JPH028530B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting zero-sequence current in a power system, particularly in a power transmission line.

Conventionally, when a fault occurs in a power system, the method of detecting it is generally to use a current transformer or zero-sequence current transformer to detect the zero-sequence current, but these devices cannot handle high voltages. The higher the dielectric strength becomes, and the larger the current capacity, the larger the size, so that they are installed only in the minimum number of places necessary for measuring instruments and protective relays.

However, if zero-sequence current can be easily detected even in the middle of a power transmission line, if a fault occurs on a power transmission line, it will be useful in determining the fault section, and it will be extremely effective in recovering from a power transmission line fault.

In order to meet the above-mentioned needs, the present inventor previously filed an application for the invention of a zero-sequence current detection method with the aim of easily detecting zero-sequence current in the middle of a power transmission line (Japanese Patent Application No. 173,689/1989). No., filed on December 8, 1980). The gist of this is that ``a long and thin iron core for forming a magnetic path is arranged at right angles to the power lines of a three-phase AC power transmission line, and at intervals between each power line that are sufficient to withstand the pressurized voltage of the power lines. , the iron core is provided with a coil for each phase, and the length and disconnection of the iron core are adjusted so that the combination of the electromotive force generated in the coil by electromagnetic induction from the power line becomes zero or minimum when the current in each phase of the power line is equal. Zero-sequence current detects zero-sequence current by setting magnetic constants such as area, position, and number of coil turns, and detecting zero-sequence current by the composite electromotive force of the coil that is induced in proportion to zero-sequence current when it occurs in a power transmission line. Detection method. However, since this method requires three coils to be provided for each phase of a three-phase AC power transmission line, it is difficult to determine each magnetic constant, especially the position-related parameters, and it is difficult to move one coil. The position of the coil and the other two coils also had to be moved, and there was a problem in that the adjustment work required time and skill.

The present invention is an improvement over the previous invention to enable equal zero-sequence current detection using two coils, thereby significantly facilitating the adjustment work.

The present invention will be explained below.

Figures 1-1, 1-2, and 1-3 are explanatory diagrams showing the principle of the present invention, and each is an example of a standard transmission line tower with two circuits. The case of a line installation pole is shown. In the figure, A, B, and C are three-phase alternating current A, B, and C phase electric wires, G is an overhead ground wire, and Figure 1-1 is a front view seen in the length direction of the power transmission line. Figures 1-2 are side views seen from the side.
D ₁ and D ₂ are long and thin iron cores wound with coils m and n, respectively, which maintain a sufficiently safe insulation distance from wires A, B, and C, and the height of coil m is close to phase A, then close to phase B. , the height of the coil n is close to the C phase, then the B phase, and the farthest from the A phase, and the electric wires A, It is installed so that it is perpendicular to B, C and the overhead ground wire G, and its direction is toward the overhead ground wire. coil m, n
As shown in Fig. 1-3, the coils are connected so that a composite value E〓m+E〓n of the electromotive forces E〓m and E〓n generated in each coil is obtained. (Note that E〓 is a vector quantity, and a dot is placed above it to distinguish it from the scalar quantity E. The same applies hereinafter.) Now, when three-phase alternating current flows through electric wires A, B, and C, the current causes each Magnetic field lines a centered around the electric wire,
b and c are generated and pass through the coils m and n using the iron cores D ₁ and D ₂ as magnetic paths, so that electromagnetic induced electromotive force is generated in the coils. Now, due to the A phase current, coils m and n
The electromotive force generated in the coils m and n due to the B-phase current is E〓mb, E〓nb, and the electromotive force generated in the coil due to the C-phase current is
If E〓mc, E〓nc, the combined electromotive force is: A phase component E〓 _A = E〓ma + E〓na, B phase component E〓 _B = E〓mb + E〓nb, C phase component E〓 _C = E〓 mc＋E〓nc.

