JPS62255880A - Discriminating method for accident section of power cable - Google Patents

Abstract

PURPOSE:To execute decision with high reliability with simple constitution of a small number of detectors, by taking one piece out of three pieces of cross-bond currents, etc., in a phase opposite to other two pieces, and executing decision in accordance with the quantity of detected current. CONSTITUTION:As for parallel three-phase power cable A-C, a metallic sheath is connected to adjacent electrode sheaths by three pieces of cross-bond wires 11-13, a cross-bond current is detected in a phase opposite to the wire 12 by a sensor 14, and an accident current is detected by a detector. When a ground-fault accident is generated in the cable A between joints IJ, a current of 2I0 flows by I0 to both sides from an accident point X. Also, in a distant place from adjacent ground joints NJ, a current 1/3. I0 is generated in the wires 11-13, and in the wires 11-13 of both sides of the accident pint X, large unbalance is generated by a large current of the accident, and the accident point is decided through the detector. At the time of an accident between the joints NJ, IJ, as well, it is decided by a current 1/3. I0 and an unbalanced large current, and it is unnecessary to provide a detector on every cross-bond wire and discrimination is executed with high reliability with simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for detecting a fault section of a power cable for detecting a fault section of a power cable in a long-distance power transmission system having cross bonds.

<Prior art> In parallel power cables, insulation joins 1 to I
The metal sheath separated by a J is connected to the metal sheath of an adjacent power cable by a cross bond wire. Detection of ground faults in cables is being carried out.

Figure 7 shows the conventional fault section detection method for single-core power cables, in which the metal sheath separated by the insulation joint IJ of each power cable A-C is connected to the metal sheath of the adjacent power cable and the cross bond wire. A single core with no conductor serves as a return path for the fault current, and the current flowing through the metal sheath at the time of an accident is canceled as 0 PGW in the cross bond wire. Therefore, the fault current can be extracted by CT2.

Apply this to each insulation joint IJ section (each C
Depending on the direction of the current flowing through T2, the optical F/1's BSO sensor determines the phase and determines the accident zone.

<Problems to be Solved by the Invention> By the way, the method for detecting fault sections as described above is to take one CT for one cross bond line (=j) and calculate the phase of the signal and the relative Since the fault section is identified by comparing and determining the phase of the fault current, it is necessary to take a CT (=J There are problems in that delicate circuit processing is required and it is expensive, and it is also unreliable and difficult to maintain.In addition, the ground joint NJ has no insulation between the metal sheaths at both ends of the joint.
If a ground fault occurs between IJ and N
When a ground fault occurred between J and IJ, it was impossible to distinguish between NJ and 10, and the identification of the section where the fault occurred was insufficient.

<Purpose of the Invention> The present invention was made to solve the above-mentioned problems, and it is possible to reduce the number of detectors used for cross bond points or ground points, and to provide a simple and reliable method. The purpose of the present invention is to provide a method for detecting fault sections of power cables that can perform high fault section discrimination.

<Means for Solving the Problems> In order to solve the above-mentioned problems, the present invention provides a power transmission line including a cross-bond connection, in which a metal sheath return current of a ground fault current is connected to a cross-bond wire or to the ground. This method detects fault sections based on whether the three cross bond currents at one cross point or the three ground currents at one ground point are equal or unequal. Regarding the points, the judgment of equality and inequality is made by using 3 cross bond points where an equal current flows at a certain distance from the accident area.
One of the main cross-bond currents is taken out in the opposite phase to the two wires, and detected by a current sensor.If the detected fault current output is 1/2 of the fault current, then it is approximately Ho or approximately I○/ The accident section is determined by the difference in size of 3 or less, and the equality and inequality of cities or grounding points is determined by comparing one grounding wire current at one grounding point to the other two. The fault section is determined by taking out the fault current output in reverse phase and detecting it with a current sensor, and determining whether the detected fault current output is approximately 2/3 I 0 or more or significantly smaller than that. The accident area is determined by combining both methods.

<Function> Connect the metal sheaths of the parallel power cables to each insulated joint h.
If a ground fault occurs with the NJ part connected by a cross bond wire, first I
At the cross-bond point near the lie, one of the three cross-bond currents is taken out with the phase opposite to the other two for the current sensor 1 node, and this cross-bond point is Find out whether the cross-bond current is approximately ■O or ICl3, and at the grounding point, take out one of the three grounding wire currents with the opposite phase to the other two, and the grounding current at this grounding point is 2/3
The accident area is detected by determining whether it is within or outside Io or is very small.

