Patent GB-293378-A (GB)
Title: Improvements in or relating to test sets for locating faults in electric transmission lines
IPC: G01R31/08
Filed: 1928-05-25
Abstract: 293,378. West Manufacturing Go., (Assignees of Anderson, C. A.). July 5, 1927, [Convention date]. Detecting, indicating, and locating faults.-A portable testing set for locating faults in telegraph, telephone, and other transmission lines includes a telephone receiver 18, Fig. 1, and a finder coil 19 in series across two line clips 20, 21, and is provided with switch contacts 2, 3, 4 which on operation connect a magneto generator 1 in place of the receiver and coil, these being connected in a closed loop. On operating the generator 1, the contacts 3, 4 open and the contact 2 closes, the shaft 5, to which is connected one end of the armature winding contacting .with the spring of the contact 4. The finder coil 19 is shown in Fig. 5 and consists of a coil 30 having an. iron core, the magnetic circuit of which is closed through a pair of spring clips 38 of magnetic material, to the lower of which the coil is fastened by screws 32. The clips may thus be forced open and fitted over either the line to be tested or a link 22, as shown in Fig. 2, which is the normal position. If alternating current is passing through the wire encircled by the clip, a current is induced in the coil 30, and produces a sound in the receiver 18. In order to test a circuit for earth, the finder coil is left in its normal position encircling the link 22 and one of the test clips 21 is connected to earth, the other clip 20 being connected first to one line and then to the other, the generator 1 being operated on each occasion. This opens the contacts 3, 4, closes the contact 2, and connects the spring 4 to the shaft 5 of the generator. If the clip 20 is on the faulty line, a current is passed through the fault, thereby inducing a current in the coil 30 and producing a note in the receiver 18. On the shaft 5 of the generator is a pair of contacts 23 which close just after the voltage wave passes its maximum. The generator is thereby short-circuited over the back contact of a switch S1 and a discharge path is provided for a condenser 10 through the line that is being tested. This produces a sharp peak in the current wave and intensifies the voltage induced in the coil 30. In order to determine the approximate distance to the fault, the switch S2 is depressed so as to substitute a resistance 6 for the line under test. This resistance is adjusted until the same result is obtained as with the line, and the length of line having the same resistance gives the distance of the fault. In order to determine on which side of the clip 20 the fault lies, the finder coil 19 is removed from the link 22 and clipped round the line wire first on one side of the clip 20 and then on the other. The presence of a sound in the receiver indicates that the clip 20 on which the finder coil is situated. A short-circuit may be located by attaching the clips 20, 21 to the two lines and adjusting the resistance 6 until the same intensity of sound is heard in the receiver with the switch S2 up and down. The length of line having the same resistance gives the combined length of the two line conductors to the fault. A lamp 11 may be used to. determine which of two conductors is earthed by depressing the switch S1 so as to close its first contact, thereby placing the lamp 11 in parallel with the condenser 10 and disconnecting the interrupter contacts 23. By operating the switch S1 to its full extent the lamp 11 and condenser 10 are short-circuited and the full voltage of the generator is applied to the lines, whereby a highresistance fault may be broken down, so as to enable its position to be determined as described above. A transmitter 7 enables telephonic communication to be established through the line to the exchange. The apparatus is contained in a box 60, Fig 2, having a cover formed in two sections 62, 63, of which the latter is additionally secured by screws 67 and is only opened when repairs are necessary. The box is divided into two sections by a plate 70. The telephone receiver 18, line clips 20, 21 and the generator handle are carried in the left-hand compartment, the generator 1, transmitter 7, induction coil 8, battery 9, condenser 10, and contacts of the switches S1, S2, S3 being mounted as a unitary structure in the right-hand compartment.