JP2004061358A - Method and apparatus for detecting partial discharge in insulator of power equipment - Google Patents

Abstract

A partial discharge generated in an insulator of a power device is detected with high accuracy and simply using ultrasonic waves. A partial discharge detector for a power device is attached to the insulator of a power device. An ultrasonic sensor 10 that detects ultrasonic waves generated during the supply of AC power to the electric power device, a periodic component detection unit 18 that detects a periodic component by frequency analysis of the ultrasonic waves detected by the ultrasonic sensor 10, The generation period of the ultrasonic periodic component is compared with the power supply frequency that is the period of the AC power supplied to the power device, and the generation period of the ultrasonic periodic component is within the predetermined range of the power supply frequency or twice the power supply frequency. If so, a determination unit 19 that determines that partial discharge has occurred is provided.
[Selection] Figure 1

Description

【００４６】
各測定点Ｐ１〜Ｐ６における、包絡検波した超音波の波形はそれぞれ図８（Ａ）〜（Ｆ）に示す通りである。図８（Ａ），（Ｂ）より明らかなように、欠陥Ｄを設けた銅帯母線３０Ｂ上にあり、かつ欠陥Ｄに近い測定点Ｐ１、Ｐ２では、０．０１秒周期（１００Ｈｚ）の発生周期を有する超音波の振幅のピークが非常に明瞭に認められた（表１の検出感度の欄で◎で示す。）。また、図８（Ｄ）から明らかなように、奥側の銅帯母線３０Ｃ上にあり、かつ欠陥Ｄに近い測定点Ｐ４でも、同一発生周期の超音波の振幅のピークが明瞭に認められた（表１の検出感度の欄で○で示す。）。さらに、図８（Ｃ），（Ｅ）から明らかなように、奥側の銅帯母線３０Ｃ上にあり、かつ欠陥Ｄから銅帯母線３０Ａ〜３０Ｃの長さ方向に４０ｍｍの位置の測定点Ｐ３、並びに手前側の銅帯母線３０Ａ上にあり、かつ欠陥Ｄに近い位置にある測定点Ｐ５でも、同一周期の超音波の振幅のピークが認められたが、測定点Ｐ１、Ｐ２、及びＰ４と比較すると振幅のピーク値は小さい（表１の検出感度の欄で△で示す。）。これに対して、図８（Ｆ）から明らかなように、欠陥Ｄが設けられた銅帯母線３０Ｂ上にあるが、欠陥Ｄから２００ｍｍ離れた測定点Ｐ６では、振幅のピークは殆ど認められなかった。
【００４７】
測定点Ｐ１〜Ｐ５で超音波の振幅にピークが認められその周期が１００Ｈｚであることから、超音波は電源周波数の２倍の発生周期の周期成分を有することが確認できた。また、欠陥Ｄからの距離が離れると振幅のピーク値が小さくなることから、絶縁体の複数箇所で測定された周期成分の強度が変化しているときは、当該周期成分が部分放電によるものであると推定できることが確認できた。
【００４８】
【発明の効果】
以上の説明から明らかなように、本発明に係る電力機器の絶縁体中の部分放電検出方法及び装置では、超音波センサにより検出される超音波の周期成分を周波数解析により検出し、この周期成分の発生周期が電力機器へ供給される交流電力の周波数である電源周波数又はその２倍の所定範囲であれば部分放電検出であると判断する。従って、活線状態を維持しつつ、高精度かつ簡易に絶縁体中の部分放電を検出することができる。また、前記超音波の周期成分を時間−周波数解析により検出することにより、Ｓ／Ｎ比が低い場合でも高精度で部分放電を検出することができる。
【図面の簡単な説明】
【図１】本発明の実施形態に係る部分放電検出装置を示す概略図である。
【図２】プリアンプを内蔵した超音波センサを示す概略図である。
【図３】銅帯母線を示し、（Ａ）は概略平面図、（Ｂ）は正面図、（Ｃ）は横断面図である。
【図４】ロードブレークエルボを示し、（Ａ）は側面図、（Ｂ）は正面図である。
【図５】短時間フーリエ変換による超音波の周期成分（５０Ｈｚ）の検出の一例を示し、（Ａ）は計測波形を示すグラフ、（Ｂ）は短時間フーリエ変換により得られる周波数スペクトルを示す概念図、（Ｃ）は周期成分のスペクトル強度と時間の関係を示すグラフである。
【図６】短時間フーリエ変換による超音波の周期成分（１００Ｈｚ）の検出の一例を示し、（Ａ）は計測波形を示すグラフ、（Ｂ）は短時間フーリエ変換により得られる周波数スペクトルを示す概念図、（Ｃ）は特定周期成分のスペクトル強度と時間の関係を示すグラフである。
【図７】実験例における欠陥の位置及び測定位置を示す銅帯母線の部分平面図である。
【図８】（Ａ）、（Ｂ）、（Ｃ）、（Ｄ）、（Ｅ）、及び（Ｆ）は、銅帯母線を使用した実験例における、超音波の包絡線検波波形を示すグラフである。
【図９】（Ａ）は電力機器の絶縁体中の欠陥近傍に作用する電圧と欠陥に作用する電圧の関係を示すグラフ、（Ｂ）は（Ａ）に対応する部分放電パルス波形を示すグラフである。
【符号の説明】
１０　超音波センサ
１０ａ　ハウジング
１１　プリアンプ
１２　フィルタ
１３　アンプ
１４　処理部
１６　接触媒質
１７　電力機器
１８　周期成分検出部
１９　判定部
２１　モニタ
２３　信号線
２４　フェライトコア
３０Ａ，３０Ｂ，３０Ｃ　銅帯母線
４０　ロードブレークエルボ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for detecting partial discharge in an insulator of a power device. The present invention is applied to, for example, detection of partial discharge generated in an insulator of a power cable peripheral device such as a copper band bus or a load break elbow of a molded disc.
[0002]
[Prior art]
