Patent Application
20110244702
The present invention relates to connectors for high voltage electrical power cables and, more particularly, to connectors used to inject a dielectric enhancement fluid into the power cable's interior.
High voltage (e.g., 5 to 35 kV) electrical power cables, which generally comprise a stranded conductor surrounded by a semi-conducting conductor shield, a polymeric insulation jacket, and an insulation shield, tend to deteriorate and lose dielectric integrity after being in service for a decade or more due to exposure to high electric fields and the effects of ambient moisture. The integrity, or dielectric strength, of the cable can be at least partially restored by injecting a dielectric enhancement fluid into the interstitial void volume associated with the stranded conductor, as is well known in the art (e.g., U.S. Pat. Nos. 4,766,011 and 5,372,841). Various specialized connectors have been designed to facilitate the injection of such a fluid into the cable's interior and some of these devices allow the injection process to be carried out while the cable is still energized. However, a problem associated with such a live injection process soon became apparent. In brief, when an injection component, such as that described in U.S. Pat. No. 4,946,393, is used to deliver the dielectric enhancement fluid, the energized conductor is exposed between the time an injection plug (cap) is withdrawn from the injection port after the fluid has been introduced and the time an insulating permanent plug is inserted in its stead to seal the injection port. During this interval it is possible that the high voltage may ionize the air, water, injection fluids, or other materials in the injection port and a flashover may occur between the conductor or the conductive insert of the component and a ground plane. Such an arc flash can damage the equipment, the component, the transformer or other equipment in the immediate area and presents a thermal and electrical danger for the operator as these plugs are being swapped. Although flashover is possible at all power cable voltages, the risk increases with increasing voltage and the risk is greatest with 35 kV systems. In fact, the risk is so great at 35 kV that such “live plug swapping” is not practiced with currently utilized technology, and the cable is de-energized before the swap. While de-energizing the cable eliminates the potential for electrical flashover, there is a cost and customer service penalty that must be borne by the circuit owner for the additional time, expense and inconvenience of this approach, as well as stress on the cable.
The above mentioned flashover problem is described in greater detail in U.S. Pat. Nos. 6,517,366 and 6,929,492, and a solution thereto is disclosed such that the whole injection process can be carried out without de-energizing the cable. These patents are directed towards a method and apparatus for creating a barrier after the injection of remediation fluid to block the conductive pathway between the conductive portion of an energized cable and the ground plane. Basically, this barrier comprises some sort of a mechanical valve that can be actuated to isolate the conductor from the exterior of the component, a breakaway tip which lodges in the injection port, or a high viscosity dielectric fluid which is introduced into the injection port of a component after injection of the dielectric enhancement fluid has been completed to temporarily block the port while the permanent plug is swapped for the injection plug. Complex mechanical valves add cost to the process and, if they reside within the outer boundary of the connector's conductive insert, they do not foreclose the possibility of a flashover even if they operate properly. Injecting a second fluid into the cap or plug adds another layer of complexity and cost. There is thus a need for a simpler and more cost-effective approach to provide safe operation during the injection of an energized cable.
In one embodiment, the present invention is directed to a connector for introducing fluid to an electrical cable affixed in a chamber internal to the connector, the connector comprising:
(i) an injection port exposed to at least one exterior surface of the cable connector, the injection port having fluidic communication with the chamber internal to the connector; and
(ii) a reticulated plug positioned within an insulated segment of the injection port so as to fill at least a portion thereof.
In another embodiment, the present invention is directed to a high voltage electrical connector comprising: (a) an insulative body portion; (b) a conductive body portion external shield at least partially surrounding the insulative body portion; (c) a projection of electrically insulating material having a first end connected to the insulative body portion and a second end extending from the body portion; (d) an injection port extending through the projection and having an opening in the second end of the projection, the injection port communicating an exterior of the electrical connector with a conductive insert of an interior of the electrical connector; and (e) a reticulated plug positioned within an insulated segment of the injection port so as to fill at least a portion thereof.
In another embodiment, the present invention is directed to a method for introducing a dielectric enhancement fluid into the interior of a cable affixed in an internal chamber of a connector having an injection port in fluidic communication with the chamber, the method comprising:
(i) inserting a reticulated plug into an insulated segment of the injection port so as to fill at least a portion thereof;
(ii) installing an injection plug at the injection port;
(iii) injecting the fluid into the interior of the cable through said injection plug; and
(iv) swapping said injection plug with a permanent plug to seal the injection port, wherein the cable is energized during at least step (iv)
The present reticulated flash prevention (RFP) plug or device, also referred to herein as a reticulated plug, may advantageously be used in combination with various types of conventional injection connectors to allow swapping of an insulative permanent plug (such as shown in
Conventional load-break elbow, dead-break elbow, tee-body or splice-type connectors are examples of connectors and components which occur at cable junctions and include injection or direct access ports, as contemplated herein. U.S. Pat. Nos. 4,946,393 and 6,332,785 exemplify the contemplated components. Such conventional injection connectors are typically limited to pressures below about 30 pounds per square inch gage (psig), but it is contemplated that the instant connectors can be employed as described herein as long as the pressure drop across the reticulated plug is not large enough to displace it during the injection step. For illustrative purposes, the use of the reticulated plug will be described in more detail in combination with a conventional load-break injection elbow connector as follows.
