JPH04198764A - Zero-phase current detecting device - Google Patents

Abstract

PURPOSE:To improve precision by adding light signals of individual phases with no photoelectric transfer of them. CONSTITUTION:Individual phase light signals from photo-magnetic field sensors 5a-5c are fed to a photo-adder 8 via optical fibers 7a-7c, synthetically added in the light signal state, photoelectrically transferred by a light receiving element 9, and transferred into signals with proper magnitudes by a signal processing circuit 10. The sensors 5a-5c have different temperature characteristics. Ratios between the currents of three-phase distribution lines 1a-1c and output signals of the sensors 5a-5c differ among three phases due to the change of the ambient temperature. The output signal from the circuit 10 has noises and is not made zero even when the zero-phase current is not flowing, and a protective relay is erroneously operated. A correction arithmetic circuit 11 removes the error component, and the zero-phase current caused by a grounding accident is surely detected. High-precision detection can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a zero-sequence current detection device for detecting zero-sequence current flowing during a ground fault or the like.

[Conventional technology]

For example, the conventional zero-phase current detection device described in "Instrument Transformer J (Okishoin, written by Mihoji Ikeda), p.
As shown in the figure.

In the figure, the annular core (2) is the three-phase power distribution 1! (la)
(lb) and (lc), and a secondary winding O) is provided on the annular core (2). A secondary load (A) is connected to the secondary winding (3).

In steady state, three-phase power distribution II (la) (lb)
(The current flowing through each phase of the tel does not contain any component due to an accident, and only alternating current consisting of a positive phase component and a negative phase component with equal amplitude flows.) The magnetic field in the ring core (2) is The result is zero due to the combination of the induced magnetic fields.As a result, no current flows through the secondary winding β) and the secondary load (A) does not operate.

On the other hand, three-phase power distribution! If a ground fault occurs in any of (la), (Ib), and (lc), even if the currents flowing in each phase are combined, the current will not become zero and a zero-phase current will flow. When a zero-sequence current flows, a magnetic field is induced in the annular core (2), and the secondary winding (
3) A secondary current corresponding to the zero-sequence current flows. The secondary current flowing through the secondary winding (3) activates the secondary load 4, and the three wires (la), (Ib), and (Ic) are disconnected from the t source to prevent the accident from spreading.

[Problem to be solved by the invention]

In general, it is desirable to install zero-sequence current detection devices not only inside substations but also on outdoor power distribution poles, etc., in order to quickly and accurately find fault points and limit power outage sections as much as possible.

However, the conventional zero-phase current detection device detects a three-phase power distribution line (la
) (lb) An annular iron core surrounding (Ic) ■
Since the iron core is used to ensure insulation, the size of the iron core becomes larger, and this tendency becomes especially noticeable as the distribution voltage increases.
It is inappropriate to use it on overhead electric wires, etc.
Also, there was a problem in that accidents were aggravated due to lightning strikes, etc.

In addition, if a current measuring means is provided for each phase and the detection outputs are combined, the characteristics of the current measuring means will differ for each phase and this will cause an error, causing an apparent zero-sequence current to flow and causing the protection circuit to malfunction. Then, b) there was a problem.

This invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide a small and highly accurate zero-sequence current detection device that can be used for overhead electric wires, etc.

[Means and operations for solving the problem] The zero-sequence current detection device according to the invention of claim 1 includes a measuring means that is provided for each phase of an AC circuit and detects the current of each phase in the form of an optical signal; Adding means for adding the optical signals from this measuring means, converting it into an electrical signal and outputting it as a zero-sequence current component; and a predetermined value of the latest output from the adding means for a period of at least one cycle of the commercial frequency. a first storage means for storing instantaneous values at each electrical angle as a data group;
from the same number of past addition means corresponding to each electrical angle of the instantaneous value data group detected before the instantaneous value data group stored in the storage means and stored in the first storage means. a second storage means for storing a group of instantaneous value data of the output as a first reference storage value; a first calculation means for subtracting the first reference stored value of each corresponding electrical angle stored in the means and outputting the result as a first subtraction value for each electrical angle; a second calculation means for calculating only the commercial frequency component value, 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 calculating an effective value from the commercial frequency component value calculated by the second calculation means; It is determined whether the effective value is greater than or equal to the set value, and if the effective value is less than or equal to the set value, the instantaneous value data group stored in the second storage means is erased and the first updating the instantaneous value data group stored in the storage means, and updating the instantaneous value data group stored in the second storage means for at least one cycle thereafter if the effective value is equal to or greater than the set value; The present invention is equipped with a fourth arithmetic means that does not carry out the calculation, and an output means that outputs the data from the second arithmetic means to the burden means.

