JPH0778517B2 - Cable current detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable current detecting device, and more particularly to a device useful for fault location of an underground power cable line.

[Prior Art] A cable that constitutes an underground power line has a metal sheath such as a corrugated aluminum sheath or a wire shield on a cable core, and an induced current, that is, a sheath current flows through the metal sheath or the wire shield. It is important to measure the sheath current and the current flowing through the inner conductor of the cable core separately, especially in order to locate the ground fault section from the ground fault current distribution at the time of ground fault of the line.

That is, the ground fault can be estimated from the distribution of the zero-phase current flowing through the inner conductor of the cable core or the metal sheath (or wire shield), but in reality, most of the ground fault current flowing through the inner conductor is Flows through the metal sheath etc. as a return path, the inner conductor current and sheath current are combined even if an attempt is made to measure the ground fault current from the outer circumference of the cable with a current transformer (CT) or magnetic sensor etc. It has been considered that effective measurement is impossible due to the detection of.

Therefore, in general, at the insulation connection (IJ) where the metal sheath is cut off in the length direction of the cable, the current flowing through the cross bond wire connected for twisting the metal sheath circuit is measured by CT or the like. Therefore, the method of obtaining the zero-phase current of the sheath circuit and determining the faulty section has been adopted.

However, in this method, the measurement point was limited to IJ, and the location of the accident point was limited to the section between IJ and IJ.

In other words, since the inner conductor current and the sheath current can be separated only in IJ, the location of the ground fault section is
In the section limited to the span of IJ and IJ, where the metal sheath (or wire shield) includes the normal connection part (NJ) formed continuously in the length direction of the cable, on either side of the grounded NJ as a boundary. It was difficult to determine if there was an accident on the span.

Therefore, in the above method, it is necessary to replace NJ with IJ when it is desired to locate the faulty section in the line including NJ, and it cannot be said that the method can be widely used.

Recently, in place of this method, a new method has been proposed that enables localization of accident points before and after NJ on a line including NJ. In other words, the magnetic field in the axial direction of the inner conductor or the wire shield generated by the segment twist of the cable forming the underground power line or the twist of the inner conductor or the twist of the wire shield is used as a sensor coil (magnetic flux detection coil). ), The fault current flowing in the inner conductor or the wire shield is detected, and the fault point of the cable is located based on its direction and size. (See Japanese Patent Application No. 1-108439) Hereinafter, this device will be described with reference to the drawings.

FIG. 6 is a view for explaining this device for locating an accident in an underground power cable line, and is a side view showing an upper half of a sensor coil mounting portion only in cross section. That is, the cable 1 is constructed by forming a corrugated metal sheath 5 such as a corrugated aluminum sheath on a cable core 4 mainly composed of an inner conductor 2 and an insulator 3, and forming a plastic anticorrosion layer 6 on the corrugated metal sheath 5. The sensor coil 7 is directly wound and arranged on the surface of the plastic anticorrosion layer 6.

The inner conductor 2 of the cable core 4 is usually configured by twisting a plurality of segments 2a, 2a. Based on the current flowing through the inner conductor 2 due to this segment twist, the magnetic field of the surface orthogonal to the inner conductor is Not only that, an axial magnetic field of the two inner conductors is generated. This axial magnetic field is linked to the sensor coil 7 arranged on the surface of the anticorrosion layer 6.

Since the sensor coil 7 is linked to the magnetic field of the conductor axial direction component, it is wound on the plastic anticorrosion layer 6 in a state of intersecting at right angles with the conductor axial direction, and the magnetic field of the conductor axial direction component is Since the metal sheath 5 cancels out a considerable amount and becomes weak on the surface of the plastic anticorrosion layer 6, the sensor coil 7 needs to be arranged in a large number of turns to pick up this weak magnetic field.

[Problems to be Solved by the Invention] Although the above-mentioned method is an excellent method, the power that can be taken out is small, and therefore there are problems such as amplification of a signal after detection, securing of its power supply, and complication of a device. Further, since the sensor coil (time flux detection coil) is not magnetically shielded, it is easily affected by the ambient magnetic field and easily influenced by external induction.