When defects such as voids exist in the insulator of the power equipment, partial discharge occurs. Specifically, partial discharge occurs when the voltage applied to the defect exceeds a critical voltage, that is, a spark voltage, due to partial breakdown in the defect. If this partial discharge is repeated, the insulation as a whole eventually breaks down, and there is a possibility that a situation in which power transmission / distribution such as a power failure due to a ground fault is hindered may occur. On the other hand, it is extremely complicated to stop power transmission and distribution for detection of this partial discharge.
[0003]
Therefore, in order to detect the partial discharge of the insulator without stopping power transmission / distribution, that is, in the live line state, a method of detecting the partial discharge by detecting the ultrasonic wave generated during the partial discharge has been proposed ( For example, JP-A-58-7572, JP-A-62-201375).
[0004]
However, it is difficult to determine whether the ultrasonic wave measured by the ultrasonic sensor is caused by partial discharge or noise such as ultrasonic wave caused by disturbance noise or air discharge. Therefore, various attempts have been made to increase detection accuracy.
[0005]
For example, in Japanese Patent Laid-Open No. 63-177073, an electric pulse is measured together with an ultrasonic pulse, and whether the ultrasonic pulse is due to partial discharge or noise is determined based on the time difference between the ultrasonic pulse and the electric pulse. A method of determination is described. However, this method requires a device that measures the AC voltage supplied to the power device, and cannot easily detect partial discharge.
[0006]
JP-A-5-240903 and JP-A-8-320357 describe that it is determined that an ultrasonic wave having a duration of a predetermined time or less (for example, 5 msec) is due to partial discharge. However, since there is a sudden noise with a short duration, it is difficult to discriminate ultrasonic waves and noise caused by partial discharge with high accuracy by this method.
[0007]
Furthermore, Japanese Patent Laid-Open No. 63-8571 describes that detection accuracy is improved by amplifying a specific frequency band including the frequency of ultrasonic waves caused by partial discharge. However, in this method, all components included in the frequency band are amplified regardless of whether the ultrasonic wave is due to partial discharge or noise. Therefore, when noise is included in the frequency band, the noise is amplified, and as a result, highly accurate detection is difficult.
[0008]
[Problems to be solved by the invention]
As described above, in the conventional method for detecting partial discharge using ultrasonic waves, it is not possible to guarantee with high accuracy that the measured ultrasonic waves are caused by the partial discharge. When the signal intensity of the signal is weak, the detection accuracy is lowered.
[0009]
The present invention has been made to solve the problems in the conventional partial discharge detection method using ultrasonic waves, and a portion generated in an insulator of a power device using ultrasonic waves with high accuracy and simplicity. It is an object of the present invention to provide a method and an apparatus for detecting discharge.
