Analysis of power frequency electric field distortion caused by substation inspection robot

In the era of intellectualization, many substation inspection robots are being put into operation, but they will cause electric field distortion in the surrounding space during operation. This paper establishes a three-dimensional simplified simulation calculation model for 500kV substations and inspection robots. Based on the boundary element method, we simulate the power frequency electric field of the substation switchyard and analysis the distortion electric field when the inspection robot is in the station. The results show that when the electric field intensity is strong, the distortion coefficient caused by the robot will be larger, and the maximum can reach 2.25 times, and when the electric field intensity is small, the distortion coefficient will be smaller, and the distortion coefficient is 1.42 times on average.

Frequency and Temperature-Dependent Space Charge Characteristics of a Solid Polymer under Unipolar Electrical Stresses of Different Waveforms

In this paper, we studied the space charge phenomena of a solid polymer under thermal and electrical stresses with different frequencies and waveforms. By analyzing the parameter selection method of a protection capacitor and resistor, the newly built pulsed electro-acoustic (PEA) system can be used for special electrical stresses under 500 Hz, based on which the charge phenomena are studied in detail under positive and negative DC and half-wave sine and rectangular wave voltages. Experimental results show that the charge accumulated in the polyimide polymer under DC conditions mainly comes from the grounded electrode side, and the amount of charge accumulated with electric field distortion becomes larger in a high-temperature environment. At room temperature, positive charges tend to accumulate in low-frequency conditions under positive rectangular wave voltages, while they easily appear under high-frequency situations of negative ones. In contrast, the maximum electric field distortion and charge accumulation under both half-wave sine voltages occur at 10 Hz. When the measurement temperature increases, the accumulated positive charge decreases, with a more negative charge appearing under rectangular wave voltages, while a more positive charge accumulates at different frequencies of half-wave sine voltages. Therefore, our study of the charge characteristics under different voltage and temperature conditions can provide a reference for applications in the corresponding environments.

High Breakdown Strength and Energy Storage Density in Aligned SrTiO3@SiO2 Core–Shell Platelets Incorporated Polymer Composites

Dielectric nanocomposites with high energy storage density (Ue) have a strong attraction to high-pulse film energy-storage capacitors. Nevertheless, low breakdown strengths (Eb) and electric displacement difference (Dmax − Drem) values of nanocomposites with incorporating the randomly distributed high dielectric constant additions, give rise to low Ue, thereby hindering the development of energy-storage capacitors. In this study, we report on newly designed SrTiO3@SiO2 platelets/PVDF textured composites with excellent capacitive energy storage performance. SrTiO3@SiO2 platelets are well oriented in the PVDF when perpendicular to the electric field with the assistance of shear force in the flow drawing process to establish microscopic barriers in an inorganic–polymer composite that is able to substantially improve the Eb of composites and enhance the Ue accordingly. Finite element simulation demonstrates that the introduction of the highly insulating SiO2 coating onto the SrTiO3 platelets effectively alleviates the interface dielectric mismatch between filler and PVDF matrix, resulting in a reduction in the interface electric field distortion. The obtained composite film with optimized paraelectric SrTiO3@SiO2 platelets (1 vol%) exhibited a maximum Dmax − Drem value of 9.14 μC cm−2 and a maximum Ue value of 14.4 J cm−3 at enhanced Eb of 402 MV m−1, which are significantly superior to neat PVDF and existing dielectric nanocomposites.

Fan-Intake Coupling With Conventional and Short Intakes

The current trend in civil engine fans towards lower pressure ratio and larger diameter is accompanied by a need to shorten the engine intake length to reduce weight and drag. This paper uses full-annulus, unsteady CFD simulations of two coupled fan-intake configurations to explain the impact of flow field coupling and intake length on fan and intake performance. On-design and off-design operating points are considered at cruise and high angle of attack, respectively. The fan efficiency at cruise is shown to be determined by a trade-off between two effects. Cruise efficiency is reduced by 0.11% with a short intake due to increased potential flow field distortion, which alters the incidence and diffusion of the rotor. This is partially offset by a reduction in casing boundary layer thickness due to lower intake wetted area. At high angle of attack conditions, a short intake leads to increased potential flow field distortion and an earlier onset of intake flow separation due to a higher adverse pressure gradient approaching the fan. Both effects combine to reduce the fan thrust at such conditions, although the fan is shown to remain stable at attack angles up to 35°. The reduction in performance is shown to be dominated by flow separations in the rotor, which increase in size and severity for a given attack angle as the intake length is decreased. The fan is also shown to have a stronger influence on the form of the intake flow field in a short intake, suggesting that it is necessary to model the fan in the intake design process for a successful design.

Numerical Modeling of Nondestructive Testing of Various Conductive Objects inside Metal Enclosures Using ELF/VLF Magnetic Fields

Nondestructive evaluation of various conductive objects through metal enclosures is investigated by using ELF/VLF magnetic induction fields in detailed simulations. ELF/VLF magnetic fields (<30 kHz) have a unique ability to penetrate highly conductive or permeable shields. Using a magnetic dipole source antenna, objects hidden inside a metal enclosure are imaged via examining distortions to the field outside the enclosure. The field distortion is parametrically studied by varying the size, conductivity, and permeability of the hidden objects. Furthermore, the importance of the conductivity of the enclosure itself is investigated using both low (106 S/m) and high (108 S/m) conductivity metallic shields. It is shown that the responses are quite sensitive to the object and shield parameters; both qualitative and quantitative properties of the field distortions are described in detail. The simulation results suggest that properties of hidden conductive or permeable objects, over a relatively wide range of parameters (both geometry and material), can be inferred nondestructively using ELF/VLF magnetic induction fields.

The Investigation on the Flow Distortion Effect of Header to Guarantee the Measurement Accuracy of the Ultrasonic Gas Flowmeter

The quantification of the flow distortion effect on the measurement accuracy of the ultrasonic gas flowmeter downstream of the header is important but an area that has been of less concern in the research. By experiments and computational fluid dynamics (CFD), the influence of flow field distortion was studied. Experimental results under three different installation conditions showed that when there was flow field distortion downstream of the header, the measurement results of the gas ultrasonic flowmeter were 1% higher than those when there was no distortion, while a flow conditioner could effectively eliminate flow field distortion. Based on the experimental tests, the flow field distribution was analyzed with CFD, which showed that the flow field distortion effect generated by the header had a significant influence on the parameter of nonconforming Profile factor, while the parameters of Symmetry and Cross-flow could be obviously eliminated by the double-cross-section designing.