Chijie Zhuang

A local discontinuous Galerkin method for 1.5-dimensional streamer discharge simulations

Streamer discharges are important both in theory and industry applications. This paper proposed a local discontinuous Galerkin method to simulate the convection dominated fluid model of streamer discharges. To simulate the rapid transient streamer discharge process, a method with high resolution and high order accuracy is highly desired. Combining the advantages of finite volume and finite element method, local discontinuous Galerkin method is such a choice. In this paper, a simulation of a double-headed streamer discharge in nitrogen was performed by using 1.5-dimensional fluid model. The preliminary results indicate the potential of extending the method to general streamer simulations in complex geometries.

Modeling of Trichel Pulses in the Negative Corona on a Line-to-Plane Geometry

In this paper, a 2-D time domain method is proposed to simulate Trichel pulses in the negative corona discharge on a line-to-plane geometry. Three ionic species in the ionization layer, including electrons, positive ions, and negative ions, are taken into consideration. The FEM is used to solve the Poissons equation, while the finite volume method is used to solve the charge transport equations. Trichel pulses on a line-to-plane geometry are analyzed and compared with the measured results of a designed experiment in the laboratory. Good agreement is obtained between the calculated results and the measured ones, verifying the validity of the proposed scheme.

Electric field step in air gap streamer discharges

Electric field (E-field) in air gap streamer discharges under positive lightning impulse was measured by specifically developed integrated electro-optic sensors. An E-field step phenomenon was observed. The E-field firstly agreed with the Laplace field, then suddenly increased with a rise time of μs. The occurrence probability of this phenomenon increased as the applied voltage increased. The discharge current waveforms and photos taken by a fast camera prove the E-field step was caused by the space net charge. From the E-step rise time and the corona area range, the average electron drift speed under the experiment situation was estimated about 0.2 × 106 – 0.6× 106 m/s.

The Optimization of Entering Route for Live Working on 750 kV Transmission Towers by Space Electric-Field Analysis

Live working is important for the continuity of electricity supply in power system. Experiment results of 50% switching impulse sparkover voltages (U50) for different live working entering routes on a real tower are presented. The potential and electric-field distribution around the 750 kV straight tower window with a line worker inside, was analyzed via an approach combing charge simulation method and indirect boundary element method. The comparison demonstrates the close relationship between electric-field distribution and U50. The sparkover voltage and the maximum electric-field strength change synchronously for a specific structure. Generally speaking, the higher the electric filed strength is, the lower the sparkover voltage will be. Thus, the experiment procedure for deciding the best entering route can be simplified according to the electric-field distribution calculation.

A Positivity-Preserving Scheme for the Simulation of Streamer Discharges in Non-Attaching and Attaching Gases

Assumed having axial symmetry, the streamer discharge is often described by a fluid model in cylindrical coordinate system, which consists of convection dominated (diffusion) equations with source terms, coupled with a Poisson’s equation. Without additional care for a stricter CFL condition or special treatment to the negative source term, popular methods used in streamer discharge simulations, e.g., FEM-FCT, FVM, cannot ensure the positivity of the particle densities for the cases in attaching gases. By introducing the positivity-preserving limiter proposed by Zhang and Shu [15] and Strang operator splitting, this paper proposes a finite difference scheme with a provable positivity-preserving property in cylindrical coordinate system, for the numerical simulation of streamer discharges in non-attaching and attaching gases. Numerical examples in non-attaching gas (N 2 ) and attaching gas (SF 6 ) are given to illustrate the effectiveness of the scheme.

Study on the Influence of the DC Voltage on the Upward Leader Emerging From a Transmission Line

The evaluation of the lightning shielding failure of a transmission line is very important in power transmission system design, and the operation voltage has rarely been considered before. However, when the operation voltage reaches 800 kV and the tower height is near 100 m, the influence of operation voltage may not be ignored. In this paper, an experimental system consisting of an air gap between a plate/rod and a conductor was established, where the dc voltage could be applied to the conductor and was accompanied by a negative impulse voltage on the plate/rod electrode. An upward leader up to 1.54 m in length was observed, and the leader velocity and charge density were obtained in a 11-m-long air gap, whereas the voltage on the conductor was 800-kV dc. The influence of dc operation voltages on the upward leader was studied. The experimental results showed that the upward leader will emerge much earlier and may progress longer with dc operation voltages. That is, the lightning attachment to the conductor may occur more easily when the voltage of the conductor is opposite in polarity to that of the downward lightning than when the conductor has no operation voltage.

A WENO Scheme for Simulating Streamer Discharge With Photoionizations

This paper proposes a weighted essentially nonoscillatory (WENO) finite difference method to simulate the 2-D fluid model of streamer discharges between two parallel plates. To simulate the rapid transient streamer discharge process, traditional linear schemes would fail and a nonlinear method with high resolution and high-order accuracy is greatly desired. WENO scheme is a good choice. In addition, the exact photoionization model is considered. A simulation of a double-headed streamer discharge was performed using the exact photoionization model and simplified uniform background photoionization model. Finally, the results were compared.

2-D Discontinuous Galerkin Method for Streamer Discharge Simulations in Nitrogen

This paper proposes a discontinuous Galerkin (DG) method combined with hierarchical reconstruction to simulate the fluid model of streamer discharges. To simulate the rapid transient streamer discharge process, a method with high resolution and high order accuracy is highly desired. Combining the advantages of finite volume and finite element method, DG is such a choice. A simulation of a double-headed streamer discharge in Nitrogen was performed using 2-dimensional fluid model. The preliminary results are quantitatively agreed with those obtained by finite volume method combined with moving mesh, indicating the potential of extending the method to general streamer simulations in complex geometries.

Switching impulse breakdown characteristics of large sphere-plane air gaps compared with rod-plane air gap

With the increase of operation voltage to 800 kV-1100 kV, the sphere-plane gaps with radius of 0.5-1 meter are widely used in the converter station of UHVDC power transmission system. In order to ensure the safety of UHVDC system and reduce the investment, it is necessary to investigate the breakdown characteristic of large radius sphere-plane gap. This paper implemented experiments on three different gap configurations: rod-plane, sphere (R=0.55 m)-plane, and sphere (R=0.75 m)-plane. The 50% breakdown voltages and the current injected into the high voltage electrode were measured. Besides, the discharge process was observed by a high speed CCD camera. Three types of current waveforms related to different streamer progression characteristics were found. With the increase of sphere radius, it can be found that the streamer gradually becomes dominant in the discharge process, which leads to higher average breakdown field, longer streamer length and much more injected charge of first streamer.

A neural network short-term load forecasting considering human comfort index and its accumulative effect

Short-term load forecasting is one of the most important fields of electricity demand research. Many traditional models and artificial intelligence techniques have been evaluated and tested in this task, and the Artificial Neural Network (ANN) is received much attention. In this paper a development of the artificial neural network based short-term load forecasting model considering the impact of human comfort index and its accumulative effect was proposed. The ANN structure and the training data set selection are described in the paper, and holiday load forecasting correction are adapted in this model. The implementation and results in a southeast city of China indicate that the load forecasting model developed carries out accurate forecasts.