JPH01299475A - Method for determining failed section of underground transmission line - Google Patents

Abstract

PURPOSE:To make it possible to determine a grounded position quickly and accurately, by detecting the synthesized currents in a conductor and a sheath at a plurality of positions for every phase, comparing the synthesized currents, and determining the failed section. CONSTITUTION:When, grounding occurs in a conductor 2, the conductor 2 and a sheath 6 are shorted. Therefore, a sheat current -IB whose direction is reverse with respect to a conductor current IC flows through the sheath 6 in the phase of the conductor 2. Said sheath current is divided into the sheath in each phase by 1/3IB through a grounding wire 9 at a connecting part on the side of a power source. Therefore, the current IC which is the normal value is detected with a current transformer 10 of the conductor 2 on the side of a load from the grounded point. But the synthesized current IC + 2/3IB is detected with a transformer 10 which is separated from the connecting part 6 on the side of the power source from the grounded point. The synthesized currents IC + 1/3IB is detected with transformers 11 and 12 in conductors 3 and 4 in other phases where there is no grounding. In a judging device 16, these current values are regenerated and compared. The section between the transformers wherein the level of the synthesized current is abruptly changed, i.e., the section between CT Nos 2 and 3, is determined to be the failed section.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for locating a faulty section of an underground power transmission line for identifying a faulty section of an earth fault caused by insulation breakdown of the underground power transmission line.

[Conventional technology]

BACKGROUND OF THE INVENTION As the demand for electrical energy increases, a stable power supply becomes necessary, and technologies related to the reliability of underground power transmission lines such as cables are being developed. Similarly, in the event of a sudden accident, it is necessary to quickly locate the failure location and carry out appropriate restoration work. A typical accident on underground power transmission lines is a ground fault where the conductor and sheath are short-circuited due to insulation breakdown, and when this ground fault occurs, it is necessary to identify the ground fault section as soon as possible. Various methods have been adopted, such as the Murray loop method, the pulse radar method, and the search coil method. In addition, in contrast to these methods, for single-core cable cable lines with cross-bond connections, a current transformer detects the current flowing through the cross-bond wire during a ground fault, and the current level and current phase distribution are analyzed. The ground fault section is being located.

[Problem to be solved by the invention]

However, the former method, such as the Murray loop method, requires a great deal of time and effort to locate the ground fault location, and has the disadvantage that the ground fault location cannot be detected if the resistance value of the ground fault point is high. .

On the other hand, the latter method of detecting the current in the cross-bond line allows for quick and accurate location of the ground fault section, but this method is only applicable to single-core power cables with cross-bond connections. It is something that can be used. That is,
Underground power transmission lines without cross-bond wires, such as three-core cables in which the conductors of three phases are inserted in a single sheath, or triplex cables in which the conductors of each phase are inserted in individual sheaths. It cannot be applied to other countries, and its versatility is limited.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a fault section locating method for underground power transmission lines that can quickly and accurately locate the ground fault location for underground power transmission lines having power cables of various structures. shall be.

[Means to solve the problem]

In order to locate a ground fault section of a power transmission line consisting of a power cable in which each phase conductor is individually inserted into a sheath, such as a trib-wax cable, the present invention combines the sheath current caused by the ground fault with the conductor current to generate a composite current. This detection signal is compared with the combined current at other parts. That is, the present invention targets the following underground power transmission lines and performs the following means.

(11 Applicable underground power transmission line This is a power cable in which the conductors of each phase are inserted into individual sheaths, and each phase is connected by a ground wire. In this cable, the sheath current caused by a ground fault is The current is shunted to other phases via the ground wire and becomes the sheath current of the other phase, and these currents are detected as a composite current with the conductor current of each phase.In other words, the present invention This method detects fluctuations in the level and phase of the composite current by dividing the sheath current using a ground wire.Therefore, as long as the sheath current is divided by a ground wire, it is not limited to the above-mentioned power transmission line. It may be a power transmission line in which two or more power cables are provided, each line is connected to a ground wire, and the sheath current is divided.

(2) Applicable means The sheath current caused by the ground fault is detected as a composite current with the conductor current, and the fault area is located by comparing the detected composite current with composite currents in other parts.

In this case, if the power cable has one line, the combined current is detected for each phase, and if the power cable has two or more lines, the combined current is detected for each line. In the former case, the sheath current is shunted from the phase where the ground fault occurred to other phases in the same line, and detected as a composite current for each phase. In the latter case, the sheath current is shunted to other lines and detected as a composite current for each line. Since the absolute value and phase of this composite current vary greatly before and after the ground fault point, these displacement points are detected to locate the fault area.

