Xiangxian Zhou

Impact Factors in Measurements of Ion-Current Density Produced by High-Voltage DC Wire's Corona

The reduced-scale model of HVDC transmission lines in the laboratory is widely used to investigate the ionized fields. This paper is aimed at analyzing impact factors of the ion-current density measurement system based on Wilson plates in the laboratory. Both experimental and numerical simulation methods are used to obtain the characteristics of the measurement system. The results show that measurement data can be calibrated with different Wilson plates, and suitable parameters are proposed in this paper to meet the requirement of measurements. The measurement system described in this paper can be used in other similar applications.

Shielding Effect of HVAC Transmission Lines on the Ion-Flow Field of HVDC Transmission Lines

The HVDC and HVAC transmission lines running on the same tower is a promising technology to improve the transmission capacity of an existing corridor. The ions generated by corona discharge of HVDC transmission lines will strengthen the ground-level electric field, which may endanger human exposure. To investigate how the presence of HVAC transmission lines changes the ion-flow field, experiments are carried out on an indoor test model with bipolar dc and three-phase ac lines. The experiment results are then compared with the simulation results. The experiment and simulation results show that the HVAC transmission lines have a shielding effect on the ion-flow field from the HVDC transmission lines running above. Finally, the ground-level electric field and ion current density of the ±800-kV HVDC and 500-kV HVAC transmission lines running on the same tower are calculated.

The Ionized Fields and the Ion Current on a Human Model Under

The ultra-high-voltage direct-current (UHVDC) system has many advantages in long-distance power transmission. This paper is aimed at analyzing the distributions of the ionized fields and the ion current on the human model under ±800-kV UHVDC transmission lines; therefore, a numerical method which combines the 3-D charge simulation method and Deutschs assumption is used. And the validity of the presented method is demonstrated through a test in the laboratory. For ±800-kV UHVDC transmission lines, the ionized fields and the ion current on the human model are calculated, and numerical results show that the ionized fields and the ion current density on the top of the human model increase evidently when the human model stands under ±800-kV UHVDC transmission lines. And the total ion current flowing on the human model is far lower than the permitted limit.

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The ac-dc hybrid transmission line is an effective way to enhance the transmission capacity of a power corridor. However, the corona discharge of ac and the dc transmission lines may interact with each other, which makes the electric field at the ground level difficult to be predicted. This paper presents a simulation method for the calculation of the field effects caused by the corona activities of hybrid ac-dc transmission lines. This approach can simulate the convection and recombination of the space charge generated by ac or dc corona without improper simplifications, and the conductor surface gradient strictly kept to the onset value. The calculated electric field and ion current density at the ground level agree well with the measurement results of a hybrid line model.

800-kV HVDC Transmission Lines

As many high voltage direct current (HVDC) projects are constructed in China, the ionized field problem is of wide concern. The upstream finite element method (Upstream FEM) has good adaptability and is widely used to analyze the ionized field under HVDC lines. Galerkins scheme is used to improve the charge density precision. Poissons equation solution technique and charge density updating strategy are adopted to accelerate the calculation. The charge density precision and the calculation efficiency is remarkably improved. For the 15 000-nodes-scale ionized field problem of bipolar-6-bundled HVDC lines, the calculation time is less than 5 s. The algorithm also shows good robustness to the charge density initial value in the numerical cases.

A Time-Efficient Method for the Simulation of Ion Flow Field of the AC-DC Hybrid Transmission Lines

The ion flow from the bundle conductors of HVDC transmission lines is different from that of a single conductor. This paper presents systematic research on the spatial distribution of ion current due to corona around bundle conductors. A corona cage capable of fitting different bundle conductors is designed for the experiments. Extensive measurements are carried out in different voltages and polarities for four kinds of bundle conductors. To determine the roughness factor of the wires, the experiment with a single conductor is also included. The numerical methods, based on computation along the electric flux lines or based on triangle meshes, are used to calculate the ion current distribution around bundle conductors. Charge density distributions on different bundles are compared. To improve the accuracy of the mesh-based method, a new scheme of surface charge density distribution on the bundle is proposed. The characteristics of the ion current distribution and the total ion current of the bundle are also analyzed in this paper.

High Efficiency FEM Calculation of the Ionized Field Under HVDC Transmission Lines

An improved method to simulate the ion-flow field generated from the corona discharge on HVDC transmission lines is proposed. To remove the oscillations in simulation of charge conservation law, an upwind weighting function is adopted in the finite-element method. The Poissons equation and the charge conservation law are solved simultaneously through Newtons method of iterations, which accelerates the convergence of the algorithm. A rule for charge density on boundary in the bipolar problem is proposed in this paper, which ensures the stability of the iterations. The computation time, convergence rate, and accuracy of the proposed method are analyzed. The proposed method is verified by analytical and experimental results, and then it is applied to the prediction of the ion-flow field from a ± 1100-kV HVDC transmission line.

Spatial Distribution of Ion Current Around HVDC Bundle Conductors

This paper aims at developing a simulation method for the ion-flow field when HVDC transmission lines cross over HVAC transmission lines. A time-domain 3-D method is proposed in this paper, where the 3-D finite-element method and 3-D finite volume method are used to solve the Poissons equation and the charge conservation law, respectively. The implicit temporal discretization scheme is used to accelerate the computation. An indoor test model is set up in this work, and the simulation results agree well with the measured results from this test model, which validates the proposed method. The proposed method is then used to calculate the ground-level electric field and ion current density under the crossing of ± 800-kV HVDC transmission lines and 500-kV HVAC transmission lines. The presence of HVAC transmission lines is found to have a significant influence on the ion-flow field under the crossing.

Simulation of Ion-Flow Field Using Fully Coupled Upwind Finite-Element Method

This paper aims at investigating the mechanism of hybrid ac/dc corona which is usually accompanied with the hybrid HVAC/HVDC power transmission lines. A coaxial wire-cylinder corona cage is designed in this paper, and the combined ac/dc voltage is applied to the wire and cage. The low-frequency component of corona current from the hybrid ac/dc corona in this corona cage with five types of wires is measured. To obtain the detailed characteristic of the interaction between the space charge and ionized electric field, a 1-D method is developed to simulate the hybrid ac/dc corona in the symmetrical corona cage. This method is validated through the comparison with measurement results. Based on this simulation method, analysis of the evolution of space charge and ionized electric field in one time cycle is presented. The regular pattern of charge injection from the discharge electrode is summarized, where the charge injection is found not linearly dependent on the applied voltage. Finally, the corona loss of hybrid ac/dc corona is calculated, and the similar result with the quadratic law in ac corona is found from the calculation results. This research provides useful knowledge for the engineering computation of the effects of hybrid ac/dc corona.

Simulation of Ion-Flow Field at the Crossing of HVDC and HVAC Transmission Lines

With more HVDC transmission lines being built in China, the situation of the plastic greenhouses existing underneath the HVDC lines is becoming more common when the transmission lines pass over the farmland. The ionic space charges generated by corona discharge of HVDC transmission lines strengthen the electric field at the ground level. And with the accumulation of the ionic space charges on the surface of the plastic greenhouses, the ion-flow fields are highly perturbed. In this paper, a set of single conductor experiments is performed in the laboratory. Extensive measurements are carried out for different voltages and polarities with different types of plastic greenhouse models. The main goal of this work is to make it clear that whether or not the presence of greenhouses would affect the ion-flow fields and ion current density inside the greenhouse models. And through the analysis and discussion, we find out the differences of the ion-flow fields when the greenhouse models exist or not, which is the foundation of the future research.