The present invention has been made in view of the above circumstances, and provides a cable current detection device that is based on a new detection principle and that facilitates localization of accident points before and after a normal connection (NJ). With the goal.

[Means for Solving the Problems] That is, in order to solve the above problems in the present invention, a magnetic flux detection line is vertically arranged in a corrugated shape along a valley portion of a corrugated metal sheath of a power cable line having a corrugated metal sheath. When a reciprocating current flows through the inner conductor of the power cable line and a corrugated metal sheath, the magnetic field due to the reciprocating current is
A cable current detection device, characterized in that an electromotive force generated by a circumferential magnetic field passing between the magnetic flux detection line and an external lead wire is measured at the end of the lead wire to detect the reciprocating current. provide.

In order to solve the above problems in the present invention, a magnetic flux detecting coil is wound around the wire shield of a power cable line having a wire shield wound at a predetermined winding angle on a cable core, and the magnetic flux detecting coil is further provided. When the magnetic flux on the circumference of is easily arranged to pass through the magnetic shield, when an electric current flows through the wire shield, the electromotive force generated by the axial magnetic field in the magnetic field due to the electric current is Provided is a cable current detection device characterized by being configured to detect an electric current measured at an end of a detection coil.

Further, in the present invention, in order to solve the above problems, a magnetic flux detection coil is wound around the circumference of a power cable line having segment twisted internal conductors twisted at a predetermined twist angle, and further on the circumference of the magnetic flux detection coil. A magnetic flux is arranged to arrange a ferromagnetic material that easily passes, and when a current flows in the segment twisted inner conductor,
There is provided a cable current detection device, characterized in that, of magnetic fields generated by the current, an electromotive force generated by an axial magnetic field is measured at an end of the detection coil to detect the current.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram for explaining a cable current detection device. That is, of the magnetic field due to the reciprocating current flowing from the inner conductor 9 to the corrugated metal sheath 5 ', the electromotive force generated in the circumferential magnetic field is connected to the magnetic flux detection line 7a arranged along the valley of the metal sheath 5'. External lead wire 11
An example of detection at the edge 12 is shown. The state of the cable cross section in this case is shown in FIG. D ₁ is the outer diameter of the valley of the corrugated metal sheath 5 ′, D ₂ is the outer diameter of the crest of the corrugated metal sheath 5 ′, d is the diameter of the inner conductor 9, and 15 is the cable insulator.

In this case, assuming that the current flows at a uniform current density in the cross section of the metal sheath, the magnetic flux due to the current in the portion from the outer diameter D _S to D ₂ will interlink with the detection line 7a. An electromotive force will be generated on the line 7a. That is, the round trip current is the same, and the current can be detected without the zero phase component.

3 and 4 show the magnetic flux detection coils 7b and 7c provided on the outer circumference of the cable having the segment-twisted inner conductor as the center and the cable having the wire shield on the cable core.
FIG. 9 is a side sectional view in the case where ferromagnetic bodies 8 and 8a are provided on the outside thereof.

That is, a cable 1 having a twisted segment inner conductor shown in FIG. 3 as a center comprises a corrugated aluminum sheath on a cable core 4 having an inner conductor 2 in which a plurality of segments 2a and 2a are twisted together and an insulator 3 as main elements. A metal sheath 5 such as is provided and a plastic anticorrosion layer 6 is formed on the metal sheath 5, and a magnetic flux detection coil (sensor coil) 7b is directly wound around the surface of the plastic anticorrosion layer 6 and arranged. It The ferromagnetic body 8 is arranged around the magnetic flux detecting coil 7b.

The wire shielded cable shown in FIG. 4 is formed by spirally winding the wire shield 14 made of the wire 13 around the inner conductor 9 ′ and the cable insulator 15.
A magnetic flux detecting coil 7c is wound around the outer circumference. Then, a ferromagnetic body 8a is arranged around the magnetic flux detecting coil 7c.

