High Voltage Cable System With Factory Installed Potheads And Method Of Installing Same

Abstract

The high-voltage cable system and its preattached potheads facilitate installation of cable in underground work. The method of installation using the improved cable package of this invention permits rapid installation without the necessity of expensive field splicing of the cable to the pothead. Pressure accumulators located within the potheads maintain a positive pressure in the cable system to avoid contamination of the insulating oil. A unique oil submerged, ultrashort pothead and automatic oil purifier form another feature of the system.

Description

This invention relates to a high-voltage cable system, a method of preassembling the cable used in the system, and a method of installing the cable at the desired location. More particularly, the invention relates to a unique oil filled high-voltage cable with factory installed potheads to reduce, so far as is possible, the present high labor cost for field splicing. In addition, the invention relates to a unique method of installing both the cable system of this invention as well as other high-voltage cables.

In recent years, the trend in the power industry has been toward cable systems capable of carrying current in high-voltage ranges. The reason for transmitting power at high voltage is that losses are substantially reduced for a particular size and length of cable when the voltage is very high, since the current will then be lower for the same transmitted power.

At present, both underground and aboveground transmission systems are used to transmit electrical power from the generating station to the consumer. Because of their lower cost, aboveground systems are used whenever there is available space for the supporting towers for the cables of the system. However, in urban areas property costs are too high to justify aboveground installation, and in addition, high-voltage aboveground cables present an extreme hazard in highly populated areas and are usually prohibited by local regulations in such areas. Therefore, it was customary, in the past, to use aboveground systems to transmit power to an area adjacent a highly populated area, and then connect the aboveground system to an underground system which feeds the power to transformed stations where the voltage is stepped down considerably for local distribution. However, the trend today is to use underground cable systems wherever possible because of the unsightly appearance of aboveground systems.

Studies show that the costs of high-voltage underground systems are many times higher than aboveground systems of the same length and current carrying capacity. At least a portion of this increased cost for underground systems is attributable to the trenching and shielding of the underground cable. In addition, cooling underground cable and providing for heat dissipation also increase costs over aboveground cable systems which are usually convection cooled. However, a large portion of the present high cost of underground cable systems stems from the need to field splice these cables at high labor costs to attach potheads as well as to join the ends of cables where a single cable of sufficient length to complete the installation is not available. Problems of splicing are especially complicated where the cable is of the oil-filled type since the splicing is presently done in the field where factory splicing equipment is not available. This is especially true where the cable is of the aluminum-sheathed type, since aluminum is difficult to weld even where the best factory equipment is available.

While underground cables of various types are presently used, some having the more recently developed resinous extruded insulations, cooling and heat dissipation problems are present with underground systems. Because of the high voltage carrying capability of oil-filled cable, the oil-filled cable is frequently used. The oil provides better insulation than any "dry" cable, and in addition, the oil provides for better heat dissipation by circulating inside the cable, and therefore reduces "hot spots."

At present, high-voltage cables of the oil-filled type are assembled by the manufacturer who also fills the cable with oil and then seals the ends. Advantageously, the oil is maintained under a slight positive pressure to exclude moisture and air which can contaminate the oil and reduce its insulating properties. These cables are presently wound on large reels to facilitate shipping to the installation site. Usually, a cable of a length long enough to complete the installation is shipped on a single reel. At the installation site, a trench is dug and the cable is laid underground. With high-voltage cables, however, it is necessary that a pothead be connected to the end of the cable at a termination where the cable connects to other transmission apparatus, such as a transformer. Attaching the pothead is presently done in the field either before or after the cable is laid, depending on the number of obstructions, such as pipes and other cables which extend transversely to the one being laid and under which the cable being laid must be pulled.

Frequently, local ordinances prohibit an open trench more than several hundred feet in length. Since only one end of the cable is free with existing reels, it is customary practice, where there are such local ordinances, to connect the pothead in the field to one end of the cable, lay the first several hundred feet of the cable, and then close the trench before proceeding with the next several hundred feet of trench. When an obstruction is encountered after the first run of trench is closed, it is necessary to completely unreel the entire cable so that a free end is available which can be pulled under the obstruction, and then it is necessary to wind the excess cable back onto the reel at the end of the second run of trench. Thus, where a cable of several thousand feet is to be laid under ground, substantial time and expense is involved merely in reeling and unreeling the cable to fine a free end when an obstruction is encountered. In addition, it is presently customary to install pipe under thoroughfares by boring under the thoroughfare from one side to the other so traffic will not be interrupted when the cable is laid, as would be the case where a trench is dug, and then, it is necessary to uncoil and recoil the cable so a free end is available to pull under the thoroughfare. If short cables are used, the nuisance of uncoiling and recoiling the cable is not present. However, field splicing the cable ends, using the usual potheads is so costly that short lengths of cable are seldom used.

Another substantial expense of existing underground cable systems is the care which must be taken in the field to avoid contamination of the oil within the cable when the pothead is connected and when splices are made. A well-known technique to prevent contamination of the oil is to maintain a positive pressure within the cable. However, where a field splice is required, this positive pressure is indeed a hindrance since strong welds and soldered connections are quite difficult to obtain where the oil films are present on the surfaces to be joined. An additional expense of existing cable systems is the high cost of reservoirs which must be installed at the potheads to compensate for changes in volume of the oil in the cable and potheads due to temperature expansion and contraction of the oil resulting from varying loads carried by the cable system.

Applicant's unique oil-filled cable system and its method of installation eliminates many of the shortcomings and disadvantages of the prior known cable systems and the methods of installing these prior systems. Applicant's cable system comprises a length of oil filled cable having a factory installed pothead at each end. Both the potheads and the cable are filled with oil and the oil is maintained under positive pressure by pressure cells located within the potheads. Thus, there is no need for any field splicing of applicant's cable at the installation site as is customarily done with presently available cable. Thus, it is merely necessary to transport the cable to the site, form the necessary trench, and bury the cable. Where connections are required, between the pothead, for example, at one end of the cable and a pothead at a transformer to which the cable is connected, such connections are relatively simple compared to the extensive field splicing required to connect an oil-filled cable to a pothead.

