JP2011072163A - Ground fault direction finding apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce errors in phase difference detection in a ground fault direction finding apparatus which finds the direction of a ground fault by detecting the phase difference between a zero-phase current and a zero-phase voltage that occurs at a ground fault accident. <P>SOLUTION: The ground fault direction finding apparatus includes a zero-phase current peak detecting means 71 which detects timing at which a zero-phase current detection signal from a zero-phase current detector reaches a peak, and a zero-phase voltage peak detecting means 72 which detects timing at which a zero-phase voltage detection signal from a zero-phase voltage detector reaches a peak. The difference between the timing detected by the zero-phase current peak detecting means 71 and the timing detected by the zero-phase voltage peak detecting means 72 is determined to detect the phase difference between the zero-phase current detection signal and the zero-phase voltage detection signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a ground fault direction detecting device that is connected to a section switch or the like grounded to a power distribution system and detects the direction of a ground fault accident point.

  As a method for detecting a ground fault direction, as shown in Patent Document 1, a method for detecting the direction of a ground fault point from a phase difference between a zero phase current and a zero phase voltage detected from a three-phase distribution line is known. ing. The ground fault direction detection device that detects the method of the ground fault point in this way is the zero phase current detection device that detects the zero phase current from the three phase distribution line, and the zero phase that detects the zero phase voltage from the three phase distribution line. The voltage detection device includes a phase difference detection unit that detects a phase difference between the zero phase current detection signal and the zero phase voltage detection signal obtained from the zero phase current detection device and the zero phase voltage detection device, respectively.

  In the conventional ground fault direction detection device, the phase difference detection unit includes a zero cross detection unit that detects a zero cross point of the zero phase current detection signal, and a zero cross detection unit that detects the zero cross point of the zero phase voltage detection signal. The phase difference between the zero-phase current and the zero-phase voltage is detected by calculating the difference between the zero-phase current and the zero-phase voltage detected by the zero-cross detection means. It had been.

  FIG. 5 shows an example of a method for detecting the phase difference between the zero-phase current and the zero-phase voltage from the difference between the zero-cross points of the two. FIG. 5A shows the zero-phase current detection signal Io. FIG. 4B shows a rectangular wave signal Iqo ′ obtained by waveform shaping the zero-phase current detection signal Io by a waveform shaping circuit that outputs a high level signal when the input signal level is greater than 0V. Is shown. FIG. 5C shows the zero-phase voltage detection signal Vo, and FIG. 5D shows the zero-phase voltage detection signal Vo when the input signal level is higher than 0V. A rectangular wave signal Vqo ′ obtained by waveform shaping by the waveform shaping circuit is shown. In the conventional method, the phase difference Δt is obtained from the difference between the rising edge of the rectangular wave signal Iqo ′ (zero-phase current zero-crossing point) and the rising edge of the rectangular wave signal Vqo ′ (zero-phase voltage zero-crossing point). It was.

JP 11-355955 A

  If the ground fault that occurred in the distribution system is a complete ground fault that is grounded through zero impedance, the waveform of the zero-phase current detection signal Io becomes a sine wave. When a ground fault occurs through a relatively large impedance due to an object contact) or when a gap ground fault occurs, the waveform of the zero-phase current detection signal Io is greatly distorted as shown in FIG. High value becomes minute.

  When the waveform distortion of the zero-phase current detection signal Io is not large, the zero-phase current and zero are detected from the zero-cross point of the zero-phase current detection signal Io and the zero-phase voltage detection signal Vo as in the conventional ground fault direction detection device. Even if the phase difference between the phase voltages is detected, a large error does not occur. However, as shown in FIG. 6, when the waveform distortion of the zero-phase current detection signal Io is large and the peak value is small, the zero-cross point of the zero-phase current detection signal cannot be accurately detected. If the phase difference between the zero-phase current and the zero-phase voltage is detected from the zero-crossing point of the zero-phase current detection signal and the zero-crossing point of the zero-phase voltage detection signal, the detection error increases and there is a risk of erroneous detection of the ground fault direction. It was.

  An object of the present invention is to detect a phase difference between a zero-phase current and a zero-phase voltage without a large error even when the waveform distortion of the zero-phase current detection signal is large and the peak value is small. An object of the present invention is to provide a ground fault direction detection device capable of accurately detecting the ground fault direction.

  The present invention relates to a zero-phase current detection device that detects a zero-phase current from a three-phase distribution line, a zero-phase voltage detection device that detects a zero-phase voltage from a three-phase distribution line, a zero-phase current detection device, and a zero-phase voltage detection device. The present invention relates to a ground fault direction detection device including a phase difference detection unit that detects a phase difference between the obtained zero phase current detection signal and the zero phase voltage detection signal.

  In the present invention, the zero-phase current peak detection means for detecting the first peak timing, which is the timing at which the zero-phase current detection signal reaches a peak, and the second peak timing, at which the zero-phase voltage detection signal reaches a peak. And detecting a phase difference between the zero-phase current detection signal and the zero-phase voltage detection signal by obtaining a difference between the first peak timing and the second peak timing. A phase difference detection unit is configured.

