JP6567230B1 - Arc ground fault detection method - Google Patents

Abstract

An A / D converter (20) for converting the current measured by the current transformer (3) for measuring the current of the feeder (2) connecting the DC system (1) and the load (4) into a digital signal; An arc ground fault detection device (100) comprising an arithmetic processing unit (30) for arithmetic processing of the converted digital signal, wherein the arithmetic processing unit (30) is an A / D conversion unit (20). The converted current signal of the power supply line over a predetermined frequency range of 0.1 kHz or more is subjected to FFT signal processing, converted in advance by the A / D converter (20), and subjected to FFT signal processing. Compared with the initial current signal for each frequency in the frequency range, an arc ground fault current is detected to determine whether an arc ground fault has occurred.

Description

  The present application relates to an arc ground fault detection apparatus.

  As a technique for detecting a ground fault, which is one of distribution line faults, and a position where the fault has occurred, a method for detecting the magnitude of a zero-phase current and a zero-phase voltage is known (for example, Patent Document 1). In the ground fault detection system described in Patent Document 1, a zero-phase voltage provided on the secondary side of the distribution transformer in order to identify the ground fault location that occurred on the secondary side of the distribution transformer. Equipped with a current transformer for each phase of the power cable on the secondary side of the detector, the zero-phase current detector, and the distribution transformer, and identifies the ground fault location from the zero-phase voltage and each current value doing. At this time, only the specific AC component (for example, commercial frequency 60 Hz) is extracted from the zero-phase voltage and each current value by the band-pass filter and used for the detection process.

  Moreover, the method of detecting a ground fault in the power converter connected to the photovoltaic power generation system which is one of the renewable energies is also disclosed (for example, Patent Document 2). According to Patent Document 2, a ground fault is detected from a voltage sensor that detects a voltage supplied from a photovoltaic power generation system that is a DC power supply, and an AC leakage current that is output from the DC power supply to a commercial system via a power converter. It has been proposed to detect a ground fault with high accuracy for a photovoltaic power generation system having a generated voltage fluctuation by a detection method.

Japanese Patent Laying-Open No. 2012-141232 (see FIG. 1, paragraphs 0014 to 0020, etc.) JP 2017-153272 A

In the ground fault detection system of Patent Document 1, since the current and voltage at a specific frequency and low frequency are handled by the band-pass filter, it is impossible to detect an arc ground fault in the DC system.
Also, in the ground fault detection method disclosed in Patent Document 2, the fluctuation of the voltage supplied from the photovoltaic power generation system and the fluctuation of the AC leakage current converted by the power conversion device are taken into account by taking into account the generated voltage fluctuation. This is to detect a fault and is not intended to detect an arc ground fault.

  In a DC system, a micro arc is constantly generated, and the arc current appears in a higher frequency region than a normal ground fault. However, the background noise in the high frequency region is larger than that in the low frequency region, and if it overlaps with the noise, it is difficult to detect the arc current and the arc ground fault.

  This application discloses the technique for solving said subject, and it aims at providing the arc ground fault detection apparatus for detecting the arc ground fault which generate | occur | produces in the feeder connected to a DC system. To do.

An arc ground fault detection method disclosed in the present application includes a current transformer that measures a current of a feeder line that connects a DC system and a load, an A / D conversion unit that converts the measured current into a digital signal, a converted arithmetic processing unit and method for detecting arc ground fault using the apparatus E with a for processing a digital signal, a defined transformed 0.1kHz or more in advance the a / D converter A step of Fourier transforming the current signal of the feeder line over a frequency range and storing it as an initial power spectrum; a predetermined value of 0.1 kHz or more measured during operation of the load and converted by the A / D converter Fourier transforming the current signal of the feeder line over the range of the obtained frequency, obtaining an operating power spectrum, subtracting the initial power spectrum from the power spectrum, Obtaining the power spectrum, inverse Fourier transforming the true power spectrum to calculate an arc ground fault current, comparing the calculated arc ground fault current with a preset threshold, and calculating If the arc grounding current that is exceeds the preset threshold and has a step of determining that arcing ground fault occurs.

