JP3869283B2 - Method for removing inductive noise in power cable deterioration diagnosis and power cable test apparatus - Google Patents

Description

【００１３】
表１より、誘導ノイズありの条件では、ノイズなしの条件のものと比べて第３高調波成分（１５０Ｈｚ）の振幅Ｉ３が１０倍以上の値となり、重畳位相θ３の値も大きく異なるものとなっていることが確認できる。
すなわち、誘導ノイズありの条件では、真の劣化信号（水トリーから発せられる第３高調波成分）と誘導ノイズ中の第３高調波成分の和を測定してしまうため、正確な診断が不可能なことを意味している。
【００１４】
（２）本発明による測定
測定回路としては前記図１に示すものを用い、周波数が５１Ｈｚの試験電圧６ｋＶを電力ケーブル５及び無損失標準コンデンサ６に印加し、両者に流れる電流を用いて損失電流測定ブリッジ７で試験電圧より９０°進み位相の容量性電流の平衡をとり、電力ケーブル５の損失電流を抽出した。
得られた損失電流の波形をデジタルオシロスコープ８で５１Ｈｚの試験電圧波形を基準に平均化処理を行った後に、離散数値データとして取り込み、これを波形解析コンピュータ９でＦＦＴ解析した。ＦＦＴ解析では、基本波成分を５１Ｈｚとし、その高調波成分（１０２，１５３，２０４Ｈｚ，…）ごとの振幅と重畳位相の値を得た。
この場合も従来方法と同様に、まず、誘導ノイズのない測定環境においてデータを取得した後、誘導ノイズのある測定環境においてデータを取得した。
測定により得た、劣化信号として着目すべき損失電流中の第３高調波成分（１５１Ｈｚ）の振幅Ｉ３及び重畳位相θ３を表２に示す。
【００１５】
【表２】

【００１６】
誘導ノイズなしの場合においては、表２に示した通り第３高調波成分の振振幅Ｉ３及び重畳位相θ３とも、従来方法の結果とほぼ同じ値となっており、誘導ノイズの影響がなければ従来方法及び本発明とも当然ながら真の劣化信号を測定できていることがわかる。
さらに、本発明による方法では、誘導ノイズありの場合においても、表２に示した通り、得られた第３高調波成分の振振幅Ｉ３及び重畳位相θ３の値が、誘導ノイズなしの場合の結果とほぼ一致している。
すなわち、試験電圧の周波数を商用周波数とは異なる周波数にし、それを基準に損失電流波形の平均化処理を行うことで、誘導ノイズの影響を除去し得ることが確認された。
【００１７】
以上のように、本実施例においては、商用周波数とは周波数が異なる５１Ｈｚの試験電圧を用い、該試験電圧波形と同期をとって平均化処理を行っているので、商用周波数により生ずる誘導ノイズを消去することができ、誘導ノイズに影響されることなく損失電流の第３高調波成分の振幅、位相を得ることができた。
なお、上記実施例では周波数が５１Ｈｚの試験電圧のみを電力ケーブルに印加して測定を行う場合について説明したが、例えば、５１Ｈｚの周波数の試験電圧と、その２倍の周波数である１０２Ｈｚの周波数の試験電圧を重畳して電力ケーブルに印加するように構成してもよい。
周波数が５１Ｈｚの試験電圧と、周波数が１０２Ｈｚの試験電圧を電力ケーブルに重畳印加するには、周波数が５１Ｈｚと１０２Ｈｚの２つの電源を用いて行うことも可能であるが、例えば、信号波形発生器１内で５１Ｈｚの信号と１０２Ｈｚの信号を合成して重畳信号を得たり、あるいは５１Ｈｚと１０２Ｈｚの周波数の信号を合成した波形を出力する関数発生器を用いて、５１Ｈｚの信号と１０２Ｈｚの信号を合成した波形を得て、これを電力増幅器２で電力増幅して、電力ケーブルに印加するようにしてもよい。
【００１８】
【発明の効果】
以上説明したように、本発明においては、電力ケーブルに印加する試験電圧の周波数として、商用周波数ではない周波数を選択し、この時に絶縁体を流れる電流中より前記交流電圧と同位相である損失電流を抽出し、上記試験電圧波形を基準として損失電流信号を平均化処理しているので、測定回路外部から進入する誘導ノイズ（商用周波ノイズ及びその高調波ノイズ）を除去することができる。
その結果、従来方法では誘導ノイズの影響により正確な診断が行えなかったような測定環境においても、精度の高い劣化診断方法を実現することが可能となった。
【図面の簡単な説明】
【図１】本発明の実施例の測定回路の構成を示す図である。
【図２】従来方法における測定回路の構成を示す図である。
【符号の説明】
１ 信号波形発生器
２ 電力増幅器
３ 試験用変圧器
４ 補償リアクトル
５ 測定対象電力ケーブル
６ 無損失標準コンデンサ
７ 損失電流測定ブリッジ
８ デジタルオシロスコープ
９ 波形解析コンピュータ[0001]
BACKGROUND OF THE INVENTION
The present invention eliminates the effects of commercial frequency noise entering from outside the measurement circuit and its harmonic noise in the degradation diagnosis of the power cable, and only the harmonic component in the loss current generated due to the degradation of the cable. The present invention relates to a method for removing inductive noise that can be obtained, and a power cable test apparatus that can perform the deterioration diagnosis of a power cable with high accuracy by removing the influence of the harmonic noise.
