US2275215A - Expansion chamber for bushing insulators - Google Patents

Description

March 3, 1942. T F, BRANDT E -l-AL 2,275,215

EXPANSION CHAMBER FOR BUSHING INSULATORS Filed March l5, 1939 2 Sheets-Sheet l 59 6 /Z 'rf' 40 L1 55 'l 1' vz-:Tl:

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T. F. BRANDT ET AL EXPANSION CHAMBER FOR BUSHING INSULATORS Filed March l5, 1939 Z'Sheets-Sheet 2 Patented Mar. 3, 1942 UNITED STATES PATENT OFFICE EXPANSION CHABIBER FOR BUSHING INSULATORS of New Jersey Application March 15, 1939, Serial No. 261,980

4 Claims.

This invention relates to insulators for electric conductors, and particularly to expansion chambers for high voltage, liquid filled bushing insulators. Many high voltage insulator bushings are lled with insulating liquid such as transil oil which has a rather high coeicient of expansion for temperature changes. Heretofore it has been usual to provide a connection between the interior of the bushing and the outer atmosphere by which a breathing action takes place to compensate for the expansion and contraction of the filling liquid. This breathing action produces a circulation of air to and from the chamber containing the insulating liquid, and this circulation of air is apt to carry moisture into the chamber. In time a suflicient amount of this moisture may be taken up by the insulating liquid to cause a deterioration in its dielectric properties. Various devices and schemes have heretofore been employed for restricting the breathing action of oil filled housings and for dehydrating the air admitted to the housings, but the present invention avoids all necessity for such expedients by completely sealing the expansion chamber from communication with the outer atmosphere.

The principal object of the invention is to prevent contamination of the dielectric liquid in the bushing by preventing contact between the liquid and the outer atmosphere.

A further object of the invention is to provide an expansion chamber which will permit expansion and contraction of the filling liquid without any breathing action between the interior of the bushing and the atmosphere.

A further object of the invention is to provide a completely sealed expansion chamber for bushing insulators in which the surface level of the liquid may be readily apparent from the outside of the chamber.

A further object of the invention is to provide an expansion chamber which is readily adapted to power factor measurements to ascertain the condition of the insulation.

A further object of the invention is to provide a device of the class named which shall be of improved construction and operation.

Other objects and advantages will appear from the following description.

The invention is exemplified by the combination and arrangement of parts shown in the accompanying drawings and described in the following specification, and it is more particularly pointed out in the appended claims.

In the drawings:

Fig. 1 is a fragmentary elevation with parts in section illustrating one embodiment of the present invention.

Fig. 2 is a fragmentary elevation partly in section looking from the right in Fig. 1.

Fig. 3 is a part elevation and part section of a modified form of the invention.

Referring first to the form of the invention shown in Figs. 1 and 2, the numeral I0 designates the upper portion of a bushing insulator of conventional construction, the insulator being one which is sealed at its lower end to prevent escape of the filling liquid. The insulator may be similar to that shown in Patent No. 2,082,046 granted January 1, 1937, to Thomas F. Brandt and assigned to The Ohio Brass Company of Manseld, Ohio. The parts of the insulator are held together and to the supporting flange by which the insulator is mounted on the apparatus housing by means of a tubular stress member I I having a collar I2 threaded upon its upper end and bearing on a ring I3 which rests on a helical spring I4. The lower end of the spring I4 is supported by a ring I5 which bears upon the inside of the bottom of an expansion chamber I6 and presses the bottom of the expansion chamber upon a gasket I1 resting on the top of the dielectric member I0. The stress member II extends loosely through an opening I8 in the bottom of the expansion chamber I6 which provides communication between the interior of the bushing I0 and the interior of the expansion chamber I 6. Insulating liquid I 9 completely fills the bushing I0 and partially lls the expansion chamber I6. The upper portion 20 of the expansion chamber I6 is filled with dry air or an inert gas which will not affect the dielectric properties of the insulating liquid I9. The space 2D is sealed against communication with the atmosphere by a corrugated ring or bellows 2| which is soldered or otherwise sealed to a flange 22 secured to the upper portion of thechamber I6. The lower end of the bellows 2I is soldered to a collary 23. The joints between the parts I6, 22, 2I and 23 are all-gas tight joints. An insulating packing 24 is interposed between the collar 23 and the upper end of the tube II to provide a gas tight joint between the tube and the collar 23 so that gas cannot escape from the chamber 2l). The packing may be a synthetic rubber material which should be unaffected by the liquid filler I9. The collar 23 is threaded onto an insulating ring 25 which may be made of a phenolic condensation product or other suitable material. The ring 25 is threaded onto the collar I2 so that the packing 24 may be compressed between the collars I2 and 23 to form a tight joint with the stress member II. A conductor 26 extends through the stress member II to the interior of the apparatus housing with which the bushing is connected. The upper end of the conductor 26 is provided with a terminal member 21 which rests upon a cover plate 28 on the top of the expansion chamber I6. Packing 29 isprovided to form a gas tight joint between the terminal member 21 and the cover 28 so that the cover 28 and terminal member 21 form a gas tight closure for the space communicating with the upper end of the stress member II. This is desirable for the reason that the member II communicates with the interior of the apparatus housing and it may be desirable to prevent breathing through the bushing into this housing. Gaskets 30 and 3I insulate the terminal member 21 and conductor 26 from the cover plate 28. However, a spring clip 32 normally bridges the insulation 30 and connects the terminal 21 with the expansion chamber I6 so that in normal operation these two members will be at the same potential and there will be no danger of arcing between the conductor and the expansion chamber I6. A bypass 33 is provided between the chamber 20 and the space within the expansion chamber communicating with the upper end of the tube II. This by-pass is normally closed by a plug 34 so that the space within the bushing is entirely separated from the space within the apparatus housing. However, in cases where it is desirable to provide communication between these spaces, it is only necessary to remove the plug 34 so that free breathing is permitted between the interior of the bushing and the space within the apparatus housing without communication with the out-er atmosphere. When the by-pass 33 is closed by a plug 34, sufcient room must be provided in the space 20 to accommodate the maximum expansion and contraction of the liquid I9 without producing undue diierence of pressure between the space in the expansion chamber and the outer atmosphere. Relative movement between the upper end of the tension member Il and the expansion chamber I6 is permitted by the flexibility of the corrugated bellows 2| The surface level of the liquid I9 is indicated by means of a float 35 supported on the surface of the liquid I9 and connected with a shaft 36 which communicates through a magnetic connection with an indicator 31 on the outside of the expansion chamber. Any well known form of magnetic gauge actuated by the float -35 may be used for this indication.

As shown in Fig. 2 the chamber I6 is provided with a lling tube 31 having its lower end extending into the expansion chamber a sufhcient distance sc that when liquid is poured in through the tube, a suincient quantity of gas'or air will be trapped in the upper end of the expansion chamber to provide for expansion of the liquid within the bushing. r'his filling tube will prevent the attendant from lling the entire expansion chamber with liquid as it automatically traps a quantity of gas or air, whichever is present, in the upper portion of the chamber. The filling tube is closed by a plug 38.

lt is customary in modern practice to check, periodically, the condition of electrical apparatus by measuring the power factor of the apparatus in question. This is done with alternating current by measuring the dielectric loss in terms of watts loss or power factor in a circuit including the insulation of the particular apparatus being tested. In making such a check on a bushing insulator, the measuring current is passed through the insulation between the conductor and the grounded support for the insulator. In such a test it is, 0f course, desirable that leakage currents through connected apparatus, as for instance the apparatus housing, shall be excluded from the measuring instruments. In the form of the invention shown in Fig. 1, one electrode of the test circuit may be connected to the expansion chamber I6 as by means of a spring clip which may be attached tothe cap screws of the chamber or to any other convenient projection and the other electrode s connected to the grounded ange. The test current will pass through the expansion chamber to the ring I5 and through the spring I4 to the collar I2 and thence to the tension member II. The circuit is completed from the tension mem- -er I I through the bushing insulation to the grounded iiange. If the insulation is not in good condition, the leakage through the insulation will be indicated by the watts loss or power factor of the circuit. During this test the clip 32 is insulated from the terminal member 21 by slipping a small piece of insulation between the clip and its point of contact with the terminal member 21. If .this separation were not made, there would be a parallel circuit through the conductor 26 and connected apparatus to ground, which consequently would riot give a true indication of the condition of the bushing. To prevent any danger of leakage between the expansion chamber I6 and the conductor '26, the terminal 21 may be connected to the same voltage source as the expansion chamber IE, but through an entirely separate circuit. This will give the conductor 2B and the expansion chamber I6 approximately the same voltage so that there is a minimum of leakage over or through the insulation between them. To insure separation of the test circuit from the conductor 26, an insulating tube 39 is placed within the stress member II around the exposed portion of the conductor 26. The main body or the conductor 26 is covered with insulation 43, but the upper end is exposed where lt is soldered to a terminal member 4I on which the terminal electrode 21 is threaded.

In some cases it may be desirable to connect the lead from the apparatus to the lower end of the bushing instead of drawing it up through the stress member II and connecting it directly to the terminal 21. In that case the lower end of the stress tube II is connected to the lead from the apparatus and the current, then passes through the body of the expansion chamber to the terminal electrode 21. When this arrangement is made, a part of the current would pass through the expansion bellows 2| if this bellows were not insulated from the stress member II by the insulation 25. Without insulation 25 sufcient current might pass through the bellows 2I to loosen the soldered connections or overheat the bellows.

In the form of the invention shown in Fig. 3 the stress member 45, instead of terminating inside the expansion chamber 46, extends through the top of the chamber and is provided with a short length of thread near its upper end on which is threaded a sleeve 41. A collar 48 is threaded on the stress member 45 and rests on ring 49 supported by the helical spring I4. The collar 48 and ring 49 have spherical contact surfaces so that the ring 49 may adjust itself relative to the collar 48 to compensate for any inequality of pressure produced by the spring I4.

When the ends of a helical spring terminate in a plane normal to the axis of the helix, the end portion of the spring rod will, of course, be tapered where the terminal plane intercepts the rod. This may result; in a greater pressure at one side of the spring than at the other, when the spring is compressed and unless arrangement is provided to compensate for this difference in pressure, a couple is produced on the collar 48 tending to cock the collar, and consequently shift the stress member 45 toward one side or the other. Where a spherical bearing surface is provided as shown in the drawing, between the collar 48 and ring 49, the unequal pressure, instead of cooking the collar 48 will merely shift the ring 49 to one side or the other until the inequality in pressure is overcome. A cover 50 is secured t the top of the expansion chamber 46 by cap screws I and the space between the cover 5G and the stress member 45 is sealed by a bellows 52 soldered to a ring 53 which rests on a ring 54 threaded onto the stress member 45. The ring 53 is preferably provided with one or more` teeth 55 which interlock with notches in the upper end of the ring 54 to prevent relative movement of these parts when they are in place. Packing 56 is interposed between beveled surfaces on the members 41, 53 so that when the member 41 is screwed down tight against the member 53, the packing 56 will provide a, tight seal for the opening in the upper portion of the expansion chamber through which the tension member 45 extends. The sleeve 41 is locked in place by a set screw 51 which bears upon a body 55 of soft metal such as lead and presses the metal into the threads in the tension member 45. An insert 59 is threaded into the upper end of the tension member 45 and is provided with a hexagonal opening into which a hexagonal portion of the conductor 6| is drawn and held by a nut 62. A terminal electrode 63 is threaded on the upper end of the conductor 6| and bears upon a packing 64 which forms a, tight Closure for the space about the upper end of the tension member 45. The inner portion of the tension member 45 about the upper end of the conductor 6| is lined with an insulating sleeve 65. When it is desired to make a power factor test of the bushing shown in this form of the invention, the terminal electrode 63 and the nut 62 are removed and the conductor 6| is lowered into the interior of the stress member 45 until all of the exposed portions of the conductor are enclosed within the insulating lining 65 so that there is no danger of contact between the conductor and the stress member 45. The power loss between the stress member 45 and the ground sleeve is then measured in the usual way to determine the power factor of the bushing. The. expansion chamber 46 is provided with magnetic gauge 66 by means of which the height of the liquid within the expansion chamber may be ascertained from the outside of the chamber.

We claim:

1. The combination with a bushing insulator having an expansion chamber mounted on the upper end thereof, a tension member extending through said insulator and into said expansion chamber, a spring for holding said expansion chamber against the end of said bushing insulator, a stop surrounding said tension member and secured thereto and bearing on said spring at one end thereof, the other end of said stop being inwardly beveled to form a packing groove surrounding said tension member, a flexible seal attached to the wall of said expansion chamber for closing said chamber, a collar surrounding said tension member and having fluid type connection with said seal and having a beveled face registering with said packing groove and packing in said packing groove and engaged by the beveled face of said collar to form a tight joint between said seal and said tension member.

2. The combination with a bushing insulator, of a stress member extending through said insulator, a helical spring surrounding said stress member at one end of said insulator, a stop on said stress member, and means forming a spherical seat between said spring and said stop, said seat forming means and said spring being laterally shiftable relative to said stress member to permit automatic adjustment of said stop on said seat forming means.

3. The combination with a bushing insulator, of a stress member extending through said insulator, an expansion chamber at one end of said insulator, a helical spring surrounding said stress member and holding said expansion chamber in engagement with said insulator, a stop threaded on said stress member, and a laterally shiftable ring surrounding said stress member and resting on said spring and engaging said stop, said ring having a, concave seat for engaging said stop and said stop having a convex surface resting in said seat to permit relative movement of said ring and stop to compensate forinequalities in the pressure exerted by said spring.

4. The combination with a bushing insulator having an expansion chamber mounted on the upper end thereof; a tension member extending through said insulator and into said expansion chamber; a spring for holding said expansion chamber against the end of said bushing insulator; a stop surrounding said tension member and secured thereto and bearing on said spring at one end thereof, the other end of said stop being inwardly beveled to form a packing groove surrounding said tension member; a iiexible seal attached to the wall of said expansion chamber for closing said chamber; a collar surrounding said tension member and having fluid tight connection with said seal and having a beveled face registering with said packing groove; packing in said packing groove and engaged by the beveled face of said collar to form a tight joint between said seal and said tension member; a ller pipe extending into said chamber and secured in the wall thereof; an insulating oil in said chamber which has been admitted thereto through said pipe, said pipe preventing the excessive filling of said chamber with oil by entrapping a quantity of gaseous material in the upper end of said chamber between the surface of said oil and said seals, said gaseous material permitting said oil to expand; and a plug in the upper end of said filler pipe.

THOMAS F. BRANDT. HAROLD L, BROUSE.

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