JPH0348177A - Zero phase current detector - Google Patents

Abstract

PURPOSE:To prevent malfunctioning by arranging a measuring means for each phase of an AC electric line and means for removing an error component owing to a noise or the like and an error component owing to an ambient temperature to achieve a smaller size of the apparatus while removing the error components. CONSTITUTION:Measurement signals of phases detected by a measuring means are added up with an addition circuit 10 and a zero-phase current component is stored into a first memory means 21 as instantaneous data for each electric angle. A microprocessor 20 subtracts a data of the second memory means 22 in which a previous instantaneous value data are stored as reference memory value from a data of the means 21. Then, the processor 20 develops the resulting remainder into a Fourier series to extract a commercial frequency component alone by a frequency analysis and moreover, an effective value thereof is computed to judge whether the value is below or above a specified value to determine the propriety of the updating of the data of the means 22. This achieves a smaller size of the apparatus while removing error components, thereby preventing malfunctioning.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a zero-sequence current detection device installed to detect a zero-sequence current flowing during a ground fault.

[Prior art] For example, "Instrument transformer" (Denki Shoin, written by Mihoji Ikeda)
The conventional zero-sequence current detection device described on page 79 is shown in FIG.

In the figure, the annular core 2 includes three-phase electric wires 1a, 1b,
It is provided so as to surround Ic, and a secondary winding 3 is provided on the annular core 2. Secondary winding 3 has secondary load 4
is connected.

In steady state, the current flowing through each phase of the three-phase electric wires 1a, lb, and ic does not contain any component due to an accident, and
Only alternating current consisting of a positive phase component and a negative phase component of equal amplitude flows. The magnetic field in the annular iron core 2 eventually becomes zero due to the combination of magnetic fields induced by the currents flowing in the valleys 4u. As a result, no current flows through the secondary winding 3 and the secondary load 4 does not operate.

On the other hand, three-phase 74! I Ia, Ib, Ic (7) If either one of the ground faults occurs, even if the currents flowing in each phase are combined, they will not become zero, and a zero-phase current will flow. When the zero #lA current flows, a magnetic field is induced in the annular iron core 2, and the secondary 8T5
A secondary current corresponding to the zero-sequence current flows through A3. The secondary load 4 is activated by the secondary current flowing through the secondary winding 3, and the three-phase electric wires 1a, lb, and Ic are disconnected from the power source to prevent the accident from spreading.

[Problem to be solved by the invention 1 In general, zero-phase current detection devices are installed not only inside substations but also outdoors, such as on U-pillars, in order to quickly and accurately discover fault points and limit power outage sections as much as possible. It is desirable to do so.

However, the conventional zero-phase current detection device uses three-phase electric wires 1a,
Since it uses an annular core 2 that encloses the lb and lc all at once, it is inappropriate to use on overhead wires, etc., and has the problem of aggravating accidents due to M lightning, etc. was.

Next, if you want to downsize the entire zero-phase current detection device by installing a current detection device for each phase for use with overhead wires, etc.,
There was a problem in that an apparent zero-sequence current was generated due to differences in temperature characteristics, etc. of the current detection devices provided in each phase, causing the secondary load 4 to malfunction.

This invention was made in order to solve the above-mentioned problems, and its purpose is to provide a small and highly accurate zero-phase 7!1 flow detection device that can be used even on overhead electric wires, etc. There is.