Another unique feature of applicant's invention is the manner in which the cable with the potheads connected to the cable is coiled and packaged for shipment to the installation site. In accordance with the invention, a package is provided with a first end section for one of the potheads, a central annular section where the cable is coiled, and a second end section which accommodates the other pothead. A guide nozzle facilitates feeding the cable axially of the drum or annular space in which the cable is coiled. A unique feature of this cable package is that the cable can be uncoiled as well as coiled from either end of the drum. Thus, when an obstruction is encountered while laying the cable, it is not necessary to completely unwind or remove the entire length of cable from its package to obtain a free end. Instead, cable is fed from the opposite end of the package under the obstruction. Even when it is necessary to recoil the cable where a long single length of cable is installed, a free end is always available to be pulled under obstructions. The guide nozzle is reversible and can be connected to either end of the package.

Since a pothead includes an insulator which is usually formed from porcelain or other somewhat fragile material, it is desirable to shield the pothead as it is pulled under obstructions when the cable is laid. Applicant's invention includes an advantageous embodiment of a shield which also includes a connector by which the pothead and cable can be pulled through a trench under obstructions. To further reduce the costs of field installation, this pothead shield may be connected to the pothead at the factory to also protect the pothead against damage during shipment.

Other advantages and features of this invention include a unique manner of joining cables with potheads preattached that completely avoids any field splicing and, in addition, completely prevents any possibility of contamination of the oil in the cable when forming the electrical connection between the potheads. A further feature of applicant's invention is an improved short length pothead capable of carrying substantially higher voltages without danger of breakover than existing potheads of like size and cost.

Correspondingly, an object of this invention is a preassembled oil-filled cable which includes a factory connected pothead to at least one end of the cable.

Another object is a unique cable system of the oil-filled type with pressure cells within the base of the pothead to maintain a positive pressure on the oil at all times and to cause the oil to completely fill the communicating spaces of the pothead and cable.

Another object is a cable system of the type described in which the pressure cells are mounted in the pothead in a unique manner.

A further object is a unique method of packaging and installing oil-filled cable with potheads preattached in accordance with applicant's cable system.

A further object is an improved package for cable with preattached potheads, the package providing a chamber for at least one pothead and also permitting feeding the cable from either end of the package to facilitate pulling the cable under obstructions encountered while laying the cable.

Another object is a cable system of the oil-filled type which includes a pothead preconnected to at least one end of the cable and in which an improved shield is applied to the pothead to facilitate both pulling the pothead under obstructions encountered and to prevent damage to the pothead during shipping and installation of the cable system.

A further object is a unique cable system of the oil-filled type with preattached potheads which facilitate making connections between the potheads of adjacent cables without any danger whatever of contaminating the oil or other pressure fluid within the cable.

Numerous other objects, features and advantages of applicant's invention will become apparent with reference to the drawings which form a part of this specification and wherein:

FIG. 1 is a view in perspective, with portions cut away for purposes of illustration, of a package for coiled oil-filled cable with potheads preconnected to the ends of the cable;

FIG. 2 is an enlarged sectional view taken along lines 2--2 of FIG. 1;

FIG. 2A is a sectional view taken along lines 2A--2A of FIG. 2 and showing the guide nozzle mounted on the cable drum and the cable partially withdrawn form the drum;

FIG. 3 is a longitudinal sectional view of a pothead showing its connection to an end of the cable;

FIG. 4 is a sectional view taken along lines 4--4 of FIG. 3;

FIG. 5 is a sectional view of the cable container of FIG. 1 resting on its side to permit pulling a cable from the opposite end of the container, and further showing a pulling shield secured to the pothead;

FIG. 6 is a partial view in section taken along lines 6--6 of FIG. 5;

FIG. 7 is an enlarged view in section taken along lines 7--7 of FIG. 5;

FIG. 8 is a schematic view showing the manner in which a cable with a preattached pothead is pulled under an obstruction, the pothead being shielded;

FIG. 9 is a view corresponding to FIG. 8 and showing pulling of a cable from the opposite end of the container after a length of the cable has been laid and an obstruction is encountered;

FIG. 10 is a sectional view of a unique connection between potheads of adjacent cables;

FIG. 11 is a sectional view of the connection of a cable pothead to a transformer;

FIG. 12 is a circuit diagram of an oil contamination detector; and

FIG. 13 is an elevational view of a unique ultrashort high-voltage pothead.

Referring now to the drawings in detail and particularly to FIGS. 1-4, there is shown the unique cable system of this invention and a package for the cable. As shown at FIG. 3, cable 1 is of the type having a stranded hollow core or conductor 2 with a central opening 3 therethrough. Surrounding conductor 2 is insulation 4 which advantageously is a porous oil impregnated insulation such as is known in the industry as the paper type, or may advantageously be a foamed porous plastic material which is oil impregnated. Surrounding insulation 4 is a metal shield or sheath 5 which may be a tube of aluminum or lead, aluminum being preferred because of its light weight, high-tensile strength, and low cost. For alternating current transmission, sheath 5 can also be any other nonmagnetic electrically conducting material. Surrounding sheath 5 is an outer jacket of tubular insulation 6.

In accordance with this invention, potheads 7 and 8, FIGS. 1, 2, and 2A, are advantageously connected to cable 1 after the cable is coiled in the package 10, but before the cable is transported to the installation site. Package 10 takes the form of a container or crate 11 with a square bottom 12 and four sides 13-16 which extend upwardly from and to which bottom 12 is removably connected by bolts 17. Sides 13-16 are secured by bolts 18. Thus, side 13 may be removed from the package, when necessary, for a purpose which will subsequently be explained in detail.

As shown at FIG. 2, a multipart drum 19 of a diameter somewhat smaller than the distance between the sidewalls, extends the height of container 11 and is centered in the container. Drum 19 is hollow and is comprised of three cylindrical shells 20-22. As shown at FIG. 2, shells 20-22 are each of the same diameter and are stacked one on the other to form the drum. Several connector plates 23, circumferentially spaced apart extend between and are bolted respectively to the interior of shells 21 and 22 to hold the shells together, yet permit separating them when desired by removing the bolts 24. Similarly, shells 20 and 21 are removably secured together by several spaced-apart connector plates 25 held with bolts 26.

