RU2269789C1 - Method for determining position of electric relay and communication lines disruption and device for realization of said method - Google Patents

Abstract

FIELD: electric engineering.

SUBSTANCE: method is based on determining time delay of pulse reflected from disruption location relatively to probing pulse. Probing pulse is subjected to time-frequency modulation, and reflected pulse - to appropriate demodulation, filtering and spectral analysis. Information about time delay is determined from values of received amplitude-frequency spectrums. Generator of probing pulses contains serially connected memory block, digital-analog converter, power amplifier and block of controlled output resistance for synchronizing output resistance of generator with wave resistance of line. Input of memory block and input of controlled output resistance are connected to appropriate outputs of calculating device. Device receiver additionally has lower frequencies filter, and also has additional input, to which second output of probing pulse generator is connected. Due to use of pulses with time-frequency modulation, error of time delay is decreased.

EFFECT: due to utilization of pulses with time-frequency modulation, time delay determining error is decreased.

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Description

The invention relates to electrical engineering and can be used to create devices for determining the location of damage (OMP) in power lines and communications (power lines and C).

Known methods of OMP power lines and C [A.S. USSR No. 1385108, A.S. USSR No. 1531037, RF Patent No. 2073253] are based on the pulsed method without the use of intrapulse modulation: unmodulated probing signals are sent to the line, signals reflected from inhomogeneities of the damage sites are received, and the location of the damage is determined by the time delay of the signals reflected from the damage relative to the probing ones.

The disadvantage of these known methods is the low accuracy of the measurements.

The closest technical solution to the proposed method and device is the OMP power transmission line and C and a device for its implementation [RF Patent No. 2073253, cl. G 01 R 31/11, 1997]. The method is based on sending voltage probing pulses to the line, receiving reflected pulses, storing the voltage values from the line for each time delay value, determining the location of damage by the time delay of the pulse reflected from the pulse relative to the probing one. In order to increase the reliability and accuracy of measurements, to eliminate spurious reflections from the input line, the output impedance of the probe pulse generator is matched with the line impedance cyclically: in the first cycle, half the amplitude of the probe pulse is stored when the line is turned off, and in the second cycle, the probe pulse amplitude is measured at an arbitrary value output resistance at the input of the connected line, subtract from it the value stored in the first matching cycle , the sign and value of the subtraction result are stored, in the third matching cycle, the wave resistance value is calculated from the measurement results of the first and second cycles and the output resistance of the probe pulse generator is set using its digital code with a given accuracy.

This method and its device also have low measurement accuracy.

The objective of the invention was to improve the accuracy of measuring the distance to the place of damage.

This problem is solved by the method of determining the location of damage to power lines and communications, which consists in sending probing voltage pulses from the generator to the line while matching the output impedance of the latter with the wave impedance of the line in accordance with a given range of wave impedances and the required accuracy of matching, receiving reflected pulses, determining the location of damage the time delay of the reflected pulse relative to the probing, while the probing voltage pulses subjected by time-frequency modulation, and the reflected pulses corresponding demodulation, filtering and spectral analysis, wherein the information about the time delay of the reflected pulses relative to the probing field, and damage is determined by the values received amplitude-frequency spectra.

The essence of the invention consists in the use of signals with time-frequency modulation for WMD, with high resolution and accuracy of measuring the delay time of the reflected pulse relative to the probing [Theoretical fundamentals of radar. Ed. Shirmana Y.D. Textbook for high schools. - M.: Soviet Radio, 1970].

Since the error in measuring the range with WMD is directly related to the error in measuring the time delay, it is possible to characterize the increase in the accuracy of measuring the range by reducing the errors in measuring the time delay.

It is known [Theoretical Foundations of Radar. Ed. Shirmana Y.D. Textbook for high schools. - M .: Soviet Radio, 1970, p. 190], that the standard error (standard deviation) of the measurement of the delay time is determined by the expression

where q is the signal-to-noise ratio;

P _{e is the} effective signal bandwidth.

For simplicity of reasoning, we consider in the power transmission lines and C noise "wallets" with a constant spectral density (N (f) = N _o = const), which is physically justified [Shalyt G.M. Identification of fault locations in electrical networks. - M .: Electroatomizdat, 1982, chapter 5]. In this case, for a single sounding, the signal-to-noise ratio is calculated as follows

where e _u is the energy of the probe pulse.