[Means for Solving the Problems] A zero-sequence current detection device according to the first invention is provided for each phase of an AC power line, and includes measurement means for detecting the current of each phase, and synthesis of measurement signals from the measurement means. and an addition means for calculating the zero-sequence current component; a first memory for storing instantaneous values of the latest output from the addition means for each predetermined electrical angle for a period of at least one cycle as a data group; Means, number! of the outputs from the same number of past addition means corresponding to each electrical angle of the instantaneous value data 8T detected before the instantaneous value data group stored in the first storage means and stored in the first storage means. a second storage means for storing the instantaneous value data group as a first reference storage value; a first calculation means that subtracts instantaneous value data of corresponding electrical angles and calculates a subtracted value for each electrical angle; expands the first subtracted value into a Fourier series and calculates only the commercial frequency component value; a second calculation means; a third calculation means for calculating an effective value from the commercial frequency component value calculated by the second calculation means; and a third calculation means for determining whether the effective value is greater than or equal to a predetermined set value. , when the effective value is less than a predetermined value, the instantaneous value data group stored in the second storage means is deleted and updated to the instantaneous value data group stored in the first storage means, and the effective fi & a fourth calculation means that does not update the instantaneous value data group stored in the second storage means for at least one cycle thereafter when the value is equal to or higher than a predetermined value; and a commercial frequency calculated by the second calculation means. An output means for outputting the component value to the burden means is provided.

The zero-sequence current detection device according to the second invention is provided for each phase of an AC circuit, and includes a measurement means for detecting the current of each phase, and a measurement signal from the measurement means is synthesized to calculate a zero-sequence current component. an addition means; a first storage means for storing instantaneous values of outputs from the addition means for each predetermined electrical angle of the latest output for at least one period or more as a data group; stored in the first storage means; A group of instantaneous value data of the output from the same number of past adding means corresponding to each electrical angle of the instantaneous value data group detected before the instantaneous value data n¥ stored in the first storage means. a second storage means for storing as a first reference storage value, a corresponding one stored in the second storage means from each instantaneous value data group for each electrical angle stored in the first storage means a first calculation means that subtracts the instantaneous value data of the electrical angle and calculates a first subtraction value for each electrical angle; and a first calculation means that expands the first subtraction value into a Fourier series and calculates only the commercial frequency component value. a second calculation means, a third calculation means for calculating an effective value from the commercial frequency component value calculated by the second calculation means, a third storage means for storing the effective value calculated by the third calculation means, a fourth storage means for storing a past effective value calculated before the effective value stored in the third storage means as a second quasi-memory value; 4th from the effective value of
fourth calculation means for calculating a second subtraction value by subtracting a second reference storage value stored in the storage means; the second subtraction value is greater than or equal to a predetermined set value; If the second subtraction value is less than or equal to a predetermined value, the instantaneous value data group stored in the second storage means is deleted and the instantaneous value data group stored in the first storage means is deleted. and updates the second reference storage value stored in the fourth storage means to the effective value stored in the third storage means, and the second subtraction value is equal to or greater than a predetermined value. and a fifth calculation means that does not update the instantaneous value data group stored in the second storage means for one cycle thereafter, and an output that outputs the commercial frequency component value calculated by the second calculation means to the burden means. Equipped with means.

[Function] Hereinafter, the function will be explained by illustrating the case where the sampling period is one period and the predetermined electrical angle is 30 degrees. ◎ The measuring means is, for example, an optical magnetic field sensor using the Faraday effect, a light emitting element, and a light receiving element. It outputs a signal proportional to the current flowing through the wires of each phase.

The adding means is an analog adding circuit or a digital adding circuit using a microprocessor or the like, and adds the current values flowing through each phase detected by the measuring means and outputs the added value. That is, the adding means outputs data corresponding to the latest zero-sequence current moment by moment.

The first and second storage means according to the first and second inventions and the third and fourth storage means according to the second invention are, for example, RAM memories connected to a microprocessor.

The first storage means is the output from the addition means! An alternating current of more than a period is sampled at every predetermined electrical angle (30 degrees), and each instantaneous value is converted into a digital signal and stored. In this case, 12 ffl data (instantaneous value data group) is stored in the first storage means. The data stored in the first storage means is always updated to the latest data.

After the past instantaneous value data group outputted from the addition means and stored in the first storage means is transferred, the second storage means stores these data as a reference storage value (or a first reference storage value). be memorized as . In the normal case where zero-sequence current is not occurring, the data group stored in the second storage means is updated to the instantaneous value data group that was sampled one time ago and stored in the first storage means. be done.

