JPH02264876A - Measuring method for current separation in wire shield cable - Google Patents

Abstract

PURPOSE:To enable separate measurement of a necessary shield current by detecting one/both of the composite component of axial-direction components of a conductor current and a shield current and a circumferential component of the shield current. CONSTITUTION:In a wire shield cable, a shield circuit current flows along wires 4 which are wound round at a winding angle theta on a cable core 3 comprising a conductor 1 and an insulator 2 as main elements and form a prescribed shield layer. Accordingly, a wire shield current Io flows in a different direction, in inclination of theta, from a conductor current Ie which has only an axial component. Its circumferential component IoSin theta of the cable is generated only by the shield current, and it can be evaluated by measuring this current. Besides, the axial-direction component Io(1 - Cos theta) is detected as a composite component, and the current Io can be determined by multiplying an axial current detected from outside of the cable by 1/(1 - Cos theta).

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a completely new current separation measurement method that makes it possible to measure the core current and shield current of a wire shielded cable using detection means from outside the cable. This is what I am trying to do.

(Conventional technology) For wire silt cables, the technology that separates and measures the current flowing through the core wire of the cable, that is, the core current, and the current flowing through the wire shield, that is, the shield current, is particularly useful for measuring the ground fault current distribution in the event of a ground fault accident. This is essential in the method of locating the accident section.

In other words, the ground fault point can be estimated from the distribution of zero-sequence current flowing through the cable core wire or shield, but in reality, most of the ground fault current flowing through the core wire flows through the shield as a return path, so Even if measurements are taken using a CT (current transformer), magnetic field sensor, etc., the core current and shield current will be combined and canceled, resulting in a current component being detected, making it impossible to make effective measurements. was.

Therefore, in general, the shield circuit is interrupted in the length direction of the cable and taken out to the outside with a bond wire (insulated connection part).
In IJ), a method was adopted in which the zero-sequence current of the shield circuit was determined by measuring the shield current flowing through the bond wire with a current transformer (CT), etc., and the fault section was determined.

[Problem to be solved by the invention]

However, in this method, the measurement point is limited to the insulated connection part, and the fault point location is limited to the section between the insulated connection part and the insulated connection part.

In other words, since it is possible to separate the core current and shield current only at the insulated connection, the location of the ground fault area is limited to the insulated connection and the span of the insulated connection, and the normal junction box (NJ) In the section including the grounded junction box, it was difficult to determine on which side of the span the accident occurred, with respect to the grounded ordinary junction box.

For this reason, when span-by-span orientation is required, it is necessary to change the ordinary junction box to an insulated junction box, and it is difficult to say that it can be used widely.

The present invention has been made in view of the above-mentioned prior art, and it is an object of the present invention to provide a method capable of separating and measuring the truly necessary shield current from the outside of the cable without requiring any special insulated connections. It is.

[Means for solving problems]

Means for achieving the above object of the present invention focuses on a wire shield wound on a cable core at a predetermined winding angle, and the shield wire flows in the circumferential direction of the wire shield wound on the cable core at a predetermined winding angle. The shield current or the core current is determined by detecting either or both of the core current flowing through the core wire of the cable core and the composite component of the axial component of the shield current flowing through the wire shield.

The above-mentioned means in the present invention have been made based on the following findings.

That is, in a wire-shielded cable, the shield circuit current flows along the wire forming the shield layer, but the wire has a cable core whose main elements are a core vAl and an insulator 2, as shown in FIG. Since the winding angle θ around cable core 3 is 4°4... to form a predetermined shield layer 5, the current flowing through it is necessarily directed against the axis X of cable core 3. The current becomes inclined by θ and flows around the cable core 3. This is detected as a current that is inclined by θ with respect to the axial current flowing through the core wire 1 of the cable core 3.

FIG. 2 schematically shows the flow of current as described above, and F indicates a ground fault point.

As is clear from the figure, the wire shield current 16 is the core wire current! . In this case, the core wire current has only an axial component, and the cable circumferential component of the wire shield current! . Sinθ is generated only by the shield current, and therefore,
By measuring only the circumferential component, it is possible to evaluate the shield current. On the other hand, for the axial component, 1
Since o(1-Cosθ) is detected as a composite current,
The axial current detected from outside the cable is 1/(1-Co
sθ) by multiplying ■. can be found.