According to the detection method of the arc ground fault disclosed herein, by calculating the background noise accurate arc grounding current removed, it is possible to detect the arc locations絡発raw existence.

1 is a configuration diagram illustrating an arc ground fault detection apparatus according to Embodiment 1. FIG. 2 is a hardware configuration diagram of the arc ground fault detection device according to Embodiment 1. FIG. 3 is a flowchart illustrating a procedure for detecting an arc ground fault using the arc ground fault detection apparatus according to the first embodiment. It is a spectrum figure which shows the relationship between an arc ground fault electric current and background noise. 6 is a flowchart illustrating a procedure for detecting an arc ground fault using the arc ground fault detection apparatus according to the second embodiment. It is a block diagram which shows the arc ground fault detection apparatus which concerns on Embodiment 3. FIG. 10 is a flowchart illustrating a procedure for detecting an arc ground fault using the arc ground fault detection apparatus according to the third embodiment.

  Hereinafter, the present embodiment will be described with reference to the drawings. In addition, in each figure, the same code | symbol shall show the same or an equivalent part.

Embodiment 1 FIG.
Hereinafter, the arc ground fault detection apparatus according to the first embodiment will be described with reference to FIG.
In the figure, the DC system 1 is not grounded, is a high-resistance ground, or is not insulated. Although a load 4 is connected to a feeder 2 that is branched from the DC system 1, detection of an arc ground fault 6 generated with respect to the ground 5 in the feeder 2 will be described in the present embodiment. The ground fault current flowing through the feeder line 2 is measured by a zero phase current transformer (ZCT) 3 and input to the ground fault current measuring unit 10 of the arc ground fault detector 100. The arc ground fault detection device 100 includes a ground fault current measurement unit 10, an A / D conversion unit 20, an arithmetic processing unit 30, a storage unit 40, an output unit 50, and a communication circuit connected to a zero phase current transformer (ZCT) 3. 60.
The ground-fault current input to the ground-fault current measuring unit 10 is converted (amplified) into a signal level necessary for processing in the next A / D conversion unit 20, and is digitized by the A / D conversion unit 20. Converted to a signal. The data converted into the digital signal is arithmetically processed by the arithmetic processing unit 30 to perform abnormality determination (determination of arc ground fault).
The load 4 may be a single load or a plurality of loads, and may be a load to which power converted into alternating current by a power converter (not shown) connected to the feeder line 2 is supplied. .

The storage unit 40 is connected to the arithmetic processing unit 30 and exchanges data with the arithmetic processing unit 30.
The output unit 50 outputs signals such as an abnormal state (arc ground fault occurrence) and a warning from the arithmetic processing unit 30 to the outside.
The arc ground fault detection device 100 is often incorporated in another instrument such as a protective relay. In this case, a signal from the output unit 50 is transmitted to the main protective relay.

  The external monitoring device 200 is configured by a PC (personal computer) or the like, and is connected to one or a plurality of arc ground fault detection devices 100, and receives information from the arithmetic processing unit 30 through the communication circuit 60 as appropriate. The operation status of the arc ground fault detection device 100 is monitored. The connection between the external monitoring device 200 and the communication circuit 60 of the arc ground fault detection device 100 may be a cable or may be wireless. A network may be configured between the plurality of arc ground fault detection devices 100 to connect via the Internet.

  In addition, when the arc ground fault detection apparatus 100 is incorporated in another instrument such as a protective relay as described above, the arc ground fault detection apparatus 100 itself does not need to include the communication circuit 60 and is connected to the monitoring apparatus 200. There is no need to

  FIG. 2 is a diagram illustrating a hardware configuration example of the arc ground fault detection apparatus 100. It comprises a processor 110 and a storage device 120. Although not shown, the storage device 120 includes a volatile storage device such as a random access memory (RAM) and a nonvolatile auxiliary storage device such as a flash memory. Further, an auxiliary storage device of a hard disk may be provided instead of the flash memory. The processor 110 executes the program input from the storage device 120. In this case, a program is input from the auxiliary storage device to the processor 110 via a volatile storage device (EEPROM: Electrically Erasable Programmable Read Only Memory). The processor 110 may output data such as a calculation result to the volatile storage device of the storage device 120, or may store the data in the auxiliary storage device via the volatile storage device. The processor 110 may include various logic circuits such as an application specific integrated circuit (ASIC), an integrated circuit (IC), and a digital signal processor (DSP), various signal processing circuits, and the like as an arithmetic processing unit.

