Voltage Grade Research Articles

Graphene-Enhanced CuW Composites for High-Voltage Circuit Breaker Electrical Contacts

To address the issue of over-standard short-circuit currents in a power system, it is imperative to enhance the comprehensive performance of the electrical contacts, which serve as the lynchpin of circuit breakers, so as to improve the breaking capacity of high-voltage circuit breakers. Graphene, as the most prominent two-dimensional carbon material in recent years, has garnered widespread applications across various fields. In this study, graphene-enhanced CuW composites for high-voltage circuit breaker electrical contacts were prepared innovatively using integrated vacuum infiltration technology. The innovative graphene-enhanced CuW composites significantly improved the mechanical, electrical, and ablation resistance properties, and have been successfully applied in the 252 kV/63 kA high-voltage SF6 circuit breakers, achieving 20 times effective consecutive full-capacity short-circuit current breaking. It provides a new route for the development and application of high-performance CuW electrical contacts. Looking ahead, it is planned to extend their application to higher voltage grade high-voltage circuit breakers.

Charge injection characteristics and charge migration mechanism of magnetic particle-modified EBA-based semi-conductive shielding layers

The space charge accumulation problem within insulation layer of high voltage direct current (HVDC) cable in engineering applications has attracted much attention. The inner semi-conductive shielding layer is located between the conductor and the insulation layer, which is the only way for charge injection into the insulation layer. The performance of the inner semi-conductive shielding layer has an important influence on the charge accumulation of the insulation layer. In this paper, the matrix resin EBA of high voltage grade DC cable shielding material is used as the research object. The magnetic particle SrFe12O19 is used to modify the EBA-based shielding material. The semi-conductive composites of CB/SrFe12O19/EBA with different SrFe12O19 concentrations (with different Lorentz Forces) are prepared. The mechanism of the influence of Lorentz Forces on the space charge injection characteristics of insulation layers and the mechanism of the charge migration are investigated. The trajectories of space charges in shielding layers are simulated using the finite element method. The experimental results show that SrFe12O19 can significantly reduce the space charge accumulation of the insulation layer. When SrFe12O19 is 5%, the shielding layer has the most obvious inhibition effect on the charge injection of the insulation layer. The simulation results show that the critical value of magnetic induction intensity is B′= 0.6 T when space charge moves in the shielding layer. This work provides a new way to solve the problem of space charge accumulation in HVDC cables, and has important reference significance for the development of HVDC cables.

Comparative study on matrix resins in two low‐density polyethylene based cable insulation materials with different voltage grades

AbstractIn industry, crosslinked polyethylene (XLPE) cable insulation is usually produced from crosslinkable compounds consisting of low‐density polyethylene (LDPE) and additives, which known as “cable materials”. Considering that in addition to additives, the structure of matrix resin is a key factor in determining the property of XLPE, it is worthy to study the structure requirements of matrix resin for the development of cable materials with different voltage grades. In this work, the structure of matrix resins of a high voltage grade and an extra high voltage grade cable material were comparatively investigated. Interestingly, it was found that the matrix resins have no significant difference in chain structure parameters including molecular weight and its distribution and vinyl content between two samples, and their crystalline structure as well as the melt rheology and melting crystallization behavior are also very similar. These results suggest that these matrix resins may not substantially differ. Our work shows that cable materials with different voltage grades are not necessarily diverge in terms of matrix resin structure, and it could be possible to develop higher grade cable materials using the same matrix resin as lower grade counterparts.

Investigation of active voltage support control approach of DC distribution networks based on virtual inertia coordination

AbstractDC distribution networks (DCDNs) possess the advantages of high power efficiency, low operation loss, and favourable control flexibility, and are regarded as an essential form of future power distribution systems. In order to increase the voltage transient performance of DCDNs against disturbances, this paper proposes a methodology for realising the active voltage support control of DCDNs based on virtual inertia coordination. Firstly, the impact of the inertia of DCDNs towards the transient voltage change is analysed, and the active voltage support mechanism considering the variable droop inertia control and virtual DC motor inertia (VDCMI) control is explored. Then, a time sequence coordination strategy based on the voltage grading of DCDNs is developed, and an adaptive inertia coefficient is designed to achieve the inertia adjustment in terms of the voltage sag and recovery processes. Using MATLAB/Simulink, a detailed model of the double‐terminal DCDNs is created to check the efficacy of the proposed approach. Different voltage disturbance scenarios are imitated, and the comparative simulations demonstrate that the proposed approach can fully utilise the inertia potential of the DCDNs to suppress the voltage sag and smooth the voltage recovery procedure. The proposed method's validity and feasibility can be well validated.The cover image is based on the Original Article Investigation of active voltage support control approach of DC distribution networks based on virtual inertia coordination by Lei Chen et al., https://doi.org/10.1049/esi2.12123.

