JPH0534266A - Method for diagnosing deterioration of electric wire/ cable - Google Patents

Abstract

PURPOSE:To simply diagnose the deterioration state of an electric wire/cable by bonding a strain gauge to the constitutional insulating material of the electric wire/cable and monitoring the volumetric change of the insulating material accompanying by deterioration. CONSTITUTION:Strain gauges 5 detecting minute strain are bonded to the outermost layer of a three-core low voltage cable 1 constituted by receiving conductors 3 each coated with an insulating material 2 such as crosslinked polyethylene in a polyvinyl chloride sheath 4 being an insulator at several appropriate places along the cable 1 before laying and operation or after laying by an adhesive. The volume of the cable 1 is changed by deterioration after the elapse of a long time to appear as strain. This strain is detected by the strain gauges 5 and the electric signals thereof are inputted to a measuring condition 7 through lead wires 6 to be monitored. By this constitution, the deterioration of the cable 1 and the degree thereof can be always detected in a live wire state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a power plant low voltage cable,
The present invention relates to a method for diagnosing deterioration of electric wires / cables for nondestructive deterioration diagnosis in a live state such as an electric wire.

[0002]

2. Description of the Related Art A large number of various electric wires and cables are installed in various power plants including a nuclear power plant under various environments.

Generally, most of the electric wires used in a power plant have low voltage. These electric wires deteriorate over time due to various factors and their mechanical and electrical characteristics deteriorate.

From the viewpoint of long-term stable operation and long service life of a power plant, a method for easily and clearly predicting the degree of deterioration and remaining life of installed electric wires and cables is required.

[0005]

However, in the conventional diagnosis of deterioration of low-voltage electric wires / cables, evaluation was carried out by visual inspection at the time of regular inspection or by a destructive test (mechanical characteristics) by removal. In particular, the diagnosis of low-voltage wires and cables, which occupy most of the power plant, is visually inspected at the time of regular inspection. However, the visual inspection tends to cause individual error and is not quantitative, and there is a problem in reliability. Further, when the cable is removed and inspected, there is a problem that it takes a lot of labor and time to remove the cable. As described above, conventionally, there is no suitable nondestructive deterioration diagnosis method, and further, a method for monitoring deterioration over time and in a live state other than regular inspection has not been established.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for diagnosing deterioration of electric wires / cables by solving the drawbacks of the prior art and easily diagnosing the deterioration status of electric wires / cables.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention attaches a strain gauge to a constituent insulating material of an electric wire / cable, and monitors a change in volume of the insulating material due to deterioration with the strain gauge to deteriorate the material. Is to detect.

[0008]

According to the above construction, the volume change of the insulating material due to the deterioration is monitored by the change of the electric signal of the strain gauge,
It is possible to detect deterioration and the degree of deterioration of the cable and the like over time while the cable is installed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 is a three-core low-voltage CV (crosslinked polyethylene insulated vinyl sheath) cable, each of which is a conductor 3 covered with an insulator 2 such as crosslinked polyethylene.
Are housed in a polyvinyl chloride sheath 4 which is an insulator. A strain gauge 5 (manufactured by Kyowa Gauge, for biaxial torque 35) that detects a minute strain is formed in the outermost layer of the cable 1.
0Ω gauge) is attached using CC-15A which is a typical adhesive. These strain gauges 5 are appropriately attached at several points along the cable 1 before or after installation, and are connected to measurement conditioners (Kyowa strain gauge converter, WGA-700A) 7 via lead wires 6, respectively. deep.

In the above, the cable 1 changes its volume due to deterioration after a long period of time, and this appears as distortion. Therefore, by monitoring the electric signal from the strain gauge 5 via the lead wire 6 by the measuring conditioner 7, the deterioration and its degree can be detected.

A specific experimental example will be described below.

The cable sample was appropriately simulated for actual environment deterioration and placed in a constant temperature bath set at 50 ° C., and under oxygen pressure, 1
Irradiation was performed at a dose rate of KGy / h, and deterioration was given for approximately 40 years. At a predetermined time (every predetermined number of years), three samples were taken out and subjected to tests of the change of elongation with time, the change of volume contraction with time, and the strain amount of the strain gauge.

FIG. 2 shows the change over time in the elongation of the vinyl sheath, FIG. 3 shows the volume contraction of the vinyl sheath due to deterioration over time as a relative value to the initial value, and FIG. 4 shows the volume contraction of the vinyl sheath as the amount of strain through a strain gauge. It shows the result of detection. Further, FIG. 5 shows the correlation between the elongation of the vinyl sheath and the response (strain amount) of the strain gauge.

From FIG. 2, the relative elongation of the sheath decreases to 25% of the initial elongation in 40 years, and as shown in FIG. 3, the relative volume of the sheath decreases to about 80% of the initial year in 40 years. Furthermore, if the initial strain of the sheath is zero,
It was confirmed that the strain increased by 2.5 × 10 ^-3 in 40 years. Also, as shown in Fig. 5, when the correlation between the elongation of the vinyl sheath due to heat and radiation deterioration and the response (strain amount) of the strain gauge is found to be good, the strain gauge is attached to the insulator such as the sheath. However, it is possible to nondestructively estimate the elongation that determines the lifespan of the electric wire / cable by the signal change, and further, it is possible to make a diagnosis and predict the remaining lifespan over time in a live state.

In the above embodiments, polyvinyl chloride was used as the insulator, but it is needless to say that it can be applied to insulators made of many organic materials. In other words, it is no exaggeration to say that organic materials generally undergo a change in outer shape such as volume contraction due to deterioration, and therefore, the deterioration and the degree can be detected by observing this change with a strain gauge.

[0017]

In summary, according to the present invention, the degree of deterioration of the cable can be detected by detecting the strain amount of the cable sheath. In addition, deterioration can be constantly monitored in a live state.
Further, if a large number of strain gauges are provided along the cable, it is possible to specify which section of the cable length is deteriorated and the deterioration degree thereof.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a view showing a change with time of elongation of a vinyl sheath in the present invention.

FIG. 3 is a diagram showing a change in volumetric shrinkage of a vinyl sheath due to deterioration over time in the present invention.

FIG. 4 is a diagram showing a result of detecting volume contraction of a vinyl sheath as a strain amount via a strain gauge in the present invention.

FIG. 5 is a diagram showing the correlation between the elongation of the vinyl sheath and the response (strain amount) of the strain gauge in the present invention.

[Explanation of symbols]

 1 Cable 4 Vinyl sheath (insulator) 5 Strain gauge 7 Conditioner for measurement

Claims (1)

Claims: 1. An electric wire characterized in that a strain gauge is attached to a constituent insulating material of an electric wire / cable, and a change in volume of the insulating material due to deterioration is monitored by the strain gauge to detect the deterioration. -Cable deterioration diagnosis method.