Injection elbow connectors are well known in the art and are used to inject a dielectric enhancement fluid, or some other fluid component, into the interior (i.e, void space associated with the stranded conductor geometry) of an electrical power cable at the above mentioned relatively low pressures. Again, both the injection and the above mentioned plug swap can be carried out while the cable is energized using appropriate hot-stick procedures.
As shown in
The connector 50 includes an insulating body portion 59 and an external conductive shield 52 molded from a conductive elastomeric material, such as a terpolymer elastomer made from ethylene-propylene diene monomers filled with carbon, and/or other conductive materials well known in the art. A preferred conductive material is carbon loaded ethylene-propylene terpolymer (EPT or EPDM). The conductive external shield 52 is preferably pre-molded in the shape of an elbow and includes a cable opening for receiving a high voltage cable 37 and a connector opening 54 for receiving an electrical connection device. Thus, the body portion conductive external shield 52 partially surrounds the body portion 59. The body portion 59 is made from an insulative material, preferably EPDM, and occupies the space between the conductor coupling assembly 34 and the conductive external shield 52. Thus, the insulative body portion 59 surrounds the semi-conductive insert 35 of the conductor coupling assembly 34 and forms a dielectric and electrically insulative barrier between the high voltage internal components and the conductive external shield 52. The insulative body portion 59 also includes openings for receiving the high voltage cable 37 and an electrical connection device such that they may be electrically connected to the conductor coupling assembly 34 within the interior of the connector 50.
It is often desirable to gain access to the interior of the connector 50, e.g., to inject a dielectric enhancement fluid or to make direct voltage test measurements. To enable this access, the connector 50 includes an injection port 58 located in a projection 62 of insulative material extending from the body portion 59. The injection port 58 is preferably a straight hole extending from the exterior of the connector 50 through the insulative projection 62 and through the insulative body 59 and the conductive insert 35 such that at least a portion of the high voltage items within the connector, preferably at least the interior of the conductor coupling assembly 34, is exposed. Although the injection port 58 is preferably a straight cylindrical hole, other shapes are possible. For instance, the injection port 58 may be inclined with respect to the conductive external shield 52, and be conical, square, triangular, oval, or other numerous configurations, so long as the interior of the connector 50 is exposed.
The reticulated plug contemplated herein is fabricated or punched from a reticulated material having good dielectric strength and resistivity. The term “reticulated” is defined as a grid-like, porous structure which blocks the passage of items larger than its characteristic pore size, while letting smaller items and fluids pass therethrough. Non-limiting examples of suitable reticulated materials include organic sponge materials, synthetic sponge materials, cotton, woven or non-woven textiles, plastic or elastomeric open-celled foams, felt, fiber glass, sintered glass, or sintered ceramic or a solid material modified to allow fluid passage. Preferably, this plug is formed from a compressible material with a density of less than 2.5 pounds per cubic foot, a 50% compression set of less than 15%, and a 25% compression force deflection less than 0.5 psi, as would be typical of a polyurethane open-celled foam that has been processed to create a reticulated structure. One such preferred polyurethane foam is available commercially from IR Specialty Foams as part number 60PPI, manufactured by Crest Foam Industries under the name of FilterCrest® Industrial Foam Grade S-60. This is a reticulated polyester polyurethane foam having a nominal 60 pores per inch. Similar foams having more or fewer pores per inch are also suitable.
Although there is no specific limitation on the cross-sectional shape of the reticulated plug, it should fit snuggly within the injection port 58 of the connector 50 being injected and match the configuration of the port. Preferably the reticulated plug is a right circular cylinder which fits the injection port of a conventional injection connector, as described above. The outside diameter of the reticulated plug should be greater than the inside diameter of the injection port so that the former when inside the injection port is in radial compression, and thus held firmly in place, while the cable is injected. This radial compression also assures that the fluid in the reticulated plug is in full contact with the walls of the injection port to create closure of the injection port. Although the term “diameter” is used, it should be understood that this can refer to a generalized cross-sectional dimension of the reticulated plug so as to contemplate shapes other than circular, such as rectangles, triangles or other polygons. The length of the reticulated plug is not critical, but generally represents a compromise. On the one hand, there should be a sufficient open length of the injection port 58 for insertion of the stem portion 60 of a permanent plug (cap) 61 of the type shown in
When the reticulated material is a relatively soft (low modulus) material, such as the above mentioned polyurethane open-celled foam, it is preferred that a modified reticulated plug is used in the instant connectors to aid in holding the foam in place while injecting fluid. One embodiment of a modified reticulated foam plug 40, shown in cross-section in
The above described modified reticulated plug 40 can be inserted into the injection port 58 of the conventional connector 50, such as the elbow electrical connector shown in
In another embodiment of a modified reticulated foam plug, the above described reticulated foam plug 42 is inserted into a relatively rigid (high modulus) insulative tube or jacket having an inner diameter and length slightly less than, or equal to, the corresponding values for the reticulated material, as shown in
Referring now to
During the introduction of fluid to a cable within connector 50, as shown in
If a live injection is being carried out, the injection plug 301 can be released from the connector 50 by means of a hot stick engaging a pull ring 311 passing through the eye of an eye bolt 309 and moving the pull ring away from the body of the connector 50. As the eye bolt 309 is moved outward by the pull ring 311, it draws the sleeve 308 longitudinally outward along a bore 313 until the end of the sleeve clears the ramp 307 to create an escape passageway between the end of the sleeve and the ramp, thereby allowing the end of the adjustable strap 306 retained at the ramp 307 to slide off the ramp and fall away, thereby releasing the injection plug 301 from the connector.