Next, an arc ground fault detection method using the arc ground fault detection apparatus 100 will be described with reference to the flowchart of FIG.
In order to detect an arc ground fault in the present embodiment, it is necessary to acquire the background noise of the feeder 2 and remove it from the measured ground fault current. Therefore, first, the ground fault current in the initial state of the feeder 2 is measured.

  When the initial ground fault current that is the initial state of the feeder 2 is not stored in the storage unit 40 (NO in step S1), the ground fault current is measured by the zero-phase current transformer (ZCT) 3, and the measured ground The fault current is input to the ground fault current measuring unit 10. After the ground fault current measuring unit 10 converts the signal to a predetermined level, it is sampled by the A / D converter 20 and converted into a digitized digital signal (step S2). At this time, a digital signal over a predetermined frequency range of 0.1 kHz or more is acquired. The frequency range is determined in advance.

  The arithmetic processing unit 30 performs arithmetic processing on a digitized digital signal over a predetermined frequency range by a fast Fourier transform (hereinafter referred to as FFT), and a power spectrum component (initial value) SECin of each frequency. Is calculated (step S3). The calculated power spectrum component is stored in the storage unit 40 as initial value data (step S4).

Next, the operation during operation of the load 4 will be described.
The ground fault current is measured by the zero phase current transformer (ZCT) 3, and the measured ground fault current is input to the ground fault current measuring unit 10. After the ground fault current measuring unit 10 converts the signal to a predetermined level, it is sampled by the A / D converter 20 and converted into a digitized digital signal (step S5). At this time, a digital signal over a predetermined frequency range of 0.1 kHz or more is acquired in the same manner as when the initial value is acquired.

The arithmetic processing unit 30 performs arithmetic processing on the digitized digital signal over a predetermined frequency range by FFT, and calculates the power spectrum component (during operation) SECop of each frequency (step S6).
At each frequency, the power spectrum component (initial value) SECin is subtracted from the power spectrum component (during operation) SECop to calculate the power spectrum component (true value) SECtr of each frequency (step S7).

An arc ground fault current from which background noise has been removed is calculated by performing inverse FFT on the power spectrum component (true value) SECtr over a predetermined frequency range (step S8).
If the calculated arc ground fault current exceeds a preset threshold value, it is determined that an arc ground fault has occurred (YES in step S9), an abnormal signal or the like is output from output unit 50, and a warning is issued (step S10). ).

If arc grounding current calculated in step S8 does not exceed the predetermined threshold value (in step S9 NO), returns to the ground fault current measured at the zero-phase current transformer (ZCT) 3.

  Rather than calculating the arc ground fault current by using the difference between the ground fault current measured by the zero-phase current transformer (ZCT) 3 and the initial ground fault current to determine the occurrence of the arc ground fault, the signal is generated by FFT. Only the frequency component of the arc ground fault current generated at the time of the arc ground fault is detected by analyzing the difference from the initial value in the spectral component using the processed spectrum, so the arc ground fault can be detected with high accuracy. It becomes easy.

  As described above, according to the first embodiment, the ground fault current is measured by providing the zero-phase current transformer (ZCT) 3 in the feeder 2 connected to the DC system, and the frequency is 0.1 kHz or more in advance. By using the difference between the spectrum component obtained by FFT processing of a signal in a predetermined frequency range and the initial signal spectrum component after FFT processing, a highly accurate arc ground fault current from which background noise has been removed is calculated. By doing so, it is possible to detect whether or not an arc ground fault has occurred.

