JP2009047663A - Partial discharge detecting technique for electric equipment and device thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attempt to solve controversial object that since, when partial discharge of electric equipment is detected with the high frequency CT technique, measuring of two earthing wire currents is required for denoising, workability is poor resulted in difficulty of accurate denoising. <P>SOLUTION: A high frequency CT is attached to each of the two earthing wires with different partial discharge signals and levels of noise. Comparing the amplitude of signals detected from a first and a second high frequency CT, when signals from the first high frequency current transformer is equal or less than signals from the second high frequency current transformer, the output is set to 0, while when signals from the first high frequency current transformer is larger than signals from the second high frequency current transformer, the output is generated to maintain as n periods classification of power supply voltage. When it counts n periods, by superimposing the maintained output signals of n periods, existence or nonexistence of partial discharge is detected based on whether output signal concentrates in a specific time period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and apparatus for detecting partial discharge in electrical equipment such as a transformer.

Electrical devices such as transformers and circuit breakers are weak, which is called partial discharge because the electric field concentrates on the part due to the presence of minute void defects in the insulator and the contamination of the insulator surface. Discharge occurs. When the partial discharge occurs, the insulator in the generated portion deteriorates, and there is a risk that the dielectric breakdown will progress after a long period of time.
As a technique for detecting this partial discharge, as described in Patent Document 1,
(A) An electrical method (hereinafter referred to as CC method) in which a coupling capacitor is directly connected to a main circuit of a measurement target device such as a transformer, and partial discharge is detected from voltage fluctuations accompanying partial discharge.
(B) An electrical method (hereinafter referred to as a high-frequency CT method) in which a high-frequency CT (current transformer) is attached to the ground wire and the occurrence of partial discharge is measured as a leakage current.
(C) A diagnostic measurement method (hereinafter referred to as AE method) for acoustically detecting elastic wave vibration and discharge sound accompanying partial discharge generation.
There is.

Among the detection methods described above, Patent Document 2 is known for the high-frequency CT method (b). In this document, a high-frequency CT is attached to the ground line of the device to be measured, and a weak pulse current generated by partial discharge is detected to flow through the ground line. Besides, noise is detected. In order to eliminate this noise, it is described that the ground line current is measured at two points and the difference is taken to cancel the noise.
Further, the noise removal in the AE method of (c) is described in Patent Document 1.
JP 2006-17753 A JP-A-9-5386

In order to remove noise at the time of partial discharge measurement by the high frequency CT method, it is necessary to measure two ground line currents. One is noise and a partial discharge signal, and the other is only noise. For this purpose, it is necessary to install the high frequency CT for measuring the ground line current on a ground line separated to some extent, which causes the following problems.
(1) At a distant position, the noise waveform is similar, but its magnitude, phase, etc. are different. A phase adjuster and an amplifier (attenuator) are required to cancel the noise by matching the magnitude and phase. Depending on the measurement site, even if the size and phase are matched, the waveforms are not exactly the same, and accurate noise removal cannot be performed.
(2) When the noise and the partial discharge signal are similar, the partial discharge signal is mistakenly deleted when matching the magnitude and phase, and there is a risk of erroneous measurement as a measurement result.
(3) In the actual work at the measurement site, the installation of the high-frequency CT is located at two places apart from each other, so that the work such as routing of the measurement cable becomes difficult.

  An object of the present invention is to provide a partial discharge detection method and apparatus for an electrical device that enables close placement of two high-frequency CT mounting positions and enables accurate noise removal.

According to claim 1 of the present invention, in partial discharge detection of an electrical device having a plurality of ground wires,
A high-frequency current transformer is attached to each of two ground lines having noise levels different from those of the partial discharge signal flowing through the ground line, and the magnitudes of the signals detected by the first and second high-frequency current transformers are reduced. In comparison, the output is 0 when the first high-frequency current transformer ≦ the second high-frequency current transformer, and the output is generated when the first high-frequency current transformer> the second high-frequency current transformer. And detecting the presence or absence of partial discharge based on whether or not the output is concentrated in a specific time zone by superimposing the stored output signals for n cycles It is.

  A second aspect of the present invention is a detection method characterized in that one of the two different ground lines is a neutral point ground line of a three-phase primary winding.

