Abstract:
A method and apparatus are described to prevent the unwanted energizing of equipment not normally intended to be energized when delivering a fluid to an energized power cable. The method and apparatus relate to the installation of a fluid back-flow prevention device in the line or equipment carrying a fluid to the cable, and also providing a pressure relief device that may relieve excess pressure to prevent damaging equipment.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/607,339, filed on Sep. 3, 2004, the disclosure of which is hereby expressly incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The described embodiments relate to a process for power cables, and more particularly to a check value for a charge tank. 
     BACKGROUND OF THE INVENTION 
     The insulation of high voltage power cables will degrade after a period of time. One remediation process for the insulation of medium and high voltage power cables requires the injection of a remediation fluid into the free spaces of a cable. In many instances, the injection process takes place while the cables are energized. When the remediation process is performed on energized cables, special injection terminations (injection “elbows”) may be used. Injection terminations are similar to industry standard cable terminations except that they have a special access port designed to allow for the injection of fluid into the cable. The fluid is commonly injected into underground cables from a fluid feed line, which is connected to a fluid feed tank. 
     One remediation process for the insulation of medium and high voltage power cables requires the injection of a remediation fluid into the free spaces of a cable&#39;s conductor. In many instances, the injection process takes place while the cables are energized. When the remediation process is performed on energized cables, a class of special injection terminations may be used. Injection terminations are similar to industry standard cable terminations except that they are sealed to the environment and have special access ports designed to allow for the injection of fluid into the cable. 
     The fluid is commonly injected into underground cables from a fluid feed line, which is connected to a fluid feed tank, at the injection termination. When fluid is injected into the cables at the injection port of the injection terminations, it is assumed that the fluid flow is only in one direction, flowing from the feed tank to the cable. However, as the cable fills and the fluid system begins to stabilize, temperature changes that occur inside the cable or outside in the environment around the feed tank can cause the pressure of the system to fluctuate. The pressure fluctuations can lead to instances where the pressure inside of the injection elbow is greater than the pressure inside of the fluid feed tank. At this point, fluid flow would reverse, moving from the injection elbow back into the fluid feed tank. 
     The fluid that travels in the reverse direction, out of the injection elbow, carries contaminants from the cable to the feed tank. These contaminants can be conductive or semi-conductive, effectively reducing the insulating value of the remediation fluid in the fluid feed line that separates the energized cable from the feed tank and a conductive pathway can be formed. 
     Therefore, there exists a need to prevent back flow of contaminated fluid from the injection elbow to the fluid feed tank. 
     SUMMARY OF THE INVENTION 
     A method for preventing energizing equipment is provided. One such method includes providing a fluid back-flow prevention device in a line carrying fluid between the equipment and an energized power cable. 
     A system for preventing energizing a fluid reservoir is also provided. In one embodiment, the system includes a line from the fluid reservoir leading to an energized power cable. The system also includes a back-flow prevention device installed in any part of the line or within the fluid reservoir, wherein the back-flow prevention device may prevent the flow of fluid contaminated with conductive materials that may energize the fluid reservoir. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a process flow diagram of a system to carry fluid from a fluid feed tank to an injection termination with a back-flow prevention device and pressure relief device in the line between the fluid feed tank and the injection termination; 
         FIG. 2  is a process flow diagram of a system to carry fluid from a fluid feed tank to an injection termination with the back-flow prevention device and pressure relief device in the fluid feed tank; 
         FIG. 3  is a process flow diagram of a system to carry fluid from a fluid feed tank to an injection termination with the back-flow prevention device and pressure relief device in the injection termination; 
         FIG. 4  is a cross-sectional illustration of an injection termination and injection plug for preventing back-flow of remediation fluid and preventing over-pressure in the injection termination or cable; and 
         FIG. 5  is a cross-sectional illustration of an injection termination for preventing back-flow of remediation fluid and preventing over-pressure in the injection termination or cable. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , a remediation fluid delivery system for remediating power cable insulation is schematically illustrated. The system includes a remediation fluid reservoir, such as feed tank  3 , a fluid line  2  leading from the tank  3  to an injection termination  1 , wherein the injection termination  1  is attached to power cable  7 . 
     Remediation fluid is stored in the fluid feed tank  3  and can be supplied to the injection termination  1  (such as an injection elbow or other separable-type connector) via the fluid line  2 . Fluid is drawn from the fluid feed tank  3  at the fluid inlet  6  of the fluid line  2 . Fluid may flow by gravity from the tank  3  to the injection termination  1 . A back-flow prevention device  4  is installed in the line  2  that allows the flow of fluid from the tank  3  to the injection termination  1 , but prevents the flow of fluid from the injection termination  1  to the tank  3 . 
