JPH0424455Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device for detecting zero-sequence current that occurs when a grounding fault occurs on a power transmission line.

[Prior art and its problems]

Conventionally, when a grounding fault occurs in a power system, current transformers and zero-sequence current transformers are generally used to detect the zero-sequence current, but these devices are used for meters and protective relays, and the minimum necessary It is only provided in the following locations.

The present applicant previously filed an application for the invention of a zero-sequence current detection device with the aim of easily detecting zero-sequence current in the middle of a power transmission line (Utility Application No. 119318-1983).
No., filed on August 11, 1981).

The gist of this is that ``a long, slender iron core for forming a magnetic path is placed in a power line within a power line tower that maintains a sufficiently safe insulating distance from the pressurized voltage of each phase power line of a three-phase AC power transmission line. 1. A zero-sequence current detection device, characterized in that the iron core is arranged at right angles, and a coil for detecting unbalance of each phase current of a power transmission line is arranged in the iron core.

In the case of a two-circuit power transmission line, this device has the iron core and coil that make up the magnetic sensor installed vertically on the center line of the tower, so the output of the magnetic sensor is , there is a difference between the electromotive force caused by the line 1 current and the electromotive force caused by the line 2 current, and the application of the detection device is limited to the detection of zero-sequence current when lines 1 and 2 are operated as two radial circuits. It was hot.

[Purpose of invention]

The present invention aims to solve such conventional problems and provide a zero-sequence current detector that can be applied not only to two radial circuits but also to two parallel transmission lines.

[Structure of the idea]

The zero-phase current detector of the present invention uses two magnetic sensors with coils arranged in the center of an elongated iron core to form a magnetic path that detects the magnetic field generated by the current flowing through the power transmission line. The magnetic sensor should be placed above and below the outside of the polygon obtained by connecting the positions of the power lines of each phase of the electric wire, at right angles to the power line, and so that the longitudinal direction of the magnetic sensor is horizontal, and sufficiently withstand the applied voltage of each phase power line. The length of the iron core, cross-sectional area, number of turns of the coil, etc. should be adjusted so that the combined output voltage of the differential connection of the two magnetic sensors is always zero or very small when installed at intervals, and due to electromagnetic induction from the power line. The constants of the magnetic sensor and its position are set.

[Effect]

In this invention, two horizontal magnetic sensors are arranged above and below the outside of the polygon connecting the positions of the power lines of each phase.
Obtain the difference between the outputs of the magnetic sensors. Inside the polygon, the sensitivities of the magnetic sensors for each power line cannot be made equal, and zero-sequence current cannot be detected. Therefore, a horizontal magnetic sensor is placed outside the polygon, but since one sensor cannot equalize the sensitivity for each power line, two sensors are placed one above the other and differentially connected to obtain a composite output voltage. This makes it possible to detect zero-sequence current not only in two radial circuits, but also when lines 1 and 2 are operated as two parallel circuits.

In addition, the above idea had the advantage of suppressing the generation of induced electromotive force in the coil due to the current flowing through the overhead ground wire, since the magnetic sensor was arranged so that the longitudinal direction of the magnetic sensor was directed toward the overhead ground wire. In this invention, the iron core that makes up the magnetic sensor is placed horizontally, so the current flowing through the overhead ground wire will have a direct effect.
By adjusting the length, cross-sectional area, number of coil turns, etc. of the iron cores of the plurality of magnetic sensors, the influence can be reduced to a practically acceptable level.

〔Example〕

Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

Although FIG. 1 shows an example in which two magnetic sensors (hereinafter simply referred to as sensors) are arranged on a standard two-line power transmission line tower, the case of one-line implementation will be described first.

A, B, and C are three-phase alternating current A-phase, B-phase, and C-phase electric wires, and G is an overhead ground wire. Sensors K ₁ and K ₂ , which have detection coils u and v wound around the center of elongated iron cores D 1 and D ₂ , _respectively , are installed so that their longitudinal directions are perpendicular to both the power line and the center line of the steel tower. . Sensors K ₁ and K ₂ are placed outside the polygon (indicated by dotted lines in the figure) connecting the power lines of each phase.
Sensor K ₁ is placed closer to the overhead ground wire than the height of the A phase wire.
Sensor K ₂ is placed closer to the ground than the height of the C-phase wire and on the center line of the tower, so that the components of the electromotive force generated in the sensor by electromagnetic induction from the three-phase power line current due to each phase are approximately equal. The terminals of both sensors are connected as a differential connection so that the respective electromotive forces are added.

The positions of sensors K 1 and K 2 and the coils are adjusted so that the combined value of the outputs of sensors K ₁ and K ₂ is zero or very small when the A _- phase, B-phase, and C _-phase currents are normally balanced. Adjust the number of turns.

When an accident occurs on a power transmission line and imbalance occurs in each phase current, the combined electromotive force of sensors K ₂ and K ₂ proportional to the zero-sequence current can be extracted as an output voltage, and the zero-sequence current can be detected.

