JPH0627761B2 - Electric power cable fault detection method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power cable fault section detection method for detecting a ground fault section in a long-distance power transmission system having a cross-bond connection.

<Prior Art and Problems> In parallel three-phase power cables, a metal sheath separated by an insulation joint is connected to a metal sheath of an adjacent power cable by a cross bond wire. In a long-distance power transmission system having a bond wire, a ground fault of a cable occurring between joints is detected.

As a conventional method of detecting an accident section, for example, a current transformer is installed on a cross bond wire, and a light emitting element is connected to the secondary side of this current transformer so as to have opposite polarities between the current transformers in the sections adjacent to each other. It is proposed that the output of the led light emitting element is photoelectrically converted, and a logical product of two electric signals provided from the light emitting elements in adjacent sections is obtained by an AND circuit.

The detection method as described above is a method of comparing the currents of the cross bond wires applied to the insulation joint, and therefore only the section between the insulation joint and the insulation joint can be specified, and the insulation joint-ground joint (normally There is a drawback in that it is impossible to identify and identify where the accident between the joint) and the insulation joint has occurred during this time.

In order to eliminate such drawbacks, a current sensor is attached to the grounding wire of the grounding joint in addition to the cross bond wire of the insulating joint, and the ground fault current is measured at the grounding joint as well. The present applicant has already proposed a detection method that enables discrimination of an accident section even between joints.

Such a detection method can be applied to both an existing line and a new line because it is sufficient to attach a current sensor to the cross bond line and the ground line. In addition, since the line body does not need to be processed, it is cheap and easy. Although it has the advantage that it can be implemented on all cross-bond wires and ground wires, it requires a large number of current sensors and discriminators, which is very expensive to implement. There is a problem.

The present invention has been made to solve the above problems, and it is possible to identify and identify an accident in any section between an insulation joint, a ground joint, and an insulation joint by reducing the use of a current sensor and a discriminator. It is an object of the present invention to provide a method for detecting a faulty section of a power cable, which can identify the faulty section without needing to process the main body of the line regardless of existing or new installation.

<Means for Solving the Problems> In order to solve the above-mentioned problems, the present invention comprises repeating combinations of a ground joint, an insulation joint, and an insulation joint for each phase. A power transmission line including a so-called cross-bonded ground, in which metal sheaths of phases are connected by a cross-bond line, and the ground wire of the ground joint has a large and / or small fault current flowing in the ground line. Attaching a sensor that detects the phase difference, including the accident point inside, adjacent to each other 2
Comparing the magnitude of the fault current and / or the phase difference of the fault current of the current flowing through each of the three ground lines of the pair of ground points, cut all ground points that are almost the same and cut two ground lines. Find the ground wire whose phase is different from that of the other wire by about 180 °, and that the current of one wire is about twice the current of the other two wires, and connect two pairs of ground wires connected to this ground wire that are adjacent to each other. The phases of the joints are made clear, and the accident phase is discriminated by combining with the detection of the accident phases separately performed.

<Operation> A so-called cross-bonded power cable line in which metal sheaths of parallel power cables are connected by cross-bond wires at both ends of the insulation part of each insulation joint. Of the ground fault consisting of the ground joints (normal joints) of each of the three ground lines, the magnitude of the fault current of the current flowing through each of the three ground lines and / or the phase difference of the fault currents is detected by the sensor, Approximately twice the size of the other two ground lines, approximately 180 in phase
゜ By finding one different grounding wire, find the fault current outflow grounding joint at both grounding points, and combine it with the fault phase detected by using a separate current sensor, etc. It can be clearly specified even between joints and between insulated joints.

<Example> An example of the present invention will be described below with reference to the accompanying drawings.

First, a power transmission line including a cross bond connection will be described.

As shown in Fig. 1, in a long-distance power line, three parallel lines are used.
The power cables A, B and C of the phases are connected to the metal sheath of the adjacent power cable by the metal sheath separated by the insulating joint IJ by three cross bond wires 11, 12 and 13, and the sheath current flowing through each metal sheath. Are transferred one by one to the adjacent phase by these cross bond lines. A grounding wire 14 is connected to each grounding joint NJ, in which the metal sheath is grounded in all phases, and
The metal sheath current of each phase is shared through the ground.

A sensor 15 for detecting a ground fault accident current is attached to each ground wire 14 of the ground joint NJ as shown in FIG. 3, and the sensor 15 detects the magnitude and / or the phase difference of the fault current to detect an accident. The phase of the ground joint NJ from which the current flows is clarified, and the accident section can be detected and discriminated by the combination with the separately detected accident phase.

