JP7057718B2 - High resistance ground fault detector for DC feeders - Google Patents

Description

The present invention relates to a feeder ground fault detecting device in an electric railway, and more particularly to a technique effective for detecting a high resistance ground fault in a DC feeder.

Conventionally, a high voltage of several thousand V is applied to a feeder in a DC electrified section of an electric railway, and it is insulated from the ground by a beam or bracket extending from a support column via an insulator such as an insulator. It is suspended in a state of being suspended. In such a feeder, the insulator may be damaged and the feeder may hang down and come into contact with the support column or the ground, and a ground fault current may flow to the ground. When such a ground fault occurs, a circuit breaker usually provided in a substation can detect the ground fault current and cut off the current flowing through the electric wire.

However, when a ground fault called a high resistance ground fault occurs, the circuit breaker may not be able to detect the ground fault because the ground fault current that is smaller than the current supplied to the electric vehicle may flow. .. In particular, in the section where a large current flows due to the traveling of multiple electric vehicles between substations, the circuit breaker's breaking current is set to a relatively large value, so depending on the situation of a ground fault, the circuit breaker may be used. It was found that there is a problem that the ground fault current can be detected and the current flowing through the electric wire cannot be cut off.
Conventionally, as inventions relating to a high resistance ground fault detection system, a detection device, and a detection method, for example, Patent Documents 1, 2 and 3 have been proposed.

Japanese Unexamined Patent Publication No. 2009-247155 Japanese Unexamined Patent Publication No. 2016-577 Japanese Unexamined Patent Publication No. 2018-36054

The invention described in Patent Document 1 describes the harmonic component of the current flowing through all the high-voltage side DC current cables connected to the rectifier and all the harmonic components connected to the rectifier in the premises of the electric railway substation. The high resistance ground fault of the high-voltage side DC current cable is detected by detecting the difference current from the harmonic component of the current flowing through the return-side DC current cable with the search coil.
However, in a general electric railway substation premises, not all high-voltage side DC feeder cables and all return-side DC feeder cables are on the same wiring route, so the high-voltage side and the return line side It is difficult to arrange the search coil so as to surround the entire cable. Further, the above invention targets a high resistance ground fault inside the substation, and has a problem that it is difficult to detect a high resistance ground fault generated outside the substation.

Further, since the inventions described in Patent Documents 2 and 3 are all methods for detecting the voltage and potential difference caused by the flow of ground fault current, as described above, a plurality of electric vehicles are provided between the substations. In a section where a large current flows due to traveling, there is a problem that it is difficult to distinguish between the ground fault current when a high resistance ground fault occurs and the current supplied to the electric vehicle.

The present invention has been made by paying attention to the above-mentioned problems, and the object thereof is that the current detector can be easily arranged and the high resistance ground fault of the DC feeder generated outside the substation. It is an object of the present invention to provide a high resistance ground fault detector capable of detecting.
Another object of the present invention is a high resistance ground that can reliably detect a high resistance ground fault of a DC feeder by distinguishing between a ground fault current when a high resistance ground fault occurs and a current supplied to an electric vehicle. The purpose is to provide an entanglement detection device.

In order to achieve the above object, the present invention is:
High resistance based on the current detection means provided corresponding to the feeder line that supplies the DC current output from the rectifier of the substation that supplies DC power to the DC wire, and the data measured by the current detection means. In a high-resistance ground fault detection device equipped with an arithmetic processing means for determining the presence or absence of a ground fault,
The arithmetic processing means is
A frequency analysis means for frequency analysis of data measured when the current is increased by the current detection means, and a frequency analysis means.
A spectrum level extraction means for extracting a spectrum level in a predetermined frequency range from the data converted by the frequency analysis means, and a spectrum level extraction means.
A determination means for determining a high resistance ground fault based on the spectrum level extracted by the spectrum level extraction means is provided .
The frequency analysis means can perform a fast Fourier transform and can perform a fast Fourier transform.
The rectifier is composed of a bridge circuit having n diodes.
The spectrum level extraction means has a frequency between n × f0 and 2n × f0 from the spectrum calculated by the fast Fourier transform when the frequency of the three-phase AC voltage input to the substation is f0. Alternatively, it has a function of extracting a spectral level between 2n × f0 and 3n × f0 or between 3n × f0 and 4n × f0.
The determination means is configured to compare the spectrum level extracted by the spectrum level extraction means with a preset threshold value to determine the presence or absence of a high resistance ground fault .

