JPH09211063A - Method and apparatus for injecting calibration pulse - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inject the calibration pulses having the different polalities and the same crest value and to transmit the calibration pulses under the state, wherein the distortion of the high frequency signals is very small. SOLUTION: The rectangular wave outputted from a crest-value adjusting part 11 is differentiated in a differentiating circuit 9, and the result is given to an unbalance-balance conversion circuit 15. The unbalance-balance conversion circuit 15 forms the balanced outputs having the different polarities and the same crest value from the output of the differentiating circuit 9. The balanced outputs are transmitted to foil electrodes 4, which are attached to an insulated connecting part 2 through high-frequency coaxial cables 10a and 10b and injected into the insulated connecting part 2. The shieldings of the high-frequency coaxial cables 10a and 10b are short-circuited by short-circuit parts 16 and 17 at the side of the unbalance-balance conversion circuit 15 and the side of the coil electrodes 4, and a closed loop is formed. Thus, the distortion of the waveforms caused by the electrostatic capacity between the cores of the coaxial cables 10a and 10b and the shields can be prevented, and the excellent transmission characteristics provided in the coaxial cables 10a and 10b can be efficiently utilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power device, and more particularly to a method and apparatus for injecting a calibration pulse used for charge amount calibration in partial discharge measurement of power cables.

[0002]

2. Description of the Related Art The partial discharge measurement of a power cable, particularly the partial discharge measurement of a long-distance power cable line after laying a power cable is performed by the method shown in FIG. In FIG. 4, 1 is a power cable, 2 is an insulating connection portion provided in the power cable 1, and two foils each for detection and calibration are provided on the anticorrosion layer on both sides of the insulating tube of the insulating connection portion 2. An electrode 4 is attached, and a calibration pulse generator 3 and a partial discharge detector 5 are connected to the foil electrode 4.

In the figure, in order to calibrate the partial discharge charge amount, a calibration pulse is injected from the calibration pulse generator 3 through the foil electrode 4, and the injected charge amount and the partial discharge detector 5 are used.
The relationship with the voltage appearing at both ends of is calculated. Power cable 1
Alternatively, when a partial discharge occurs in the insulating connection portion 2, a partial discharge pulse signal is generated at both ends of the partial discharge detector 5 via the foil electrode 4. This partial discharge pulse signal is sent to the partial discharge measuring device 6, where the partial discharge measuring device 6 performs analysis such as frequency analysis to distinguish between the partial discharge pulse and the noise signal, and based on the calibration result, the partial discharge pulse signal is detected. The discharge charge amount is measured.

[0004]

Since the partial discharge measurement by the method shown in FIG. 4 generally uses a frequency band of several MHz to several tens of MHz, the foil electrode 4 and the partial discharge detector 5 and the foil electrode 4 are connected to each other. It is necessary to make the frequency characteristics between the calibration pulse generators 3 as good as possible. Therefore, it is necessary to take measures such as shortening the length of the connecting lead wire between them as much as possible. However, in particular, the calibration pulse generator 3
In order to remotely control and to inject the calibration pulse into the connection part of the other phase, a certain length of lead wire is required.

As one of means for solving the above problem, the method disclosed in Japanese Patent Laid-Open No. 151815/1995 has been proposed. In the technique disclosed in the above publication, two rectangular waves having the same crest value and different polarities are respectively injected into two high-frequency coaxial cables whose both ends are impedance-matched, and the two rectangular waves after propagating the lead wire. The wave is differentiated by two differentiating circuits having the same circuit constant to obtain a calibration pulse.

FIG. 5 is a diagram showing the configuration of the calibration pulse generator disclosed in the above publication. In the figure, 1 is a power cable, 2 is an insulation connection part, and 4 is a foil electrode attached to the insulation connection part 2. Further, 7 is a commercial frequency synchronizing section used when synchronizing a rectangular wave with a commercial frequency, 8 is a rectangular wave oscillating section, 9a and 9b are differentiating circuits, 10a and 10b are high frequency coaxial cables, and 11a and 11b are peak value adjustments. Department,
12 is a meter, 13 is a DC / DC converter, and 14 is a battery.