In this case, an optical fiber or the like transmits the optical signal and at the same time provides electrical insulation between the electrical circuit and the ground, and addition of each phase is performed at the optical signal stage, so only one photoelectric converter is required. Therefore, there is no zero-phase error due to differences in characteristics between photoelectric converters.

Now, assuming that there is a difference in characteristics between the measuring means for each phase, the output of the adding means will include an apparent zero-sequence current component.

Then, the first σ storage means stores the output from the addition means at a predetermined electrical angle, for example, 30 degrees, for example, at 1 of the commercial frequency.
Data sampled over a period is stored.

The second storage means stores data sampled one cycle before in a similar manner.

The first calculation means subtracts the data stored in both the storage means, but since the apparent zero-sequence current component due to the difference in characteristics of the measurement means does not change within this period unit time difference, this The error amount is removed from the output of the first calculation means.

Therefore, if zero-sequence current is not flowing in the actual AC circuit, the first subtraction value will be approximately zero, and the commercial frequency component value determined by the second calculation means and its effective value determined by the third calculation means will also be It becomes almost zero.

In this case, the fourth calculation means sequentially updates the data in the storage means and continues the same operation.

Here, if a ground fault or the like occurs in the AC line at a certain period and a zero-sequence current actually flows, the subtraction value from the data in the previous period will rise significantly, and the commercial frequency component will be borne by the output means. The signal is output to the means and used for protection operations, etc. Further, the effective value of the component exceeds the setting value of the fourth calculation means, and the data of the second storage means is not updated for a predetermined period. The calculation means continuously outputs a signal corresponding to the zero-sequence current component that actually flows.

The zero-sequence current detection device according to the invention of claim 2 further includes a third storage means for storing the effective value calculated by the third calculation means in the device according to the invention of claim 1; a fourth storage means for storing a past effective value calculated before the effective value stored in the storage means as a second reference storage value; the latest effective value stored in the third storage means; Adding a fifth calculation means for subtracting the second reference storage value stored in the fourth storage means from the fourth storage means and outputting the result as a second subtracted value, and also replacing the fourth calculation means of the device. determine whether the second subtraction value is greater than or equal to a predetermined set value, and if the second subtraction value is less than or equal to the set value, the second subtraction value is stored in the second storage means. The current instantaneous value data group is deleted and updated to the instantaneous value data group stored in the first storage means, and the second reference storage value stored in the fourth storage means is updated to the third reference storage value. The instantaneous value data group stored in the second storage means is updated to the effective value stored in the storage means, and if the second subtracted value is equal to or higher than the set value, the instantaneous value data group stored in the second storage means is updated for at least one cycle thereafter. A sixth calculation means that does not perform updating is provided.

In this case, the third and fourth storage means store the temporally successive values of the effective value from the third calculation means, and the fifth calculation means subtracts both of the effective values to obtain the second effective value. Output as a subtracted value.

Then, the detection of the zero-sequence current is determined based on the magnitude of the second subtraction value, and if this value is less than the set value, the data in the second storage means is updated to new data, and the data in the fourth storage means is updated. The effective value is also updated to a new one.

〔Example〕

FIG. 1 is a block diagram showing the configuration of a zero-sequence current detection device according to an embodiment of the present invention.

In Figure 1, three-phase distribution wires (Ia) (lb) (
lc) have annular cores (2a) (2b) (2
c) is provided.

And, in the air gap of each annular core (2a) (2b) (2c), an optical magnetic field sensor (5a> (5b) (5c) is provided. Each optical magnetic field sensor (5a> (5b)
(5c) has optical fibers (7a) and (7b), respectively.
(7c), the light emitting elements (6a) (6b) (6
c), an optical adder (5) as an adding means, and a light receiving element (9) are connected. Therefore, electrical insulation between the power distribution line (la) and the ground where this detection device is installed is provided by an optical fiber (7a) or the like. A measuring means (100) is composed of a circular iron wire (2a), an optical magnetic field sensor (5a), an optical fiber (7a), and the like.

