JP2673573B2 - Zero-phase current detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a zero-phase current detecting device installed to detect a zero-phase current flowing in a ground fault.

[Prior Art] For example, "Transformer for measuring instruments" (Denki Shoin, Miho Ikeda)
FIG. 5 shows a conventional zero-phase current detecting device described on page 79.

In the figure, an annular core 2 is provided so as to surround the three-phase electric wires 1a, 1b, 1c, and an annular core 2 is provided with a secondary winding 3. A secondary burden 4 is connected to the secondary winding 3.

Under normal conditions, the current flowing in each phase of the three-phase electric wires 1a, 1b, 1c does not include a component due to an accident, and only an alternating current having a positive phase component and a negative phase component having the same amplitude flows. The magnetic field in the annular core 2 eventually becomes zero due to the combination of the magnetic fields induced by the currents flowing in the respective phases. As a result, no current flows through the secondary winding 3 and the secondary burden 4 does not operate.

On the other hand, if a ground fault occurs in any of the three-phase electric wires 1a, 1b, 1c, even if the currents flowing in the respective phases are combined, the current does not become zero, but a zero-phase current flows. When the zero-phase current flows, a magnetic field is induced in the annular core 2 and a secondary current corresponding to the zero-phase 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, 1b, 1c are disconnected from the power source, and the accident is prevented from spreading.

[Problems to be Solved by the Invention] In general, in order to detect an accident point accurately at an early stage and limit a power failure section as much as possible, a zero-phase current detection device is installed not only in a substation premises but also in an outdoor distribution pole or the like. Is desirable.

However, the conventional zero-phase current detecting device is a three-phase electric wire 1a, 1
Since the annular core 2 that surrounds b and 1c collectively is used,
Unsuitable for use on overhead wires, etc.
In addition, there was a problem that accidents were expanded due to lightning strikes and the like.

Next, when a current detector is provided for each phase for use in the processed electric wire, etc., and the overall zero-phase current detector is miniaturized, it is apparent due to differences in temperature characteristics of the current detectors provided for each phase. However, there is a problem that the secondary load 4 malfunctions due to the generation of the zero-phase current.

The present invention has been made to solve the above problems, and has as its object to provide a small and high-precision zero-phase current detection device that can be used for overhead electric wires and the like.

[Means for Solving the Problems] A zero-phase current detection device according to the present invention is provided for each phase of an AC circuit, and a measuring means for detecting a current of each phase, a measuring signal from the measuring means are combined, An addition means for calculating a zero-phase current component; a first storage means for storing, as a data group, an instantaneous value of the output of the latest at least one cycle or more among the outputs from the addition means, for each predetermined electrical angle; From the same number of past addition means that are detected before the instantaneous value data group stored in the first storage means and correspond to the respective electrical angles of the instantaneous value data group stored in the first storage means. Second storage means for storing the output instantaneous value data group, and corresponding electrical information stored in the second storage means from each of the instantaneous value data group for each electrical angle stored in the first storage means. Instantaneous value data for corners To calculate a first subtraction value for each electrical angle, a first effective value from the latest instantaneous value data group stored in the first storage means, and The 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 to obtain the second effective value.
Second calculation means for calculating the subtraction value of the second subtraction value, determining whether the second subtraction value is equal to or more than a predetermined set value or less than the predetermined setting value, and when the second subtraction value is less than the predetermined value, the second 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 when the second subtracted value is equal to or more than a predetermined value, a predetermined time Comprises a third computing means for not updating the instantaneous value data group stored in the second storage means, and an output means for outputting the first subtraction value and the second subtraction value to the burden means. There is.

[Operation] The operation will be described below while exemplifying the case where the sampling cycle is one cycle and the predetermined electrical angle is 30 degrees.

The measuring means is composed of, for example, a magneto-optical sensor utilizing the Faraday effect, an issuing element, a light receiving element, etc., and outputs a signal proportional to the current flowing through the electric wire of each phase.

