Akiyoshi Tatematsu

Three-Dimensional FDTD Calculation of Lightning-Induced Voltages on a Multiphase Distribution Line With the Lightning Arresters and an Overhead Shielding Wire

To suppress the lightning-induced voltages on a distribution line, lightning arresters and/or overhead shielding wire can be installed, and the effectiveness of these countermeasures are usually studied by simulations. Traditionally, field-to-transmission line coupling techniques based on the distributed-parameter circuit theory are used for the calculation of the lightning-induced voltages. Recently, the finite-difference time-domain (FDTD) method that directly and numerically solves Maxwells equations was applied to the calculation of the lightning-induced voltages. Compared with the conventional methods, the FDTD-based calculation is advantageous in terms of the modeling of inhomogeneous ground parameters, 3-D structures, and grounding systems. But, in the previous works, the distribution line was simulated simply by a single-phase line. Moreover, the representation of lightning arresters in the FDTD method was not yet established. This paper proposes a technique to incorporate the lightning arresters in the FDTD-based lightning overvoltage calculations. In this technique, the voltage-current relationships of the lightning arresters are represented by piecewise linear curves, which can be obtained directly from the data sheets or measured results. For validation purpose, the lightning-induced voltages on a three-phase distribution line equipped with the lightning arresters and a multipoint-grounded overhead shielding wire are calculated by the proposed method, and the results are compared with those obtained by the conventional method and a very good agreement is found.

Development of Locating System of Pulsed Electromagnetic Interference Source Based on Advanced TDOA Estimation Method

A locating system based on an advanced time difference of arrival (TDOA) estimation method is developed to locate the position of a discharge source to avoid pulsed electromagnetic interference (PEMI) with the surrounding radio communication environment. In general, from the waveforms of PEMI waves received by an antenna array, the source position can be located or the direction of arrival (DOA) of the EM waves can be estimated by applying TDOA-based methods. However, owing to noises and multipath waves that occur at the metal surfaces of electric power equipment, the estimation accuracy of the TDOA may decrease, and the location accuracy will be degraded. To improve the accuracy of TDOA estimation, we propose a new TDOA estimation technique. In our developed locating system, PEMI waves are received by a four-antenna-square array and the DOA is estimated from the TDOA, which is estimated using the generalized cross-correlation phase transform method in combination with the proposed technique. A PEMI source is ultimately located by aiming a charge-coupled device camera, installed at the center of the antenna array, at the estimated DOA. The estimation accuracy of the locating system is evaluated through experimental measurements. The results show that the developed locating system can locate the position of a PEMI source existing within about 30 m from the system with high accuracy.

Analysis of Electromagnetic Fields Inside a Reinforced Concrete Building With Layered Reinforcing Bar due to Direct and Indirect Lightning Strikes Using the FDTD Method

Lightning electromagnetic pulse (LEMP) is a severe threat to sensitive electronic devices installed in buildings. To protect these devices from LEMP effects, the evaluation of the electromagnetic fields inside of the building is required. Although numerous studies have been devoted to the analysis of these fields stemming from direct and indirect lightning strikes, no thorough study on the analysis of the electromagnetic environment inside a building with layered reinforcing bars has been presented in the past. In this paper, using the 3-D finite-difference time-domain method, we present a systematic analysis of the electromagnetic field inside a full-scale building associated with direct and nearby lightning strikes, taking into account the presence of reinforced concrete, to evaluate the effect of the structure of the reinforced concrete on the lightning electromagnetic fields.

A Technique for Representing Coaxial Cables for FDTD-Based Surge Simulations

The finite-difference time-domain (FDTD) method is a very effective tool for predicting surge phenomena in 3-D structures such as buildings and transmission line towers and in grounding systems such as grounding grids. In this paper, we propose a new technique for representing a coaxial cable for FDTD-based surge simulations. In this technique, the metal sheath of the cable and the electromagnetic field outside the metal sheath are simulated in the FDTD method, while the surge phenomena inside the metal sheath are solved on the basis of transmission line theory. Therefore, this technique can take into account the effect of the metal sheath of the coaxial cable, the traveling wave inside the cable, and wires connected to the internal conductor of the cable at the same time. Using the proposed technique, we predicted the surge phenomena in a coaxial cable and compared them with measured results for the purpose of validation.

Development of a surge simulation code VSTL REV based on the 3D FDTD method

The prediction of surge phenomena is required for the design of effective lightning protection methodologies. Traditionally, transmission-line-theory-based simulation techniques have been employed, but such simulation techniques based on the assumption of the transverse electromagnetic mode cannot rigorously treat surge phenomena in three-dimensional structures and grounding structures such as buildings and grounding grids. Recently, full-wave numerical approaches have been widely and successfully applied to such surge phenomena. Central Research Institute of Electric Power Industry (CRIEPI) has developed a surge simulation code, which is called VSTL REV (Virtual Surge Test Lab. Restructured and Extended Version), based on the three-dimensional finite difference time domain method, which is one of the numerical electromagnetic field computation methods used to solve Maxwells equations. In this paper, we present an outline of VSTL REV and some examples of its application to the surge analysis of a building, a grounding grid, and an overhead distribution line.

