US 3252085 A
Description (OCR text may contain errors)
y 1966 H. c. WHITEKETTLE. JR 3,252,035
METHOD OF LOCATING COAXIAL CABLE ARCING FAULTS UTILIZING A MAGNETIC BLOWOUT PRINCIPLE Filed Sept. 12, 1965 VOLTAGE SENSING DEVICE HIGH VOLTAGE SOURCE INVENTOR. H6. WH/TEKETTLE JR.
ATTORNEY United States PatentOH 3-,Z5Zfi85 Patented ,May 1 7, 1-966 3,252,085 1 METHOD OF LOCATHNG COAXIAL CABLE ARCIN G FAULTS UTILIZING A MAGNETIC BLGWOUT PRINCELE Howard C. Whitekettlc, .lla, Cockeysville, Md., assignor to Western Electric Company, Incorporated, New York, N.Y., a corporation of NewYork Filed Sept. 12, 1963, Ser. No. 308,554 4 Claims. (Cl. 324-52) This invention relates to methods of locating faults in coaxial cables and particularly relates to methods of locating such faults utilizing a magnetic blowout principle for extinguishing arcing faults existing between the inner conductor and the outer conductor of the coaxial cable.
In the manufacture of certain coaxial cable, a center metallic conductor is surrounded by an outer conductor with a space existing between the outer surface of the inner conductor and inner walls of the outer conductor. Frequently, imperfections appear in the surfaces of the conductors utilized in cable. When a high voltage is applied between the inner and outer conductors, a breakdown, results in the area of imperfection whereby a current-carrying arc stretches between the imperfection and the adjacent surface of the opposed conductor. Such imperfections must be detected and correctedbefore the cable can be utilized. In some instances, an ear detectiOn system is utilized which is extremely tedious and time-consuming and does not always locate precisely the trouble area.
It is, therefore, an object of this invention to provide a method of locating arcing faults in coaxial cables.
With this and other objects in view, the present invention contemplates a method of locating faults in coaxial cables by producing an arc between the inner and outer conductors in the area of the cable fault, thereafter causing relative movement between a produced magnetic field and successive axial portions of the cable in the area of the arcing fault to extinguish the arc and sensing the extinguishment of the arc to determine the location of the fault relative to the magnetic field.
In a preferred embodiment of the invention in locating an arcing fault in a coaxial cable, a high potential of a voltage source is applied between the inner and outer conductors of the cable whereby an arc occurs between the conductors in an area of conductor imperfection. The arc presents a low impedance path to current flow in the system whereby a substantial voltage drain results upon the high voltage source. A voltage-sensing device is utilized to analyze the voltage condition of the faulted cable when the arc is extended between the inner and outer conductors. Thereafter, the cable and a magnetic field are moved relatively so that the arc is extinguished by the magnetic blowout principle. The voltage-sensing device detects a voltage change in the circuit when the arcing fault is extinguished, thereby indicating the loca-.
tion of the fault.
Other objects and advantages of this invention will be more readily understood from the following detailed description of the method embodying the principles of the invention when read in conjunction with appended drawings in which:
FIG. 1 is a view showing the for locating an arcing fault in a the magnetic blowout principle;
arrangement of a system coaxial cable embodying FIG. 2 is a perspective view showing an arcing fault in a coaxial cable and the relation between magnetic fields surrounding the arc, and
FIG. 3 is a view showing an arrangement of magnets for applying sequentially, different magnetic fields in different directions relative to the arcing fault.
The method of extinguishing an arc utilizing a magnetic blowout principle involves an interaction between mag netic fields resulting from two different sources. When an are results between two metallic surfaces having a high potential applied therebetween, a current flow results within the arc, thereby developing a magnetic field about the arc in the same manner in which a magnetic field is developed about a conductor having current flow therein.
If the arc is placed in a magnetic field which extends through the surrounding area of the arc, an interaction results between the magnetic field developed about the are by current flow passing therethrough and the second magnetic field wherein a cancellation of the flux occurs on one side of the arc due to the opposed magnetic lines of force. An additive effect results on the opposite side of the are where the magnetic lines of force are going in the same direction. This action has a tendency to move the arc toward the weak side wherein the lines of force are being cancelled. Subsequently, the arc is stretched to such a point that the potential existing between the two metallic surfaces is insuificient to sustain the arc in the stretched position. Since such arcs occur between the inner and outer conductors of the coaxial cable where an imperfection appears on the surface of such conductors, the magnetic blowout principle can easily be utilized in the locating of faults existing in the areas of the imperfections.