In FIG. 1, the peak value adjusting section 11a, the output of the DC / DC converter 13 supplied with power from the battery 14 and the signal given from the rectangular wave oscillator 8
11b generates two rectangular waves having the same peak value but different polarities. The two rectangular waves are propagated to the differentiating circuits 9a and 9b via the high-frequency coaxial cables 10a and 10b, respectively, and the two rectangular waves after the high-frequency coaxial cable are propagated are differentiated in the differentiating circuits 9a and 9b and used as a calibration pulse for the foil electrode. It is injected into the insulating connection 2 via 4.

With the above structure, the insulating connection portion 2
It becomes possible to inject the calibration pulse symmetrically on both sides of the, and it is possible to perform the charge calibration in which the high frequency component is not attenuated even from a point some distance from the power cable. Furthermore, since the balanced circuit is used, It is possible to reduce the influence of noise. However, the above method requires means 11a and 11b for obtaining rectangular waves having the same crest value but different polarities, and two differentiating circuits 9a and 9b having the same circuit constant, and these are several tens of MH.
Implementation in the z frequency domain makes the device very expensive.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to add an unbalanced-balanced conversion circuit to a conventional calibration pulse generator. It is possible to obtain calibration pulses with the same crest value but different polarities, and by transmitting this to the foil electrode via the high frequency coaxial cable, there is very little distortion of the high frequency signal even if the high frequency coaxial cable is long to some extent. It is an object of the present invention to provide a method and an apparatus for injecting a calibration pulse capable of transferring the calibration pulse in a state.

[0010]

According to the present invention, the above-mentioned object is solved as follows. (1) The pulse signal output from the calibration pulse generator is applied to the unbalanced-balanced conversion circuit to obtain pulse signals of the same crest value with different polarities, and this pulse signal is injected as a calibration pulse into the power equipment and power cable. . (2) In the above (1), when injecting the calibration pulse into the electrodes provided on the metal sheath on both sides of the metal sheath edge portion of the power cable or on the anticorrosion layer on the metal sheath,
The unbalanced-balanced conversion circuit outputs the pulse signals of the same crest value with different polarities, the core wires of which are connected to the balanced output terminal of the unbalanced-balanced conversion circuit and the electrode, and the shielding is the unbalanced-balanced. Transmission is performed via two coaxial cables connected by a short-circuit wire on the conversion circuit side and the electrode side.

According to the inventions of claims 1 to 3,
As described above, the pulse signal output from the calibration pulse generator is input to the unbalanced-balanced conversion circuit, pulse signals of the same peak value with different polarities are obtained, and this pulse signal is injected as the calibration pulse. The calibration pulse can be injected in a form faithful to the principle of indirect calibration in partial discharge measurement.

According to the present invention, the pulse signals of the same crest value having different polarities output from the unbalanced-balanced conversion circuit are sent to the balanced output terminals of the unbalanced-balanced conversion circuit. The shield is connected to the electrode and the shield is unbalanced-
Since the transmission is performed through two coaxial cables connected by a short-circuit wire on the balance conversion circuit side and the electrode side, it is possible to prevent distortion of the waveform due to the capacitance between the core wire and the shield of the coaxial cable. Therefore, the good transmission characteristics of the coaxial cable can be utilized.

[0013]

FIG. 1 is a diagram showing an embodiment of the present invention. In the figure, 1 is a power cable, 2 is an insulating connection part, 4 is a foil electrode, and the foil electrode 4 is a metal sheath on both sides of an insulating cylinder (sheath edge part) of the insulating connection part 2 or an anticorrosion layer on the metal sheath. Is mounted on. Reference numeral 20 is a conventional calibration pulse generator, 7 is a commercial frequency synchronizing unit used when synchronizing a rectangular wave with a commercial frequency, 8 is a rectangular wave oscillating unit, 9 is a differentiating circuit, and 11 is a single rectangular wave. , 12 is a meter, 13 is a DC / DC converter, and 14 is a battery. A conventional calibration pulse generator 20 generates a single rectangular wave.