[0010]
[Means for Solving the Problems]
First, the principle of the present invention will be described with reference to FIG. FIG. 9A shows a voltage V acting in the vicinity of a defect such as a void when an AC voltage is applied to an insulator of a power device. _a (Two-dot chain line) and the voltage V acting on the defect _b (Solid line). Voltage V _a Corresponds to the AC voltage supplied to the power equipment, and the voltage V _a The frequency of is the same as the frequency (power supply frequency) of the AC voltage supplied to the power device.
[0011]
Voltage V until time t1 _a Increases, so the voltage V _b Is positive spark voltage + V _th And partial discharge occurs as shown in FIG. When partial discharge occurs, a reverse electric field is formed at the defect, and the voltage V _b Instantaneously drops to almost 0V. Voltage V from time t1 _a Begins to drop, the voltage V ₂ Will also drop with the spark voltage -V _th And partial discharge occurs. This partial discharge causes the voltage V _b Momentarily returns to 0V, but the voltage V _a As the voltage drops, the voltage V _b Again, the spark voltage -V _th And partial discharge occurs. Since the two partial discharges are generated at an extremely short time interval, it can be regarded as one partial discharge PD. Voltage V from time t3 _a When the voltage starts to rise, the voltage V _b Rises accordingly, and spark voltage + V _th And partial discharge occurs. This partial discharge causes the voltage V _b Instantaneously drops to almost 0V, but the voltage V _a As the voltage rises, the voltage V _b Will also rise, so the spark voltage is again -V _th And partial discharge occurs. Since these partial discharges are also generated at extremely short time intervals, they can be regarded as one partial discharge PD.
[0012]
As a result of the above process being repeated, the voltage V _a The partial discharge PD is repeatedly generated in the vicinity of the zero crossing, and the generation period of the partial discharge PD is the voltage V _a , Ie, twice the power frequency. Depending on the situation, the voltage V ₂ Partial discharge PD may occur only in one of the positive and negative phases. In this case, the generation period of the partial discharge PD is the same as the power supply frequency. Therefore, if the ultrasonic wave detected by the ultrasonic sensor includes a periodic component and the periodic component has a generation cycle that is the same as or nearly twice that of the power supply frequency, the periodic component is due to partial discharge. You can think of it. The present invention has been made based on such knowledge.
[0013]
Accordingly, in the first invention, an ultrasonic sensor is disposed on an insulator of a power device, the ultrasonic wave is detected by the ultrasonic sensor while AC power is supplied to the power device, and the ultrasonic sensor detects the ultrasonic wave. Analyzing the frequency of the ultrasonic wave to detect the periodic component, comparing the generation period of the periodic component of the ultrasonic wave with the power supply frequency that is the frequency of the AC power supplied to the power device, and the periodic component of the ultrasonic wave A partial discharge detection method in an insulator of a power device is provided that determines that a partial discharge has occurred if the generation period is within a predetermined range of the power supply frequency or twice the power supply frequency.
[0014]
The predetermined range is, for example, a power supply frequency or ± 10% that is twice the frequency. In addition, the frequency analysis may be to obtain the frequency distribution of the ultrasonic wave itself detected by the ultrasonic sensor, or the frequency distribution of the waveform detected by the envelope detection.
[0015]
The partial discharge detection method according to the first aspect of the present invention is not to detect a partial discharge only from the duration of the pulse included in the waveform of the ultrasonic wave or its intensity, but to generate the ultrasonic wave generation cycle and power supply caused by the partial discharge. The occurrence of partial discharge is detected based on knowledge about the relationship with frequency. That is, the periodic component of the ultrasonic wave detected by the ultrasonic sensor is detected by frequency analysis, and if the generation period of this periodic component is within a predetermined range of the power supply frequency or twice that, it is determined that partial discharge is detected. Therefore, partial discharge can be detected with high accuracy. Further, since the generation period of the periodic component of the ultrasonic wave is compared with the power supply frequency, it is not necessary to detect a voltage pulse or a current pulse, and a partial discharge can be detected easily.
[0016]
Specifically, the periodic component is detected by time-frequency analysis of the ultrasonic waves detected by the ultrasonic sensor. Here, the time-frequency analysis is a vibration analysis for obtaining a frequency spectrum every minute time. By this time-frequency analysis, even when the S / N ratio is low, that is, even if the amplitude or intensity of the periodic component is similar to noise such as thermal noise of electric power equipment, the periodic component can be reliably detected, Partial discharge can be detected with higher accuracy. Time-frequency analysis includes, for example, short-time Fourier transform, wavelet transform, and Wigner distribution function.