  According to a third aspect of the present invention, the electric device is a molded grounding-type instrument transformer, and a sensor by an AE method is attached to a molded portion of the transformer, and a detection signal of the AE sensor and the first and second high-frequency elements are attached. The detection method is characterized in that the phase in which partial discharge occurs is specified when the output time of the comparison output of the current transformer is within a predetermined value range.

According to a fourth aspect of the present invention, there is provided a partial discharge detection device for an electrical apparatus having a plurality of ground lines, wherein a high frequency current transformer is attached to each of two ground lines having different levels of noise and partial discharge signals flowing through the ground line. In the processing of the detected signal by the arithmetic processing unit,
The arithmetic processing unit compares the magnitude of the signal detected by the first high frequency current transformer with the magnitude of the signal detected by the second high frequency current transformer among the two high frequency current transformers, When 1 high-frequency current transformer ≦ second high-frequency current transformer, the output is set to 0, and when first high-frequency current transformer> second high-frequency current transformer, the means for generating the output and the generated output signal as the power supply voltage Means for superimposing and storing n periods when n periods, and whether or not the superimposed signal exceeds a threshold and the output is concentrated in a specific time zone. It is characterized by comprising means for determining.

  The fifth aspect of the present invention is characterized in that one of the two different ground lines is a neutral point ground line of a three-phase primary winding.

  According to a sixth aspect of the present invention, the electrical device is a molded grounding-type instrument transformer, and a sensor by an AE method is attached to a molded portion of the transformer, and a detection signal of the AE sensor and the first and second high-frequency components are attached. The present invention is characterized in that it is configured to identify a phase in which partial discharge has occurred when an output time with a comparative output signal of the current transformer is within a predetermined value range.

  As described above, according to the present invention, since the partial discharge signal and the noise can be easily distinguished by the magnitude of the two high-frequency CT outputs, the adjustment work for canceling the noise becomes unnecessary, and the phase adjuster and the amplifier are provided. It becomes unnecessary. In addition, the workability for measurement is improved due to the close attachment positions of the two high-frequency CTs. In addition, by using the AE method in combination, it is possible to specify the phase of the partial discharge location, and the noise flowing from the ground line is cut by the two high-frequency CTs, and the electric noise is detected by the AE sensor. Can cut the measurement accuracy.

  FIG. 1 is a block diagram showing an embodiment of the present invention, and shows a case where the present invention is applied to a grounded instrument transformer GPT. In the case of a grounded instrument transformer GPT, the grounding wire includes a neutral point terminal (terminal 0) grounding of the primary winding, a frame (frame) grounding, a secondary winding grounding, a tertiary winding grounding, and a plurality of Although a ground wire exists, the first high-frequency CT1 is attached to the ground wire of the terminal 0 of the primary winding neutral point, and the second high-frequency CT2 is attached to the frame ground wire E. The detection signals of CT1 and CT2 are output to the detection device shown in FIG.

  In FIG. 2, reference numerals 1 and 11 denote pulse extraction units which extract pulses in a specific frequency band. Reference numerals 2 and 12 are amplifiers for amplifying the signal input from the pulse extraction unit, and reference numerals 3 and 13 are A / D converters for converting the input pulse signal into a digital signal. Reference numerals 4 and 14 denote storage units that sequentially store the size of the extracted pulse and the angle of one cycle of the power supply voltage waveform. Reference numeral 5 denotes a comparison processing unit, and the detection signals of CT1 and CT2 stored in the storage units 4 and 14 are compared at an angle at the same time point in one cycle waveform of the power supply voltage, and noise removal is executed. Reference numeral 6 denotes a superposition storage unit, which stores the partial discharge signal from which noise has been removed n times and stores the result, and visually displays the result on the display unit 7. A personal computer is used for the functions 5, 6 and 7.

