JPH02240575A - Zero-phase current detector - Google Patents

Abstract

PURPOSE:To miniturize a device, to prevent a malfunction and to use the device for an overhead electric wire by providing a current measuring means of an AC electric line on every phase, and also, eliminating an error component caused by a temperature characteristic and the noise of the measuring means. CONSTITUTION:A magnetic field being proportional to a current flowing through electric wires 1a-1c of three phases is induced in annular iron cores 2a-2c, and a light beam which reaches magneto-optical field sensors 5a-5c from light emitting elements 6a-6c is modulated in proportion to the magnetic field, and received 7a-7c. Subsequently, this electric signal is brought to current conversion by signal processing circuits 9a-9c and synthesized by an adding circuit 10, but becomes zero at the stationary time and there is no output from the circuit 10, and at the time of a ground accident, a zero-phase current is made flow, the output of the circuit 10 becomes a value being proportional thereto and the accident can be detected. In this case, an error component based on the difference of a temperature characteristic between each phase is offset by subtracting 11 the corresponding instantaneous data of an n/2 period before from the respective instantaneous value data of sampling data of a prescribed frequency, and an error component caused by a noise is reduced by averaging 11 plural subtraction value data at every electrical angle, and the malfunction can be prevented.

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" (II Kishoin, 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, the three-phase i! III la, lb
The current flowing through each phase of , lc 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 core 2 eventually becomes zero due to the combination of magnetic fields induced by the currents flowing through 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 current flowing through the secondary winding 3 activates the secondary load 4, and the three-phase electric wires 1a, lb
, 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 the zero-sequence current component; sampling the output from the adding means for n consecutive periods (n is an even number of 2 or more) as instantaneous value data at every predetermined electrical angle for each period; a first storage means for storing a group of instantaneous value data; a period (k is n/2) stored in the first storage means;
+ l≦k≦n), the first calculation means subtracts the instantaneous value data of the corresponding electrical angle n72 cycles ago from each of the instantaneous value data of each electrical angle; and a second calculation means for calculating an average value data group of n/2 subtraction value data corresponding to each predetermined electrical angle in each period from among the subtraction value data group for n/2 periods; a second storage means for storing a group of average value data corresponding to each predetermined electrical angle calculated by the second calculation means; If the value is greater than or equal to the value of If all of the value data is less than or equal to a predetermined value, a third calculation means updates all the instantaneous value data for n cycles stored in the first storage means, and the average value data group is sequentially transferred to the burden means. It is equipped with an output means for outputting.

[Effect] Hereinafter, the sampling period is 12 periods, that is, n=
12, the predetermined electrical angle is 30 degrees, and AC 6011 z
The operation will be explained by illustrating the case where:

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.

The first storage means is, for example, a RAM memory connected to a microprocessor, and samples the alternating current for n consecutive cycles outputted from the addition means at every predetermined electrical angle, and stores the respective instantaneous values. Convert it into a digital signal and store it.

The instantaneous value data stored in the first storage means is A(m,j
) (m is the number sampled in consecutive n periods, j is the number sampled in each period), then the first storage means stores A (1, 1) to A (12, 12). A total of 144 instantaneous value data are stored.

The first calculation means and the second calculation means are each, for example, a microprocessor, and the first calculation means is used for each instant of each electrical angle in the period (-period from the 7th period to the 12th period). Instantaneous value data for each corresponding electrical angle in a cycle n/2 cycles earlier (-cycles from the corresponding first cycle to the sixth cycle) is subtracted from the value data.

That is, the subtracted data (subtraction value data) is expressed as B(k
, j), then B (1,1) = A (?, 1)-A (1,l
).

B (2,1> = A (8,l)-A (2,1)
.

B (6,12) = A (12,12) −A (
6,12). Generally, the difference in temperature characteristics of the measurement means hardly changes in a short period of time (175 seconds in this case), so
It is considered that all sampling data (instantaneous value data) uniformly include an error amount due to this temperature characteristic difference. Therefore, the first calculation means uses this subtraction to remove the error component due to the difference in temperature characteristics of the measurement means.

There is a possibility that each subtracted value data, that is, B (1, 1)...-8 (12, 12), obtained by the first calculation means contains an error component due to white noise or the like.