According the instant method, the following steps are carried out in the injection of a dielectric enhancement fluid into the interior of an electrical cable having an inlet end and an outlet end. Although described for the case of an injection elbow connector 50, it is contemplated that the general method applies equally to other injection components, such as an injection splice connector.
1. If the cable does not already have an injection connector attached at each end thereof, de-energize the cable and replace each existing connector with an injection connector having a reticulated plug within its injection port, as described above.
2. If the cable is already fitted with a conventional injection connector at each end thereof, de-energize the cable and insert a reticulated plug into the injection port of each connector, as described above. Preferably, wet the reticulated plug with the dielectric enhancement fluid to be used (e.g., 0.5 to 1 ml). It is believed that the fluid fills, or partially fills, many of the air and water vapor filled voids of the reticulated plug and thus improves the dielectric properties thereof as air and water vapor are more easily ionized than a dielectric fluid. Air and water vapor facilitate the undesired flashover. At this point, the cable can be re-energized, but it is preferred that this be done after step 3, below. Alternatively, it is also possible to carry out the insertion of the reticulated plug while the cable is still energized using appropriate hot-stick techniques.
3. Install an injection plug, such as that shown in
Injection Steps (the Following Steps are Generally Carried Out while Cable is Energized, but May Also be Performed on De-Energized Cables.)
4. Inject the dielectric enhancement fluid at the inlet end connector using a pressure compatible with the component(s) and cable until the fluid starts to exit the outlet end.
5. Swap the injection plug with a permanent plug, such as shown in
6. Discontinue fluid injection and swap a permanent plug for the injection plug at the inlet end, thereby sealing the injection connector at the inlet end, in the same manner as described in above step 5. Optionally, a “soak period” of several days to several months is contemplated between steps 5 and 6 while the cable is typically energized, wherein the fluid flow into the cable continues as the fluid within the cable diffuses through the insulation jacket thereof, as is well known in the art.
Thus, there is also disclosed an improved method for introducing a dielectric enhancement fluid into the interior of a cable affixed in an internal chamber of a connector having an injection port in fluidic communication with the chamber, the method comprising:
(i) inserting a reticulated plug into an insulated segment of the injection port so as to fill at least a portion thereof;
(ii) installing an injection plug at the injection port;
(iii) injecting the fluid into the interior of the cable through the injection plug; and
(iv) swapping the injection plug with a permanent plug to seal the injection port, wherein the cable is energized during at least step (iv), and thereby suppressing flashover between the energized conductor (or conductive insert) and a ground plane.
Several modified reticulated plugs used in subsequent testing were prepared as follows. With reference to
Six injection elbow connectors (Elastimold® 168 DELR-7495) of the type shown in
Each of the elbow connectors was secured such that its injection port faced directly upward, the permanent cap was removed and the injection port left open, whereupon 2.5 ml of Ultrinium™ 732 g/40 dielectric enhancement fluid formulation (see table below) was introduced into the annular region of the internal chamber, between the semi-conducting insert 35 and the conductor 32/compression connector 38 (see
This was followed by the introduction of 2.5 ml of tap water into the above mentioned annular region of each elbow connector, again using a syringe and being careful not to let any water contaminate the interior of the injection port. These injections of dielectric enhancement fluid and water filled the annular region between conductive insert and conductor/crimp connector as well as a portion of the injection port at the conductive insert, but not the insulated portion of the port. The water-fluid mixture simulates field conditions of a contaminated fluid injection.
Each elbow connector was randomly assigned a number from 1 to 6, the odd numbered elbow connectors serving as controls having open injection ports and the even numbered elbow connectors being fitted with a modified reticulated plug, as follows. A modified reticulated plug, as prepared above, was inserted into the entrance of the injection port of each even numbered elbow connector such that its longitudinal axis was coincident with that of the port. Tip 71 of the insertion tool 70 shown in
Each cable length was energized and the voltage increased 1 kV per minute until a flashover to ground occurred. The table below reports observed flashover voltages for the six elbow connectors. It can be seen that the use of the instant modified reticulated plug provided an approximately 39% increase in mean flashover voltage over the control having an open injection port.
| Number | Date | Country | |
|---|---|---|---|
| 61252587 | Oct 2009 | US |