The first arithmetic means, second arithmetic means, third arithmetic means, fourth arithmetic means according to the first and second inventions and the fifth arithmetic means according to the second invention each include a microprocessor and a memory. Consists of etc.

The first calculation means subtracts the instantaneous value data of the corresponding electrical angle stored in the second storage means from each of the instantaneous value data groups for each electrical angle stored in the first storage means, A subtraction value (or a first subtraction value) for each electrical angle is calculated.

The second calculation means calculates the first value calculated by the first calculation means.
The subtracted value of is expanded into a Fourier series, and the commercial frequency (50H
z or 6011. z) Calculate only component values.

In general, error components due to differences in temperature characteristics of measurement means installed in each phase hardly change over a short period of time (for example, 1 second), so by subtracting the past data sampled just before from the latest data, Error components due to differences in temperature characteristics can be removed. Furthermore, in addition to the commercial frequency component, the output of the addition means has high frequency components and low frequency components due to noise etc. superimposed on it, so it is possible to remove error components by expanding it into a Fourier series and calculating only the commercial frequency component. can.

The third calculation means calculates an effective value from the commercial frequency component value calculated by the second calculation means.

The third storage means according to the second invention stores the effective value of the commercial frequency component calculated by the third calculation means.

The fourth storage means according to the second invention stores a past effective value calculated before the latest effective value stored in the third storage means as a second reference storage value.

In the second invention, the fourth calculation means subtracts the second reference memory chain stored in the fourth storage means from the latest effective value stored in the third storage means, and Calculate the effective value.

In the first invention, the fourth calculation means first determines whether the effective value is greater than or equal to a predetermined set value. Then, when the effective value is less than or equal to a predetermined value, the first reference memory value (instantaneous value data group) stored in the second storage means is deleted, and the instantaneous value stored in the first storage means is Update to data group. Furthermore, when the effective value is equal to or greater than the predetermined value, the reference storage value stored in the second storage means is not updated for at least one cycle thereafter.

In the second invention, the fifth calculation means first determines whether the second effective value is greater than or equal to a predetermined set value. Then, when the second effective value is less than or equal to a predetermined value, the first μ quasi-memory value (
rR time value data f! F) is deleted and updated to the instantaneous value data group stored in the first storage means. Furthermore, the fourth
The second reference storage value stored in the storage means is erased, and the content to be stored is updated to the effective value stored in the third storage means. Further, when the second subtraction value is equal to or greater than the predetermined value, the first reference storage value stored in the second storage means and the second reference storage value stored in the fourth storage means are used for at least one cycle thereafter. Do not update the reference memory value.

The output means outputs the commercial frequency component value calculated by the second calculation means to the burden means.

[Example] A zero-sequence current detection device according to the present invention will be explained using FIG. 1, FIG. 2, and FIG. 3 showing an example thereof.

In FIG. 1, three-phase electric wires 1a, lb, and lc are provided with annular cores 2a, 2b, and 2c, respectively. Optical magnetic field sensors Sa and 5b are provided in the gaps between the respective annular cores 2a, 2b, and 2c.

5c is provided. Optical magnetic field sensors 5a, 5b,
Light emitting elements 6a, 6t+, 6c are connected to 5c via optical fibers 8a, ah, 8c. Also,
Each optical magnetic field sensor 5a, 5b, 5c includes a light receiving element 7a,
7b, 7c are connected via optical fibers 8a, 8b, 8c. Annular iron cores 2a, 2b, 2c optical magnetic field sensors 5a, 5b, 5c, light emitting elements 6a, 6
The measurement means is constituted by the optical fibers 8a, 8b, 8c, the light receiving element 73.7b, and the 'lcs optical fibers 8a, 8b, 8c.