[0017]
You may detect the periodic component of an ultrasonic wave by methods other than time-frequency analysis. For example, when the S / N ratio is high, the ultrasonic periodic component may be detected by applying a fast Fourier transform to the detected ultrasonic wave or its envelope-detected waveform.
[0018]
Since the ultrasonic wave attenuates when propagating through the insulator, the intensity of the ultrasonic wave generated by the partial discharge increases as the measurement position is closer to the partial discharge generation position, that is, the defect. Therefore, when the intensity of the periodic component of the ultrasonic waves at a plurality of locations is changed, it is possible to further improve the detection accuracy of the partial discharge by determining that the periodic component is due to the partial discharge.
[0019]
According to a second aspect of the present invention, there is provided an ultrasonic sensor that is attached to an insulator of a power device and detects an ultrasonic wave generated during the supply of AC power to the power device, and frequency analysis is performed on the ultrasonic wave detected by the ultrasonic sensor. The periodic component detection unit that detects the periodic component and the generation period of the periodic component of the ultrasonic wave detected by the periodic component detection unit and the power supply frequency that is the cycle of the AC power supplied to the power device are compared. A partial discharge in an insulator of a power device, comprising: a determination unit that determines that a partial discharge is generated if the generation period of the periodic component of the ultrasonic wave is within a predetermined range of the power supply frequency or twice the power supply frequency. A detection device is provided.
[0020]
The detection signal of the ultrasonic sensor is amplified by the preamplifier and then transmitted to the periodic component detection unit. Since the detection signal of the ultrasonic sensor is weak, inductive noise whose noise source is unknown may be mixed in the signal line connecting the ultrasonic sensor and the preamplifier. By introducing a ferrite core into which a signal line for connecting the ultrasonic sensor and the preamplifier is inserted, or by incorporating the preamplifier in the ultrasonic sensor, this induction noise can be prevented from being mixed. By preventing the induction noise from mixing, the S / N ratio can be improved and the partial discharge detection accuracy can be increased.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in detail with reference to embodiments shown in the drawings.
As shown in FIG. 1, the partial discharge detection device according to the embodiment of the present invention includes an ultrasonic sensor 10, a preamplifier 11, a filter 12, an amplifier 13, and a processing unit 14. The detection signal of the ultrasonic sensor 10 is sent to the processing unit 14 through the preamplifier 11, the filter 12, and the amplifier 13.
[0022]
The ultrasonic sensor 10 is, for example, a piezoelectric element type ultrasonic sensor, and is installed on the surface of a power device 17 that is a detection target of partial discharge of an insulator via a contact medium 16 such as silicon grease. However, the ultrasonic sensor 10 is not limited to the piezoelectric element type, and may be any sensor that can detect ultrasonic waves propagating through an insulator with good sensitivity. The contact medium 16 is used for reducing transmission loss of ultrasonic waves at the contact portion between the ultrasonic sensor 10 and the power device 17 and ensuring insulation between the power device and the partial discharge detection device.
[0023]
The preamplifier 11 amplifies a weak detection signal output from the ultrasonic sensor 10 in order to reduce the influence of noise. The filter 12 is for removing disturbance noise and electrical noise included in the detection signal of the ultrasonic sensor 10. The filter 12 can adjust the low-pass filter cut-off frequency and the high-pass filter cut-off frequency, and passes only the optimum band according to the dominant frequency of the ultrasonic wave when the partial discharge occurs in the target power device. The amplifier 13 amplifies the detection signal in order to improve the S / N ratio in the processing unit 14.
[0024]
The processing unit 14 includes a periodic component detection unit 18 and a determination unit 19. The periodic component detection unit 18 performs frequency analysis on the ultrasonic wave detected by the ultrasonic sensor 10 based on detection signals received from the ultrasonic sensor 10 via the preamplifier 11, the filter 12, and the amplifier 13 to obtain a periodic component. To detect. The determination unit 19 determines whether or not partial discharge has occurred in the insulator of the power device 17 by comparing the generation period of the periodic component of the ultrasonic wave detected by the periodic component detection unit 18 with the power supply frequency. The processing unit 14 is connected to a monitor 21, an input device (not shown), and the like so that an operator operates the partial discharge detection device.
[0025]
The partial discharge detector can be configured by combining various analog circuits and digital circuits, and various devices including measurement devices. For example, the processing unit 14 including the filter 12, the amplifier 13, and the monitor 21 can be configured by an ultrasonic waveform discriminator and a digital oscilloscope.
