Materials In Electrical Equipment Research Articles

Surface Flashover Characteristics of Epoxy Resin Under DC Voltage and its Modification Method

Epoxy resin is used as insulating material in electrical equipment due to its perfect electrical, mechanical and thermal properties. The accumulation of charge on the surface of the material and its promotion of surface flashover, however, often lead to insulation failure and directly endanger the operation of electrical equipment safety. Therefore, improving the insulation performance of epoxy materials is of great significance for protecting high-voltage power equipment. In this paper, a blend-modified epoxy resin was synthesized by DGEBA and DCPDE, and its surface charge dissipation and surface flashover characteristics with DC voltage were tested. The experimental results show that the surface charge distribution can be effectively changed by changing the ratio of epoxy resin, which is meanful to improve the material’s insulation properties.

Measurement and analysis of vibration characteristics of nanocrystalline magnetic core under symmetrical/asymmetrical waveforms

PurposeBecause the nanocrystalline core is widely used in power electronic equipment, and the excitation waveform of its working mode is complex, the vibration at medium and high frequencies cannot be ignored. Therefore, this study aims to study the vibration mechanism of nanocrystalline strip and the vibration characteristics of nanocrystalline magnetic ring under different excitation waveforms.Design/methodology/approachFirst, the electromagnetic vibration mechanism between nanocrystalline strips is analyzed by finite element analysis, and the force of the magnetic ring with and without air gap is compared and analyzed. Then, the vibration of nanocrystalline magnetic ring under different excitation waveforms such as sine wave, triangular wave, symmetric rectangular wave and asymmetric rectangular wave is analyzed by experimental method. The acceleration time domain waveform measured by the experiment is analyzed by fast Fourier transform, and the vibration is analyzed according to the spectrum.FindingsBecause of the increase of magnetic flux leakage, the volume force density and the Maxwell force on the surface of the nanocrystalline magnetic ring will increase after the air gap is opened, resulting in the intensification of vibration. Under symmetric/asymmetric rectangular wave excitation, the vibration acceleration varies with the duty cycle. Due to the influence of harmonic excitation, the relationship between the main frequency of vibration and the excitation frequency is not two times, and its multiple decreases with the increase of excitation frequency.Originality/valueThe research and analysis of this paper can promote the application of new magnetic materials in electrical equipment in small and medium-sized and medium- to high-frequency fields.

The 3-D vector hysteresis model of SMC materials based on the SAE and play operator

The hysteresis modeling of ferromagnetic materials in electrical equipment is one of the basic theoretical studies in the field of electrical engineering. In this paper, a 3-D vector hysteresis model is proposed based on Stacked Auto-Encoder (SAE) model and hysteresis operator space theory. Multiple 3-D vector Play hysteresis operators are used to construct an hysteresis operator space to create the high-dimensional operator data. By the operator space, the nonlinear hysteresis relationship in the hysteresis data is transformed into a nonlinear mapping between the operator data and the output of the model. And the SAE model is used to characterize this nonlinear mapping. In the training of the SAE model, training set is composed of operator data and magnetic field strength data. The structure of the vector hysteresis model is determined by taking the output of the operator space as the input of the SAE model. The simulation results show that the model can effectively describe the nonlinear characteristics and anisotropic of the Soft Magnetic Composite under 3-D vector excitation. In addition, this model has certain generalization ability.

Hybrid intelligent hysteresis model based on DBN-DNN algorithm and fusion Preisach operator

The hysteresis modeling of ferromagnetic materials in electrical equipment is one of the basic theoretical studies in the field of electrical engineering. Long training time and poor accuracy are the main challenges of the traditional hysteresis models. In this paper, a Hybrid Intelligent Hysteresis Model (HIHM) is proposed by combining the hysteresis operator space theory and Deep Belief Networks-Deep Neural Network (DBN-DNN) algorithm. The Preisach Fusion Operator (PFO) is constructed by fusing multiple traditional Preisach operators with coefficients satisfying the Gaussian distribution. And multiple PFOs are used to construct an operator space to create the high-dimensional operator data. By the operator space, the nonlinear hysteresis relationship in the hysteresis data is transformed into a nonlinear mapping between the operator data and the output of the model. The DBN-DNN model is used to characterize this nonlinear mapping. The structure of the HIHM is determined by taking the output of the operator space as the input of the DBN model. The generation of first-order reversal curve proves that the model has certain practicality. In addition, the validity and generalization of this model is verified through the simulation with experimental data of non-orientation (NO) silicon steel B35A210 at quasi-static frequency.

Reactive molecular dynamics simulation on the pyrolysis characteristics of epoxy resin under the effect of partial discharge active products

Aromatic amine cured Bisphenol F epoxy resin is used as a pivotal solid insulation material in electrical equipment at low temperature and extreme environment. Partial discharge (PD) can lead to an increase in local temperature, which leads to pyrolysis, and the existence of PD active products will aggravate the pyrolysis process of insulating materials. In order to investigate the effect of PD active products on the pyrolysis characteristics of aromatic amine cured epoxy resin, the pyrolysis process of epoxy resin under partial discharge active products is simulated based on ReaxFF. The types and changing trend of small molecular products and the mechanism of PD active products acting on the pyrolysis process of epoxy resin are analyzed. The results show that the oxidation of hydroxyl and C-N bridge bonds by PD active products is the main reason for accelerating the pyrolysis of epoxy resin, which changes the main pyrolysis path of epoxy resin cross-linked structure. The thermal stability of cross-linked epoxy resin decreases under the action of active products, and the types and change trend of small molecular products generated in the pyrolysis process also changes greatly with the change of pyrolysis path.