Experimental study and characteristic analysis of vacuum arc between cup-type axial magnetic contacts under different diameter-to-gap ratios

Since vacuum circuit breakers gradually advanced to higher voltage levels, axial magnetic field (AMF) contacts have drawn a great deal of attention due to their excellent breaking ability. The cup-type AMF contact is a common kind of AMF contact, which has much potential in contact design and application of high voltage grade systems due to the advantages of strong structural strength, uniform magnetic field distribution, lower resistance, etc. This study analyzes the arcing characteristics of a cup-type AMF contact with a large slotted rotation angle at various diameter-to-gap ratios (DGRs). The arcing process is divided into five stages as follows: initial diffusion, contracting, fully constricted, re-diffusion, and extinguished. Arc self-rotation and anode separation phenomena in the re-diffusion stage appear when the DGR is 58/24. The reasons for these occurrences were discussed and explained with regard to the magnetic field vector's spatial distribution. The duration of each stage and the current threshold of a fully constricted arc will both differ with the change of the DGR. The structural parameters of the fully constricted arc were computed through the method of imaging the luminous intensity distribution after the arc was fully constricted. The source of the change in the arc voltage can be seen in the variation of arc structural parameters, which also reflect anode activity intensity to a certain extent. The transient magnetic field simulation method was used to explain why the arc under the same instantaneous current shows variable morphology at the extinguished stage and contracting stage in one arcing process. The research results presented in the article can be used as a reference for developing high-voltage cup-type AMF contacts.

Modeling and Experimental Studies of a Multi-Gap Gas Switch for Linear Transformer Drivers

This work is presenting the modeling of and the experimental studies performed on multi-gap gas switch (MGS) designed for linear transformer drivers (LTD). The MGS employs corona discharge in dry air for voltage grading across its six gaps, and therefore, achieves compactness and environmentally friendliness. Circuit modeling of the MGS was performed, followed by analysis and tests on corona current and voltage grading, showing a good self-break property of the switch. Trigger properties of the MGS were subsequently analyzed and experimentally investigated. The modeling and analysis were verified by evaluation experiments. The MGS was fired for 10020 shots in a typical LTD brick with a charging voltage of ±90 kV, which is 60% of the self-break voltage of the MGS when pressurized with 3.13 ata dry air, and a peak discharging current of 23.7 kA. The standard deviation of the time-delays between the trigger voltage and the discharging current is 3.3 ns for all the shots, during which only one pre-fire of the MGS occurred.

Development of line abnormal diagnosis system for overhead transmission lines

Overhead transmission line is the main way of power transmission, and its safe and stable operation is particularly important. Due to the complex network, transmission distance, large voltage grade serious problems such as frequent failure, this paper breaks through the transmission line fault location of traditional single, set induction electric wires, fault location, line insulation monitoring technology at an organic whole, developed of the transmission line abnormal diagnosis system, and realized the electrical characteristics of overhead transmission line multidimensional awareness. In this way, it can provide accurate information for maintenance personnel and ensure the safe and stable operation of the transmission network.

Design Methodology of Bidirectional Resonant CLLC Charger for Wide Voltage Range Based on Parameter Equivalent and Time Domain Model

The bidirectional CLLC resonant converter has distinguished potential in battery chargers and energy storage systems for its advantages in soft switching and bidirectional power flow capability. However, traditional CLLC converters generally adopt symmetrical design to maintain bidirectional symmetrical characteristics, which means the secondary <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> network is designed to be equal to the primary <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> network after reflection. The symmetrical design is only suitable for voltage grade matching scenarios where a wide voltage range is not required, such as CLLC-type dc transformers. Whereas in the field of bidirectional chargers, due to the wide voltage range of battery, there are significant differences in the characteristics required between charging and discharging mode, which makes symmetrical design no longer applicable. To cope with this issue, this paper proposes a novel design methodology of CLLC based on parameter equivalent and time domain model. With the parameter equivalent principle, the CLLC resonant tank with arbitrary parameters is investigated to satisfy the requirements of wide voltage range for bidirectional charger application. Compared with the symmetrical design, the proposed method can meet the requirements of bidirectional gain within preset frequency range and guarantee the achievement of zero-voltage switching under required load conditions with the minimum reactive power. In addition, the area product capacity of the magnetic part of the CLLC resonant tank is minimized based on the parameter equivalent principle. Finally, experiments have been performed on a 1 kW prototype to confirm the validity and feasibility of the proposed design methodology.