Reference numeral 15 is an unbalanced-balanced conversion circuit added in the present invention.
As an example, the balun (BALUN: bala shown in FIG.
nceto unbalance transformer) can be used. The unbalanced-balanced conversion circuit 15 shown in FIG. 2 is based on the principle of a transmission line transformer using a ferrite core, and aa, bb, cc in the figure are the same winding. 3B, by applying the unbalanced input shown in FIG. 3A to the unbalanced input terminal Z, as shown in FIGS. 3B and 3C between each balanced output terminal Z ′, Z ″ and the ground. It is possible to obtain the balanced outputs A and B. Instead of using the unbalanced-balanced conversion circuit shown in Fig. 2, an unbalanced-balanced conversion circuit using an electronic circuit using an inverting amplifier and a non-inverting amplifier is used. It is also possible to do so.

Reference numerals 10a and 10b are high-frequency coaxial cables, and one ends of the cores of the high-frequency coaxial cables 10a and 10b are balanced output terminals Z and Z'of the unbalanced-balanced conversion circuit 15.
, And the other end is connected to the foil electrode 4 attached to the insulating connection 2. Also, the high frequency coaxial cable 10
The shield layers a and 10b are short-circuited by the calibration pulse generator side coaxial shield short-circuit portion 16 and the connection portion side coaxial shield short-circuit portion 17.

In FIG. 1, the peak value adjusting section 11 outputs a rectangular wave whose peak value is adjusted by the output of the DC / DC converter 13 supplied with electric power from the battery 14 and the signal given from the rectangular wave oscillator 8. . The differentiating circuit 9 differentiates the rectangular wave output from the peak value adjusting unit 11,
The pulse signal shown in (a) is generated. This pulse signal is given to the unbalanced-balanced conversion circuit 15, and the unbalanced-balanced conversion circuit 15 outputs balanced outputs A and B having the same crest value but different polarities as shown in FIGS. . The unbalanced-balanced conversion circuit 15 outputs the balanced outputs A and B having different polarities and the same peak value as the high frequency coaxial cable 10a,
It is transmitted to the foil electrode 4 attached to the insulating connection portion 2 by 10b and injected into the insulating connection portion 2.

As described above, in the present embodiment, the unbalanced-balanced conversion circuit 15 is provided in the subsequent stage of the conventional calibration pulse generator to obtain pulse signals having the same peak value but different polarities. As in the example, without providing the means 11a and 11b for obtaining the rectangular wave having the same crest value and the two differentiating circuits 9a and 9b having the same circuit constant,
Calibration pulses having the same peak value but different polarities can be injected to both sides of the insulating cylinder of the insulating connection portion. Further, since the high-frequency coaxial cables 10a and 10b are used to transmit the balanced output of the unbalanced-balanced conversion circuit 15 to the foil electrode 4, the balanced output terminals Z ', Z "and the foil electrode 4 are connected. A sufficiently good waveform can be transmitted even at a distance.

Here, by simply replacing the conventional insulated wire with a coaxial cable, the high frequency coaxial cables 10a, 1
Due to the capacitance between the core wire of 0b and the shield, the high-frequency signal output from the unbalanced-balanced conversion circuit 15 escapes from the core wire to the shield side, which causes waveform distortion. This is for the core side of the high frequency coaxial cables 10a and 10b,
While the closed circuit passing from the unbalanced-balanced conversion circuit 15 through the foil electrode 4 is formed, the high frequency coaxial cable 10a,
It is considered that the shield side of 10b is because the closed circuit as described above is not formed. Therefore, in this embodiment,
Shield the high-frequency coaxial cables 10a and 10b with the short-circuit portion 1
By 6 and 17, the balanced output side and the foil electrode side are short-circuited, respectively, and a closed circuit is formed on the shield side as well as the core side. This makes it possible to take advantage of the good transmission characteristics of the high frequency coaxial cable.

