JP2002350488A - Direct current grounding point searching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve problems in a conventional direct current grounding point searching method that noise is determined as a ground-fault line when it exists due to easy affection by noise, a current necessary for determination cannot be obtained since it takes time to charge or discharge and a rectangular wave pulsating current becomes small when earth capacitance of the whole direct current control circuit becomes large, and particularly, a ground point cannot be searched at an extra high voltage substation having noise or a 5000 kV substation with large earth capacitance. SOLUTION: In the direct current grounding point searching method, a ground-fault current is converted into a rectangular wave pulsating current by opening and closing a contact 4a of a flicker relay 4 connected to a grounded circuit of a ground detecting relay 3 of a direct current control circuit 2, and the ground-fault current is detected by an alternating current clamp CT 6. Low frequency noise is canceled out and converged by dividing the rectangular wave pulsating current into unit cycles and superimposing and adding it a multiplicity of times. The ground-fault current is detected by the alternating current clamp CT 6 by composing a flicker circuit facilitating charge and discharge of earth capacitance and increasing the rectangular wave pulsating current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a ground fault point in a method of detecting a DC ground fault generated in a DC circuit.

[0002]

2. Description of the Related Art Conventionally, as a method of searching for a fault point when a ground detection relay connected to a DC power supply circuit of this type detects a fault, a DC ground detection relay (64D) 3 detects a ground fault and issues an alarm. When displayed, a method of searching for a grounding point by checking whether or not the DC grounding detection relay (64D) 3 is restored by separating and stopping the circuit sequentially through a separation switch. A method of automatically detecting a grounding point for each trunk line via a DC current transformer connected to the DC control circuit 2, and stopping and searching for the circuit in the same manner as described above. When the DC grounding detection relay (64D) 3 performs detection operation, 1
A method of injecting a low-frequency alternating current of about 0 to 30 Hz into a circuit and detecting this. And other methods have been used.

[0003] Therefore, in this type of conventional DC ground fault point searching method, there is no control and no protection from the moment when the circuit is stopped, and the functions of the automatic control equipment and the production equipment of the power generation and substations are reduced. Not only is it shut down, but it takes several stops to find the ground that needs recovery.
In addition, there is a problem that it takes time to remove the wiring, and the stop time is extremely long. In addition, the method of injecting a low-frequency AC current into a circuit has a problem that detection may not be possible depending on the ground capacitance.

As another method of searching for a fault point of a DC control circuit, Japanese Patent No. 1829 filed by the present applicant is disclosed.
No. 635, "Flicker-type DC grounding point searcher (FK-M1)", as disclosed in the patent publication, converts a ground fault current into a square wave pulsating current, and uses the change as an AC clamp C
There are methods to detect with T, but in these methods, the detected current is measured by analog measurement of only the magnitude and the indicator is shaken (FK-M1). There is a DC ground fault point search method (FK-M3), which digitally calculates the area of the waveform mainly composed of the flowing current and the area of the capacitive waveform flowing through the healthy line and makes a comparison in the form of a waveform. Is also susceptible to noise, and in the presence of noise, even when a healthy DC circuit is measured, it is often determined erroneously as a ground fault line.

[0005] Furthermore, when the capacitance to ground of the entire DC control circuit becomes large, it takes time to charge or discharge the capacitance to ground, and within a certain period (for example, 0.88 sec) during which a rectangular wave pulsating current is converted. In this case, since the discharge is not sufficiently performed, the ground voltage cannot be recovered, and the fault current flows only at a value corresponding to the ground voltage. For this reason, the rectangular wave pulsating current becomes a level lower than the detection sensitivity of the searcher, and the search becomes impossible. As described above, in the conventional technology, it is impossible to search for a ground point in an ultra-high voltage substation where noise is present or in a 5000 kV substation having a large ground capacitance.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a ground fault as disclosed in Japanese Patent No. 1829635 "Flicker-type DC ground point searcher (FK-M1)" filed by the present applicant. The present invention is an improved invention of a method for searching for a fault point of the DC control circuit 2 which converts a current into a rectangular pulsating current and detects the change with an AC clamp CT6. That is, in the first invention, when a ground fault occurs in the DC control circuit 2 of a substation or the like, a DC ground fault point searcher (FK-M3) that searches for the fault point uses the measurement principle of the present search method. The grounding circuit of the grounding detection relay 3 in which a certain grounding fault current flows is turned on and off at regular intervals to convert it into a rectangular wave pulsating current, and noise is removed from the input waveform that is detected by the AC clamp CT6 and determines the grounding fault. Is the way.