Sensor 15 for detecting fault current attached to the above ground wire 14
May be any as long as it detects the magnitude of the fault current flowing through the ground line 14 and / or the phase difference of the fault current. For example, a temperature sensor may be used, or CT for each ground line 14,
An optical sensor, a magnetic field sensor (Hall element, SMD element, etc.) may be attached, or two or three ground lines 14 may be combined together for detection by, for example, finding a zero-phase current.

However, as shown in FIG. 4, it is preferable that the ground wire 14 is as short as possible and connected so that the ground joints NJ of the three phases A, B and C are evenly connected.

Also, to connect two or three ground wires 14 together,
As shown in the figure, there is a method of combining the phases (a) to (c), and in some cases, a method of further combining (d).
~ Find the ground joint NJ with different phase in (c),
In (d), it is effective to detect whether or not the accident at each NJ point is on both sides.

In order to discriminate the accident phase to be combined with the detection of the NJ point by the sensor 15 '(for example, CT) attached to the ground wire 14, generally, a CT or an optical magnetic field sensor for conductor current measurement is attached to both ends of the line and each phase is attached. Since it is customary to measure the conductor current every time, it can be easily discriminated by an abnormal increase in the conductor current in the fault phase.

Alternatively, the sound 2 phase excluding the 3 phase AC fault phase produces an abnormally high fault voltage at the power transmission end compared to the normal voltage, and the fault phase shows an abnormally low voltage, so that the fault phase can be easily identified. Is.

The fault section detection method of the present invention is as described above, and when a ground fault occurs in a section where the power cables A to C are arranged in parallel, a ground fault current flowing through the ground line 14 at two adjacent ground points. Sensor 15 'to compare the magnitude of the fault current of the currents flowing through the three ground lines and / or the phase difference of the fault currents, and cut all ground points that are almost the same, As shown by the one-dot chain line in the figure, the two ground wires of the ground joint NJ of different phase and the other one
Find a grounding wire that has a phase difference of about 180 ° in one book, and one that has about twice the current as the other two.

This occurs at two adjacent ground points including the fault point inside, and the total fault current (current flowing from the conductor to the metal sheath)
Is 2 Io, for example, in the case of FIG. 1 in which an accident occurs between IJ and IJ, the metal sheath return impedance in both directions seen from the accident point is almost equal in the long distance line.
One by one in both directions, and after passing through the metal sheath as indicated by the alternate long and short dash line, the ground joint (NJ-1-C) and (NJ +
If an accident current of about 2/3 Io flows out to the ground wire of 1-B) and an accident occurs between NJ and IJ in Fig. 2, the accident current also flows as the one-dot chain line and then (NJ -1-A)
A fault current of about 2/3 Io flows out to the ground line of (NJ + 2-C), and a fault current of about 1/3 Io flows into the ground line of each of the other ground points. There will be one ground wire that produces fault currents that differ in phase by approximately 180 °.

When two ground wires from which this fault current flows are found, the fault current flows in the cable sheath between NJ-IJ-IJ-NJ only in each phase 1 section due to the combination, so One section of each phase will be specified.

Therefore, separately from this, if the fault phases are separately specified at both ends of the line, the passing section of the fault current included in both of them can be specified as the fault section.

Note that the return current at the time of an accident flows through the metal sheath (usually an aluminum sheath) of the power cable and the ground, but the cross section of the metal sheath of the normal cable is very large. Since the three-phase metal sheaths are all return conductors, the return impedance to the fault current is much smaller with the metal sheath of the cable than with the assumed earth return circuit, so the return current during most faults is aluminum. Return through the sheath.

Therefore, since the fault current return path impedances of the phases A, B, and C outside the two ground points adjacent to each other including the fault point are substantially equal, outside of this point, the fault current 1/3 Io is almost equal. Will return.

This is more noticeable in cable lines that are twisted, and is usually twisted in long-distance lines.

Further, it will be described with reference to the drawings.

By checking the ground fault current flowing between the ground points of two adjacent ground points and finding the NJ where the fault current flows out, it is found that the ground fault has occurred somewhere in the dashed line in Fig. 1. Become.

In the figure, it is between the A-phase insulating joints IJ-1 to IJ + 1.

However, in the portion indicated by the alternate long and short dash line in FIG. 1, no matter where the ground fault occurs, different ground fault currents flow in the ground lines of adjacent ground points, and the same phenomenon appears.

