JPH0778516B2 - Ground fault fault location method for wire shielded power cables - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ground fault fault section locating method for a wire shielded power cable, and more particularly to a locating method for separately measuring a core wire current and a shield current.

[Conventional technology]

The technique of separating and measuring the cable core current and the shield current is particularly important in locating the fault current distribution in the ground fault fault section of the power transmission and distribution cable system. It is theoretically possible to estimate the ground fault accident point from the distribution of the zero-phase current flowing through the cable core or the shield. However, in reality, most of the ground fault current that flows through the cable core is returned to the shield, so the core current and shield current often cancel each other, and the current transformer (hereinafter referred to as CT) It has been considered difficult to effectively measure the ground fault current using a magnetic field sensor. Therefore, in order to locate the accident section, conventionally, the shield circuit is separated in the length direction of the cable and the insulation connection part (hereinafter referred to as IJ) that is taken out to the outside by the cross bond wire is used. The method of measuring the zero-phase current of the shield circuit by measuring with CT etc. was generally used.

[Problems to be Solved by the Invention]

However, in the method of measuring the current flowing in the cross bond line with IJ by CT etc., the orientation of the accident section is limited to only the section of IJ and IJ, and in the section including the normal connection part (hereinafter referred to as NJ),
It was difficult to determine which side of the accident section or NJ the span was on. Therefore, when the orientation for each span is required, it is necessary to change all NJs in the section requiring orientation to IJs.

Therefore, the object of the present invention is not limited to the section between IJ and IJ, but NJ
An object of the present invention is to provide a method of locating an accident section that enables determination of the span of the accident section even in the section including (ordinary connection part).

[Means for Solving the Problems]

To achieve the above object, in the present invention, in a cable having an S-Z twisted wire shield, a current is measured from outside the cable at two points on the S twist and the Z twist, and the core wire is calculated from the vector sum of the measured currents. Only the current and only the shield current are obtained from the vector difference.

The position where the current is measured from the outside of the cable is ½ (1/2) cycle of the twist pitch on the cable with the S-Z twist wire shield, especially the center of the S twist section and the center of the Z twist section. Is preferred.

In order to measure the vector sum of the electric currents, the electric currents may be detected at the positions on both sides of the twist reversal part of the SZ twist, for example, by a coil or the like, and added in vector.

In order to measure the vector difference of the electric current, the electric current may be detected at the position on the cable by a coil or the like and subtracted in vector.

〔Example〕

Before describing the embodiments of the present invention, the principle of the present invention will be described.

In a wire-shielded cable, the sheath circuit current flows along the shield wire. The shield wire is wound around the cable at a certain winding angle θ. The current flowing therethrough is therefore observed as a current offset in angle by θ with respect to the cable axis.

The SZ twisted wire shielded cable has the structure shown in FIG. 1, and includes a cable core wire 1 twisted at an angle δ and an insulator 2.
And a shield wire 3 having an S twist portion 3a and a Z twist portion 3b. In the SZ twisted wire shielded cable, the winding angle θ of the shield wire 3 changes depending on the position on the cable. Since the cable core wire 1 is also twisted at a certain angle δ, the current flowing through the core wire 1 is observed as a current whose angle is offset by δ with respect to the cable axis.

In the case of the SZ twisted wire shielded cable, the magnitude and phase of the current observed from the outside differ depending on the location on the cable, as shown in FIG. 2 (A). The winding direction of the cable core wire is only one direction, for example, S direction, whereas
Since the wire shield consists of S twist and Z twist, the Z twist portion (Fig. 1 Fig. 3a) adjacent to the center of the S twist portion (Fig. 1a).
When the core current and the shield current are vector-displayed at the two points in the center of b), the core current is as shown in Fig. 2 (A).
i ₀ is in the same direction, while the shield current (i _1S and
i _1Z ) are 180 ° out of phase with each other in the circumferential direction. Therefore, if signals detected at these two points are added in vector, a signal corresponding only to the core current is obtained, and if a difference between them is taken in vector, a signal corresponding to only shield current is obtained.

