Properties Of Cable Insulation Research Articles

Synergism of radiation and steam on mechanical properties of cable insulation removed from a nuclear power plant

ABSTRACT A three-phase AC low-voltage cable insulated with flame-retardant ethylene-propylene-diene rubber (FR-EPDM), laid in a nuclear power plant (NPP) for 23 years, was removed. Several pieces of tubular insulation samples were obtained by removing the conductors out of the cable. For comparison, similar insulation samples were also prepared using a similar unaged cable and those aged artificially in different manners by the irradiation with gamma rays. In addition, the irradiation with gamma rays and exposure to steam, which simulated a plausible environment during a severe accident, were also given to some of those tubular samples. Tensile tests were performed to measure the elongation-at-break and tensile strength of those aged and unaged samples. As a result, it has become clear that the cable removed from the NPP did not severely deteriorate. In addition, it was found that the subsequent steam exposure can alleviate the mechanical degradation of FR-EPDM caused by the gamma-ray irradiation. The validity of the method to simulate the aging suffered in the NPP is discussed.

Insulation Degradation Mechanism and Diagnosis Methods of Offshore Wind Power Cables: An Overview

The marine environment in which offshore wind turbines are located is very complex and subjected to a variety of random loads that vary with time and space. As an important component of offshore wind power, the cable also bears the impact of the environment in which most of the turbines are located. Under the long-term action of mechanical stresses such as tension, torsion, and vibration, the cable insulation will crack due to stress fatigue leading to partial discharge, which seriously affects its electrical performance. The study of the mechanism of the change of electrical properties of cable insulation due to mechanical behavior is of great theoretical guidance to improve the reliable operation of cables. This paper first introduces the basic characteristics and operating conditions of torsion-resistant cables and submarine cables. Then the mechanical behavior of the cables is summarized, and the deterioration mechanism and deterioration effect of wind power cable insulation under the influence of multiple factors such as heat, oxygen, and mechanical stress are sorted out. Then, the basic principles of wind power cable operation condition monitoring methods and their characteristics are described. Finally, the relevant methods for the detection of hidden defects inside the insulation are summarized.

Towards a Kinetic Modeling of the Changes in the Electrical Properties of Cable Insulation during Radio-Thermal Ageing in Nuclear Power Plants. Application to Silane-Crosslinked Polyethylene.

The radio-thermal ageing of silane-crosslinked polyethylene (Si-XLPE) was studied in air under different dose rates (6.0, 8.5, 77.8, and 400 Gy·h−1) at different temperatures (21, 47, and 86 °C). The changes in the physico-chemical and electrical properties of Si-XLPE throughout its exposure were determined using Fourier transform infrared spectroscopy coupled with chemical gas derivatization, hydrostatic weighing, differential scanning calorimetry, dielectric spectroscopy and current measurements under an applied electric field. From a careful analysis of the oxidation products, it was confirmed that ketones are the main oxidation products in Si-XLPE. The analytical kinetic model for radio-thermal oxidation was thus completed with relatively simple structure–property relationships in order to additionally predict the increase in density induced by oxidation, and the adverse changes in two electrical properties of Si-XLPE: the dielectric constant and volume resistivity R. After having shown the reliability of these new kinetic developments, the lifetime of Si-XLPE was determined using a dielectric end-of-life criterion deduced from a literature compilation on the changes in R with for common polymers. The corresponding lifetime was found to be at least two times longer than the lifetime previously determined with the conventional end-of-life criterion, i.e., the mechanical type, thus confirming the previous literature studies that had shown that fracture properties degrade faster than electrical properties.

Aging Mechanisms and Non-Destructive Aging Indicators of XLPE/CSPE Unshielded LV Nuclear Power Cables Subjected to Simultaneous Radiation-Mechanical Aging.

Low-voltage cable systems in nuclear power plants are key components that have a crucial role in the safe operation of nuclear facilities. Thus, the aging management of cable systems is of utmost importance as they cannot easily or economically be replaced or upgraded. Therefore, there is a continuous need to develop reliable non-destructive condition monitoring techniques, mostly based on the measurement of the dielectric properties of cable insulation. This paper introduces the changing of dielectric and mechanical properties of XLPE insulated and CSPE jacketed unshielded low-voltage nuclear power plant power cable in case of simultaneous mechanical and radiation aging. The cable samples were bent and exposed to 400 kGy gamma irradiation with a 0.5 kGy/hr dose rate. Dielectric response (real and imaginary permittivity) in the 0.1 Hz−1 kHz frequency range, extended voltage response (EVR), and the Shore D hardness test techniques were measured to track aging. The electrical and mechanical parameters have increased monotonically with aging, except the imaginary permittivity, which increased only at frequencies higher than 10 Hz. Furthermore, different quantities were deducted based on the frequency and permittivity data. The electrical parameters and deducted quantities correlation with aging and mechanical parameters were investigated. Since the deducted quantities and the electrical parameters are strongly correlated with absorbed dose and mechanical properties, the electrical measurements can be applied as a non-destructive aging indicator for XLPE/CSPE unshielded low-voltage nuclear power cables.

