JPH02240574A - Zero-phase current detector - Google Patents

Abstract

PURPOSE:To miniaturize a device and to use if for an overhead electric wire by providing a current value measuring means of each phase of an AC electric line on every phase. CONSTITUTION:A measuring means is constituted of, for instance, magneto-optical field sensors 5a-5c utilizing a Faraday effect, light emitting elements 6a-6c and light receiving elements 7a-7c. In this state, by a current flowing through electric wires 1a-1c of three phases, a magnetic field being proportional thereto is induced in annular iron cores 2a-2c, and a light beam which reaches the sensors 5a-5c from the elements 6a-6c is modulated in proportion to this magnetic field and received by the elements 7a-7c, and converted to an electric signal. Subsequently, this electric signal is converted 9a-9c to a signal being proportional to a current flowing through the electric wires 1a-1c and added 10. A synthetic current of each phase added 10 in this case becomes zero at the stationary time, therefore, it is not outputted, does not become zero at the time of a ground accident and a zero-phase current is made flow, and a proportional output can be obtained from the circuit 10, therefore, the ground accident of the electric wires 1a-1c can be detected. In such a manner, since a measuring means is provided on each phase of an AC electric line, the device is miniaturized and can be used for an overhead electric wire, etc.

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, lb,
The annular core 2 is provided with a secondary winding 3 so as to surround the annular core 2. Secondary winding 3 has secondary load 4
is connected.

In steady state, three-phase electricity La la, lb, l
The current flowing through each phase of c 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 annular iron core 2 eventually becomes zero due to the combination of the magnetic fields induced by the currents flowing in each phase. As a result, no current flows through the secondary winding 3 and the secondary load 4 does not operate.

On the other hand, when a ground fault occurs in any of the three-phase electric wires 1a, lb, and lc, even if the currents flowing in each phase are combined, the current does not become zero, and a zero-phase current flows. When zero-sequence current flows,
A magnetic field is induced in the annular iron core 2, and a secondary current corresponding to the zero-sequence current flows in the secondary winding 3. The secondary load 4 is activated by the secondary current flowing through the secondary winding 3, and the three-phase electric wires 1a and tb
, lc will be disconnected from the power supply to prevent the accident from spreading.

[Problem to be solved by the invention] In general, zero-sequence current detection devices are installed not only inside substations but also on outdoor distribution poles, etc., in order to quickly and accurately discover fault points and limit power outage sections as much as possible. This is desirable.

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

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.

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

[Means for Solving the Problems] A zero-sequence current detection device according to the present invention comprises: a measuring means that is provided for each phase of an AC circuit, detects the current of each phase, synthesizes measurement signals from the measuring means, Adding means for calculating a zero-sequence current component; first storage means for storing, as a data group, instantaneous values for each predetermined electrical angle of the latest output for at least one period or more among the outputs from the adding means; Means for adding the same number of past values detected and outputted before the instantaneous value data group stored in the first storage means and corresponding to each electrical angle of the instantaneous value data group stored in the first storage means a second storage means for storing a group of instantaneous value data of the output from the first storage means; a correspondence 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 first calculation means for subtracting instantaneous value data of electrical angles to calculate a first subtraction value for each electrical angle; A second effective value is calculated from the past instantaneous value data group stored in the second storage means, and the second effective value is subtracted from the first effective value. a second calculation means for calculating a subtraction value; determining whether the second subtraction value is greater than or equal to a predetermined set value; The instantaneous value data group stored in the storage means is deleted and updated to the instantaneous value data group stored in the first storage means, and if the second subtraction value is greater than or equal to a predetermined value, then a certain period of time thereafter. comprises: a third calculation means that does not update the instantaneous value data group stored in the second storage means; and an output means that outputs the first subtraction value and the second subtraction value to the burden means. There is.

[Operation] The operation will be described below by illustrating the case where the sampling period is one period and the predetermined electrical angle is 30 degrees.

The measuring means includes, for example, an optical magnetic field sensor using the Faraday effect, a light emitting element, a light receiving element, etc., and outputs a signal proportional to the current flowing through the electric 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 are connected to, for example, a microprocessor. AM memory, etc.