  3A and 3B are waveform diagrams for explaining the principle from pulse detection to display. FIG. 3A is a pulse waveform of CT1 detected by the first measurement unit (1 to 4), and FIG. 2 is a pulse waveform of CT2 detected by (11-14) of No. 2 and is a waveform at the same phase of the power supply voltage waveform. In each figure, PD indicates a partial discharge signal, and NO indicates noise. The CT1 partial discharge signal PD is a larger signal than the CT2 partial discharge signal PD. Conversely, the noise NO is small on the CT1 side and large on the CT2 side. (C) The figure shows the combined processing waveform at the same time in the one-cycle waveform of the power supply voltage in the comparison processing unit 5, and the noise is removed and the PD signal is left. Based on the phenomenon that the partial discharge concentrates on a specific phase of one cycle of the power supply voltage, the removal calculation is collectively displayed n times as shown in FIG.

  The magnitudes of the partial discharge signals shown in FIGS. 4A and 4B are also apparent from the experimental results shown in FIG. This experiment was conducted when a partial discharge occurred in the primary winding portion inside the grounded-type instrument transformer GPT, and an electric charge of 500 pC was injected into the primary coil of the grounded-type instrument transformer GPT. The measured value of the ground wire of the terminal 0 at the neutral point of the primary winding indicated by A is larger than the measured value of the frame ground wire E indicated by the wire D.

FIG. 5 shows a specific processing flow of the comparison processing unit 5 and the superposition storage unit 6.
The means S1 acquires CT1 and CT2 data at the same point stored in the storage units 4 and 14, and the means S2 executes the first calculation process. In the processing in means S2, the data of CT1 and CT2 are sequentially compared for each time and output when CT1> CT2, and 0 when CT1 ≦ CT2. That is, in the waveform diagrams shown in FIGS. 3A and 3B, the first pulse data is noise NO. In the case of this noise, CT2 is large and the output is 0. Next, the second pulse data is PD and is output because CT1 is larger. In the same manner, the time series data of the partial discharge waveform from which noise is removed as shown in FIG. This is divided into a certain amount of time, for example, the length of one cycle applied to the grounded instrument transformer GPT, and n times of the divided cycle are stored.

The means S3 performs the second arithmetic processing. In this means, the length of the time axis is divided every period and added n times as shown in FIG. Since the addition result is synchronized with the applied voltage of the power supply, the output is not uniformly generated over the entire time axis.
The means S4 determines that partial discharge has occurred when the added data exceeds a predetermined threshold and the output is concentrated in a specific time zone. Otherwise, it is determined that there is no partial discharge.

  Therefore, according to this embodiment, since the partial discharge signal and the noise can be easily distinguished by the magnitude of the two high-frequency CT outputs, the work for canceling the noise is not required, and the phase adjuster and the amplifier are not required. . In addition, the workability for measurement is improved due to the close attachment positions of the two high-frequency CTs.

FIG. 6 shows a second embodiment. In this embodiment, detection by the AE method is added to the first embodiment described above. That is, in the first embodiment, since the current from the neutral point of the primary winding is detected in one of the high-frequency CTs, it is impossible to determine which phase the partial discharge is in. In this embodiment, this is supplemented by attaching a sensor AE based on the AE method to measure ultrasonic waves. At that time, for example, in the case of a three-phase grounding-type instrument transformer GPT, each phase is molded and is constituted by three molded parts. For this reason, in the measurement, each phase is measured once three times, or three phases are measured simultaneously by installing an AE sensor in each phase.
As a detection apparatus based on the AE method, one having a configuration as shown in FIG. 7 is used. AE is a sensor for collecting sound, 20 is a measuring unit including an amplifier, a filter and an A / D converter, 21 is a digital oscilloscope, 22 is a personal computer, and has an arithmetic processing unit and a display unit. This personal computer is shared with the personal computer shown in FIG.

  The calculation results by the high-frequency CT method and the calculation result by the AE method are as shown in FIG. FIG. 8 (a) shows the waveform of FIG. 3 (c) after the pulse detected by the high frequency CT is processed by the means S2 shown in FIG. FIG. 8B shows a waveform detected by the AE sensor. In the case of the AE sensor, the waveform is divided into lengths of one cycle applied to the grounded instrument transformer GPT, and n times of the divided cycles are stored. . When the difference between the output of the signal detected by the high frequency CT and the signal detected by the AE sensor is, for example, within a certain time range within 2 ms, the combination processing operation is executed. The waveform is as shown in FIG. By adding 1 to n cycles by means S3, the phase waveform to be measured is displayed as shown in FIG. By switching this for each phase, it can be determined in which phase partial discharge has occurred.