According to the high resistance ground fault detection device having the above-mentioned configuration, the current detector can be easily arranged and the high resistance ground fault of the DC feeder generated outside the substation can be detected. Further, it is possible to reliably detect the high resistance ground fault of the DC feeder by distinguishing between the ground fault current when the high resistance ground fault occurs and the current supplied to the electric vehicle.
In addition, it is possible to detect the high resistance ground fault of the DC feeder more accurately and reliably.

Here, preferably, the current detecting means is an AC current transformer. Then, the spectrum level extraction means is configured to be able to sample the current value in a period of several microseconds in several tens of milliseconds.

Further, preferably, a notification means capable of outputting an alarm is provided.
The arithmetic processing means is configured to control the notification means to output an alarm when the determination means determines the occurrence of a high resistance ground fault.
According to this configuration, the maintenance personnel are made aware that a high resistance ground fault has been detected, and the maintenance personnel turn off the circuit breaker of the substation that supplies DC power to the electric wire in which the high resistance ground fault is detected. By setting this, it is possible to prevent the ground fault current from continuing to flow.

According to the present invention, the current detector can be easily arranged and the high resistance ground fault of the DC feeder generated outside the substation can be detected. Further, the present invention provides a high resistance ground fault detecting device capable of distinguishing between the ground fault current when a high resistance ground fault occurs and the current supplied to an electric vehicle and reliably detecting the high resistance ground fault of a DC feeder. It has the effect of being able to.

It is a system configuration diagram which shows the schematic structure of the ground fault detection system to which the high resistance ground fault detection apparatus which concerns on this invention is applied. It is a block diagram which shows the structural example of the high resistance ground fault detection apparatus of embodiment. It is a schematic diagram which shows an example of the frequency characteristic obtained by the fast Fourier transform of the current value at the time of occurrence of a high resistance ground fault measured by the high resistance ground fault detection apparatus of embodiment. It is a system configuration diagram which shows the schematic structure of the test target system which performed the ground fault detection on a trial basis using the high resistance ground fault detection apparatus of embodiment. It is a flowchart which shows an example of the procedure of the high resistance ground fault detection processing in the high resistance ground fault detection apparatus of embodiment.

Hereinafter, an embodiment of the high resistance ground fault detection device and the detection method according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a ground fault detection system to which the high resistance ground fault detection device according to the present embodiment is applied.

As shown in FIG. 1, in the ground fault detection system according to the present embodiment, DC power is supplied to the DC feeder 10 from substations 20A and 20B located at both ends of the substation section. The substations 20A and 20B convert the transformer 21 that converts the voltage of tens of thousands of volts supplied from the power plant, the electric power company, etc. into the voltage of several thousand volts suitable for the DC electric wire of the train line, and the transformer 21 that converts the alternating current into direct current. A rectifier 22 and the like are provided. The rectifier 22 is composed of, for example, a three-phase diode rectifier (bridge circuit) that converts a three-phase AC voltage (for example, 50 Hz) formed by bridging six diodes into a DC voltage.

In the present embodiment, the AC component included in the DC current flowing through the DC wire 10 is measured in the middle of the power supply line 23 that supplies DC power from the current transformers 22 of the substations 20A and 20B to the DC wire 10. An AC CT (current transformer) 24 is provided, and a detection device 25 for analyzing the data measured by the AC CT 24 and detecting a high resistance ground fault is provided.
When an arc or spark is generated due to a ground fault, it is considered that the DC current flowing through the DC feeder 10 includes current fluctuations. Therefore, the present inventors measure the current fluctuation (alternating current component) contained in the direct current by the AC CT24, and perform frequency analysis of the measured data by FFT (Fast Fourier Transform) processing to extract the frequency characteristics. We decided to detect a high resistance ground fault.

As shown in FIG. 2, for example, the detection device 25 includes a program-type arithmetic processing unit 51 such as a microprocessor (MPU), a ROM (read-only memory) 52, and a RAM (memory that can be read and written at any time) 53. It can be configured by a storage means, a user interface (user I / F) 54, an input device 55 such as a keyboard and a mouse, and a general computer device including a display device 56 such as a liquid crystal display panel. A data analysis program executed by the arithmetic processing apparatus 51 is stored in the ROM 52, and the data analysis means is configured by the arithmetic processing apparatus 51 and the data analysis program.