The root-mean-square error of measuring the delay time when using pulses without intrapulse modulation is [Theoretical basis of radar. Ed. Shirmana Y.D. Textbook for high schools. - M.: Soviet Radio, 1970, p. 192]

where Р = Э _u / t _u is the pulse power (for a radio pulse, the power of its high-frequency oscillations).

When using signals with time-frequency modulation, such as a pulse with linear frequency modulation (LFM) and a rectangular envelope, the standard error of the measurement of the delay time is [Theoretical basis of radar. Ed. Shirmana Y.D. Textbook for high schools. - M.: Soviet Radio, 1970, p. 191]

where P _u = Δf = f _k -f _n is the width of the spectrum, the frequency deviation of the LFM pulse with a rectangular envelope.

Moreover, in accordance with formula (3) for fixed values of P, N _o and under the condition of optimal processing of a rectangular pulse without intrapulse modulation, the root-mean-square error of measuring the delay time στ ₁ does not depend on its duration.

Let the power of the emitted pulse (probe pulse generator) P = 1 W, N _o = -30 dB = 10 ^-3 W · s. Then

where B = P _u · t _u is the signal base.

In the paths of high-frequency processing of power lines, probing signal radiation is possible within the band П _u = Δf = 10 ⁶ Hz = 1 MHz [Shalyt G.M. Identification of fault locations in electrical networks. - M .: Electroatomizdat, 1982]. In this case, choosing the duration of the LFM signal t _u = 10 ^-1 s (B = 10 ⁶ · 10 ^-1 = 10 ⁵ ), it is possible to increase the accuracy of measuring the delay time by more than 10 ⁴ times compared to pulses without modulation.

It should be noted that, due to the non-fluctuating nature of reflections from the damage site, it is advisable to increase the duration of the probe pulse with time-frequency modulation to values within which coherent accumulation is possible. In order to further improve the accuracy characteristics of measuring the delay time and to ensure a high signal to noise ratio, it is advisable to emit sequences of modulated pulses with subsequent coherent and incoherent processing [Theoretical Foundations of Radar. Ed. Shirmana Y.D. Textbook for high schools. - M.: Soviet Radio, 1970].

To clarify the accuracy advantages of the proposed method, another approach is possible. Since the error in measuring the delay time is inversely proportional to the band of the probe pulse (formula (1)), for equal signal-to-noise ratios q for signals with and without intrapulse modulation, we have:

- for the LFM pulse, the band (spectrum width) depends on the frequency deviation and does not depend on the pulse duration t _u . In this case, it is possible to increase the duration of the LFM pulse without reducing the accuracy characteristics of the delay time measurements. On the contrary, an increase in the duration of the LFM pulse will increase the signal-to-noise ratio and increase the accuracy of measurements;

- for a signal without intrapulse modulation and a rectangular envelope, the band is determined by the pulse duration [Theoretical basis of radar. Ed. Shirmana Y.D. Textbook for high schools. - M.: Soviet Radio, 1970]

Thus, for such signals, it is not possible to increase the duration of the probe pulse without reducing the accuracy of the delay time measurements. On the other hand, an increase in the duration of the probe pulse leads to an increase in the "dead zone", i.e. the power line section and C, where damage is not possible due to blocking of the receiver for the duration of the transmitter pulse emission. An increase in the energy for sounding by pulses without intrapulse modulation is thus possible only by increasing the amplitude of the oscillations, which complicates the construction of the corresponding probing pulse generators and, ultimately, has limitations due to the possibility of a breakdown (up to the value of breakdown voltages).

The proposed method can be implemented by a device containing a probe pulse generator, connected by a second output to a line, with a controlled output resistance block, the second input and second output of which are the second input and second output of the generator, the computing unit, the second output of which is connected to the second input of the generator , the receiver, the first input connected to the first output of the probe pulse generator, and the input / output - with the input / output of the computing unit, and the display unit, the input is connected connected to the third output of the computing unit, in which, according to the proposal, a memory unit, a digital-to-analog converter and a power amplifier are installed in series with the probe pulse generator, the input of the memory block being the first input of the probe pulse generator and connected to the first output of the computing unit, and the output of the power amplifier is the first output of the generator and is connected to the input of the controlled output impedance block, the receiver additionally contains a low-pass filter, and the second output of the probe pulse generator is additionally connected to the second input of the receiver.