Prediction of transformer full-domain temperature based on fluid network decoupling

In this paper, a large oil-immersed self-cooling power transformer with a capacity of 180 MVA and a voltage grade of 220 kV is taken as the research object, and the global fluid network model of the transformer is established according to the oil circuit structure of the transformer and the circulation path of the cooling medium. Based on the decoupling method of fluid network, a three-dimensional finite element calculation model of local fluid field and temperature field is established at the decoupled location. Finally, the hot spot temperature of the winding appears at the 5th layer of the high-voltage winding, which is 89.2 °C, and the lowest temperature appears at the bottom of the low-voltage winding, which is 55.1 °C. The top oil temperature is 69.2 °C, and the bottom oil temperature is 47.6 °C. The temperature experiment of the prototype shows that the relative error of the calculation result of the hot spot temperature of the high voltage winding is 4.45%, the relative error of the calculation result of the hot spot temperature of the medium voltage winding is 4.43%, and the relative error of the calculation result of the hot spot temperature of the low voltage winding is 3.58%. It proves the accuracy of the global fluid network decoupling method to calculate the global temperature of the transformer, which provides a reference for the prediction of the global temperature of the transformer.

Test and Research on Noise Distribution Characteristics of 220kV Oil-immersed Transformer

Large power transformer is the main noise source of substation. With the increase of voltage grade and rated capacity, the noise radiation value of power equipment continues to increase, which has a great influence on the noise standard of substation boundary. In this paper, two test conditions of no-load voltage and load current are considered. The transformer noise testing datum is constructed. The distribution law of factory noise SPL of 220kV oil-immersed transformer is obtained. The test results provide accurate test data for transformer factory noise evaluation.

Pollution Flashover Characteristics of Composite Crossarm Insulator with a Large Diameter

The composite crossarm insulator differs greatly from the suspension insulator in structure and arrangement. This study aims to determine the pollution flashover characteristics of composite crossarm insulators under different voltage grades. Four types of AC composite crossarm insulators with diameters ranging from 100 mm to 450 mm are subjected to artificial pollution test, and then the effects of the surface hydrophobicity state of silicone rubber, core diameter, umbrella structure, arrangement, and insulation distance on the pollution flashover voltage of the composite crossarm insulators are analyzed. Under the pollution grade 0.2/1.0 mg/cm2 and voltage grade from 66 kV to 1000 kV, if the silicone rubber surface changes from HC5 to HC6, the pollution flashover voltage of the composite crossarm insulator will increase by 13.5% to 21.0% compared with the hydrophilic surface. If the core diameter changes from 100 mm to 300 mm, the pollution flashover voltage gradient decreases with the increase in core diameter; if the core diameter changes from 300 mm to 450 mm, the pollution flashover voltage gradient increases with core diameter. Under the same insulation height and core diameter, the umbrella structure will have a certain impact on pollution flashover voltage by up to 1.7% to 5.4%. Under the horizontal arrangement, the pollution flashover voltage can increase by 10.5% to 12.1% compared with that under the vertical arrangement. Under the hydrophilic surface and weak hydrophobicity state, the pollution flashover voltage has a linear relationship with the insulation distance. The above results can provide a reference for the structural design and optimization of the composite crossarm insulator.

Research on Fault Diagnosis of Launch Vehicle’s Power Transformation and Transmission System Based on Big Data

The on-board power supply system provides power for the launch vehicle. The power transmission and transformation system plays an irreplaceable role to ensure that the on-board power supply system receives the normal working voltage of the launch vehicle. There are many types of faults in power transmission and transformation systems. The traditional faulty diagnosis method of power transmission and transformation equipment has the disadvantages of being susceptible to experts’ subjectivity and model’s ossification. In this paper, a new method of equipment fault diagnosis based on big data is proposed. On the basis of big data, this paper introduces the failure mode clustering algorithm, the state parameter correlation analysis algorithm, the fault diagnosis method based on the correlation matrix, and other key fault diagnosis technologies. The fault record data of the 400 kV voltage grade oil-immersed transformer bushing in the past ten years by a Chinese combat unit is used as a case for demonstration. The results show that the accuracy rate of SC-LSTM-K-means clustering model exceeds 95%. And the fault classification mode can be accurately obtained. A priori correlation algorithm with TA coefficient can be used to evaluate the strong and weak relationship between the state parameters; the fault diagnosis matrix based on Pearson’s correlation coefficient can accurately determine the fault mode consistent with the actual operation and maintenance test results. Therefore, the fault diagnosis method of power transmission and transformation system based on big data can both effectively obtain the inherent laws of historical data and realize more accurate fault diagnosis with data adaptability.

