JPH09178802A - Partial discharge measuring method for cv cable line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of measuring a partial discharge of a long-distance line without impairing quantitativeness and without being affected by propagation attenuation in the partial discharge measurement of the CV cable line via an indirect calibration system. SOLUTION: Known charges are injected to a CV cable line from foil electrodes 61, 62 by a pulse generator PG via electrostatic coupling. Signals containing partial discharge pulses detected by separate foil electrodes 21, 22 are amplified by an amplifier 4 at the resolution (100kHz) not affected by the overlapping of reflected pulses in the line, they are swept in the range of about 1-10MHz by a measuring instrument 5, and detection signals amplified at a proper frequency for the direct calibration/indirect calibration ratio = 2 are displayed. Since measurement is made at the direct/indirect ratio = about 2, the same result as the direct calibration with calibration charges two times the injected charges can be obtained without exposing a cable conductor and a shield layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring partial discharge of a CV cable line by indirect calibration, and more particularly to a method for selecting an amplification frequency of a partial discharge detection signal which is important when performing quantitative measurement in an indirect calibration method. It is a thing.

[0002]

BACKGROUND OF THE INVENTION The partial discharge measuring method has been conventionally used as one of the methods for testing the insulation state of a CV cable line. For partial discharge measurement, a so-called direct calibration method in which an electric charge is directly injected between the conductor of the cable and the shielding layer to detect discharge based on minute defects in the insulator, and direct contact with the charging part as described above. Instead, for example, there is an indirect calibration method in which a foil electrode is installed on the outer peripheral portion of an insulating connection portion of a cable line, a known charge is injected by using electrostatic coupling, and a partial discharge is detected. This indirect calibration method has advantages that it does not require disassembly of the line and that measurement can be performed in a live state.

Certain conditions are required to quantitatively measure partial discharge by the indirect calibration method. FIG. 2 shows a partial discharge measuring circuit, where a is the capacitance of the sample (capacitance of the cable line insulator to be tested), k is the capacitance of the coupling capacitor, and Zd is the detection impedance. .
In the case of direct calibration, the charge Q is directly injected into the sample, and in the case of indirect calibration, the charge q is injected into both ends of the detection impedance Zd.
It can be expressed by a relational expression of (1 + a / k) q. Here, when a = k, Q = 2q, that is, quantitative measurement is possible if the charge q of indirect calibration is set to half of the charge Q of direct calibration as long as this condition is satisfied.

This condition is referred to as a ratio of direct calibration and indirect calibration (hereinafter referred to as direct ratio) = 2. Even in the CV cable line, if this condition, that is, the condition of direct ratio = 2 is known, indirect calibration is performed. The partial discharge can also be quantitatively measured in this method. For example, when performing partial discharge measurement by indirect calibration at an insulated connection portion of a CV cable line, the direct ratio is the cable impedance Z on one side of the insulated connection portion.
Since it is determined by the voltage division ratio between 1 and the cable impedance Z2 on the other side, and the direct ratio = 2 when Z1 = Z2, the indirect calibration method can be applied if this Z1 = Z2 is satisfied. However, in order for Z1 = Z2 to be satisfied, the cable lengths on both sides of the insulated connection portion are required to be equal, but generally the cable lengths are not the same.

Therefore, in order to substantially satisfy Z1 = Z2, it has been attempted to select the amplification frequency of the detected partial discharge signal based on the convergence characteristic of the cable impedance. That is, the direct frequency ratio = 2 is achieved by setting the amplification frequency to a frequency at which the cable impedance converges to the surge impedance Z0 and setting Z1 = Z2 = Z0.

FIG. 3 shows 6.6k with lengths of 250 m and 350 m.
V CV cable insulation connection is provided to construct a simulated line, the detected partial discharge signal is subjected to narrow-band resonance amplification at frequencies from 2MHz to 20MHz, and the maximum and minimum responses are checked while changing, and each frequency is changed. Shows the direct ratio calculated. As shown in the drawing, the direct ratio is 2 in the high frequency region of 13 MHz or more, and the maximum of the arithmetic series is obtained in the lower frequency region. The condition of direct ratio = 2 of 13MHz or more corresponds to the convergence operation of the cable impedance. In this case, if the detection signal is amplified at an appropriate frequency of 13MHz or more, the measurement by indirect calibration with quantitativeness can be performed. You can do it.

