Abstract:
A holder for a current sensor having separable portions with inner surfaces forming an opening and opposing outer surfaces having a groove to accommodate a current sensing coil. The holder includes flexible members on the portions and extending toward the opening such that the flexible members can hold a power cable substantially centered within the opening and concentric with the current sensing coil. The portions are joined together with a hinge pivotally mounted between them at one end and a releasable clasp joining them together at another end, providing for ease of installation around the power cable by hand and without requiring tools or additional fasteners.

Description:
BACKGROUND 
       [0001]    Rogowski type current sensors are used to measure current on power cables for underground applications. Managing a way to attach these sensors in the field and keeping the cable highly concentric in the holder can be challenging. The existing designs are burdensome for attachment by field personnel and usually require other components, such as tie wraps, for mechanical attachment and which makes it difficult to hold in a correct orientation on the power cable. 
       SUMMARY 
       [0002]    A holder for a current sensor, consistent with the present invention, includes first and second portions at least partially separable from one another and each having an inner surface, an opposing outer surface, and a groove on the outer surface. The inner surfaces form an opening through the first and second portions, and the grooves in the outer surfaces join one another. The holder also includes a plurality of flexible members on the first and second portions and extending toward the opening such that the flexible members can hold a line conductor substantially centered within the opening. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, explain the advantages and principles of the invention. In the drawings, 
           [0004]      FIG. 1  is a perspective view of the holder; 
           [0005]      FIG. 2  is a perspective view of the holder as disassembled; 
           [0006]      FIG. 3  is a perspective view of the holder partially assembled for installation around a line conductor; 
           [0007]      FIG. 4  is a side view of the holder in use positioned around a line conductor; and 
           [0008]      FIG. 5  is a perspective view of an alternate embodiment of a portion of the holder with recess for accommodating a circuit board. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Embodiments of this invention cover a holder design for Rogowski type current sensors or other sensors. The holder allows for self-alignment and concentric positioning for various size low and medium voltage cables within grade level and underground utility applications. The holder is hinged on one end and provides a snap feature clasp on the other, which enables easy hands-on attachment with bare hands, or utility personnel with gloves, and without tools or additional aligning pieces. The holder has flexible features which allow for tension and the ability to self-align to a variety of different power cable diameters, while keeping its concentricity to within a tight tolerance, which is an important factor in calibration and thus accuracy of the measurement from the sensor. The holder can self-align to the power cables without requiring any other type of alignment parts such as tie-wraps or springs. The holder also has an integral feature for removing and attaching the current sensor with minimal intrusion or damage to the sensor coil. 
         [0010]      FIG. 1  is a perspective view of the holder with a current sensing coil.  FIGS. 2 and 3  are, respectively, perspective views of the holder as disassembled and as partially assembled for installation around a line conductor. As shown in  FIGS. 1-3 , the holder includes a portion  12  and a portion  14  that fit together. Portion  12  includes an inner surface  29 , an opposing outer surface, and flexible members  21 ,  23 ,  24 , and  25  on an edge of portion  12  adjacent inner surface  29 . Portion  14  includes an inner surface  30 , an opposing outer surface, and flexible members  22  and  26  on an edge of portion  14  adjacent inner surface  30 . The flexible members can include a void, for example void  28  in flexible member  21 , to obtain a longer flexure length of the flexible members. Portion  12  includes a groove  16 , and portion  14  includes a groove  18  that joins with groove  16 . Grooves  16  and  18  together form a continuous groove within or on the outer surfaces of portions  12  and  14  to accommodate a current sensing coil  20 . Portions  12  and  14  include a hinge formed by curved fingers  32  on an end of portion  14  that mate with posts  31  on and end of portion  12 . Portions  12  and  14  also includes a releasable clasp formed by latching fingers  34  on an end of portion  12  that releasably interlock with extended portions  33  forming apertures on an end of portion  14 . Portions  12  and  14  can be completely separable at the hinge and clasp, as shown, or alternatively portions  12  and  14  can be partially separable by having a fixed hinge and a clasp that releasably interlocks. 