[Effect]

In the above configuration, the sheath current is shunted to other phases in the same line or cables of other lines via the ground wire, and then
It is detected for each phase or line as a composite current with the conductor current.

The detected composite current changes with the ground fault point as a boundary. Therefore, by comparing the detected composite current with composite currents in other parts, it is possible to detect a failure point.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the accompanying drawings.

In the present invention, when a conductor and sheath are short-circuited due to dielectric breakdown, the fault area is located by utilizing the fact that the level and phase of the current flowing through the sheath changes rapidly from the ground fault point. , the principle is shown in Figure 6+a), 0))
This is explained by: In these figures, a conductor 42 is insulated by an insulator 42a and inserted into a sheath 43 to form a power cable 41 (semiconductor layers, etc. are omitted).
. In FIG. 6(a), both ends of this conductor 42 are connected to a power source 44, and in FIG.
The right end side is connected to the power supply 44, and the left end side is connected to the load 45.

Under normal conditions, current flows through the conductor 4 due to power supply from the power source 44.
2 in the direction of arrow 47. When such a ground fault occurs in the cable 41, the conductor current 47 is reversed on both sides of the ground fault point 46, and the conductor current 47 is reversed inside the sheath 43 and flows through each power source 44.
A sheath current 48 is generated that flows toward the side (see figure (a)
)). That is, the phase of the sheath current flowing in the sheath 43 is shifted by 180 degrees on the left and right sides of the ground fault point 46.

On the other hand, in the same figure (bl), most of the conductor current 47 in the conductor 42 becomes a sheath current 48 at the ground fault point 46 and returns to the power supply 44 side. As a result, the absolute value of the sheath current on the load 45 side is smaller than the absolute value of the sheath current on the power source 44 side, centering on the ground fault point 46. The value decreases, and the current value suddenly changes.Such a reversal of the phase of the sheath current and a sudden change in the current value can occur either or both together, depending on the power supply conditions of the underground power transmission line. ,
By measuring the sheath current at a predetermined location and comparing the measured value with the sheath current at other locations, the ground fault point can be located.

FIG. 1 schematically shows an underground power transmission line to which the present invention is applied, and an underground power transmission line 1 is formed with three-phase conductors 2, 3, and 4. Each power cable is constructed by inserting the conductors 2, 3, 4 of each phase into a sheath 5 having a metal shield such as a copper tape or a wire shield, and twisting these together. In the figure, reference numeral 6.7.8 is a connection part that connects the conductor 2.3.4 of each phase of the power cable with the conductor of the adjacent power cable. Further, each connection portion is connected by a ground wire 9, and collectively grounded. In order to locate the ground fault section of the underground power transmission line 1, current transformers 10, 11, and 12 are arranged at predetermined intervals (near the connection portion). Here, the current transformer 10 is a sheath 6 of the conductor 2.
The current transformer 11 is attached to the outer circumference of the sheath 6 of the conductor 3, and the current transformer 12 is attached to the outer circumference of the sheath 6 of the conductor 4,
Each current transformer 10.11.12 has a corresponding conductor 2.3
．． 4 in the longitudinal direction. In the embodiment, the current transformer 10.1 is connected to the connecting portion 6.1 of each conductor 2.3.4.
7.8. These current transformers 1
0.11.12 is the conductor current ■ flowing through the conductor 2.3.4 under normal conditions. However, when the conductor and sheath are short-circuited due to a ground fault, a composite current of the conductor current IC flowing through the conductor and the sheath current flowing through the sheath is detected. That is, the present invention detects fluctuations in the sheath current as fluctuations in the composite current of the conductor current and sheath current by detecting the composite current of the conductor current and the sheath current. These current transformers 10 and IL 12 are individually connected to an electrical/optical converter 14 by lead wires 13, and the converter 14
is connected to a determination device 16 via an optical fiber cable 15. In such a configuration, the current transformer 10.
11. The current signal detected in 12 is connected to the electrical/optical converter 14.
After the signal is converted into an optical signal, it is transmitted to the determination device 16. The determination device 16 reproduces this optical signal into a current value and its phase and stores it in memory. Further, the determining device 16 compares the signals transmitted from the current transformers 10, 11, and 12 with each other to locate the ground fault section.