  Even when the waveform distortion of the zero-phase current detection signal is large, the peak point can be detected relatively easily. Therefore, as described above, if the phase difference between the two signals is detected from the difference between the peak point of the zero-phase current detection signal and the peak point of the zero-phase voltage detection signal, the zero-phase current detection signal and the zero-phase voltage detection are detected. The detection error of the phase difference can be reduced as compared with the case where the phase difference between both signals is detected from the zero cross point of the signal.

  According to the present invention, the phase difference between the two signals is detected from the difference between the peak point of the zero-phase current detection signal and the peak point of the zero-phase voltage detection signal, which are easy to detect. In addition, even when the ground fault occurs and the waveform distortion of the zero-phase current detection signal increases and the peak value decreases, the phase difference between the zero-phase current and the zero-phase voltage can be accurately detected. Therefore, according to the present invention, the detection error of the phase difference between the zero-phase current and the zero-phase voltage can be reduced, and the probability of erroneous detection of the ground fault direction can be reduced.

1 is a block diagram schematically showing a configuration of an embodiment of the present invention. It is the circuit diagram which showed the structural example in the switch shown by FIG. It is the block diagram which showed one Embodiment of the ground fault direction detection apparatus concerning this invention. It is a wave form diagram for demonstrating the method to detect the phase difference of a zero phase current and a zero phase voltage in the ground fault direction detection apparatus by this invention. It is a wave form diagram for demonstrating the method to detect the phase difference of the zero phase electric current and zero phase voltage which were performed in the conventional ground fault direction detection apparatus. It is the wave form diagram which showed an example of the waveform of the zero phase current detection signal and zero phase voltage detection signal which are obtained when the ground fault and gap ground fault by another object contact generate | occur | produce.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a hardware configuration of an embodiment of the present invention. In FIG. 1, 1a, 1b and 1c are three-phase distribution lines of A, B and C, and 2 is inserted in the middle of the distribution line. Is a divided switch. 3 is a ground fault direction detection device according to the present invention, and 4 is a transformer that takes in, for example, a voltage between A-phase and C-phase distribution lines into the ground fault direction detection device 3 as a power supply voltage.

  A ground fault direction detection device 3 shown in FIG. 1 includes a power source 301 that rectifies a single-phase AC voltage supplied from a transformer 4 and outputs a constant DC voltage, and 302 includes a microprocessor. A signal processing unit 303 that operates by being supplied with a voltage is a measurement that inputs information provided from a measuring instrument such as a zero-phase current transformer or a zero-phase voltage transformer provided in the switch 2 to the signal processing unit 302. An information interface 304 is a display unit that displays a determination result such as a ground fault direction determined by the signal processing unit 302.

  FIG. 2 shows the configuration of the switch 2, in which 4a to 4c are switches connected in series to the distribution lines 1a to 1c, and ZCT is a zero-phase current flowing through the three-phase distribution line. ZPD is a capacitor-type zero-phase voltage transformer that detects a zero-phase voltage and outputs a zero-phase voltage detection signal. The ZPD has a capacitor voltage dividing circuit composed of capacitors C1a to C1c having one end connected in common and the other end connected to the distribution lines 1a to 1c, and a capacitor C2 having one end connected to a common connection point of one end of these capacitors. , And an instrument transformer PT in which the output voltage of the capacitor voltage dividing circuit obtained at both ends of the capacitor C2 is applied to the primary winding. In this example, current switches CTa and CTb for detecting an A-phase current and a C-phase current are also provided in the switch 2 in order to detect an overcurrent. The outputs of the zero-phase current transformer ZCT, the zero-phase voltage transformer ZPD and the current transformers CTa and CTb are measured by the ground fault direction detector 3 through the output terminals u1 to u5 and signal cables connected to these output terminals. The information is input to the information interface 303.

  As shown in FIG. 3, the signal processing unit 302 of the ground fault direction detection device 3 of the present embodiment includes a first component that extracts a fundamental wave component from the zero-phase current detection signal Io obtained from the zero-phase current transformer ZCT. Low-pass filter 51, first amplifying unit 61 that amplifies the output of filter 51, and zero-phase current peak that detects the timing when the zero-phase current detection signal amplified by amplifying unit 61 reaches the peak as the first peak timing A detection means 71; a second low-pass filter 52 for extracting a fundamental wave component from the zero-phase voltage detection signal Vo obtained from the zero-phase voltage transformer ZPD; a second amplification unit 62 for amplifying the output of the filter 52; A zero-phase voltage peak detection means 72 for detecting a timing when the zero-phase voltage detection signal amplified by the unit 62 reaches a peak as a second peak timing, and zero-phase current peak detection A phase difference detector 80 for detecting a phase difference between the zero phase current detection signal and the zero phase voltage detection signal from the first and second peak detection timings detected by the stage 71 and the zero phase voltage peak detection means 72, respectively; Is provided. The phase difference detection unit 80 detects the phase difference between the zero-phase current detection signal and the zero-phase voltage detection signal, determines the direction of the ground fault point from the detected phase difference, and displays the determination result on the display unit 304. To give.