The adding means is an analog adding circuit or a digital adding circuit using a microprocessor or the like, and can add the current values flowing in the respective phases detected by the measuring means and output the added values. That is, the data corresponding to the latest zero-phase current is output from the adding means every moment.

The first and second storage means are, for example, RAM memories connected to a microprocessor.

From the first storage means, the alternating current output from the addition means for one cycle or more is sampled at every predetermined electrical angle (30 degrees), and each instantaneous value is digitized and stored. 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 constantly updated.

The second storage means stores these data after the past instantaneous value data group output from the addition means and stored in the first storage means is transferred. In the normal case where the zero-phase current is not generated, the data group stored in the second storage means is sampled one time before and updated to the instantaneous value data group stored in the first storage means. To be done.

The first arithmetic means, the second arithmetic means and the third arithmetic means are respectively constituted by a microprocessor and a memory.

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, The first subtraction value for each electrical angle is calculated.

The second calculation means calculates a first effective value from the latest instantaneous value data group stored in the first storage means, and from the past instantaneous value data group stored in the second storage means. The second effective value is calculated. Further, the second effective value is subtracted from the first effective value to calculate the second subtracted value.

In general, the error component due to the temperature characteristic difference of the measuring means provided in each phase hardly changes in a short time (for example, 1 second). Therefore, by subtracting the past data sampled immediately before from the latest data, An error component due to the temperature characteristic difference can be removed.

The third calculation means first determines whether the second subtraction value is equal to or greater than or equal to a predetermined set value. And
When the second subtraction value is less than or equal to the predetermined value, the instantaneous value data group stored in the second storage means is erased and updated to the instantaneous value data group stored in the first storage means. Further, when the second subtraction value is equal to or larger than the predetermined value, the instantaneous value data group stored in the second storage means is not updated for a certain time (for example, 1 second) thereafter.

The output means outputs the first subtraction value and the second subtraction value to the burden output. The first subtraction value and the second subtraction value correspond to phase information and amplitude information of the zero-phase current,
As a result, the occurrence of a ground fault accident and the time thereof are specified.

[Embodiment] A zero-phase current detection device according to the present invention will be described with reference to FIGS. 1 and 2 showing an embodiment thereof.

In FIG. 1, three-phase electric wires 1a, 1b, 1c are provided with annular cores 2a, 2b, 2c, respectively. Each annular core 2a, 2b,
The optical magnetic field sensors 5a, 5b, 5c are provided in the gap 2c. Light emitting elements 6a, 6b, 6c are connected to the optical magnetic field sensors 5a, 5b, 5c via optical fibers 8a, 8b, 8c. Each of the optical magnetic field sensors 5a, 5b, 5c is provided with a light receiving element 7a, 7b, 7c.
They are connected via a, 8b, 8c. Annular iron cores 2a, 2b, 2c optical magnetic field sensors 5a, 5b, 5c, light emitting elements 6a, 6b, 6c, light receiving elements 7a, 7
The measuring means is constituted by b, 7c and the optical fibers 8a, 8b, 8c.

A magnetic field proportional to each current is induced in the annular cores 2a, 2b, 2c by the currents flowing through the three-phase electric wires 1a, 1b, 1c. At this time, the light reaching the magneto-optical sensors 5a, 5b, 5c from the light emitting elements 6a, 6b, 6c through the optical fibers 8a, 8b, 8c is the annular cores 2a, 2b, 2c.
Is modulated in proportion to the magnetic field in each air gap of the optical fiber 8
It reaches the light receiving elements 7a, 7b, 7c via a, 8b, 8c and is converted into an electric signal. The optical magnetic field sensors 5a, 5b, 5c are composed of, for example, a polarizer, a Faraday element, and an analyzer. While the light linearly polarized by the polarizer passes through the Faraday element, the plane of polarization rotates in proportion to the magnetic field applied in the light traveling direction of the Faraday element, and this changes the amount of light passing through the analyzer. Is modulated. The modulated light has a light amount change proportional to the AC magnetic field superimposed on the light amount transmitted when the magnetic field applied to the optical magnetic field sensors 5a, 5b, 5c is zero.