Next, a description will be given of locating a ground fault section when the right end of the power transmission line in FIG. 1 is connected to a power source and the left end is connected to a load. If ground fault 17 occurs in conductor 2, ground fault 1
Since the conductor 2 and its sheath 6 are short-circuited by 7, a conductor current I and a sheath current -■ in the opposite direction flow through the sheath 6 of the phase of the conductor 2. This sheath current is divided into the sheaths of each phase by approximately 1/3Is via the ground wire 9 at the connection portion on the power supply side. Therefore, in the current transformer 10 of the conductor 2 on the load side from the ground fault point 17, the conductor current I is the same as in the normal state,
However, in the current transformer 10 located on the power supply side from the ground fault point 17 and across the connecting portion 6, a composite current (IC+2/31B) of the conductor current and sheath current is detected. Furthermore, the current transformer IL 12 in the conductor 3.4 of the other phase in which no ground fault has occurred detects a composite current (Ic + 1/3 re ) of the conductor current and the shunted sheath current. Judgment device 7
reproduces these current values and compares them with each other. FIG. 2 shows the comparison result by the determination device 7, and shows the comparison result between the current transformers where the level of the composite current changes suddenly, that is, between CT-m2 and C
A ground fault occurs between T and patient 3, and this section can be identified as a ground fault section.

FIG. 3 shows an example of application to an underground power transmission line in which two circuits of power cables are provided, and two circuits of underground power transmission line 1 and underground power transmission line 21 are configured. Since the underground power transmission line 1 is the same as that shown in FIG. 1, its explanation will be omitted. The other line 21 has the same configuration as this line 1, and has conductors 22.2 for each phase.
3.24 are individually inserted into the sheath 26 and connected by connections 26, 27, 28, and the three phases are collectively grounded by a ground cotton 29 at the connections 26, 27, 28. Also, current transformer 30.31.32
are provided at predetermined intervals on the sheath of each phase. In this example, the current transformers 30, 31, 32 are connected by a lead 33 with a resistor 35;
The outputs of the three-phase current transformers 31, 32, and 33 are combined and then output to the electrical/optical converter 14. The line 1 side has a similar configuration, and the outputs of the three-phase current transformers 10, 11, and 12 are combined and then optically converted. That is, the electrical/optical converter 14 and the optical fiber cable 15 connected thereto are 3-phase, 1&
Since it is provided to correspond to the current transformer that has become 11,
The structure can be kept simple. In such a configuration, if a ground fault occurs in any phase of either line, the sheath current generated from that phase will be shunted to the other line by the ground wire 9 or 29, resulting in a similar situation as shown in Figure 1. It becomes a circuit. That is, since the composite current of the conductor current and sheath current detected in each line changes rapidly with the ground fault point as a boundary, the ground fault section can be located.

Figure 4 shows the detection results of the combined current in the case of the above two circuits, showing the current transformers CT-Ni12 and CT-111h.
Between 3 and 3, the level of the combined current suddenly changes and its phase is reversed, and this period is a ground fault section.

FIG. 5 shows a modification of FIG. 3, in which the current transformer 18 is installed so as to span the entire sheath of the three-phase conductor of the power cable, and the composite current of the conductor current and sheath current is It is now detected in a separated and synthesized state.

Therefore, in this case, a resistor for combining three-phase outputs is not required.

〔Effect of the invention〕

As explained above, the present invention divides the sheath current using the ground wire, detects the composite current of the sheath current and the conductor current for each predetermined fault, and compares the detected composite currents to determine the fault area. Since the location is performed, even if the conductor of each phase is individually inserted into the sheath of a power transmission line, the faulty section can be located instantly and accurately.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of an underground power transmission line to which the present invention is applied, FIG. 2 is a characteristic diagram showing a comparison of the composite current in FIG. A schematic diagram showing the configuration when applied to a power transmission line, FIG. 4 is a characteristic diagram showing the comparison results in FIG. 3, FIG. 5 is a schematic diagram showing a modification of FIG. 3, and FIG. Schematic diagram showing the basic principle. Explanation of symbols 1.2t---1...-Underground power transmission line 2.3.4.2
2.23.24・-----1----Conductor 5----
-・----1-Sheath 6.7.8.26.27.28-・----11--
Conductor connection part 9.29--1-----Ground wire 1
0.11.12.18.30.31.32...-1-
---Current transformer 13.33-1---Lead wire 14--
・・・−Electrical/optical converter 15−−−−−−−−One optical fiber 16・−−
---1----Judgment device 17---Ground fault point

Claims (2)

[Claims] (1) In a fault section locating method for an underground power transmission line having a power cable in which the conductors of each phase are inserted into individual sheaths and each sheath is connected by a ground wire, A method for locating a faulty section of an underground power transmission line, characterized by detecting a composite current at multiple points for each phase, and locating a faulty section by comparing the detected composite currents. (2) When the power cable is provided with at least two circuits, the composite current is detected at a plurality of points for each phase of each circuit, and the failure point is located by the change in the level or phase. A method for locating a faulty section of an underground power transmission line as described in Section 1.