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"electrical machinery"
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Development and Validation of Reliability Testing Methods for Insulation Systems in High-Voltage Rotating Electrical Machinery on Ships
Lloyd’s Register became the first classification society to mandate reliability testing for insulation degradation in rotating electrical machinery. As the maritime industry shifts toward eco-friendly practices, high-voltage rotating electrical machinery on ships increasingly features higher voltages and larger capacities. However, incidents involving insulation systems have also become more frequent. Additionally, testing facilities with the necessary equipment to perform such reliability tests are lacking, and standardized testing methods are yet to be established. This study proposes test items, methods, and evaluation criteria for the reliability testing of high-voltage rotating electrical machinery. The testing methods are broadly categorized into four types: thermal, electrical, multifactor, and thermomechanical degradation reliability testing. The proposed methods were validated by conducting long-term testing over approximately one year. Key results showed a breakdown time of 7056 h in thermal evaluation, 5040 h in electrical evaluation, and 258.5 d in multifactor evaluation, as well as a 63rd percentile value of 245.7 h in thermomechanical evaluation, all of which fulfill the required criteria. The study offers practical guidelines for ensuring the durability and safety of high-voltage electrical machinery, aligning with the sustainability and safety goals of the maritime industry.
Journal Article
Optimization of diesel electric machinery system configuration in conceptual ship design
In this paper an optimization based decision support model for determining diesel electric machinery system configuration in conceptual ship design is presented. Load distribution on the engines is considered in the model to ensure that required demand is met with sufficient power supply for all future operational states. A method for fuel consumption calculation is presented, based on determining optimal load distribution amongst the engines related to each engines generalized specific fuel consumption curve. Total fuel costs and appropriate NO
X
taxes are calculated based on the ship’s future operational profiles. A case study is presented to exemplify the use of the model. Results show that the model might be used to obtain valuable insight to expected operational costs and decision support for selecting machinery system configuration.
Journal Article
Energy System 4.0: Digitalization of the Energy Sector with Inclination towards Sustainability
The United Nations’ sustainable development goals have emphasized implementing sustainability to ensure environmental security for the future. Affordable energy, clean energy, and innovation in infrastructure are the relevant sustainable development goals that are applied to the energy sector. At present, digital technologies have a significant capability to realize the target of sustainability in energy. With this motivation, the study aims to discuss the significance of different digital technologies such as the Internet of Things (IoT), artificial intelligence (AI), edge computing, blockchain, and big data and their implementation in the different stages of energy such as generation, distribution, transmission, smart grid, and energy trading. The study also discusses the different architecture that has been implemented by previous studies for smart grid computing. Additionally, we addressed IoT-based microgrids, IoT services in electrical equipment, and blockchain-based energy trading. Finally, the article discusses the challenges and recommendations for the effective implementation of digital technologies in the energy sector for meeting sustainability. Big data for energy analytics, digital twins in smart grid modeling, virtual power plants with Metaverse, and green IoT are the major vital recommendations that are discussed in this study for future enhancement.
Journal Article
Tomek Link and SMOTE Approaches for Machine Fault Classification with an Imbalanced Dataset
Data-driven methods have prominently featured in the progressive research and development of modern condition monitoring systems for electrical machines. These methods have the advantage of simplicity when it comes to the implementation of effective fault detection and diagnostic systems. Despite their many advantages, the practical implementation of data-driven approaches still faces challenges such as data imbalance. The lack of sufficient and reliable labeled fault data from machines in the field often poses a challenge in developing accurate supervised learning-based condition monitoring systems. This research investigates the use of a Naïve Bayes classifier, support vector machine, and k-nearest neighbors together with synthetic minority oversampling technique, Tomek link, and the combination of these two resampling techniques for fault classification with simulation and experimental imbalanced data. A comparative analysis of these techniques is conducted for different imbalanced data cases to determine the suitability thereof for condition monitoring on a wound-rotor induction generator. The precision, recall, and f1-score matrices are applied for performance evaluation. The results indicate that the technique combining the synthetic minority oversampling technique with the Tomek link provides the best performance across all tested classifiers. The k-nearest neighbors, together with this combination resampling technique yielded the most accurate classification results. This research is of interest to researchers and practitioners working in the area of condition monitoring in electrical machines, and the findings and presented approach of the comparative analysis will assist with the selection of the most suitable technique for handling imbalanced fault data. This is especially important in the practice of condition monitoring on electrical rotating machines, where fault data are very limited.
Journal Article
Study on Dispersion of Impulse Discharge in SFsub.6 and Eco-Friendly Insulating Gas Csub.4Fsub.7N/COsub.2
In recent years, C[sub.4]F[sub.7]N/CO[sub.2] gas has been widely studied as an eco-friendly alternative to SF[sub.6], which is commonly used in electrical equipment. To ensure electrical equipment reliability, the dispersion of impulse discharge voltage of insulated gas is generally required to be less than 3%. However, experimental results indicate that under fault conditions, such as sudden pressure changes or electric field distortion, the discharge dispersion of both C[sub.4]F[sub.7]N/CO[sub.2] and SF[sub.6] often exceeds 3%. This paper investigates the impact of pressure and electric field nonuniformity on the dispersion of impulse discharge voltage for conventional and eco-friendly insulating gases under varying degrees of electric field nonuniformity. Experiments reveal that under identical conditions, the 9%C[sub.4]F[sub.7]N/91%CO[sub.2] mixture exhibits lower impulse discharge voltage dispersion compared with SF6. As pressure increases, the dispersion decreases for both gases. Conversely, dispersion increases with higher electric field nonuniformity, and the 9%C[sub.4]F[sub.7]N/91%CO[sub.2] mixture demonstrates greater sensitivity to electric field nonuniformity than SF[sub.6]. In practical applications, electrical equipment typically operates under slightly nonuniform electric fields and high pressure, meeting dispersion requirements. However, if electric field distortion causes the nonuniformity factor (f) to exceed 2.4 or if pressure drops below 0.3 MPa then dispersion increases significantly, reducing the reliability of insulation performance data.