Figure 1 presents the device that implements the proposed method; figure 2 presents a variant of the unit controlled output impedance of the probe pulse generator; figure 3, 4 presents examples of the implementation of the receiver and the computing unit; 5, 6 explain the operation of the proposed device.

The device (Fig. 1) contains a probe pulse generator 1, consisting of a controlled output impedance block 2, a memory block 3, a digital-to-analog converter 4 and a power amplifier 5, a receiver 6, a computing unit 7 (for example, a microcomputer), an indication unit 8.

The first output of the generator 1, which is the output of the power amplifier 5, is connected to the first input of the receiver 6, the output of the power amplifier 5 is also connected to the input of the controlled output resistance unit 2, the second output of the generator 1 is connected to the line (power line or C) and simultaneously to the second the input of the receiver 6. The first input of the generator 1, which is simultaneously the input of the memory unit 3, is connected to the first output of the computing unit 7, and the second input of the generator 1, which is also the second input of the unit of the controlled output resistance 2, is connected to about the second output of the computing unit 7. The computing unit 7 input / output is connected to the input / output of the receiver 6, and the third output is connected to the input of the display unit 8.

The receiver 6 (figure 3) contains a mixer 9, a low-pass filter 10 and an analog-to-digital converter with controlled amplification 11. The first and second inputs of the mixer 9 are respectively the first and second inputs of the receiver 6, and the input / output of the converter 11 is the input / output receiver 6.

The computing unit 7 (Fig. 4) in the general case may be a microcomputer containing an address, data, control bus 12, a processor module 13, a keyboard control device 14, a memory module 15.

The device operates as follows.

Consider the operation of the device for determining the location of damage (OMP) using the example of radiation and processing of LFM pulses (pulses with linear frequency modulation) with a rectangular envelope.

At the beginning of the measurements (before the OMP), the output impedance of the probe pulse generator 1 is matched (Fig. 1) with the wave impedance of the line connected to the output of the controlled output impedance block (Fig. 2). The matching mode set block 14 of the microcomputer 7 (figure 4) in accordance with a given range of wave impedances and the required accuracy of matching.

After the process of matching the output impedance of the generator 1 is completed under the influence of the instructions of the microcomputer block 14, the processor module 13, with the participation of the software stored in the memory module 15, calculates digital codes of discrete values of the LFM pulse samples of a given duration t _u . Digital codes from output 1 of the microcomputer 7 enter the memory unit 3 of the probe pulse generator 1, where they are recorded and stored. The parameters of the LFM pulse (for example, the duration, the width of the spectrum) are selected on the basis of ensuring the required measurement accuracy, taking into account the parameters of the power lines and C.

Under the influence of control signals from the first output of the microcomputer 7, the digital codes of the samples of the LFM pulse are sent to a digital-analog converter 4 and then to a power amplifier 5, at the output of which a probing LFM pulse is generated. Passing through the controlled output impedance block 2, the pulse from the LFM output enters the line, and from the output of the power amplifier 5 to the first input of the receiver it is a reference signal for mixer 9. The radiated probe signal (LFM pulse with a rectangular envelope) has the form

where U _m is the amplitude of the LFM pulse;

ω _n = 2πf _n is the initial frequency;

β = dω / dt is the rate of change of frequency.

In the case of specular reflection from the place of damage (for example, the location of a short circuit in the power transmission line), the reflected pulse will arrive at the input 2 of the receiver 6 with a time delay τ ₃ (Fig. 5) with respect to the emitted pulse (probe _n pulse generator start time t _n ). The pulse reflected from the damage site is depicted in FIG. 5 by a dashed line. In this case, the voltage of the reflected pulse at the first input of the receiver will be described by the expression

where R _o - coefficient characterizing the attenuation of the probe pulse in the process of propagation through power lines (or communication lines) and reflection from the place of damage.

Due to the identity of the characteristics of the emitted pulse and the reference signal of the mixer at its input, the low-frequency component of the voltage will have the form

where Ω = 2πf = βτ ₃ is the difference frequency;

ψ (τ ₃₎ ⁼ (ω _n τ ₃ -βt ^2/2) - phase shift.

