The increasing permeability of renewable energy render the traditional static security analysis method based on deterministic load flow no longer applicable. In power systems with uncertain renewable energy sources, probabilistic load flow (PLF) analysis must be conducted to achieve static security analysis of the power system by examining voltage and branch load flow during the operation. This paper proposes a PLF calculation method based on C-type Gram-Charlier series expansion and cumulant (CGC-CM), which can determine the distribution characteristics of bus voltage and branch transmission power. The proposed method solves the problem of negative values in the calculation of PLF for the results of the traditional A-type Gram-Charlier series expansion (AGC) method. Additionally, three typical wind and photovoltaic power generation output scenarios are created using k-means clustering, followed by an assessment of the static security of the power system. In this paper, the accuracy and efficiency of the algorithm is verified using the IEEE30 test system. Besides, it is observed that the static stability of the power system decreases with an increase in wind and photovoltaic power output. Subsequently, a real power system model was established and demonstrated that the branch capacity increase can improve the stability of the system operation.

Due to the uncertainty factors in the output of new energy such as wind power and photovoltaics,it is necessary to recalculate the probability power flow and analyze the static safety stability of new power systems with access to new energy.The Monte-Carlo method currently used has the problem of long computation time,making it difficult to apply in practical engineering.Based on the probability distribution characteristics of light intensity and wind speed,the output probability density function models for photovoltaic arrays and wind turbines respectively is constructed,and the semi-invariant method based on Gram-Charlie series expansion for probabilistic power flow calculation is used to realize power flow calculation and static stability analysis for new power systems with wind power and photovoltaic.In this paper,the IEEE(Institute of Electrical and Electronics Engineers)30 standard testing model is taken as an example to verify the proposed algorithm.The results show that the proposed algorithm maintains the high accuracy advantage of Monte-Carlo method while having a high computational speed.Furthermore,the influence of wind power and photovoltaic permeability on power flow and static safety stability of power system is studied.The results show that as the permeability increases,the range of flow distribution values expands and some branches may have negative values,leading to power reverse transmission issues and the increase of operational risk of the system.Then,the effects of line capacity expansion on reducing the risks of active power and node voltage exceeding limits,as well as improving static safety and stability are explored.

In order to study the influence of drizzle weather on the total electric field of ultrahigh-voltage direct current (UHVDC) transmission lines, an ion flow field model considering drizzle weather is established. This model calculates not only the positive and negative ions but also the charged tiny water droplets, dust particles, and falling raindrops, enabling accurate simulation of the total electric field in drizzle weather. Meanwhile, the ion flow field model is solved by the improved upstream finite element method. First, the influence factors and mechanism of drizzle weather on the ion flow field of UHVDC transmission lines are studied in this article. Then, the improved upstream finite element method is used to solve the ion flow field under different degrees of drizzle weather. Finally, the influence rule of drizzle weather on the total electric field at ground level is obtained. In this article, the accuracy of the ion flow field model is proved by the measurement data of the ground-level ion flow field of the +/- 800-kV UHVDC transmission line from Chuxiong to Suidong. The research results show that the ion flow field of drizzle weather at ground level is larger than that of sunny weather. With the degree increase of drizzle weather, the peak value and distribution curve of the ground-level total electric field gradually increases. This article has a guiding role for the construction and the safe operation of UHVDC transmission lines considering drizzle weather.

The fast and accurate solution of the total electric field and ion current density is crucial for the electromagnetic environment of ultra high voltage direct current (UHVDC) transmission lines. In this article, an improved method based on Newton–Raphson method (NRM) and upstream finite element method (UFEM) is proposed to calculate the ion flow field under complex conditions. According to the gas motion theory, the corona-onset electric field, ion mobility, and recombination coefficient are obtained at high altitude and put into the ion flow field model in this article. Subsequently, the charge density is used to solve Poisson’s equation, and the current continuity equations are calculated by UFEM. After that, the charge density of the conductor surface is updated based on NRM. These three parts are iterated repeatedly until the convergence conditions are met. According to the test results of ±800-kV UHVDC transmission line at high altitude, the validity and rationality of the proposed method are verified. The result demonstrates that due to the reduction of atmospheric pressure at the high altitude, the corona-onset electric field decreases, and the ion mobility and recombination coefficient increase, which makes the total electric field and ion current density at ground level increase. Compared with the traditional methods, the improved method is insensitive to the initial value of the surface charge density. Moreover, this proposed method can effectively improve the convergence ability and achieve the stable and fast calculation of the ion flow field at high altitude.