The first storage means samples the alternating current for one cycle or more outputted from the addition means at every predetermined electrical angle (30 degrees), converts each instantaneous value into a digital signal, and stores it. In this case, 12 pieces of data (instantaneous value data group) are stored in the first storage means. The data stored in the first storage means is always updated to the latest data.

The second storage means stores the past instantaneous value data group outputted from the addition means and stored in the first storage means after being transferred thereto. 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, the second arithmetic means, and the third arithmetic means are each composed of a microprocessor, a memory, and the like.

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 first subtraction value is calculated for each electrical angle.

The second calculation means calculates the first effective value from the latest instantaneous value data group stored in the first storage means, and also calculates the first effective value from the latest instantaneous value data group stored in the first storage means.
A second effective value is calculated from the past instantaneous value data group stored in the storage means.

Furthermore, the second effective value is subtracted from the first effective value.
Calculate the subtracted value of .

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.

The third calculation means first determines whether the second subtraction value is greater than or equal to a predetermined set value. Then, when 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 updated to the instantaneous value data group stored in the first storage means. . Also,
When the second subtraction value is equal to or greater than a predetermined value, the instantaneous value data group stored in the second storage means is not updated for a certain period of time (for example, one second) thereafter.

The output means outputs the first subtraction value and the second subtraction value to the burden means. The first subtraction value and the second subtraction value correspond to the phase information and amplitude information of the zero-sequence current, respectively, and thereby specify the occurrence of the ground fault frequency, etc., and the time thereof.

[Embodiment] A zero-sequence current detection device according to the present invention will be explained using FIG. 1 and FIG. 2 showing one embodiment 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 Sb are installed in the gaps between the annular cores 2a, 2b, and 2c.

Sc is provided. Optical magnetic field sensor Sa, 5b,
5c, light emitting elements 6a, 6b, 6c are connected to optical fiber 8.
a, 8b, and 8e. In addition, each of the optical magnetic field sensors Sa, 5b, and 5e 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, 50% light emitting elements 6a, 6
b, 6c, light receiving elements 7a, 7b, 7cs optical fiber 8
A, 8b, and 8c constitute a measuring means.

The annular iron cores 2a, 2b, 2c include three-phase electric wires 1a,
The current flowing through lb and lc induces a magnetic field proportional to each current. At this time, the light emitting elements 6a, 6b,
The light reaching the optical magnetic field sensors 5a, 5b, 5c from the optical fibers 8a, 8b, 8c from the optical fibers 8a, 8b, 8c is modulated in proportion to the magnetic field in each air gap of the annular cores 2a, 2b, 2c. , 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 optical magnetic field sensors Ss, Sb,
The amount of light that passes through when the magnetic field applied to 6c 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.
, lb, lc into signals proportional to the flowing current. Adder circuit IO adds these signals.

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

On the other hand, when a ground fault occurs in the three-phase electric wires 1a, tb, and lc, even if the currents of each phase are combined, the current does not become zero and a zero-phase current flows. Therefore, the output of the adder circuit lO becomes a value proportional to this zero-phase current, and the three-phase electric wires 1a, l
B, LC ground faults can be detected.

However, in reality, the optical magnetic field sensors 5a, 56.5c and the signal processing circuits 9a, 9b, 9c have temperature characteristics, and there are usually differences in the temperature characteristics. Therefore, three-phase electric wires 1a, lb, lc
The ratio between each current and each output signal of the 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 lO
The output signal does not become zero even when zero-sequence current is not flowing through the three-phase electric wires 1a, lb, and lc, causing the secondary load 4 to malfunction.

The correction calculation circuit 11 is provided to prevent the above-mentioned malfunction, and is implemented by the microprocessor 20. First and second memories 21 and 22 consisting of RAM memories
have. First and second memories 21 and 2
It goes without saying that each of the data storage areas 2 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 this embodiment will be explained below using the flowchart shown in FIG.