The output signal of the light receiving element (9) is input to a signal processing circuit (10), and the output signal of the signal processing circuit (lO) is further input to a correction calculation circuit (11).

A magnetic field proportional to each current is induced in the annular iron core (2a) and the like by the current flowing through the three-phase distribution line (1a) and the like. At this time, the light reaching the optical magnetic field sensor (5a) etc. from the light emitting element (6a) etc. via the optical fiber (7a) etc. is modulated in proportion to the magnetic field in each air gap of the annular iron core (2a) etc. receive.

Here, the optical magnetic field sensor (5a) and the like 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 the amount of light that is transmitted when the magnetic field applied to the optical magnetic field sensor (5a) or the like is zero, and a change in the amount of light that is proportional to the alternating current magnetic field is superimposed.

Each phase optical signal from the optical magnetic field sensor (5a) (5b) (5c) is input to the optical adder (a) via the optical fiber (7a) (7b) (7c), where it is converted into an optical signal. The signals are combined and added, and then photoelectrically converted by the light receiving element (9).
Furthermore, it is converted into a signal of an appropriate magnitude by a signal processing circuit (lO).

Here, optical adders include the so-called mixer rod type star coupler in which a mixing rod is inserted between multiple optical fibers, and the so-called twist fusion type star coupler in which multiple optical fiber core wires are twistedly fused. An appropriate one is selected from those listed.

In this case, the configuration is such that the optical signal, which is the original information of each phase current, is added up in the optical signal state without photoelectrically converting the optical signal, so when a light receiving element and a signal processing circuit are provided for each phase, The zero-phase current component error based on the unavoidable characteristic difference between each device can be removed, and the error factors are reduced accordingly. Accuracy as a current detection device is greatly improved.

Here, assuming that there is no difference in characteristics between the equipment of each phase,
When the three-phase distribution line is in a normal steady state, the sum of the phase currents becomes zero, and the output signal of the optical adder 6 also becomes zero. In addition, if a ground fault occurs in a three-phase distribution line, the output signal of the optical adder (8) will be proportional to the zero-sequence current because the current of each phase will not become zero even if the current is added. This output signal can be used to detect a ground fault in a three-phase power distribution line, and, for example, by operating a protection relay, appropriate protection of the power distribution line can be achieved.

However, in general, the optical magnetic field sensor (5a) and the like have temperature characteristics, and there are differences in individual characteristics.

Therefore, the ratio between each current of the three-phase power distribution &1 (Ia), etc. and each output signal of the optical magnetic field sensor (5a), etc. differs between the phases due to changes in the ambient temperature, etc. In addition, the signal processing circuit (1
0) generally includes noise such as white noise. Therefore, the output signal from the signal processing circuit (lO) does not become zero even when no zero-sequence current is actually flowing in the three-phase distribution line, causing the protective relay to malfunction.

The correction calculation circuit (II) is intended to prevent the above-mentioned malfunctions, and has a microprocessor (
12), memory consisting of RAM memory (13>,
(14) It has... Memory (13), (
It goes without saying that 14)... each have a storage area greater than the number of samples of data to be stored.

Generally, the error component of the zero-sequence current changes relatively quickly due to the difference in temperature characteristics of each magneto-optical field sensor, and the error component due to noise is instantaneous. Furthermore, although the zero-sequence current component due to a ground fault occurs instantaneously, it lasts for a relatively long time compared to the case due to noise.

The correction arithmetic circuit (If) was invented focusing on the above points, and removes the error component in the above-mentioned front stage portion, and reliably detects the zero-sequence current due to a ground fault. The operation will be explained below using the flowchart shown in FIG.

In step Sl, initial values are stored in, for example, a memory (14) that acts as a second storage means.

Each instantaneous value data group stored in the memory (14) is stored in B1.
(j is a predetermined electrical angle, here it represents the order of data sampled every 30 degrees), then B (+
) to B (+2) are stored. Normally, O is input to all these addresses as initial values. Note that the sampling period for one data group is set to 1 of the commercial frequency (here, 60 Hz).
It is set as the period.

Next, in steps S2, B3, and B5, initial values are set to =o, 1=60, and j=1.

In step S6, data for the latest one cycle of the AC output, which is the output signal from the signal processing circuit (10), is converted into a digital signal as an instantaneous value at every predetermined electrical angle, 30 degrees in this case, and stored in the first storage means. , for example, memory (1
3) is stored as A <j).