That is, in the first invention, in the method using the conventional ground fault point searcher, when the detected input waveform includes noise, the search device makes an erroneous determination. In order to solve the problem, high-frequency noise is removed from an input waveform for determining a ground fault by an analog filter, and low-frequency noise is removed by digital operation using a filter and a microcomputer together. It is an object of the present invention to provide a method (FIGS. 2, 3 and 15) for improving the existing search method for searching for.

Further, the above-described conventional ground fault point search (FK-M3)
The flicker relay 4 is a problem which the method according to
When the contact 4a is opened, the ground circuit is opened and the discharge from the capacitance (capacitor) is not sufficiently performed. On the other hand, the second invention provides a circuit 5 that can discharge without opening the ground circuit. To speed up the recovery of the ground voltage at the fault point by smoothly charging and discharging the capacitance (capacitor), and the flicker relay 4 of the DC ground fault point searcher.
The flicker current can be finally amplified by causing the fault current to rise quickly and sufficiently within the switching interval of the contact 4a.

In the second invention, when the input waveform of the square-wave pulsating current is small and does not reach the detection sensitivity level of the searcher used in the present search method, it is amplified to enable determination. This is an effective means for reducing the pulsating current of the rectangular wave due to the increase in the capacitance of the DC control circuit 2 to the ground.

[0010]

According to a first aspect of the present invention, means for removing harmonic noise and ultra-low frequency noise superimposed on the DC control circuit 2 by an analog filter is used. If the filter removes low-frequency noise in the same range as the period (0.57 Hz) to be converted into a pulsating current, even a rectangular pulsating current will be removed. Therefore, a filter cannot be used. Absent. The “noise removal method in the low frequency region” of the “additional noise removal method” applied to such a case is performed by dividing the rectangular wave pulsating current into one cycle unit and adding a large number of times. Since the square-wave pulsating currents have the same period,
The sum is multiplied by the number of additions, but since the low-frequency noise has no periodicity, it is canceled and converged by adding many times.

That is, in the first invention, a flicker relay 4 is connected to a grounding circuit of a grounding detection relay 3 connected to a DC control circuit 2 having a DC power supply 2a comprising a storage battery 1 and the like, and a contact 4a of the flickering relay 4 is fixed. In the DC ground fault point search method of converting the ground fault current into a square wave pulsating current by detecting the ground fault current with the AC clamp CT6, the square wave pulsating current detected by the AC clamp CT6 This is a DC ground fault point search method characterized in that a current is divided into unit periods, superimposed and added many times to cancel and converge low-frequency noise.

According to a second aspect of the present invention, in the method of searching for a DC ground fault point according to the first aspect of the present invention, when the ground fault current is converted into a rectangular wave pulsating current by opening and closing the contact 4a of the flicker relay 4, the contact is grounded when the contact 4a is opened. The DC control circuit 2 is formed by forming the bypass circuit 5 so that the discharge can be performed without opening the circuit.
Smoothly charges and discharges the entire ground capacitance, speeds the recovery of the terminal voltage at the fault point, and quickly and sufficiently starts the fault current within the flicker interval of the DC ground fault point searcher. A DC ground fault point search method is characterized in that a rectangular wave pulsating current (flicker current) is amplified by making it possible to make the determination.

