Search

Because of the high cost and limitations of the traditional lightning protection methods, this paper proposes a new method to improve the lightning withstand level of 110kV transmission lines by installing current limiting coil between the tower cross arm and lightning rod. In order to verify the feasibility, this paper established the finite element model of current limiting coil to calculate the distribution parameter accurately. Then the EMTP model of lightning striking 110kV transmission lines is set up to study the effect of coil inductor on the lightning protection. The results show that the appropriate value of current limiting inductance is 0.1mH. After the installation of the 0.1mH current limiting coil, the tower current falls by 19.9%, the lightning withstand level increases by 11.8%. Finally, this paper puts forward the optimization design scheme of the current limiting coil, and checks the thermal stability and insulation level of the coil when 55kA lightning current flowing through the coil, the result of electric field strength simulation show that the feasibility of the device in the 110kV transmission lines lighting protection is remain to be verification by experiment.

DC deep well grounding electrode has high engineering value due to its small footprint and easy site selection. Because a single deep well grounding electrode’s maximum diagonal distance is less than one meter, it is obviously not appropriate to measure the grounding resistance directly by using the manual recommended 5 times diagonal distance from the manual wiring [1]. Therefore, we built a DC deep well grounding electrode model and calculated its grounding resistance. Moreover, studied the law of the surface potential distribution under the action of current field created by current electrode, combining the calculated grounding resistance value, we analyzed the layout requirements for voltage electrode. By changing the position of current and voltage electrode, we studied the relationship between measurement error and wiring distance, and put forward a scheme of current and voltage electrode layout for the measurement of the grounding resistance. The scheme of the research was used to measure the grounding resistance of the deep well grounding electrode, which verified it’s validity and accuracy. Finally, we analyzed the similarities and differences of resistance measurement between deep well grounding electrode and horizontal and vertical grounding, which provides a reference for the measurement of deep grounding resistance and related standards revision.

Room temperature vulcanized (RTV) silicone rubber is extensively used in power system due to its hydrophobicity and hydrophobicity transfer ability. Temperature has been proven to markedly affect the performance of silicone rubbers. This research investigated the degradation of RTV silicone rubber under temperature cycling treatment. Hydrophobicity and its transfer ability, hardness, functional groups, microscopic appearance, and thermal stability were analyzed using the static contact angle method, a Shore A durometer, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TG), respectively. Some significant conclusions were drawn. After the temperature was cycled between −25 °C and 70 °C, the hydrophobicity changed modestly, but its transfer ability changed remarkably, which may result from the competition between the formation of more channels for the transfer of low molecular weight (LMW) silicone fluid and the reduction of LMW silicone fluid in the bulk. A hardness analysis and FTIR analysis demonstrated that further cross-linking reactions occurred during the treatment. SEM images showed the changes in roughness of the RTV silicone rubber surfaces. TG analysis also demonstrated the degradation of RTV silicone rubber by presenting evidence that the content of organic materials decreased during the temperature cycling treatment.

The outdoor ultra-high voltage (UHV) dry-type air-core smoothing reactors (DASR) of High Voltage Direct Current systems are equipped with a rain cover and an acoustic enclosure. To study the convective heat transfer between the DASR and the surrounding air, this paper presents a coupled model of the temperature and fluid field based on the structural features and cooling manner. The resistive losses of encapsulations calculated by finite element method (FEM) were used as heat sources in the thermal analysis. The steady fluid and thermal field of the 3-D reactor model were solved by the finite volume method (FVM), and the temperature distribution characteristics of the reactor were obtained. Subsequently, the axial and radial temperature distributions of encapsulation were investigated separately. Finally, an optical fiber temperature measurement scheme was used for an UHV DASR under natural convection conditions. Comparative analysis showed that the simulation results are in good agreement with the experimental data, which verifies the rationality and accuracy of the numerical calculation. These results can serve as a reference for the optimal design and maintenance of UHV DASRs.

Put geosynthetic clay liners around underground oil-gas pipelines can reduce the potential damage to environment but it will also affect the distribution of cathodic protection current. Geosynthetic clay liners can be regarded as anisotropic soil structure and the potential distribution on the pipeline between two adjacent cathodic protection stations was calculated based on boundary element method (BEM). The calculation results indicate that potential distribution on the pipeline with geosynthetic clay liner is lower than before. A 1500 m built pipeline with geosynthetic clay liners was selected to be calculated and to perform field test, which shows that the calculation results tally well with the field test results and the validity of the arithmetic in this paper was verified.