Next, step S7 is processed by the microprocessor (12) as the first calculation means, and the first storage means (
j-th data A stored in memory [3) )
An operation is performed to subtract the same j-th data B(j> stored in the second storage means (memory (+4)) from (j>
), then Cl=A (J)-B (j) is executed.

Note that steps S6 and S7 are repeated until 12 pieces of data for one cycle are obtained (steps S8゜B9).
.

Generally, the difference in temperature characteristics of the optical magnetic field sensor used as a measurement means is short-lived (
For example, since there is almost no change over a period of 1 second), it is considered that all sampling data uniformly includes an error amount due to this difference in temperature characteristics.

Therefore, each subtraction value C(
In j), error components due to differences in temperature characteristics of the measuring means, etc. are removed. In other words, the actual zero-sequence current component occurring in the distribution line can be detected with high accuracy.

However, Step S! In the calculation step immediately after the initialization, that is, in the calculation step of k = 1 (step s4), all data B (j) is 0, so C (j) = A (j). , the actual purchase price is not subtracted, but the data B is
After the next calculation step in which (j) is updated, the above-mentioned effect of error component removal can be obtained.

The microprocessor (12) 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 is calculated (step 5IO).Generally, the output from the signal processing circuit (10) contains noise due to the commercial frequency component as well as the commercial frequency component. High frequency components and low frequency components are included and these are superimposed. Therefore,
If only the commercial frequency component is extracted by expanding it into a Fourier series and performing frequency analysis, the calculated commercial frequency component will not include an error component.

Next, the microprocessor (12) acts as an output means and outputs the commercial frequency component value calculated for the secondary load (4) (step 5ll). From this output value, the magnitude of the zero-sequence current can be calculated. Since the phase can be obtained, it is possible to understand situations such as ground faults by combining with other voltage information, etc.

In step SI2, the microprocessor (12)
acts as a third calculating means, and calculates the effective value E from the commercial frequency component value calculated in step SIO.

Further, in step SI3, it is determined whether or not =1. In other words, if the counter value k is 1 (k=1)
, immediately after the operation of the zero-phase current detection device has started, and the reference memory values to be stored in the second storage means are each 0 (nothing has been input). Therefore, the next Step S is performed in order to transfer all data stored in the first storage means, which was first sampled, to the second storage means before performing the sampling period of .
Proceed to 18.

Once step SI8 is passed, the value in the counter is advanced (step S4), so the determination in step S13 is NO and the process proceeds to step S14, but here, 1
= 60 (step S3), the process directly advances to step S16, and the effective value E is initialized to the predetermined set value S.
The setting value S used to determine whether it is above or below (fourth calculating means) is suitably 50-90% of the operating level of the ground fault detection relay of secondary burden (2).

Here, if the effective value E is smaller than the predetermined set value S,
Since this is a normal situation with no ground faults occurring,
A second storage means (memory) is used to prepare for the next calculation process.
14) Delete all data stored in ), and save the instantaneous data group and effective value stored in the first storage means (memory (13) ') as new stored values in the second storage means. Update the contents of (step 518)
.

If the effective value E is larger than the predetermined set value S, a ground fault or the like has occurred, and the three-phase distribution line must be disconnected from the power source. In general, it is sufficient to output a current corresponding to the zero-sequence current for about 1 second to operate the secondary load (2) in order to disconnect the three-phase distribution line from the power supply. However, once a zero-sequence current due to a ground fault occurs, it is expected to continue at least until the three-phase distribution line is disconnected.

If the data group in the second storage means is updated here, all the newly sampled instantaneous value data will contain the zero-sequence current component due to the ground fault, so in the subtraction process executed in step S7, The zero-sequence current component due to the ground fault is canceled out, so for example, 1
In order to continue outputting the commercial frequency component value corresponding to the zero-sequence current per second, the past data stored in the second storage means, that is, the data that does not include the component due to the ground fault accident, is left as is, and the data stored in the first storage means is Update only the data that includes the component due to the latest ground fault that should be stored. 1 second after detecting the zero-sequence current component due to a ground fault, that is, AC 6
In the case of 0 Hz, the above calculation process is repeated for 60 cycles. Steps S14 and S15 are for performing the above process and form part of the action of the fourth calculation means.