Accordingly, the DC ground fault point search method of the present invention
Efficient means for removing noise superimposed on the DC control circuit 2 of the ultra-high voltage substation and reducing the pulsating current of the rectangular wave due to the increase in the ground capacitance of the DC control circuit 2 Can be.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a waveform of a noise including a flicker current of the present searcher. (The horizontal axis is a time (every 2 seconds) axis.) FIG. 2 shows a superimposed waveform obtained by dividing a noise waveform in synchronization with a flicker cycle. FIG. 3 shows a flicker current waveform obtained by performing the addition process 30 times. (Noise waveform has disappeared.) FIG. 4 is a diagram showing a circuit configuration of a conventional DC ground detection relay (64D) 3. As shown in FIG. FIG. 5 is a diagram showing the relationship between the ground fault current and the charge / discharge current of the circuit of FIG. (The charge / discharge current is larger.) FIG. 6 is a diagram showing a circuit configuration of the DC ground detection relay (64D) 3 of the first invention. FIG. 7 is a diagram showing the relationship between the ground fault current and the charge / discharge current of the circuit of FIG. (The charge / discharge current is reduced.) FIG. 8 is a diagram showing a circuit configuration of the DC ground detection relay (64D) 3 of the second invention. (The resistance value was changed.) FIG. 9 is a diagram showing the relationship between the ground fault current and the charge / discharge current of the circuit of FIG. (The flicker value of the ground fault current has increased.) FIG. 10 shows a waveform of a transient phenomenon of the ground fault current when the capacitance to ground is small. (The rise is within 2 seconds.) FIG. 11 shows the waveform of the transient phenomenon of the ground fault current when the capacitance to ground included in the circuit is large. (It takes 10 seconds or more to rise.) FIG. 12 shows a waveform of the flicker current (2 mA) when the ground capacitance is small. FIG. 13 shows a mode in which the flicker current waveform when the ground capacitance is large is attenuated to 0.6 mA. FIG. 14 shows a waveform of a flicker current when there is a “swell” of low frequency noise. FIG.
Shows a circuit capable of removing the "undulation" component and extracting only the flicker signal. FIG. 16 shows an input waveform. FIG. 17 shows a waveform of a flicker signal including a “swell” on the output side subjected to a high cut filter. FIG.
8 shows a waveform of a flicker signal on the output side on which digital operation has been performed, from which "undulation" has been removed. FIG. 19 shows a flicker unit 1 of a set of FK-M3 used in carrying out the present invention.
6, the external appearance of the determination unit 15, and the appearance of the AC clamp CT6 are shown.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first invention of the present application has the features as described above, and the embodiments thereof will be described below.
The “additional noise elimination method” is a method of removing low-frequency noise from the waveform handled by the determination circuit of the present search method when it is mixed, and performs the following processing. In order to form a reference timing synchronized with the flicker signal, which serves as a reference for the addition processing, the flicker unit 1
The test signal for checking the function of No. 6 is captured by the AC clamp CT6, the cycle of the flicker signal is measured by the determination unit 15, and the sync signal having the same cycle as the value is generated by the sync signal generator 8. After the synchronizing signal generator 8 generates a "synchronizing signal" serving as a reference timing for the addition processing, an AC clamp CT6 is attached to the actual circuit, and a flicker current is input. An addition processing buffer is newly provided, the input waveform is divided for each cycle by the synchronization signal obtained in the above, and the addition processing is performed by the number of additions set by the addition circuit 10. The number of additions is infinite. When the number of times of addition is repeated, if the waveform accuracy becomes equal to or less than a threshold value (a waveform state having periodicity that can be determined by the searcher), an output is made to the determination circuit. After that, when the addition is repeated and the waveform is purified to a better waveform than the previous state, an output for replacing the previous data is performed. When a waveform equal to or less than the threshold value is obtained by adding several times, completion is indicated by an indicator. Judgment is made with the captured waveform for one cycle, and the difference between the waveform due to resistance grounding and the waveform of charging / discharging current due to capacitance causes the red lamp (failed line) to be turned on for the waveform of the line where a ground fault has occurred. In the case of the charge / discharge current waveform of the capacitance, the green lamp (healthy line) is turned on. This determination operation is repeatedly performed.