The annular iron cores 2a, 2b, 2c include three-phase electric wires 1a,
The current flowing through Ib and lc induces a magnetic field proportional to each current. At this time, the light emitting elements 6a, 6b,
The light that reaches the optical magnetic field sensors 5a, 5b, 5c from the optical fibers 8a, 8b, 8c from the optical fiber 6c is modulated in proportion to the magnetic field in each air gap of the annular iron cores 2a, 2b, 2c, and is transmitted to the optical fiber 8a. , 8b, 8c, the light reaches the light receiving elements 7a, 7b, 7c and is converted into an electrical signal.

The optical magnetic field sensors 5a, 5b, and 5c are composed of, for example, a polarizer, a Faraday element, and an analyzer. While the light that has become linearly polarized by the polarizer passes through the Faraday element, the plane of polarization rotates in proportion to the magnetic field applied to the direction of the light traveling through the Faraday element, and the analyzer detects this as a change in the amount of transmitted light. Modulated. The modulated light is transmitted to the optical magnetic field sensor Sa, 5b,
The amount of light transmitted when the magnetic field applied to 5e is zero is superimposed with a change in the amount of light that is proportional to the alternating current magnetic field.

In the signal processing circuits 9a, 9b, and 9c, the light receiving elements 7a,
The electrical signals converted by 7b and 7c are transferred to the three-phase electric wire 1a.
, Ib, and lc into signals proportional to the flowing current. Adder circuit IO adds these signals.

In a steady state, the sum of the currents of the three-phase electric wires 1a, lb, and Ic becomes zero, so the output of the adder circuit 10 also becomes zero.

On the other hand, if a fault occurs in the three-phase 21 wires 1a, Ib, and lcE, the current will not become zero even if the currents of each phase are combined, and a zero-phase current will flow. Therefore, the output of the adder circuit 10 has a value proportional to this zero-phase current, and the three-phase electric wires 1a,
LB, LC ground faults can be detected.

However, in reality, the optical magnetic field sensors 5a, Sb, 5c
The signal processing circuits 9a, 9b, and 9c have temperature characteristics, and it is normal that these temperature characteristics differ. Therefore, three-phase electric wires 1a, lb, l
The ratio between each current of e and each output signal of signal processing circuits 9a, 9b, and 9c varies between each phase due to changes in ambient temperature. Due to this difference in temperature characteristics between each phase, the adder circuit 1
The output signal of 0 does not become zero even when zero-sequence current is not flowing in the three-phase wires 1a, lb, and lc, and the secondary burden 4
may cause malfunction.

Correction calculation circuit! 15 second, third, and fourth memories (for simplicity, only memories 21 and 22 are shown) are provided to prevent the above-mentioned malfunctions, and are comprised of a microprocessor 20 and a RAM memory.
have. It goes without saying that each memory 21, 22, . . . has a storage area larger than the number of samples of data to be stored.

Generally, the error component of the zero-sequence current changes relatively slowly due to the difference in temperature characteristics between the phases. Furthermore, the zero-sequence current component due to a ground fault occurs instantaneously. Focusing on the above points, the correction calculation circuit 11 removes the error component by executing the flowchart shown in FIG. 2, and detects the zero-sequence current due to the ground fault.

The operation of the embodiment according to the first invention will be described below using the flowchart shown in FIG.

In step St, the initial value is stored in, for example, the memory 22, which acts as a second storage means.

Normally, 0 is entered in all addresses. Each instantaneous value data group B(j) stored in the memory 22 (J represents the order of data sampled for each predetermined electrical angle).
Then, 12 pieces of data from B(1) to mouth(12) are stored. Next, in steps S2 and S5, initial values are set to =o, 1-60, and j=1.

In step S6, the data for the latest one cycle of the alternating current, which is the output signal from the adder circuit 17, is converted into a digital signal as an instantaneous value at every predetermined electrical angle, for example, every 30 degrees, and the first recording means, for example, a memo IJ. -21. Each data stored in the memory 21 is expressed as A(j)(J
represents the order of data sampled for each predetermined electrical angle. ), 12 pieces of data from A (+) to A (12) are sampled and stored in the memory 21.