Journal Article
Correction: Economic policy uncertainty, intra-industry trade, and China’s mechanical and electrical product exports
[This corrects the article DOI: 10.1371/journal.pone.0290866.].
Journal Article
Analysis of Breaking Characteristics of Csub.4Fsub.7N/COsub.2 Mixture Gas in Circuit Breaker
In recent years, the C[sub.4]F[sub.7]N mixed gas has attracted considerable attention for its outstanding insulation and arc-extinguishing capabilities, positioning it as a potential substitute for sulfur hexafluoride, SF[sub.6]. However, there remains a limited understanding of the arc-extinguishing and insulation performance of C[sub.4]F[sub.7]N/CO[sub.2] mixed gas. In addition, there is limited research on high-current breaking in circuit breakers. Therefore, this study aims to investigate the arc characteristics and breaking behavior of 10%C[sub.4]F[sub.7]N/90%CO[sub.2] and 15%C[sub.4]F[sub.7]N/85%CO[sub.2] mixed gases using a magnetohydrodynamic model based on the 252kV air pressure circuit breaker. The dynamic characteristics of this mixed gas are compared with pure SF[sub.6] under short-circuit current breaking conditions, while analyzing different parameters of the C[sub.4]F[sub.7]N configuration. The results indicate that the mixed gas exhibits lower levels in terms of arc temperature, axial diffusion distance and pressure difference at the moment of arc initiation compared to pure SF[sub.6]. Furthermore, increasing the inflating pressure can effectively enhance the breaking performance of the circuit breaker with 0.6 MPa, making it more suitable. Additionally, increasing the proportion of C[sub.4]F[sub.7]N in the mixed gases will cause the arc temperature to rise slightly at the initial arc and current crossing zero, but decrease at the peak current. The core pressure also rises significantly, with a greater pressure difference established in the compressor at moment of arc initiation. This study provides a reference for the design of an environmentally friendly circuit breaker and the selection of the mixed gas ratio.
Journal Article
Lightweight, Flexible Cellulose-Derived Carbon Aerogel@Reduced Graphene Oxide/PDMS Composites with Outstanding EMI Shielding Performances and Excellent Thermal Conductivities
HighlightsCellulose aerogels were prepared by hydrogen bonding driven self-assembly, gelation and freeze-drying.The skin-core structure of CCA@rGO aerogels can form a perfect three-dimensional bilayer conductive network.Outstanding EMI SE (51 dB) is achieved with 3.05 wt% CCA@rGO, which is 3.9 times higher than that of the co-blended composites.In order to ensure the operational reliability and information security of sophisticated electronic components and to protect human health, efficient electromagnetic interference (EMI) shielding materials are required to attenuate electromagnetic wave energy. In this work, the cellulose solution is obtained by dissolving cotton through hydrogen bond driving self-assembly using sodium hydroxide (NaOH)/urea solution, and cellulose aerogels (CA) are prepared by gelation and freeze-drying. Then, the cellulose carbon aerogel@reduced graphene oxide aerogels (CCA@rGO) are prepared by vacuum impregnation, freeze-drying followed by thermal annealing, and finally, the CCA@rGO/polydimethylsiloxane (PDMS) EMI shielding composites are prepared by backfilling with PDMS. Owing to skin-core structure of CCA@rGO, the complete three-dimensional (3D) double-layer conductive network can be successfully constructed. When the loading of CCA@rGO is 3.05 wt%, CCA@rGO/PDMS EMI shielding composites have an excellent EMI shielding effectiveness (EMI SE) of 51 dB, which is 3.9 times higher than that of the co-blended CCA/rGO/PDMS EMI shielding composites (13 dB) with the same loading of fillers. At this time, the CCA@rGO/PDMS EMI shielding composites have excellent thermal stability (THRI of 178.3 °C) and good thermal conductivity coefficient (λ of 0.65 W m-1 K-1). Excellent comprehensive performance makes CCA@rGO/PDMS EMI shielding composites great prospect for applications in lightweight, flexible EMI shielding composites.Graphic abstract
Journal Article
Carbon Nanotubes as an Alternative to Copper Wires in Electrical Machines: A Review
The surge in electric vehicles (EVs) and their electrical appliances requires highly efficient, lightweight electrical machines with better performance. However, conventional wire used for electrical machine windings have certain limits to the current requirements. Copper is a commonly used material in electrical windings, and due to its ohmic resistance, it causes 75% of total losses in electrical machines (copper losses). The high mass of the copper results in a bulky system size, and the winding temperature of copper is always maintained at less than 150 °C to preserve the thermal insulation of the electric machine of the windings. On the other hand, carbon nanotubes and carbon nanotube materials have superior electrical conductivity properties and mechanical properties. Carbon nanotubes ensure 100 MS/m of electrical conductivity, which is higher than the copper electrical conductivity of 59.6 MS/m. In the literature, various carbon nanotubes have been studied based on electrical conductivity, temperature co-efficient with resistivity, material thickness and strength, insulation, and efficiency of the materials. Here, we review the electrical and mechanical properties of carbon nanotubes, and carbon nanotube composite materials are reviewed with copper windings for electrical wires.
Journal Article