〔Example〕

FIG. 3 shows an example of the method for detecting the circumferential component of the shield current according to the present invention, in which the pickup coil PC is arranged so as to be wound crosswise at right angles to the axis X of the cable core. It is.

By arranging them in this manner, only the circumferential component of the shield current can be detected without detecting the composite component of the core wire current of the cable core and the axial component of the shield current. More specifically, the circumferential component of the shield current■. ′
A predetermined magnetic field is generated in the direction of arrow (A), and accordingly, a current of 1. l flows and a predetermined voltage is generated between the coil terminals, so by detecting these currents and voltages, the circumferential component of the shield current can be determined. . ′ is detected.

Then, the current detected there is ■, assuming that the winding angle of the shield wire is θ. Since it has a relationship proportional to Sin θ, the shield current can be determined from that value.

FIG. 4 shows an example of a method for detecting the composite component of the axial components of the core current and the shield current according to the present invention, in which the cable core passes through the current transformer CT as a detection element. This is an example where the

In other words, the above synthetic ingredients! . ′ generates a predetermined magnetic field in the direction of the arrow (b), and accordingly, a current i,″ flows through the coil of the transformer ICT, and a predetermined voltage is generated between the coil terminals, so these currents and voltages By detecting , a composite component 10' of the axial components of the core current and the shield current is detected.

The synthetic component 1o II detected here is 1o (
1 cos θ), Io can be determined.

It should be noted that the above embodiment is just one example, and
The invention should not be construed as being limited to the concept described in the claims of the present invention, but rather various modifications may be made within the scope of the concept described in the claims.

For example, the wire shield can be applied not only to a unidirectional winding type but also to an S-Z winding type in which the cable is alternately reversed in the longitudinal direction. In that case, the winding angle differs in the cable length direction, but as described above, the current detected by the detection sensor has a correlation with the wire winding angle, so the detected current differs depending on the sensor mounting position. This can be handled by understanding the relationship between the shield current and the detected current through initial settings, that is, adjusting the sensor mounting position and initial adjustment by energizing the reference current.

Further, according to the present invention, it can also be applied to ground fault surge detection and high frequency current detection that occur during a ground fault.

[Action/effect of the invention]

As is clear from the above description, according to the shield wire current separation measurement method according to the present invention, an element detects a composite component of the axial component of the core current and the shield current, and a circumferential component of the shield current is detected. Simply attach one or both of the elements to the outer circumference of the cable.
Since the core wire current and the shield current can be measured separately, by attaching the detection element at any position on the cable, it becomes possible to arbitrarily set the section for ground fault section location. This means that current measurement can be performed without the need for an insulating junction box, which was conventionally required to separate the shield current from the core current.

In addition, depending on the installation spacing of the current detection elements, it is possible to locate the point of a ground fault, and by attaching detection elements to the cable at both ends of the connection, it is possible to distinguish between cable failures and connection failures. becomes.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a wire shielded cable, Fig. 2 is an explanatory diagram of the flow of each current component in the wire shielded cable, and Figs. 3 and 4 show a specific example of the current separation measurement method in the present invention. FIG. 3 shows an example of detecting the circumferential component of the shield current, and FIG. 4 shows an example of detecting the combined component of the core current and the axial component of the shield current. In the figure, l is the core wire, 2 is the insulator, 3 is the cable core, 4 is the wire, 5 is the shield, PC is the pickup coil, and C
T is a current transformer. Atsushizu Figure 3 (〒-γ) and Fano Old Age

Claims (2)

[Claims] (1) The cable circumferential component of the shield current that flows through the wire shield wound at a predetermined winding angle on the cable core, and the composite component of the core wire current that flows through the core wire of the cable core and the axial component of the shield current that flows through the wire shield. 1. A current separation measurement method in a wire shielded cable, characterized by detecting either or both of the above to determine the shield current or the core current. (2) The current separation measurement method according to claim 1, wherein the means for detecting the circumferential component of the shield current comprises a pickup coil wound on the cable at right angles to the axial direction of the cable.