Abstract The Tower grounding grids are important power facilities for transmission line grounding protection. The accurate measurement of grounding resistance provides data support for the safe operation of the grounding grids. The existing measurement methods for grounding resistance are mainly based on the 0.618 method, which has two disadvantages: (1) The distance between the voltage electrode and the measuring point should not be less than 2.5× the length of the scattered grounding electrode; (2) the long measuring wires ensure the measurement accuracy of the 0.618 method, but the long‐distance between the electrodes and measuring point makes it difficult to carry out in the complex environment. To accurately solve the problems, this paper proposes a novel measurement method of grounding resistance with shorter measuring wire based on Green's theorem. Combined with the physical model of the actual tower grounding grid, this paper establishes the potential equations in local space around the grounding grid and analyses the distribution of the equipotential surface. The results show that the proposed novel method of measuring tower grounding resistance can conveniently measure the grounding resistance, which greatly shortens the length of the measuring wire and has better adaptability for towers in a complex environment.
During operation, converter transformers enter a saturation state, leading to phenomena such as magnetising inrush currents. Accurately measuring the excitation characteristic curve of an iron core under deep-saturation conditions is essential for analysing low-frequency transient phenomena in transformers. This paper presents a method for calculating the excitation characteristics of a converter transformer under deep iron core saturation. The method involves establishing an improved T model for the converter transformer and conducting open-circuit experiments in the linear working region to obtain the excitation characteristic curve and knee point parameters. AC-DC hybrid excitation is used to achieve deep saturation, and measurements of saturated inductance at different levels of saturation at the transformer terminals are taken. The mathematical relationship between saturated inductance and magnetic impedance is derived, allowing deduction of the magnetising characteristic curve of the converter transformer under deep-saturation conditions based on measured saturated inductance values. A finite element simulation analysis was performed on a single-phase four-column converter transformer with a capacity of 250 MVA. Additionally, a test platform for toroidal transformers and dry-type transformers has been set up to carry out excitation characteristic measurement and verification. Experimental results demonstrate that errors are maintained within 10% or less, validating this approach’s effectiveness.
This study presents a novel method for measuring the collisional charge of micron-sized particles in insulating oil. Specific studies involves measuring the charge of micron carbon particles and cellulose particles in insulating oil and fitting the data to develop calculation formulas for collisional charge under various charging modes. The developed formulas provide crucial charge data to study impurity particle migration and aggregation in oil-immersed power equipment. The study also examines the impact of wall material, particle size, and electric field intensity on the collisional Charging Characteristics of particles. The collisional charge of particles is proportional to their surface area. As the electric field is strengthened, the collisional charge will tend to saturate. Furthermore, the polarity of the collisional charge of particles has been summarized. The measurement method proposed in this study has an error of approximately ±3.5% and performs well in measuring the collisional charge of micron-sized particles in liquid media.
The three-electrode method is the most commonly used grounding resistance measurement method. But the electrode wire of the three-electrode method is too long to be used in mountainous areas or densely built areas. Therefore, it is of great application value to effectively shorten the electrode wire under the condition of ensuring measurement accuracy. In this article, a novel method for measuring the grounding resistance of towers with short electrode wire is proposed. Based on the connectivity of soil inside and outside the tower foundation, the limited space inside the tower foundation is fully used to arrange the electrodes. The principle of arranging electrodes inside the tower foundation to measure the grounding resistance is deduced in detail. The calculation method of the compensation point position and measurement error is studied. The best way of arranging electrodes is proposed. Through simulation experiments and field tests, we confirmed that the measurement accuracy of this novel method is similar to that of the three-electrode method. Its electrode wire length is shorter than the three-electrode method and other improved methods. Only the length of electrode wire needs to be the same as the length of the grounding conductor, and the measurement error can be controlled at about 3%. The novel grounding resistance measurement method has a wider application range and higher measurement efficiency.