In these cases, the axial magnetic flux 1 passing through the coil outer portion is increased by the ferromagnetic bodies 8, 8a, the magnetic flux interlinking with the coils 7b, 7c is increased, and the electromotive force can be increased. .

A modification is shown in FIG. In the case of this example, a ferromagnetic body 8b (a bidirectional ferromagnetic body or a non-directional ferromagnetic body) is provided outside the cable core 4, and one or more independent windings in the circumferential direction orthogonal to the ferromagnetic body 8b are provided. 18 and an axial winding 17 are provided. The two windings 17 and 18 enable independent detection of the axial component or the circumferential component of the cable external magnetic flux. When these windings 17 and 18 are connected in series, the electromotive force (size,
Phase) can be generated.

[Effects of the Invention] As described above, according to the cable current detection device of the present invention, when a reciprocating current flows through the inner conductor of the power cable line having the corrugated metal sheath and the corrugated metal sheath, the current is passed through the corrugated metal sheath. At the end of the external lead wire, based on the electromotive force generated by the circumferential synthetic magnetic field between the magnetic flux detection line vertically arranged in a corrugated shape along the sheath trough and the external lead wire connected to the detection line. The round trip current can be accurately detected by measuring, and the cable fault point can be located by detecting the magnitude, waveform, phase, and the like.

Further, when a ferromagnetic material is provided outside the magnetic flux detection coil, the detection sensitivity of the combined magnetic flux of the cable can be improved, and inductive interference from the outside of the detection coil can be suppressed to enable accurate detection.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a detecting portion for explaining a cable current detecting device of the present invention, and FIG. 2 shows a positional relationship for explaining the principle of generating electromotive force in FIG. 3 and 4 are side sectional views for explaining a device for detecting magnetic flux by the segment twisted cable and the wire shielded cable, and FIG. 5 is a perspective view showing a modified example. FIGS. 6A and 6B are side views in which a part is omitted for explaining the prior art. 1 …… Cable 2,9,9 ′ …… Inner conductor 2a …… Conductor segment 3,15 …… Cable insulator 4 …… Cable core 5,5 ′, 14 …… Corrugated metal sheath 6 …… Plastic anticorrosion layer 7a ...... Magnetic flux detection line 7,7b, 7c …… Magnetic flux detection coil (sensor coil) 8,8a, 8b …… Ferromagnetic material 11 …… External lead wire 14 …… Wire shield 17,18 …… Winding

Claims (3)

[Claims] 1. A magnetic flux detection line (7a) is vertically arranged in a corrugated shape along a valley portion of a corrugated metal sheath (5 ') of a power cable line having a corrugated metal sheath. When a reciprocating current flows through the inner conductor (9) of the power cable line and the corrugated metal sheath (5 '), the magnetic field due to the reciprocating current is surrounded by the magnetic flux detecting wire (7a) and the outer lead wire (11). A cable current detecting device, characterized in that an electromotive force generated by a directional magnetic field is measured at the lead wire end (12) to detect the reciprocating current. 2. A magnetic flux detection coil (7c) is wound around a wire shield (14) of a power cable line having a wire shield wound on a cable core at a predetermined winding angle, and the magnetic flux detection coil (7c) is further provided. When a current flows through the wire shield (14), a ferromagnetic material (8a) through which magnetic flux easily passes is arranged on the circumference of the A device for detecting a cable current, characterized in that the electromotive force generated is measured at the end of the detection coil (7c) to detect the current. 3. A magnetic flux detecting coil (7b) is wound around the circumference of a power cable line having segment twisted internal conductors (2) twisted together at a predetermined twist angle, and further around the magnetic flux detecting coil (7b). When a current flows through the segment-twisted inner conductor (2), a ferromagnetic material (8) through which magnetic flux easily passes is arranged in the A cable current detection device, characterized in that the electromotive force is measured at the end of the detection coil (7b) to detect the current.