Development and Testing of a 252 kV/2500 A-40 kA Multi-Break Bus-Coupler Fast Vacuum Circuit Breaker

It is effective to open the bus-coupler circuit breaker in case of a short-circuit fault. A fast vacuum circuit breaker (FVCB) is an ideal bus-coupler circuit breaker due to its high velocity. The objective of this study was to develop and test a 252 kV/2500 A-40 kA multi-break bus-coupler FVCB. The 252 kV FVCB contained 12 FVCB units. Each phase consisted of four FVCB units connected in series. Each FVCB unit had an electromagnetic repulsion mechanism with an average opening velocity reaching 6.5 m/s. Test results showed the opening time was 1.11 ± 0.08 ms. The capacitance of the voltage grading capacitor of each break was determined to be 10 nF. The prototype 252 kV bus-coupler FVCB passed all partial test duties according to the IEC 62271-100: 2008 and IEC 62271-1: 2007 standards, which include an insulation test and a terminal fault test among others. A 252 kV/2500 A-40 kA multi-break bus-coupler FVCB can be used to quickly cut off a short-circuit fault and effectively limit a short-circuit current.

Short-term Transmission Line load and State Evaluation method based on improved gradient lifting Stochastic Forest algorithm

In order to accurately predict the short-term load change of power system and provide guidance for the safe, economical and efficient operation of power system, a power system load forecasting method which combines fuzzy clustering and random forest regression algorithm is proposed. the rough set is used to construct compensation rules to modify and compensate the prediction results. Based on the analysis of the factors affecting the state of overhead transmission lines, the state quantity system of overhead transmission lines containing 79 state variables is constructed based on the state variables selected by 8 units of the lines and the state quantities of special cases. In the random forest regression prediction, the same kind of data after clustering is used as the training set sample to construct the decision tree. Considering that the stochastic forest regression prediction is conservative and the power system load fluctuates greatly at the peak, the rough set theory is used to generate compensation rules to modify the load forecasting. Accurate state evaluation of overhead transmission lines in the power grid can effectively reduce the failure rate and improve the power supply performance of the system. Finally, an example is given to analyze the actual data of 66 kV voltage grade overhead transmission lines in a city. The results show that the accurate evaluation of the state of overhead transmission lines can be realized by using this method, so as to provide decision support for the operation and regulation of regional power grid.

Design and implementation of one-dimensional liquid crystal holographic coding phased array antenna

Face to the precise signal guidance application of small fully polarimetric phased array radar, in order to reduce the design and debugging complexity of traditional T/R phased array antenna and feed system, and meet the needs of low power consumption, low insert loss, low cost manufacture, low profit phased array antenna, a liquid crystal holographic coding phased array antenna is proposed. One-dimensional holographic electronically controlled scanning phased array antenna is composed of miniaturized holographic radiation unit, slow wave structure and parallel plate waveguide feeding system. Making use of mature LCD panel manufacturing process, a holographic coding phased array antenna is constructed by controlling the deflection state of the liquid crystal molecules under the holographic radiation unit to adjust the resonant frequency of the antenna. Deterioration of sidelobe performance caused by coupling effect is reduced by holographic optimization algorithm and voltage grade control based on a real object processed and tested, and the optimal control of antenna pattern is achieved by the gradient decreasing search algorithm and the optimization algorithm of the appropriate objective function. The measured results indicate that the beam scanning angle of the antenna reaches ±49°, and after optimized algorithm, the beam pointing angle accuracy reaches 3°, the sidelobe suppression level reaches 1.7 dB.

Calculation and Analysis of Transient E-Field Distribution of 110kV Dry Type Transformer Under Lightning Impulse

The 110kV dry type epoxy casting transformer had the characteristics of high voltage grade, great difficulty and uncertainty in research. Especially in the field strength control under lightning impulse, higher requirements were put forward for its insulation structure design. In this paper, an equivalent circuit model was built based on the heap winding structure, and the voltage distribution of winding nodes under lightning impulse was calculated. According to the actual drawing, a two-dimensional transformer model was established, and the E-field distribution of transformer under lightning impulse was obtained by simulation. The results showed that the maximum field strength at sampling point 1 was 4.1kV/mm, appearing around 65μs and 157μs. From the simulation results, the insulation performance of the pile winding did not meet the safety requirements. The research results in this paper could provide an important basis for the design of 110kV dry type transformer and technical support for the product development and safe operation of large capacity dry type transformer.

