Current Calculation Model Research Articles

Study on current carrying capacity calculation model for dynamic capacity increase of carbon fiber reinforced composite core conductor

Abstract With the “dual-carbon” as the goal of the new power system construction gradually in-depth, transmission lines must have energy-saving capacity for the direction of development. A new type of large-capacity overhead transmission conductor is the carbon fiber reinforced composite core (CFCC) conductor. The conductor has high capacity, low loss, high-temperature resistance, low high-temperature sag, and other characteristics. It is one of the key technologies and equipment applied to the transformation of old overhead transmission lines to enhance its capacity. At the same time, it can also realize the dynamic transmission capacity regulation of the overhead line. The application of the prospect is very promising. The accurate assessment and calculation model for the conductor’s allowable current carrying capacity is the key core technical problem of the overhead transmission line dynamic capacity increase capability. The paper establishes a maximum allowable current capacity calculation model for carbon fiber-reinforced composite core conductors based on Morgan’s formula. The results of the load flow calculation are compared with the actual load flow test results to verify the calculation model, and the maximum error is 3.59%, which proves the reliability of the calculation model. On this basis, the influence of external environmental factors (ambient temperature, sunlight intensity, wind speed, and direction) on the maximum allowable current capacity of the conductor is discussed. The correlation coefficient of the model is analyzed.

Experimental study on the joint load-bearing behaviour of segmented concrete towers under combined loading

Hybrid towers have become increasingly established for tall wind turbines. The concrete part of these towers consists of several stacked circular ring segments. To reduce the amount of fabrication and erection effort, the joints between the segments are usually designed as dry ground joints. This paper presents experimental investigations aimed at determining the torsional load-bearing capacity of such dry ground concrete joints subjected to combined loading of prestressing, bending and torsion. Based on previous investigations, a test set-up consisting of three circular ring segments was developed. The torsional load-bearing capacity was determined by monitoring the tangential joint displacements in detail. The test results demonstrate that an increasing bending load leads to a uniform decrease in the torsional load-bearing capacity. The comparison with the current calculation model shows significant differences and confirms the weaknesses of the model regarding its inadequate interaction with the bending load. In contrast, numerical simulations agree well with the test results.

Analysis and Compensation of Lorentz Force Magnetic Bearing Magnetic Flux Density Uniformity Error.

Aiming at the influence of the magnetic flux density uniformity error (MFDUE) of the Lorentz force magnetic bearing (LFMB) on the sensitivity accuracy of magnetically suspended control and sensing gyroscopes (MSCSGs) on the angular rate of a spacecraft, a high precision measurement method of the angular rate of a spacecraft based on the MFDUE compensation of LFMB is proposed. Firstly, the structure of MSCSG and the sensitivity principle of MSCSG to the spacecraft angular rate are introduced. The mechanism influencing the accuracy of MSCSG to spacecraft angular rate sensitivity is deduced based on the definition of magnetic flux density uniformity. Secondly, the 3D magnetic flux distribution of LFMB is analyzed using ANSYS. The relationship between the rotor tilt angle, tilt angular rate, and magnetic flux density is established. The induced current calculation model due to MFDUE is proposed, and the LFMB magnetic flux density error compensation is realized. Finally, the simulation results show that the estimation accuracy of the induced current by the proposed method can reach 96%, and the simulation and the experiment show that the error compensation method can improve the accuracy of MSCSG in measuring the spacecraft angular rate by 12.5%.

Electron ITB formation in EAST high poloidal beta plasmas under dominant electron heating

Plasma confinement and transport in tokamaks play a crucial role in the development of high poloidal beta steady-state operation scenarios. Therefore, it is very important to study the relevant mechanism of internal transport barriers (ITBs), which can help plasmas to obtain better confinement in order to achieve higher fusion gain. This paper mainly introduces the analysis of the characteristics of electron heat transport of discharges with ITB in high βP operation regime in Experimental Advanced Superconducting Tokamak (EAST). Based on the statistical analysis of stable discharges with βP > 1.5, it is found that there is an obvious bifurcation of the normalised electron temperature gradient (ETG) ( R/LTe ) in the range of βP = 2–2.2. Then the discharges of lower βP ( βP < 2, where the value of βP is below the bifurcation threshold) and of higher βP ( βP > 2.2, where the value of βP is above the threshold) were selected for analysis. The diagnostic data provided by Thomson scattering, x-ray crystal spectrometry and charge exchange recombination spectroscopy are used to provide reliable parameter profiles and then combined with the data of external magnetic probe measurements and the polarisation interferometer diagnosis system to fully reconstruct the balance. A relevant plasma current calculation model is used to calculate and analyse the current density profiles and power deposition, and then the transport analysis is carried out. Interestingly, in the higher βP discharges, it is found that the turbulence intensity provided by the CO2 laser collective scattering system gradually decreases and the normalised ETG R/LTe gradually increases. It is also found that the electron heat transport coefficient decreases in the discharge with higher βP and the growth rate of the electron-scale turbulence calculated by transport gyro-Landau fluid (TGLF) is significantly reduced. Meanwhile, similar conclusions are also obtained in the discharges when the βP is further increased.

