JP2636448B2 - Diagnosis method for wire / cable deterioration - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for non-destructively improving the insulation deterioration of relatively low-voltage wires and cables laid in a nuclear facility such as a nuclear power plant. The present invention relates to a novel insulation deterioration diagnosis method for performing diagnosis with accuracy.

[Related Art] In nuclear facilities such as nuclear power plants, a great variety of electric wires and cables are laid, and they are more or less exposed to an atmosphere of heat or radiation. Generally, electric wires and cables, including those under such an environment, are electrically or mechanically deteriorated due to various factors due to long-term use, and eventually need to be replaced.

The main form of deterioration of insulators of electric wires and cables is considered to be oxidative deterioration, and structural changes such as molecular weight changes such as breaking or cross-linking of molecular chains occur by the oxidation reaction. As a result, the mechanical characteristics or the electrical characteristics of the electric wires and cables are reduced, and the wires and cables do not operate normally and safely. Therefore, in order to improve the safety of the laying facilities such as a nuclear power plant and prevent an accident from occurring, it is possible to detect the state of deterioration of the wires and cables used therein in a simple and reliable manner. Is very important and such a method has been strongly desired.

In order to meet such demands, research and development of a so-called hot-line diagnostic method for non-destructively diagnosing insulation deterioration status in a high-voltage cable in a live state has been promoted from an early stage, and has been implemented as a mainstream conventionally. In addition to the insulation resistance, dielectric loss tangent, and DC leakage current methods, methods such as the reverse absorption current method, the residual voltage method, and the potential decay method have recently been proposed. It is almost possible to diagnose.

The high-voltage cable has a shield layer on the cable structure, and uses this shield layer to diagnose deterioration by an electric nondestructive method. Therefore, it is difficult to apply the above-described method for determining the degree of deterioration of a cable applied to a high-voltage cable to a relatively low-voltage wire or cable having no shield layer.

For this reason, such low-voltage wires / cables should be evaluated by visual inspection requiring skill, or by measuring the decrease in electrical and mechanical properties by the method of breaking down the removed products, especially the residual elongation rate. Has been evaluated.

[Problems to be Solved by the Invention] However, the above-mentioned visual inspection method, which is most widely used to determine the deterioration of low-voltage electric wires and cables that occupy the majority in nuclear facilities such as nuclear power plants, requires considerable skill. In addition, even if the inspector is a skilled person, there are individual differences,
It is very difficult to make an accurate and appropriate deterioration determination.

Although the destructive test method using a removed product is extremely reliable from the viewpoint of improving the accuracy, it is inevitable that much time, labor and cost are required.

An object of the present invention is to provide a low-voltage electric wire and a power supply that occupy a large part in a nuclear power plant or the like in view of the above-described circumstances.
A new wire / cable insulation deterioration that can perform non-destructive cable deterioration diagnosis reliably and accurately, and can be easily applied without stopping the live state like the high-voltage cable described above. It is intended to provide a diagnostic method.

[Means for Solving the Problems] The present invention uses the same composition material as the polyvinyl chloride sheath of the actually laid wire / cable, and irradiates the radiation in a heated atmosphere to cause simultaneous deterioration of radiation and heat. Predetermining the decrease in tensile elongation in relation to the integrated dose of radiation in advance, and performing thermogravimetric analysis on samples taken from the polyvinyl chloride sheath of the actually laid wires and cables to change the weight at a specified rate by pyrolysis The temperature is measured, and the degree of deterioration of the sheath of the wire / cable is determined by comparing the measurement result with the relationship between the previously obtained decrease in tensile elongation and the integrated dose of radiation.

[Action] The sample required for thermogravimetric analysis is extremely small (1
22 mg), and sufficient analysis can be performed on a sample obtained in an amount that does not cause a risk of losing the function of the wire or cable that is actually loaded.

Therefore, it is necessary to collect only a small amount of the above-mentioned sample from the live wires / cables, without removing the wires / cables. It is possible to accurately diagnose the degree of deterioration of the cable.

Examples Hereinafter, the present invention will be described in detail with reference to examples.

The degradation of many low-voltage wires and cables used in nuclear power plants tends to be preceded by a decrease in mechanical properties over a decrease in electrical properties, and the life of such cables is determined by their mechanical properties (elongation or tensile strength). ).

In general, at a nuclear power plant or the like, periodic inspections are performed to ensure safety. At this time, wires and cables that are susceptible to deterioration are removed and the above-described mechanical characteristics are measured.

The inventors used the removed wires and cables,
Along with measuring the mechanical properties with the period of use, a small amount of 1 to 2 mg from the surface of the same removed product, that is, under the hot wire condition and cutting it to the extent that the function of the wire / cable is not affected at all A sample was taken from the sheath surface in a possible small amount, and T _5% (temperature at which the weight decreased by 5%, the same applies hereinafter) of the organic insulating material was also measured by thermogravimetric analysis (TGA).

As a result, the inventors have found that there is a close correspondence between the decrease of T5 _% measured from the collected sample and the decrease behavior of the mechanical properties.