The electromotive force increases as the current in the wire increases. In addition, the closer the distance between the coil and the wire is, the larger the value becomes, and the closer the angle between the magnetic axis, that is, the line that passes through the coil in the longitudinal direction of the iron core, and the line that connects the wire and the coil becomes a right angle, the larger the value becomes. , depending on the position of the coil relative to the wire. In addition, it varies depending on the length of the iron core, cross-sectional area, number of turns of the coil, etc., so by adjusting these, the overall Make sure that the value of the combined electromotive force E〓 _A + E〓 _B + E〓 _C becomes zero or very small. By the way, since E〓 _A + E〓 _B + E〓 _C = E〓m + E〓n, in order for E〓 _A + E〓 _B + E〓 _C = 0, that is, E〓m = −E〓n to hold, the As shown in Figure 2, Em=En, |θm
It is sufficient that |+|θn|=180°. In addition, θm, θn
are the respective phase angles of the voltages induced in the coils m and n when taken with respect to the current phase.

However, if a fault occurs in the power transmission line and imbalance occurs in each phase current, imbalance will also occur in E〓 _A , E〓 _B , and E〓 _C.
The composite electromotive force proportional to the zero-sequence current of the transmission line is the first -
The zero-sequence current can be detected at the output of the composite circuit shown in Figure 3. Although FIGS. 1-3 show an example in which two coils are connected in series, they may also be connected in parallel for detection.

The above is a case without an overhead ground wire, but generally there is an overhead ground wire G as shown in Figure 1-1, and A
An induced current flows in the overhead ground wire due to induction from the phase, B phase, and C phase, and if there is no fault on the transmission line, the current value is generally small, but if there is a fault, the value becomes large. In addition, the current value increases due to the addition of ground fault current, and the induced electromotive force generated by the magnetic lines of force g ₁ and g ₂ passing through the coils m and n is the above E〓 _A , E〓 _B , E〓 _C , and a composite output that is not proportional to the zero-sequence current of the power transmission line appears at the output of the composite circuit shown in Fig. 1-3, resulting in an error in zero-sequence current detection. The current flowing through the overhead ground wire is not constant due to changes in the grounding resistance of the steel tower due to weather, changes due to distance from the electrical station at both ends of the transmission line, and other reasons, so the above error value also changes.
This makes zero-sequence current detection increasingly difficult.

In the present invention, the longitudinal direction of the coil and the iron core are directed toward the overhead ground wire, and the angle between the two is at right angles, so that the magnetic lines of force generated by the current in the overhead ground wire do not penetrate the coil. , it is possible to detect the zero-sequence current of the power transmission line without being affected by the current of the overhead ground wire.

In addition to the method in which the iron core is provided separately between each phase as described above, it is also possible to have an integral structure common to each phase as shown in FIG.

The above is a case of a standard two-line steel tower with a single line installed on a pole, but FIG. 3 shows a case where a two-line line is installed on a pole.
A, B, C are wires A phase, B phase, C phase of line 1,
R, S, and T represent the R phase, S phase, and T phase of the wires of Line 2, respectively. Generally, in a standard steel tower with two circuits, the wire arrangement of lines 1 and 2 is symmetrical, so the iron core D and coils m and n are placed on the center line of lines 1 and 2, and the overhead ground wire G , and at right angles to the electric wires A, B, C, R, S, and T and the overhead ground wire G.
The combined electromotive force induced in coils m and n by the balanced currents of phase, B phase, and C phase is A phase component E〓 _A , B phase component E〓 _B , C phase component E〓 _C is the height of iron core D , by adjusting the length, cross-sectional area, position of coils m and n, and number of turns, and reducing the total combined electromotive force E〓 _A + E〓 _B + E〓 _C for three phases to zero or very small, an accident on power transmission line No. 1 can be avoided. When , an electromotive force proportional to the zero-sequence current is generated, and zero-sequence current detection is possible.