Calculation Method and Characteristic Analysis for Fault Current of Permanent Magnet Direct-Drive Wind Power System considering Positive and Negative Sequence Decomposition

In view of the fact that the influence of positive and negative sequence decomposition, which is widely used in positive and negative sequence decoupling control in control system, on the fault current calculation process is not deeply considered in the existing transient analysis methods of permanent magnet direct-drive wind farm short circuit current, this paper proposes a transient short circuit current calculation model that takes into account positive and negative sequence decomposition. The influence of the transient characteristics of positive and negative sequence decomposition on the control system is studied, and the mechanism of its action on the transient change of short circuit current is revealed. The positive and negative sequence decoupling processes of the circuit equation are modified, and the characteristics of the coupling equation are analyzed. The difference in the converter output voltage between the circuit equation and the control equation and the depth of its influence on the calculation process is revealed. On the basis of quantifying the difference at the converter output voltage, the circuit equation and the control equation are combined to form a short-circuit current calculation model with positive and negative sequence decomposition, which accurately characterizes the transient characteristics of fault current under different voltage drops and effectively improves the accuracy of the calculation results.

Retracted: Practical Model for Short-Circuit Current Calculation of Photovoltaic Power Station Based on Improved RLS Algorithm

Retracted: Practical Model for Short-Circuit Current Calculation of Photovoltaic Power Station Based on Improved RLS Algorithm

Fast and accurate method for short-circuit current calculation in distribution network with IIDGs

The fault behavior of Inverter Interfaced Distributed Generators (IIDGs) diverges from that of synchronous generators. When a substantial number of IIDGs are integrated into the distribution network, the conventional short-circuit current calculation technique, grounded in a mechanical framework, struggles to simultaneously satisfy the demands for both rapid computation and precision. This study introduces an alternative approach reliant on data analysis, enabling swift and precise computation of short-circuit currents across the IIDG-infused distribution grid. The investigation delves into the efficacy of multi-output regression techniques and the selection of the foundational learning algorithm. Specifically, two strategies are advanced: Multi-Target Regressor Stacking and Regressor Chains, both utilizing the Light Gradient Boosting Machine as the base learner. The influence of varying sample sizes on the multi-output computational model's performance is assessed. To ascertain the real-world viability of the multi-output regression methodology, two distinct fault characteristics pertaining to data-driven short-circuit current calculation are scrutinized using existing distribution network measurement conditions. The study reveals that, given a known distribution network structure, the proposed method can compute network-wide short-circuit currents across diverse IIDG penetration levels and fault scenarios through a singular model, maintaining a balance between computation precision and speed. If the distribution network's structure undergoes minor modifications, the model demonstrates reasonable adaptability, yet a retraining of the short-circuit current calculation model is recommended to ensure sustained accuracy in the face of significant network changes.

Investigating Aging Characteristics of Oil-Immersed Power Transformers' Insulation in Electrical-Thermal-Mechanical Combined Conditions.

The condition and health of large oil-immersed power transformers' insulation have a direct impact on the safety and stability of the power grid. Therefore, it is crucial to investigate the aging characteristics of oil-paper insulation in power transformers. In this study, we developed a computational model for reclosing current calculation and multiphysics coupling models for magnetic-circuit-force, electrostatic field, and temperature field simulations. The calculated aging resulted in a mechanical stress of 8.71 MPa, an electric field strength of 2.26 × 106 V/m, and a temperature of 113.7 °C. We conducted combined electrical-thermal-mechanical aging tests on the oil-paper insulation and measured various insulating paper performance parameters at different aging stages. Our study revealed that both the mechanical and electrical properties of the insulating paper deteriorated in both aging groups. However, the changes were more pronounced in the electrical-thermal-mechanical aging group compared to the electrical-thermal aging group, indicating that mechanical stress accelerated the aging process of the insulating paper. In the early stages of aging, the rate of performance changes in the electrical-thermal aging group was similar to that in the electrical-thermal-mechanical aging group. However, as the aging time increased, the degradation of performance induced by mechanical aging became more significant. This suggests that the insulating paper's resistance to mechanical damage, specifically short-circuit resistance, noticeably decreased after prolonged aging.