Platforms 27 and 28 extend outwardly, from adjacent the opposite ends of shell 21 to the sides of the container. Platform 27 is coplanar with the joint between shells 20 and 21, whereas platform 28 is coplanar with the joint between shells 21 and 22. Platform 27 is removably held in the position of FIG. 2 by bolts which extend through angle brackets 30 secured to the platform. The bolts and angle brackets secure the platform to the sides 13-16 of the container as well as to the drum 19. Similarly, platform 28 is removably secured in the position of FIG. 2 by bolts passing through angle brackets 32 secured to the bottom of platform 28. Platform 28 is also secured to drum 19 by similar bolts and angle brackets. The platforms 28 and 29 divide the space between drum 19 and sides 13-16 into three compartments 33-35.

The upper end of the container 11, when in the position of FIG. 1 and 2, is closed by a cover 36. The cover 36 is a combined cover and guide to facilitate withdrawing cable 1 from its compartment 34. Thus, the cover 36 has a centrally located nozzle or guide 37 with smoothly rounded sides 38. The flat portion 39 of cover 36 radially outwardly of nozzle 37 extends across the upper end of compartment 33 to close the compartment when the cover is in the position of FIG. 2. Cover 36 is vertically split into two halves 40 and 41. Thus, when cover 36 is removed, the halves 40 and 41 are separated from each other and can then be closed over cable 1 after pothead 8 has been lifted out of container 11 so cable 1 extends through nozzle 37. This procedure, which is followed during laying of the cable, will subsequently be described in detail.

A significant advantage of applicant's cable assembly and packaging system is that it substantially reduces both handling and labor costs, and virtually eliminates field splicing of the cable.

In the use of container 11, the container is forwarded to the manufacturer of cable, who coils the cable in the container as shown at FIG. 2. Preferably, the cable is coiled into the container with the container in the position of FIG. 2 and with platform 28 in place. The cable is coiled spirally from outside in along its bottom layer 42. Thus, convolution 43 is first coiled, and then convolution 44 is coiled. The remaining convolutions are coiled until layer 42 is complete. The next layer, layer 45 is coiled from inside out, then the next layer from outside in, and this procedure is repeated for successive layers of the cable until top layer 46 is completed. Advantageously, an opening 47 (FIG. 2A) is provided in platform 28 to permit an end portion of the cable to be threaded through the opening so it extends into compartment 35. A similar opening (not shown) is provided in platform 27 to permit the other end of cable 1 to be threaded through that opening so it is in compartment 33. Advantageously, a sufficient length of each end of cable 1 is placed respectively, in compartments 33 and 35, to permit attaching potheads 7 and 8 without disturbing the coiled cable.

For the manufacturer of the cable to package same in container 11, it is merely necessary to remove cover 36, platform 27, and upper shell 20 of drum 19. Then, the end of the cable is threaded through opening 47 (FIG. 2A) of platform 28 and may also be fed through opening 48 of sidewall 16, so the lower end of the cable is accessible, opening 48 being normally closed with a cover plate 49. Then, the cable is coiled in the manner described and when the desired amount of cable has been coiled into compartment 34, the end of the cable is fed through the opening in platform 27 so that this end is in compartment 33.

With container 11, the manufacturer of the cable has the option of purging and filling the cable with oil or other insulating fluid either before or after the cable is coiled in the container. The fluid used completely fills the spaces inside sheath 5 including opening 3 of conductor 2. When oil is used as the fluid, the oil impregnates insulation 4. Such purging is accomplished by drawing a vacuum on the cable, and then filling the cable with oil or other fluid. The purging may also be done by forcing an inert gas through the cable to displace oxygen and moisture and then filling the cable with the desired fluid. If the purging and oil filling is done before the cable is coiled, the manufacturer merely seals the ends of the cable and coils the cable into the container as described, with end portions of the cable extending respectively into compartments 33 and 35 so these ends will later be available to permit installing potheads 7 and 8 while the cable is in the container, so unpacking the cable is not necessary. If the manufacturer prefers to purge and fill the cable with fluid after it is coiled in the container, the free end of the cable available through opening 48 of sidewall 11, and the free end available in compartment 33 before cover 36 is attached to the container permit connecting the necessary purging and fluid filling equipment to fill the cable with the insulating medium after the cable is coiled into the container. After the purging operation is completed, the ends of the cable are sealed in the customary manner, and drum shell 20 and cover 36 are bolted in position. If necessary, a reservoir containing fluid of the type in the cable can be connected to one of the cable ends. The reservoir will include an accumulator to maintain a positive pressure on the fluid, and thus compensates for changes in volume of the fluid due to temperature changes. Hence, the cable will not be subjected to either excessive inside pressure or vacuum during shipping as a result of abnormal ambient temperatures. Then, the container can be transported to another factory where potheads 7 and 8 are attached to the cable in a manner which will now be described in detail.

To attach the potheads 7 and 8 to the cable in container 11, the container is first turned up so it rests on one of sides 13-16. Next, cover 36 and bottom 12 are removed whereupon compartments 33 and 35 are open and access is obtained to the ends of the cable threaded through the openings in platforms 27 and 28.

While only pothead 7 is shown in detail at FIGS. 3 and 4, it is to be understood that pothead 8 is identical to pothead 7 and that the installation procedure is the same for both potheads. The first step in connecting pothead 7 to end 50 of cable 1 is to strip several feet of both jacket 6 and sheath 5 from the end of the cable. As shown at FIG. 3, the sheath 5 extends a short distance beyond insulating jacket 6. Paper insulation 4 is removed from the end of conductor 2.