Since the error component due to white noise etc. is instantaneous,
By averaging the sampling data, it is possible to distinguish from cases such as ground faults that continue for a relatively long time. That is, the second calculation means calculates the subtraction value data B (1, 1) for 6 cycles obtained by the first calculation means B (
12, 12) from each predetermined electrical temperature of O degrees, 30 degrees, 60 degrees,
... Calculates the average value of 6 pieces of data for each period corresponding to 12 cases of 330 degrees.

If the average value data is C(j), becomes.

The second storage means is, for example, a RAM memory connected to a microprocessor, and stores the average value data group obtained by the second calculation means.

The third calculation means is, for example, a microprocessor, and the electrical angles stored in the second storage means are 0 degrees, 30 degrees,
Average value data C(j) corresponding to 60 degrees...330 degrees
It is determined whether each of (j-t...12) is greater than or equal to a predetermined value. If at least one of them is greater than a predetermined value, a ground fault or the like has occurred, so the secondary load must be activated and the wires of each phase must be disconnected. That is, the average value data C(j) (j=x...12) corresponding to the zero-sequence current must be output for at least the time required to operate the secondary load (for example, 1 second). . Therefore, the third calculating means leaves 1.1 period's worth of data out of the 12 periods' worth of instantaneous value data group stored in the first storage means, and stores the latest data, the first data.
Only the instantaneous value data for two cycles is updated, and the average value signal corresponding to the zero-sequence current is continued to be output.

On the other hand, if all of the average value data C(j) (j=1...12) are below the predetermined value, no ground fault has occurred, so the third calculation means stores the data in the first memory. All the instantaneous value data stored in the means are updated, and each procedure described above is repeated from the beginning.

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

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

5c is provided. Optical magnetic field sensors 5a, 5b,
5c, light emitting elements 6a, 6b, 6c are connected to optical fiber 8.
They are connected via a, 8b, and 8c. Further, each optical magnetic field sensor 5a, 5b, 5c includes a light receiving element 7a,
7b, 7c are connected via optical fibers 8a, 8b, 8c. Annular iron cores 2a, 2b, 2c optical magnetic field sensors sa, sb, 5c, light emitting elements 6a, 6
The measurement means is composed of the light receiving elements 7a, 7b, and 1cs optical fibers 8m, 8b, and 8c.

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 5a, 5b,
The amount of light that passes through when the magnetic field applied to 5c is zero is superimposed with a change in the amount of light that is proportional to the alternating current magnetic field.

Are the signal processing circuits 9a, 9b, and 9c light receiving elements? a,
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 10 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, lb, 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, Sb, 5e
The signal processing circuits 9a, 9b, and 9c have temperature characteristics, and it is normal that these temperature characteristics differ. Therefore, three-phase electric wires 1a, lb, l
The ratio between each current of c and each output signal of signal processing circuits 9a, 9b, and 9c varies between each phase due to changes in ambient temperature. Also - signal processing circuits 9a, 9b, 9 for boat fishing
c has noise such as white noise. Due to the difference in temperature characteristics between each phase and noise, the output signal of the adder circuit 10 does not become zero even when zero-sequence current is not flowing in the three-phase electric wires 1a, lb, and lc, and the secondary load 4 malfunctions. cause

The correction arithmetic circuit 11 is provided to prevent the above-described malfunctions, and has a microprocessor 20 and first and second memories 21 and 22 consisting of RAM memories. First and second memories 21 and 22
Needless to say, each has 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 slowly due to the difference in temperature characteristics between the phases, 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. Focusing on the above points, the correction calculation circuit 11 removes error components by executing the flowcharts shown in FIGS. 2(a), (b), and (C).
Detects zero-sequence current due to ground fault.

The operation of this embodiment will be explained below using the flowcharts shown in FIGS. 2(a), 2(b) and 2(c).

In step Sl, the number of sampling cycles n (for example, n=12) required for one calculation process of the alternating current, which is the output signal from the adder circuit 10, is set. Next, in step S2, a count number 1 of the counter is set for setting the time (for example, 1 second) for operating the secondary load 4 in the event of a ground fault. 60
In the case of II z, it is 1-60.

Further, in steps S3, S4, and S5, the initial value of each counter is 1=0. ■ Set = 1 and j = 1.