[0026]
A signal line 23 connecting the ultrasonic sensor 10 and the preamplifier 11 is inserted through the ferrite core 24. This is because inductive noise whose cause is not necessarily clear may be mixed between the ultrasonic sensor 10 and the preamplifier 11, so that the influence of this type of noise is reduced.
[0027]
As shown in FIG. 2, the preamplifier 11 may be built in the ultrasonic sensor 10. In FIG. 2, reference numeral 26 denotes an ultrasonic detection element such as a piezoelectric element, and the preamplifier 11 is accommodated in the housing 10 a of the ultrasonic sensor 10 together with the element 26. Since the preamplifier 11 is built in, the length of the signal line between the element 26 and the preamplifier 11 can be greatly shortened, so that the introduction of inductive noise can be prevented.
[0028]
Although the electric power apparatus which is a measuring object is not specifically limited, For example, there exists copper strip | bus bus | bath 30A, 30B, 30C for mold discons shown to FIG. 3 (A)-(C). As shown in FIG. 3C, the copper band buses 30A to 30C are provided around the conductor 30a, the internal semiconductive rubber layer 30b provided around the conductor 30a, and the internal semiconductive rubber layer 30b. An EP rubber layer 30c, which is an insulating material, and an external semiconductive rubber layer 30d covering the outer surface are provided. Each of the copper strip buses 30A to 30C includes a distribution side connection portion 30e, 30f and a power supply side connection portion 30g.
[0029]
The power equipment that is the measurement target may be a road break elbow 40 shown in FIGS. The load break elbow 40 is for connecting a high voltage side electric wire 41 to a transformer 42. Similar to the copper strip bus bars 30A to 30C, the load break elbow 40 includes a conductor 40a, an inner semiconductive rubber layer 40b surrounding the conductor 40a, an EP rubber layer 40c surrounding the inner semiconductive rubber layer 40b, and an outer surface. An external semiconductive rubber layer 40d is provided.
[0030]
Other power devices that can be measured include cable connections (cable intermediate connections, cable termination connections, insulation plugs), high-voltage pass ducts, molded transformers, generator stator coils, motors, transformers, etc. .
[0031]
Next, a partial discharge detection method using this partial discharge detection device will be described.
First, the ultrasonic sensor 10 is disposed on the surface of the power device 17 via the contact medium 16. Next, ultrasonic waves are detected by the ultrasonic sensor 10 in a state where AC power is supplied to the power equipment, that is, in a live line state. The frequency of the AC power of the power device (power supply frequency) is input to the determination unit of the processing unit 14.
[0032]
The detection signal of the ultrasonic sensor 10 is sent to the processing unit 14 via the preamplifier 11, the filter 12, and the amplifier 13. At this time, the signal line 23 between the ultrasonic sensor 10 and the preamplifier 11 is inserted into the ferrite core 24, or the preamplifier 11 is built in the ultrasonic sensor 10, whereby the ultrasonic sensor 10 and the preamplifier 11 are connected. It is possible to improve the S / N ratio by preventing the induction noise from being mixed.
[0033]
The detection signal of the ultrasonic sensor 10 sent to the processing unit 14 is input to the periodic component detection unit 14. The periodic component detection unit 14 performs frequency analysis based on the input detection signal, and detects an ultrasonic periodic component. Moreover, the periodic component detection part 14 evaluates the generation period of the detected periodic component. The detection of the periodic component and the evaluation of the generation period can be performed based on the frequency distribution of the waveform of the detection signal detected by the ultrasonic sensor 10, that is, the frequency distribution of the detected ultrasonic wave itself. These detections and evaluations can also be performed based on the frequency distribution of the waveform detected by the envelope.
[0034]
The detection signal of the ultrasonic sensor 10 includes noise such as thermal noise and disturbance noise of power equipment. Since the periodic component resulting from the partial discharge contained in the detected ultrasonic wave is pulse-like, the proportion of this periodic component in the entire waveform is very small. Since normal fast Fourier transform obtains the frequency spectrum of the entire waveform, instantaneous changes are averaged within the number of data points, making it difficult to detect. If the S / N ratio is low, the periodic component is highly accurate. Is difficult to detect. Therefore, it is preferable to use time-frequency analysis as a frequency analysis method used by the periodic component detection unit 18 in order to detect the periodic component and its generation period with high accuracy. In this time-frequency analysis, an ultrasonic waveform is divided in the time axis direction, and a frequency spectrum is detected for each divided time section.
