RU2715360C1 - Method for cable insulation damage point determining - Google Patents

Abstract

FIELD: measuring equipment.SUBSTANCE: invention relates to electric measuring equipment and can be used for determination of cable insulation damage point. Method comprises feeding a frequency-modulated test signal between cable sheath and ground. Sensor is moved along the cable. Sensor is used to register signals. Amplitude of interference is limited, signals are extracted with the help of band-pass filter with frequency f1 and by means of detector with frequency f2. Frequencies are selected from the condition f2·N=f1, where N is an integer. Signals are converted into signals with equal frequency and phase shift is determined.EFFECT: high accuracy of determining the point of damage to the cable insulation by using a frequency-modulated signal, and therefore providing constant output power of the generator portion and high noise-immunity of the signal.1 cl, 1 dwg

Description

The invention relates to electrical engineering and can be used to determine the location of damage to the cable insulation.

A known method for determining the location of cable damage, including the supply of a test sinusoidal signal of frequency f from a highly stable master oscillator between the cable sheath and the ground, moving the sensor along the cable, registering a test signal with a frequency f in the receiving part and comparing it with a signal of the same frequency from a highly stable reference generator, previously synchronized with the master, the determination of the phase shift between the signals, the value of which is judged on the place of cable damage. (Invention patent No. 2361229, Russia, IPC G01R 31/08. “Method for determining the location of cable damage” / V. Kandaev, Yu.M. Elizarova).

The disadvantage of this method is the need to use highly stable master and reference generators previously synchronized with each other. The use of such specialized generators significantly increases the cost of equipment, and the task of synchronizing generators is not simple and requires an additional solution. Moreover, the small instability of the master and reference generators can lead to significant errors in finding the place of damage to the cable insulation.

Closest to the proposed one is a method for determining the location of cable damage, including applying a test amplitude-modulated signal, moving the sensor along the cable, registering signals, converting the selected signals to signals with the same frequency and determining the phase shift, the value of which judges the location of the cable damage, amplitude -modulated signal is fed between the cable sheath and the ground, signals with upper f1 and lower f2 side frequencies are isolated in the receiving part, the conversion of these s the signals to the signals with the same frequency are carried out by the condition mf1 = nf2 = const, where m and n are integers. (Patent No. 2207582, IPC G01R 31/08. Method for determining the location of cable damage. / Kandaev V.A., Sveshnikova N.Yu.).

The disadvantage of this method is the constant change in the output power of the generator part due to different amplitudes of the output amplitude-modulated signal, which complicates the implementation of this method of determining the location of cable damage and increases the cost of equipment, as well as low noise immunity of the amplitude-modulated signal, which leads to a decrease in accuracy and Efficiency of determining the place of cable damage.

The purpose of the invention is to increase the accuracy of determining the location of damage to the cable insulation by providing a constant output power of the generator part and increasing the noise immunity of the signal.

To achieve this goal, in the proposed method for determining the location of a cable insulation damage, including applying a test signal between the cable sheath and the ground, moving the sensor along the cable, registering signals, converting the selected signals to signals with the same frequency and determining the phase shift, the value of which is used to determine the location cable damage, give a frequency-modulated signal, limit the interference amplitude in the receiving part, extract signals using a band-pass filter with a frequency of f1 and with the help of detectors torus with frequency f2, the frequencies are selected from the condition f2⋅N = f1, where N is an integer.

In FIG. presents a functional diagram of a device that implements measurements by this method.

The device consists of a generator and receiving parts. The generator part 7 contains a master oscillator 1, frequency dividers 2 and 3, a frequency modulator 4, a power amplifier 5 and a matching device 6 connected to an insulated metal sheath of a cable 8 having insulation damage 18. The receiving part 17 contains a sensor former 9, an amplitude limiter 10, a selective amplifier 11, a band-pass filter 12 for isolating a signal of frequency f1, a frequency divider by N 13, a frequency detector 14, which extracts a signal of frequency f2, a phase meter 15, an indicator 16.

The process of determining the location of damage to the cable insulation is as follows.

Using a master oscillator 1 and a frequency divider 2, a sinusoidal signal is generated with a carrier frequency f1, using a frequency divider 3 this signal is divided by N, thus, a modulating signal with a frequency f2 is obtained, which is rigidly connected to the carrier signal. These signals are fed to a frequency modulator 4, the output of which produces a frequency-modulated signal. After the necessary amplification using a power amplifier 5, the signal through the matching device 6 is fed into the cable sheath-ground circuit. Since frequency modulation is used, the output power of the generator part remains constant. The signal propagating through the cable creates an electromagnetic field on the surface of the earth.

The receiving part serves to register these fields and detect a phase shift at the site of damage. The magnitude of the phase shift is a function of frequency. The electromagnetic field is detected by the imaging sensor 9. The generated signal is fed to an amplitude limiter 10 to reduce the interference amplitude, a selective amplifier 11 tuned to the frequency-modulated signal frequency band and amplifying this signal to the required value, which is then fed to the band-pass filter 12 and detector 14 The band-pass filter 12 selects a signal with a frequency f1, after which, using a frequency divider 13, this signal is divided by N, thus, a signal with a frequency f2 is obtained. The frequency detector 14 emits a signal of frequency f2. Next, the signals from the output of the frequency divider 13 and the frequency detector 14 are fed to the inputs of the phase meter 15, which determines when the receiver moves along the cable path the phase shift between the signals of frequency f1 and f2. This phase difference is recorded by the indicator 16. The damage to the insulation of the cable 18 is judged by the increment of the phase difference between the signals, which occurs at the place of damage to the insulation of the cable.

This method improves the accuracy of determining the location of damage to the cable insulation by using a frequency-modulated signal, and therefore, ensuring a constant output power of the generator part and increasing the noise immunity of the signal.

Claims (1)

A method for determining the location of a cable insulation damage, including applying a test signal between the cable sheath and the ground, moving the sensor along the cable, registering the signals, converting the extracted signals to signals with the same frequency and determining the phase shift, the value of which determines the location of the cable damage, characterized in that a frequency-modulated signal is supplied, the interference amplitude is limited in the receiving part, the signals are isolated using a band-pass filter with a frequency f1 and with a detector with a frequency f2, hour Hots are selected from the condition f2⋅N = f1, where N is an integer.

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