Embodiment 2. FIG.
In the first embodiment described above, the method of performing FFT processing on a signal having a predetermined frequency range of 0.1 kHz or more has been described, but the frequency band at the time of occurrence of an arc ground fault is mainly from 0.1 to 100 kHz. The calculation processing is reduced to a digital signal over a predetermined frequency range of 0.1 kHz or higher and preferably within a predetermined frequency range of 0.1 to 100 kHz, thereby reducing the calculation load and limiting to the arc ground fault. Detection accuracy can be improved. In the present embodiment, a processing method of arc ground fault current detection in which the frequency range is narrowed down in the arc ground fault detection apparatus 100 of FIG. 1 shown in the first embodiment will be described.

  FIG. 4 is a spectrum diagram showing the relationship between the arc ground fault current and the background noise. The horizontal axis is frequency and the vertical axis is current value. The current value at the time of arc generation is indicated by a solid line, and the background value at which no arc is generated is indicated by a broken line. In the range of 0 to 200 kHz shown in the figure, the noise as the background appears in a state having discrete peaks, and the arc ground fault current gradually attenuates as the frequency increases. From this figure, although the arc ground fault current and noise are superimposed, the region where the arc ground fault current is to be detected is generally larger than 0 in the range of 150 kHz, preferably in the range of 0.1 to 150 kHz, more preferably 0. .1 to 100 kHz, and by detecting the arc ground fault current in this frequency range, the calculation load can be reduced and the detection accuracy can be improved by detecting in the arc ground fault. It turns out that it is possible.

A method for detecting an arc ground fault in the frequency range will be described with reference to the flowchart of FIG.
In the flowchart of FIG. 5, detection and storage of the ground fault current in the initial state from step S1 to step S4 is the same as in FIG.

The operation during operation of the load 4 will be described.
The ground fault current is measured by the zero phase current transformer (ZCT) 3, and the measured ground fault current is input to the ground fault current measuring unit 10. After the ground fault current measuring unit 10 converts the signal to a predetermined level, it is sampled by the A / D converter 20 and converted into a digitized digital signal (step S5). At this time, similarly to the acquisition of the initial value, a digital signal is acquired over a predetermined frequency range of 0.1 kHz or higher.

The arithmetic processing unit 30 performs arithmetic processing on the digitized digital signal over a predetermined frequency range by FFT, and calculates the power spectrum component (during operation) SECop of each frequency (step S6).
At each frequency, the power spectrum component (initial value) SECin is subtracted from the power spectrum component (during operation) SECop to calculate the power spectrum component (true value) SECtr of each frequency (step S7a).

The power spectrum component (true value) SECtr of each frequency is narrowed down to the power spectrum component (true value) SECtr-a in the frequency range of 0.1 to 150 kHz or 0.1 to 100 kHz (step S7b).
An arc ground fault current from which background noise has been removed is calculated by performing inverse FFT on the power spectrum component (true value) SECtr-a over the frequency range of 0.1 to 150 kHz or 0.1 to 100 kHz (step) S8).
If the calculated arc ground fault current exceeds a preset threshold value, it is determined that an arc ground fault has occurred (YES in step S9), an abnormal signal or the like is output from output unit 50, and a warning is issued (step S10). ).

  As described above, according to the second embodiment, the zero-phase current transformer (ZCT) 3 is provided in the feeder 2 connected to the DC system, the ground fault current is measured, and the FFT-processed spectral component and the FFT By using the difference from the processed initial signal spectrum component and calculating the highly accurate arc ground fault current from which background noise has been removed, it is possible to detect whether or not an arc ground fault has occurred. At this time, since signal processing is performed for a current signal in a frequency range of 0.1 to 150 kHz or 0.1 to 100 kHz, the calculation load is reduced and an arc ground fault can be detected at high speed. Detection accuracy can be improved.

Embodiment 3 FIG.
Hereinafter, the arc ground fault detection apparatus according to the second embodiment will be described with reference to FIG.
In the first embodiment, the DC system is ungrounded or high-resistance grounding. However, in this embodiment, an example in which one side is grounded as in the DC system of a railway facility will be described.

