Patent Publication Number: US-6211764-B1

Title: Waterproof current transformer

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to current sensing devices for electrical systems, and more particularly to underwater magnetic core assemblies for use therein. 
     Electrical power distribution systems may require the use of a variety of circuit condition monitoring devices to facilitate the detection and location of system malfunctions. Such devices include manually and automatically resetting current fault indicators, such as those manufactured by E. O. Schweitzer Manufacturing Co., and described in U.S. Pat. Nos. 4,288,743, 4,086,529 and 3,676,740 of the present inventor, as well as voltage monitoring devices, such as described in U.S. Pat. Nos. 4,251,770, 4,152,643, 4,263,350 and 4,550,288 of the present inventor. The devices are typically either of the test point mounted type for mounting on a system test point, or of the clamp-on type, for clamping directly onto a cable of the system. However, at times these devices may need to be somewhat remotely located from the cable of the system. 
     Clamp-on type fault indicators typically derive their operating power directly from current flow in the monitored conductor. In such current-reset fault indicators a magnetic core assembly is generally required to provide a concentrated magnetic flux from current flow through the conductor. A magnetic winding in magnetic association with the core assembly converts the concentrated flux to an electrical current which is rectified for use in powering the fault indicator. 
     For optimum flux pick-up it is desirable that the magnetic core assembly be in the form of a closed loop which completely encircles the conductor. However, to enable the core assembly to be installed and removed from the conductor, it is necessary that connection means be provided by which the loop can be opened. One form of magnetic core assembly which has proved particularly successful in this regard is described in U.S. Pat. No. 3,725,832, which issued to the present inventor on Apr. 3, 1973. In this construction a circular magnetic core is provided which comprises a plurality of laminations of pre-stressed oriented silicon steel secured together near their juxtaposed ends so as to form an annular loop around a monitored conductor. The ends are provided with interlocking tongue-and-groove type members formed of corrosion resistant magnetic material which allow the loop to be opened for installation and removal on a conductor. 
     One requirement of closed loop magnetic core current-reset fault indicators having magnetic sensing means such as a reed switch or magnetic sensing coil for fault detection is that adequate coupling be maintained between the magnetic sensing means and the monitored conductor. Because there are only a limited number of different sized cables that are left underwater, the present invention is designed to emcompass one of these dimensions whereby the monitored cable is always maintained in close proximity to the magnetic sensing means of the fault indicator. 
     Similarly, closed loop magnetic core assemblies have been susceptible to being inadvertently pulled off the monitored conductor, as when force is exerted on leads connected to the circuit module. But again, because the present invention is designed for a specific size of underwater electrical cable and in effect produces a locked engagement, removal is possible only by deliberate manipulation of the core assembly. 
     The most significant drawbacks of prior art closed loop magnetic core assemblies for use with underwater electrical cable is their corrosive and/or collection of sedimentary deposits properties. On the one hand if the assembly were to corrode and subsequently breakdown via an underwater chemical reaction, then the cable could not be maintained in close proximity to the magnetic sensing means. Conversely, if sediments were to deposit on the assembly it could effect current flow as well as prevent the assembly from being removed from its original attachment and placed downline or on another cable altogether. The present invention obviates these problem&#39;s by providing a construction whereby the magnetic core assembly is fully submerseable for an indefinite amount of time while immune from collecting harmful deposits and/or corroding. 
     Accordingly, it is a general object of the present invention to provide a new and improved underwater current transformer. 
     It is a more specific object of the present invention to provide a new and improved clamp-on type underwater current transformer having an improved magnetic core assembly. 
     It is another object of the present invention to provide an underwater current transformer which is less susceptible to being inadvertently pulled free of the monitored cable. 
     It is another object of the present invention to provide an underwater current transformer which is fully submerseable for an indefinite amount of time while immune from collecting harmful deposits and/or corroding. 
     It is another general object of the present inventin to provide a new and improved underwater current transformer for use in fault indicators and the like. 
     SUMMARY OF THE INVENTION 
     A removable current transformer for installation on an electrical conductor located underwater includes a plurality of elongated strips of resilient magnetic material arranged side-by-side and joined at the ends thereof to form a magnetic core. The core is formed into a closed loop and has four sides being generally rectilinear and dimensioned to receive the electrical conductor. One side includes an interlocking connection means for establishing a separable connection between segments of that side. One side includes a current carying means for supplying a current to a remote condition monitoring device. The transformer includes a means for resisting moisture so as to enable said core to be submersed underwater. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which: 
     FIG. 1 is an elevated frontal view of the underwater current transformer of the present invention installed on an electrical conductor. 
     FIG. 2 is an elevated side view of the underwater current transformer of FIG.  1 . 
     FIG. 3 is a perspective view of the sleeve and clamping mechanism of the preferred embodiment of the present invention. 