In the context of the energy Internet, research on regional energy management is of great significance. Focusing on this topic, this paper proposes a model of demand-responsive(DR)energy cells, and establishes a hierarchical optimization scheduling model. The upper layer takes the total cost of the smart community as the objective function, and the lower layer, considering the DR management, takes the lowest comprehensive cost of each energy cells as the objective function. This study is aimed at presenting a two-layer optimization model for the smart community based on the DR energy cell. In this paper, the optimization strategy of maximizing economic benefits is obtained through the iteration of the upper and lower models. The model can improve the economics of the smart community.
Grounding electrodes are used to ensure safe operation of electrical apparatus. The limited axial construction space for grounding electrodes is a significant constraining factor. Grounding performance will attenuate rapidly under the influence of the reduced length of horizontal or vertical grounding electrodes. However, if additional resistance-reducing measures are adopted, the operation and maintenance cost of grounding electrodes will considerably increase. To solve above problem, this study proposed a novel grounding model that uses a helical grounding electrode to improve grounding performance within limited axial construction space. Firstly, a calculation model of finite element methods (FEM) is built based on the concept of increasing the contact area between the grounding electrodes and the soil. Grounding performance parameters of helical grounding electrodes, grounding resistance, electrical potential rise (EPR) distribution and maximum touch voltage, are analyzed. At the same time, structural parameters and buried depth for the helical grounding electrodes are studied and the optimal design criteria for the parameters are given. Results show that the helical grounding electrode exhibits better grounding performance in a limited axial construction area.
General methods of detecting partial discharge of transformers include the pulse electric current, DGA, the ultrasound, RIV, the light detection, the radio frequency and the chemistry etc.. A new partial discharge of transformers method based on ultraviolet pulse detection proposed in this paper. After analyzing the relation of partial discharge of transformers with ultraviolet ray and the detection principle, the monitor method of ultraviolet pulse convert to light current pulse and carried on the first step experiment have been designed. As a result, when insulate was break in initial stage, the method of ultraviolet pulse can detect weak discharge and be applicable to on line monitoring for partial discharge of transformers.
Based on the analysis of critical factors and solutions of the detecting depth of open electrical impedance tomography(EIT),two-dimensional physical models and corresponding mathematical models for the human torso aiming at practical application were set up,and three excitation patterns,namely surface excitation(SE),back excitation(BE) and hand excitation(HE) were proposed.The validity of these presented excitation patterns was proved by simulation with finite element method(FEM).The simulation results indicate that the BE and HE make more excitation current distributed in deep region than SE,which lead to the boundary voltage is more sensitive to the internal impedance of object,then the detecting depth of open EIT is increased.Therefore,BE and HE are more suitable for application in open EIT.
A Fast-DPM method applicable to large-scale, long-term particle dynamics simulation was proposed based on the motion characteristics of micrometer-sized particles in highly viscous media. This method significantly improves computational efficiency while ensuring computational accuracy and was employed to simulate the motion and aggregation characteristics of carbon particles within the valve-side bushing turret under rated operating conditions. By considering the internal structure of the valve-side bushing turret, the influence of factors such as electric field, oil flow, and gravity on the motion characteristics of carbon particles was discussed. The simulation captured the aggregation characteristics exhibited by large-scale carbon particles after prolonged motion and assessed the contamination risk of carbon particles in different regions within the valve-side bushing turret. This study provides a fundamental approach for simulating the dynamic processes of impurity particle motion in liquid dielectrics, serving as a crucial foundation for evaluating insulation contamination risk and guiding insulation optimization within the valve-side bushing.
Because of less pollution and low consumption, electric vehicles play an important role in solving the energy shortage and environmental degradation problems. But harmonics will be generated during the charging process of electric vehicles because of the existence of nonlinear equipments, it will affect the power quality and system operating seriously. In this paper, the simulation model of electric vehicle charging station is built and the characteristic of harmonics generated during charging process are analyzed, then passive filters are added to the model.
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