When the capacitance to the ground (capacitor) of the DC circuit of the "flicker current amplifying system" increases, the time constant increases and it takes time to charge and discharge. Occurs, causing the rise of the fault current to be delayed, causing the DC ground fault searcher (FK-
M3) rectangular wave pulsating current (flicker current) is reduced.
If this phenomenon progresses, a flicker current of a level higher than the detection sensitivity of the DC ground fault point detector (FK-M3) cannot be obtained, and measurement becomes impossible.

In the method of the second invention, a charge / discharge circuit is formed,
This is to increase the flicker current. FIG.
3 shows a circuit diagram of a conventional DC grounding detection relay (64D) 3. Since the flicker relay 4 (relay) is connected to the grounding circuit, the grounding circuit is opened when the switch is turned off, and discharge from the capacitor becomes impossible. R1
/ R2 / R3 = 20 kΩ / 20 kΩ / 10 kΩ, and flicker current = 0.42 mA. FIG. 5 shows the relationship between the ground fault current and the charge / discharge current in FIG.

FIG. 6 shows a DC ground detection relay (64) according to the present invention.
D) The circuit diagram of 3 is shown. FIG. 3 is a diagram in which a circuit that bypasses a resistance of a ground circuit is provided, and a flicker relay 4 (relay) is provided here. R1 / R2 / R3 = 20kΩ / 20kΩ / 1
0 kΩ and flicker current = 0.35 mA. Even if this switch is turned on and off, the ground circuit of the DC ground detection relay (64D) 3 does not enter an open state, so that the capacitor is easily discharged and the value of the charge / discharge current is reduced. FIG. 7 shows the relationship between the ground fault current and the charge / discharge current in FIG.

FIG. 8 shows a DC ground detection relay (64) according to the present invention.
D) The circuit diagram of 3 is shown. FIG. 3 is a diagram in which a circuit that bypasses a resistance of a ground circuit is provided, and a flicker relay 4 (relay) is provided here. Although the fault current increases in this state,
Since the flicker current does not change, the DC ground detection relay (6
4D) By changing the resistance value of the circuit element 3 as shown in FIG. 8, the flicker current increases from 0.35 mA (FIG. 7) to 1.11 mA (FIG. 9). At this time, the resistance value is R1 / R2 / R3 = 10 kΩ / 10 kΩ / 50 k
Ω, and flicker current = 1.11 mA. FIG.
Shows the relationship between the ground fault current and the charge / discharge current in the circuit shown in FIG. This switch circuit is configured by a DC ground detection relay ground circuit of the flicker unit 16 of the DC ground fault point searcher (FK-M3).

FIG. 10 shows the waveform of the transient phenomenon of the ground fault current when the capacitance of the circuit to ground is small. The ground fault current reaches 100% in a relatively short time. (The vertical axis represents the current mA, and the horizontal axis represents 2 sec / scale time.)
FIG. 11 shows a waveform of a transient phenomenon of the ground fault current when the capacitance to ground included in the circuit is large. The ground fault current takes a long time to charge and discharge the capacitance to the ground, so the rising and falling waveforms become dull.
(FK-M3) is a major obstacle in generating flicker current used for determination. Also, if a leakage current always exists due to a decrease in insulation resistance, as shown in the figure, the ground fault current of 3.6 mA does not become a flicker current but attenuates to 2.4 mA obtained by subtracting the constant leakage current. . That is, the waveform of the flicker current (2 mA) when the ground capacitance shown in FIG. 12 is small is attenuated to 0.6 mA like the flicker current waveform when the ground capacitance shown in FIG. 13 is large. .