高比例新能源的逐步接入改变了电力系统的运行方式,新能源接入配网侧的变压器运行环境也发生了极大改变,基于传统电力系统"源随荷动"的变压器风险评估体系已无法满足现有新型电力系统"源荷互动"的评估需求.基于Copula模型与变压器Susa模型,建立风电接入的新能源配电网中"源""荷"新型相关性模型,并引入绝缘劣化概率等指标,提出了一种考虑风电-负荷相关性的变压器运行风险联合概率评估方法,利用蒙特卡罗法计算各个风险指标值并对变压器运行风险进行评估.研究结果表明,传统不考虑"源""荷"相关性的变压器评估体系会导致整体风险评估结果偏低,指标最高误差可达 55.02%,且随着相关性提升,变压器热缺陷风险不断增加.研究结论可辅助提升新型电力系统变压器运行风险等级评估准确度,为今后变压器状态评估与检修计划制定提供参考.

The random fluctuations in the output of new energy increase the risk of power system operation. This paper proposes a power system probabilistic power flow calculation method based on LHS-CGC method, which solves the problem that the probability density function is negative when fitting data with A-type Gram Charlie Series expansion. Taking the calculation results of the Monte Carlo method as a reference, the accuracy and effectiveness of the proposed method were verified in an improved IEEE30 testing system, with higher computational speed. Then, the probability density distribution of each state variable and output variable of the system in three typical operation modes is checked according to the actual power grid model. This article analyzes the probabilistic load flow calculation results of the system under different operating modes and believes that the seasonal output changes of new energy have a more significant impact on the load flow of the new power system, and the risk of branch load flow exceeding the limit increases. Similarly, the node voltage distribution range under the new energy generation mode is larger, reaching 0.92 to 1.03 p.u.. This provides a reference for practical power optimization scheduling problems in engineering.

The proportion of resistive current in the leakage current of lightning arrester is very small, and it is difficult to judge the health state of lightning arrester directly by the leakage current in the degraded state. In view of the problem that it is difficult to extract the resistive current from the leakage current of 500 kV arrester, the spatial capacitance matrix of the arrester is obtained through fine modeling of the arrester and simulation calculation. Based on the resistance capacitance network theory and the field circuit coupling method, the accurate equivalent network model of 500 kV arrester is constructed. Based on the idea of partial capacitance concentration equivalence, a fast extraction method of resistive current is proposed, which improves the accuracy and efficiency of 500 kV arrester resistive current extraction, and is verified by the field measured data. Finally, the applicability of the calculation method is verified by analyzing the inconsistent resistance of each phase. The results show that the phase error of the proposed method is within 4

Due to the varieties of actual operation conditions of the transmission lines and complex surrounding environment, safety accidents caused by entering the danger range of live lines by mistake often occur. Aiming at the problem that it is difficult for the staff to judge whether the transmission line is electrified during the operation and maintenance of the transmission line, based on the space electric field detection technology, this paper proposes an effective and simple method to judge the electrification of the transmission line by adding an electric field probe on the top of the crane arm. It establishes a three-dimensional finite element model of an extendable crane to analyze the influence of crane intrusion and suspension length of crane arm hook on the electric field distribution near the transmission line. According to different operation conditions of the line, the paper proposes the characteristic positions, characteristic components and criteria of live circuit identification. The results show when the characteristic position is right below 4 m of the double-circuit line and the characteristic component is the electric field intensity component at the side of the crane, the operation state of the transmission line is determined as double-circuit electrification if the difference between the characteristic components of the right and the left probes is within 50%. While if the characteristic component of the probe at one side is more than three times of that the other probe, the circuit at this side is determined as single electrification state.

The random fluctuations in the output of new energy increase the risk of power system operation. This paper proposes a power system probabilistic power flow calculation method based on LHS-CGC method, which solves the problem that the probability density function is negative when fitting data with A-type Gram Charlie Series expansion. Taking the calculation results of the Monte Carlo method as a reference, the accuracy and effectiveness of the proposed method were verified in an improved IEEE30 testing system, with higher computational speed. Then, the probability density distribution of each state variable and output variable of the system in three typical operation modes is checked according to the actual power grid model. This article analyzes the probabilistic load flow calculation results of the system under different operating modes and believes that the seasonal output changes of new energy have a more significant impact on the load flow of the new power system, and the risk of branch load flow exceeding the limit increases. Similarly, the node voltage distribution range under the new energy generation mode is larger, reaching 0.92 to 1.03 p.u.. This provides a reference for practical power optimization scheduling problems in engineering.