Remote Optical Thermography Detection Method and System for Silicone Polymer Insulating Materials Used in Power Industry

Live detection of composite insulating materials in electrical equipment is highly demanded for the reliability and safety of the power system. This article proposes a remote optical thermography detection method and system for detecting defects in silicone polymer materials with the advantages of quick and simple operation, safety, visual results, and automatic remote measurement. First, the remote optical thermography detection system was established. Then, silicone polymer insulating materials with typical defects were tested by the proposed system at a long distance of 5 m. Images sequence processing techniques, including fast Fourier transform, principal component analysis, independent component analysis, and partial least-squares regression, were used to enhance defect contrast and reduce background noises. The experiment results have shown that defects with the size of 2 mm in silicone polymer insulating materials can be accurately detected at a long distance of 5 m by the proposed system. Finally, the performance of these adopted processing techniques in remote detection was quantitatively evaluated by two metrics, contrast and signal-to-noise ratio, to provide a reference for industrial applications of thermography detection at a long distance.

Study of treeing in epoxy-alumina nanocomposites using electroluminescence

Dielectric materials in electrical equipment are mostly subjected to non-uniform or divergent field conditions. Localized high electric field may give rise to space charge which may initiate material degradation, and eventually lead to dielectric breakdown. Thus, it is important to assess the performance of nanocomposites under divergent fields before deployment as insulation. Past research has shown a positive correlation between space charge and electroluminescence (EL). In this work, EL is used as a diagnostic tool to study space charge and field-related material degradation in epoxy-alumina nanocomposites. Various experiments are undertaken to detect early stages of material degradation through EL. These include endurance tests (below and above EL emission threshold), and characterization of EL from samples pre-stressed with DC and/or AC voltages. The effect of repeated square waves on material degradation is also analyzed. Visual inspection for physical damage is carried out using a high resolution camera. The EL signature is observed to deviate significantly from its initial value at the onset of material degradation, and may therefore serve as an aging marker. In addition, the EL studies show that nanocomposites exhibit a relatively high resistance to field-assisted material degradation. The experiments on pre-stressed samples indicate that charge kinetics play a crucial role in defect initiation and material degradation.

Thickness-Dependent DC Electrical Breakdown of Polyimide Modulated by Charge Transport and Molecular Displacement.

Polyimide has excellent electrical, thermal, and mechanical properties and is widely used as a dielectric material in electrical equipment and electronic devices. However, the influencing mechanism of sample thickness on electrical breakdown of polyimide has not been very clear until now. The direct current (DC) electrical breakdown properties of polyimide as a function of thickness were investigated by experiments and simulations of space charge modulated electrical breakdown (SCEB) model and charge transport and molecular displacement modulated (CTMD) model. The experimental results show that the electrical breakdown field decreases with an increase in the sample thickness in the form of an inverse power function, and the inverse power index is 0.324. Trap properties and carrier mobility were also measured for the simulations. Both the simulation results obtained by the SCEB model and the CTMD model have the inverse power forms of breakdown field as a function of thickness with the power indexes of 0.030 and 0.339. The outputs of the CTMD model were closer to the experiments. This indicates that the displacement of a molecular chain with occupied deep traps enlarging the free volume might be a main factor causing the DC electrical breakdown field of polyimide varying with sample thickness.

Theoretical evaluation of the interaction between C5-PFK molecule and Cu (1 1 1)

C5-PFK has drawn much attention in recent years as an environmental friendly gas-insulated medium. Many studies have proved that it has the potential to replace SF6 using in medium voltage electrical equipment. However, there are few reports about the compatibility between C5-PFK and materials used in the gas-insulated switchgear. C5-PFK may react with materials such as metal inside the equipment due to the strong activity of carbonyl group (C = O) in its molecular structure. Investigations about the material compatibility between C5-PFK and the materials are required to decide about a long term behavior. In this paper, the interaction between C5-PFK and copper, a common metallic material in electrical equipment, is discussed based on the density functional theory. We found that the interaction between the O atom in the C5-PFK molecule and Cu (1 1 1) surface is strong. The interaction between F atom and Cu (1 1 1) surface is weak, which belongs to physical adsorption. Relevant results not only clarify the compatibility between C5-PFK and copper but also provide guidance for prediction of long-term behavior of C5-PFK gas mixture and the selection or modification of materials used in the equipment.

Studies on the kinetic theory of polymer dielectric breakdown due to partial discharge

With the improvement of voltage level of electrical equipment, the requirement for the reliability of polymer dielectric materials in electrical equipment is much more strict. However, there are inevitably some defects in the manufacturing process of polymer dielectric materials, such as bubbles, inclusions, and so on. Therefore the life of electrical equipment will be greatly decreased when partial discharge occurs in a high electric field. In order to prevent and reduce the accident caused by the aging of polymer dielectric material in the electrical equipment, electrical aging life needs to be reasonably estimated. Based on the microscopic mechanism of partial discharge aging model, this paper suggests a stochastic differential equation for the electrical crack growth by using a non-equilibrium statistical physics theory, and then functions of breakdown probability, reliability, and electrical aging life due to the application of electric field are derived. Finally, a detailed analysis for the polyetllyleneterephthalate (PET) film is carried out, and the theoretical life of electrical aging is compared with experimental data. Results show that the theoretical values are consistent with the experimental data. So the aging life equations of polymer dielectrics derived in this paper can be used effectively in the quantitative analysis and may be helpful for the estimation of electrical life.

Study on Application of Insulating Materials in Electrical (Electronic) Equipment

Various types of insulating materials in electrical equipment is not only widely used, but also play a crucial role to enhance the insulation of electrical equipment performance and to improve the quality of electrical equipment. Different devices require different types of electrical insulating materials reliability,and in order to improve the safety factor of electrical equipment, it is necessary to strengthen the study on reliability of electrical insulating materials.