The details are as follows. The current observed at the center of the S twist part is the sum of the core current vector i ₀ and the shield current vector i _1S i ₀ + i _1s as shown in FIG. 2 (B).
Is. The current observed at the center of the Z twisted portion is the sum i ₀ + i _1Z of the core current vector i ₀ and the shield current vector i _1z , as shown in FIG. 2 (C). As is clear from FIG. 2 (B), the current (i ₀ + i _1s ) at the center of the S twist part
The circumferential component of the _{i 1S sinθ + I 0 sin (} 180 ° _{+ δ) = I 1S sinθ-} it 0 circumferential component of sinδ ...... (1) Z twist section centrally of the current (i ₀ + i _1Z) is I _1S sin (360 ° −θ) + I ₀ sin (180 ° + δ) = − I _1z sin θ−I ₀ sinδ ........ [2]. Therefore, if the vector sum of the components in the circumferential direction is taken, I _1S sin θ−I _1Z sin θ−2I ₀ sinδ = −2I ₀ sinδ ... [3] (I _1S = I _1Z ) It corresponds to the circumferential component of ₀ + i _1S + i _1Z .

I _1S sin θ − I ₀ sin δ − [−I _1Z sin θ − I ₀ sin δ] = I _1S sin θ + I _1z sin θ = 2I ₁ sin θ …… [4] (I _1S = I _1Z ) This is the difference between the vectors i ₀ + i _1S and i ₀ + i _{1Z in} Fig. 3.
It corresponds to i _1S −i _1Z .

In this way, a signal corresponding to only the core wire current and a signal corresponding to only the shield current are obtained, so that it is possible to determine in which span the fault section exists even in the section including NJ.

4 and 5 show an example of a measuring circuit used in the ground fault accident locating method according to the present invention.

FIG. 4 shows a core current detection circuit. The coil 41 and the coil 42 are two coils wound on the cable in the same direction with a half pitch of the twist pitch separated from each other in the twist direction, and are connected in series in the same direction. Coil 41
Is located at the center of the Z twist portion, and a voltage is generated by the magnetic field in the cable axial direction at that position. The coil 42 is located at the center of the S twist portion, and a voltage is generated by the magnetic field in the cable axial direction at that position. Since the magnetic field in the cable axial direction is generated in proportion to the circumferential component of the electric current, each coil produces a voltage proportional to the circumferential component of the electric current at each position. After all, the outputs of both coils connected in series give the vector sum 2I ₀ sin δ (see the equation [3]) of the circumferential component of the current at each position. That is, the circuit shown in FIG. 4 provides an output proportional to the circumferential component I ₀ sin δ of the core wire current.

FIG. 5 shows a shield current detection circuit. The coil 51 and the coil 52 are two coils that are wound on the cable in the same direction and separated from each other by 1/2 cycle, and are connected by subtraction (operational connection) as illustrated. Similar to the coil of FIG.
The coil 51 is located at the center of the Z twist portion and the coil 52 is located at the center of the S twist portion, and produces a voltage proportional to the circumferential component of the current at each position. Therefore, the outputs of both coils connected in series in opposite directions give a vector difference 2I ₁ sin θ (see the equation [4]) of the circumferential component of the current at each position. That circumferential component I _1S sin shielding current by the circuit of FIG. 5
An output proportional to θ can be obtained.

〔The invention's effect〕

According to the present invention, it becomes possible to locate a ground fault accident in a section other than the IJ (insulated connection) and IJ sections, and it is possible to determine in which span the fault section exists even in the section including the NJ (ordinary connection section). Unlike the conventional method of measuring the current flowing through the cross bond line, the ground fault accident location is not limited to the section including only IJ, and therefore, in the case of the section including NJ, it is not necessary to change the connecting portion to IJ.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the structure of an S-Z twisted wire shielded cable, and FIGS. 2 (A), (B) and (C) are core wires at the S twisted portion and the Z twisted portion of the SZ twisted wire shielded cable. FIG. 3 is an explanatory view showing the vectors of the electric current and the shield current, FIG. 3 is an explanatory view showing the principle of the present invention by the electric current vector, and FIGS. 4 and 5 show the measuring circuit used in the ground fault locating method of the present invention. FIG. Explanation of code 1 …… Cable core wire 2 …… Insulator 3 …… Shield wire 3a …… S twist part, 3b …… Z twist part 41,51 …… Coil, 42,52 …… Coil

Claims (2)

[Claims] 1. In a wire shielded cable having an S-Z twisted wire shield, a current is measured from the outside of the cable at two points, an S twisted portion and a Z twisted portion, and the core wire current is calculated from the vector sum or vector difference of the measured currents. Alternatively, a ground fault accident section locating method for a wire shielded power cable, characterized by obtaining a shield current and locating a ground fault accident section based on the core current or the shield current. 2. The core wire current or the shield current is obtained by winding a coil around each of the S-twisted portion and the Z-twisted portion of the wire shielded cable and connecting the two coils by addition connection or subtraction connection. The method of locating the ground fault accident section of the wire-shielded power cable of paragraph 1.