As shown at FIGS. 3 and 4, pothead 7 includes an elongated, thin walled, hollow cylindrical base 60, a porcelain insulator 61, and a mounting plate assembly 62 via which the porcelain insulator is secured to the base and which is used to support the pothead. Base 60 has an outwardly extending flange 63 at one end which has openings to receive bolts to secure the base to flat connector plate 62'. At its other end, base 60 has a frustoconical end wall 64 with a central opening 65 to receive end 50 of cable 1. Spaced from end wall 64, at a location approximately one-third the distance from end wall 64 to flange 63, is a second outwardly extending flange 66 with circumferentially spaced bolt receiving openings formed therein. Flange 66 is secured to base 60 by welding. Located within base 60 are a plurality of accumulator cell assemblies 67. Each cell assembly includes a plurality of thin wall air-filled cells 68-70. Each cell is generally flat and has a circular outline. Cells 68-70 are each formed from relatively thin stainless steel, which is nonmagnetic and has high strength characteristics. The cells can also be of flexible nonmetallic oil resistant material such as polyvinyl chloride. The cells act as accumulators to maintain a positive pressure within the pothead and cable system. When cable sheath 5 is of aluminum, the pressure of oil in the cable may be 20-100 p.s.i. If lead sheath is used, the lead sheath must be reinforced, and stop joints must be used. The number of and size of the cells used with a particular cable system depends on the volume of oil in the system. Advantageously, the cells are so selected that a positive pressure is maintained within the cable system for any expected temperature to which the system is subjected. Thus, it is merely necessary to provide in the pothead, the desired cells for use with a particular cable system.

The cells are secured to the inside surface of cylindrical base 60. The supporting means for the cells include a plurality of spaced apart support rods 71 which extend inwardly from the inside surface of base 60 and are secured to the base as by welding. Each cell is connected to a rod at the edge of the cell, preferably by welding as at 72. Weld 72 may be a spot weld since the cells are relatively light even when they are of large diameter, for example, 10 to 15 inches, and hence, require only minimum support.

Insulator 61 is formed from porcelain and has the usual flat top and bottom ends 73 and 74, respectively. Extending around bottom end 74 is a metal connector bushing or base ring 75 which is cemented to the insulator with an epoxy cement 76. Connector bushing 75 has openings to receive bolts which extend through connector plate 62'. End 74 is sealed to connector plate 62' by a sealing gasket 77, a gasket 78 is also placed between the transverse face of connector bushing 75 and connector flange 62 where bolts 79 extend through the connector flange, to prevent leakage along the bolts.

End 73 of insulator 61 is provided with a connector bushing or ring 80 similar to bushing 75. Connector bushing 80 is also advantageously cemented to insulator 61. Secured to the connector bushing with bolts 82 is a closure plate 81. A gasket 82' between plate 81 and end 73 of the insulator prevents leakage between the plate and insulator 61.

At the upper end of pothead 7 is a combined connector valve assembly 83 which can be operated to close the port. Communicating with port 84 are a plurality of transverse ports 84' which communicate with the space within pothead 7 and base 60. Ports 84' are formed in a bushing 86 which has external threads 88 and is threaded into an internally threaded end plate 89. Plate 89 is sealed to plate 81 by a gasket 90. At the terminal stud end of valve assembly 83 is an internally threaded opening 91, which is provided to receive a pipe or other fluid passing connector for a purpose that will subsequently be described in detail, opening 91 communicating with port 84 when valve 85 is open.

Pothead 7 is connected to cable 1 in the following manner. First, the pothead is disassembled so base 60, insulator 61, bushing 86, plate 81, plate 89 and valve assembly 83 are separated from each other. Then, the stripped cable is slipped through opening 65 of base 60 so it extends through the space between cell assemblies 67, and its upper end is exposed. Next, bushing 86 is abutted against tip 92 of conductor 2 and the conductor is welded to the bushing as by weld material 93. Where the conductor is aluminum and is also oil filled, it is a distinct advantage to accomplish the welding at the factory under controlled conditions where the conductor can be thoroughly cleaned prior to forming weld 93, and where the weld can be done under the necessary protective atmospheres required to weld aluminum. Of course, where conductor 2 is formed from aluminum, the bushing 86 is also formed from aluminum. Next, the conventional electrical stress cone 94 is formed or built on the cable in the usual manner. Then, aluminum sheath 5 is welded to end wall 64 of base 60 under the same factory controlled conditions so that a secure leak free weld 95 is provided where the cable enters the base of the pothead. After welds 93 and 95 are made, plate 62 is sealed to base 60 and insulator 61 is slipped over the end of the cable to which bushing 86 is attached. The insulator is bolted into position on connector plate 62 with bolts 79, gaskets 77 and 78 insuring a fluidtight seal. The upper end of the insulator is then sealed by first bolting plate 81 to the insulator with gasket 82' in the position shown and then threading plate 89 downwardly on the bushing 86 until gasket 90 is firmly seated. Finally, valve assembly 83 is threaded into bushing 86. Pothead 8 is connected to the other end of the cable 1 in a similar manner.

After both potheads are connected to cable 1, it is necessary to purge the pothead as well as the adjacent ends of the cable to assure that no contaminants are present in either the pothead or the cable. This is accomplished by removing a threaded plug such as plug 96 from base 60 and then attaching conduit 97 and vacuum pump 98 to the pothead to remove gases and other contaminants. Next, a supply of pressurized fluid 102, advantageously oil, is connected to branch pipe 99 which communicates with base 60. Valves 100 and 101 are then manipulated to disconnect the vacuum pump 98 and connect supply 102 to the pothead. Oil from supply 102 then completely fills all the purged spaces within the pothead as well as any then empty spaces within opening 3 of conductor 2. The oil also impregnates portions of insulation 4 which may have lost oil during the connecting of the pothead to the cable end. Oil from supply 102 is forced into the pothead at a pressure above atmospheric and the pressurized oil will collapse some of the accumulator cells 68-70. Thus, even though slight leakage of oil may occur during subsequent transportation and handling of the cable, the positive pressure within the cable which is maintained by the cells prevents any contamination of the oil or other fluid within the cable system, and the cells compensated for volume change of the oil due to temperature variations. Where sheath 5 is aluminum, a positive pressure of 20-100 p.s.i. is applied to the cable.