Lightning Surge Analysis of a Microwave Relay Station Using the FDTD Method

Microwave relay stations are key components in controlling power grids and maintaining their stability, but lightning strikes to the stations may cause faults, malfunctions, or even physical damage to microwave radio equipment. To protect equipment from lightning, it is necessary to predict surge phenomena in a microwave relay station, and design effective lightning protection methodologies. Recently, numerical electromagnetic field computation methods to solve Maxwells equations have entered widespread use for analyzing surge phenomena in 3-D structures such as buildings and towers and in grounding structures such as grounding grids. In this paper, we apply the finite-difference time-domain (FDTD) method to the surge analysis of a microwave relay station. First, to validate the applicability of the FDTD method, we set up a reduced-scale model of a microwave relay station. Using this model, we measured the distribution of the currents flowing through the station and compared the measured results with those simulated by the FDTD method. Second, through FDTD-based surge simulations, we analyzed the effects of the reinforcing bars of a building, the route of the ground wire of a waveguide, and the layout of a deep earth electrode on the lightning current distribution.

Stable simulation of nonlinearly loaded lossy transmission lines with time marching approach

A stable method for the analysis of lossy transmission lines with nonlinear loads is presented. The simulation employs the time marching (TM) method for solving the convolution equations in the time domain. To cope with the late-time instability of the TM method, a novel approach based on the application of Z-transform analysis and cepstrum is presented. The efficiency of the proposed method is demonstrated by comparing its results with simulations obtained using (i) a full-wave FDTD approach, and (ii) CST Cable Studio.

FDTD-Based Lightning Surge Simulation of an HV Air-Insulated Substation With Back-Flashover Phenomena

The operating voltages of low-voltage control circuits in power plants and substations have decreased with the installation of digital control equipment. This increases the susceptibility of control equipment to abnormal surges, which arise mainly from lightning. To protect control equipment from lightning, it is necessary to predict lightning surges invading power plants and substations and design effective lightning protection methodologies. Compared with conventional simulation techniques based on circuit theory, full-wave numerical approaches are advantageous in handling three-dimensional structures such as transmission line towers, grounding structures, nonhorizontal wires, such as incoming power lines to power plants and substations, and lightning-induced effects. In this study, to apply the finite-difference time-domain (FDTD) method to the lightning surge analysis of an air-insulated substation, we first propose techniques for simulating the nonlinear breakdown characteristics of short-air-gap arcing horns and transmission line surge arresters installed in 77 kV transmission lines for FDTD-based surge simulations, and compare the breakdown characteristics calculated using the proposed techniques with measured results for validation. Second, as an example of the application of the proposed techniques to practical surge analysis, it is confirmed that we can reproduce the measured results of lightning surges invading a 77 kV air-insulated substation in the case of a direct lightning strike to its nearby transmission line tower by taking into account lightning-induced voltages arising from the lightning current flowing through the lightning channel and transmission line tower, which are commonly ignored in conventional circuit-theory-based simulations, multiphase back-flashover phenomena, and the effect of applied AC voltages.

FDTD transient analysis of grounding grids a comparison of two different thin wire models

A thin wire model for FDTD simulations is proposed for the study of transient potential rises and currents in a grounding grid. The model is an extension of the formalism of Holland, and it is compared with the thin wire model of Baba, Nagaoka, and Ametani, using a case study previously validated with measurements. Special interest is drawn on the computation of the potential close to the surface of conductors. To do so, an approximated formula based on the previous work of Noda and Yokoyama is proposed. The results are compared in terms of transient potential rises and currents in a grounding grid. The comparisons are in good agreement.

Applying FDTD Simulation to Lightning Surge Route Analysis in Microwave Relay Stations

Microwave multiple radio relay stations are often built on mountains, and the stations are susceptible to damage from lightning. Therefore, it is important to take adequate lightning protection measures to ensure that communication devices are not damaged by any lightning surge current that penetrates from a lightning rod fitted on such stations. In most cases, the penetration route of the lightning surge current is uncertain, and it is difficult to specifically evaluate the effectiveness of measures against lightning. We calculated the branch aspect of lightning surge current in actual microwave relay stations using the finite difference time domain (FDTD) method, which is one way to numerically analyze electromagnetic fields, to directly solve Maxwells equations. By comparing the calculated results with measured results obtained by injecting a pulse current into a microwave relay station, we verified that the current peak value of the calculated results corresponded with the measured results well, both when a steel tower was located on the ground and when it was located on the roof of a microwave relay station. We confirmed that the FDTD method can be used to understand the branch current of lightning surges and to study lightning protection measures at microwave relay stations.