The signal processing circuits 9a, 9b, 9c convert the electric signals converted by the light receiving elements 7a, 7b, 7c into signals proportional to the current flowing through the three-phase electric wires 1a, 1b, 1c. The addition circuit 10 adds these signals.

In the steady state, the currents of the three-phase electric wires 1a, 1b, 1c are combined to be zero, so that the output of the adder circuit 10 is also zero.

On the other hand, when a ground fault occurs in the three-phase electric wires 1a, 1b, 1c, even if the currents of the respective phases are combined, the current does not become zero but the zero-phase current flows. Therefore, the output of the adding circuit 10 has a value proportional to the zero-phase current, and the ground fault of the three-phase electric wires 1a, 1b, 1c can be detected.

However, in reality, the optical magnetic field sensors 5a, 5b, 5c and the signal processing circuits 9a, 9b, 9c usually have temperature characteristics, and in addition, the individual temperature characteristics generally differ. Therefore,
The ratio of each current of the three-phase electric wires 1a, 1b, 1c and each output signal of the signal processing circuits 9a, 9b, 9c causes a difference between each phase due to a change in ambient temperature. Due to the difference in the temperature characteristics between the phases, the output signal of the adder circuit 10 does not become zero even when the zero-phase current does not flow in the three-phase electric wires 1a, 1b, 1c, and the secondary load 4 malfunctions. Becomes

The correction arithmetic circuit 11 is provided to prevent the above-mentioned malfunction, and has a microprocessor 20 and first and second memories 21 and 22 which are RAM memories. It goes without saying that the first and second memories 21 and 22 each have a storage area larger than the number of samples of data to be stored.

Generally, the change in the error component of the zero-phase current due to the difference in temperature characteristics between the phases is relatively gradual. Moreover, the zero-phase current component due to the ground fault accident is instantaneously generated. Focusing on the above points, the correction arithmetic circuit 11 executes the flowchart shown in FIG. 2 to remove the error component and detect the zero-phase current due to the ground fault.

The operation of this embodiment will be described below with reference to the flow chart shown in FIG.

In step S1, the initial value is stored in the second memory 22 which functions as the second storage means. Normally, enter 0 for all addresses. Assuming that each instantaneous value data group B (j) stored in the second memory 22 (where j represents the order of data sampled for each predetermined electrical angle), B (1) to B (12) 12 data items are stored. Next, in steps S2 and S3, the initial value i = 60
And j = 1.

In step S4, the data for the latest one cycle of the alternating current, which is the output signal from the adding circuit 10, is set to a predetermined electrical angle,
For example, it is converted into a digital signal as an instantaneous value every 30 degrees and stored in the first memory 21. Assuming that each data stored in the first memory 21 is A (j) (j represents the order of data sampled for each predetermined electrical angle), 12 from A (1) to A (12) are obtained. Data is 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 obtained from each data group A (j) for each electrical angle stored in the first memory 21 stage. Subtract and calculate the first subtraction value for each electrical angle. That is, assuming that the first subtraction value is C (j), the microprocessor acting as the first calculation means.
Twenty implements C (j) = A (j) -B (j).

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

Generally, the temperature characteristic difference of the measuring means is short (for example, 1 second).
Therefore, it is considered that all the sampling data uniformly include the error due to this temperature characteristic difference. Therefore, each first subtraction value C (j) obtained by the above subtraction processing has the error component due to the temperature characteristic difference of the measuring means removed.

In steps S9, S10 and S11, the microprocessor 20 acts as a second computing means. That is, the first effective value D is calculated from all the data A (1) ... A (12) stored in the first memory 21 in step S9, and then stored in the second memory 22 in step S10. The second effective value E is calculated from all the stored data B (1) ... B (12). Further, in step S11, the first
The second effective value E is subtracted from the effective value D to calculate the second subtracted value F.

