JPH11160385A - Partial-discharge monitoring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a partial-discharge monitoring apparatus in which an external noise is removed so as to obtain an accurate measured value by a method wherein a partial-discharge current which is generated across a conductor and a ground potential is converted into a voltage signal by a detecting impedance so as to be divided into two signals, the phase of the signal on one side is delayed and a partial discharge is detected on the basis of the difference signal between the signal on one side and the signal on the other side. SOLUTION: A partial-discharge current which is generated across a conductor 1 and a ground potential 2 is converted into a voltage signal. The voltage signal as the output signal of a detecting impedance 3 is attenuated by an attenuator 5, it is amplified by an amplifier 6, and a level is adjusted. The voltage signal is divided into two signals by a branching filter 10. The phase of the divided signal on one side is delayed by a delaying device 11. The difference between the divided signal on the other side and the signal which is delayed by the delaying device 11 is found by a computing unit 12. An amplifier 13 amplifies the voltage difference signal of the computing unit 12. A detection circuit 7 detects a generation frequency on the basis of the signal of the amplifier 13. A signal processing part 8 judges whether an abnormality exists in the output signal of the detection circuit 7. An output part 9 outputs a result to the outside.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial discharge monitoring device, and is particularly useful as a device used as part of preventive maintenance of power distribution equipment. FIG. 3 is a block diagram showing a partial discharge monitoring apparatus according to the prior art. As shown in FIG. 1, the partial discharge monitoring device converts a partial discharge current generated between a conductor 1 such as a wiring and a ground potential 2 such as an outer wall of a case into a voltage by a detection impedance 3 and detects the voltage. The filter 4 extracts a target signal from the voltage signal, and the attenuator 5 and the amplifier 6 adjust the signal level. Thereafter, the occurrence frequency and the like are detected by the detection circuit 7, and the output signal is input to the signal processing unit 8 to determine the presence or absence of an abnormality. The result is displayed on the display unit via the output unit 9 or output as an external signal. [0003] In the partial discharge monitoring device according to the prior art as described above, external noise enters the detection impedance 3 together with the partial discharge current, and the noise thus entered is filtered. Since it is difficult to discriminate using only the device 4, it is necessary to take additional measures such as removing a noise source. [0004] In view of the above prior art, an object of the present invention is to provide a partial discharge monitoring device capable of removing external noise and obtaining an accurate measurement value without being affected by the noise. [0005] The structure of the present invention that achieves the above object has the following features. 1) A partial discharge current generated between a conductor such as a wiring and a ground potential such as an outer wall of a case is converted into a voltage signal by a detection impedance and divided into two, and the phase of one of the divided signals is changed. While delaying, the difference between the delayed signal and the other demultiplexed signal is obtained, and the partial discharge is detected based on the resulting difference signal representing the voltage difference. According to the present invention, the signal representing the voltage difference reflects the partial discharge current. Since the signal component based on the external noise current is a signal with a gradual level change, it is divided and delayed and then canceled by subtracting one from the other, whereas the signal component based on the partial discharge current is pulse-shaped. This is because the signal component is extracted as a result of the delay. 2) A partial discharge current generated between a conductor such as a wiring and a ground potential such as an outer wall of a case is converted into a voltage signal by a detection impedance, and the voltage signal is attenuated or amplified to adjust its level. The voltage signal thus level-adjusted is divided into two, and the phase of one of the divided signals is delayed, and the difference between the signal thus delayed and the other divided signal is calculated. Detecting a partial discharge based on a difference signal representing a voltage difference obtained as a result. According to the present invention, based on the voltage signal adjusted to an appropriate level, signal processing after the division of the voltage signal can be performed in the same manner as in the invention of the above 1). 3) In the partial discharge monitoring device according to 1) or 2), a delay time after the division of the voltage signal is equal to or longer than a cycle of a signal component based on the partial discharge current which is a pulse signal. According to the present invention, a delayed pulse-like signal and a pulse-like signal that is not delayed can be shifted on the time axis by more than the period. Therefore, the difference between the two signals can be reliably extracted as a signal having the opposite phase. Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a partial discharge monitoring device according to the present embodiment. The same parts as those in FIG. 3 are denoted by the same reference numerals. As shown in FIG. 1, a partial discharge monitoring apparatus according to the present embodiment includes a conductor 1 such as a wiring, a ground potential 2 such as an outer wall of a case, a detection impedance 3, an attenuator 5, an amplifier 6, a duplexer 10, It includes a delay unit 11, a subtractor 12, an amplifier 13, a detection circuit 7, a signal processing unit 8, and an output unit 9. Among them, the detection impedance 3 converts a partial discharge current signal generated between the conductor 1 such as a wiring and the ground potential 2 such as an outer wall of the case into a voltage signal, as in the related art.
The voltage signal as the output signal of the detection impedance 3 is attenuated by the attenuator 5 and then amplified by the amplifier 6. The attenuator 5 and the amplifier 6 perform appropriate level adjustment of the voltage signal detected by the detection impedance 3. Duplexer 10
Divides the voltage signal amplified by the amplifier 6 into two.