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

Normally, 0 is entered in all addresses. Assuming that each instantaneous value data group B(j) (J represents the order of data sampled at each predetermined electrical angle) stored in the second memory 22, B(1) to 8(12) 12 of
data is stored. Next, steps S2 and S
In step 3, initial values ■=60 and J=1 are set.

In step S4, 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 memory 21. Each data stored in the first memory 21 is expressed as A(j) (j represents the order of data sampled at each predetermined electrical angle).
Then, 12 pieces of data from A(1) to A(12) are sampled and stored in the first memory 21.

In step S5, the corresponding electrical angle data B (j) stored in the second memory 22 is extracted from each electrical angle data group A (j) stored in the first memory 21 stage. A first subtraction value is calculated for each electrical angle. That is, the first subtraction value is C(j)
Then, the microprocessor 20 that acts as the first calculation means has the following formula: C(j) = A (j) −B (
Execute j).

Next, the microprocessor 20 acts as an output means and outputs the first subtraction value C(j) for the secondary burden 4 (
Step S6). Steps S7 and S8 function as counters for calculating the first subtraction value C(j) for every electrical angle.

Generally, the difference in temperature characteristics of the measuring means hardly changes over 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 difference in temperature characteristics. Therefore, the subtracted value C(j) for each army 1 obtained by the above-mentioned subtraction process has the error component due to the difference in temperature characteristics of the measuring means removed. Also, the first subtraction value C(
In j), the amplitude information of the alternating current component of the zero-sequence current is deleted by the above-mentioned subtraction process, and only the phase information is included.

In steps S9, SIG and Sll, the microprocessor 20 acts as a second calculation means.

That is, all data A (1)...A (12) stored in the first memory 21 in step S9
Then, in step SlO, all the data B (
1)...113 Calculate the second effective value E from (12). Furthermore, in step Sll, a second subtraction value F is calculated by subtracting the second effective value E from the first effective value.

In step S12, the microprocessor 20 functions as an output means and outputs the second subtraction value F to the secondary burden 4. In the above subtraction process, all data A (1)...A (12) and B(1)...B stored in the first and second memories 21 and 22, respectively.
By converting (12) into an effective value, instantaneous error components caused by, for example, white noise are averaged, and the relative proportion of error components in the effective value is reduced. Furthermore, by subtracting the second effective value E from the first effective value, the error component due to the difference in temperature characteristics of the measuring means described above is removed, so the error component is removed from the second subtracted value F. In addition, the information is extremely reliable. By converting it into an effective value, the second subtraction value F includes only amplitude information of the alternating current component of the zero-sequence current.

In step S15, the microprocessor 20 functions as a third calculation means and determines whether the second subtraction value F is greater than or equal to a predetermined value S. The predetermined value S is
50-90 of the operating level of the ground fault detection relay of secondary burden 4
% is appropriate.

Here, if the second subtraction value F is smaller than the predetermined value S, it is a normal state in which no ground fault has occurred, so it is stored in the second memory 22 in preparation for the next calculation process. The contents of the data are updated by erasing all the data stored in the first memory 21 and using the data group stored in the first memory 21 as new values stored in the second memory 22 (step Sl?).
.

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

Ib　lc must be disconnected from the power supply, etc.

Generally, in order to operate the secondary load 4 to disconnect the three-phase electric wires 1a, lb, and Ic from the power source, it is sufficient to output a current corresponding to a 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 wires la, lb, and Ic are disconnected. If the data group in the second memory 22 is updated here, all the newly sampled instantaneous value data will contain a zero current component due to the ground fault, so in the subtraction process executed in steps S5 and Sll, , the zero current component due to the ground fault is canceled out.

Therefore, in order to continue outputting the first and second subtraction values C(j) and F corresponding to the zero-sequence current for -seconds, for example, the component due to the past ground fault fault stored in the second memory 22 is used. The data that does not include the component will be left as is, and only the data that includes the component due to the latest ground fault accident will be updated. One second after detecting the zero-sequence current component due to the ground fault,
That is, in the case of AC 60 It Z, the above calculation process is repeated for 60 cycles. Step S16. S13 and S14 function as counters.