[0035]
An example of the time-frequency analysis is a short-time Fourier transform. In the short-time Fourier transform, a window is set by dividing an ultrasonic waveform in the time axis direction, and the fast Fourier transform is applied to each window by shifting the window little by little on the time axis. If the window width is set to be sufficiently shorter than the ultrasonic waveform, only a part of the original waveform will be present. By applying the Fast Fourier Transform to this waveform, the frequency spectrum at the moment can be obtained. It is possible to extract changes in a short time.
[0036]
5 and 6 schematically show an example in which frequency analysis is performed by applying short-time Fourier transform to an ultrasonic waveform. FIG. 5 shows a case where a periodic component caused by a partial discharge having the same generation cycle (50 Hz) as the power supply frequency (50 Hz) is included, and FIG. 6 shows a partial discharge having a generation cycle (100 Hz) twice the power supply frequency. The case where the periodic component resulting from is included is shown.
[0037]
As shown in FIGS. 5A and 6A, the periodic component X is buried in the noise Y in the original waveform of the ultrasonic wave. When a short-time Fourier transform is applied to this waveform, a periodic component X appears in the frequency spectrum as shown in FIGS. 5 (B) and 6 (B). Then, as shown in FIGS. 5C and 6C, the generation period of the periodic component is detected from the temporal change of the spectrum intensity.
[0038]
The frequency analysis may be performed by other time-frequency analysis such as wavelet transform and Wigner distribution function. When the S / N ratio is high, that is, when the amplitude or intensity of the periodic component is larger than noise such as thermal noise or disturbance noise of electrical equipment, the waveform of the ultrasonic wave or its envelope detected May be subjected to frequency analysis by fast Fourier transform.
[0039]
The generation period of the ultrasonic periodic component detected by the periodic component detection unit 18 as described above is sent to the determination unit 19. The determination unit 19 compares the generation period of the periodic component with the power supply frequency, and if the periodic component is equal to the power supply frequency or within a predetermined range with respect to twice the power supply frequency, the period detected by the periodic component detection unit 18 It is determined that the component is due to partial discharge. For example, when the power supply frequency is 50 Hz, the determination unit 19 determines that the periodic component of the ultrasonic wave is a partial discharge if the generation period of the ultrasonic periodic component detected by the periodic component detection unit 18 is within a predetermined range of 50 Hz or 100 Hz. That is, it is determined that partial discharge is generated in the insulator. The predetermined range is set in consideration of measurement error, error accompanying frequency analysis, and the like. For example, the predetermined range is set to a range of ± 10% that is the same as or twice the power supply frequency.
[0040]
In the present embodiment, as described above, the partial discharge is not detected only from the duration or the intensity of the pulse included in the waveform of the ultrasonic wave, but the generation cycle of the ultrasonic wave caused by the partial discharge, the power supply frequency, and the like. The occurrence of partial discharge is detected based on the knowledge about the relationship. That is, the periodic component detection unit 18 detects the periodic component of the ultrasonic wave detected by the ultrasonic sensor 10 by frequency analysis. Is determined to be partial discharge detection. Therefore, partial discharge can be detected with high accuracy. Further, since the generation period of the periodic component of the ultrasonic wave is compared with the power supply frequency, it is not necessary to detect a voltage pulse or a current pulse, and a partial discharge can be detected easily. Furthermore, by detecting the periodic component by time-frequency analysis, detection with higher accuracy becomes possible.
[0041]
Since the ultrasonic wave is attenuated when propagating through the insulator, the intensity of the ultrasonic wave generated by the partial discharge becomes stronger as the attachment position of the ultrasonic sensor 10 is closer to the partial discharge generation position, that is, the defect. Accordingly, when the ultrasonic sensor 10 repeatedly detects ultrasonic waves during the supply of AC power at a plurality of locations on the insulator and the intensity of the periodic component of the ultrasonic waves due to the partial discharge at the plurality of locations changes, the determination unit 19 If it is determined that the periodic component is due to partial discharge, the detection accuracy of partial discharge can be further improved.
[0042]
An experiment was conducted to confirm the principle of the present invention. In this experiment, as shown in FIG. 7, a defect D is provided at one of the copper strip buses 30 </ b> A to 30 </ b> C, and ultrasonic waves during AC power supply at six measurement points P <b> 1 to P <b> 6 are measured by the ultrasonic sensor 10. . The power supply frequency is 50 Hz, and the effective power value is 4242V.