During the commissioning stage or pole outage of high-voltage direct current (HVDC) links, ground-return currents (GRCs) are injected into dc grounding electrodes. Therefore, earth surface potential (ESP) is induced by GRC. Moreover, nonuniform distribution of ESP in wide areas usually leads to half-cycle saturation of power transformers and interference of metallic underground infrastructures, especially pipelines and cables in long distance. As GRCs flow into the earth by dc grounding electrodes, ESP is determined by the resistivity of the earth. However, the heterogeneity of the earth brings difficulty in simulating ESP. In this paper, measurement and estimation of the earth resistivity is studied in detail. First, measurement technique for earth resistivity is introduced, including both the four-point method (FPM) and the magnetotelluric method (MT). A group of apparent resistivity can be obtained by changing the interval of FPM, which indicates the shallow earth resistivity. By using MT, another group of apparent resistivity representing the deep earth is scanned by tuning the receiving frequency. Second, both FPM and MT are proposed to measure the earth resistivity of wide areas. Measurement data of both methods are used as raw data for earth parameter estimation (EPE). EPE is an optimal problem of finding a good enough earth model to interpret the measured data. Third, this paper introduces an overall objective function (OOF) for EPE. The horizontal layered soil (HLS) is chosen as the ideal earth type. Then based on this assumption, HOF is set to a linear combination of the objective functions of FPM and MT. Finally, a hybrid optimization method named LevenbergMarquardt based artificial bee colony (LMABC) algorithm is presented to minimize OOF. Other optimization method such as genetic algorithm (GA), Levenberg-Marquardt (LM), and artificial bee colony (ABC) are also used to compare the performance of EPE. Results shown that LMABC is the most sophisticated method of EPE, which is capable of interpreting the measured data of FPM and MT precisely. This paper helps converting the field-test data into an HLS model, which enable the computation of ESP of wide areas. The numerical analysis of ESP and its applications will be introduced in the second part of this paper.

In the first part of this paper, the methodologies of earth resistivity measurement and estimation have been studied. The horizontal layered soil (HLS) model obtained by the first part of this paper is usually with over 10 layers, which is far more than the existing HLSs used for grounding design. The parameters of the HLS of wide areas are also irregular, which means the resistivity or thickness of some layers may be much larger or smaller than the others. In this situation, highly accurate algorithm should be used to calculate earth surface potential (ESP). Numerical analysis of ESP is presented in this paper. First, theoretical expression of the scalar Green's function (SGF) of HLSs is derived by using a mathematical induction based on symbolic equations. Moreover, the limits of SGF can also be obtained, which can help sampling algorithm to determine the sample range. Second, an enhanced complex image method (CIM) name multi-resolution CIM (MRCIM) is proposed to calculate SGF of HLS with extra accuracy. MRCIM is able to fit the SGF in full range. Tested by a real case, MRCIM is capable of calculating singular SGF of HLSs, which is far more accurate than the existing tools, such as CDEGS and COMSOL. With MRCIM, ESP induced by ground-return currents (GRCs) are carefully analyzed. The proposed method can be used to solve the GRCs in ac power grid and in underground metallic infrastructures.

Deep-well earth electrode has advantages of covering small area and investing few. Temperature rise is one of the key quantity to take into consideration during designing. After analyzing the current and temperature field, infinite length cylinder model is used to calculate the temperature, and the partial differential equation is deduced to express the temperature field. Uniform space temperature is chosen as initial condition, while lower and upper boundary conditions are thermal insulating and constant temperature separately. An example result is gotten through solving the equation. The characteristics and the reason leading them are analyzed.

A novel method that is been used to simulate the lightning progress process was presented. The base of the simulation the calculation of electric field intensity, the purpose of the simulation is to find out whether the lightning will strikes phase conductors or not. In the simulation model, the descending leader is been considered as cylinder discharge, and placing a concentrated discharge in the tip of the cylinder, choosing gap-criterion to judge the upward-directed leader inception. The system voltage and the ground obliquity's influence to the electric intensity are both considered. The calculation result of a transmission line is a little smaller than the statistical data.

The design of such a novel software application that can be used to calculate the backflashover rate of transmission line is presented. The software application was developed by combining ATP with VC++. The software structure and the input/output interface are provided, as well as the implementation details. In the calculation, compares the insulators' volt-time curves to the overvoltage to judge the insulators' behavior, considers the system voltage and the induced voltage's influence on backflash lightning withstanding level. A total line backflashover rate calculation example shows that it's convenient for estimating the backflashover rate of a total line and studying the effect of lightning performance improvement methods such as reducing grounding resistance with the software application. This software application's design way is suitable for other transient calculation which using ATP.