<Example> Hereinafter, an example of the present invention will be described based on the accompanying drawings. In the following, explanation will be given first focusing on the cross bond points.

As shown in Figure 1, in a long-distance power line, three
Phase power cables Δ, B, and C have metal sheaths separated by insulating joints IJ and connected to electrode sheaths of adjacent power cables by three cross bond wires 11, 12, and 13.

A current sensor 1-14 for detecting fault current is arranged at each of the above-mentioned cross-bond points, and one cross-bond wire 13 is connected to the other two cross-bond wires 11 and 12 for this sensor 1-14. Take it out in reverse phase.

FIG. 1 shows the relationship between cross-bonds, fault points, and metal sheath return current in a long-distance power line.

Note that the conductor current is not shown and the metal sheath is grounded at the ground joint NJ where no insulation is provided between the metal sheaths at both ends of the joint. Now, if a ground fault occurs in power cable A between insulating joints IJ and IJ, a fault current of 2Io will separate from the fault point X to both sides, and the metal sheath will have Fault current ■0 as shown by the dashed line in the figure
will flow, and the grounding join in the accident section]~IJ
-1, IJ+1 and beyond, fault currents of approximately the same magnitude return to the metal sheaths of each phase in approximately the same phase on average.

Therefore, the adjacent ground joints NJ-1, NJ +
1 and beyond, an in-phase return current of 1/10, which is 1/2, of the fault current flows through the cross bond lines 11, 12, and 13.

However, the insulation join l to IJ on both sides of the accident point
-1 and IJ+1, the fault large current flows with the same magnitude only in the cross bond wire connected to the fault phase. Therefore, the three cross bond lines described above cause a large unbalance.

Next, Figure 2 shows the grounding joint IJ and the insulation joint N.
This shows a case where an accident occurs in power cable A between cables A and J.

In this case as well, from the explanation for the case in Figure 1, the grounding joint N
If an accident occurs between J-1 and insulation joint IJ+1,
A fault current of 1° flows through one of the cross bond wires of the two rows of insulating joints IJ+1 and IJ+2 as shown by the dashed line in FIG. 2, causing an imbalance in the cross bond wires 11, 12, and 13.

The above-mentioned Figures 1 and 2 represent all cases of ground fault occurrence, and in all cases, if unbalanced current between cross bond wires 11, 12, and 13 is detected,
It turns out that the area of the accident point can be determined by calculation. Or the two NJs closest to the accident point.
In the case of a grounding wire, the magnitude of the fault current flowing in the grounding wire from which the fault current flows and the other two grounding wires into which the fault current flows change, and the phase also changes almost completely by nearly 180 degrees, so it is a fault phase fault. It becomes possible to distinguish points.

Now, generally speaking, to determine the fault phase, it is customary to install CT or optical magnetic field sensors for measuring conductor current at both ends of the line and measure the conductor current for each phase. It can be easily identified by an abnormal increase in

Alternatively, two healthy phases of three-phase AC, excluding the fault phase, produce an abnormally high fault voltage at the transmission end compared to the normal voltage, and conversely, the fault phase shows a much lower voltage, so it is possible to easily identify the fault phase. It is.

Therefore, if the accident section is determined, the accident section and accident phase can be determined by combining the above-mentioned accident phase determination at both ends of the line.

3 and 4 illustrate a combination structure of the cross bond wires 11, 12, 13 and the current sensor 14 for determining the accident section.

In the example shown in FIG. 3, each cross bond line 11.12.
One 0-piece is attached to 13, and these three are connected in series to take out the output. As shown in the figure, in the event of an accident, the two working magnetic fields of the cross bond wires in the section where equal in-phase fault current flows cancel, and the output is ■0/
3 will come out.

The example in Figure 4 has three cross bond lines 11.12.13.
is passed through one CT, and as mentioned above, 3 of the insulation joints in the section where the equal cross bond current flows in the event of an accident.
At least one of the cross-bond wires passes through the CT so as to flow in the opposite direction.

As mentioned above, if the current sensor 14 is combined with the cross bond wires 11, 12, and 13 and the dUG is applied, unbalanced
Io of 1/2 of the total fault return current in one cross bond wire
The cross bond line of the insulating joint IJ in the section where the current flows is as shown in FIG. 5, and in both FIGS. 3 and 4, an output equivalent to Io is output.