[0043]
The formation of the defect D will be described with reference to FIG. 3. The external semiconductive rubber layer 30 d and the EP rubber layer 30 c are partially peeled off, and the EP rubber layer 30 c is scratched with protrusions, resulting in void-like defects. Was provided. Next, the peeled external semiconductive rubber layer 30d and EP rubber layer 30c were restored to close the defect. Finally, the part where the external semiconductive rubber layer 30d and the EP rubber layer 30c were peeled was firmly wound with an adhesive polyethylene tape.
[0044]
The positions of the measurement points P1 to P6 are as shown in FIG. 7 and Table 1 below. At any of the measurement points P1 to P6, the ultrasonic sensor 10 was attached to the upper surface of the copper strip bus bars 30A to 30C.
[0045]
[Table 1]

[0046]
The waveforms of the ultrasonic waves detected by the envelope detection at the respective measurement points P1 to P6 are as shown in FIGS. 8 (A) to (F), respectively. As is apparent from FIGS. 8A and 8B, a 0.01 second period (100 Hz) is generated at the measurement points P1 and P2 on the copper band bus 30B provided with the defect D and close to the defect D. The peak of the amplitude of the ultrasonic wave having a period was recognized very clearly (indicated by ◎ in the column of detection sensitivity in Table 1). Further, as apparent from FIG. 8D, the peak of the amplitude of the ultrasonic wave having the same generation period was clearly recognized even at the measurement point P4 on the copper strip bus 30C on the back side and close to the defect D. (Indicated by a circle in the detection sensitivity column of Table 1). Further, as is apparent from FIGS. 8C and 8E, the measurement point P3 is located on the copper strip bus 30C on the back side and is 40 mm from the defect D in the length direction of the copper strip buses 30A to 30C. In addition, at the measurement point P5 on the copper band bus 30A on the near side and close to the defect D, the peak of the amplitude of the ultrasonic wave having the same period was observed, but the measurement points P1, P2, and P4 In comparison, the peak value of the amplitude is small (indicated by Δ in the column of detection sensitivity in Table 1). On the other hand, as is clear from FIG. 8 (F), although it is on the copper strip bus 30B provided with the defect D, an amplitude peak is hardly observed at the measurement point P6 200 mm away from the defect D. It was.
[0047]
Since a peak was observed in the amplitude of the ultrasonic wave at the measurement points P1 to P5 and the period was 100 Hz, it was confirmed that the ultrasonic wave had a period component having a generation period twice the power supply frequency. Further, since the peak value of the amplitude decreases as the distance from the defect D increases, when the intensity of the periodic component measured at a plurality of locations of the insulator changes, the periodic component is due to partial discharge. It was confirmed that it could be estimated.
[0048]
【The invention's effect】
As is clear from the above description, in the partial discharge detection method and apparatus in the insulator of the power equipment according to the present invention, the periodic component of the ultrasonic wave detected by the ultrasonic sensor is detected by frequency analysis, and this periodic component If the generation cycle is a power supply frequency that is the frequency of the AC power supplied to the power device or a predetermined range that is twice that frequency, it is determined that partial discharge detection has occurred. Therefore, it is possible to detect the partial discharge in the insulator with high accuracy and simplicity while maintaining the live line state. Further, by detecting the periodic component of the ultrasonic wave by time-frequency analysis, partial discharge can be detected with high accuracy even when the S / N ratio is low.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a partial discharge detection device according to an embodiment of the present invention.
FIG. 2 is a schematic diagram showing an ultrasonic sensor incorporating a preamplifier.
3A and 3B show a copper strip bus, FIG. 3A is a schematic plan view, FIG. 3B is a front view, and FIG. 3C is a cross-sectional view.
4A and 4B show a road break elbow, where FIG. 4A is a side view and FIG. 4B is a front view.
FIG. 5 shows an example of detection of a periodic component (50 Hz) of an ultrasonic wave by short-time Fourier transform, (A) is a graph showing a measured waveform, and (B) is a concept showing a frequency spectrum obtained by short-time Fourier transform. FIG. 4C is a graph showing the relationship between the spectral intensity of the periodic component and time.
6A and 6B show an example of detection of a periodic component (100 Hz) of an ultrasonic wave by short-time Fourier transform, where FIG. 6A is a graph showing a measured waveform, and FIG. 6B is a concept showing a frequency spectrum obtained by short-time Fourier transform. FIG. 4C is a graph showing the relationship between the spectral intensity of a specific periodic component and time.