In the case of 2-line implementation, A, B, and C are connected to A of line 1.
phase, B phase, and C phase, and R, S, and T are R of line 2.
In general, in a standard two-line steel tower, the wire arrangement of line 1 and line 2 is symmetrical, so the balanced currents of phase A, B, and C of line 1 are assumed. Therefore, when the combined output of sensors K ₁ and K ₂ is adjusted to zero or very small, the R phase and S phase of line 2
Due to the balanced current of the phase and T phase, the sensors K ₁ and K _{2
The combined} output induced by
It is the same whether it is adjusted from each phase current of Line or Line 2 or from each phase current of Line 1 and Line 2.

In the case of the two radial circuits in Figure 2, if a fault occurs in either line 1 or line 2, a zero-sequence current (arrow) flows from the zero-sequence power supply at the transmission end 10 to the point of fault, but between the faulty line and the healthy line. Since there is no mutual influence with the line, the output power of the sensors K ₁ and K ₂ will be the same as in the case of the single line implementation described above. In the figure, 20 and 30 are the power receiving end, P is the fault point, ○ is the state of the circuit breaker "on",
〓〓〓 represents the “off” state of the circuit breaker.

In the case of two parallel lines in Figure 3, the zero-sequence current flows in a divided manner from the zero-sequence power source at the transmission end 10 to the faulty line and the healthy line, and the zero-sequence current of both lines flows from the fault point to the zero-sequence power source side. The combined output of the sensors K ₁ and K ₂ installed in the section where the phase currents are in the same direction is combined as the sum of the electromotive forces of lines 1 and 2, so an output voltage proportional to the zero-sequence current is generated.

On the other hand, in areas where the zero-sequence currents of the faulty line and the healthy line are the same but opposite in direction, such as on the load side from the fault point, the output voltages of sensors K ₁ and K ₂ are zero or very small. . In the figure, 20 indicates the power receiving end, P indicates the fault point, and ○ indicates the "on" state of the circuit breaker.

In this way, even if the power transmission line is operated with two radial circuits or two parallel circuits, it is possible to detect the zero-sequence current of the first line and the second line.

Regarding the influence of overhead ground wires, power lines A phase and B
An induced current flows in the overhead ground wire due to induction from the phase, C phase, R phase, S phase, and T phase, but if there is no fault on the transmission line, the current value is generally small and the sensor The effect on the output voltage is negligible.
If an accident occurs, the ground fault current will be shunted to the overhead ground wire, and the induced electromotive force will be added to the electromotive force induced by the fault current in the power line, which may interfere with the detection of zero-sequence current. will occur.

In this invention, both sensors K ₁ and K ₂ are installed below the overhead ground wire, and since sensors K ₁ and K ₂ are connected differentially, the induced electromotive force due to the overhead ground wire current is canceled out. . Therefore, by adjusting the number of turns of the sensor's coil, the length of the iron core, the cross-sectional area, etc., the influence from the overhead ground wire was significantly reduced, so that there was no practical problem in detecting zero-sequence current. .

FIG. 4 is an example in which two magnetic sensors are used and applied to a single-line steel tower. In the same figure, A, B,
C is an electric wire, G is an overhead ground wire, K ₁ and K ₂ are magnetic sensors, D ₁ and D ₂ forming the sensor are iron cores, and u and v are coils.

[Effect of idea]

As described above, according to the present invention, it is possible to safely and economically easily detect the zero-sequence current of a power transmission line, not only for a radial transmission line but also for a parallel two-circuit system. It is.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an embodiment of the detector according to the present invention in the case of a two-line steel tower, Fig. 2 is an explanatory diagram showing the zero-sequence current distribution of two radial lines, and Fig. 3 is an explanatory diagram showing the distribution of zero-sequence current of two radial lines.
An explanatory diagram showing the distribution of zero-sequence current in the line, Figure 4 is 1
FIG. 3 is an explanatory diagram showing the arrangement of detectors in the case of a triangular line arrangement. A, B, C, R, S, T...electric wire, G...overhead ground wire, _K1 , _K2 ...magnetic sensor, _D1 , _D2 ...iron core, u, v...coil, 10... ...Transmission end, 20,
30...Power receiving end, P...Fault point.

Claims (1)

[Claims for Utility Model Registration] 1. A three-phase AC power transmission line equipped with two magnetic sensors each having a coil arranged in the center of a long and thin iron core to form a magnetic path for detecting the magnetic field generated by the current flowing through the power transmission line. space above and below the outside of the polygon obtained by connecting the positions of the power lines of each phase, at right angles to the power line, so that the longitudinal direction of the magnetic sensor is horizontal, and at least enough to withstand the pressurized voltage of each phase power line. The length of the iron core, cross-sectional area, number of turns of the coil, etc. are adjusted so that the combined output voltage of the differential connection of the two magnetic sensors due to electromagnetic induction from the power line is always zero or very small. A zero-sequence current detector characterized in that a sensor constant and its position are set. 2. In the case of an even-numbered power transmission line where the wire arrangement is symmetrical, the zero-sequence current detection according to claim 1 of the utility model registration claim is characterized in that the magnetic sensor is arranged on the center line of the symmetrical wires. vessel.