After potheads 7 and 8 are attached to cable 1, pothead 7 is placed in compartment 35 and is secured within the compartment to prevent damage during further handling of container 11. Then, bottom 12 is bolted to the container. Similarly, pothead 8 is placed in compartment 33, is fixed in position within the compartment, and cover 36 is then bolted to the end of the container. The cable system, including the cable 1 with potheads 7 and 8 attached to its respective ends, is then ready for transportation to the installation site. Since the cable may be several thousand feet long and since the potheads are also quite heavy, the cable is advantageously transported on a large truck capable of carrying the packaged cable. Three conductor cables can also be terminated and transported in a like manner using suitable potheads.

When container 11 is transported to the site where cable 1 will be buried or installed under ground, cover 36 is removed, upper drum shell 20 is removed, and platform 27 is removed. Next, a spacer 103 is secured to the top edge of sides 13-16 with bolts 104 (FIG. 2A). Pothead 8 is then removed from the container. Next, cover 36, which is transversely split, is placed on spacers 103 with the opening through nozzle 37 closed around cable 1 as shown at FIG. 2A and the cover is bolted into position with bolts 105. Next, an arcuately curved guide assembly 106, having a long radius of curvature, is bolted to top flange 107 of nozzle 37. This guide assembly is formed from a plurality of longitudinally split semicircular halves which are bolted together with bolts 108 that extend through longitudinal flanges 109. First section 110 of guide assembly 106 is substantially identical to second section 111, the two sections being joined by bolts extending through end flanges 112 and 113 at the mating ends of the sections. Section 111 also has an end flange 114 to which is connected a flange 115 of a straightening tube 116. Straightening tube 116 is also longitudinally split so it can be closed over cable 1. The purpose of straightening tube 116 is to remove any bends from cable 1 resulting from the coiled storage of the cable.

With reference to FIG. 2A, it will be observed that removing upper drum shell 20 and adding spacer 103 provides sufficient space within container 11 to assure that cable 1 will feed freely from coil 117 through the opening in guide nozzle 37 without abrasion or scuffing when the cable is withdrawn.

To install the cable, a trench 120 (FIG. 9) is first formed. As previously mentioned, many localities have ordinances limiting the permissible length of an open trench. Thus, the usual procedure in laying cable is to open a short length of trench, lay the cable, and then immediately close the trench. While machinery is available to form a trench, such machinery cannot be used in urban areas where the cable to be laid must be pulled under existing obstructions, such as gas mains or already laid cable. Thus, the trench is of a length not exceeding that specified in the local ordinance. Then, if any obstructions are encountered, the cable is fed toward the desired termination such as the termination at support 121 for pothead 8.

As shown at FIG. 9, container 11 is at a location some distance from termination support 121. The cable has already been laid in the now closed portion 122 of the trench and in portion 122 an obstruction 123 was encountered which required feeding cable 1 under the obstruction. The manner in which cable 1 was installed in portion 122 of the trench will be explained subsequently.

The portion 131 of the cable in portion 122 of the trench was laid while container 11 was in the generally upright position of FIG. 2A. In order to lay portion 130 of the cable under the group of obstructions 126 of trench 120, it is first necessary to manipulate container 11 to the position of FIGS. 5 and 9, in which the container is on its side, and to rearrange the bottom and cover of the container. After portion 131 of the cable was laid in the trench, nozzle sections 110, 111, and 116 were removed and container 11 was rotated 90.degree. in a counterclockwise direction from the position of FIG. 2A so that sidewall 15 of the container was horizontal. Next, cover 36 and spacer 103 were removed, platform 27 was positioned in the container, and bottom 12 was removed from the opposite end of the container and was secured as shown at FIG. 5. Then, drum section 22 and platform 28 were removed from the container and pothead 7 and a portion 130 of the cable were pulled from the container. Next, spacer 103 and cover 36 were assembled around portion 130 of the cable as shown at FIG. 5.

Arcuately curved nozzle section 110 was then connected to flange 107 of cover 36 to provide the arrangement shown at FIG. 9. With reference to FIGS. 5 and 9, it is apparent that portion 130 of the cable can now be drawn through nozzle 38 by applying a pull to the cable, thereby unwinding the cable from coil 117 within container 11.

To install portion 130 of the cable under the group of obstructions 126 as shown at FIGS. 8 and 9, it is necessary to pull the pothead 7 under the obstruction. However, since the pothead includes a fragile porcelain insulator 61 (FIG. 3) the pothead could be damaged were it not for the unique shield 132 of this invention. As shown at FIGS. 5-7, the pothead 7 is completely enclosed within the shield 132.

Shield 132 includes a longitudinally spit shell 133 and a rounded bullet-shaped nose portion 134 which is bolted to the front end of shell 133. As shown at FIGS. 5-7, shell 133 is comprised of a pair of semicircular half shells 135 and 136 which are connected together by bolts 137 that pass through the mating flanges 138 of the half shells. Shield 132 has a reduced diameter end portion 139 dimensioned to tightly grip cable 1 when bolts 137, which extend through the flanges of this end portion, are tightened. End portion 139 clamps on portion 130 of cable 1, when the shield is installed, as shown at FIG. 7.

Nose 134 is hollow and is connected to the forward end of shell 133 by a plurality of circumferentially spaced apart bolts 140. Extending through an opening in the center of nose 134 is a threaded eyebolt 141 having an exposed eye 142 and a threaded end 143 which has threads that mate with the internal threads 91 (FIG. 3) at the end of the pothead.

To install shield 132, shell 133 is first loosely assembled around the pothead. Next, nose 134 is aligned with the end of the pothead and threaded end 143 of eyebolt 142 is threaded into threads 91 at the end of the pothead. Then, shield 132 is moved forwardly into the end of nose 134 and bolts 140 are inserted and tightened to secure the nose to the shell halves. Finally, bolts 137 are inserted through flanges 138 and are tightened to close shell 133 and clamp end 139 of the shell onto the cable.