From the above expression (7) it follows that the difference frequency Ω = βτ _{3 is} uniquely determined by the propagation time of the probe pulse to the place of damage. Thus, the process of demodulating the received oscillation at the mixer 9 of the receiver 6, using the reference signal of the probe pulse generator 1, converts the information about the location of the damage laid down in the delay time τ ₃ into information expressed in the frequency of the low-frequency component of the output voltage of the mixer 9 of the receiver 6. The signal from the output of the mixer is to be isolated by a low-pass filter (low-pass filter) 10. The low-pass filter 10 does not additionally pass demodulated signals from the output 2 of the probe pulse generator 1 and demodulated and Pulses reflected from the transition space "sounding pulse generator - line", which is at the input of the mixer 9 are arranged in the region of zero frequency (τ ₃ close to zero). The filtering band of the low-pass filter 10 in the zero frequency region is indicated by the shaded section in Fig.6.

From the output of the low-pass filter 10, the processed signal is fed to the analog-to-digital conversion (ADC) module with controlled gain 11 for amplification and digitalization. The gain is controllable, since the gain of module 11 can change under the influence of signals from the input / output of the microcomputer 7 to the input / output of the receiver 6. Digital samples of the received signals through the input / output and the address bus, data, control 12 are supplied to the processor module 13 for implementation spectral analysis computational procedures. The software stored in the memory module 15 is used. The discrete Fourier transform (DFT) or the fast Fourier transform (FFT), as well as other digital spectral analysis algorithms [Marple - ml] can be the spectral analysis procedures implemented by the processor module 13. . S.L. Digital spectral analysis and its applications: Per. from English - M.: Mir, 1990]. The dimension of the DFT (FFT) is determined by the parameters of the probing signal and the range of the analyzed ranges to the place of damage.

The result of the execution by the module 13 of the computational procedures for one probe signal (impulse) is to obtain samples of the amplitude-frequency spectrum for each resolved range element within the potential range to the place of damage. An example of such an amplitude-frequency spectrum is shown in Fig.6. The results of spectral analysis (amplitude-frequency spectrum and its equivalents) are reflected on display unit 8. Based on these results (for example, by the maximum value of the amplitude-frequency spectrum), one can judge the location of the damage.

When the subsequent pulses are emitted, the line impedance can be refined, as well as the results of the OMP by a joint analysis of the amplitude-frequency spectra for each probe pulse.

To increase the signal-to-noise ratio and the accuracy characteristics of the device, it is possible to supply to the input 1 of the mixer 9 of the receiver 6 (but not to the test line) a pulse of increased duration t _u = t _k + τ _3max -t _n . Such a pulse is depicted by a dash-dot line in Fig. 5 and its use allows to increase the time of coherent accumulation of the reflected signal at the limiting ranges during OMP. The shortening of the probe pulses entering the line from the output 2 of the probe pulse generator 1, in comparison with the probe pulses coming from the first input of the generator 1, is achieved by control signals from the output 2 of the microcomputer 7.

Claims (2)

1. A method for determining the location of damage to power lines and communications, which consists in sending a probe voltage pulse to the line from the generator when matching the output impedance of the latter with the wave impedance of the line in accordance with a given range of wave impedances and the required accuracy of matching, receiving reflected pulses, determining the location of damage by the time delay of the reflected pulse relative to the probe, characterized in that the probing voltage pulses are subjected often modulation, and the reflected pulses of the corresponding demodulation, filtering and spectral analysis, moreover, information about the time delay of the reflected pulses relative to the probing and damage sites is determined by the values of the obtained amplitude-frequency spectra. 2. A device for determining the location of damage to power lines and communications, comprising a probe pulse generator with a controlled output impedance block, the second input and second output of which are respectively the second input and second output of the generator associated with the line, a computing unit, the second output of which is connected to the second the input of the generator, the receiver, the first input connected to the first output of the probe pulse generator, and the input / output - with the input / output of the computing unit, and the display unit, input p Connected to the third output of the computing unit, characterized in that the memory pulse generator, a digital-to-analog converter and a power amplifier are additionally introduced into the probe pulse generator, the input of the memory block being the first input of the probe pulse generator and connected to the first output of the computing unit, and the amplifier output power is the first output of the generator and is simultaneously connected to the input of the controlled output impedance block, the receiver additionally contains three low frequencies, and the second output of the probe pulse generator is additionally connected to the second input of the receiver.

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