Evaluation of Fault Level of Sensitive Equipment Caused by Voltage Sag via Data Mining

So far, there is no literature to evaluate the fault level of sensitive equipment (FLSE) caused by voltage sag from the perspective of the power grid. In practice, although the FLSE are dominated by the voltage sag of node, the voltage sag of the node is associated with whole power grid, including the voltage grade and location of the node, the distance between the concerned node and location of fault, and the weather and date at the time of fault, which are all named as voltage sag properties (VSP). In view of this gap, this paper evaluates the FLSE using the long-time monitoring data of VSP of some regional power grid by data mining method based on multidimensional matrix simplification and the improved gray target theory. The data mining process can be divided into three steps: 1) construct a database consisted of VSP and FLSE using long-time monitoring data, 2) mine the association rules between VSP and FLSE by multidimensional matrix simplification, and 3) match some actual scenario with the mined association rules by the improved gray target theory. Performance and effectiveness of the proposed method are verified through the simulation and field case.

Bifurcation of a finitely deformed functionally graded dielectric elastomeric tube

Soft functionally graded materials have attracted intensive attention owing to their special material inhomogeneity and are realized as various applications. In this paper, we theoretically investigate the finite deformation and superimposed bifurcation behaviors of an incompressible functionally graded dielectric tube subject to a combination of axial stretch and radial voltage. The theoretical framework of nonlinear electroelasticity and the related linearized incremental version is employed. We assume that the modulus and permittivity of the elastomer vary linearly along the thickness of the tube. The surface impedance matrix method is adopted to obtain the bifurcation equation for buckling of the tube. We present numerical calculation for the ideal neo-Hookean dielectric elastomer to study the effects of the applied voltage, geometrical size and material grading parameters on the nonlinear response and the incremental buckling behavior of the tube. We validate our results through comparison with those of the elastic problem. The results can provide solid guidance for the design and realization of dielectric actuators.

Thermal Diffusivity of Fresh Silicone Rubber Composite Insulators Determined by Photothermal Radiometry

Thermal diffusivity was confirmed to be a useful parameter for evaluating the aging degree of silicone rubber composite insulators widely used in high-voltage–power systems. However, the aging induced thermal diffusivity change of composite insulators not only is related to the initial thermal diffusivity of fresh silicone rubber, but also could be within a certain range for fresh composite insulators due to composition differences of base polymer and fillers and additives, makes the direct correlation of thermal diffusivity of aged composite insulator to aging degree difficult. In this work, thermal diffusivities of fresh composite insulators with different voltage grades, different mechanical load grades, and manufactured by different vendors are determined with photothermal radiometry (PTR) by fitting experimental frequency dependences of PTR amplitude and phase to an appropriate theoretical model. The thermal diffusivities of composite insulators from two vendors are approximately 3.70 × 10−7 m2·s−1 to 3.76 × 10−7 m2·s−1 and 4.87 × 10−7 m2·s−1 to 4.94 × 10−7 m2·s−1, respectively, showing significant difference, due to composition difference. The thermal diffusivities of composite insulators with voltage grades 35 kV, 110 kV, and 220 kV, and with mechanical load grades 70 KN, 100 KN, and 120 KN are also measured and found to be only slightly divergent, due to the same composition. In addition, the thermal diffusivity uncertainties of two vendors are quite different, indicating sample homogeneity discrepancy. This variation is useful information for evaluating aging process of silicone rubber composite insulators from the thermal diffusivity measurements of aged composite insulators.

Modular multilevel converter based on arm transfer to clear dc fault

Modular multilevel converter (MMC) has great prospects in voltage source converter-based high-voltage direct current (HVDC) transmission. Although the typical half-bridge MMC can bring huge economic benefits, it is unable to clear dc fault. An MMC based on arm transfer (AT-MMC) and corresponding timing control are presented to effectively solve this drawback. Compared with the half-bridge MMC, the AT-MMC adds the arm-transferring branch to the each phase unit of the converter and adds the current-breaking branch and the energy-absorbing branch to the dc line. Through these branches cooperating with each other, the fault current is cleared. Referring to the half-bridge MMC with the same voltage grade, the AT-MMC has a good economy and its additional device cost is low and additional conduction loss is very small. A model of 51-level MMC–HVDC system is built in RT-LAB OP5600 to verify the effectiveness of the proposed solution.