     FIG. 4 is an elevated frontal view of the underwater current transformer of the present invention in the process of being installed on an electrical conductor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the Figures, and particularly to FIG. 1, an underwater current transformer  10  constructed in accordance with the principles of the present invention is shown attached to the outer surface of cable  12 . This electrical cable  12  may include a central conductor  14 , a concentric insulating layer  16 , and an electrically-grounded rubber outer sheath  18 . 
     Basically, transformer  10  includes a magnetic core assembly  20  for attaching the transformer to a monitored conductor such as cable  12  and for deriving the necessary magnetic flux in sufficient concentration for powering any circuitry which may be coupled to the transformer downline. The core assembly is preferrably formed as a closed loop of generally rectangular configuration so as to completely encircle cable  12 , and includes connection  22  means by which the core can be opened to facilitate installation on or removal from a monitored conductor. 
     The core assembly  20  of the current transformer  10  is seen to consist of a plurality of individual strips or laminations  24  formed of oriental silicon steel arranged side-by-side in a generally rectangular closed-loop configuration. The core assembly is preferably encapsulated in a layer  26  of resin epoxy insulating material which also prevents the core assembly from corroding or forming sedimentary deposits while immersed underwater. The rectangular configuration includes a generally rectilinear first or left side portion  28 , a generally rectilinear second or right side portion  30  opposed to first portion  28 , a generally rectilinear third or bottom portion  32 , and a generally rectilinear fourth or top portion  34  opposed to third portion  32 . The closed loop consisting of side portions  28 - 34  includes connection point  22  at the juncture of the top portion  34 . 
     In accordance with the invention, the top portion  34  of the core assembly  20  consists of an upper half  36  and a lower half  38 . When the assembly is installed on an electrical conductor, these halves are clamped together via a sleeve  40  and at least are clamp  42 . Elements  36 - 42  of the preferred embodiment encompass the preferred connection means  22 . 
     So installed, as shown in FIG. 1, the magnetic core assembly  20  derives current due to the magnetic flux of the cable so as to power any circuitry which may be used downline from the transformer to monitor the cable. This current flows to such circuitry via connector line  44  which is electrically coupled to the core. FIG. 1 shows a gap  46  in the line  44  and then an extension  48 . This gap  46  represents an inexact distance between the core assembly and some remote circuitry. A positive lead  50  and a negative lead  52  are contained within the line, each including a protective sheath  54 . A single clamp  56  holds the line  44  within the nipple  58  extending from the bottom portion  32 . This clamp  56 , as with clamps  42 , protect those elements within the core while its submersed. 
     The side illustration of FIG. 2 better depicts the functionality of the clamps of the preferred embodiment. The ring  60  of the clamp  42  is shown as it is compressed against the sleeve  40 . The exploded perspective view of FIG. 3 shows the clamp  42  independent of sleeve  40  and in its open and loose position. When the tight seal of the present invention is desired, the ring  60  is passed over sleeve  40  and clamped down. Such clamping is accomplished via bolt  62  and slots  64 . When bolt  62  is tightened within its housing  66 , it transverses the slots  64  and this decreases the circumference of the ring  60  thereby clamping the sleeve tight. When submersed, this tight fit prevents any corrosion or deposition of sedimentary products within the core. 
     The method of installation of an underwater current transformer incorporating the magnetic core assembly  20  on an electrical cable  12  to be monitored is illustrated in FIG.  4 . Installation is most readily accomplished by the manual separation of the top portion. Upon the loosening of the clamps  42  over the sleeve  40 , the installer can manually separate the connecting means  22  to allow a cable  12  to pass through the gap formed by such separation. Once the cable has passed through this gap, the connecting means  22  may once again be tightened via clamps  42 . 
     In its installed position, as shown in FIG. 1, the cable  12  is essentially locked into place as the inside surface of the four sides of the rectangular configuration of the core assembly frictionally engaged it. When in this locked position, it can be seen, as compared to FIG. 4, that the upper half  36  and the lower half  38  of the top portion  34  are butted against each other and secured in place via connecting means  22 . Because the inside surfaces  68  of the upper half  36  and the lower half  38  are not encased with the resin epoxy (FIG.  4 ), when they are matted (FIG. 1) and the connecting means is engaged, the core assembly  20  is a true closed loop encompassed with resin epoxy with such a structure, the current produced by the magnetic flux in the cable is at its optimum. 
     The present invention is particularly useful in the monitoring of underwater electrical cables. This monitoring may include but is not limited to the utilization of fault current indicators and voltage indicators. These devices may themselves be positioned underwater in close proximity to the present current transformer, or they may be coupled to the transformer and remotely located so as to enable facilitated monitoring. In either case, these devices will be typically powered and/or connected to the current transformer via leads  50  and  52 . 
     While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that charges and modifications may be made therein without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.