A New Short-Circuit Current Calculation and Fault Analysis Method Suitable for Doubly Fed Wind Farm Groups.

The transient characteristics of wind farms in groups are quite different; in addition, there is a strong coupling between the wind farms and the grid, and these factors make the fault analysis of the grid with wind farm groups complicated. In order to solve this problem, a mathematical model of the converter is established based on the input-output external characteristics of the converter, and a transient model of a doubly fed wind turbine (DFIG) is presented considering the influence of the low-voltage ride-through control (LVRT) of the converter, and the effect mechanism of the LVRT strategy on the short-circuit current is analyzed. Finally, a short-circuit current calculation model of a doubly fed wind turbine with low-voltage crossing control is established. The interaction mechanism between wind farms during the fault is analyzed, and a short-circuit current calculation method of doubly fed wind farm groups is proposed. RTDS is used to verify the accuracy of the proposed short-circuit current calculation method for doubly fed field groups. On this basis, a method of power grid fault analysis after doubly fed field group access is discussed and analyzed.

Optimization study of overvoltage problem in PV distribution network based on electrical energy router

Photovoltaic power generation has the advantages of being clean and efficient, but it poses a threat to the voltage quality of distribution networks due to unstable power output. In order to solve the overvoltage and power utilization problems of a high-penetration PV distribution network, this paper proposes a tidal current analysis model based on a four-port power router. First, the steady-state modeling of different ports of the electrical energy router is carried out, and the corresponding voltage control strategy is proposed. Then, by establishing a unified tidal current calculation model, a solution for the optimal operation of the distribution network is proposed. Finally, based on the overvoltage data of a regional power grid, the impact on the voltage level of the grid-connected PV system before and after the addition of the power router is compared. From the analyzed data, it is concluded that the introduction of a four-port power router for corresponding port control strategies can effectively improve overvoltage problems in high-permeability PV distribution networks.

148 Economic Assessment of Beef Cattle Backgrounding in Brazil at Pre and During the Covid-19 Pandemic

Abstract The production costs of beef cattle grazing backgrounding systems between 2018/2019 (pre) and 2020/2021 (during) pandemic were evaluated. A comprehensive mathematical model for the cost of production was used according to the Economic Theory. Costs were collected and allocated into Fixed Cost (FC), Variable Cost (VC), and Total Cost (TC). In addition, analyses were performed concerning total income and profitability. A survey was carried out in 2018 with a rancher in the state of Minas Gerais (Brazil) to define major technical indicators of production. The spot prices used in our analysis were collected in 2018/19 and 2020/21. The base-animal used for such growing phase assessment represented the Nelore breed (Bos indicus), intact males and females, weaned at approximately 7-10 mo, and averaging 195 ± 15 kg of live shrunk BW (body weight), which remained in a grazing system for 12 mo. The average selling weight was 360 ± 15 kg shrunk BW. Animals (n = 34) were separated into three lots according to the ranch of origin and sex. Mineral supplementation was provided for 150 d during the greatest forage supply, while protein supplementation was offered for 210 d during the least forage supply for all animals. After comprehensively accounting for inputs, the cost index was compared between the two periods. The total cost for the 2018/19 production-period was US$ 1.13kg of BW, while an increase of approximately 53% (US$ 1.70kg of BW) was observed for 2020/21. The FC represented in the year 20/21 was 2.66 % less than 2018/19, which represented 22.9% of all costs combined. The VC represented 66.3% of the total cost in 2018/19, in which cattle purchase cost and feed cost represented 58.8% and 7.1%, respectively. For 2020/21, the VC increased to 70.7% of the total cost, in which cattle purchase cost and feed cost represented 62% and 8.5%, respectively. Regardless of the period, the most representative items analyzed were the cattle purchase price and feed costs. There was a 68.9% increase in gross income, followed by a raise in profit from US$ 0.26/kg BW in 2018/19 to US$ 2.9/kg of BW in 2020/21. The factors that influenced profitability the most were the purchase and sale price of animals. The shorter feeder cattle supply during the pandemic induced greater overall costs, although also positively affecting the final sale price of long-yearlings, which generated widened margins. The current cost calculation model showed to be helpful while allowing testing scenarios, possibilities, and helping producers to manage risk in such cattle enterprises.

