V. T. Kontargyri

Measurement and Verification of the Voltage Distribution on High Voltage Insulators

The paper presents a study into the potential and electric field distribution along an insulator string, which is used for the suspension of 150 kV overhead transmission lines. In order to calculate the voltage distribution, a model of the insulator string was set up using OPERA, an electromagnetic analysis program based on the finite elements method. Simulation results have been compared with experiments which were successfully conducted in the High Voltage Laboratory of the National Technical University of Athens. The experimental procedure is also presented in the paper and discrepancies between simulated results and experiment are discussed

Simulation of the Electric Field on High Voltage Insulators using the Finite Element Method

The paper presents a study into the potentials and electric field distribution on insulator strings, which are used for suspension of overhead transmission lines of 400 kV and are stressed by power frequency voltage. The investigated insulator strings are used by the Public Power Corporation of Greece in high voltage transmission networks. The finite element analysis (FEA) program OPERA was used to carry out the electric analysis on the insulators. Two types of insulator strings were investigated, the first using porcelain and the second using glass as the insulating material. A comparative analysis of these insulators is presented

Analysis of various power quality phenomena in a highly electrified vessel

This paper deals with analyzing and resolving Power Quality (PQ) issues in electric energy systems of ships with extensive electrification. Within this framework, optimized configurations of critical subsystems are studied in depth: shaft generators, thrusters, pods and protection against lightning. The anticipated results obtained from a large scale research project are summarized as aiming at a greener, safer and more reliable ship.

Study on Wind Farm Grounding System

In this paper, a complete step-by-step analysis for the designing of a wind farm grounding system is carried out. The soil structure is determined based on soil resistivity measurements. The use of the appropriate method and the rigorous application of the method are very important. Thereafter, a grounding system for each wind turbine (WT) and the control station is designed and enhancements of the grounding system are proposed in cases of increased values of ground resistance and unsafe touch and step voltages. The appropriate way of enhancement of the grounding system is investigated for different cases. In addition, the effect of the concrete on WT foundation is investigated aiming to the most efficient designing of a wind farm grounding system. The results and the proposed methodologies are verified with measurements that are carried out after the construction of the wind farm.

Estimation of the Earth Resistance by Artificial Neural Network Model

The aim of this paper is to investigate the estimation of the variation of ground resistance throughout the year by using artificial neural networks (ANNs). An ANN was trained, validated, and tested with different training algorithms by using experimental data of soil resistivity, ground resistance, and rainfall in order to select the optimum training algorithm and the respective parameters and predict the behavior of the ground resistance of a single rod. Moreover, a sensitivity analysis of the proposed ANN was carried out in order to determine the impact of certain factors on the efficiency of the ANN. The high value of the correlation index between estimated and experimental values demonstrates the high efficiency of the ANN. The proposed methodology based on ANN is a useful tool for the estimation of the grounding resistance during the year in case of difficulties in measuring its value.