Next, the output signal from the adder circuit 10 for 12 consecutive periods described above is divided into 12 parts each having a predetermined electrical angle, for example, 30 degrees, for each period, and each electrical angle is 0 degrees, 30 degrees,
The instantaneous values at 60 degrees...330 degrees are converted into digital signals and stored in the first memory 21 (step S6).

Each instantaneous value data stored in the first memory 21 is A(
+e, j) (m represents the order of sampling periods in n consecutive periods, and j represents the order of sampling for each predetermined electrical angle in each period.)
Then, a total of 144 pieces of data from A(1,1) to A(12,12) are sampled and stored in the first memory. Step S? , S8. S9 and SIO perform a counter function for sampling data. The steps from step S5 to SIO and the first memory 21 correspond to the first storage means.

Next, in step S14, the instantaneous value data for the aforementioned 12 periods are divided into groups from the first period to the n72nd period (first period to the sixth period) and from the n/2+1 period to the nth period (the seventh period). From the instantaneous value data corresponding to each electrical angle in the - period from the 7th period to the 12th period, n/2, that is, 6 periods earlier. The instantaneous value data of the corresponding electrical angle in the period of is subtracted. That is, if the subtracted data (subtraction value data) is n(k, j), then in step S14 B (k, j) = A (k, J) - A
Execute (k-n/2.j). Step Sll,
S12. SIS, S16. SIT and S1g
executes a counter function to perform arithmetic processing on all subtraction value data. Steps Sll to 318 correspond to the first calculation means. The subtraction value data obtained in each step above is from B (1, 1) to B (6,
12), that is, 72 cycles.

Generally, the difference in temperature characteristics of the measurement means is short-term (in this case, 175
(seconds), it is considered that all sampled instantaneous value data uniformly includes error components due to this difference in temperature characteristics. Therefore, each subtracted value data B (1, 1) obtained by the above subtraction process...
- B (6, 12) has the error component due to the difference in temperature characteristics of the measuring means removed.

In step S20, 6 obtained from the above subtraction process
Subtraction value data for the period (1, 1>...B (6, 1
2) to the specified electricity of 0 degrees, 30 degrees, 60 degrees...33
6g for each period corresponding to each of the 12 cases of 0 degrees
Calculate the average value of the data. The average value data is C(j)
Then, it becomes .

Each subtracted value data of [3(1,1)...B (6,12) above may contain error components due to white noise or the like. Since error components due to white noise and the like are instantaneous, by averaging these subtracted value data groups, the proportion of error components due to noise is relatively reduced and distinguished from cases due to ground faults and the like.

Steps S19, S22 and S23 execute a counter function for averaging all subtraction value data. Steps S19 to S23 correspond to the second calculation means. Average value data C(1) calculated in step S20
to C(12) is a second storage means acting as a second storage means.
It is stored in the memory 22 of.

Further, in step S25, each electrical angle stored in the second memory 22 is 0 degrees, 30 degrees, 60 degrees...3.
Average value data C(j) corresponding to 30 degrees (j=1...
12) is greater than or equal to a predetermined value S. As the value of the predetermined value S, it is desirable to set the operation level of the ground fault detection relay of the secondary load 4 to 50 to 90%.

Then, if the average value data C(J) (j・1...12) is small (both of which are greater than a predetermined value), it is determined that a ground fault has occurred, and in this case, two The secondary load 4 must be activated and the wires 1a, lb, and lc of each phase must be disconnected.In order to operate the secondary load 4,
It is sufficient to output a current corresponding to the zero-sequence current for about 1 second. However, once a zero-sequence current due to a ground fault occurs, at least the three-phase electric wires 1a and 1b are affected.

Since it should last until the lc is disconnected, if all the instantaneous value data is updated here, all the newly sampled instantaneous value data will include a zero current component due to the ground fault, and the current will be lost in step S14. In the subtraction process executed in , the zero current component due to the ground fault is canceled out. Therefore, in order to continue outputting the average value data C(j) (j-1...12) corresponding to the zero-phase current for -seconds, for example, in step S29, the 12 cycles stored in the first memory 21 are Of the instantaneous value data for the minute, the data for the first 11 cycles is left as is,
Only the instantaneous value data for the latest 12th cycle is updated. One second after detecting the zero-sequence current component due to the ground fault,
That is, in the case of AC 60 Hz, the above calculation process is repeated for 60 cycles. Step S24. S26. S2
7. S28. S30 and S31 function as counters.