FIG. 3 is a flowchart illustrating the operation of another embodiment. The difference from the content in Figure 2 is data C (
This is a method of accident determination based on the effective value E of the commercial frequency component obtained from j), and this point will be mainly explained below.

Immediately after the start, the determination in step S13 becomes YES and data B(j) is updated in step 318, which is the same as in the case of FIG.

Next, when k=2 and the determination in step SJ3 becomes NO, the microprocessor (12) acts as the fifth calculation means. That is, from the effective value E of the commercial frequency component value obtained in step S12 and stored in another storage area of the memory (13) as the third storage means, for example, the fourth storage means is stored in the memory (14). A second reference storage value H stored in another storage area is subtracted to calculate a second subtraction value F.

(Step 519).

Further, in step S20, the microprocessor (12) acts as a sixth calculation means and determines whether the second subtraction value F is greater than or equal to a predetermined set value S.

The appropriate setting value S is 50-90% of the operating level of the ground fault detection relay of secondary burden (4).

Here, if the second subtraction value F is smaller than the predetermined set value S, it is a normal state in which no ground fault has occurred, so the second and fourth subtraction values are All data stored in the storage means (memory (14)) is erased, and the first and third storage means (memory (13)
), the data contents are updated by using the instantaneous data group and effective value stored in the second and fourth storage means as new storage values (step S18.522).

If the second subtraction value F is larger than the predetermined set value S, a ground fault or the like has occurred, and the three-phase distribution t! In this case, in anticipation of the continuation of the accident, steps S14 and S15 are performed to prevent the data from being updated for 60 cycles, for example, as in the case of Fig. 2. . However, here, the first reference storage value Bl stored in the second storage means and the second reference storage value H stored in the fourth storage means are the targets.

In this embodiment, since the zero-sequence current is detected by the difference F between the effective values of the commercial frequency components, it is expected that the influence of residual errors in the measurement system etc. will be further reduced.

In each of the above embodiments, the predetermined electrical angle for sampling data was set to 30 degrees, but if the arithmetic processing speed of the input processor, etc.
It may be further subdivided into 30 degrees or less, or on the other hand, if high accuracy is not required, it may be coarsened to 30 degrees or more.Also, to calculate the number of data stored in memories (13) and (14) and the effective value. Although the number of instantaneous values is 12 for each cycle, it may be set for two cycles or more. By increasing this number, the calculation accuracy improves, but the processing speed decreases.

Furthermore, after the detection of zero-sequence current due to a ground fault accident, the time to continue outputting the average value data corresponding to the zero-sequence current was set to 1 second (60 cycles), but the operation of the ground fault detection relay of secondary burden (4) If the time is short, the above period may be shortened, or the correction calculation circuit <11) and the signal processing circuit (10) may all be configured by a microprocessor.

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

A resistor (16
a) (16b) (16c) are connected, and an optical voltage sensor (+7&) (17b) (17c) using the Boggels effect is used to measure the voltage of each resistor (16a), etc.
) is provided. In this embodiment, a secondary current proportional to the negative current of the three-phase distribution lines (la, lb, and lc) is obtained by the winding (15a) or the like.

These secondary currents are converted into voltage by a resistor (16a) or the like, and detected by a photovoltage sensor (17a) or the like.

Another embodiment of the measuring means is shown in FIG. 5, in which an optical magnetic field sensor (18a) (
18b) (18c) is configured in a ring shape, and in the center of each ring =
It is arranged to surround the reciprocal t11 (la) (lb) (lc). In this case, the optical fiber (7a) (7
b) The light incident through (7c) is
a), etc., and is again input to the optical adder (to) and the light receiving element (9) via the optical fiber (7a), etc. Therefore, each optical magnetic field sensor (18a) etc. circulates internally and repeats reflection.

〔Effect of the invention〕

Since the present invention is configured as described above, it is possible to eliminate the detection error of the zero-sequence current component based on the difference in the characteristics of each phase of the measuring means and the effects of high-frequency and low-frequency noise, thereby reducing the zero-sequence current caused by ground faults, etc. Abnormalities in components are reliably detected and appropriate protective actions are ensured.