Considering the influence of R phase, S phase, and T phase of line 2 in this case, since lines 1 and 2 are symmetrical as mentioned above, the balanced current of line 2 R phase, S phase, and T phase Therefore, the composite electromotive force induced in coils m and n is R phase component E〓 _R , S phase component E〓 _S , T phase component E〓 _T by line 2 of the composite electromotive force E〓 _R + E〓 _S + E〓 _T When the total combined electromotive force E〓 _A + E〓 _B + E〓 _C due to Line 1 is zero or minute, it automatically becomes zero or minute and does not occur.
That is, there is no mutual influence between line 1 and line 2, and even if an accident occurs in line 1 or line 2, the zero-sequence current in line 1 or line 2 can be detected.

If iron core D and coils m and n are not on the center line of lines 1 and 2, the total combined electromotive force E〓 _A + E〓 _B + E〓 _C for the above three phases of line 1 is zero or very small. Even if _the iron core and _coil are _adjusted so that is also large, causing a phenomenon as if a zero-sequence current is occurring, making it unsuitable for detecting a zero-sequence current.

Next, the magnitude of the current flowing through the overhead ground wire in the event of a transmission line accident varies depending on the distance from the electrical stations at both ends of the transmission line to the accident point, the value of the grounding resistance of the steel tower, etc. By the way, the electromotive force induced in coils m and n is
In addition to being induced by each phase current of the electric wire, it is also induced by the current flowing through the overhead ground wire, so an electromotive force is generated that is not proportional to the zero-sequence current, which is inconvenient for zero-sequence current detection. In order to eliminate this drawback, the present invention aims to orient the longitudinal direction of the iron core in the direction of the overhead ground wire, so that the lines of magnetic force generated by the current flowing through the overhead ground wire do not pass through the coil through the iron core, thereby causing the magnetic field lines induced in the coil to As already mentioned, it is designed not to generate electricity.

Figures 1-1, 1-2, and 3 show the case of one overhead ground wire. In the case of two overhead ground lines, the fourth
As shown in the figure, the overhead ground wires are generally placed in symmetrical positions at the top of the tower, so by placing the iron core D on the center line, the overhead ground wires will be generated in the coils m and n.
The electromotive force due to the current flowing through _G1 and the electromotive force due to the current flowing through the overhead ground wire _G2 are opposite in direction and cancel each other out, so regardless of the magnitude of the current flowing through the overhead ground wire,
Always zero.

In the case of three overhead ground wires, as shown in Figure 5, generally one overhead ground wire G ₀ is placed in the center of the transmission line, and the other two G ₁ ,
Since G ₂ is placed symmetrically across it, by installing the iron core D and the transmission lines m and n on the center line of the transmission line, coils m and n are connected to the overhead for the same reason as above. No induced electromotive force is generated due to the current flowing through the ground wires G ₀ , G ₁ , and G ₂ .

The above description has been made using the case of a standard two-line steel tower as an example, but it is also applicable to the case of a multi-line steel tower or a single-line steel tower with a different three-phase power line arrangement structure.

An example of application to a multi-line tower is shown in Figure 6. As an example of application to a single-line tower, Figure 7 shows a case where there is an overhead ground wire for power transmission lines arranged in a triangular arrangement, and Figure 7 shows a case where there is no overhead ground wire. Figure 8 shows the case where there is no overhead ground wire for horizontally arranged power transmission lines, and Figure 9 shows the case where there is no overhead ground wire. These effects are similar to those described for the example above.

Among these application examples, in the case of FIG. 7, the iron core and coil are arranged so that the longitudinal direction of the iron core is directed toward the overhead ground wire and is symmetrical from the center line of the tower. As shown in Figure 1-3, the coils m and n are such that the composite value of the electromotive forces E〓m and E〓n generated in each coil is obtained as the vector difference E〓m−E〓n only in this case. Connect so that it can be connected.