Study on the circulating current calculation model and its influence factors of 500kV GIS branch bus

Study on the circulating current calculation model and its influence factors of 500kV GIS branch bus

Research on Delamination Failure of Insulator in Electromagnetic Rail Launcher

The electromagnetic rail launcher (EMRL) G10 insulator is prone to delamination failure during launch, which affects the life of EMRL. In order to explore the reasons for the delamination failure of the insulator, the EMRL eddy current field calculation model is constructed firstly, and then the transient electromagnetic (EM) force distributions of the armature and the rail are calculated and verified by the combination of finite element and experiment. Finally, the EM force is used as the input, and combined with bolt pretightening force, friction force, and impact force, the multitype mechanical coupling solution is carried out. The simulation indicates that stress concentration occurs at the inner chamfer of the insulator end. The interlaminar shear stress exceeding the ultimate strength of the material and the fatigue damage caused by stress cyclic loading are the main reasons for the delamination failure of the insulator. The delamination crack is parallel to the direction of the glass fiber layer, and the interlaminar shear force peels off the upper fiber from the resin, forming a through-type delamination damage of the test prototype insulator. Optimizing the structure or material to improve the shear resistance of the insulator can prolong the life of the insulator.

Practical Model for Short-Circuit Current Calculation of Photovoltaic Power Station Based on Improved RLS Algorithm

In recent years, with the rapid economic development, the development speed of all walks of life has entered a new level, and the power industry has also developed rapidly. Driven by market demand, China’s power transmission range and power transmission capacity will enter a new level. At the same time, the problems brought about by the development of the power system are equally severe. Due to the large load density in individual areas, the detection of short-circuit current must be improved as an important issue. The purpose of this paper is to study how to improve the practical model of short-circuit current calculation of photovoltaic power plants, so that it can be well applied to the current high-density current detection in China. Therefore, this paper improves the recursive least squares (RLS) algorithm and applies it to the practical model of short-circuit current calculation of photovoltaic power plants and describes the improvement process of the algorithm in detail. At the same time, this paper designs relevant experiments and analysis to count the data of the improved RLS algorithm in the short-circuit current calculation of the actual photovoltaic power station and combines the data of this part to test and analyze the ability of the algorithm. The experimental results in this paper show that the improved RLS algorithm has a very good improvement in the calculation accuracy of the short-circuit current calculation of photovoltaic power plants in the actual model calculation. At the same time, the calculation efficiency is also improved, and the current tracking effect is also improved by 7%.

Seismic vulnerability assessment of reinforced concrete buildings having nonlinear fluid viscous dampers

Seismic resilience is the residual capacity of a damaged system for recovering and sustaining an acceptable level of performance as a consequence of a seismic event. Firstly, this paper summarizes the current calculation framework of seismic resilience using fragility analyses. After that, a new metric based on vulnerability analyses is developed to calculate seismic resilience. Finally, a typical hospital building is adopted as a single building and then retrofitted with supplemental Energy Dissipation Systems (EDS) to show the applicability of the new metric and compare it with the current calculation model of the seismic resilience. The considered supplemental EDS is the Nonlinear Fluid Viscous Damper (NFVD) located as the diagonal damper-brace system. The seismic performance of the supplemental EDSs is to enhance structural performance by reducing induced lateral displacements and as a result the level of physical damages and losses. To this end, Incremental Dynamic Analysis (IDA) is implemented to achieve the damage fragility and vulnerability curves. A comparison of the fragility, vulnerability, and functionality curves indicates that NFVDs are potentially useful for attenuating seismic damages to structural and non-structural components.

A CALPHAD-based model on the viscosities: A case study on Zr–Fe–Cu liquid alloys

Viscosity is an important thermodynamic property for alloy design, especially for refractory alloy. CALculation of PHAse Diagram (CALPHAD)-based viscosity calculations are highly desirable since they can accurately predict the viscosity in the alloy with different compositions. However, the current viscosity calculation model lacks the ability to fit the situations where the viscosity varies largely with temperature. Here, we propose a new equation to describe the excess viscosity using an exponential equation. The physical meaning of each parameter is explained. Moreover, the proposed model is not only compatible with the previous model but also suitable for all the situations. We further calculate the viscosity using different models in the Zr–Fe–Cu system which is important in the fields of nuclear fuel and magnetic refrigerants. The proposed model gives a better description than the other two models with fewer optimizing parameters, verifying the advantages of the current model. Based on the established viscosity database of Zr–Fe–Cu, we further predict its metallic glass-forming ability. The theoretical analyses together with the viscosity calculation examples suggest that the proposed model can provide accurate viscosity calculations in liquid alloys as a function of temperature and composition. Therefore, the proposed model is suitable for the design of refractory alloys.