With the increasing penetration of new energy in the new power system, the influence of the uncertainty of wind power output and the correlation with load on the system operation are increasingly prominent. Thus, the traditional transformer risk assessment can no longer meet the demand. Based on Copula model and Susa model, this paper proposes a joint probability assessment method of transformer operation risk considering correlation between wind power and load. Monte Carlo method is used to calculate each risk index value and evaluate transformer operation risk. The research results show that the traditional transformer evaluation system that does not consider the wind-load correlation will lead to a lower overall risk assessment result, with the maximum error of the index up to 52.39

With the rapid development of ultra high-voltage DC (UHVDC) transmission technology, the total electric field problem in high-altitude dc transmission lines is more important. Therefore, this article proposes a calculation model of the ion flow field at high altitude based on the natural wind model and the gas motion theory. First, the initial charge density is assumed, and then, Poisson’s equation is solved by the finite-element method (FEM). The measured wind speed and altitude are introduced into the natural wind model and the ion mobility model, and the natural wind speed and the ion mobility of each node are obtained. Subsequently, the current continuity equation is calculated by this information and the upstream FEM. When the calculation results do not meet the steady-state convergence conditions, the charge density on the conductor surface is iteratively corrected. The calculation model is verified by the measurement results of the ±800-kV UHVDC transmission line at the National Engineering Laboratory for Ultrahigh Voltage Technology (Kunming) of the China Southern Power Grid. The research shows that with the increase of altitude, the ion mobility gradually becomes larger, and the total electric field at ground level also increases. Due to the influence of wind, the peak value of the total electric field at ground level is obviously shifted, and the maximum peak values are on the downwind side. This model in this article can accurately calculate the total electric field of UHVDC transmission lines at high altitude considering the natural wind and provide a reference for the design of transmission lines.

Purpose The purpose of this paper is to develop a numerical simulation method based on the transient upstream finite element method (FEM) and Schottky emission theory to reveal the distribution characteristics of space charge in oil-paper insulation. Design/methodology/approach The main insulation medium of the converter transformer in high voltage direct current transmission is oil-paper insulation. However, the influence of space charge is difficult to be fully considered in the insulation design and simulation of converter transformers. To reveal the influence characteristics of the space charge, this paper proposes a numerical simulation method based on Schottky emission theory and the transient upstream FEM. This method considers the influence of factors, such as carrier mobility, carrier recombination coefficient, trap capture coefficient and diffusion coefficient on the basis of multi-physics field coupling calculation of the electric field and fluid field. Findings A numerical simulation method considering multiple charge states is proposed for the space charge problem in oil-paper insulation. Meanwhile, a space charge measurement platform based on the electrostatic capacitance probe method for oil-paper insulation structure is built, and the effectiveness and accuracy of the numerical simulation method is verified. Originality/value A variety of models are calculated and analyzed by the numerical simulation method in this paper, and the distribution characteristics of the space charge and total electric field in oil-paper insulation medium with single-layer, polarity reversal of plate voltage and double-layer are obtained. The research results of this paper have the guiding significance for the engineering application of oil-paper insulation and the optimal design of converter transformer insulation.

The surface of grading rings in DC voltage divider may cause surface wear or scratch, resulting in corona phenomenon. Due to the influence of space charges and surface charges, the total electric field near DC voltage divider is different from the nominal electric field. For the problem of solving the ion-flow field near the DC voltage divider, this paper proposes an improved method based on upwind Finite Element Method (FEM). According to the nominal electric field results, the updated switch state of the charge density is determined, and then the upwind FEM is used to update the node charge density. This method uses a dual-scene iterative method to converge for the multiple grading rings, which improves the convergence. The correctness of the method is verified by the coaxial cylindrical electrode. Finally, the ion-flow field near 500 kV DC voltage divider is calculated. The results show that the total electric field near the grading ring becomes more uniform due to the effect of space charges and surface charges. In the space far from or close to the grading rings, the total electric field will increase or decrease compared with the nominal electric field. The method in this paper provides guidance for the calculation of the ion-flow field near the DC divider and its insulation design.

特高压直流输电线路下方的离子流场是电磁环境重要评估指标之一.基于牛顿-拉夫逊法和上流有限元法提出了一种快速稳定地求解离子流场算法.首先,通过有限元法来求解泊松方程,之后将获得的空间电场信息用于上流有限元法计算电流连续性方程.随后,利用基于牛顿-拉夫逊的迭代收敛算法更新导体表面电荷密度.将上述3部分反复迭代即可实现迭代过程的快速稳定收敛.同时,研究了风速对±800 kV特高压输电线路的地面合成电场和离子流场影响规律.试验结果验证了该算法的有效性和正确性.研究结果表明:本算法与迭代收敛控制因子法和传统方法相比不但对导线表面电荷密度初值不敏感,而且具有较高的快速收敛能力.研究结论可以提升离子流场计算的稳定收敛能力,实现特高压直流输电线路电磁环境的快速准确计算.