J5, even if approximately Io/3 is not detected accurately at all cross-bond points, the current of the three cross-bond wires is 1/2 of the fault current, one with Io and two with O. If you find a cross bond point that is a combination, all the cross bond line currents at the nearby cross bond points will be Io/3 or even I
All you have to do is check whether it is a combination of o2 and 02, so it goes without saying that the key is to find a cross bond point where Io flows into one cross bond line.

In the case of a grounding point, as shown in Figure 3 or 4 (similarly, the grounding point is placed in the direction of the arrow), the grounding current can be taken out at the point of failure, as shown in Figure 1. The grounding wires of the two grounding points closest to each other have approximately 2/31o flowing out from one and approximately 1/31o flowing into the other two.
Since a current of 3.0 flows, the current sensor has 2/3Io or 4/3Io due to each cancellation or addition effect.
will flow. In NJs other than these two sets, most fault currents flow through the grounding wires, but only very small currents are detected.

As described above, the section where the unbalanced cross-bond fault current or the unbalanced ground line fault current flows can be detected, and based on this, the fault section of the power transmission line can be determined in units of sections of two adjacent joints.

In addition, the current sensor combined with the loss bond wire or the ground wire can be directly replaced with an optical magnetic field sensor that has a Faraday effect on CT in both cases of Fig. 3 and Fig. 4, or as shown in Fig. 6. , a part of the ring-shaped magnetic core 15 is cut out, and the optical magnetic field sensor is inserted therein.
16 may be inserted, or a Hall element may be used in place of the optical magnetic field sensor.

Furthermore, when using a CT, its output is 0 PGW optical CT.
The light may be transmitted to an optical fiber via light emitted from an LED, as in the example shown in FIG.

<Effects> As described above, according to the present invention, one of the three cross bond wires connecting the metal sheaths of parallel power cables or the three ground wires of one grounding point is connected to the other two wires in reverse phase. When the fault current output is taken out and detected at the cross bond point and Io is 1/2 of the fault current, it is approximately Io or approximately ■
The fault area is determined based on the difference in size between o/3 or less, and at the grounding point, the fault area is determined based on whether the detected fault current output is approximately 2/3 or more or significantly smaller than that. Since the discrimination is made, the fault section can be detected by on/off judgment based on the difference in the magnitude of the fault current, and complicated phase detection and comparison circuits before and after the fault section using each CT are not required. Also next to each other ■J~
It is possible to determine the section not only between I and J but also between NJ and IJ by measuring the ground line current.

Also, between one cross pound point or ground point, immediately 3
It is also possible to use one CT for each of the three phase cross-bond wires or the ground wire, which has the economical effect of reducing the number of CTs used, as well as providing compact and highly reliable fault area identification. can be realized.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the case where a ground fault occurs between the insulating joints of a long-distance power transmission system. Figure 3 shows an example of a current sensor [quadruple, Figure 4 is an explanatory diagram showing another example of the same as above, Figure 5 is an explanatory diagram showing the relationship between the current flowing in the cross bond wire, and Figure 6 is a current sensor FIG. 7 is an explanatory diagram showing still another example of the conventional discrimination method.

Claims (3)

[Claims] (1) A power transmission line including a cross bond connection,
Detects the metal sheath return current of the ground fault current from the cross bond wire or the ground wire, and determines whether the three cross bond currents at one cross bond point or the three ground wire currents at one ground point are equal or unequal. This is a method of detecting an accident section based on whether the fault is equal or unequal.One of the three cross-bond currents at the cross-bond point where an equal current flows at a certain distance from the accident section is set in reverse phase to the other two. It is taken out and detected by a current sensor, and the detected fault current output is 1/2 of the fault current.
o, the fault section can be determined based on the difference in size between Io and approximately Io/3 or less, or one of the grounding wire currents at one grounding point is taken in the opposite phase to the other two wires. The detected fault current output is approximately 2/3 Io.
A method for determining an accident section of a power cable, characterized in that an accident section is determined based on whether it is greater than or significantly smaller than that, or a combination of both is used to determine an accident section. (2) A current sensor that extracts and detects one of the cross bond currents or ground wire currents in the opposite phase to the other two has a CT attached to each cross bond wire or each ground wire, and three CTs.
A method for determining an accident section of a power cable according to claim 1, wherein the power cables are connected in series to obtain an output. (3) A current sensor that extracts and detects one of the cross-bond currents or ground wire currents in a phase opposite to the other two wires has at least one cross-bond wire or ground wire in the opposite direction to the other two wires. The method for determining an accident section of a power cable according to claim 1, wherein the output is extracted by passing the CT through the CT so that the current flows through the CT.