[0019]

As described above, the following effects can be obtained in the present invention. (1) Since the unbalanced-balanced conversion circuit obtains pulse signals of the same crest value with different polarities and injects this pulse signal as a calibration pulse, it uses a conventional calibration pulse generator and has different polarities. A calibration pulse having the same peak value can be obtained. (2) The unbalanced-balanced conversion circuit outputs the pulse signals of the same peak value with different polarities, the core wire is connected to the balanced output terminal of the unbalanced-balanced conversion circuit and the electrode, and the shield is the unbalanced- Since the transmission is performed through two coaxial cables connected by a short-circuit wire on the balance conversion circuit side and the electrode side, it is possible to prevent distortion of the waveform due to the capacitance between the core wire and the shield of the coaxial cable. This makes it possible to take advantage of the good transmission characteristics of the coaxial cable.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an unbalanced-balanced conversion circuit used in this embodiment.

FIG. 3 is a diagram showing input / output waveforms of the unbalanced-balanced conversion circuit of FIG.

FIG. 4 is a diagram showing a general partial discharge measurement method.

FIG. 5 is a diagram showing a conventional example in which calibration pulses having the same crest value but different polarities are generated.

[Explanation of symbols]

1 Power Cable 2 Insulated Connection Section 3 Calibration Pulse Generator 4 Foil Electrode 6 Partial Discharge Measuring Device 5 Partial Discharge Detector 7 Commercial Frequency Synchronizer 8 Rectangular Wave Oscillator 9, 9a, 9b Differentiation Circuit 11, 11a, 11b Crest Adjustment Part 12 Meter 13 DC / DC converter 14 Battery 15 Unbalanced-balanced conversion circuit 10a, 10b High frequency coaxial cable 16 Calibration pulse generator side coaxial shield short circuit part 17 Connection part side coaxial shield short circuit part 20 Conventional calibration pulse generator

Claims (3)

[Claims] 1. A method of injecting a calibration pulse used to calibrate a charge amount in a partial discharge measurement of a power device, wherein a pulse signal output from a calibration pulse generator is applied to an unbalanced-balanced conversion circuit and the polarities are the same. A method for injecting a calibration pulse, which comprises obtaining a pulse signal having a peak value and injecting the pulse signal into a power device as a calibration pulse. 2. A method of injecting a calibration pulse for injecting a calibration pulse into an electrode provided on a metal sheath or an anticorrosive layer on the metal sheath on both sides of a metal sheath edge cut portion of a power cable to perform charge amount calibration in partial discharge measurement. Then, the pulse signal output from the calibration pulse generator is applied to the unbalanced-balanced conversion circuit to obtain a pulse signal of the same crest value with different polarities, and the pulse signal of the same crest value with different polarities is used for the core wire. Is connected to the balanced output terminal of the unbalanced-balanced conversion circuit and the electrode, and the shield is transmitted via two coaxial cables connected by a short-circuit wire on the unbalanced-balanced conversion circuit side and the electrode side. A method for injecting a calibration pulse, which comprises: 3. A calibration pulse injection for injecting a calibration pulse into an electrode provided on a metal sheath on both sides of a metal sheath edging portion of a power cable or on an anticorrosive layer on the metal sheath for calibrating a charge amount in the partial discharge measurement. A calibration pulse generator that generates a calibration pulse and a pulse pulse signal that is connected to the latter stage of the calibration pulse generator and that has the same crest value but different polarity from the pulse signal that the calibration pulse generator outputs. A balance-balance conversion circuit, and 2 connected between the electrode and the unbalance-balance conversion circuit
The coaxial cables of the two coaxial cables are connected to the balanced output terminals of the unbalanced-balanced conversion circuit and the electrodes, and the shields are connected to the unbalanced-balanced conversion circuit side and A calibration pulse injection device, characterized in that it is short-circuited on the electrode side to form a closed loop of shielding.