FIG. 7 is a partial plan view of a copper strip bus showing a defect position and a measurement position in an experimental example.
FIGS. 8A, 8B, 8C and 8F are graphs showing ultrasonic envelope detection waveforms in an experimental example using a copper strip bus; FIGS. It is.
9A is a graph showing a relationship between a voltage acting in the vicinity of a defect in an insulator of a power device and a voltage acting on the defect, and FIG. 9B is a graph showing a partial discharge pulse waveform corresponding to FIG. It is.
[Explanation of symbols]
10 Ultrasonic sensor
10a housing
11 Preamplifier
12 Filter
13 Amplifier
14 Processing unit
16 Contact medium
17 Electric power equipment
18 Periodic component detector
19 Judgment part
21 Monitor
23 Signal line
24 Ferrite core
30A, 30B, 30C copper band bus
40 Road break elbow

Claims (13)

An ultrasonic sensor is placed on the insulator of power equipment,
Detecting ultrasonic waves with the ultrasonic sensor during AC power supply to the power equipment,
Periodic components are detected by frequency analysis of the ultrasonic waves detected by the ultrasonic sensor,
Compare the generation period of the periodic component of the ultrasonic wave and the power supply frequency that is the frequency of the AC power supplied to the power device,
The partial discharge detection method in the insulator of an electric power apparatus which determines with the partial discharge having generate | occur | produced if the generation period of the periodic component of the said ultrasonic wave is in the predetermined range of the said power supply frequency or twice that. The partial discharge detection method according to claim 1, wherein the predetermined range is a range of ± 10% of the power supply frequency or twice the frequency. The partial discharge detection method according to claim 1, wherein the periodic component is detected by time-frequency analysis of the detected ultrasonic wave. The partial discharge detection method according to claim 3, wherein the time-frequency analysis is a short-time Fourier transform, a wavelet transform, or a Wigner distribution function for a time-amplitude waveform of the ultrasonic sensor. The partial discharge detection method according to claim 1, wherein the periodic component is detected by applying a fast Fourier transform to the detected ultrasonic wave or an envelope detection waveform thereof. When the ultrasonic sensor repeats the detection of ultrasonic waves during the supply of AC power to the power device by the ultrasonic sensor at a plurality of locations of the insulator, and the intensity of the periodic component of the ultrasonic waves due to the partial discharge at the plurality of locations is changing. The partial discharge detection method according to any one of claims 1 to 5, wherein the periodic component is determined to be a partial discharge. An ultrasonic sensor that is attached to an insulator of a power device and detects an ultrasonic wave generated during the supply of AC power to the power device;
A periodic component detector for detecting a periodic component by frequency analysis of the ultrasonic waves detected by the ultrasonic sensor;
The generation period of the periodic component of the ultrasonic wave detected by the periodic component detection unit is compared with the power supply frequency that is the period of the AC power supplied to the power device, and the generation period of the ultrasonic wave component is determined. A determination unit that determines that partial discharge occurs if the power source frequency is within a predetermined range that is twice the power frequency;
A partial discharge detection device in an insulator of electric power equipment. The partial discharge detection device according to claim 7, wherein the predetermined range is a range of ± 10% of the power supply frequency or twice thereof. The partial discharge detection according to claim 7 or 8, wherein the periodic component detection unit detects a periodic component of the ultrasonic wave by time-frequency analysis of a time waveform of the ultrasonic wave detected by the ultrasonic sensor. apparatus. The periodic component detection unit detects the periodic component of the ultrasonic wave by a short-time Fourier transform, a wavelet transform, or a Wigner distribution function with respect to a temporal waveform of the ultrasonic wave detected by the ultrasonic sensor. Partial discharge detection device. The part according to claim 7 or 8, wherein the periodic component detection unit detects a periodic component of the ultrasonic wave by a fast Fourier transform on the ultrasonic wave detected by the ultrasonic sensor or an envelope detection waveform thereof. Discharge detection device. The preamplifier that amplifies the output of the ultrasonic sensor and sends it to the periodic component detection unit, and a ferrite core through which a signal line connecting the ultrasonic sensor and the preamplifier is inserted. The partial discharge detection apparatus of any one of these. The portion according to any one of claims 7 to 11, further comprising a preamplifier that amplifies an output of the ultrasonic sensor and sends the amplified signal to the periodic component detection unit, and the preamplifier is built in the ultrasonic sensor. Discharge detection device.

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