Guangning Wu

A simple formula of grounding grid resistance in vertical two-Layer soil

Large ground grids usually were located in vertical two-layer soil. A study was done in this paper to get a simple and accurate grounding resistance expression of it. At first, some simulations were done about a same grid buried in different vertical two-layer soil to get resistances of it. An analysis was given about the relationship of grounding resistances when the grid buried in homogeneous medium or vertical two-layer medium. Then, the curve of the relationship was fitted and a formula was gotten. By discuss the mathematical and physical significance of the formula; the coefficients of it were determined. At last, an error analysis of the formula was done and an example was given to show how to calculate grounding resistance of a grid locate in vertical two-layer soil using this formula.

New Method for Calculating Ground Resistance of Grounding Grids Buried in Horizon Two-Layer Soil

With the development of ultra high voltage AC and DC power system, fault current of power plants, substations and convertor station are great than before. Larger grounding grids are needed to meet the safety regulation. Grounding grids usually located in horizon multilayer or vertical multilayer soil structure which parameters such as thickness, resistivity of each layer can be estimated. This paper presents a new method for calculating ground resistance of grounding grid buried in horizon two-layer soil. It is consisting of three chapters. In the first part, simulations were done to obtain ground resistance of grounding grid in horizon two-layer soil and uniform soil. Then, results were preprocessed to two variables, one is the ratio of resistance of grid in horizon two-layer soil to uniform soil, the other is the ratio of soil resistivity about the top layer to the borrow layer. The relationship curve between the two ratios was plotted out. In the second part, an engineering estimation formula was simplified for calculating ground resistance in horizon two-layer soil. Results of the formula proposed are compared with results of simulation software and its error is acceptable. In the last part, examples of how to use this formula are illustrated.

Analysis and research prospect of lightning-induced voltages in overhead transmission lines

The evaluation of electromagnetic transients in overhead power lines due to nearby lightning return strokes requires accurate models for the calculation of both the incident lightning electromagnetic pulse (LEMP) and the effects of coupling of this field to the overhead lines. Meanwhile, the influence of ground resistivity and the number of line conductors should be considered on analyzing the distribution characteristic of lightning-induced voltage. This paper reviews the most significant results obtained by well-known experts concerning the calculation of lightning-induced voltages, and points out some problems to be taken into account from now on. First, the theoretical basis and computation model for the calculation of lightning electromagnetic and lightning-induced voltage in overhead power lines is illustrated; then, combining with the results of domestic and foreign scholars, the distribution characteristic and influencing factors of lightning-induced transient in overhead power lines are analyzed; finally, some problems which can be studied are proposed: 1) the influence of multi-coupling among the conductors on lightning-induced voltage, 2) model for lightning-induced voltage in overhead lines considering ground layered structure.

The status of Arch Arc in the High-speed electrified railway

With the speed of electrified railway improving, the getting worse arch arc, has become one of constraining bottleneck in the development of China high-speed railway. This paper has discussed the hazards of arc to the contact wire, pantograph skateboards, communication signals, radio signals and power quality. From the aspects of arc model, arc energy, arc erosion and carrier friction, summarizes the research actuality of to arc issues ,and affords information in research work for further reference.

Research on effects between grounding module and grounding eesistance

One of the methods to decrease the resistance of ground grids to safety regulation is to use the grounding module at present. In the first part, the ingredients and the principle of resistance reducing of grounding module were introduced. Then, set up the model of ground grids and simulated under different situations like the different fixed position of grounding module, ground grids acreage and soil resistivity by CDEGS software.. Regarded that these changes were influential. At last, some practical advised about grounding module were given.

The Survey of Insulation Problems of UHV Transmission System

The energy distribution and load center in China are very unbalanced, and along with the continued increase of power demand, the tendency of developing and building UHV power transmission line in China is inevitable. With the increase of voltage classification, insulation problem has become more and more important,. In this paper, some characteristics of overvoltage of UHV transmission system are presented. And some insulation levels of transformation equipments (including transformer, breaker, GIS) are discussed. Insulation level of UHV transmission line of China could be confirmed by analyzing the distance between transmission line and ground, the amount of insulator, support insulator and casing wear. According to Chinas national situation and operational experience of foreign countries, some advice is given. At last, it is pointed out that metal-oxide arrester (MOA) is the appropriate arrester to UHV power system, and ZnO valve element is the key part of MOA, which should be paid more attention to.

Study of AC/DC Power Coordinated Control for Multi-circuit UHVDC Transmissions of Sichuan

There is an AC/DC transmission system in Sichuan power grid include 1000kV UHVAC transmission and ±800 kV UHVDC transmission, after Jingsha river hydropower stations and their UHVDC transmission were finished. Power network structure of Sichuan power grid will be more complicated. According to the characteristic of Sichuan power grid, the control method of DC active power coordinated control is selected. And the influence of Sichuan power grid stability of ample flow period maximum method caused by DC active power coordinated control is analyzed. The result of research shows that the capability of Sichuan power grid against serious fault can be improved with DC active power coordinated control.

Analysis of the sheath voltage in High-speed railway feeder cable grounding in single-ended mode

With the scale construction of passenger dedicated line, in order to improve the reliability of traction power supply, 27.5 kV single core line cable is widely used in the power contact line of outlet and catenary power supply line. The high reliability of traction power supply system directly affects the overall reliability. When AC current flows through the conductor in cable, the shielding layer will generate a corresponding induced electromotive force of which the magnitude is mainly proportional to length of the cable and value of the current in the conductor. When value of induced electromotive force on the sheath is too large, it may cause the grounding fault of the cable and endanger the safety of the people and the equipment. In this paper, the simulation software PSCAD/EMTDC is used to build the model of the High-speed Railway All-parallel AT Traction Power Supply System. The feeder cable sheath one end direct grounding, the other end through the Cable sheath protector grounding, which is called Cable sheath single-grounded way; The feeder cable sheath middle direct grounding-two ends protector grounding, which is called Cable sheath midpoint-grounded way. Using PSCAD/EMTDC simulation software to measure the voltage of cable sheath under different length of cable, graph of voltage in cable sheath is obtained. Analyzing the voltage of cable sheath and graphic, applicable distance of the cable sheath single-grounded way and Cable sheath midpoint-grounded way are obtained. The result provides reference for the engineering.

Study of the Influences on Soil Resistivity Caused by HVDC Mono-polar Operation

UHVDC transmission system has many advantages, such as transferring large amounts of electrical power over long distances. It plays an important role in the west to east power transmission project. The ground electrode of UHVDC was working in several kA currents for long-term when it works in mono-polar operation. And there is high temperature of the soil around the ground electrode in that time. The normal operation of ground electrode can be impacted by the soil resistivity around it. Porous media model is introduced in this paper. Based on this model, impact of temperature on soil resistivity is presented. And the relationship of current density and soil resistivity is analyzed. Then, an experiment was done to validate it.

Effects on Transformer due to UHVDC Mono-polar Operation and Calculation of Ground Electrode Current

Recently years, UHVDC transmission system is paid more attention to in the field of Chinas power system. It takes key part in the tactic of China electrical power development. But, many problems caused by UHVDC system, such as DC bias, corrosion of metal underground and so on. DC flows through the neutral point and causes DC bias of transformer, as well as some other problems, such as vibrations, overheating, or noise, which will harm the operation of transformer. In this paper, the influences of DC grounding current on transformer, caused by UHVDC Mono-polar operation, are introduced. And, some suggestions of DC bias solution were provided.