On the other hand, if all of the average value data C(j) (j=1...12) are below the predetermined value, no ground fault has occurred, so step S32. S33. S34.
S35. S36. In S37 and S38, the first
All the instantaneous value data A (m, j) for 12 cycles stored in the memory 21 of is deleted and updated to the newly sampled instantaneous value data for 12 cycles, and the arithmetic processing from step Sll is performed. Repeat from the beginning.

In the above embodiment, the predetermined electrical angle for sampling the instantaneous value data was set to 30 degrees, but if the calculation processing speed of a microprocessor etc. can be increased, it may be set to 30 degrees.
It may be further subdivided into 0 degrees or less, or conversely, if high precision is not required, it may be made coarser to 30 degrees or more. Further, although the instantaneous value data group to be subtracted is for 6 cycles and the number of subtracted value data to be averaged is set to 6, it is sufficient that they are for 2 cycles and 2 or more, respectively. 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 operating time of the ground fault detection relay of secondary burden 4 If the period is short, the period may be shortened. Furthermore, the correction calculation circuit 11. Signal processing circuit 9
a, 9b, 9c and the adder circuit 1O 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. Resistors 14aj are installed at both ends of these windings 13a, 13b, and 13c.
4b, 14c are connected, and each resistor 14a, 1
Optical voltage sensors 15a, 15b, 15c using the Pockels effect are provided to measure the voltages of voltages 4b, 14c. In this embodiment, three-phase electric wire 1a
A secondary current proportional to the temporary current of , lb, lc is obtained by windings a13a, 13b, and Hc. These secondary side currents are converted into voltages by resistors 14a, 14b, and 14c, and optical voltage sensors 15a, ISb, and IS
Detected by c.

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

[Effects of the Invention] As described above, according to the 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, the error component of the zero-sequence current that changes depending on the ambient temperature of the measuring means is determined by sampling data of a predetermined number of cycles (n/2+
Subtract the corresponding instantaneous value data n72 cycles ago (instantaneous value data group from the 12th cycle to the n72nd cycle) from each instantaneous value data. offset by (subtraction value data),
Since instantaneous error components due to white noise and the like are reduced by averaging a plurality of subtracted value data for each predetermined electrical angle, there is an effect that the error is extremely small and malfunction does not occur.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a zero-sequence current detection device according to the present invention, and FIG. 2(a). (b) and (c) are flowcharts showing the operation of the correction calculation circuit 11, FIG. 3 is a diagram showing another embodiment of the measuring means of the zero-sequence current detection device according to the present invention, and FIG. 5 is a diagram showing still another embodiment of the measuring means, and FIG. 5 is a diagram showing a conventional zero-sequence current detection device. Ia, lb, lc are three-phase electric wires, 2a, 2b,
2c is an annular iron core, 5a, 5b, 5c are optical magnetic field sensors, aa, 8b, ♂C are optical fibers, 10 is an addition circuit,
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) Measuring means provided for each phase of the AC circuit to detect the current of each phase, an adding means for synthesizing the measurement signals from the measuring means and calculating the zero-sequence current component, and continuous n from the adding means. a first storage means that samples the output for a period (n is an even number of 2 or more) as instantaneous value data at every predetermined electrical angle for each period, and stores the sampled instantaneous value data group; The kth period (k is n/2) stored in the means
+1≦k≦n), the first calculation means subtracts the instantaneous value data of the corresponding electrical angle n/2 cycles ago from each of the instantaneous value data of each electrical angle; a second calculation means for calculating an average value data group of n/2 subtraction value data corresponding to each predetermined electrical angle in each period from among the n/2 period subtraction value data group; , a second storage means for storing a group of average value data corresponding to each predetermined electrical angle calculated by the second calculation means; and one of the average value data stored in the second storage means. If the value is greater than or equal to the predetermined value, only the latest one cycle of instantaneous value data of the n cycles of instantaneous value data stored in the first storage means is updated for at least a certain period thereafter, and each average If all of the value data is less than or equal to a predetermined value, a third calculation means updates all the instantaneous value data for n cycles stored in the first storage means, and sequentially sends the average value data group to the burden means. A zero-sequence current detection device comprising an output means for outputting an output.