  Among the units shown in FIG. 3, the low-pass filters 51 and 52 and the amplifying units 61 and 62 are constituted by hardware circuits, and the peak detecting means 71 and 72 and the phase difference detecting unit 80 are constituted by a microprocessor.

  The zero-phase current peak detecting means 71 digitally converts the sampled value by sampling the instantaneous value of the fundamental wave component of the zero-phase current detection signal Io output from the amplifying unit 61 at a constant sampling period, and detects the zero-phase current. Each time the instantaneous value of the signal Io is sampled, the digital value of the newly sampled signal is compared with the digital value of the previously sampled signal to detect the timing at which the zero-phase current detection signal reaches each positive and negative peak.

  For example, as shown in FIG. 4B, the zero-phase current peak detecting means 71 is from the timing when the zero-phase current detection signal Io shown in FIG. 4A reaches the positive peak to the timing when the negative peak is reached. And the period Ti2 from the timing when the zero-phase current detection signal Io reaches the negative peak to the timing when the zero-phase current detection signal Io reaches the positive peak, are detected separately. Of these periods, for example, the zero-phase current detection signal Io A period Ti1 from the timing when the positive peak is reached to the timing when the negative peak is reached as the phase difference detection section, and the start timing t1 is stored as the first timing.

  The zero-phase voltage peak detection means 72 converts the sampled value by sampling the instantaneous value of the fundamental wave component of the zero-phase voltage detection signal output from the amplifying unit 62 at a constant sampling period, and converts the sampled value into a digital signal. Each time the instantaneous value is sampled, the digital value of the newly sampled signal is compared with the digital value of the previously sampled signal to detect the timing at which the zero-phase voltage detection signal reaches each positive and negative peak.

  For example, as shown in FIG. 4D, the zero-phase voltage peak detecting means 72 is from the timing when the zero-phase voltage detection signal Vo shown in FIG. 4C reaches the positive peak to the timing when the negative peak is reached. Period Tv1 and period Tv2 from the timing when the zero-phase voltage detection signal Vo reaches a negative peak to the timing when the zero-phase voltage detection signal Vo reaches a positive peak, are detected separately. Of these periods, for example, the zero-phase voltage detection signal Vo A period Tv1 from the timing when the positive peak is reached to the timing when the negative peak is reached as the phase difference detection section, and the start timing t2 is stored as the second timing.

  The phase difference detector 80 calculates the difference between the first timing t i and the second timing t 2 to obtain the phase difference between the zero phase current detection signal Io and the zero phase current detection signal Vo. The direction of the ground fault point is determined based on the phase difference, and the result is displayed on the display unit 304.

  As shown in FIG. 6, even when the waveform distortion of the zero-phase current detection signal is large, the peak point can be detected relatively easily. Therefore, as described above, when the phase difference between the two signals is detected from the difference between the peak point of the zero-phase current detection signal Io and the peak point of the zero-phase voltage detection signal Vo, the zero-phase current detection signal and the zero-phase current signal Compared with the case where the phase difference between the two signals is detected from the zero cross point of the voltage detection signal, the detection error of the phase difference can be reduced.

  In the above embodiment, the zero-phase current transformer ZCT is used as the zero-phase current detection device. However, a current transformer for detecting a three-phase distribution line current is provided, and the outputs of these current transformers are added. Thus, the zero-phase current detection device can be configured to detect the zero-phase current. Further, the zero-phase voltage detection device can be configured to detect the zero-phase voltage by adding the outputs of the instrument transformers that detect the three-phase phase voltages instead of using the zero-phase voltage transformer ZPD. .

1a to 1c Three-phase distribution line 2 Section switch 3 Ground fault direction display device 51 First low-pass filter 52 Second low-pass filter 61 First amplifying unit 62 Second amplifying unit 71 First peak detecting means 72 Second peak detecting means 80 phase difference detecting section

Claims (1)

Obtained from a zero-phase current detection device that detects a zero-phase current from a three-phase distribution line, a zero-phase voltage detection device that detects a zero-phase voltage from the three-phase distribution line, and the zero-phase current detection device and the zero-phase voltage detection device, respectively. In a ground fault direction detection device comprising a phase difference detection unit for detecting a phase difference between a zero phase current detection signal and a zero phase voltage detection signal,
Zero-phase current peak detection means for detecting a first peak timing that is a timing at which the zero-phase current detection signal reaches a peak; and a second peak timing at which the zero-phase voltage detection signal reaches a peak. Comprising zero-phase voltage peak detection means,
The phase difference detection unit is configured to detect a phase difference between the zero-phase current detection signal and the zero-phase voltage detection signal by obtaining a difference between the first peak timing and the second peak timing. Being
A ground fault direction detecting device.

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