  FIG. 9 shows the measurement results based on the actual machine model. In this experiment, the measurement of the grounded instrument transformer GTP was simulated, the high frequency CT was attached to the grounding point of the primary winding neutral terminal 0, and the AE sensor was attached to the mold part, and the measurement was carried out. did. The measurement results are obtained when partial discharge 100 pC is generated. Line A is a power supply voltage waveform, line A is a waveform by high-frequency CT, and line C is a waveform by an AE sensor. As is clear from FIG. 9, partial discharge occurs in the vicinity of the power supply voltage waveform of 60 °, 220 °... In both the high frequency CT method and the AE method, and by using the high frequency CT method and the AE method together, It was found that the generation phase can be grasped.

  Therefore, according to this embodiment, in addition to the first embodiment, it is possible to specify which phase the partial discharge portion is in, and the noise flowing from the ground line is cut by two high frequency CTs. Since the electrical noise can be cut by the AE sensor, the measurement accuracy can be further improved.

The block diagram which shows embodiment of this invention. The block diagram by the high frequency CT method of this invention. The pulse signal waveform diagram for demonstrating the effect | action of this invention. The wave form diagram in the different detection position by high frequency CT. The operation processing flowchart of this invention. The block diagram by the other Example of this invention. The block diagram of the detection apparatus by AE method. Waveform diagram for explanation. The measurement result figure by a real machine model.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11 ... Pulse extraction part 2, 12 ... Amplifier 3, 13 ... A / D converter 4, 14 ... Memory | storage part 5, ... Comparison processing part 6, ... Superimposition memory | storage part 7, ... Display part 20 ... Measurement part 21 ... Digital oscilloscope 22 ... PC

Claims (6)

In partial discharge detection of electrical equipment having a plurality of ground wires,
A high-frequency current transformer is attached to each of two ground lines having noise levels different from those of the partial discharge signal flowing through the ground line, and the magnitudes of the signals detected by the first and second high-frequency current transformers are reduced. In comparison, the output is 0 when the first high-frequency current transformer ≦ the second high-frequency current transformer, and the output is generated when the first high-frequency current transformer> the second high-frequency current transformer. Characterized in that it is divided into n periods and stored, and the presence or absence of partial discharge is detected by superimposing the stored output signals for n periods and determining whether the output is concentrated in a specific time zone. Method for detecting partial discharge of electrical equipment. 2. The partial discharge detection method for an electric device according to claim 1, wherein one of the two different ground lines is a neutral point ground line of a three-phase primary winding. The electrical equipment is a molded grounding-type instrument transformer. A sensor by the AE method is attached to the molded part of the transformer, and the detection signal of the AE sensor and the comparison output of the first and second high-frequency current transformers are output. The method for detecting a partial discharge of an electric device according to claim 2, wherein the phase in which the partial discharge is generated when the time is generated within a predetermined value range is specified. A partial discharge detection device for an electrical device having a plurality of ground lines, in which a high frequency current transformer is attached to each of two ground lines having different noise levels from the partial discharge signal flowing through the ground line, and the detected signal is processed. In what is processed by the department,
The arithmetic processing unit compares the magnitude of the signal detected by the first high frequency current transformer with the magnitude of the signal detected by the second high frequency current transformer among the two high frequency current transformers, When 1 high-frequency current transformer ≦ second high-frequency current transformer, the output is set to 0, and when first high-frequency current transformer> second high-frequency current transformer, the means for generating the output and the generated output signal as the power supply voltage Means for superimposing and storing n periods when n periods, and whether or not the superimposed signal exceeds a threshold and the output is concentrated in a specific time zone. An apparatus for detecting partial discharge of electrical equipment, characterized by comprising means for determining. 5. The partial discharge detection device for an electric device according to claim 4, wherein one of the two different ground lines is a neutral point ground line of a three-phase primary winding. The electrical equipment is a molded grounding type instrument transformer. A sensor by the AE method is attached to the molded part of the transformer, and a detection signal of the AE sensor and a comparison output signal of the first and second high-frequency current transformers 6. The partial discharge detection device for an electric device according to claim 5, wherein a phase in which partial discharge has occurred is specified when the output time is within a predetermined value range.

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