To pull portion 130 of the cable under obstructions 126, a winch line 143' from a winch 144 located at the opposite side of the obstruction from container 11 on wheeled vehicle 125 is first pulled under the obstruction to the general vicinity of the container. Next, winch line 143' is secured to eye 142 of the eye bolt, and when the winch is operated, shield 132 with pothead 7 therein is pulled under obstructions 126. As the pothead is pulled, portion 130 of the cable is uncoiled from the coil of cable 117 within container 11 and hence, portion 130 of the cable is laid. As shown at FIG. 9, guide rollers 145-148 can be used during the pulling operation in which pothead 7 and cable 130 are pulled under obstructions 126.

For purposes of explanation, assume that there is substantially more cable in container 11 than the open length of trench 120. Where such excess length of cable is present, a new container 149 identical to container 11 is provided adjacent the end of the trench, container 149 advantageously being supported by a wheeled vehicle 150. The container 149 is positioned on the vehicle with the container upright. Pothead 7 is placed in the bottom section of the container (generally in the position shown at FIG. 2A) and platform 28 and drum sections 21 and 22 are then installed. The excess length of cable is recoiled into new container 149. The recoiling of cable 1 in container 149 is advantageously accomplished with the assistance of drive rollers 151 which simultaneously pull cable from container 11 and push the cable into container 149. When substantially all the cable is withdrawn from container 11 the pulling and recoiling operation at container 149 is stopped, and container 11 is disassembled. Such disassembly will include removing cover 36, spacer 103, bottom 12, and one sidewall of the container 11. With the container so disassembled, the cable is free to be pulled through one side of the container whereupon, the pulling and recoiling at container 149 is continued until the cable lies in the bottom of trench 120.

Then, trench 120 is filled and trenching is continued so the cable now coiled in container 149 can be laid. If no additional obstructions are encountered for a certain length of additional trench, nozzle 38 and nozzle sections 110, 111, and 116 are connected to the upper end of container 149, and the cable is then pulled from the container by moving vehicle 150 along one side of the trench. If additional obstructions are encountered, container 149 is again turned up on one side, pothead 7 is removed through the bottom of container 149 and cover 36 is connected to the container, in the manner shown at FIG. 5, so that the cable extends through nozzle 38. The pothead is then pulled under the existing obstructions and the cable may again be recoiled into a containerlike container 11 or 149. In the past, cable without potheads attached to its ends was coiled on large reels. In order to thread such cable under obstructions, it was customary to completely unreel the cable to obtain a free end and then pull the entire length of cable under the obstruction, and subsequently again coil the cable onto the reel. The likelihood of damage to the cable when using a reel rather than the container, which forms a part of this invention, is readily evident when one considers that only the portion of the cable which is actually pulled through the trench under the obstruction is exposed. Thus, where lengths of cable on the order of one thousand feet are used, there is no need to string the cable out along side the trench where an obstruction is encountered.

In view of the foregoing explanation on the manner in which portion 130 of the cable is laid, it is believed evident that portion 131 of the cable was laid by using a nozzle arrangement similar to that of FIG. 2A but with the nozzle sections 110, 111, and 116 extending in an opposite direction so that the cable with pothead 8 connected to its end could readily be pulled under the obstruction 123. Of course, a shield 132 was connected around pothead 8 before the pothead was pulled under the obstruction.

Since container 11, with cable coiled into the container and potheads at the ends of the cable, will be quite heavy, suitable handling eyes such as those provided by eyebolts 152 and 153 secured to container 11 are provided. Eyebolts 152 and 153 can also be used for connecting suitable rope or other holddown devices to the container to prevent shifting during transportation by truck. It is contemplated that a crane may be needed to lift container 11 or container 149 to the various positions necessary to coil and uncoil cable 1 in the manner previously described.

In view of the foregoing it is apparent that a long length of cable can be buried or laid, the cable having potheads connected to each of its ends, without the need for field splicing or any extensive field work which was necessary in the past. Since the potheads and cable are filled with pressurized oil, there is also no need to purge and purify the system, refilling it with oil, after the potheads are in their desired positions at the appropriate terminations. Thus, the only labor involved for this field installation is the connections that are normally made to the end of the pothead which are ordinarily simple mechanical connections and do not require skilled field splicers.

FIGS. 10 and 11 show arrangements for connecting the preassembled cable without danger of contaminating the oil or other fluid within the potheads 7 and 8 and cable 1. FIG. 10 shows the splicer arrangement as applied to a splice between two lengths of cable, one having the pothead 7 at an end, and the other having a pothead 160 at an end, pothead 160 being identical to pothead 7. Here, the potheads extend in axially aligned relation to each other into a vertically split generally rectangular parallelepiped tank 161. Tank 161 is vertically split and is provided with bolt-receiving flanges 161' so it can be closed over the potheads and sealed after a combined electrical and mechanical connector 162, having a passage therein through which oil from pothead 7 communicates with oil from pothead 160, is installed between the potheads.

Pothead 7 is secured to one end wall of tank 161 with suitable bolts that pass through connector plate 62'. Suitable gaskets are used to prevent leakage of oil from inside the tank outwardly along base portion 60 of the pothead which projects from the end of the tank. Similarly, pothead 160 is mounted in tank 161 with its connector plate 162' bolted to the other end wall of tank 161. Suitable gaskets are used to prevent leakage of oil from inside tank 161 along base 163' of pothead 160, which extends through the other end wall of the tank. The top of tank 161 has access openings 163 and 164 which are generally in vertical alignment with the respective operating handles 167 and 168 of the valves for the potheads. Extending across openings 163 and 164 are resilient closures 165 and 166 respectively, the closures each taking the form of a pair of semicircular discs of resilient material such as thick rubber. These split cover discs permit inserting a suitable tool through the split in the discs to manipulate operating handles 167 and 168 without losing fluid from tank 161. The access openings and closures are closed by a cover 169 which is bolted to the top of the tank and seals the space surrounding access openings 163 and 164.

