JPH04286970A - Measuring equipment of deterioration of insulation under live wire of power cable - Google Patents

Abstract

PURPOSE:To measure an insulation deterioration accurately by cutting current according to a natural potential of a ground portion with a rectifier and then eliminating its flow to a detection resistance element. CONSTITUTION:A filter circuit 17 for flowing an AC current to a ground 1 and a detection resistance element 22 for flowing a DC current to the ground are connected in parallel between a screening layer 14 of a power cable 11 and a ground 18 and then a measuring portion 23 which detects voltage at both edges of the detection resistance element 22 is provided. A rectifier 24 for preventing flow of current from a side of the ground 18 is connected between the detection resistance element 22 and the ground 18.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device for measuring insulation deterioration of power cables under live wire conditions.

0002

2. Description of the Related Art When a power cable such as a cross-linked polyethylene insulated power cable is used for a long period of time under energized conditions, conductive trees may be generated within the cable insulator, resulting in deterioration of the insulation performance. When a tree occurs in the cable insulator, a direct current flows through the cable shielding layer, so by detecting this direct current, it is possible to detect deterioration of the cable insulator.

A conventional insulation deterioration measuring device is shown in FIG. 11
is a cross-linked polyethylene insulated power cable that has been laid and is in a energized state, and is composed of a conductor 12, an insulator 13, a shielding layer 14, an anti-corrosion layer 15, etc. (the internal semiconductive layer and the external semiconductive layer are not shown) . 16 is a cable terminal. 17 is a filter circuit connected between the shielding layer 14 and the ground 18, which includes a resistive element 19, two capacitors 20,
It consists of 21. 22 is the shielding layer 14 and the ground 18
A detection resistor element 23 is connected in parallel with the filter circuit 17 in between, and is a measuring section that measures the voltage across the detection resistor element 22.

[0004] In this measuring device, when a tree occurs in the cable insulator 13, a DC current flows through the shielding layer 14 due to insulation deterioration. The remaining DC current is passed through the detection resistance element 22 to the ground 18, and the voltage across the detection resistance element 22 at this time is measured by the measurement unit 2.
3 to measure the DC component current corresponding to insulation deterioration.

[0005]

[Problems to be Solved by the Invention] However, it has been found that the conventional insulation deterioration measuring device has the following problems. That is, during actual measurement, an existing copper mesh or the like is used as the grounding part, and a natural potential is generated between the copper as the grounding member and the soil. Therefore, when the resistance of the anticorrosion layer 15 is low, a circulating current as shown by the dashed line in FIG. 2 flows, and a voltage is generated by this current across both ends of the detection resistive element 22, making accurate measurement impossible.

[0006]

[Means for Solving the Problems] The present invention provides an instrument for measuring insulation deterioration under live wires of power cables that solves the above-mentioned problems. A filter circuit that causes an alternating current component to flow to ground and a detection resistor element that causes a direct current component to flow to ground are connected in parallel, and a measuring section that detects a voltage across the detection resistor element is provided. This device is characterized in that a rectifier is connected between the resistive element and the ground to prevent current from flowing from the ground side.

[0007]

[Operation] By doing this, the circulating current due to the natural potential between the copper serving as the grounding member and the soil is cut by the rectifier and no longer flows to the detection resistor element, making it possible to perform accurate measurements.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the invention. A feature of this measuring device is that a rectifier 24 is connected between the detection resistive element 22 and the ground 18 to prevent current from flowing from the ground 18 side. The rest of the configuration is the same as the measuring instrument shown in FIG. 2 described above, so the same parts are given the same reference numerals and the explanation will be omitted.

By providing the above rectifier 24, no current flows into the detection resistor element 22 from the ground 18 side, allowing accurate measurement.

0010

[Effects of the Invention] As explained above, according to the present invention, a rectifier is provided between the detection resistor element and the earth to prevent current from flowing from the earth side, so that the current due to the natural potential of the earth part is prevented by the rectifier. Since it is cut and no longer flows to the detection resistor element, there is an advantage that accurate insulation deterioration measurement can be performed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an instrument for measuring insulation deterioration under live wires of power cables according to the present invention.

FIG. 2 is a circuit diagram showing a conventional power cable live line insulation deterioration measuring device.

[Explanation of symbols]

Claims (1)

[Claims] 1. A filter circuit that causes an alternating current component to flow to the ground and a detection resistor element that causes a direct current component current to flow to the ground are connected in parallel between the shielding layer of the power cable and the ground, and An instrument for measuring insulation deterioration under live wires of power cables, which is equipped with a measuring section for detecting voltage, characterized in that a rectifier is connected between the detection resistive element and the ground to prevent current from flowing from the ground side. Instrument for measuring insulation deterioration under live cable conditions.