Analysis and Control of Current Harmonic in IPMSM Field-Oriented Control System

There is a certain amount of current harmonics in interior permanent magnet synchronous motor. In order to accurately control the current harmonic, this article focuses on three aspects: establishing current harmonic calculation model, extracting current harmonic, and designing current harmonic regulator. A current harmonic calculation model, which considers the effect of voltage harmonics induced by current controllers and digital control delay on the initial phase angle of voltage harmonics, is established for the first time. With the help of multiple synchronous rotating frame transformation, a current harmonic extraction method more suitable for motor drive field, which aims to extract the current harmonic characteristics of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis currents, is proposed. On this basis, the controlled quantity and control quantity are unified in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> coordinate frame for analyzing the coupling relationship of current harmonic characteristics. And then a PI current harmonic regulator, including current harmonic decoupling and voltage harmonic initial phase angle compensation, is constructed, so as to realize the effective control of current harmonics. Finally, the effectiveness and superiority of the proposed method are verified by simulation and experiments.

Ion Current Simulation Model Design for a Spark-Ignited Engine

The use of ion current signals generated during the combustion process of mixed gas as a function of initial mixture composition, temperature and pressure to detect cylinder combustion states is the most recent approach in the design, development, and optimisation of automotive engine combustion control. This paper aims to design predictive identification and computationally fast and accurate ion current models for obtaining combustion information in the engine cylinder in real time. To build a more comprehensive ion current calculation model, the effect of the flame ionisation process, the geometry of the spark plugs, and the combustion pressure and temperature are considered in the new building ion current model. The simulation ion current waveform, which has a double-peak structure, is in good agreement with the experiment values; thus, the ion current model has the potential to be used for real-time control and optimisation of engine cylinder combustion.

Massively Parallel DNA Computing Based on Domino DNA Strand Displacement Logic Gates.

DNA computing has gained considerable attention due to the characteristics of high-density information storage and high parallel computing for solving computational problems. Building addressable logic gates with biomolecules is the basis for establishing biological computers. In the current calculation model, the multiinput AND operation often needs to be realized through a multilevel cascade between logic gates. Through experiments, it was found that the multilevel cascade causes signal leakage and affects the stability of the system. Using DNA strand displacement technology, we constructed a domino-like multiinput AND gate computing system instead of a cascade of operations, realizing multiinput AND computing on one logic gate and abandoning the traditional multilevel cascade of operations. Fluorescence experiments demonstrated that our methods significantly reduce system construction costs and improve the stability and robustness of the system. Finally, we proved stability and robustness of the domino AND gate by simulating the tic-tac-toe process with a massively parallel computing strategy.

An iterative optimization algorithm for posture and geometric parameters of grinding wheel based on cross-section sensitivity and matching constraints of solid end mills

Grinding wheel posture and geometric parameters are the key to optimizing the grinding process for helical grooves of solid end mills. However, the current envelope calculation models have not done enough research on the influence of the grinding wheel discretization method and grinding kinematics models mainly focus on helical grooves with constant core radius. Moreover, the matching error of the overall cross-section curve is ignored. These problems can reduce model generality, affect final calculation results, and cause inferior cutting performance. Therefore, a novel optimization algorithm for grinding wheel posture and geometric parameters is developed in this paper. Firstly, a parametric grinding wheel modeling method with adaptive adjustment of control variables is proposed, and a generalized grinding kinematics model for variable core radius is established. Then, by analyzing the sensitivity of cross-section parameters and the formation mechanism of the core radius, an iterative strategy based on parameter sets is established. Under the condition that the core radius is ensured in advance, the matching errors of rake angle, groove width, and overall cross-section curve are considered comprehensively to optimize the grinding wheel posture and geometric parameters. Finally, the proposed method is verified by simulation and machining. The results indicate that the proposed method can realize the envelope calculation of the helical groove with variable core radius, and optimize the grinding wheel posture and geometric parameters accurately and efficiently.