Experimental and predicted XLPE cable insulation properties under UV radiation

This paper deals with the behavior of the crosslinked polyethylene (XLPE) used as high-voltage power cable insulation under ultraviolet (UV) radiations. For this, XLPE samples have been irradiated for 240 h using low-pressure vapor fluorescent lamps. Electrical (surface and volume resistivities), mechanical (tensile strength, elongation at break and surface hardness) and physical (weight loss, water absorption, work of water adhesion and contact angle) tests have been first carried out. Experimental results show that the XLPE characteristics are affected by UV radiation. Indeed, a decline in surface resistivity, mechanical properties, and contact angle, and an increase in the water retention amount and weight loss have been recorded. In order to predict and extrapolate some XLPE properties, a supervised artificial neural network (ANN) trained by Levenberg-Marquardt algorithm has been designed. The collected database is used to train and test the ANN performance. The obtained results show that the proposed ANN algorithm presents good estimation and prediction since the predicted output values agree with the experimental data.

Features of thermal ageing of cables with different type of insulation

A wide range of temperature and duration of cable routes operation requires the development of objective methods for assessing the properties of cable insulation. While working, preparing and repairing cable routes, it is important to use express methods to determine the technical condition of insulation, to search for diagnostic parameters indicating the process of crack formation. An ongoing monitoring of cable insulation with standard devices controlling electrical resistance and leakage currents is not sufficiently effective for evaluating the performance and predicting the properties of cable insulation. The study is aimed at further testing of the technique by analysing the properties of materials used in cable engineering, as well as comparing the results obtained by various devices manufactured by national and foreign companies. Tests were carried out to assess the quality of insulation based on the monitoring of hardness of the hose insulation and the conductor insulation of KNR and KNREk cables. In the KNREk type cables, the core insulation is also made of the RTI type rubber, but the hose insulation is created on the basis of a material from polyvinyl chloride compound. The method of assessing the quality of insulation and assessing the degree of ageing of cable material is implemented by measuring the hardness of insulation material using the Shore method using portable hardness testers of the following types: TH-200, NOVOTEST TS D-A (TS D-D) up to 100 HSА (HSD). It is shown that the proposed technique makes it possible to identify objective statistical parameters of the material hardness and to diagnose the quality of insulation in operation without dismantling cable routes. The hardness parameters of hose insulation from polyvinyl chloride compound can be controlled by TS D-D devices. The heat resistance of hose insulation of the KNREk type cables is higher than that of the cables of the KNR type, which creates opportunities for their longer operation at high temperatures.

Analysis of Physical and Chemical Properties of XLPE Insulation for Long Term Running Cable

High temperature caused by copper core would have a certain impact on the performance of XLPE insulation during the long running process of the cable. In this paper, the XLPE/PVC cable running for 17years was investigated by using thermal analysis, microstructure analysis, mechanical property analysis and dielectric properties analysis. The influences of long-term operation for the physical and chemical properties of cable insulation are analyzed by the performance of the insulation material. DSC results indicated that position of shoulder peak would characterize the thermal history of material and express the crystal size distribution of XLPE indirectly. Mechanical property test results showed that effect of long term high temperature would decrease the elongation at break and breaking strength of XLPE. SEM results showed that the effect of long term high temperature increased the average size of crystal and the distribution of the crystal became concentrated, meanwhile it verified the relevant conclusion of DSC.

A Study of the Composite Insulation Breakdown Properties for Wrapping Cables in Liquid Nitrogen

To optimize the insulation design of high-temperature superconductivity (HTS) cable, the multilayer wrapping cable insulation properties in the liquid nitrogen should be studied. In this paper, we investigated the breakdown properties of multilayer wrapping of cable insulation in liquid nitrogen. AC and dc breakdown tests of a minimodel cable with an insulation floor composed of polypropylene laminate paper (PPLP), PPLP/100HN (DuPont polyimide film), PPLP/100CR (DuPont polyimide film), and PPLP/150FCR019 (DuPont polyimide film) and of singer-layer sheets, including PPLP, 100HN, 100CR, and 150FCR019, respectively, were performed in liquid nitrogen. The breakdown characteristics of the sheets and model cable insulation consisting of PPLP and composite insulation schemes according to the arrangement of PPLP/HN, PPLP/100CR, and PPLP/150FCR019 were compared. For the sheets, the ac breakdown strength of 100HN is greater than that of 100CR; this may be because there are large amounts of organic-inorganic interface in 100CR. The dc breakdown strength of 100CR is greater than that of 100HN, which may be because the space charge of 100CR homogenizes the electric field. For the minimodel cable insulation, the dc and ac breakdown strengths of the composite insulation in which the third layer of wrapping tape insulation material was composed of three layers of 100HN, which is overlapped completely, are greater than those of the insulation consisting of PPLP and other composite insulations.

Changes of Thermoplastic PE Cable Insulation Properties Caused by the Overload Current

Experiments were conducted to determine structural changes (degree of crystallinity) of PE (polyethylene), the development of treeing (velocity, shape), and changes of tan delta and breakdown strength as a result of thermal aging. The results show that thermal aging causes increased separation of spherulites. Overheating leads to the appearance of amorphous regions with dimensions exceeding the diameter of the neighboring spherulites. It is shown that the treeing channels develop faster in amorphous thermoplastic PE insulation than in a partially crystalline one and that tan delta increases, but the breakdown decreases with the time of thermal aging. >

Changes of thermoplastic PE cable insulation properties caused by the overload current

Experiments were conducted to determine structural changes (degree of crystallinity) of PE (polyethylene), the development of treeing (velocity, shape), and changes of tan delta and breakdown strength as a result of thermal aging. The results show that thermal aging causes increased separation of spherulites. Overheating leads to the appearance of amorphous regions with dimensions exceeding the diameter of the neighboring spherulites. It is shown that the treeing channels develop faster in amorphous thermoplastic PE insulation than in a partially crystalline one and that tan delta increases, but the breakdown decreases with the time of thermal aging.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>