Ageing Inspection for Cross-Linked Polyolefin Insulation Cable in NPP Using Dielectric Property

The paper use a new dielectric frequency response method to measure the cable insulation’s complex dielectric spectrum at wide frequency domain. During the experiment, Cross-linked polyolefin insulated cables are accelerate aged under thermal and irradiation environment, and measured with elongation at break, Fourier transform infrared spectrum, oxidation induced temperature, and dielectric spectrum as well, to study the property degradation rule. The result indicate that the thermal ageing mechanism is similar to irradiation ageing, of which is the degradation due to polymer molecular chain unlinking, oxidizing material increase and additives content reduce. This chemical constituent changing in insulation could not result traditional electric property change but could be monitored by dielectric loss spectrum curve among wide frequency domain, which stayed stable but shifted to lower frequency as cable degradation. Finally, the paper discussed the main mechanism of cross-linked polyolefin dielectric property changing while ageing according to the electrophysical characteristic of solid insulation, and provided some suggestions about the non-destructive techniques for nuclear power plant cables using dielectric spectrum.

To the method of studying the permittivity of soils (on an example of soils of ravine forests of the northern variant of the steppe zone of Ukraine)

The article is devoted to the establishment of the peculiarities of the method for studying the dielectric permittivity of soils, which is its important electrophysical characteristic. The dielectric permittivity of the soil, which is a complex multiphase medium, depends on the dielectric properties of the mineral composition of its solid phase, the chemical composition, structure and composition of soil particles, their shape and size, and also the dielectric features of inter-porous air and moisture. Now it is possible to greatly simplify the technique of measuring the dielectric permittivity of soils due to the wide dissemination of compact digital instruments that provide high accuracy in measuring the capacitive characteristics of various media. For the approbation of the method, samples of soils of ravine forests of the northern variant of the steppe zone of Ukraine were used, as well as individual soil fractions of 2–3, 1–2 and 0.5–1 mm. All samples were studied in an air-dry state to level out the effect of moisture on the dielectric permittivity of soils, as described in many scientific papers. For measurements, a cylindrical condenser made of organic glass was manufactured, which does not conduct an electric current. The diameter of the capacitor plates was 20 mm, the distance between them was 0.7 mm. After placing the sample in the condenser, it was sealed by pressure from above the weight of about 0.3 kg to create a better contact with the covers of the capacitor. The measurements were carried out using a digital capacitance meter CM-9601A in the range of 0.1–200 picofarads at a test frequency of 800 Hz. At the end of the measurement, the soil sample was weighed to calculate its density. All measurements were performed three times. As a result of using this technique, it was found that the permittivity of a general soil sample is generally higher than that of individual soil fractions. This is explained by the more compact placement of soil particles in the soil sample and its greater density, while in studies of individual fractions, due to their shape, there remain pores between the aggregates that are not filled with soil material, which cause a decrease in sample density. As a result, the maximum density is typical for the soil fraction 0.5–1 mm, and the minimum for the fraction 2–3 mm. This is due to the fact that the maximum permittivity, as a rule, is characteristic for the fraction 0.5–1 mm, and the minimum for the fraction 2–3 mm. This assertion was proved by the measurements carried out. It was also found that the value of dielectric permittivity is significantly affected by soil enrichment of the clay fraction, the increased content of which causes an increase in the dielectric permittivity. Thus, as a result of the research, a method for measuring the dielectric permittivity of soils was tested using a modern digital capacitive meter. An increase in the dielectric permittivity of soils with an increase in their density and an increase in the content of the clay fraction was established. Soils, in general, have an increased permittivity in comparison with soil fractions of 2–3, 1–2 and 0.5–1 mm. There was a need to develop and approbate a technique for measuring the dielectric permittivity of soils in the field using undisturbed addition samples. In the future, in complex studies of soils, it is also desirable to perform a measurement of their dielectric permeability.