FIG. 3 shows the result of FFT analysis of the data measured by the AC CT 24 by the detection device 25. The horizontal axis of FIG. 3 is the frequency, and the vertical axis is the spectrum level. As the measurement data to be analyzed, the data obtained by measuring for 65 ms (milliseconds) at a cycle of 1 μs (microseconds) was used. For the measurement, as shown in FIG. 4, the substation section sandwiched between the M substation and the T substation is selected as a test target, and an AC CT 24 and a detection device 25 are provided at each substation, and the target substation is measured. A high resistance ground fault was artificially generated near the A substation in the middle.

In FIG. 3, B1 uses the data detected by the detection device 25 of the A substation (to be exact, the substation) immediately after the start of power running of the train at the time of normal power transmission (during train running) in the target substation section. B2 shows the spectrum obtained by frequency analysis of the data detected by the detection device 25 of the M substation, and B3 shows the spectrum obtained by frequency analysis of the data detected by the detection device 25 of the A substation. B4 shows the spectrum obtained by frequency analysis of the detected data, and B4 shows the spectrum obtained by frequency analysis of the data detected by the detection device 25 of the T substation.

In addition, the "Kiden Substation" is a facility that is installed mainly in consideration of measures against voltage drop, and it connects the Kedden line with a bus to accommodate electricity and reduce the voltage drop under high load. Although it has neither a device nor a rectifier and does not have a power supply capacity, the present invention can be applied even when the substation is a voltage dividing station, and therefore, in the present embodiment, it is described as a substation having a more general configuration. ing.
From FIG. 3, it can be seen that there are portions where the spectral level rises like a mountain in the vicinity of 0 Hz, 300 Hz, 600 Hz, and 900 Hz, respectively. The present inventor has considered the causes of these peaks. As a result, the peaks at the spectral level near 0 Hz in B1 are based on the current flowing through the train running by force, and the peaks near 300 Hz and the peaks near 600 Hz are based on the operation of the rectifier 22 in the substation. I found that.

Further, from FIG. 3, when a high resistance ground fault is generated, the mountain near 300 Hz becomes large, and the spectrum level becomes larger as a whole when a high resistance ground fault is generated than when a normal feeder is generated. ing. In particular, it can be seen that the spectral levels between 300 Hz and 600 Hz and the spectral levels between 600 Hz and 900 Hz are clearly higher than at normal feeders.
Based on the above findings, the present inventor has devised and filed a high resistance ground fault detection method as described below. Hereinafter, the high resistance ground fault detection method according to the present invention will be described.

FIG. 5 is a flowchart showing an example of a processing procedure of the high resistance ground fault detection method according to the present invention.
The following processing according to the flowchart of FIG. 5 is performed by the arithmetic processing unit 51 executing the program stored in the ROM 52 of the high resistance ground fault detection device 15. Since the duration of the high resistance ground fault is not constant, the detection flow consisting of the series of processes in FIG. 5 may be configured to be repeatedly executed at a cycle of, for example, 100 ms (milliseconds).
When the high resistance ground fault detection process of FIG. 5 is started, the arithmetic processing apparatus 51 first samples the measured value of the AC CT 24 for several tens of ms in a cycle of several μs and stores it in the RAM 53 (step S1). Subsequently, the measured data sampled and stored is read from the RAM 53 and subjected to FFT processing to calculate the data as shown in FIG. 3 (step S2).

Next, the arithmetic processing apparatus 51 extracts the spectrum level between 300 Hz and 600 Hz from the Fourier spectrum (frequency spectrum) obtained by the FFT process, and calculates the average value (step S3). Instead of calculating the average value, the spectrum level at the midpoint may be selected.
Subsequently, it is determined whether or not the average value is higher than the preset threshold value (step S4). Then, when it is determined that the average value of the spectrum levels is lower than the threshold value (No), the process ends. On the other hand, if it is determined in step S4 that the average value of the spectrum level is higher than the threshold value (Yes), the process proceeds to step S5 to output an alarm to notify the maintenance personnel.