FIG. 14 shows a waveform of a flicker current when there is a "swell" of low frequency noise. As described above, to extract the flicker current buried in the “undulation”, FIG.
In the low frequency elimination circuit 9 shown in (1), a steep high cut filter 11 is applied to generate a flicker signal (0.57 Hz).
And cut the 60Hz and high frequency components, "undulation"
Extract only (extremely low frequency noise) components. Furthermore, a multi-stage band cut filter 12 corresponding to the existing harmonics
To remove only the higher harmonics and extract the low frequency component in which the flicker signal is buried. Further, in the digital operation circuit 13, the signals subjected to the filters 11 and 12 are simultaneously sampled by the high-precision A / D converter of the digital operation circuit 13, and the phases of the “undulation” are matched on the memory to thereby obtain the two filters. The calculation of the output waveforms of the circuits 11 and 12 is processed by a microcomputer. In this way, the "undulation" component can be removed and only the flicker signal can be extracted. That is, the output of the synchronizing signal generator 8 and the output of the AC clamp CT6 are input to the addition circuit 10, and the output is passed through a high-cut filter 11 and a band-cut filter 12 connected in parallel with the output to extract "undulation" by the former. The flicker signal and the “undulation” are extracted, the outputs of both are input to the digital arithmetic circuit 13, and the output signal is calculated as (flicker signal + “undulation” − “undulation” = flicker signal) to obtain the flicker signal. Take out as.

FIG. 16 shows an input waveform, FIG. 17 shows a waveform of a flicker signal including "undulation" on the output side subjected to a high cut filter, and FIG.
The waveforms of the flicker signal from which "undulation" has been removed are shown. FIG. 19 shows the external appearance of the flicker unit 16, the judging unit 15, and the AC clamp CT6 of the FK-M3 set used when implementing the present invention.

As described above, when a ground fault occurs in the DC control circuit 2 of a substation or the like, an input for judging a ground fault is required for searching for the fault point by the DC ground fault point searcher (FK-M3). In addition to removing noise from the waveform, amplifying a low input waveform level, the ground circuit of the ground detection relay 3 in which the ground fault current is flowing is intermittently switched at regular intervals and converted into a rectangular wave pulsating current, and the AC clamp is performed. When the detected input waveform contains noise due to the configuration of detecting with CT6,
In order to prevent the searcher from making erroneous determinations, noise is removed, and if this rectangular wave pulsating current does not reach the detection sensitivity level of the searcher, it is amplified to enable determination. In addition, the present invention has an effect of removing noise superimposed on the DC control circuit 2 of the ultra-high-voltage substation and having an effective effect on the reduction of the rectangular wave pulsating current due to the increase in the capacitance to the ground of the DC control circuit 2. It was possible to expect.

Although the embodiments which are considered to be representative of the present invention have been described above, the present invention is not necessarily limited to only the structures of the embodiments, but has the above-mentioned constitutional requirements according to the present invention, and The present invention achieves the object of the present invention and can be appropriately modified and implemented within the range having the following effects.

[0025]

As described above in detail, according to the first and second aspects of the present invention, even in a DC circuit on which noise is superimposed and a DC circuit with a large capacitance to the ground, the search for the ground fault point is performed with high accuracy. Made possible. As a result, a DC ground point search can be performed in a wide range of substations having different voltage classes and ground capacitances in a short time, easily handled, and reliably determined by the portable search device. Further, the present invention has a remarkable effect that can be expected even if the ground capacitance further increases in the future, which cannot be expected from the conventional one.

Since the circuit is not stopped until the grounding point is located, the circuit is not in an uncontrolled and unprotected state, the automatic control equipment and the production equipment are not stopped, and the stop work for restoration is slightly reduced. And the time required for removing the wiring is not required, so that the stop time can be reduced. Also, even if the ground capacitance of the entire DC control circuit becomes large, it takes no time to charge or discharge the ground capacitance, so that the discharge is sufficiently performed and the ground voltage is immediately recovered, and the fault current is also hindered. It flows with no value. Therefore, the square wave pulsating current becomes
The level is not lower than the detection sensitivity of the searcher, and the search is not disabled. Therefore, the ultra-high voltage substation where noise exists and the 5000 kV
There is an effect that a ground point can be easily searched even in a substation.

[Brief description of the drawings]

FIG. 1 shows a waveform of a noise current including a flicker current. (Vertical axis is current (mA), horizontal axis is time (every 2 seconds)
Is shown. )

FIG. 2 shows a waveform obtained by extending a noise waveform in a time axis direction in synchronization with a flicker cycle and dividing the noise waveform. (The vertical axis represents current (mA), and the horizontal axis represents time (0.88 seconds × 2).)