The time-corruption fault current shown by the alternate long and short dash line in FIG. 1 always passes through the A, B, and C phases one by one, and this relationship is exactly the same for all faults.

Therefore, by finding the fault current outflow grounding joint or the grounding wire at both grounding points and combining it with the ground fault phase detected separately, the faulty section is between the grounding joint NJ and the insulating joint IJ and between the insulating joints IJ and IJ. It can be clearly identified everywhere.

In addition, in the bridge part of the power cable, accident current flows out to the bridge through the ground joint and may harm cars and people,
In order to prevent damage to the bridge itself, in most cases, the ground joint will not be grounded by connecting it to the bridge, but simply three ground joints will be connected to each other by ground wires. In this case, , There is no return circuit corresponding to the earth return route, so as shown in Fig. 2,
The accident current of 1/3 Io comes to flow evenly from both contacts across the accident section, and the detection method of the present invention becomes effective.

When a ground fault occurs at a portion near both ends of the line, the ground fault current 2Io is equally divided into two and is not divided in both directions, but flows in a direction closer to the end. become.

Thus, although the imbalance occurs in the fault currents flowing in both directions, the magnitude relation of the fault currents flowing in the ground line at the ground point or the relation of the phase difference does not change at all, and therefore the process intended by the present application can be carried out as it is. Is.

In addition, in order to identify the section with higher accuracy, in addition to the two closest ground points including the fault point, also compare the fault currents of the ground lines of two pairs of ground points adjacent to the outside of the section. It is effective if it is done.

That is, if the fault currents are compared by using one set of the ground lines at the four adjacent ground points, the accuracy will be higher than in the case of two locations, which is effective.

Further, although the metal sheath is described in the present embodiment, it goes without saying that all the cables adopting the cross bond system are possible.

<Effects of the Invention> As described above, according to the present invention, the sensor is attached to the ground wire of the ground joint in the parallel current cables, and the fault currents flowing through the ground wires of the two adjacent ground points are compared, Detect the ground wire from which the accident current flows out, clarify the phase of the ground joint connected to this ground wire, and combine the combination of these two sets of the ground joint for the fault current outflow and the detected accident phase separately. By
Since it is designed to detect the accident section, it can be detected simply by mounting the sensor on the ground wire of the ground fault of the power cable,
It is possible to reduce the number of sensors used and improve economic efficiency, reliability, and maintainability.

In addition, even if a ground fault accident occurs between the ground joint and the insulation joint by mounting the sensor on the ground line, the accident point can always be identified between the ground joint and the insulation joint, so the accident point is always between the two joints that sandwich the accident point. Therefore, it is possible to detect an accident zone with extremely high accuracy.

Furthermore, since it is only necessary to set the sensor to the ground wire, there is no need to process the power cable body,
It is possible to economically introduce ground fault detection regardless of new construction.

[Brief description of drawings]

FIG. 1 is an explanatory diagram in the case where a ground fault accident occurs between the insulation joints of the long-distance power transmission system, and FIG. 2 is an explanatory diagram in the case where a ground fault accident similarly occurs between the insulation joint and the ground joint. FIG. 4 is an explanatory view showing how the sensor is attached to the ground wire, and FIGS. 4 and 5 are explanatory views showing a combination of the ground wire and the sensor. 11,12,13 …… Cross bond wire 14 …… Ground wire, 15 …… Sensor NJ …… Grounding joint (normal joint) IJ …… Insulation joint

Claims (2)

[Claims] 1. A power transmission line including a three-phase cross-bond connection, wherein a sensor for detecting a magnitude of a fault current flowing in the ground line and / or a phase difference of the fault current is attached to the ground line of the ground joint. The magnitude of the fault current and / or the phase difference of the fault current flowing through each of the three ground lines of two adjacent ground points including the fault point are compared, and the contact points are almost the same and small. Cut all points, 2
The phase of one ground wire differs from that of the other one by about 180 °, and
The book finds a grounding wire that has a current that is about twice as large as the other two by comparing the currents and / or the phases, and reveals the phase of the grounding joint connected to the two adjacent grounding wires. , A method of detecting an accident section of a power cable, characterized in that an accident section is discriminated by combining it with detection of an accident phase. 2. The method for detecting an accident section of a power cable according to claim 1, wherein the grounding wire of the grounding joint is a connecting wire of the grounding joint of each phase of the power transmission line on a bridge or the like.