The combined electromotive force is: A phase component E〓 _A = E〓ma−E〓na B phase component E〓 _B = E〓mb−E〓nb C phase component E〓 _C = E〓mc−E〓nc, and the difference is It is expressed in the form of

In the non-fault power transmission state, the total combined electromotive force E〓 _A +
In order to make the value of E〓 _B + E〓 _C zero, E〓m−E〓n = 0, and from this the relationship between vector magnitude and phase as shown in Figure 2 is derived.

As described above, the zero-sequence current detection method of the present invention uses an elongated iron core for forming a magnetic path.
The core is placed perpendicular to the power line of the three-phase AC power line, and the distance between each power line is sufficient to withstand the pressurized voltage of the power line, and two coils are installed on the iron core, and the coils are connected by electromagnetic induction from the power line. The length, cross-sectional area, position, and
By setting the magnetic constants such as the number of turns of the coil, and when a zero-sequence current is generated in the power transmission line, the zero-sequence current is detected by the composite electromotive force of the coil that is induced in proportion to this. Compared to the method according to the previous invention in which individual cores and coils are installed, the adjustment work is significantly improved.

[Brief explanation of drawings]

Figure 1-1 is a front view explaining the principle of zero-sequence current detection according to the present invention, Figure 1-2 is a side view thereof, Figure 1-3 is an explanatory diagram showing an example of coil connection, and Figure 2 is Figure 3 is a vector diagram explaining the phase relationship of the electromotive force of each coil when ideal adjustment is made.
Figures 4 and 5 are front views showing examples of line installation on poles; Figures 4 and 5 are explanatory diagrams showing the arrangement of cores and coils when there are two and three overhead ground wires; Figure 6 is an illustration of the arrangement of the iron core and coils in the case of a four-line tower. An explanatory diagram showing the arrangement of the iron core and coils. Fig. 7 is an explanatory diagram showing the arrangement of the iron core and coils when there is only one overhead ground wire in a single-circuit triangular arrangement. Figs. It is an explanatory view showing arrangement of an iron core and a coil when there is no overhead ground wire of symmetrical wiring. D ₁ , D ₂ , D: iron core, m, n, m ₁ , n ₁ , m ₂ ,
n ₂ : Coil, G, G ₁ , G ₂ , G ₀ : Overhead ground wire, A,
B, C, R, S, T, A ₁ , A ₂ , B ₁ , B ₂ , C ₁ ,
C ₂ , R ₁ , R ₂ , S ₁ , S ₂ , T ₁ , T ₂ : Electric wire.

Claims (1)

[Claims] 1. An elongated iron core for forming a magnetic path,
The core is placed perpendicular to the power line of the three-phase AC power line, and the distance between each power line is sufficient to withstand the pressurized voltage of the power line, and two coils are installed on the iron core, and the coils are connected by electromagnetic induction from the power line. The length, cross-sectional area, position, and
A zero-sequence current is set by setting a magnetic constant such as the number of turns of the coil, and when a zero-sequence current is generated in a power transmission line, the zero-sequence current is detected by the composite electromotive force of the coil induced in proportion to the zero-sequence current. Phase current detection method. 2. In the case of an even-numbered power transmission line in which the wire arrangement is symmetrical, the zero-sequence current detection method according to claim 1, characterized in that the iron core is arranged on the center line of the symmetrical wire. 3. In the case of a power transmission line with one overhead ground wire,
Claim No. 1, characterized in that the iron core is arranged so that the longitudinal extension direction thereof points toward the overhead ground wire, thereby suppressing the generation of induced electromotive force in the coil due to the current flowing through the overhead ground wire. The zero-sequence current detection method according to item 1 or 2. 4. In the case of a power transmission line with two or more symmetrically arranged overhead ground wires, the overhead ground wire should be installed so that the longitudinal extension of the core coincides with the symmetrical center line of the overhead ground wire. The zero-sequence current detection method according to claim 1 or 2, characterized in that generation of induced electromotive force in the coil due to current flowing in the coil is suppressed.