Initially, acompleted reel of coaxial cable is subjected to a high voltage test wherein a sensing device determines whether or not an arcing fault exists within the cable. In the event an arcing fault exists in the cable, the cable is connected to a system as shown in FIG. 1 wherein a reel 11 supports a coaxial cable 12 having the fault. A reel 13 is spacially positioned from the reel 11 for taking up the faulted cable as the fault locating operation is being conducted. A shaft 14 extends centrally from, and is attached for rotation with, the reel 11. A slip ring 16 is mounted for rotation on, but insulated from, the shaft 14 and is provided witha clip 17 which is attached to a center conductor 18 of the coaxial cable 12. An outer con ductor 19 of the coaxial cable 12 is connected to one of the flanges of the reel 11 wherein the flange is connected to ground potential for the system. A brush 21 is positioned adjacent to the slip ring 16 and is further connected to a high D.C. voltage source 22 and a voltage-sensing device 23 which is capable of sensing load changes in the system in terms of voltage. It is noted that the high voltage source 22 and the voltage-sensing device 23 are each connected to the ground potential. A pair of spacially opposed electromagnets 24 and 26 are positioned between the reels 11 and 13 and are connected to an electric potential source 29 to provide a magnetic field between the spaced ends of the electromagnets.
As the arc occurs, the voltage-sensing device 26 registers a low voltage reading which is lower than the level of voltage of the high voltage source 22, thereby indicating that an arcing load has been placed upon the system.
The coaxial cable 12 is then passed between the opposed electromagnets 24 and 26 and through the magnetic field 3 developed between the magnets. As the arcing fault passes within the area of the magnetic field developed by the e-lectro'magn'ets 24 and 26, a reaction will occur as previously described wherein the arcing fault will be extinguished. When the arc is extinguished, the drain on the high voltage source 22 is substantially relieved whereby the voltage-sensing device 23 registers a high voltage reading substantially equal to the high voltage of the source 22 to indicate the load change in the circuit, thereby indicating that the arc has been extinguished. By observing the voltage-sensing device 23 with respect to the passage of the cable 12 between the electromagnets 2'4 and 26, an arcing fault can be located by such means as marking the cable or reversing the cable by reverse jogging the cable driving mechanism to position the arcing fault directly between pole pieces 27 and 28 of electromagnets 24 'and 26, respectively. As shown in FIG. 2, the center conductor 18 of the coaxial cable 12 is held in a spaced relation relative to the outer conductor 19 by axially displaced, nonconductive discs 31. Further, the pole pieces 27 and 2-8 are shown positioned about the outer surface of the coaxial cable 12 to provide the second magnetic field which reacts with the first magnetic field developed by'the current flow through the arcing fault whereby the arc is extinguished.
2, can be mechanically rotated about the cable 12 to extinguish the are as previously described.
In the event the coaxial cable should be provided with an outer shield, such as a steel tape Wrapped helically therearound, the second magnetic field must be sufficiently strong to penetrate the steel tape and to produce the concentrated field within the area of the arcing fault. In addition, in order to determine the direction in which the arc will be stretched, should it be necessary, Flemings Left Hand Motor Rule can be'used where each of three digits of the left hand, the thumb, forefinger and middle fingerare extended at right angles relative to the other two digits. The middle finger is pointed in the direction of the current flow through the arc, the forefinger is pointed in the direction of the flux of the second magnetic field and the thumb is pointed in the direction of the stretch of the arc.
It is to be understood that the above-described methods are simply illustrative of the principles of the invention;
Other methods may be devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.
