JPS5858889B2 - Three-phase distribution line disconnection detection device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a disconnection detection device for a power distribution line.

When a break occurs in a high-voltage distribution line, it is necessary to immediately disconnect the line.

Therefore, it is required to promptly detect a disconnection at a substation.

To do this, a device is installed at the end of the branch line to detect a disconnection, and when a disconnection is detected, the line is forcibly grounded and the ground fault detection relay at the substation is activated. It is possible to do so.

According to this, a broken line can be cut off by the operation of a ground fault detection relay.
In this method, a device for detecting wire breakage must be installed at the end of each branch line, so a large number of devices of this kind are required, resulting in high equipment costs and troublesome maintenance and inspection.

Possible methods for detecting this type of wire breakage include detecting zero-sequence voltage, negative-sequence voltage, and detecting a drop in voltage, but the configuration of either method is extremely complicated. be.

An object of the present invention is to easily and reliably detect a break in a power distribution line at a substation.

In this invention, a break in a distribution line is detected in a substation by using the phase current and line current (vector difference between one phase current and another phase current) of the distribution line.

As described above, when attempting to detect a wire breakage using the phase current and line current, the phase current and line current of the phase in which the wire breakage occurred changes, but these currents of the healthy phase also change.

In addition to disconnection, these currents change when a single-phase load or a three-phase load is opened, and the amount of change often takes on different values.

Now, for each of these currents, the current values before and after the change, the vector difference and the difference in absolute value (scalar difference) of the current change were actually determined, and the following results were obtained.

Here, each balanced load Z with a resistance value of 10 ohms is assumed to be a load on a three-phase distribution line with a line voltage of 100 V, and if the a phase is disconnected as shown in Figure 1, the single-phase load becomes as shown in Figure 2. When the line is opened, and when the three-phase load is opened as shown in Figure 3 (in both Figures 1 and 1, it is assumed that the line is opened at the location marked with an x).

), the phase current and line current of each phase before and after the change were actually measured, and the results shown in Table 1 were obtained.

(Iab-Ia-Ib). The same applies to other phases).

Further, as a result of calculating the changes in the phase current and line current as vector differences and scalar differences for these values, the results shown in Tables 2 and 3 were obtained.

Based on these positions, we calculated the ratio of the vector difference or scalar difference in one phase current to the vector difference or scalar difference in line current between the other phases.
The following results were obtained.

That is, Table 4 shows the ratio between the scalar difference in phase current and the scalar difference in line current**, Table 5 shows the ratio between the scalar difference in phase current and the vector difference in line wire, and Table 6 shows the ratio between the scalar difference in phase current and the vector difference in line wire. The ratio between the vector difference of 64-phase currents and the vector difference of line-to-line currents is shown.

Now, when considering the ratios shown in Table 4, as shown in Figure 1, a
When a phase is disconnected, the ratio of the change in the phase current of the a phase before and after the disconnection to the change in the line current between the b and C phases becomes infinite, whereas the change in the phase current of the b phase The ratio of the line current between the C phase and the a phase, and the change in the phase current of the C phase and the a phase, b phase
The ratio to the line current between phases takes on a finite value.

As shown in FIGS. 2 and 3, even when a single phase or three phases are open, the ratios described above all take zero or finite values.

If it can be determined from these whether the above-mentioned ratio is infinite, a finite value, or zero, it will be possible to distinguish and detect when the A-phase is disconnected from when it is single-phase or three-phase open. The above-mentioned ratios when a single phase or three phases are open are all 2 or less, which is much smaller than the infinite ratio when the A phase is disconnected.In other words, the difference between the two ratios is sufficiently large, so It becomes extremely easy to distinguish and detect the ratio between the two.

The same thing can be said about each ratio shown in Tables 5 and 6 below.

