JPH05322964A - Device for measuring insulation deterioration of power cable - Google Patents

Abstract

PURPOSE:To improve measurement accuracy by providing a diode which blocks current from a detection resistance element side to a ground side between the detection resistance element and the ground. CONSTITUTION:A filter circuit 17 which feeds AC current and a detection resistance element 22 which feeds DC current are connected in parallel between a shield layer 14 of a power cable 11 and a ground 18 and a measuring instrument 23 which detects voltage across both terminals of the detection resistance element 22 is provided to measure insulation deterioration. A diode 24 is provided between the detection resistance element 22 and the ground 18 to reject current which flows from the detection resistance element 22 to the ground 18, thus blocking current according to natural potential of the ground 18 by the diode 24, preventing current from flowing to the detection resistance element 22, and measuring insulation deterioration accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring insulation deterioration of power cables.

[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 in a charged state, a conductive tree may be generated in the cable insulator to deteriorate the insulation performance. When a tree is generated in the cable insulator, a direct current flows through the cable shielding layer, and therefore it is possible to detect deterioration of the cable insulator by detecting this direct current.

FIG. 2 shows a conventional insulation deterioration measuring device. 11
Is a cross-linked polyethylene insulated power cable that has been laid and is in the state of being charged, and is composed of conductor 12, insulator 13, shielding layer 14, anticorrosion layer 15, etc. (inner semiconductive layer, outer semiconductive layer are not shown) .. 16 is a cable terminal. Reference numeral 17 is a filter circuit connected between the shielding layer 14 and the ground 18, and is a resistance element.
It consists of 19 and two capacitors 20 and 21. Reference numeral 22 is a detection resistance element connected in parallel with the filter circuit 17 between the shield layer 14 and the ground 18, and 23 is a measuring device for measuring the voltage across the detection resistance element 22.

In this measuring apparatus, when a tree is generated in the cable insulator 13, a DC current flows through the shield layer 14 due to insulation deterioration. Therefore, an alternating current component of the current flowing through the shield layer 14 is passed through the filter circuit 17 and remains. A direct current component current is passed through the detection resistance element 22, and the voltage across the detection resistance element 22 at this time is measured by the measuring device 23 to measure the direct current distribution current corresponding to insulation deterioration.

[0005]

However, it has been found that the conventional insulation deterioration measuring device has the following problems. That is, at the time of actual measurement, an existing copper mesh or the like is used for the ground portion, and a natural potential is generated between copper as the ground member and the soil. Therefore, when the resistance of the anticorrosion layer 15 is low, a circulating current flows as shown by the alternate long and short dash line in FIG. 2, and a voltage due to this current is generated at both ends of the detection resistance element 22, and accurate measurement can be performed. Disappear.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides an apparatus for measuring insulation deterioration of a power cable which solves the above-mentioned problems, and has the structure of a power cable in a state where an AC voltage is applied. A power cable in which a filter circuit for flowing an alternating current component and a detection resistance element for flowing a direct current component are connected in parallel between the shielding layer and the ground, and a measuring device for detecting the voltage across the detection resistance element is provided. In the insulation deterioration measuring device, a diode for blocking a current flowing from the detection resistance element side to the ground side is connected between the detection resistance element and the ground.

[0007]

By doing so, the circulating current due to the natural potential between the copper as the earth member and the soil is cut by the diode and does not flow to the detection resistance element, so that accurate measurement can be performed.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. A feature of this measuring device is that a diode 24 that blocks a current flowing from the detection resistance element 22 side to the ground 18 side is connected between the detection resistance element 22 and the ground 18. Since the other configuration is the same as that of the measuring device of FIG. 2 described above,
The same parts are designated by the same reference numerals and the description thereof will be omitted.

By providing the above diode 24,
A current due to the natural potential of the ground portion does not flow through the detection resistance element 22, and accurate measurement can be performed.

[0010]

As described above, according to the present invention, the diode for blocking the current flowing from the detection resistance element side to the ground side is provided between the detection resistance element and the ground. Since the current is cut by the diode and does not flow to the detection resistance element, there is an advantage that accurate insulation deterioration measurement can be performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an insulation deterioration measuring device for a power cable according to the present invention.

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

[Explanation of symbols]

11: Power cable 12: Conductor 13: Insulator 14: Shielding layer 15: Anticorrosion layer 17: Filter circuit 18: Ground 22: Detection resistance element 23: Measuring instrument 24: Diode

Claims (1)

[Claims] 1. A filter circuit for flowing an alternating current component and a detection resistance element for flowing a direct current component are connected in parallel between a shield layer of a power cable to which an alternating voltage is applied and a ground, and In a power cable insulation deterioration measuring device provided with a measuring device that detects the voltage across the detection resistance element,
A device for measuring insulation deterioration of a power cable, wherein a diode that blocks a current flowing from the detection resistance element side to the ground side is connected between the detection resistance element and the ground.