After tank 161 is closed around the potheads and connector 162 is installed between the ends of the potheads, the inside of tank 161 is purged to remove any contaminants. This can be accomplished either by bleeding an inert gas through the tank or by first drawing a slight vacuum on the tank and then filling the tank with the inert gas. Next, oil is introduced into the tank to completely fill the tank and displace the inert gas. While the oil is under relatively low pressure, cover 169 is removed and a tool is inserted through cover disc 165 into engagement with operating handle 167, and the valve at the end of pothead 7, is then opened. Similarly, operating handle 168 is manipulated with a suitable tool inserted through closure disc 166 so the valve at the end of pothead 160 is opened. Ports 170 of connector 162 communicate with the interior of the tank 161, as well as with the interior of the potheads, when the valves at the ends of the potheads are open. After these valves are opened, cover 169 is immediately replaced and additional oil is introduced to the tank to completely fill the tank. When the tank is completely filled and the oil in the tank is pressurized, it is to be noted with particularity that the pressure of the oil within the tank is the same as the pressure of the oil within each of the potheads. This pressure balance is extremely significant where there are long lengths of cable and the oil in the cable communicates with the oil in the potheads. Since the cable may not be level, but may be at a different elevation from the pothead throughout a substantial portion of its length, the pressure head developed by the oil in the cable could be sufficient to cause bursting of the fragile insulators of the potheads. However, where the oil within the pothead communicates with the interior of tank 161, the pressure in the tank is the same as the pressure within the pothead and, hence, there is no significant pressure differential between the inside and the outside of the pothead. The pressure within tank 161 is maintained by cell assemblies 67 located in both pothead 7 and pothead 160. These cell assemblies, of course, also maintain the system including the cable, potheads, and tank full by expanding to compensate for a decrease of volume of the oil, when the oil is cool, and by contracting to compensate for an increase in volume of the oil when the oil is heated.

Locating potheads 7 and 160 within a tank filled with oil permits the use of potheads substantially shorter than those customarily used today. The usual reason for using potheads of considerable length is to assure that no flash over will occur between the end of the pothead and the cable. Thus, it is necessary at present to provide a pothead sufficiently long to assure that no such flash over will occur. However, when the potheads are immersed in oil, the oil itself acts as an insulator to reduce the tendency for flash over. Hence, the potheads used with tank 161 need only be approximately one-half the length of a pothead used without tank 161. This, of course, represents a substantial saving because of the need to transport the potheads and cable, and in addition, provides for conveniently circulating oil through the cable system to assist cooling of the cable under operating conditions.

FIG. 11 shows a termination arrangement where a pothead 8 of an oil filled cable system is connected to a pothead 172 of a transformer 173. Here, a tank 174, similar to tank 161, and which is also vertically split (details of the split are like those explained for tank 161) is bolted to the side to transformer 173. Pothead 8, which is preassembled to the end of underground cable 171, extends through an opening in the end wall of tank 174 and is secured to the tank by bolts passing through its connecting plate 62'. A connector assembly 175 is installed between the end of transformer pothead 172 and pothead 8. In this arrangement however, communication of the oil in pothead 8 and cable 171 with the oil in pothead 172 and transformer 173 is not desired. Hence, the oil within pothead 172 does not communicate with the inside of tank 174. Port 176 communicates with pothead 8 only when the operating handle of valve 178 is opened. A suitable split disc resilient closure 177, like closures 165 and 166, previously described, extends across an access opening at the top of tank 174. A cover 179 is bolted across split closure 177 to completely seal tank 174. The tank is provided with suitable valves 180 and 181 to facilitate purging any contaminants from the inside of tank 174 before it is filled with oil.

The operation of purging and filling tank 174 with oil is like that explained for tank 161 in that the tank is first filled to a level adjacent the access opening, and thereafter a suitable tool is inserted through the resilient closure 177 to open valve 178. The tool is then immediately withdrawn and cover 179 is secured in position to completely seal the tank. Thereafter, the tank is completely filled and the oil in the tank is pressurized to the desired value.

While the pressure on the exterior of the insulator of pothead 172 may be somewhat higher than the pressure of the oil within transformer 173 and pothead 172, the effects of a higher pressure outside the pothead are usually not detrimental. This is because porcelains such as the porcelain of pothead 172 exhibit tremendous compressive strength, yet are quite weak in tension. Hence, higher pressures on the outside of the porcelain of pothead 172 will not adversely affect nor damage the porcelain of this pothead.

With reference to FIG. 13, there is shown an aboveground arrangement which permits the use of an ultrashort pothead. As shown at FIG. 13, pothead 190 has its base extending through an opening 191 in the bottom of a vertical tank 192. A connector plate 193 of pothead 190 seats on the bottom wall of the tank and suitable gaskets and bolt 194 are provided to prevent leakage of oil from the tank. Tank 192 is filled with oil 195, which acts as an effective insulator to prevent flash over from the conductor within the pothead to the end of the pothead, along insulator 196. Extending from the upper end of pothead 190 is conductor 197 which extends through a cover 198 for tank 192. Cover 198 is formed from insulating material and is secured to conductor 197. The purpose of cover 198 is to exclude water from the surface of oil 195 in the tank. In this case, the oil does not communicate with the interior of pothead 190.

The ultrashort pothead arrangement of FIG. 13 includes an oil contamination detector, and an oil-purifying system which is normally inactive but is operated when the contamination level of the oil nears an unsafe condition. As shown at FIG. 13, the system includes a contamination detector 199 submerged in oil 195 in tank 192. Purifying system 200 includes piping 201 via which oil is withdrawn from the tank and piping 202 via which purified oil is returned to the tank. The system including detector 199 and purifying system 200 is shown schematically at FIG. 12. As shown at FIG. 12, detector 199 includes a pair of spaced-apart conductive metal plates 203 and 204 which are located in the oil of tank 192. With reference to FIG. 12, it is seen that relay coil 205 is in series circuit relation with plate 203, resistor 206, a power source which takes the form of a battery 207, and plate 204. Contacts 208 of the relay 205 are connected in the power supply lines 209, 210 which supply power to motor 211 from a suitable source. Motor 211 is connected to pump 212 by a shaft 213. The inlet of pump 212 is connected to the bottom of tank 192 by piping 201 and the outlet of the pump is connected to an oil purifying unit 215 via pipe 214. Oil is returned from purifying unit 215 to tank 192 via piping 202.