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 the data A stored in the first and second memories 21 and 22 respectively.
(1) ... A (12) and B (1) ... B (12) are converted into effective values to average instantaneous error components due to, for example, white noise, and the relative proportion of the error components in the effective values. Is being reduced. Further, by subtracting the second effective value E from the first effective value D, the error component due to the temperature characteristic difference of the above-mentioned measuring means is removed, so that the second subtracted value F has the error component removed. In addition, the information will be extremely reliable. By being converted to an effective value, the second subtraction value F includes only the amplitude information of the AC component of the zero-phase current.

In step S15, the microprocessor 20 causes the third
And the second subtraction value F is a predetermined value S
It is determined whether it is more than or less than. It is suitable that the predetermined value S is 50 to 90% of the operation level of the ground fault detection relay of the secondary load 4.

Here, when the second subtraction value F is smaller than the predetermined value S, it is a normal state in which a ground fault or the like has not occurred, and therefore is stored in the second memory 22 in preparation for the next arithmetic processing. All the stored data are erased, and the content of the data is updated by using the data group stored in the first memory 21 as a new stored value in the second memory 22 (step S17).

When the second subtraction value F is larger than the predetermined value, a ground fault or the like has occurred, and therefore the three-phase electric wires 1a, 1b, 1c must be disconnected from the power source or the like. Generally, a three-phase wire
In order to operate the secondary load 4 in order to disconnect 1a, 1b, 1c from the power supply, it is sufficient to output a current corresponding to the zero-phase current for about 1 second. However, once a zero-phase current due to a ground fault occurs, it should continue until at least the three-phase electric wires 1a, 1b, 1c are disconnected. Here the second memory 22
If the data group of is also updated, all the newly sampled instantaneous value data will include the zero current component due to the ground fault, so in the subtraction process executed in steps S5 and S11, The current components are canceled out. Therefore, for example, in order to continue to output the first and second subtraction values C (j) and F corresponding to the zero-phase current for 1 second, the past, that is, the ground fault accident stored in the second memory 22 The data that does not contain the component is left as it is, and only the data that contains the component due to the latest ground fault accident is updated. Then, the above-described arithmetic processing is repeated for one second after detecting the zero-phase current component due to the ground fault, that is, for 60 cycles in the case of 60 Hz AC. Steps S16, S13 and S14 function as a counter.

The first subtraction value C (j) may include an instantaneous error component due to white noise, but the first subtraction value C (j) is used only as phase information, and the ground fault accident Since there is no problem in practical use, since the determination of the occurrence of the above is made based on the second subtraction value F in which the error component due to white noise is also reduced.

In the above embodiment, the predetermined electrical angle for sampling the data is set to 30 degrees, but if the processing speed of the microprocessor or the like can be increased, it may be further subdivided to 30 degrees or less. If high accuracy is not required, it may be roughened to 30 degrees or more. Further, the number of data stored in the first and second memories 21 and 22 and the number of instantaneous values for obtaining the effective value are 12 for each one cycle, but it is sufficient that both are 2 or more. Furthermore, after detecting the zero-phase current due to a ground fault, the time to keep outputting the average value data corresponding to the zero-phase current was set to 1 second (60 cycles).
When the operation time of the ground fault detection relay of the secondary burden 4 is short, the above period may be shortened. Furthermore, the correction arithmetic circuit
11, the signal processing circuits 9a, 9b, 9c and the addition circuit 10 may all be configured by a microprocessor.

FIG. 3 shows another embodiment of the measuring means of the zero-phase current detecting device according to the present invention.