Although there is a possibility that the above first subtraction value C(j) contains an instantaneous error component due to white noise, the first subtraction value C(j) is used only as phase information and is used to prevent ground faults. Since the determination of the occurrence of such errors is made based on the second subtraction value F which also reduces the error component due to white noise, there is no problem at all in practice.

In the above embodiment, the predetermined electrical angle for sampling data was 30 degrees, but it may be further subdivided into 30 degrees or less if the processing speed of a microprocessor or the like can be increased. On the other hand, if high accuracy is not required, the roughness may be set to 30 degrees or more.Furthermore, the number of data stored in the first and second memories 21 and 22 and the number of instantaneous values for determining the effective value are each 1. Although the number is set to 12 for each period, it is sufficient to have at least 2 for each period.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 is 1 second (60 cycles). However, if the operating time of the ground fault detection relay of the secondary load 4 is short, the above period may be shortened.Furthermore, the correction calculation circuit 11 and the signal processing circuit 9a.

9b, 9e and the adder circuit io may all be configured by a microprocessor.

Next, another embodiment of the measuring means section of the zero-sequence current detecting 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. These windings 1
3a, 13b, ! A resistor 14a is connected to both ends of 3c.
14b, 14c are connected, and each resistor 14a,
Optical voltage sensors 15a, 15b, 15c using the Pockels effect are provided to measure the voltages of the voltages 14b, 14c. In this embodiment, three-phase electric wire 1
Secondary currents proportional to the temporary currents of a, lb, and lc are obtained by windings 13a, 13b, and 13c. These secondary side currents are connected to resistors 14a, 14b, 14
c is converted into voltage by photovoltage sensors 15a and +5b.
, 15c.

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 three-phase electric wires 1a, lb, and lc are surrounded at the center of each ring. In this case, the light incident through the optical fibers 8a, 8b, 8e 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, 1
6c circulates internally and repeats reflection.

[Effects of the Invention] As described above, according to the present invention, since the measuring means for measuring the current value of each phase of the AC line is provided for each phase, the size is reduced, and the can be used.

In addition, instantaneous error components due to white noise, etc. are reduced by calculating the effective value from multiple sampling data (instantaneous value data groups), and zero-sequence current error components that vary depending on the ambient temperature of the measurement means are reduced using the latest Sampling data (instantaneous value data group stored in the first storage means)
The error is removed by subtracting past (immediately before the occurrence of the ground fault) sampling data (instantaneous E-day 2 groups stored in the second storage means) and its effective value from the effective value. This has the effect that there are very few errors and no malfunctions occur.

[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 11, and FIG. FIG. 4 is a diagram showing another embodiment of the measuring means of the zero-sequence current detecting device, FIG. 4 is a diagram showing still another embodiment of the measuring means, and FIG. 5 is a diagram showing a conventional zero-sequence current detecting device. LA, LB, LC are three-phase electric wires, 2a, 2b,
2c is an annular iron core; 5a, 5b, and 5c are optical magnetic field sensors; 8a, 8b, and 8c are optical fibers; 10 is an adder circuit; and 11 is a correction calculation circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[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 second 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; The instantaneous value data of the corresponding electrical angle stored in the second storage means is subtracted from each of the instantaneous value data groups for each electrical angle stored in the storage means of A first calculation means for calculating a subtraction value, a first calculation means for calculating a first effective value from the latest instantaneous value data group stored in the first storage means, and a first calculation means for calculating a subtraction value, and a first calculation means for calculating a first effective value from the latest instantaneous value data group stored in the first storage means. a second calculation means for calculating a second effective value from the instantaneous value data group and subtracting the second effective value from the first effective value to calculate a second subtraction value; the second subtraction value is a predetermined value; If the second subtracted 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 second storage means is deleted. The instantaneous value data group stored in the storage means is updated, and if the second subtraction value is greater than or equal to a predetermined value, the instantaneous value data group stored in the second storage means is updated for a certain period of time thereafter. A zero-sequence current detection device comprising: a third arithmetic means that does not include a third calculation means; and an output means that outputs the first subtraction value and the second subtraction value to the burden means.