FIG. 3 shows a flicker current waveform obtained by performing addition processing many times. (The vertical axis is current (mA), and the horizontal axis is time (0.8
8 seconds x 2)) (Noise waveform disappeared.)

FIG. 4 is a diagram showing a circuit configuration of a conventional DC ground detection relay (64D).

FIG. 5 is a diagram showing a relationship between a ground fault current and a charge / discharge current of the circuit of the conventional DC ground detection relay (64D) of FIG.

FIG. 6 is a diagram showing a circuit configuration of a DC ground detection relay (64D) of the first invention.

FIG. 7 is a diagram showing a relationship between a ground fault current and a charge / discharge current of the circuit of the DC ground detection relay (64D) of FIG.

FIG. 8 is a diagram showing a circuit configuration of a DC ground detection relay (64D) of the second invention.

9 is a diagram showing a relationship between a ground fault current and a charge / discharge current of the circuit of the DC ground detection relay (64D) of FIG.

FIG. 10 shows a waveform of a transient phenomenon of a ground fault current when the capacitance to ground of the circuit is small.

FIG. 11 shows a waveform of a transient phenomenon of a ground fault current when the capacitance to ground included in the circuit is large.

FIG. 12 shows a waveform of a flicker current (2 mA) when the capacitance to ground included in the circuit is small.

FIG. 13 shows a flicker current waveform when the capacitance to ground included in the circuit is large.

FIG. 14 shows a waveform of a flicker current when there is “undulation” of low-frequency noise.

FIG. 15 shows a configuration of a low-frequency removing circuit that removes only a flicker signal by removing a “undulation” component by a digital arithmetic circuit.

FIG. 16 shows an input waveform of a flicker signal.

FIG. 17 shows a waveform of a flicker signal including a “swell” on the output side subjected to a high-cut filter.

FIG. 18 shows a waveform of a flicker signal from which “swell” on the output side subjected to digital operation has been removed.

FIG. 19 shows the appearance of a flicker unit, a determination unit, and an AC clamp CT of the FK-M3 set used when the present invention is implemented.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Storage battery 2 DC control circuit 2a DC power supply 3 DC ground detection relay 4 Flicker relay 4a Contact 5 (Bypass) circuit 6 AC clamp CT 8 Synchronous signal generator 9 Low frequency removal circuit 10 Addition circuit 11 High cut filter 12 Band cut filter 13 Digital Arithmetic circuit 15 Judgment unit 16 Flicker unit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shizuji Yashiki 1-6-1110 Oyodo-kita, Kita-ku, Osaka Kansai Keiki Kogyo Co., Ltd. F-term (reference) 2G014 AA04 AB28 AC18 2G033 AA01 AB01 AC02 AD21 AG09 5G004 AA04 AB02 BA01 CA05 DA01 DB03 DB04

Claims (2)

[Claims] A flicker relay (4) is connected to a grounding circuit of a grounding detection relay (3) connected to a DC control circuit (2) having a DC power supply (2a) composed of a storage battery (1) and the like. Contact (4
In the DC ground fault point search method of converting the ground fault current to a rectangular wave pulsating current by opening and closing a) at a constant cycle, and detecting the ground fault current with the AC clamp CT (6),
The square-wave pulsating current detected by the AC clamp CT (6) is divided into unit periods, superimposed and added many times, thereby canceling and converging low-frequency noise and detecting a ground fault current. DC ground fault point search method characterized by the above-mentioned. 2. The method according to claim 1, wherein when the ground fault current is converted into a rectangular wave pulsating current by opening and closing the contact of the flicker relay. ) Is opened, the bypass circuit (5) is formed so that it can be discharged without opening the grounding circuit. In addition to hastening the voltage recovery, the rectangular wave pulsating current (flicker current) can be achieved quickly and sufficiently within the flicker interval of the flicker relay (4) of the DC ground fault point searcher.
A DC ground fault point search method characterized by amplifying a signal to make the determination possible.