Note that the ratio between the vector difference in phase current of one phase and the scalar difference in line current between other phases is not shown in the above table, but as shown in Table 3, △Ibc is the first Considering that it is zero only in the case shown in the figure, and that it takes a finite value that is the difference between the line currents in other cases, and that △Ia takes a finite value as shown in Table 2, △Ia/ △Ibc
The ratio of becomes infinite, △rb7△Ica and △Ic/△
Since it is clear that Iab takes a finite value, it is easy to understand that exactly the same thing as above can be said.

The above explanation has been about the case of detecting a disconnection in the a phase, but it goes without saying that a disconnection in the b phase or C phase can also be detected by the same method lζ as described above.

Based on the above explanation, the present invention detects the occurrence of wire breakage by calculating the above ratio using the phase current of the three phases and the line current, and the change in the phase current and the change in the line current before and after the change. do.

Here, the scalar difference between the phase current and the line current can be obtained as the difference in the absolute value of the phase current and the difference in the absolute value of the line current, respectively, and the vector difference between the phase current and the line current can be calculated as the difference in the absolute value of the phase current and the difference in the absolute value of the line current, respectively. Since the absolute value of the vector difference between the line currents and the absolute value of the vector difference between the line currents can be obtained, the occurrence of the required disconnection can be detected by using these arithmetic circuits.

FIG. 4 shows a configuration according to the above-mentioned Table 4, and phase currents of the a phase, b phase and C phase are applied to the input terminals 1, 2, and 3Gζ, respectively.

A-phase current Ia given to terminal 1? j Enters the absolute value storage circuit 4 and absolute value detection circuit 5.

The absolute value detection circuit 5 detects the absolute value of the phase current Ia at each instant, and the absolute value storage circuit stores the absolute value of the phase current Ia at a normal time, that is, before a disconnection occurs.

Therefore, when a disconnection occurs, the detected value of the absolute value detection circuit 5 is Ia'l, and the stored value Lt of the absolute value storage circuit 4
It is l■a.

Phase current Ib of phase B and phase C applied to terminals 2 and 3,
Ic enters the line current detection circuit 6, where the line current r
bc is detected.

This current value is then applied to the absolute value storage circuit 7 and the absolute value detection circuit 81.

These circuits are almost the same as the previous circuits 4 and 5, and the absolute value detection circuit 8 detects the double value (K is a constant) of the absolute value of the line current Ibc at each instant, and the absolute value storage circuit 7 A double value of the absolute value of the line current Ibc before the disconnection occurs is stored.

Therefore, when a disconnection occurs, the detected value of the absolute value detection circuit 8 is 1iK I Ib'cl, and the stored value of the absolute value storage circuit 7 is KIIbcl.

The outputs of each of the circuits 4, 5.7.8 described above are given to the addition/subtraction circuit 9, and when a disconnection occurs, a calculation of the quartic equation is performed.

(1Ial-lIa'l) K(IIbcl-II
b'cl) The first term in the above equation is a when the a phase is disconnected.
The change in the phase current of the phases is a value expressed as a scalar difference, and the second term is also the value when the a phase is disconnected.

The amount of change in the C-phase line current is twice the value expressed as the scalar difference.

This calculation result value (4) is given to the zero level detector 10, where it is compared with the zero value.

In the case of the example shown in Table 4, if the value of K mentioned above is set to a value greater than 2, then the zero level detector 10 detects that the calculation result value of the addition/subtraction circuit 9 is greater than zero. When this is detected, it can be determined that a disconnection has occurred in the a phase.

FIG. 5 shows a configuration according to Table 5.

In this case, it is necessary to obtain the change in the line current as a vector difference, so the output from the line current detection circuit 6 is input to the AC amount storage circuit 11, where the line current alternating current amount Ibc during normal operation is remember.

This stored value and each instantaneous output value from the line current detection circuit 6 are input to the addition/subtraction circuit 12.

When the a-phase is disconnected, the addition/subtraction circuit 12 is I b c-
Perform the calculation of Ib'c.

