Composition identification, aging mechanisms and nondestructive aging indicator of commercial filled cross-linked polyethylene (XLPE) cable insulation materials

This work studies the chemical composition, physical make-up, and aging mechanisms of thermally-exposed and gamma-irradiated, commercial, cross-linked, polyethylene (XLPE) cable insulation material used in Nuclear Power Plants (NPPs), using various analytical characterization techniques. Understanding of cable aging behaviors is important for cable safety inspection, which is required as both routine inspection and in safety inspection in the process of extending the operating license of NPPs. The fillers and additives in the XLPE cable insulation materials were identified and quantified using scanning electron microscopy, energy dispersive X-ray spectroscopy, carbon-hydrogen elemental weight ratio tests, thermogravimetric analysis, and pyrolysis gas chromatography-mass spectroscopy. Laboratory-based accelerated aging experiments were designed and conducted for aging electrical cables, achieving 240 different aging conditions including thermal-only aging and simultaneous thermal and gamma radiation aging. Aging mechanisms of the XLPE cable insulation materials were studied, including discussion of the changes in antioxidant, flame retardants, and the XLPE polymer chains as the samples age. Additional analytical techniques used for studying the aging mechanisms included gel-fraction measurements, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, permittivity and dielectric loss tangent measurements, and oxidation induction time measurements. A nondestructive aging indicator was identified, that is promising for future development of a nondestructive cable aging testing method

Aging Mechanisms and Monitoring of Cable Polymers

Aging mechanisms of two polymeric insulation materials that are used widely in nuclear power plant low-voltage cables; cross-linked polyethylene (XLPE) and ethylene propylene rubber/ethylene propylene diene terpolymer (EPR/EPDM), are reviewed. A summary of various nondestructive methods suitable for evaluation of cable insulation is given. A capacitive sensor capable of making local nondestructive measurements of capacitance and dissipation factor on cable polymers, and potentially suitable for in situ cable monitoring, is introduced. Correlating values of elongation-at-break, indenter modulus, capacitance and dissipation factor measured on a set of 47 aged flame-resistant EPR samples shows a higher correlation between indenter modulus and dissipation factor than between indenter modulus and elongation-at-break

Research on dynamic load characteristics and active control strategy of electro-mechanical coupling powertrain of drum shearer cutting unit under impact load

In order to extend the service life of the long-chain gear transmission system of a drum shearer, an electro-mechanical coupling model of a drum shearer cutting unit is established. The model considers the dynamic characteristics of the motor, time-varying meshing stiffness, as well as the drum load characteristics. Additionally, the dynamic characteristics and control strategy for suppressing the dynamic load of the gear transmission system under impact load are investigated based on this model. Firstly, the influence of the gear transmission system of the drum shearer cutting unit under impact load is analyzed. Then, on that basis, the active control strategy based on motor torque compensation is proposed to suppress the dynamic load of the gear transmission system caused by mutational external load. Finally, the suppression effect on the dynamic load of the gear transmission system is analyzed. Research results indicate that this control strategy has good control effects to suppress the dynamic load caused by a mutational external load, which confirms the effectiveness of the proposed control strategy

Mode-locking Theory for Long-Range Interaction in Artificial Neural Networks

Visual long-range interaction refers to modeling dependencies between distant feature points or blocks within an image, which can significantly enhance the model's robustness. Both CNN and Transformer can establish long-range interactions through layering and patch calculations. However, the underlying mechanism of long-range interaction in visual space remains unclear. We propose the mode-locking theory as the underlying mechanism, which constrains the phase and wavelength relationship between waves to achieve mode-locked interference waveform. We verify this theory through simulation experiments and demonstrate the mode-locking pattern in real-world scene models. Our proposed theory of long-range interaction provides a comprehensive understanding of the mechanism behind this phenomenon in artificial neural networks. This theory can inspire the integration of the mode-locking pattern into models to enhance their robustness.Comment: 10 pages, 6 figure

Analysis of Reliability Correlation Degree of Rolling Bearings Based on Zero-Failure Data

Modern equipment has higher requirements for the reliability of rolling bearings. The time and economic cost of obtaining bearing failure data through test methods are getting higher. Usually, truncation time tests of small sample are used to obtain zero-failure data of bearings. Based on the zero-failure data model and multi-layer Bayesian theory, this paper improves the reliability evaluation method of rolling bearings by changing the values of hyperparameters, and calculates the estimated value of failure probability at each truncation time to obtain the reliability of the bearing. This paper adopts the theory of grey relational degree to analyze the relationship and change law of bearing reliability at each truncation time, to understand the reliability change trend of rolling bearing more comprehensively. Experiments show that the method is reasonable

