SU930168A1 - Method of locating short-circuit in cable - Google Patents

Description

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The invention relates to electrical measuring equipment and can be used to determine the location of a cable in the cable between the conductors of a cable, a cable, or a cable conductor on a metal sheath.

There is a known method for determining the locations of closures on the sheath in cable lines, in which a damaged core is connected to the output terminal of an audio frequency generator, the intact core is connected via a grounding choke to the second output of the generator, and on the other side is grounded and the shell passes a higher frequency current through the head of the sound frequency period, and the damage place is determined by the phase change of the current Li,

The disadvantages of this method are low accuracy due to the presence of capacitive currents behind the fault site and the inability to find damage between the cable cores.

The closest in technical essence to the present invention is a method for determining the location of a closure to the metal sheath of a multicore power cable based on connecting an increased frequency generator between the damaged core and the sheath and the second generator between 10 the damaged core and the intact closed at the other end to the sheath and estimating the change in EMF 2

The disadvantage of this method is low accuracy due to the presence of

15 phase shifts in the generator signals.

The purpose of the invention is to improve the accuracy of closure detection and enhance functionality.

20

This goal is achieved by the fact that in the method of determining the location of the circuit in a cable based on connecting a high-frequency generator between damaged conductive wires of the cable, fixing the magnetic field of the current generator along the cable, the fixing signal is transmitted to the generator unit, where the phase shift of the high frequency signal is highlighted relative to the output current of the generator, in accordance with which the output signal of the generator is modulated, and the cable's closing position is determined by the modulation change uemogo signal for the fault point. The drawing shows a structural block diagram of a device that implements a method for detecting a short circuit in a cable. The device comprises a generator unit 1, including a generator of increased frequency 2, a transformer 3 tOKa, a phase-shifting unit, an integrator 5, a controlled multivibrator 6 phase meter 7, switches 8 and 9 threshold element 10, separation diode 11, filter 12, detector 13. the radio receiver 1, the conductor wires of the cable 15, the additional phase-shifting capacitance 16, the search moving along the path and including a selective amplifier 18, whose input is inductively connected to the current-carrying wires of the cable 15, the recorder 19, the rectifier 20, section Diode 21, filter 22, threshold element 23, switch 2k, radio sensor 25 The device works as follows .. In the damaged cable 15 alternating current flows in the form of pulses, the filling frequency of which is constant and is determined by the frequency of the generator 2, and the frequency of the pulses determined by the frequency of the controlled multivibrator 6. With the help of search block 17, these pulses are received on the cable route during the search for a closure location and recorded by the recorder 19. The received signal at the same time after being rectified in the rectifier 20 through a com the mutator 24 enters the radio transmitter 25. and is transmitted to the installation site of the generator block 1. The duration of the transmitted pulses is determined by the length of time intervals for receiving the generator 2 signal, which is specified by the threshold element 23. The amplitude of the received signal varies along the cable path in accordance with with a twist of the cores, as well as due to modulation (manipulation) with the frequency of the controlled multivibrator 6. To stabilize the amplitude of the signal during the transmission process, automatic adjustment is made amplified and along the circuit: the output of the filter capacitor 22, the gain control input of the selective amplifier 18. The signal of the search block 17 received by the radio receiver I in the generator block 1 through the switch 8 is fed to one of the inputs of the phase meter 7. The other input of the meter 7 simultaneously receives the rectified voltage from the current transformer 3. In this case, at the output of the phase meter 7, a signal appears in the form of a voltage in magnitude proportional to the phase difference of the input signals, and in sign corresponds to the advance or delay of the phase of the received signal. The signal of the phase meter 7 changes the frequency of the controlled multivibrator 6 and also, through the integrator 5, controls the phase shift of the phase-shifting unit C. In this case, the phase shift is toward compensating for the received phase and the reference signals at the inputs of the phase meter 7. The integrator 5 performs the necessary compensation delay so that abrupt changes in the phase of the received signal occurring when the search unit 17 moves directly behind the closure location are accompanied by a sufficient change in the frequency of the controlled multivibrator 6 for reliable detection by the operator through the search unit 17. Using the separation diode 11 and the filter capacitance 12, a signal is formed at the input of the threshold element 10, which is triggered by the action of the received signal. The output voltage from the threshold element 10 is supplied to control the synchronous operation of the switches 8 The generator current behind the cable closure due to the voltage drop across the contact resistance is created through the cable capacitance and the additional phase shifting capacitor 16. Therefore, the phase of the received signal behind the closure point is ahead of phase C1- to the place of closure. In search block 17, when passing through the closure location, a change in the phase of the signal is recorded with no deviation of the pulse frequency from the nominal value. If the search block 17 is shifted back beyond the closure point, a change in the frequency of the pulses in the opposite direction from the nominal value will be registered. A change in the phase of the signal by 180 due to the stranding of the cores in the cable does not have a modulating effect, since the phase of the signals after their full-wave rectification is recorded. A slow phase shift with a large cable length is compensated for in the generator unit 1 by means of the phase-shifting unit k.

The proposed method allows to increase the accuracy of the location of the closure due to the high sensitivity of the phase measurement and control methods and to expand its area of application with increased transient resistance, as well as phase and single-phase closures.

Claims (1)

1. Authors certificate of the USSR, cl. G 01 R 31/08, 19732. USSR author's certificate tf "76524, cl. G 01 R 31/08, 1972 (prototype).