Furthermore, since the current of each phase is detected in the form of an optical signal, the measuring means is small and easy to install, and the influence of electromagnetic noise is also eliminated. In addition, since the adding means adds each phase at the optical signal stage and then performs photoelectric conversion, there may be errors due to differences in the characteristics of each phase at least in the photoelectric conversion part, and the zero-sequence current component error will be reduced accordingly. reduce

Further, in the invention of claim 2, since the zero-sequence current is detected by the time difference of the effective value of the commercial frequency component, the influence of residual error of the measuring means can be suppressed to a lower level.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a zero-sequence current detection device according to one embodiment of the present invention, FIG. 2 is a flowchart showing the operation of the correction calculation circuit, and FIG. 3 is a block diagram showing the operation of the correction calculation circuit according to another embodiment. FIGS. 4 and 5 are flowcharts showing the operation, FIGS. 4 and 5 are diagrams showing the configuration of measuring means according to other embodiments, respectively, and FIG. 6 is a diagram showing a conventional zero-sequence current detection device. In the figure, (la), etc. are three-phase distribution lines as AC lines, (2a), etc. are ring cores, (2) are secondary loads as load means, (5a), etc. are optical magnetic field sensors, (6a), etc. are A light emitting element, (7a) etc. are optical fibers, 8 is a tapered calculator as an adding means, (9) is a light receiving element, (11) is a correction calculation circuit, (12) is a microprocessor as each calculation means,
(13) (14) is memory as each storage means, (
+00) is the measurement means. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent: Masuo Oiwa, patent attorney

Claims (2)

[Claims] (1) Measuring means provided for each phase of the AC line to detect the current of each phase in the form of an optical signal; after adding the optical signals from this measuring means, converting it into an electrical signal and outputting it as a zero-sequence current component a first storage means for storing, as a data group, instantaneous values of outputs from the addition means for each predetermined electrical angle for a period of at least one cycle of the latest commercial frequency; Outputs from the same number of past addition means corresponding to each electrical angle of the instantaneous value data group detected before the instantaneous value data group stored in the storage means and stored in the first storage means. a second storage means for storing a group of instantaneous value data of as a first reference storage value; a first calculation means for subtracting first reference stored values of corresponding electrical angles stored in the respective electrical angles and outputting the result as a first subtracted value for each electrical angle; converting the first subtracted value into a Fourier series; a second calculation means for calculating only the commercial frequency component value, 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 calculating an effective value from the commercial frequency component value calculated by the second calculation means; It is determined whether the effective value is greater than or equal to the set value, and if the effective value is less than or equal to the set value, the instantaneous value data group stored in the second storage means is erased and the instantaneous value data group is stored in the first memory. updating the instantaneous value data group stored in the means, and updating the instantaneous value data group stored in the second storage means for at least one cycle thereafter if the effective value is equal to or greater than the set value; A zero-sequence current detection device comprising a fourth calculation means that does not carry out the calculation, and an output means for outputting data from the second calculation means to the burden means. (2) Measuring means provided for each phase of the AC line to detect the current of each phase in the form of an optical signal, which adds the optical signals from this measuring means, converts it into an electrical signal, and outputs it as a zero-sequence current component. a first storage means for storing, as a data group, instantaneous values of outputs from the addition means for each predetermined electrical angle for a period of at least one cycle of the latest commercial frequency; Outputs from the same number of past addition means corresponding to each electrical angle of the instantaneous value data group detected before the instantaneous value data group stored in the storage means and stored in the first storage means. a second storage means for storing a group of instantaneous value data of as a first reference storage value; a first calculation means for subtracting first reference stored values of corresponding electrical angles stored in the respective electrical angles and outputting the result as a first subtracted value for each electrical angle; converting the first subtracted value into a Fourier series; a second calculation means for calculating only the commercial frequency component value, 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 calculated effective value; and a fourth storage means for storing a past effective value calculated before the effective value stored in the third storage means as a second reference storage value. storage means; a fifth storage means for subtracting the second reference stored value stored in the fourth storage means from the latest effective value stored in the third storage means and outputting the result as a second subtracted value; a calculation means for determining whether the second subtraction value is greater than or equal to a predetermined set value;
When the second subtraction value is less than or equal to the set 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 replaced. At the same time, the second reference memory value stored in the fourth storage means is updated to the effective value stored in the third storage means, and the second subtraction value is equal to or greater than the set value. In some cases, a sixth calculation means does not update the instantaneous value data group stored in the second storage means for at least one cycle thereafter, and outputs the data from the second calculation means to the burden means. A zero-sequence current detection device equipped with an output means for