     The system may also include a pressure relief device  5 , installed in the line  2 , that relieves pressure in the injection termination  1  or the cable  7  and delivers any over-pressure fluid into the tank  3  via line  2 . Alternatively, overpressure in the line  2  may be vented to the ground or a specially designed destination for pressure relief devices. Fluid back-flow prevention device  4  and pressure relief device  5  may be installed in the line  2  in a parallel arrangement. In this embodiment, the pressure relief device  5  is installed as a bypass around the back-flow prevention device  4 . 
     While back-flow prevention device  4  permits flow from the tank  3  to the injection termination  1  and cable  7 , and prevents flow from the injection termination  1  and cable  7  to the tank  3 , the pressure relief device  5  prevents flow from the tank  3  to the injection termination  1  and cable  7 , but allows flow from the injection termination  1  and cable  7  to the tank  3  but only when the pressure in the injection termination  1  or cable  7  exceeds a predetermined pressure limit. Check valves are one example of the back-flow prevention device  4  that may take may forms.  FIG. 1  illustrates a springless, ball-type check valve as the back-flow prevention device  4 . 
     The pressure relief device  5  is illustrated as a spring-biased, ball-type check valve. The spring biases the ball against a valve seat, thus closing the valve, but will open when the fluid pressure on the left side of the ball exceeds the force of the spring pushing the ball against the valve seat. The spring may have a predetermined pressure limit, which, if exceeded will cause the valve to open. However, other implementations of the back-flow prevention device  4  and pressure relief device  5  are possible 
     The system of  FIG. 1  is designed to operate in the following manner. Under some circumstances, because of high daytime temperatures or numerous other factors, the pressure within the injection termination  1  or the cable  7 , may begin to build such that the pressure in the cable  7  or injection termination  1  exceeds the pressure at the tank  3 . In a system without a back-flow prevention device  4 , the fluid may change directions, leading to contamination present in the power cable  7  to travel through the injection termination  1 , and through the line  2 , and result in contamination of the tank  3 . 
     Because these contaminants may be electrically conductive, it is possible that the tank  3  may become energized. The embodiment of  FIG. 1  is designed to prevent energizing equipment, such as tank  3 , by providing the check valve  4  in line  2  that permits the flow of remediation fluid from tank  3  to injection termination  1  and cable  7 , but prevents the flow of fluid from cable  7  and injection termination  1 , through line  2 , to tank  3 . The system of  FIG. 1  is also designed to relieve overpressure in the cable  7  or injection termination  1  by the installation of the pressure relief device  5 , which is capable of opening at a predetermined pressure limit to relieve the pressure in injection termination  1  or cable  7  to prevent damage to the injection termination  1  or the cable  7 . 
     The system is shown relieving pressure to tank  3 , but other configurations are possible. The pressure relief device  5  may be a burst disk, a poppet valve or any other suitable device that fails or opens at a predetermined pressure limit to relieve an overpressure situation and permit fluid to back-flow to the fluid feed tank  3 , but under limited situations. In one embodiment, the pressure relief device  5  may release at a pressure of about 15 psia to about 18 psia. In another embodiment, the pressure relief device  5  may release at a pressure of about 30 psia to about 35 psia. Although certain pressure ranges have been described, any suitable pressure limit may be designated as the high pressure limit for pressure relief device  5 . 
     Referring to  FIG. 2 , in another embodiment of the invention, the back-flow prevention device  4  and the pressure relief device  5  are installed at the inlet  6  of the line  2  within the fluid feed tank  3 , preventing back-flow of fluid from returning to the fluid feed tank  3 , unless the pressure at the pressure relief device  5  exceeds the designated high pressure limit. 
     Referring to  FIG. 3 , in another embodiment of the invention, the back-flow prevention device  4  and pressure relief device  5  are installed at the injection termination  1 . Representative implementations of this configuration are described below. The back-flow prevention device  4  and pressure relief device  5  prevent the back-flow of fluid from the injection termination  1  and cable  7  to the feed tank  3 , unless the designated high pressure limit of the pressure relief device  5  is exceeded. 
       FIG. 4  illustrates an injection termination  410  and injection plug  420  formed in accordance with one embodiment of the present invention. Injection termination  410  is adapted to introduce remediation fluid into power cable  402 . Power cable  402  includes a conductive core  404  surrounded by an insulation layer  406 . The conductive core  404  includes a plurality of electrically conductive strands  413 . Although a plurality of conductive strands  413  is preferred, a cable  402  having a single conductive strand is also within the scope of the present invention. Further, although the injection termination  410  is illustrated as a load-break termination, other types of terminations, such as tee-body or splice-type terminations which occur at cable junctions, are also within the scope of the present invention. 
     The injection termination  410  includes a fluid chamber  412  and an injection port  414 . The injection port  414  permits the introduction of the remediation fluid into the cable  402  while the cable  402  is energized. Remediation fluid is injected through the injection port  414  and into the fluid chamber  412  by a canal  415 , thus, allowing fluid to enter the cable&#39;s  402  insulation through the interstitial spaces between the cable strands  413 . 