The delay unit 11 delays the phase of one of the signals split by the splitter 10. The subtracter 12 calculates the difference between the other signal split by the splitter 10 and the signal delayed by the delay unit 11. Here, since the signal component based on the external noise current is a signal with a gradual level change, even if the signal is delayed after being divided, it can be canceled by subtracting one from the other of the divided voltage signals. On the other hand, since the signal component based on the partial discharge current is a pulse-like signal component, the component is shifted in the time axis direction by delaying, and as a result, the other is subtracted from one of the divided voltage signals. The signal component remains without being canceled. That is, the signal component can be extracted. Here, in order to satisfactorily extract the signal component based on the partial discharge current, the delay time in the delay unit 11 may be set to be equal to or longer than the cycle of the pulse-like signal component. In this case, the delay component and the other component are reliably extracted as signals having opposite phases. The amplifier 13 amplifies a signal representing a voltage difference, which is an output signal of the subtractor 12. The detection circuit 7 is an amplifier 1
The occurrence frequency and the like are detected from the signal amplified in 3, and the signal processing unit 8 determines whether the output signal of the detection circuit 7 is abnormal. The output unit 9 displays the processing result of the signal processing unit 8 as display or external output. The period of the waveform obtained by converting the partial discharge current generated between the conductor 1 such as the wiring of the partial discharge monitoring device and the ground potential 2 such as the outer wall of the case into the voltage by the detection impedance 3 is several times in the insulating gas. nsec, several tens of nsec in the air, several μsec in the insulating oil (however, smaller than the external noise period), whereas the period of the voltage waveform caused by the external noise current that enters the detection impedance 3 Is several μsec. The voltage signal containing these two components (see FIG. 2A) passes through the attenuator 5 and the amplifier 6, and the signal level is adjusted. After that, the voltage signal is split into two by the splitter 10. One of the voltage signals thus divided is delayed by the delay unit 11 by a phase equal to or longer than the period of the pulse signal component based on the partial discharge current (see FIG. 2B). When this output and the other signal that has been demultiplexed are input to the subtractor 12 and the difference between the two signals is obtained, if the noise having a period of several μsec has a phase shift of several tens nsec, most of the components thereof Is removed by taking the difference, and only a pulse-like voltage component based on the partial discharge current remains (see FIG. 2C). The difference signal representing the voltage difference obtained in this way is amplified by the amplifier 13 and the frequency of occurrence is detected by the detection circuit 7 from the amplified signal. Also, based on the signal, the signal processing unit 8 determines whether there is an abnormality,
The result is displayed or output externally through the output unit 9 to monitor partial discharge. In this way, by removing this external noise from the signal containing the external noise,
A more accurate measurement value is obtained without being affected by external noise. It goes without saying that the positions and the numbers of the attenuator 5 and the amplifiers 6 and 13 shown in FIG. As described in detail with the above embodiments, the invention described in [Claim 1] relates to a partial discharge current generated between a conductor such as a wiring and a ground potential such as an outer wall of a case. Is converted into a voltage signal by the detection impedance and divided into two, and the phase of one of the divided signals is delayed, and the difference between the delayed signal and the other signal that is demultiplexed is calculated. Since partial discharge is detected based on a difference signal representing a voltage difference obtained as a result,
A signal component based on an external noise current, which is a signal with a gradual level change, is divided and delayed, and then canceled by subtracting the other from one, whereas a signal component based on a partial discharge current, which is a pulse-like signal component, is used. Even if a signal component is divided and delayed and then subtracted from one after the other, the signal component is not canceled, so that the signal component can be extracted. That is, the signal representing the voltage difference reflects the partial discharge current, and the signal component caused by the external noise can be removed. Therefore, the external noise can be removed from the signal including the external noise. Get more accurate measurements that are not affected by noise. According to a second aspect of the present invention, a partial discharge current generated between a conductor such as a wiring and a ground potential such as an outer wall of a case is converted into a voltage signal by a detection impedance and the voltage signal is attenuated. Or, the level is adjusted by amplifying the voltage signal, and the voltage signal whose level has been adjusted in this manner is divided into two, and the phase of one of the divided signals is delayed, and the signal is demultiplexed with the signal thus delayed. By taking the difference with the other signal and detecting the partial discharge based on the difference signal representing the resulting voltage difference,
Based on the voltage signal adjusted to an appropriate level, the signal processing after the division of the voltage signal can be performed in the same manner as the invention described in the above [Claim 1]. Therefore, the partial discharge can be detected with better accuracy than the invention described in claim 1. According to a third aspect of the present invention, in the partial discharge monitoring device according to the first or second aspect, the delay time after the division of the voltage signal is a pulse signal. Since the period is longer than the period of the signal component based on a certain partial discharge current, after division, the pulse-like voltage component based on the partial discharge current of the delayed voltage signal and the voltage signal that is not delayed can be shifted by one pulse period or more on the time axis. Can,
Signal components based on partial discharge can be reliably extracted. Therefore, the detection accuracy of the partial discharge as described above can be maintained satisfactorily.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a partial discharge monitoring device according to an embodiment of the present invention. FIG. 2 is a waveform chart showing waveforms at various parts in FIG. FIG. 3 is a block diagram showing a partial discharge monitoring device according to the related art. [Description of Signs] 1 conductor 2 earth potential 3 detection impedance 5 attenuator 6 amplifier 10 duplexer 11 delay unit 12 subtractor

Claims (1)

Claims 1. A partial discharge current generated between a conductor such as a wiring and a ground potential such as an outer wall of a case is converted into a voltage signal by a detection impedance and divided into two. While delaying the phase of one signal, the difference between the delayed signal and the other signal is taken, and partial discharge is detected based on a difference signal representing the resulting voltage difference. A partial discharge monitoring device characterized in that: 2. A partial discharge current generated between a conductor such as a wiring and a ground potential such as an outer wall of a case is converted into a voltage signal with a detection impedance, and the voltage signal is attenuated or amplified to adjust its level. The voltage signal thus level-adjusted is divided into two, and the phase of one of the divided signals is delayed, and the difference between the signal thus delayed and the other divided signal is calculated. A partial discharge monitoring device, wherein a partial discharge is detected based on a difference signal representing a voltage difference obtained as a result. 3. The partial discharge monitoring device according to claim 1, wherein the delay time after the division of the voltage signal is equal to or longer than the period of the signal component based on the partial discharge current that is a pulse signal. A partial discharge monitoring device characterized in that: