe sand particles can vary within rather wide limits. I have found that sand particles j mm. in thickness give satisfactory results. Preferably, the sand should be of sufficient fineness so that corona in the air spaces between the sand particles is minimized. The character of the sand particles,

Vduct 88 and are held in place and insulated from each other and from the walls of the duct by insulating plates 90 through apertures in whiclrthe ducts are passed. 4The spacing between the buses, and between the buses and duct', is suliicient to prevent flash over in air, and theduct is-completely filled with sand in the manner described above.

1. A11 electric high tension switching system comprising the combination of oil im- ,mersed electric switches, high tension buses located inthe immediate vicinity of said oil immersed switches and connected therewith, enclosures containing said buses, and electrically insulating pulverulent mobile bodies of loose discrete, solid insulating iireproof particles contained in said enclosures about said buses, and constituting means to prevent access of a conducting gas to said buses.-

2. An electric high tension switching system comprising the combination of an oil immersed electric switch, a high tension conductor adjacent said oil immersed switch, an enclosure for said conductorfand an electrically insulating mobile body composed of loose discrete solid insulating fireproof particles contained in said enclosure and about and enclosing said conductor, and constituting means to prevent access of a conducting gas to said conductor.

3.. An electric high tension switching system c omprisingthe combination of an oil immersed electric switch, a high tension conductor adjacent said oil immersed switch,an enclosure for said conductor, and a body of loose sand'contained in said enclosure and by which said conductor is enclosed, and which constitutes means to shield said high tension conductor against access of a conducting gas thereto. c

4. An lectric high tension switching system comprising the combination of an oil immersed electric switch, ahigh tension conductor located within the zone of switch gases'that may be expelled from said oil immersed switch, and means to insulate said high tension conductor from contact with such gases and also to insulate said conductor electrically consisting of a thick mobile mass of small discrete solid insulating and heat resistant particles disposed about andin enclosing relation with said conductor at its extent in said gas zone.

5.l An electric high tension `switching system comprising the combination of an oil immersed electricswitch, 'a high tension bus located at said switch and havingV a branch connected with a terminal of saidoil immersed switch, a duct containing said bus having a branch containing said bus-branch, and a mobile insulating body contained in said duct and the branch thereof and enclosing said bus land its branch, and composed of loose discrete solid insulating particles, and constituting means to prevent access of a conducting gas to said bus and said branch.

6. An electric high tension switching system comprising the combination of an o1l` immersed electric switch, a high tension bus located'at saidswitch'andhaving a branch connected with a terminal of said oil immersed switch, a duct containing said bus having a branch containing said bus-branch, and an insulating body contained in said duct and the branch thereof and enclosing said bus and its branch, and composed of discrete solid insulating particles of sand, and constituting means to prevent access of a conducting gas to said bus and said branch.

7. An electric high tensiony switching system comprising the combination of a switch,

and .a high tension conductor, and a mobile, insulating,- inert, non-combustible body ot loose solid material enclosing said conductor,

and constituting meansl to prevent access ofv conducting gas to said high tension conductor.

8. In a high tension electric distribution system, the combination of an electrical apparatus capable of giving off electrically conducting gas and fume, a high tension lconductor associated with said apparatus, and a mobile body of loose particles of insulating, non-combustible solid material enclosing said conductor and isolatingit from said gas and fume.

9. The combination of electrical apparatus capable of "giving off electrically conducting gas and fume, a high tension'c'onductor associated with' said apparatus, insulatorsy supporting said conductor, an enclosure for said conductor and insulators, and a mobile body of insulating, non-combustible solid material contained in said enclosure about said conductor and insulators and enclosing both against said gas and fume..

10. The combination of an electric conductor operated at such elevated potential that when the conductor is within the inliuence of an electrically conducting gas a current arc passes through the gas from the conductor to a lower potential part, and means to maintain said conductor out of the influence of such conducting as consisting of an enclosing envelope there or composed largely of vdiscrete particles of loosely compacted insulating and fireprooil material which is' capablewof lowing,.whereby to occupy voids ,.that may occur, within the In testimony whereof, I havesigned my name to this specification.

GEORGE A. BURNHAM.

e combination of a high tension con-

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