     Still referring to  FIG. 4 , remediation fluid enters the injection port  414  by way of the injection plug  420 . The injection plug  420  includes a conduit  424  and a stem portion  422 . In operation, the stem portion  422  is inserted into the injection port  414  to allow for the introduction of the remediation fluid into the fluid chamber  412 . Remediation fluid is fed to injection plug  402  via line  2  coming from fluid feed tank  3 . 
     Injection termination  410  includes a back-flow prevention device and a pressure relief device. In the embodiment of  FIG. 4 , the back-flow prevention device takes the form of a ball  430  biased by spring  436  to seat ball  430  against an enlarged diameter portion of canal  415 . When the fluid pressure on the left side of ball  430  exceeds the spring force of spring  436 , the ball  430  is moved away from the closed position, and allows fluid to pass by the ball  430  and exit through opening  434  leading to fluid chamber  412 . The stem portion  422  of injection plug  420  is short so as not to force open the ball valve during fluid delivery. 
     Thus, this embodiment is suited to prevent back-flow during delivery of fluid. During delivery of fluid, the ball-type, check value  430  remains open and may return to the closed position when pressure fluctuations cause the pressure in chamber  412  to be greater than the pressure at the injection port  414 . Thereby, preventing fluid with contaminants including electrically conductive materials from entering the injection port  414  and line  2 , and creating a non-conductive barrier between the conductive core  404  and a zero or lower voltage potential or “ground.” 
     An alternate configuration of a ball-type, check valve may be provided without the spring  436 , such as in a vertical configuration, so that the force to seal the ball against the valve seat is provided by gravity. 
     Injection termination  410  includes a pressure relief device. In one implementation, a port, such as port  438 , may be provided in the injection termination  410 . Port  438  is in communication with and experiences the pressure within fluid chamber  412 . A burst disk  432  (or rupture disk) is provided at one opening of port  438 . Burst disk  432  may burst at a predetermined pressure setting, depending on the thickness of the burst disk material, for example. Line  440  is connected to the opposite side of burst disk  432  that is opposite to port  438 . Upon rupturing of the burst disk  432 , fluid may be carried through line  440  back to tank  3 , or alternatively any destination designed to accept burst disk  432  discharges. 
       FIG. 5  illustrates another embodiment of an injection termination  510  constructed in accordance with the present invention. An injection plug is not shown, but may be an injection plug similar to injection plug  420  of  FIG. 4 . The injection plug is not shown for brevity. The injection termination  510  may be identical in materials and operation to the first embodiment described above with the exception that the back-flow prevention device is implemented as flap valve  530 . Injection termination  510  is adapted to introduce remediation fluid into power cable  502 . Power cable  502  includes a conductive core  504  surrounded by an insulation layer  506 . The conductive core  504  includes a plurality of electrically conductive strands  513 . Although a plurality of conductive strands  513  is preferred, a cable  502  having a single conductive strand is also within the scope of the present invention. Further, although the injection termination  510  is illustrated as a load-break termination, other types of terminations, such as tee-body or splice-type terminations which occur at cable junctions, are also within the scope of the present invention. 
     In one embodiment, the flap valve  530  is suitably located at the intersection of the injection port  514  and the fluid chamber  512 . The flap valve  530  may be integrally connected to the injection termination  510  by a live hinge, or may be fastened to the injection termination  510  by a mechanical hinge  531 . In one embodiment, the flap valve  530  is normally biased in the closed position. 
     Remediation fluid may be fed from tank  3  through a line to an injection plug (not shown) that is then inserted into injection port  514  to introduce a remediation fluid into fluid chamber  512 . As remediation fluid is introduced into the injection port  514 , the flap valve  530  is forced open by the fluid pressure of the incoming remediation fluid. The flap valve  530  is not physically opened by the stem portion of the injection plug, therefore, this embodiment prevents the back-flow of fluid during delivery and not just after discontinuing delivery, as would be the case with an injection plug that props the flap valve open. During delivery of fluid, the flap valve  530  remains open and may return to the closed position when pressure fluctuations cause the pressure in chamber  512  to be greater than the pressure at the injection port  514 . Thereby, preventing fluid with contaminants including electrically conductive materials from entering the injection port  514 , and creating a non-conductive barrier between the conductive core  504  and a zero or lower voltage potential or “ground.” Injection termination  510  also includes port  540  that is open to fluid chamber  512  Port  540  has a pressure relief device, such as burst disk  542  connected thereto. Burst disk  542  is set to relieve the pressure within chamber  512  at a predetermined pressure setting. If burst disk  542  ruptures, the fluid may be vented through line  544  to return to tank  3 . Alternatively, fluid may be routed to any suitable destination. 
     While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.