[0002]
[Prior art]
A cross-linked polyethylene insulation cable (hereinafter referred to as a cable) that is currently generally used as a power cable has a deterioration form called water tree deterioration. A water tree is an altered part in an insulator generated by the action of an electric field and moisture, and this grows in the direction of the electric field with time. As a result, the insulation performance of the cable gradually decreases.
Therefore, if this is left as it is, an insulation breakdown accident will eventually occur during operation, resulting in a great deal of damage to power consumers.
For this reason, various degradation diagnosis techniques have been studied for the purpose of preventing cable breakdown accidents in advance and obtaining a planned renewal guideline for equipment.
[0003]
As one of the prior arts, an AC voltage is applied to the cable, a loss current having the same phase as the AC voltage is extracted from the current flowing through the insulator at this time, and harmonic components contained in the loss current are extracted. There is a method of diagnosing cable deterioration using the method.
The harmonic component in the loss current used as a degradation signal in this method is generated due to the non-linear electrical conduction characteristics of the water tree. By evaluating the generation state of the harmonic component, the water tree degradation of the cable Can be diagnosed.
Specifically, an AC voltage of commercial frequency is applied to the cable and a lossless standard capacitor connected in parallel thereto, and the current flowing through the standard capacitor is used to advance 90 ° from the current flowing through the cable with respect to the applied voltage. The phase component (capacitive current) is removed to extract the loss current, and the third harmonic component therein is used as the degradation signal.
[0004]
[Problems to be solved by the invention]
In general, cable deterioration diagnosis is performed by bringing diagnostic equipment into a substation where a cable terminal is installed.
Many power devices such as cables and transformers are installed at the substation, and all the cables other than the measurement target cables are normally in operation. For this reason, inductive noise is large in substations, and it is often difficult to perform an accurate diagnosis.
This is because the induced noise is composed of the commercial frequency and its harmonic components, so the conventional method cannot separate the harmonic component in the loss current generated from the water tree from the harmonic component in the induced noise. It depends on.
[0005]
Further, when the line to be diagnosed is long and the capacitance of the cable is large, a large-capacity power source is required to apply a predetermined test voltage to the cable. There is a limit to the power sources that can be prepared at the substation where the diagnosis is performed. In that case, a generator is prepared as a power source for diagnosis.
In the prior art, the output voltage of the generator is boosted to a predetermined test voltage by a transformer and applied to the cable. However, the output of the generator is generally not stable, and the frequency and voltage fluctuate and the harmonics vary. Since a considerable amount of wave components are included, it is not suitable for the above-described cable deterioration diagnosis method.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a commercial cable that enters from the outside of a measurement circuit using a device that generates a voltage having a frequency different from the commercial frequency in the deterioration diagnosis of a power cable. It is to avoid the influence of frequency noise and its harmonic noise, and to obtain only the harmonic component in the loss current generated due to the deterioration of the cable.
[0006]
[Means for Solving the Problems]
In the present invention, as the frequency of the test voltage applied to the measurement target cable, a frequency that is not an integral multiple of the commercial frequency and is not an integral fraction of the commercial frequency is selected, and this AC voltage is applied to the power cable. Sometimes, a loss current having the same phase as the AC voltage is extracted from the current flowing through the insulator. And by averaging the loss current signal based on the frequency of the applied AC voltage, the influence of commercial frequency noise and its harmonic noise entering from the outside of the measurement circuit is avoided, resulting in cable deterioration. Only harmonic components in the generated loss current can be obtained.