As further shown in FIG. 2, an are 32 extends from I the inner conductor 1-8 to the outer conductor 19, whereby a magnetic field is developed thereabout represented by the arcuate arrow. -As the pole pieces 27 and 28 of the electromagnets 24 and 26, respectively, are positioned as shown, a magnetic field extends from pole piece 2'7 to pole piece 28 as indicated by the straight arrows on each side of the are 32. Thus, it is seen that the two magnetic fields are additive on the left side of the are 32 and are opposed on the right side of the arc and will, therefore,
cancel to the point that the total field on the right side of the arc is weaker than that on the left side of the are. As the weakening of the field occurs, the central portion of the are 32 will stretch to the right until the high potential applied between the inner and outer conductors 18 and 19, respectively, is insufficient to sustain the arc in the stretched condition. As this magnetic blowout ofthe are 32 occurs, the voltage-sensing device 23 indicates the removal of the arcing load by detecting the voltage change. The relative position of the cable 12 and the pole pieces 27 and 28 may be observed at this time to reveal the section of cable containing the undesirable fault.
Referring to FIG. 3, another embodiment is shown wherein a plurality of the opposing pole pieces 27 and 28 are staggered along the length of the coaxial cable 12 so that an effective rotating magnetic field is developed to insure proper reacting position of the second magnetic field relative to the magnetic field developed about the arcing fault. As the arcing fault passes through each successive magnetic field provided by the respective staggered pole pieces 27 and 28, one of the magnetic fields will be properly positioned to react with the magnetic field developed about the are 32. In this manner, the system has at least one magnetic field which reacts with the are 3-2 field to indicate the location of the fault. It is noted that adjacent staggered pole pieces 27 and 28 are sufliciently spaced so that no magnetic interaction occurs between adjacent pole pieces. However, the entire staggered arrangement can be confined in a relatively small area, thereby confining the fault locating to a short cable length. Hence, as the arcing fault passes through the staggered magnetic fields, the arc is subjected effectively to a rotating magnetic field which extinguishes the arc in the manner previously described. Addition-a1 magnets could be included in the staggered arrangement as well as the provision of other arrangements of the magnets without departing from the scope of the invention. Further, the pole pieces 27 and '28, as shown in FIGS. 1 and What is claimed is: 1. A method of locating an arcing fault in a coaxial cable, which comprises the steps of:
applying a high voltage potential between the inner and outer conductors of the coaxial cable whereby an are results between the inner and outer conductors in an area of imperfection, producing a magnetic field, passing axially successive portions of the cable through the magnetic field whereby the arc is extinguished when the arc passes adjacent to the field, and sensing the voltage changes in the coaxial cable whereby the extinguishment of the arc is related to a sensing of a voltage change to determine the location of the 'arcing fault-the location of the fault being in that portion of the cable adjacent to the magnetic field at the moment the arc is extinguished. 2. A method of locating arcing faults in coaxial cable, which comprise the steps of:
producing an are between the inner and outer conductors of the cable in the area of the fault, producing a magnetic field,- causing relative movement between the magnetic field and successive axial portions of the cable in the area of the arcing fault to extinguish the arc, and sensing the extinguishment of the arc to determine the location of the fault said fault being in that portion of the cable adjacent to the magnetic field at the moment the arc is extinguished. 3. A method of locating an arcing fault in a coaxial cable, which comprises the steps of: j
applying a high voltage between the inner and outer conductors of the cable, producing a rotating magnetic field, passing axially the portion of the cable with the arcing fault through the rotating magnetic field whereby the arc is extinguished when the arc passes adjacent to the field, and sensing the extinguishment of the arc to locate the fault the location of the fault being adjacent to the rotating magnetic field at the moment the arc is extinguished. 4. A method of locating an arcing fault in a coaxial cable, which comprises the steps of:
producing a current-carrying are between the inner and outer conductors of the cable at the point of an imperfection in the cable wherein the arc has a magnetic field developed thereabout, producing a magnetic field having lines of force substantially parallel to the lines'of force developed about the current-carrying arc, moving relatively successive axial portions of the cable and the produced magnetic lines of force whereby 5 6 produced magnetic lines of force cancel magnetic portion of the cable adjacent to the produced maglines of force developed on one side of the arc netic lines of force at the moment said are is exand support magnetic lines of force developed on tinguished.
the opposite side of the are so that the arc is moved to the weak side thereof and subsequently extin- 5 guished, and WALTER L. CARLSON, Primary Examiner. sensing the extinguishment of the arc to determine the G. R STRECKER Assistant Examiner.
location of the fault the location being within the No references cited.