In step S9, data group A for each electrical angle stored in the first storage means (for example, memory 21)
(j) from each corresponding 1u air angle data B stored in the second storage means (for example, the memory 22)
(j) and calculate the subtracted value for each electrical angle. That is, when the subtraction value is C(j), the microprocessor 20 acting as the first calculation means executes C(j)=A(j)-B(j).

Generally, the temperature characteristic difference of the measuring means hardly changes in a short period of time (for example, 1 second), so it is considered that all sampling data uniformly includes an error amount due to this temperature characteristic difference. Therefore, the 6th subtraction value C(j) obtained by the above-mentioned subtraction process has the error component due to the difference in temperature characteristics of the measuring means removed. Note that steps S7 and S8 function as a counter for calculating the subtraction value C(j) for every electrical angle.

Microprocessor 20 then acts as a second computing means. That is, the subtracted value C(j) is expanded into a Fourier series, and the value of the commercial frequency component (for example, 60 II z or 5 on z) is calculated (step 5IG).

In general, the output from the adder circuit 1G includes high frequency components and low frequency components due to noise etc. in addition to commercial frequency components, and these components are superimposed. Therefore, by expanding it into a Fourier series and performing frequency analysis, only the commercial frequency component can be extracted. This calculated commercial frequency component does not include an error component.

Next, the microprocessor 20 acts as an output means and outputs the calculated commercial frequency component value to the secondary burden 23 (step 511).

In step S12, the microprocessor 20 acts as a third calculation means and calculates the effective value E from the commercial frequency component value calculated as the second calculation means in step SIO.

Further, in step 13, it is determined whether or not =1. In other words, the counter value k is! In the case (k=1),
Immediately after the operation of the zero-sequence current detection device is started, O is stored as the reference storage value to be stored in the second storage means (nothing has been input). Therefore, in order to transfer all the data stored in the first storage means that was sampled first to the second storage means before performing sampling in the next cycle, step S1 is performed.
Proceed to 8.

If k=1 is not the case, it functions as a fourth calculation means and determines whether the effective value E is greater than or less than a predetermined value S (step knob 516). Appropriately, the predetermined value S is 50-90% of the operating level of the ground fault detection relay of the secondary load 4.

Here, if the effective value E is smaller than the predetermined value S, it is a normal state in which no ground fault has occurred, so the second storage means (e.g. memory 22), and the instantaneous data group and execution value stored in the first storage means (for example, memory 21) are used as new storage values in the second storage means, and the data contents are Update (step 818).

If the effective value E is larger than the predetermined value S, a ground fault has occurred, and the three-phase electric wires 1a and Ib.

The LC must be disconnected from the power source. in general,
In order to operate the secondary load 4 in order to disconnect the three-phase electric wires 1a, lb, lc from the power supply, it is sufficient to output a current corresponding to the zero-sequence current for about 1 second. However, once a zero-sequence current due to a ground fault occurs, it should continue at least until the three-phase electric wires 1a, Ib, and Ic are disconnected. If the data group in the second storage means is updated here, all the newly sampled instantaneous value data will include the zero-sequence current component due to the ground fault, so in the subtraction process executed in step S9, The zero-sequence current component due to the ground fault is canceled out. Therefore, in order to continue outputting the commercial frequency component value corresponding to the zero-sequence current for -seconds, for example, the past data stored in the second storage means, that is, the data that does not include the component due to the ground fault, is left as is, and the latest data is Only data that includes components due to ground faults will be updated. Then, the above calculation process is repeated for 1 second after detecting the zero-sequence current component due to the ground fault, that is, for 60 cycles in the case of AC 60 II 2. Steps SI4 and S15 function as a counter.

The operation of the embodiment according to the second invention will be described below using the flowchart shown in FIG.

