JPH0789137B2 - Method for measuring current separation in wire shielded cables - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a completely new method of current separation measurement that enables the core wire current and the shield current of a wire-shielded cable to be measured by means of detection from outside the cable. It is something to do.

[Conventional technology]

In wire-silled cables, the technique of separating and measuring the current flowing in the core wire of the cable, that is, the core current, and the current flowing in the wire shield, that is, the shield current, is especially effective in determining the ground fault accident section from the ground fault current distribution during a ground fault. It is essential in the method of performing.

That is, the ground fault accident point can be estimated from the distribution of the zero-phase 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 Therefore, even if measured with a CT (current transformer) or magnetic field sensor, the core current and the shield current are combined to detect the offset current component,
It was thought that effective measurement was impossible.

Therefore, in general, at the insulation connection (IJ) where the shield circuit is cut off in the cable length direction and is taken out by the bond wire to the outside, the shield current flowing through the bond wire is measured by a current transformer (CT) or the like. A method of determining the fault section by obtaining the zero-phase current of the circuit was adopted.

[Problems to be Solved by the Invention]

However, in such a method, the measurement point is limited to the insulated connection portion, and the location of the accident point is limited to the section between the insulated connection portion and the insulated connection portion.

In other words, since the core wire current and the shield current can be separated only in the insulated connection part, the location of the ground fault accident area is limited to the insulated connection part and the span of the insulated connection part, and the ordinary junction box (NJ) In the section including, it was difficult to determine which side of the span the accident occurred at the boundary of the grounded ordinary junction box.

For this reason, when the orientation for each span is required, it is necessary to change the ordinary junction box to the insulated junction box, which is not widely applicable.

The present invention has been made in view of the above prior art, and an object of the present invention is to provide a method capable of separating and measuring a truly necessary shield current from the outside of the cable without the need for a further insulated connection. Is.

[Means for solving problems]

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

The above means in the present invention is based on the following findings.

That is, in the wire-shielded cable, the shield circuit current flows along the wire forming the shield layer, and the wire has a cable core mainly composed of the core wire 1 and the insulator 2 as shown in FIG. Since the predetermined shield layer 5 is formed by winding like 4,4 ... With a winding angle θ around 3, the current flowing therethrough is necessarily relative to the axis X of the cable core 3. A current inclined by θ flows around the cable core 3. This is detected as a current inclined by θ with respect to the axial current flowing through the core wire 1 of the cable core 3.

FIG. 2 is a schematic diagram of the current flow as described above, and F indicates a ground fault accident point.

As is apparent from the figure, the wire shield current I ₀ flows in different directions with an inclination of θ with respect to the core wire current I ₀ , in which case the core wire current has only an axial component, and the wire shield current component in the cable circumferential direction. I ₀ Sin θ is generated only by the shield current, and therefore the shield current can be evaluated by measuring only the circumferential component. On the other hand, for the axial component, I ₀ (1-Co
Since sθ) is detected as a combined current, I ₀ can be obtained by multiplying the axial current detected from the outside of the cable by 1 / (1-Cosθ).

〔Example〕

FIG. 3 shows an example of a 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 cross-wind at right angles to the axis X of the cable core. Is. With such an arrangement, 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, a predetermined magnetic field is generated in the direction of arrow (a) by the circumferential component I ₀ ′ of the shield current, and the pickup coil PC
Since a current i ₀ ′ flows through the coil and a predetermined voltage is generated between the coil terminals, the circumferential component I ₀ ′ of the shield current is detected by detecting these currents and voltages.

The current detected there has a relation proportional to I ₀ Sin θ, where θ is the winding angle of the shield wire, and therefore the shield current can be obtained from that value.

FIG. 4 shows an example of a method for detecting the composite component of the axial component of the core wire current and the shield current according to the present invention, in which the current transformer CT as the detection element has the cable core passing through itself. It is an example arranged in.

That is, a predetermined magnetic field is generated in the direction of the arrow (b) by the composite component I ₀ ″, a current i ₀ ″ flows in the coil of the current transformer CT accordingly, and a predetermined voltage is generated between the coil terminals. Therefore, by detecting these current and voltage,
The composite component I ₀ ″ of the axial current components of the core wire current and the shield current is detected.

Since the composite component I ₀ ″ detected here is proportional to I ₀ (1-cos θ), I ₀ can be obtained.

It should be noted that the above embodiment is one example even if it gets tired.
According to the idea of the claims of the present invention, it should not be construed as being limited thereto, but rather various modifications may be made within the scope of the idea of the claims.

For example, the wire shield can be applied not only to the one-direction winding type but also to the SZ winding type in which the wire shield is alternately inverted in the cable longitudinal direction. In this case, the winding angle varies in the cable length direction, but the current detected by the detection sensor has a correlation with the wire winding angle as described above, and therefore the detection current varies depending on the sensor mounting position. This can be dealt with by grasping the relationship between the shield current and the detected current through initial setting, that is, adjustment of the sensor mounting position and initial adjustment by applying a reference current.

Further, according to the present invention, the present invention can be applied to detection of a ground fault surge and a high frequency current that occur at the time of a ground fault.

[Operation and effect of invention]

As is apparent from the above description, according to the current separation measuring method for the shield wire according to the present invention, the element for detecting the composite component of the core wire current and the axial component of the shield current and the circumferential component of the shield current are detected. Just attach one or both of the elements on the outer circumference of the cable,
Since the core wire current and the shield current can be measured separately, it is possible to arbitrarily set the ground fault accident section locating section by mounting the detecting element at an arbitrary position of the cable. This means that the current can be measured without the need for an insulating junction box, which was conventionally required to separate the shield current from the core current and take it out.

In addition, depending on the mounting interval of the current detection element, it is possible to locate the ground fault accident point, and by attaching the detection element to the cable parts at both ends of the connection part, it is possible to distinguish between the cable part accident and the connection part accident. Becomes

[Brief description 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, FIGS. 3 and 4 show specific examples of the current separation measurement method in the present invention, FIG. 3 is an example of detecting the circumferential component of the shield current, and FIG. 4 is an example of detecting the combined component of the core current and the axial component of the shield current. In the figure, 1 is a core wire, 2 is an insulator, 3 is a cable core, 4 is a wire, 5 is a shield, PC is a pickup coil, and CT is a current transformer.

Front Page Continuation (72) Inventor Shin Hara 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture Electric Cable Research Institute, Hitachi Cable (72) Inventor Akira Endo 5-1-1 Hidaka-cho, Ibaraki Prefecture Hitachi Cable, Ltd.

Claims (2)

[Claims] 1. A cable circumferential component of a shield current flowing through a wire shield wound at a predetermined winding angle on a cable core, and a core current flowing through a core wire of the cable core and an axial component of a shield current flowing through the wire shield. A method for measuring current separation in a wire shielded cable, which comprises detecting one or both of the combined components to obtain a shield current or a core wire current. 2. A means for detecting a circumferential component of a shield current comprises:
The current separation measuring method according to claim 1, comprising a pickup coil wound on the cable so as to intersect at right angles with the axial direction of the cable.