Capacitive Sensing for Nuclear Power Plant Cable Insulation Assessment

The ability to evaluate, nondestructively, the material state of insulation polymers widely employed in aged control and power cables has been identified as important In the process of routine safety inspection and safety inspection for license renewal of aging Light Water Reactor Nuclear Power Plants (NPPs) in the United States [1]. The present industry standard is that the insulation polymer breaking strain (or elongation-at-break, EAB) should be no less than 50% of that value measured on the pristine material, for the aged insulation polymer to be fit for service. Measurement of EAB is destructive, the method requires a relatively large quantity of sample material, and the results exhibit large uncertainty, however. Here, the ability of a capacitive sensor to indicate, nondestructively, the state of the insulation polymer is explored. The insulation material most commonly employed in U.S. NPPs, cross-linked polyethylene (XLPE), is aged simultaneously at elevated temperature and by exposure to gamma radiation. XLPE- coated wire samples are aged at 90 °C or 115 °C with a combination of three dose rates (0, 19, or 54 krad/h) and two exposure durations (10 or 25 days) to give different total doses that range between 0 Mrad, for a pristine sample, and approximately 32 Mrad, for the most severely aged sample in this set. An inter-digital capacitive sensor that conforms to the curved surface of the insulated wire [2] is used to assess the dielectric properties of the samples. The breakdown voltage of the wire insulation is measured by means of a custom-designed electrode setup. Correlation values are computed between capacitance, dissipation factor, breakdown strength, and EAB measured on the aged samples, in order to assess the effectiveness of the nondestructive capacitive method for indicating the state of the wire insulation after aging

Quantitative analysis of changes in antioxidant in crosslinked polyethylene (XLPE) cable insulation material exposed to heat and gamma radiation

Quantitative analysis of the antioxidant poly(1,2-dihydro-2,2,4-trimethylquinoline) (pTMQ) was conducted on pristine, thermally-aged, and gamma radiation-aged commercial cross-linked polyethylene-(XLPE-)based cable insulation material aged at temperatures 60, 90, and 115 °C, with gamma radiation exposure dose rates of 0, 120, 300, and 540 Gy/h for 15 days. The quantification of antioxidant was performed using pyrolysis gas chromatography-mass spectrometry (Py-GCMS). Oxidation induction time (OIT) was measured using differential scanning calorimetry (DSC) and correlation was made between the quantified depletion of antioxidant and measured OIT. It was observed that, in the case of isothermal aging, the quantity of antioxidant and OIT decreased with increasing gamma radiation dose. In the case of samples exposed to the same gamma radiation dose, the quantity of antioxidant and OIT were observed to decrease with increasing aging temperature. Depletion in the quantity of antioxidant relative to that in the pristine material ranged from 7 to 93% for differently aged samples. The measured decline in OIT ranged from 0 to 80%. Change in the quantity of antioxidant in the material was observed to follow the same trend as the change in OIT when the samples were aged under various conditions. The observations are explained in terms of the reaction between the antioxidant and free radicals created during exposure of the samples to thermal and gamma radiation

Microscopic characteristics of magnetorheological fluids subjected to magnetic fields

© 2020 Elsevier B.V. With the aim of studying the microscopic characteristics of a magnetorheological fluid (MRF) in a magnetic field, the theoretical analyses of the particles dynamics in a magnetic field are presented, and a model for the particle motion is proposed. Based on these analyses, a three-dimensional numerical simulation of the microstructure of MRFs in different magnetic fields is performed. Furthermore, the microstructures of the MRFs are investigated using industrial computed tomography (CT) imaging. The numerical simulation and industrial CT results indicate that the chain structure of the same MRF becomes more apparent as the magnetic field strength increases, and in the same external magnetic field, this chain structure also becomes more apparent with an increase in the particle volume fraction. The lengths of particle chains in different magnetic fields are also captured in the industrial CT experiments. When the magnetic field strength is 12 mT, the particle chains of the MRF with a particle volume fraction of 30% reach more than 10 mm in length, which bridge the inner diameter of the container, and the dense clusters-like structure is formed, the clusters-like structure becomes denser with an increase in magnetic field. Moreover, the particle chain lengths of MRF with high particle volume fractions increase sharply with the magnetic field. The experiments demonstrated that the industrial CT is an efficient method to study the microstructures of MRFs by providing particle distributions of MRFs more clearly and intuitively

Development and evaluation of a versatile semi-active suspension system for high-speed railway vehicles

With the increase in speed of high-speed trains, their vibration will become fiercer and fiercer, especially when the lateral resonance of the car body occurs. This paper develops a versatile semi-active suspension system with variable stiffness (VS) magnetorheological elastomer (MRE) isolators and variable damping (VD) magnetorheological (MR) dampers for high-speed trains, aiming to improve ride comfort by avoiding car body resonance and dissipating vibration energy. As the first step, a multifunction VSVD semi-active suspension system for high-speed railway vehicles was designed and prototyped, including four VS-MRE isolators and two VD-MR dampers. After that, a scaled train model, composing of a car body and a secondary lateral suspension system was designed and built to evaluate the performance of the new VSVD suspension system; a control strategy based on short-time Fourier transform (STFT) and sky-hook was proposed to control the new suspension system. Two different excitations, harmonic excitation and random excitation, were applied to evaluate the train\u27s VSVD suspension. As a comparison, four alternative suspension systems, including passive-off suspension, passive-on suspension, pure VS suspension, and pure VD suspension were also evaluated. The evaluation results verified that the VSVD suspension of the train can avoid lateral resonance of car body and dissipate the vibration energy efficiently. The comparison verified that the VSVD suspension system outperforms the passive-off suspension, passive-on suspension, pure VS suspension, and pure VD suspension