In step 5101, initial values are stored in, for example, the memory 22, which acts as a second storage means. Normally, enter O in all addresses. Each instantaneous value data group B (j) stored in the memory 22 (j represents the order of data sampled at each predetermined electrical angle).
Then, 12 pieces of data from B(1) to Il (12>) are stored.Next, in steps S2 and S5, initial values Mk=0, j=60 and J=1 are set.

In step 5106, data for the latest cycle of the alternating current, which is the output signal from the adder circuit IO, is converted into a digital signal as an instantaneous value at every predetermined electrical angle, for example, every 30 degrees, and is stored in the first storage means, for example, the memory 21. Remember. Each data stored in the memory 21 is A (j)
(J represents the order of data sampled for each predetermined electrical angle.) Then, 12 pieces of data from A(1) to A02) are sampled and stored in the memory 21.

In step 5109, from each of the data groups AU for each electrical angle stored in the first storage means (for example, the memory 21), the corresponding electrical values stored in the second storage means (for example, the memory 22) are Corner data B
(j) and calculate the first subtraction value for each electrical angle. That is, if the first subtraction value is C(j), the first
The microprocessor 20, which acts as a calculation means, executes C(j)=A(j)-B(j).

Note that steps 5107tj and 5IOII function as a counter for calculating the first subtraction value C(j) for every electrical angle.

Microprocessor 20 then acts as a second computing means. That is, the first subtraction value C(j) is expanded into a Fourier series, and the commercial frequency component (for example, 60 If z
or 50112) (Step 5II
O). In general, the output from the adder circuit 10 includes, in addition to commercial frequency components, high frequency components and low frequency components due to noise, etc., and these components are superimposed. Therefore, by expanding it into a Fourier series and performing frequency analysis, only the commercial frequency component can be extracted.

This calculated commercial frequency component does not include an error component.

Next, the microprocessor 20 acts as an output means and outputs the calculated commercial frequency component value for the secondary load 4 (step 5ill).

In step 5112, the microprocessor 20 acts as the third calculation means and calculates the effective value E from the commercial frequency component value calculated as the second calculation means in step 5IIO.

Further, in step 5113, it is determined whether or not =1. In other words, when the counter value k is 1 (k=1
), immediately after the zero-sequence current detection device starts operating,
The first and second reference storage values that are yet to be stored in the second and fourth storage means are respectively 0 (0).
nothing has been entered). Therefore, before sampling the next period, the first
The process proceeds to step S+20 in order to transfer all data stored in the second storage means to the second storage means.

Furthermore, when k=1, the microprocessor 20 acts as a fourth calculation means. That is, step 5
From the actual value E of the commercial frequency component value obtained in step 112, the fourth
The second reference storage value H stored, for example, in another storage area of the memory 22 as a storage means is subtracted to calculate a second subtraction value F (step 5114).

Furthermore, in step 5116, the microprocessor 20 functions as a fifth calculation means and calculates the second subtraction value F.
It is determined whether S is greater than or equal to a predetermined value S. Appropriately, the predetermined value S is 50-90% of the operating level of the ground fault detection relay of the secondary load 4.

Here, the second subtraction value F is smaller than the predetermined value S.

If this is the case, it is a normal state with no ground fault occurring, so all data stored in the second and fourth storage means (for example, memory 22) will be erased in preparation for the next calculation process. , update the data contents by using the instantaneous data group and the execution value stored in the first and third storage means (for example, the memory 21) as new stored values in the second and fourth storage means (Ste knob 5119.5I20)
.

If the second subtraction value F is larger than the predetermined value, the three-phase electric wire 1a has experienced a ground fault or the like.

The lb and lc must be disconnected from the power supply.