[0007]

However, when the amplification frequency is selected in the high frequency range as described above,
Since the propagation attenuation becomes more significant as the frequency becomes higher, there is a problem that the measurement sensitivity in the longitudinal direction of the cable line decreases. For example, in a real line, when partial discharge measurement is performed at a certain insulation connection part, even if the partial discharge measurement at the insulation connection part can be performed with high accuracy, a few hundred meters
The partial discharge signals of the linear connection portions separated by about a certain degree have a large attenuation, making it practically impossible to measure. The problem of attenuation in the longitudinal direction of the line can be solved by selecting a frequency of about several MHz as the amplification frequency, but such a low frequency region is not a stable state with a direct-to-direct ratio = 2, and the quantitative amount of indirect calibration is fixed. There is a problem in terms of sex.

Therefore, the present invention solves the above problems and, in the partial discharge measurement of a CV cable line by the indirect calibration method, does not impair the quantitative property and is not affected by the propagation attenuation, and the partial discharge over a long distance of the line. The purpose is to provide a method by which measurements can be performed.

[0009]

According to the method of measuring partial discharge of a CV cable line of the present invention, a known charge is injected from the detection end of the CV cable line into the cable line by using electrostatic coupling, and the detection is performed at this time. In the method of amplifying the signal detected by the impedance and measuring the partial discharge, the detection signal is amplified with a resolution that is not affected by the overlap of the reflected pulses in the line, and this amplified signal is low frequency at which the cable impedance does not converge. In addition to analyzing the frequency spectrum in the region, selecting a specific frequency from the spectrum while avoiding the resonance frequency depending on the cable length of the line, and performing the partial discharge measurement with the frequency as the amplification frequency of the detection signal. It is a feature.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention has a great significance in that a detection signal is amplified first with a resolution that is not affected by the overlap of reflected pulses in a line. According to the research by the inventors,
When a measurement pulse is injected into the cable line, reflection of the pulse occurs at the connection part, etc. However, the cable span between the connection parts of a general cable line is about several hundreds of meters, and within the cable corresponding to this distance It has been found that the direct ratio fluctuates greatly in a cycle of about several hundred kHz due to the overlapping of the reflected pulses. Moreover, it was also found that the fluctuation had a fluctuation lower limit near the direct ratio = 2.

Conventionally, in this type of partial discharge measuring method, the detection signal is amplified with a resolution of about 1 MHz for convenience of measurement, but with such a resolution, repetition of about several hundred kHz cannot be read. Therefore, although the low frequency region where the cable impedance is not converged has the advantage that the propagation attenuation is small, the frequency at which the direct-to-direct ratio is approximately 2 cannot be determined, so that quantitativeness cannot be ensured and the detection signal It was excluded from the amplified frequency.

Therefore, in the present invention, in view of the above knowledge, the detection signal is amplified with a resolution that is not affected by the overlap of the reflected pulses in the line. The resolution is determined on the basis of the span of the line, etc., but in the case of a line having a cable span of about several hundred meters between the above-mentioned connecting portions, if it is amplified with a resolution of 100 kHz or less, preferably 10 to 50 kHz, This is preferable because the period of several hundred kHz of the inter-ratio can be sufficiently read.

Next, the frequency spectrum of the signal thus amplified is analyzed in the low frequency region where the cable impedance is not converged. In this way, the fluctuation state of the direct ratio can be accurately grasped. The low frequency region in which the cable impedance does not converge refers to about 10 MHz or less as is clear from FIG. 3, but in the present invention, it is 10 MHz because it does not cover the high frequency region where propagation attenuation occurs. It suffices to do the following spectrum analysis in the low frequency region.

Then, an appropriate frequency is selected from the spectrum as the amplification frequency of the detection signal, but this is nothing but the selection of the frequency at which the condition of direct ratio = 2 is substantially satisfied. As described above, in the low frequency region, the direct ratio fluctuates in a cycle of about several hundred kHz with the fluctuation lower limit being around 2. The maximum point is the resonance frequency that depends on the cable length of the line. In the present invention, the resonance frequency is avoided, and the partial discharge measurement is performed with a frequency having a direct ratio = 2 as the amplification frequency of the detection signal. 10M
Although there are a plurality of frequencies in which the direct ratio = 2 holds even in the low frequency region of Hz or less, it is desirable to select a frequency as low as possible because the problem of the above-mentioned propagation attenuation occurs as the frequency increases, and it is preferable that the frequency is 0. 5-7MHz, especially 1
It may be selected in the range of up to 5 MHz. In a frequency region that is too low, there is usually no point with a direct ratio = 2, so it is impossible to select an amplification frequency in this region.

[0015]

An embodiment of the present invention will be described below in detail. FIG. 1 is a circuit diagram showing a case where the partial discharge measuring method according to the present invention is applied to an insulated connection portion IJ of CV cables 11 and 12. The insulating connection portion IJ is configured by covering a connecting portion of the cable conductor with a reinforcing insulating material, providing a shield layer, an anticorrosive layer, and the like thereon, and further providing an insulating cylinder 3 of the shield layer. Reference numerals 21, 22 and 61, 62 denote foil electrodes attached on the anticorrosion layer of the insulating connection portion IJ, and one set is arranged with the shielding layer insulating tube 3 interposed therebetween.

A lead wire 2 is formed from the foil electrodes 21 and 22.
3, 24 are drawn out, and the other ends are connected to the detection impedance Zd. Further, PG represents a pulse generator, which is configured so that known charges can be injected from the other foil electrodes 61 and 62 to the CV cables 11 and 12 via the lead wires 63 and 64 by utilizing electrostatic coupling. Has been done.
In this embodiment, the detection foil electrodes 21 and 22 and the pulse injection foil electrodes 61 and 62 are separately provided in the insulating connection portion IJ, but one set of foil electrodes has both functions. You can also let it.

The detection impedance Zd is connected to an amplifier 4 such as a narrow band resonance amplifier which amplifies the voltage (detection signal) generated across the detection impedance Zd at a resolution of 100 kHz. Measurement that sweeps the signal amplified in the range of 10 MHz, analyzes the frequency spectrum, selects an appropriate frequency with a direct ratio = 2 from this frequency range by calculation, and displays the detection signal waveform at the amplified frequency Device 5 is connected.

When actually measuring the partial discharge, first, a known charge is applied to the foil electrodes 61 and 62 by the pulse generator PG.
Is injected into the CV cable line using electrostatic coupling.
Then, the injected pulse is detected by the other foil electrodes 21 and 22. Here, if the insulator is sound, a signal almost equal to the injection pulse waveform will be detected by the detection impedance Zd. However, in the insulator of the cable line, minute voids or foreign matter may be mixed, or external conduction may occur. When a defect such as a protrusion is present, a minute discharge is generated in the insulator (a partial discharge is generated), and this signal is detected by the detection impedance Zd in a form superimposed on the injection pulse waveform. It will be.

Then, the signal including the detected partial discharge pulse is amplified by the amplifier 4 with a resolution (100 kHz) which is not affected by the overlap of the reflected pulses in the line as described above, and the measuring instrument 5 outputs the signal of 1 to 10 MHz. The detection signal amplified by sweeping the range and amplifying at an appropriate frequency where the direct ratio is 2 is displayed. According to this method, since the measurement is performed in the condition of the direct ratio = 2, the same result as that obtained when the calibration charge is directly calibrated with twice the injected charge without exposing the cable conductor and the shielding layer is obtained. Obtainable.

Further, since the low frequency region of 10 MHz or less is used, propagation attenuation in the longitudinal direction of the cable line hardly occurs. Therefore, even when the straight ordinary connection portion or the terminal portion is located at a position several hundred meters away from the insulated connection portion IJ shown in FIG. 1, the partial discharge signal generated at these points can be measured with high sensitivity.

[0021]

As described above, according to the partial discharge measuring method of the CV cable line of the present invention, in the indirect calibration method, the detection signal is detected in the low frequency region which is not affected by the propagation attenuation in the longitudinal direction of the cable line. It is possible to accurately select the amplification frequency of the so as not to impair the quantitativeness of the measurement. Therefore, there is an excellent effect that the partial discharge measurement over a long distance of the CV cable line can be performed with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a circuit configuration for carrying out the method of the present invention.

FIG. 2 is a circuit diagram showing a general partial discharge measurement circuit.

FIG. 3 is a graph showing measurement results of direct ratio.

[Explanation of symbols]

 11,12 CV cable 21,22 Detection foil electrode 23,24 Lead wire 4 Amplifier 5 Measuring instrument 61,62 Barus injection foil electrode IJ Insulation connection part PG Pulse generator Zd Detection impedance

Claims (3)

[Claims] 1. A method of injecting a known charge from a detection end of a CV cable line into the cable line by utilizing electrostatic coupling, amplifying a signal detected by a detection impedance at this time, and measuring a partial discharge. At, the detection signal is amplified with a resolution that is not affected by the overlap of reflected pulses in the line, and the frequency spectrum of this amplified signal is analyzed in the low frequency region where the cable impedance is not converged.
Partial discharge of a CV cable line, characterized in that a specific frequency is selected from the spectrum while avoiding a resonance frequency depending on the cable length of the line, and the partial discharge measurement is performed using the frequency as the amplification frequency of the detection signal. Measuring method. 2. The method for measuring partial discharge of a CV cable line according to claim 1, wherein the detected signal is amplified with a resolution of 100 kHz or less to analyze the frequency spectrum. 3. The range for analyzing the frequency spectrum is 1
The method for measuring partial discharge of a CV cable line according to claim 1, which is in a low frequency region of 0 MHz or less.