As described above, most of the organic insulating materials constituting the electric wires and cables laid in a nuclear power plant and the like are oxidatively degraded by radiation and heat. As a result, a structural change such as a molecular weight change such as breaking or cross-linking of a molecular chain occurs. As a result, the pyrolysis temperature changes. The present invention focuses on utilizing this development of an organic insulating material, and attempts to diagnose deterioration and predict the remaining life. A very small amount is removed from the surface of the sheath that constitutes the outermost shell of the already laid electric wire / cable so that its function is not lost. Then, using a thermogravimetric analyzer (TGA), the T5 _{% of the} trace sample is measured, and the change in the T5 _% of the insulator or sheath material depending on the operation time (laying date) is determined.

Then, using the same composition material as the real environment laid wires and cables in advance, simulating the real environment, irradiating radiation in a heated atmosphere to estimate the deterioration of mechanical properties due to simultaneous deterioration of radiation and heat It is determined in relation to the dose.

By comparing a comparison table or graph of the known mechanical properties with the integrated dose of radiation with a small sample T5 _% taken from the sheath of the already installed wires and cables, the T5 _% of the sample can be determined nondestructively with high accuracy. The degree of deterioration and the life of the sheath of the laid electric wire / cable can be diagnosed.

Examples The following describes a low-pressure cross-linked polyethylene insulated vinyl chloride sheath (hereinafter referred to as the most frequently used in nuclear power plants).
An example in which a cable (referred to as CV) is used will be described.

 A 600V low voltage CV cable was prepared and used as a sample.

These samples were simulated in a real environment, placed in a constant temperature bath set at 50 ° C., and irradiated with γ rays at a dose rate of 1 × 105 R / h in an oxygen atmosphere to be deteriorated. After irradiation with a fixed dose, four samples were collected, and the following measurements were performed for each sample.

The tensile test of the sample was performed by dividing the cable into an insulator and a sheath. For the insulator XLPE (cross-linked polyethylene), the conductor was extracted and measured in a tube at a pulling speed of 200 mm / min. The sheath material PVC (polyvinyl chloride) was punched out in a dumbbell shape and measured at a pulling speed of 200 mm / min. .

Thermogravimetric analysis of samples taken from the surface of the insulator XLPE and sheath PVC was performed using a SSC5200 type thermal analysis system manufactured by Seiko Electronics Co., Ltd., using a measurement sample of 5 mg or less and a heating rate of 10 ° C /
The measurement was performed at a gas flow rate of 300 ml / min with an N ₂ gas atmosphere and min.

FIG. 1 is a graph plotting the integrated dose and the mechanical properties, particularly the change in elongation, when the insulator XLPE and the sheath PVC have undergone combined deterioration due to radiation and heat, respectively.

From Fig. 1, it can be seen from the safety side that the reduction in the elongation of the outermost sheath due to the combined deterioration of radiation and heat is more remarkable than that of the insulator, and the life of the cable is appropriately determined based on the deterioration of the sheath. It can be understood that the determination is made.

FIG. 2 is a diagram plotting the relationship between the integrated dose of sheath PVC and T ₅ %%. Further, FIG. 3 is a diagram corresponding to the relationship between the elongation of the sheath PVC caused by simultaneous deterioration of radiation and heat and the T5 _{% of the} sheath PVC.

From FIG. 3, it can be seen that there is a very close correspondence between the two.

Therefore, if T5 _% is obtained using a sample taken from a minute surface of PVC, which is the sheath material of electric wires and cables, it is possible to nondestructively determine the degree of decrease in elongation that determines the life of the electric wires and cables. Becomes This makes it possible to diagnose the degree of deterioration and predict the life of the already laid wires and cables.

The above embodiments merely explain the effects of the present invention, and do not limit the scope of application, and it goes without saying that the embodiments can be extended to electric wires and cables other than nuclear facilities. Further, the present invention can be applied to not only low-voltage wires and cables but also high-voltage wires and cables.

[Effect of the Invention] As described in detail above, according to the method of the present invention, the insulation deterioration state of relatively low-voltage wires / cables laid in a nuclear power plant or the like is determined nondestructively with high accuracy. That can be installed,
This makes it possible to diagnose the deterioration of the cable and predict the remaining life of the cable, and it can be said that the industrial value is extremely high.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the integrated dose of radiation and elongation, FIG. 2 is a diagram showing the relationship between the integrated dose of radiation and 5% weight loss temperature (T _5% ) by thermogravimetric analysis, and FIG. FIG. 3 is a diagram showing a correspondence relationship between a decrease in elongation due to an integrated dose in FIG. 1 and T5 _% in FIG.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takao Onishi 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Inside the Hidaka Factory, Hitachi Cable Corporation (72) Inventor Yasuo Hima Watanuki-cho, Takasaki City, Gunma Prefecture 1233 Japan Atomic Energy Research Institute Takasaki Research Institute (56) References JP-A-60-173439 (JP, A) JP-A-61-145440 (JP, A)

Claims (1)

(57) [Claims] (1) Using the same composition material as the polyvinyl chloride sheath of an actually laid electric wire / cable, irradiating it in a heated atmosphere to reduce the tensile elongation caused by simultaneous deterioration of radiation and heat, and integrate the radiation. Measured in advance in relation to the dose, and performed thermogravimetric analysis on samples taken from the polyvinyl chloride sheath of the actually laid wires / cables to measure the thermal decomposition temperature at which a predetermined percentage of weight changes, and the measurement results A method of diagnosing deterioration of a wire / cable, wherein the degree of deterioration of a wire / cable sheath is determined by comparing the above-mentioned relationship with the relationship between the previously-determined decrease in tensile elongation and the integrated dose of radiation.