Generally, in order to operate the secondary load 4 to disconnect the three-phase electric wires 1a, lb, and lc from the power source, it is sufficient to output a current corresponding to the zero-sequence current for about 1 second. However, once a zero-sequence current due to a ground fault occurs, it should continue at least until the three-phase electric wires 1a, lb, and lc are disconnected. If the data groups in the second and fourth storage means are updated here, all the newly sampled instantaneous value data will include a zero current component due to the ground fault, so steps 5109 and 5l14 are executed. In the subtraction process, the zero current component due to the ground fault is canceled out. Therefore, in order to continue outputting the commercial frequency component value p corresponding to the zero-sequence current for -seconds, for example, the past data stored in the second and fourth storage means, that is, the data that does not include the component due to the ground fault, is used as is. Only the data that includes components from the latest ground faults will be updated. Then, 1 second after detecting the zero-sequence current component due to a ground fault, that is, 60 in the case of AC 60 II z
The above calculation process is repeated for the period. Step 51
15 and 5116 function as counters.

In each of the above embodiments, the predetermined electrical angle for sampling data was set to 30 degrees, but if the processing speed of a microprocessor or the like can be increased, it may be further subdivided into 30 degrees or less. On the other hand, if high accuracy is not required, it may be set coarsely (more than 30 degrees). Also, the number of data stored in memories 21 and 22 and the number of instantaneous values for determining the effective value are 12 for one cycle, respectively. However, it suffices to have two or more of them.Furthermore, after the zero-sequence current is detected due to a ground fault, the time to continue outputting the average value data corresponding to the zero-sequence current was set to 1 second (60 cycles); If the operating time of the ground fault detection relay in the next load 4 is short,
The above period may be shortened. Furthermore, the correction calculation circuit 11
．． Signal processing circuits 9a, 9b, 9c and addition circuit 1
0 may be configured entirely by a microprocessor.

Next, another embodiment of the sub-measuring means section of the zero-sequence current detection device according to the present invention is shown in FIG.

A winding 1 is attached to a part of the annular cores 2a, 2b, and 2c, respectively.
3a, 13b, and 13c are wound. A resistor 14a is installed at both ends of these windings 13a, 13b, +3c.
14b, 14c are connected, and each resistor 14a,
Optical voltage sensors 15a, 15b, 15c using the Pockels effect to measure the voltage of 14b, 14c
is provided. In this embodiment, windings 13a, 13b, and 13c obtain secondary currents proportional to the temporary currents of three-phase electric wires 1a, lb, and Ic. These secondary side currents are connected to resistors 14a, 14b, 1
4c into a voltage, and photovoltage sensors 15a, 15
b, detected by 15e.

Yet another embodiment of the measuring means is shown in FIG. In the figure, optical magnetic field sensors 16a, 16 using the Faraday effect
b, 16c are arranged in a ring shape, and a three-phase '' is arranged in the center of each ring.
? 31 lines 1a, lb, and lc. In this case, the light incident through the optical fibers 8a, 8b, 8c circulates through the three-phase electric wires 1a, lb, lc, and then passes through the optical fibers 8a, 8b, 8c again to the light receiving elements 7a, 7b, 7c and It is input to the measurement circuit 12. Therefore, each optical magnetic field sensor 16a, 16b
, 16c circulates internally and repeats reflection.

[Effects of the Invention] As described above, according to the first and second inventions, since the measuring means for measuring the current value of each phase of the AC circuit is provided for each phase, the size is reduced and the overhead Can be used for electric wires, etc.