In FIG. 6, in the DC system 1, one line is grounded. Although a load 4 is connected to a feeder 2 branched from the DC system 1, detection of an arc ground fault 6 generated with respect to the ground 5 in the feeder 2 will also be described in the present embodiment. The current flowing through each phase of the feeder 2 is measured by a current transformer (CT) 3a and input to the current measuring unit 10a of the arc ground fault detection device 100. The arc ground fault detection apparatus 100 includes a current measurement unit 10a, an A / D conversion unit 20, an arithmetic processing unit 30, a storage unit 40, an output unit 50, and a communication circuit 60 connected to a current transformer (CT) 3a.
The current measurement unit 10a calculates the difference between the input currents of the respective phases, and the difference current is converted (amplified) into a signal level necessary for processing in the next A / D conversion unit 20, and the A / D conversion unit 20 is converted into a digitized digital signal. The data converted into the digital signal is arithmetically processed by the arithmetic processing unit 30 to perform abnormality determination (determination of arc ground fault).

The load 4 may be a single load or a plurality of loads, and may be a load to which power converted into alternating current by a power converter (not shown) connected to the feeder line 2 is supplied.
In addition, the configuration of the arithmetic processing unit 30, the storage unit 40, the output unit 50, and the communication circuit 60 is the same as that of the first embodiment, and thus description thereof is omitted. The transmission of information to the external monitoring device 200 via the communication circuit 60 and the communication method to the communication circuit 60 and the monitoring device 200 are the same as in the first embodiment. The hardware configuration of the arc ground fault detection apparatus 100 is the same as that of the first embodiment.

  In the first embodiment, the ground fault current is directly measured by the zero-phase current transformer (ZCT). However, as described above, in the third embodiment, the ground fault current is measured by the current transformer (CT) provided in each phase. Specifically, it is different in that the ground fault current is calculated from the difference between the currents of the respective phases using the current.

  Next, an arc ground fault detection method using the arc ground fault detection apparatus 100 will be described with reference to the flowchart of FIG.

  When the initial ground fault current that is the initial state of the feeder line 2 is not stored in the storage unit 40 (NO in step S101), the current of each phase is measured by the current transformer (CT) 3a, and the measured current is Input to the current measuring unit 10a. The current measuring unit 10a calculates the ground fault current from the difference between the currents of the respective phases, and converts it into a signal of a predetermined level. The signal converted to a predetermined level is sampled by the A / D converter 20 and converted into a digitized digital signal (step S102). At this time, a digital signal over a predetermined frequency range of 0.1 kHz or more is acquired.

  The arithmetic processing unit 30 performs arithmetic processing on the digitized digital signal over a predetermined frequency range by FFT, and calculates a power spectrum component (initial value) SECin of each frequency (step S103). The calculated power spectrum component is stored in the storage unit 40 as initial value data (step S104).

Next, the operation during operation of the load 4 will be described.
The current of each phase is measured by the current transformer (CT) 3a, and the measured current is input to the current measuring unit 10a. The current measuring unit 10a calculates the ground fault current from the difference between the currents of the respective phases, and converts it into a signal of a predetermined level. The signal converted to a predetermined level is sampled by the A / D converter 20 and converted into a digitized digital signal (step S105). At this time, a digital signal over a predetermined frequency range of 0.1 kHz or more is acquired in the same manner as when the initial value is acquired.

The arithmetic processing unit 30 performs arithmetic processing on the digitized digital signal over a predetermined frequency range by FFT, and calculates a power spectrum component (during operation) SECop of each frequency (step S106).
At each frequency, the power spectrum component (initial value) SECin is subtracted from the power spectrum component (during operation) SECop to calculate the power spectrum component (true value) SECtr of each frequency (step S107).

An arc ground fault current from which background noise has been removed is calculated by performing inverse FFT on the power spectrum component (true value) SECtr over a predetermined frequency range (step S108).
If the calculated arc ground fault current exceeds a preset threshold value, it is determined that an arc ground fault has occurred (YES in step S109), an abnormal signal or the like is output from output unit 50, and a warning is issued (step S110). ).

