JPH0712882A - Partial discharge measuring method - Google Patents

Abstract

PURPOSE:To measure partial discharge occurring at each part on a line quantitatively at high sensitivity. CONSTITUTION:A power cable S is applied, at the insulating joint terminals 1a, 1b thereof, with foil electrodes 2a, 2b connected with a measuring unit 4 through a detection impedance 3. When a partial discharge takes place on the power cable S, a partial discharge signal is detected by the measuring unit 4 through the impedance 4. At the time of measurement, such frequency as causing low attenuation of the partial discharge signal, having the output response ratio between direct calibration and indirect calibration substantially equal to 2, is selected as a measuring frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial discharge measuring method capable of accurately measuring a partial discharge of a power cable.

[0002]

2. Description of the Related Art Conventionally, partial discharge measurement has been studied as an initial defect detection of a CV cable line. In the power cable, the measurement sensitivity fluctuates due to the overlap of the reflection of the discharge pulse, and narrow band amplification was difficult to use for the detection of partial discharge.
High-frequency narrow-band amplification is being actively studied because it is less affected by external noise.

The applicant has already proposed in Japanese Patent Application No. 4-213566 a method for measuring partial discharge in a power cable by using a relatively high frequency component where the impedance characteristic of the power cable converges. is suggesting.

FIG. 6 shows C of 1200 m using the resistance voltage dividing method.
It is a graph chart when the characteristic of the absolute value of the impedance with respect to the frequency of the V cable is measured, and the impedance is 0.053 kΩ with respect to 1 V on the vertical axis. The solid line represents the case where the far end of the CV cable is open, and the points represent the case where the far end is short-circuited. In this case, about 2MHz
At the frequencies below, the impedance value differs between the case where the far end is opened and the case where the far end is short-circuited, and the impedance fluctuates. However, it can be seen that the impedance values converge at higher frequencies.

When performing charge calibration using a relatively low frequency where the impedance does not converge, the output response ratio of indirect calibration to direct calibration is difficult to determine because the impedance changes greatly. However, if a frequency of about 2 MHz or higher at which the impedance converges is used, the impedance becomes constant and correct calibration can be performed.

[0006]

However, as shown in the graph in which the horizontal axis is the cable length and the vertical axis is the response rate as shown in FIG. 7, when a high frequency component is used, the signal propagates in the cable. As a result, the partial discharge signal is attenuated, so that there is a problem that only partial discharge in the vicinity of the insulating connection can be detected.

The object of the present invention is to solve the above problems,
Another object of the present invention is to provide a partial discharge measuring method capable of accurately and accurately measuring a partial discharge generated in each part of a line such as a normal connecting part or a terminating part which is far from the insulating connecting part.

[0008]

The partial discharge measuring method according to the present invention for achieving the above object has an output response ratio of indirect calibration to direct calibration of about 2 when measuring partial discharge of a power cable. It is characterized in that the frequency that becomes is selected as the measurement frequency.

[0009]

According to the partial discharge measuring method having the above-mentioned configuration, the attenuation of the partial discharge signal propagating in the cable can be suppressed to a small level, and the frequency at which the output response ratio of the indirect calibration to the direct calibration becomes about 2 is measured. Is used to measure partial discharge in power cables.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a circuit configuration diagram of a first embodiment for carrying out the method according to the present invention. The insulated electrode terminals 1a and 1b of the power cable S are provided with foil electrodes 2 respectively.
a and 2b are attached, and the outputs of these foil electrodes 2a and 2b are connected to the measuring device 4 via the detection impedance 3.

In this case, when a partial discharge is generated in the power cable S, the partial discharge signal is detected by the measuring device 4 via the detection impedance 3.

FIG. 2 is a configuration diagram for calibrating the power cable S, and FIG. 3 is a circuit configuration diagram thereof.
When performing indirect calibration, a pulse generator G1 is connected between the foil electrodes 2a and 2b of the insulated connection terminals 1a and 1b via a capacitor C1, and when performing direct calibration, a capacitor C2 is provided at the far end of the power cable S. Pulse generator through
Connect G2. The power cable S is pulse-divided into two by the detection impedance 3, and the insulated connection terminal 1a,
Impedance on both sides of 1b is impedance
Expressed as Z1 and Z2.

When performing charge calibration, a known charge amount is injected from the pulse generators G1 and G2 to perform calibration. Here, if a sufficiently high frequency at which the impedance value of the power cable S converges is used as the measurement frequency, the impedances Z1 and Z2 become equal as can be seen from FIG. 6, and the impedance is injected in parallel with the detection impedance 3 as indirect calibration. The pulse response is impedance Z1 or Z2 for direct calibration.
It is about twice as much as when injected into any of the above.

FIG. 4 is a graph showing the relationship between the measurement frequency and the output response ratio (direct ratio) of the indirect calibration to the direct calibration, and the solid line represents the case where a 250 m cable is measured.
The dotted line represents the case where a cable of 350 m is measured. In any of the cables, the impedance converges at a frequency of about 13 MHz, and the direct-to-direct ratio is about 2.

The actual partial discharge occurs in the portion of Z1 or Z2 which is the position of the direct calibration, but when the direct-to-direct ratio becomes about 2, the direct calibration is performed by the indirect calibration with a charge half the size of the direct calibration. You can substitute by doing. This is the principle of indirect calibration, and making the response of indirect calibration about twice the response of direct calibration during calibration is extremely effective in correctly measuring the partial discharge amount.

However, in order to detect the partial discharge occurring at a long distance from the insulated connection, the impedances Z1 and Z2 can be obtained by using a relatively low frequency that can suppress the attenuation of the partial discharge signal to a small level. As can be seen from FIG. 6, the impedance characteristic is complicated, so that the direct ratio does not become about 2, but exhibits an unstable value as shown in FIG.

Therefore, the frequency is finely swept in a relatively low frequency region where the attenuation of the partial discharge signal can be suppressed to a small level, for example, in the frequency region near 3 MHz to 5 MHz in FIG. 4, and the direct ratio becomes about 2. Like A1 point, A2
By selecting frequencies such as points A3 and A3 and using them as the measurement frequency, the partial discharge occurring at each line section such as the ordinary connection section and the terminal section, which is far from the insulated connection, is highly sensitive and accurate. It becomes possible to measure.

FIG. 5 is a circuit configuration diagram of a second embodiment for carrying out the method according to the present invention. Three-phase cable S1, S
2, S3 insulation connection terminal 11a, 11b, 1 respectively
2a, 12b, 13a, 13b, and foil electrodes 14a, 14
b, 15a, 15b, 16a, 16b are attached, and the outputs of the foil electrodes 14a, 14b, 15a, 15b, 16a, 16b are connected to the switch 17. The output of the switch 17 is connected to the measuring device 19 via the signal processing circuit 18.

Here, the switching device 17 includes cables S1, S2, S3.
Of the respective phases, the signals of the insulated connection terminal of any two phases are selected and combined, and the detection coil and the secondary coil are arranged in polarities so that the signals of both of them are canceled out, and the signal processing circuit 18 The signal from the switch 17 is differentially detected.

When a partial discharge is generated in the cable of any two phases selected by the switch 17, the partial discharge signal is canceled by the differential connection in each foil electrode and the signal processing circuit 18. The measuring device 19 can obtain only the partial discharge signal.

It is difficult to immediately judge which of the cables S1, S2, S3 of any two phases selected by the switch 17 causes the partial discharge, but by switching the switch 17, It is possible to detect which of the cables S1, S2, S3 has a partial discharge by measuring the signals between the cables S1, S2, S3 sequentially.

As in the case of the second embodiment, a method for achieving a balanced state of a two-phase power cable by a signal processing circuit and thereafter differentially detecting signals to cancel noise is also provided. If frequencies such as A1, A2, and A3 in Fig. 4 are selected and used as the measurement frequency, the parts that occur at various parts of the line, such as ordinary connections and terminations that are far from the insulation connection, Discharge can also be measured with high sensitivity and accuracy.

[0023]

As described above, the partial discharge measuring method according to the present invention can suppress the attenuation of the partial discharge signal to a small extent, and the output response ratio of indirect calibration to direct calibration is about 2.
It becomes possible to measure the partial discharge occurring in each part of the line with high sensitivity and high quantitativeness by measuring the partial discharge with the frequency that becomes as the measurement frequency.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a first embodiment.

FIG. 2 is a configuration diagram when performing calibration.

FIG. 3 is a circuit configuration diagram when performing calibration.

FIG. 4 is a graph of the relationship between the measured frequency and the output response ratio of indirect calibration to direct calibration.

FIG. 5 is a circuit configuration diagram of a second embodiment.

FIG. 6 is a graph showing the relationship between measurement frequency and impedance.

FIG. 7 is a graph showing a relationship between a distance between a pulse injection point and a measurement point and a pulse response rate.

[Explanation of symbols]

1a, 1b, 11a, 11b, 12a, 12b, 13
a, 13b Insulated connection terminal 2a, 2b, 14a, 14b, 15a, 15b, 16
a, 16b Foil electrode 3 Detected impedance 4, 19 Measuring device 17 Switcher 18 Signal processing circuit C1, C2 Capacitor G1, G2 Pulse generator S, S1, S2, S3 Cable Z1, Z2 Impedance

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[Procedure amendment]

[Submission date] August 11, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

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[Correction method] Change

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[Figure 1]

[Procedure Amendment 2]

[Document name to be corrected] Drawing

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[Fig. 2]

Front page continuation (72) Inventor Ichiro Kume 1008 Shinbori, Kumagaya, Saitama Mitsubishi Cable Industries, Ltd. Kumagaya Manufacturing Co., Ltd. Inside the Tokyo office

Claims (1)

[Claims] 1. A method for measuring partial discharge, wherein when measuring partial discharge of a power cable, a frequency at which an output response ratio of indirect calibration to direct calibration is about 2 is selected as a measurement frequency.