Further, as a configuration of a device that generates a voltage having a frequency different from the commercial frequency, in the present invention, as shown in FIG. 1, the frequency is different from the commercial frequency and is not an integral multiple of the commercial frequency. A signal waveform generator 1 capable of generating an alternating voltage signal having a frequency that is not an integral fraction of a frequency, a power amplifier 2, and a voltage from the power amplifier 2 are boosted to a predetermined test voltage, and a power cable 5 to be measured And a compensation reactor 4 that constitutes a parallel resonance circuit with the capacitance of the test transformer 3 applied to the power cable 5.
By using such a test voltage voltage generator, a test voltage having an arbitrary frequency can be generated.
Further, in the power amplifier 2 in the device configuration, the AC power received from the commercial power source or the power source of the generator is once converted into DC, and an AC voltage corresponding to the AC signal from the input signal waveform generator 1 is generated. Therefore, a constant test voltage is always applied to the power cable 5 without being affected by frequency fluctuations and voltage fluctuations commonly found in commercial power supplies and generator power supplies, and harmonic components in the power supplies. There is also an effect that can be done.
[0007]
As disclosed in the present invention, when a test voltage having a frequency ft = 51 Hz is applied to a water tree deteriorated cable, 3 × ft = 153 Hz, 5 × ft = Deterioration signals are generated in odd harmonic components such as 255 Hz.
On the other hand, since the induction noise from the surrounding power equipment is the commercial frequency f = 50 Hz and its harmonics 2 × f = 100 Hz, 3 × f = 150 Hz,..., The frequency of the degradation signal and the induction noise can be separated. .
However, the loss current at this time includes a large number of frequency components, and there are also adjacent frequencies, so that it is inappropriate for quantitative evaluation as it is. Therefore, in the present invention, the induced noise is removed by performing an averaging process for the loss current in a waveform observation device such as a digital oscilloscope in synchronization with the basic frequency of the test voltage.
In the case of the above example, 51 Hz, 153 Hz, 255 Hz, etc., which are frequency components synchronized with the test voltage frequency 51 Hz, remain unchanged after the averaging process, but 50 Hz, 100 Hz, 150 Hz,... Is not synchronized with 51 Hz and can be removed by averaging processing.
The above effect is not exhibited only when the frequency f of the test voltage is 51 Hz, and the frequency 3 × ft used as the degradation signal does not match the commercial frequency that is the frequency component of the induction noise and its harmonic component. If is selected, the same effect can be obtained.
As described above, according to the present invention, even when there is an influence of inductive noise due to an operating power device other than a measurement target cable such as a substation, only the true deterioration signal is extracted by eliminating the influence. Therefore, accurate deterioration diagnosis can be performed.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a measurement circuit according to an embodiment of the present invention.
As shown in the figure, an AC voltage signal having a frequency that is different from the commercial frequency, is not an integral multiple of the commercial frequency, and is not a fraction of the commercial frequency (for example, 48 Hz, 51 Hz, etc.) is generated. The output of the signal waveform generator 1 is given to the power amplifier 2. The power amplifier 2 generates and outputs an AC voltage corresponding to the AC signal from the input signal waveform generator 1.
The power amplifier 2 temporarily converts the AC power received from the commercial power source or the power source of the generator into a direct current, amplifies the AC signal with this direct current, and generates an AC voltage according to the output of the signal waveform generator 1. Generate. For this reason, as described above, a constant test voltage can always be applied to the cable without being affected by frequency fluctuations, voltage fluctuations, harmonic components in the power supply, and the like.
The output of the power amplifier 2 is applied to the primary side terminal of the test transformer 3 that boosts the voltage from the power amplifier 2 to a predetermined test voltage. A compensation reactor 4 is connected between the primary terminals of the test transformer 3, and the reactor of the compensation reactor 4 and the electrostatic capacity of the power cable 5 constitute a parallel resonance circuit. The flowing current can be reduced and the power supply capacity can be reduced.
[0009]
The voltage generated on the secondary side of the test transformer 3 is applied to the power cable 5 and the lossless standard capacitor 6 to be measured, and 90 ° from the test voltage by the loss current measurement bridge 7 using the current flowing in both. The loss current of the power cable 5 is extracted by balancing the forward phase capacitive current.
The loss current obtained by the loss current measurement bridge 7 is given to the digital oscilloscope 8. The digital oscilloscope 8 performs an averaging process based on the test voltage waveform applied to the power cable 5, and then captures the waveform as discrete numerical data.