Windings 13a, 13b, 13c are respectively provided on a part of the annular cores 2a, 2b, 2c.
Is wound. Resistors 14a, 14b, 14c are connected to both ends of these windings 13a, 13b, 13c, and further, each resistor 14a, 14b, 1c is connected.
Optical voltage sensors 15a, 15b, 15c using the Pockels effect for measuring the voltage of 4c are provided. In this embodiment, the secondary side current proportional to the temporary side current of the three-phase electric wires 1a, 1b, 1c is obtained by the windings 13a, 13b, 13c. These secondary currents are converted into voltages by the resistors 14a, 14b, 14c and detected by the optical voltage sensors 15a, 15b, 15c.

FIG. 4 shows still another embodiment of the measuring means. In the figure, the optical magnetic field sensors 16a, 16b, 16c using the Faraday effect
Are formed in a ring shape, and the three-phase electric wires 1a, 1b, 1c are surrounded at the center of each ring. In this case, the optical fibers 8a, 8b,
The light incident via 8c circulates through the three-phase electric wires 1a, 1b, 1c and is input again to the light receiving elements 7a, 7b, 7c and the measuring circuit 12 via the optical fibers 8a, 8b, 8c. Therefore, each of the optical magnetic field sensors 16a, 16b, and 16c 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 circuit is provided for each phase, the size is reduced, and the overhead electric wire and the like are reduced. Can be used.

Also, the instantaneous error component due to white noise or the like is reduced by calculating the effective value from a plurality of sampling data (instantaneous value data group), and the error component of the zero-phase current that changes depending on the ambient temperature of the measuring means is the latest. From sampling data (instantaneous value data group stored in the first storage means) and its effective value to the past (immediately before the occurrence of a ground fault)
Since the sampling data (instantaneous value data group stored in the second storage means) and its effective value are removed by subtraction, the error is extremely small,
Has the effect of not causing a malfunction

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the zero-phase current detecting device according to the present invention, FIG. 2 is a diagram showing a flow chart showing the operation of the correction arithmetic circuit 11, and FIG. 3 is relating to the present invention. The figure which shows another Example of the measuring means of a zero phase current detection apparatus, FIG. 4 is the figure which shows another Example of a measuring means,
FIG. 5 is a diagram showing a conventional zero-phase current detecting device. 1a, 1b, 1c is a three-phase electric wire, 2a, 2b, 2c is a ring core, 5a, 5b, 5c
Is an optical magnetic field sensor, 8a, 8b, and 8c are optical fibers, 10 is an addition circuit, and 11 is a correction operation circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masami Watanabe 8-1-1 Tsukaguchihonmachi, Amagasaki-shi, Hyogo Mitsubishi Electric Corporation Itami Works

Claims (1)

(57) [Claims] 1. A measuring means which is provided for each phase of an alternating current circuit and detects a current of each phase, an adding means for synthesizing a measuring signal from the measuring means and calculating a zero-phase current component, and an output from the adding means. Of the latest value of at least one cycle of the instantaneous value of each predetermined electrical angle for storing as a data group than the first storage means, the instantaneous value data group stored in the first storage means Second storage means for storing the same number of output instantaneous value data groups from past addition means corresponding to the respective electrical angles of the instantaneous value data group previously detected and stored in the first storage means, Subtracting the corresponding instantaneous value data group of the electrical angle stored in the second storage means from each of the instantaneous value data group of each electrical angle stored in the first storage means, The first subtraction value is calculated and the first The calculating means calculates the first effective value from the latest instantaneous value data group stored in the first storage means, and calculates the second effective value from the past instantaneous value data group stored in the second storage means. Second calculating means for calculating an effective value, subtracting the second effective value from the first effective value to calculate a second subtracted value, or if the second subtracted value is equal to or greater than a predetermined set value, or 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 to erase the instantaneous value stored in the first storage means. Third computing means for updating the value data group and not updating the instantaneous value data group stored in the second storage means for a certain period of time after the second subtraction value is equal to or greater than a predetermined value; Output means for outputting the subtracted value of 1 and the subtracted value of 2 to the burden means, Place.