         [0011]      FIG. 4  is a side view of the holder in use positioned around a line conductor. In particular, inner surfaces  29  and  30  of portions  12  and  14 , respectively, form an opening, and the flexible members hold a line conductor  36  substantially centered in the opening. As shown, flexible members  21 ,  22 , and  23  hold line conductor  36  on one side of portions  12  and  14 , and flexible members  24 ,  25 , and  26  hold line conductor  36  on the other (opposing) side of portions  12  and  14  in a similar manner. The flexible members can hold line conductors of varying sizes in the opening, as illustrated by dashed line  37  representing a line conductor with a larger diameter than line conductor  36 . By holding line conductor  36  substantially centered within the opening, line conductor  36  is also held substantially concentric with current sensing coil  20 . 
         [0012]      FIG. 5  is a perspective view of an alternate embodiment of a portion of the holder with a recess for accommodating a circuit board. In particular, portion  14  can have a recess  38  with a planar bottom surface  39  for accommodating a circuit board  40 . Current sensing coil  20  in groove  18  would be positioned over circuit board  40  through recess  38 . Portion  12  can in addition, or alternatively, include a recess for accommodating a circuit board. 
         [0013]    The following are exemplary materials and configurations for the holder described herein. 
         [0014]    The two portions ( 12 ,  14 ) that fit together and the flexible members ( 21 - 26 ) can be molded with a thermoplastic type of material. The flexible members can be molded together with the two portions, for example using the same mold. Alternatively, the flexible members can be secured to the two portions after formation, such as molding, of the two portions; for example, the flexible members can be pressed on or bonded to the two portions. 
         [0015]    A conductive wire or thin cable can be used for the current sensing coil in the groove around the outer surfaces of the two portions. The line conductor is typically a power cable. 
         [0016]    The holder preferably has at least three flexible members on each side with the flexible members preferably evenly spaced apart to make the holder self-aligning with respect to various size line conductors. The holder can have more than three flexible members on each opposing side. Having the line conductor centered or held in a concentric manner within the opening of the holder and close to the current sensing coil is important for accurate readings from a current sensor coupled to the coil. The flexible members can have sufficient flexibility and tension to hold the line conductor substantially centered in the opening formed by the two portions and preferably have enough flexibility and tension to hold line conductors of different diameters substantially centered. 
         [0017]    Holding the line conductor substantially centered involves two critical positioning variables, an angle and a position of the holder (and hence the current sensing coil) with respect to the line conductor. The phrase “substantially centered” means the line conductor is sufficiently centered within the holder to for provide an accurate reading from the current sensing coil in the holder. As one example and to provide for highly accurate current sensor readings, the phrase “substantially centered” can mean that the line conductor is held with an angle tolerance of less than two degrees with respect to the holder and is concentric in the holder within five millimeters of the line conductor diameter. 
         [0018]    The opening formed by the inner surfaces of the two portions is preferably circular as shown. Alternatively, the opening can have other shapes, and the inner surfaces can have a series of planar surfaces rather that curved surfaces as shown. The outer surfaces of the two portions preferably form a curved surface concentric with circular opening formed by the inner surfaces in order to hold the current sensing coil substantially concentric with the line conductor held in the opening. 
         [0019]    The circuit board can be a rigid or flexible circuit with a sensor and possibly a short range wireless transmitter. The sensor can monitor an environmental condition, for example, and generate sensor data providing an indication of the monitored condition. The short range wireless transmitter can send the sensor data periodically to a local receiver that can have a network connection for further transmitting the sensor data to a utility company or other entity. The sensor can be implemented with sensors to monitor one or more of the following conditions: humidity; temperature; sound; smoke; and gas. The temperature on the line conductor is important to sense and monitor for possible thermal break down and degradation of components. The circuit board can have a power harvesting circuit to self-power the sensor by power harvested from the line conductor. The circuit board can also be used for asset tagging or asset management, which is a way to identify the properties and active status of the line conductor or cable. In particular, the circuit board can have a memory for storing one or more of the following for the cable: an identifier or name; a type of the cable; a position of the cable; destinations the cable connects to; maintenance history; and whether the cable is live or not. This asset management information can be read, or transmitted, from the circuit board in the same manner as transmission of the sensor data, for example using the wireless short range transmitter. 
         [0020]    An example of a current sensor is disclosed in U.S. patent application Ser. No. 14/613,589, entitled “Electronic Integrator for Rogowski Coil Sensors,” and filed Feb. 4, 2015, which is incorporated herein by reference as if fully set forth. 
         [0021]    An example of a power harvesting circuit is disclosed in U.S. patent application Ser. No. 14/661,468, entitled “Inductive Power Harvester with Power Limiting Capability,” and filed Mar. 18, 2015, which is incorporated herein by reference as if fully set forth.