That is, in the digital oscilloscope 8, the loss current for one cycle is taken out in synchronization with the test voltage waveform, the current for one cycle is added for several cycles, and the loss current is averaged by dividing by the number of additions. Processing is performed and this is captured as discrete numerical data.
Discrete numerical data averaged by the digital oscilloscope 8 is input to a waveform analysis computer 9, and the waveform analysis computer 9 performs Fourier (FFT) analysis on this signal, and the fundamental wave component (for example, 51 Hz) and its The amplitude and the superimposed phase (phase difference with respect to the fundamental component) for each harmonic component (for example, 102 Hz, 153 Hz, 204 Hz,...) Are obtained.
As described above, the harmonic component in the loss current is generated due to the non-linear electrical conduction characteristics of the water tree. Therefore, by evaluating the amplitude and the superimposed phase for each harmonic component obtained as described above, It is possible to diagnose the state of cable water tree degradation.
[0010]
In order to verify the effect of the present invention, the following measurements were performed.
The sample used is a CV cable having a voltage class of 22 kV, a conductor size of 100 mm ² and an insulation thickness of 6 mm and a length of 8 m. This cable has been confirmed to have a breakdown voltage of 60 kV and a maximum length of a water tree generated in the insulator of 3 mm by a destructive test and an insulator observation survey conducted after this measurement.
(1) A measurement circuit for measuring a degradation signal by a conventional method is shown in FIG. 2 and is the same as the measurement circuit shown in FIG. 1, but a commercial power supply of 50 Hz was used as the power supply.
The measurement procedure involves applying a commercial voltage (50 Hz) test voltage of 6 kV to the power cable 5 to be measured and the lossless standard capacitor 6 and using the current flowing in both, the loss current measurement bridge 7 advances the phase by 90 ° from the test voltage. The loss of the measurement target power cable 5 was extracted by balancing the capacitive current.
The obtained loss current waveform is captured as discrete numerical data by the digital oscilloscope 8 and is subjected to FFT analysis by the waveform analysis computer 9 so that the loss current is converted into a fundamental wave component (50 Hz) and its harmonic components (100, 150). , 200 Hz,...) Values of amplitude and superposition phase (phase difference with respect to the fundamental wave component) were obtained.
[0011]
In the above measurement, first, data was acquired in a measurement environment without induced noise, and then data was acquired in a measurement environment with induced noise. Inductive noise was realized by passing a current of 3000 A through an experimental cable line installed in the vicinity of the measurement circuit.
Table 1 shows the amplitude I3 and the superimposed phase θ3 of the third harmonic component in the loss current to be noted as the deterioration signal obtained from the measurement data.
[0012]
[Table 1]

[0013]
From Table 1, under the condition with inductive noise, the amplitude I3 of the third harmonic component (150 Hz) is 10 times or more as compared with the condition without noise, and the value of the superposition phase θ3 is also greatly different. Can be confirmed.
That is, under conditions with induced noise, the true degradation signal (third harmonic component emitted from the water tree) and the sum of the third harmonic component in the induced noise are measured, so accurate diagnosis is impossible. It means that.
[0014]
(2) As the measurement and measurement circuit according to the present invention, the one shown in FIG. 1 is used, a test voltage 6 kV having a frequency of 51 Hz is applied to the power cable 5 and the lossless standard capacitor 6, and the current flowing through both is used as a loss current. The measurement bridge 7 is 90 ° ahead of the test voltage to balance the capacitive current in phase, and the loss current of the power cable 5 is extracted.
The obtained loss current waveform was averaged by the digital oscilloscope 8 based on the test voltage waveform of 51 Hz, and then taken as discrete numerical data, which was subjected to FFT analysis by the waveform analysis computer 9. In the FFT analysis, the fundamental wave component was set to 51 Hz, and the amplitude and superposed phase values for each of the harmonic components (102, 153, 204 Hz,...) Were obtained.
Also in this case, as in the conventional method, first, data was acquired in a measurement environment without induced noise, and then data was acquired in a measurement environment with induced noise.
Table 2 shows the amplitude I3 and the superimposed phase θ3 of the third harmonic component (151 Hz) in the loss current to be noted as the deterioration signal obtained by the measurement.
[0015]
[Table 2]

[0016]
In the case of no induced noise, as shown in Table 2, both the amplitude I3 of the third harmonic component and the superimposed phase θ3 are substantially the same as the results of the conventional method. It can be seen that both the method and the present invention are able to measure a true degradation signal.
