GB557088A - Improvements in methods and apparatus for locating faults in electric cables - Google Patents

Abstract

557,088. Detecting and locating faults. LOVE, A., and CONRADI, E. S. May 1, 1942, No. 5919. [Class 37] A break in a conductor is located by applying between its free ends an alternating or intermittent potential, earthing one free end, and traversing the conductor with a search device having an open circuit whereof one end is inductively coupled with the conductor by the search device and the other end is coupled to earth. The apparatus shown includes means for detecting discontinuous conductors in a cable and also for locating the break in discontinuous conductors. In series with a battery 18 is the primary coil 19 of an iron-cored transformer 20 and a make- and-break device 14 having a resilient armature 114 and an earth connection 16. A condenser 12 and resistance 13 form a spark-suppressing circuit. A switch 22 has three contacts 23, 24, 25, the last of which is connected to a terminal 28. The secondary winding 30 of the transformer 20 is connected to terminals 33, 34 and to the contacts 35, 37 of a jack, the outer contact 37 being earthed. The terminal 34 is connected to terminals 41, 43. To detect a discontinuous conductor a plug connected to head phones is inserted in the jack 35, 37 and the switch 22 is engaged with the contact 25. Conductors are connected in turn between the terminals 28, 29, causing a sound in the phones if the conductor is continuous. To locate the break in a discontinuous conductor, one end of this conductor is connected to the terminal 33 and the corresponding ends of the remaining conductors of the cable are connected to the terminal 34. All the ends of the conductors at the second end of the cable are connected to the terminal 43, so that all metallic parts of the cable other than the part of the discontinuous conductor connected to the terminal 33 are at earth potential. The switch 22 is moved to the contact 24 and the plug is disconnected from the jack 35, 37 and inserted into a search device 48, Fig. 4, comprising a metal plate forming one plate of a condenser, of which the other plate is the conductor under test. This is passed along the cable from the earthed end until it reaches the break, which is indicated by the emission of a note of the impressed frequency in the head phones 54. An amplifier and loud speaker may be employed instead of the head phones, or a visual signal such as a lamp or gas discharge tube may be used. The signal potential applied may be of alternating, pulsating, or intermittent form. The plate 48 may be replaced by an inductance coil.