The alarm may be an alarm lamp that displays the occurrence of a high resistance ground fault on the screen of the display device 56 in characters or the like, or an alarm sound may be output by a voice output means such as a speaker or a buzzer (not shown). good.
As a result, the maintenance personnel recognize that a high resistance ground fault has been detected, and for example, by turning off the circuit breaker of the substation that supplies DC power to the electric wire in which the high resistance ground fault is detected, the ground fault is detected. It is possible to prevent the entanglement current from continuing to flow.
The arithmetic processing unit 51 may be configured to generate and output a signal for turning off the circuit breaker instead of outputting the alarm.

In the above embodiment, it is determined whether or not the spectral level between 300 Hz and 600 Hz of the data obtained by the FFT process is higher than the threshold value, and the high resistance ground fault is detected. It is not limited to such a determination. For example, from FIG. 3, at the time of normal feeder (B1), the peak at 600 Hz is larger than the peak at the spectral level of 300 Hz, whereas at the time of high resistance ground fault (B2, B3, B4), the peak is larger. Since the 300 Hz mountain is larger than the 600 Hz mountain, the 300 Hz mountain and the 600 Hz mountain may be compared to determine the presence or absence of a high resistance ground fault.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the above embodiment, the detection method when the rectifier of the substation is composed of a bridge circuit having 6 diodes has been described as an example, but the rectifier is composed of a bridge circuit having 12 diodes. If so, a large peak is seen in the vicinity of 600Hz, 900Hz, and 1.2kHz in the distribution of the Fourier spectrum, so the average value of the spectral level between 600Hz and 900Hz and the spectrum between 900Hz and 1.2kHz. A high resistance ground fault may be detected by determining whether or not the level is higher than the threshold value.

In the above embodiment, the case where the AC voltage input to the substation is 50 Hz is described, and when the input AC voltage is 60 Hz, the spectral levels of the Fourier spectrum are 360 Hz, 720 Hz, 1080 Hz, and 1440 Hz. Since peaks appear, the same detection as above may be performed by focusing on the peaks at those frequencies. Further, since some rectifiers are composed of a bridge circuit having 12 diodes, in that case, the same detection as above is performed by paying attention to the peak of the spectrum level at a frequency twice the above frequency. Good to do.
Further, in the above embodiment, the AC CT is used as the current measuring device, but the DC CT may be used. In the frequency analysis of the measured value of CT, the wavelet transform may be performed instead of the fast Fourier transform.

10 DC feeder 20A, 20B Substation 21 Transformer 22 Rectifier 24 AC CT (current transformer)
25 Detection device 50 High resistance ground fault detector 51 Arithmetic processing device

Claims (3)

High resistance based on the current detection means provided corresponding to the feeder line that supplies the DC current output from the rectifier of the substation that supplies DC power to the DC wire, and the data measured by the current detection means. A high-resistance ground fault detection device equipped with an arithmetic processing means for determining the presence or absence of a ground fault.
The arithmetic processing means is
A frequency analysis means for frequency analysis of data measured when the current is increased by the current detection means, and a frequency analysis means.
A spectrum level extraction means for extracting a spectrum level in a predetermined frequency range from the data converted by the frequency analysis means, and a spectrum level extraction means.
A determination means for determining a high resistance ground fault based on the spectrum level extracted by the spectrum level extraction means, and a determination means.
Equipped with
The frequency analysis means can perform a fast Fourier transform and can perform a fast Fourier transform.
The rectifier is composed of a bridge circuit having n diodes.
The spectrum level extraction means has a frequency between n × f0 and 2n × f0 from the spectrum calculated by the fast Fourier transform when the frequency of the three-phase AC voltage input to the substation is f0. Alternatively, it has a function of extracting a spectral level between 2n × f0 and 3n × f0 or between 3n × f0 and 4n × f0.
The determination means is characterized in that the presence or absence of a high resistance ground fault is determined by comparing the spectrum level extracted by the spectrum level extraction means with a preset threshold value. Resistance ground fault detector. The high resistance ground fault detecting device for a DC feeder according to claim 1, wherein the current detecting means is an AC current transformer. Equipped with a notification means that can output an alarm
The arithmetic processing means is
The DC feeder according to claim 1 or 2 , wherein the determination means is configured to control the notification means to output an alarm when the determination means determines the occurrence of a high resistance ground fault. High resistance ground fault detector.

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