In addition, error components such as high frequency components and low frequency components due to noise etc. are removed by expanding the output from the adder circuit into a Fourier series and calculating only the commercial frequency component value. The error component is calculated from the latest sampling data (the instantaneous value data group stored in the first storage means) and, in the second invention, further from its effective value (the execution value stored in the third storage means). Past (immediately before the occurrence of the ground fault accident) sampling data (the (first) reference memory value stored in the second storage means) and its effective value (the (first) reference value stored in the fourth storage means) Since the reference memory value (2) is removed by subtracting the reference memory value, the error is extremely small and there is an effect that no malfunction occurs.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the zero-sequence current detection device according to the present invention, FIG. 2 is a flowchart showing the operation of the correction calculation circuit U according to the first invention, and FIG. FIG. 4 is a flowchart showing the operation of the correction calculation circuit 11 according to the second invention, FIG. 4 is a diagram showing another embodiment of the measuring means of the zero-sequence current detection device according to the invention, and FIG. 6 is a diagram showing still another embodiment of the measuring means.
The figure shows a conventional zero-sequence current detection device. LA, LB, LC are three-phase 1! line, 2a, 2b,
2c is an annular iron core, Sa, 5b, Sc are optical magnetic field sensors, 8a, 8b, 8c are optical fibers 10 is an adder circuit,! 1 is a correction calculation circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (2)

[Claims] (1) Measurement means provided for each phase of the AC circuit to detect the current of each phase; addition means for synthesizing the measurement signals from the measurement means and calculating the zero-sequence current component; and output from the addition means. , a first storage means for storing instantaneous values at each predetermined electrical angle of the latest output over a period of at least one cycle as a data group; prior to the instantaneous value data group stored in the first storage means; A first storage means for storing instantaneous value data groups of outputs from the same number of past adding means corresponding to respective electrical angles of the instantaneous value data groups detected and stored in the first storage means as first reference storage values. The second storage means subtracts the instantaneous value data of the corresponding electrical angle stored in the second storage means from each of the instantaneous value data groups for each electrical angle stored in the first storage means, and a first calculation means that calculates a subtraction value for each electrical angle; a second calculation means that expands the first subtraction value into a Fourier series and calculates only the commercial frequency component value; A third calculating means calculates an effective value from the commercial frequency component value, and determines whether the effective value is above or below a predetermined set value, and when the effective value is below a predetermined value, a second memory is stored. The instantaneous value data group stored in the means is deleted and updated to the instantaneous value data group stored in the first storage means, and if the effective value is equal to or higher than a predetermined value, the second A zero-sequence current comprising: a fourth calculation means that does not update the instantaneous value data group stored in the storage means; and an output means that outputs the commercial frequency component value calculated by the second calculation means to the burden means. Detection device. (2) Measuring means provided for each phase of the AC circuit to detect the current of each phase; addition means for synthesizing the measurement signals from the measurement means and calculating the zero-sequence current component; and output from the addition means. , a first storage means for storing instantaneous values at each predetermined electrical angle of the latest output over a period of at least one cycle as a data group; prior to the instantaneous value data group stored in the first storage means; A first storage means for storing instantaneous value data groups of outputs from the same number of past adding means corresponding to respective electrical angles of the instantaneous value data groups detected and stored in the first storage means as first reference storage values. The second storage means subtracts the instantaneous value data of the corresponding electrical angle stored in the second storage means from each of the instantaneous value data groups for each electrical angle stored in the first storage means, and A first calculation means that calculates a first subtraction value for each electrical angle, a second calculation means that expands the first subtraction value into a Fourier series and calculates only the commercial frequency component value, and a second calculation means that calculates only the commercial frequency component value. A third calculation means for calculating an effective value from the calculated commercial frequency component value, a third storage means for storing the effective value calculated by the third calculation means, and an effective value stored in the third storage means. a fourth storage means for storing past effective values calculated before as a second reference storage value;
fourth calculation means for calculating a second subtraction value by subtracting a second reference storage value stored in the storage means; the second subtraction value is greater than or equal to a predetermined set value; If the second subtraction value is less than or equal to a predetermined value, the instantaneous value data group stored in the second storage means is deleted and the instantaneous value data group stored in the first storage means is deleted. and updates the second reference storage value stored in the fourth storage means to the effective value stored in the third storage means, and the second subtraction value is equal to or greater than a predetermined value. and a fifth calculation means that does not update the instantaneous value data group stored in the second storage means for one cycle thereafter, and an output that outputs the commercial frequency component value calculated by the second calculation means to the burden means. A zero-sequence current detection device comprising means.