The absolute value of this output is detected by the absolute value detection circuit 13, and this is multiplied by 2 and output.

Therefore, the output directly LtK I Ibc-Ib'c
becomes.

This value is nothing but the vector difference multiplied by the change in line current.

The output of circuit 4.5.13 is given to addition/subtraction circuit 14,
When a wire break occurs, the following calculation is performed.

(l Ia l-I Ia'l) -K I Ibc
-Ib'c This calculation result is given to the zero level detector 10 and compared with the zero value, but in the case of Table 5, K
If the value of is set to a value lζ larger than 0.73, when the above-mentioned calculation result becomes larger than zero, it becomes clear that the a-phase is disconnected.

FIG. 6 shows the configuration according to Table 6.

In this case, it is necessary to obtain both the change in phase current and the change in line current as vector differences.

Therefore, the AC amount storage circuit 11 shown in FIG. Using the addition/subtraction circuit 12 and the absolute value detection circuit 13, the change in line current Ibc is multiplied by the vector difference, that is, KI Ibc - Ib'c l is calculated and similarly applied to terminal 1. The phase current of the a-phase is applied to the alternating current amount storage circuit 21 to store the phase current of the a-phase during normal operation, and its output and each instantaneous phase current are inputted to the addition/subtraction circuit 22.

Therefore, when the a phase is disconnected, the addition/subtraction circuit 22
Perform the calculation of a'.

The absolute value of this calculation output is detected by the absolute value detection circuit 23.

The output of the above-mentioned two paper pair value output circuits 13 and 23 is the addition/subtraction circuit 2.
4, and when a disconnection occurs, the following equation is calculated.

Ia-Ia'l -K I Ibc -Ib'c This calculation result is given to the zero level detector 10 and compared with the zero value, but in the case of Table 6, the value of K is set to a value larger than 1. If this is set, when the above calculation result becomes greater than zero, it becomes clear that the a-phase is disconnected.

Although it has been explained that the zero level detector 10 is used to compare with the zero value, it is not necessary to be particular about the zero value, but to appropriately dull the sensitivity and compare with an appropriate value other than the zero value in consideration of practical performance. You can also do it.

The above explanations have all been about the detection of disconnection in the a phase, but it is also possible to detect the disconnection in the b and c phases by using the same configuration as shown in Figures 4 to 6. Not even.

For example, to detect a disconnection in the b-phase, the b-phase current may be applied to terminal 1, and the a-phase and C-phase currents may be applied to terminals 2 and 3.

Further, for each circuit shown in the drawings, well-known circuits other than those shown in the drawings can be used, and furthermore, it is also possible to use a microcomputer or the like.

As detailed above, according to the present invention, it becomes possible to detect a wire breakage at a substation simply by detecting the phase current and line current, instead of detecting a wire breakage at each end of a branch line as in the conventional method. There is no need to install any equipment, and as a result, it becomes possible to detect wire breaks easily and inexpensively, and the ratio of changes in phase current and line current is significantly different between wire breaks and non-wire breaks. This has the effect of making the discrimination extremely easy.

[Brief explanation of drawings]

1 to 3 are circuit diagrams showing states when the three-phase line is broken and not broken, and FIGS. 4 to 6 are block diagrams showing embodiments of the present invention. 1.2,3... Phase current input terminal, 4,1...
... Absolute value storage circuit, 5, 8 ... Absolute value detection circuit, 6 ... Line current detection circuit, IL21.
..., AC amount memory circuit, 13.23...
Absolute value detection circuit, 14°12.24...Addition/subtraction circuit, 10...Zero level detector.

Claims (1)

[Claims] 1. When the phase current of one phase that is subject to disconnection detection in a three-phase distribution line changes, the ratio of the change in phase current before and after that change to the change in line current between the other two phases at that time. A disconnection detection device for a three-phase distribution line, comprising means for determining the ratio, and detecting disconnection of the one phase when the ratio exceeds a certain value.