If arc grounding current calculated in step S108 does not exceed the preset threshold (NO in step S109), it returns to the current measurement in the current transformer (CT) 3a.

  As described above, according to the third embodiment, an arc ground fault can be detected with high accuracy in the same manner as in the first embodiment, even for a feed line connected to a DC system in which one line is grounded. This is possible and has the same effect as in the first embodiment.

  Also in the third embodiment, as in the second embodiment, the detection of the arc ground fault current is preferably performed in a frequency range of 0.1 to 150 kHz, more preferably 0.1 to 100 kHz. It is possible to reduce the calculation load and improve detection accuracy by performing detection focusing on the arc ground fault.

  In the first to third embodiments described above, it is assumed that the FFT arithmetic processing is executed on software. However, the arithmetic processing unit 30 is executed by the FPGA using an FPGA (Field Programmable Gate Array). It may be. The FPGA is an arithmetic processing device that can be freely programmed and can read from the storage unit 40 and change or update the program. For this reason, when the digital signal sampled and digitized by the A / D conversion unit 20 is input and the initial value is read from the storage unit 40, not only the FFT calculation processing but also the occurrence of an arc ground fault occurs. It is possible to incorporate processing up to the determination.

  As described above, according to the present disclosure, it is possible to detect an arc ground fault of a power supply line connected to a DC system, so that the technology according to the present disclosure is a regeneration that is a DC system such as the solar power generation system described above. By applying it to possible energy systems and railway facilities, it is possible to construct highly reliable distribution systems.

Although this disclosure describes various exemplary embodiments and examples, various features, aspects, and functions described in one or more embodiments may be described in terms of particular embodiments. The present invention is not limited to the application, and can be applied to the embodiments alone or in various combinations.
Accordingly, countless variations that are not illustrated are envisaged within the scope of the technology disclosed herein. For example, the case where at least one component is deformed, the case where the component is added or omitted, the case where the at least one component is extracted and combined with the component of another embodiment are included.

  1: DC system, 2: Feeder (feeder), 3: Zero phase current transformer (ZCT), 3a: Current transformer (CT), 4: Load, 5: Ground, 6: Arc ground fault, 10: Ground Fault current measuring unit, 10a: current measuring unit, 20: A / D conversion unit, 30: arithmetic processing unit, 40: storage unit, 50: output unit, 60: communication circuit, 100: arc ground fault detection device, 110: Processor, 120: storage device, 200: monitoring device.

Claims (4)

A current transformer for measuring the current of the feeder line connecting the DC system and the load;
An A / D converter that converts the measured current into a digital signal;
A transformed method of detecting arc ground fault using an arithmetic processing unit, an apparatus example Bei the arithmetically processing the digital signal,
Fourier transforming the current signal of the feeder line over a predetermined frequency range of 0.1 kHz or more converted by the A / D conversion unit and storing it as an initial power spectrum;
Fourier transform of the current signal of the feeder line over the predetermined frequency range of 0.1 kHz or more measured at the time of operation of the load and converted by the A / D conversion unit, the power spectrum during operation Step to get,
Subtracting the initial power spectrum from the power spectrum to obtain a true power spectrum;
An inverse Fourier transform of the true power spectrum to calculate an arc ground fault current;
Comparing the calculated arc ground fault current with a preset threshold;
And method for detecting arc ground fault where the arc grounding current calculated has a step of determining that if the arc ground fault occurs beyond the preset threshold. 2. The arc ground fault detection method according to claim 1, wherein the predetermined frequency range is a range of 0.1 kHz to 150 kHz . The method for detecting an arc ground fault according to claim 1 , further comprising a step of outputting an abnormal signal when it is determined that an arc ground fault has occurred . The arc ground fault detection method according to claim 1 or 2 , wherein if it is not determined that an arc ground fault has occurred, the process returns to the step of acquiring the operating power spectrum .

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