As oil 195 becomes contaminated, the oil becomes electrically conductive. Hence, the resistance of the circuit, including relay coil 205, decreases until sufficient current flows to close contacts 208. It is to be appreciated that the relay, including coil 205 and contacts 208, is of an extremely sensitive type which will close the contacts in response to a current flow of a few milliamps. When contact 208 closes, motor 211 is energized and pump 212 is driven. Oil is drawn from tank 192 through piping 201 and is then forced through purifying unit 215, whereupon it is returned to tank 192 through piping 202.

The relay, including energizing coil 205 and contacts 208, is so selected that it drops out at a substantially lower current flow than the current flow for pull-in. Hence, motor 211 is energized and drives pump 212 until the dropout valve of current in coil 205 is reached and contacts 208 open. Thus, this system insures that oil in tank 192 will be purified each time the contamination level is high enough to energize relay coil 205 sufficiently to close contacts 208.

While a preferred embodiment of applicant's new cable system and its method of installation have been shown and described with reference to an oil filled cable system, it is to be understood that the invention herein is not intended to cover only an oil-filled system but also other systems where various fluids are used. In addition, while cable 1 has been shown and described with a pothead preassembled at each end, it is within the contemplated scope of this invention to connect only one pothead to the cable before installation and burying of the cable, especially where it is desired to have a small diameter end such as the cable itself presents, at one end of the cable. It is also within the contemplated scope of this invention that solid dielectric type cables which are not fluid filled can be packaged in container 11 to facilitate installing such cables, since they can be pulled from both ends from the container 11. In addition, it is within the contemplated scope of this invention that numerous changes and variations can be made in the embodiments and techniques disclosed herein without departing from the intended scope of this invention.

Claims

What is claimed is:

1. A method of making cable with factory installed potheads and of installing high voltage sheathed cable comprising the steps of

providing a length of cable of the type having a conductive core and a sheath extending around and spaced from said core;

providing a pothead having a chamber therein;

connecting said pothead to one end of said cable at a location remote from the installation site for the cable, said connecting including sealing said sheath to said pothead with said chamber in fluid communication with the space between the sheath and conductor;

purifying said chamber and communicating space;

introducing fluid under pressure to said chamber and communicating space;

coiling said cable;

transporting said cable with attached pothead to its installation site;

installing said able; and

electrically connecting said pothead to apparatus at said site.

2. A method according to claim 1 wherein

said sheath is of aluminum; and

said step of connecting said sheath to said pothead includes welding the sheath to the pothead.

3. A method according to claim 1 which further includes

connecting a second pothead having a chamber to the other end of said cable before transporting the cable and potheads to the installation site;

said step of connecting including sealing said sheath to said second pothead with said chamber of said second pothead communicating with the space between the sheath and conductive core of the cable.

4. A method according to claim 1 wherein

said step of introducing fluid under pressure to said chamber and communicating spaces includes

filling said chamber and spaces with a purified insulating oil.

5. A method according to claim 1 which further includes

providing a container;

coiling said cable in said container before connecting said pothead to the cable; and

closing said container.

6. A method according to claim 5 wherein

said step of installing the cable includes

connecting a shield to said pothead, and

guiding said shield and pothead under obstructions in a trench to install said cable.

7. A package for high-voltage cable comprising

a generally rectangular boxlike structure having sidewalls, a bottom wall, and a cover;

a drum of cylindrical exterior configuration within said container;

means releasably securing said drum within said container in centered relation to said sidewalls;

first partition means and second partition means;

means securing said first partition means in spaced relation to said bottom wall to define a first compartment;

means securing said second partition means in spaced relation to said cover to define a second compartment; and

a length of high-voltage cable having a sheath surrounding a conductive core, coiled on said drum;

a first pothead secured to one end of said cable, and disposed in said first compartment; and

a second pothead secured to the other end of said cable and disposed in said second compartment.

8. A package according to claim 7 wherein

said cover includes

a first section, and

a second section;

means releasably connecting said sections together to form a cover including

a base portion, and

a longitudinally split nozzle portion; and

means releasably securing said cover to said end walls

in a first position in which said nozzle extends into said container, and

a second position in which said nozzle projects from said container;

said nozzle presenting a smoothly curved interior surface to guide said cable through the nozzle.

9. A package according to claim 7 which further includes

means releasably securing said bottom wall to said sidewalls;

said bottom wall having an opening therein of a size to receive said cable.

10. A method for making factory installed potheads and of installing high-voltage cable comprising the steps of

providing a container having a removable cover, a removable bottom wall, and a removable top wall;

coiling a length of cable comprising a conductive core and a sheath surrounding the core into said container, said sheath and core having a space therebetween;

providing a first pothead and a second pothead, at least one of said potheads having a chamber therein;

securing said potheads to the respective ends of said cable with said chamber in fluid communication with said space between said core and sheath;

introducing fluid under pressure into said chamber and space between said core and sheath;

positioning said potheads within said container;

transporting said container with cable and potheads to the installation site;

forming a first length of trench for said cable;

connecting a shield to said pothead;

pulling said first pothead under any obstructions in said trench;

uncoiling at least a portion of said cable during said pulling;

providing a second container at a location beyond the obstructions;

positioning said first pothead in said second container;

uncoiling the remaining cable from said first container and coiling at least a portion thereof in said second container;

forming a second length of trench for said cable;

pulling said first pothead under any obstructions in said second length of trench; and

feeding cable from said second container during pulling of the pothead through said second trench.

11. A method according to claim 10 wherein

said step of positioning said potheads within said container includes

positioning said first pothead adjacent said top wall, and

positioning said second pothead adjacent said bottom wall.

12. A method according to claim 11 wherein

said first pothead is removed from said container after said cover is removed; and

which further includes

removing said bottom wall;

removing said second pothead from said container;

pulling said second pothead into position in said trench by pulling same in a direction opposite to the pulling direction of said first pothead; and

removing one sidewall of said first container after the cable therein is substantially uncoiled.

13. A method according to claim 12 wherein

said container is positioned with one sidewall horizontal during said pulling operation.