Furthermore, in the method according to the present invention, as shown in Table 2, the values of the amplitude I3 and the superposed phase θ3 of the obtained third harmonic component are the results when there is no induced noise even when there is induced noise. Is almost the same.
That is, it was confirmed that the influence of the induction noise can be removed by setting the frequency of the test voltage to a frequency different from the commercial frequency and performing the averaging process of the loss current waveform based on the frequency.
[0017]
As described above, in this embodiment, a 51 Hz test voltage different from the commercial frequency is used, and the averaging process is performed in synchronization with the test voltage waveform. The amplitude and phase of the third harmonic component of the loss current could be obtained without being affected by the induction noise.
In the above embodiment, the case where the measurement is performed by applying only the test voltage having a frequency of 51 Hz to the power cable has been described. For example, the test voltage having a frequency of 51 Hz and the frequency of 102 Hz which is twice the frequency are described. You may comprise so that a test voltage may be superimposed and applied to a power cable.
In order to superimpose and apply a test voltage with a frequency of 51 Hz and a test voltage with a frequency of 102 Hz to a power cable, it is possible to use two power sources with a frequency of 51 Hz and 102 Hz. For example, a signal waveform generator A 51 Hz signal and a 102 Hz signal are synthesized by combining a 51 Hz signal and a 102 Hz signal, or using a function generator that outputs a waveform obtained by synthesizing a 51 Hz and 102 Hz frequency signal. It is also possible to obtain a combined waveform, amplify the power with the power amplifier 2, and apply it to the power cable.
[0018]
【The invention's effect】
As described above, in the present invention, a frequency that is not a commercial frequency is selected as the frequency of the test voltage applied to the power cable, and at this time, a loss current that is in phase with the AC voltage from among the current flowing through the insulator. Since the loss current signal is averaged with reference to the test voltage waveform, induction noise (commercial frequency noise and its harmonic noise) entering from the outside of the measurement circuit can be removed.
As a result, it has become possible to realize a highly accurate deterioration diagnosis method even in a measurement environment where the conventional method cannot perform an accurate diagnosis due to the influence of induced noise.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a measurement circuit according to an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of a measurement circuit in a conventional method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Signal waveform generator 2 Power amplifier 3 Test transformer 4 Compensation reactor 5 Measuring object power cable 6 Lossless standard capacitor 7 Loss current measurement bridge 8 Digital oscilloscope 9 Waveform analysis computer

Claims (2)

When an AC voltage is applied to the power cable, a loss current having the same phase as the AC voltage is extracted from the current flowing through the insulator at this time, and deterioration diagnosis is performed using the harmonic component contained in the loss current. A method for removing inductive noise in power cable deterioration diagnosis,
An AC voltage having a frequency different from the commercial frequency, not an integer multiple of the commercial frequency, and having a frequency that is not an integral number of the commercial frequency is applied to the power cable;
The alternating current voltage is synchronized with the frequency of the alternating voltage from the measured loss current signal, and the loss current for one cycle is taken out, the loss current for one cycle is added for several cycles, and divided by the number of times of addition. A method for removing induced noise in a deterioration diagnosis of a power cable, wherein an averaging process synchronized with a voltage frequency is performed to remove an induced noise component included in the loss current. When an AC voltage is applied to the power cable, a loss current having the same phase as the AC voltage is extracted from the current flowing through the insulator at this time, and the degradation of the power cable is performed using the harmonic component contained in the loss current. A power cable testing device for performing diagnosis,
A signal waveform generator capable of generating an AC voltage signal having a frequency different from the commercial frequency, not an integral multiple of the commercial frequency, and a frequency that is not an integral fraction of the commercial frequency;
A power amplifier that amplifies power based on the signal;
Boosting the voltage from the power amplifier to a predetermined test voltage and applying it to a power cable to be tested;
A compensation reactor connected between the terminals of the test transformer and the capacitance of the power cable and the parallel resonant circuit;
A loss current measurement bridge that extracts a loss current that is in phase with the AC voltage from the current flowing through the insulator of the power cable;
By synchronizing the frequency of the AC voltage from the loss current signal measured by the loss current bridge , taking out the loss current for one cycle, adding several cycles of the loss current for one cycle, and dividing by the number of additions, An apparatus for testing a power cable, comprising: means for performing an averaging process synchronized with the frequency of the AC voltage; and means for extracting a harmonic component contained in the loss current.

Images