Eleftheria Pyrgioti

Impact of noise related waveforms on long term field leakage current measurements

Leakage current (LC) monitoring is widely employed in order to investigate electrical surface activity on high voltage (HV) insulators. Long term field monitoring is required in order to obtain an actual view of the phenomena. Therefore any monitoring system is bound to encounter data size problems. A number of solutions have been proposed to address this problem by extracting different values from the measured waveforms as a performance indication. However, a parameter that is fully representative of the waveform is yet to be determined. Hence, measuring and storing of the actual LC waveform is still required on sites for research and monitoring purposes. In addition, field related noise can result to misinterpretation of the actual activity. In this paper, a number of 26089 waveforms, recorded in a 150 kV Substation on four different post insulators that are part of the grid, are investigated. The monitoring period exceeded six years. Different techniques are applied and evaluated on the data set, employing simple numeric criteria and more advanced techniques such as Fourier and Wavelet analysis. Results are presented towards addressing the problems of noise and data size. The study objective is the incorporation of the results in improved leakage current monitoring systems.

Ultrastable Natural Ester-Based Nanofluids for High Voltage Insulation Applications

Nanofluids for high voltage insulation systems have emerged as a potential substitute for liquid dielectrics in industrial applications. Nevertheless, the sedimentation of nanoparticles has been so far a serious barrier for their wide and effective exploitation. The present work reports on the development and in-depth characterization of colloidally ultrastable natural ester oil insulation systems containing iron oxide nanocrystals which lift the problem of sedimentation and phase separation. Compared to state-of-the-art systems, the final product is endowed with increased dielectric strength, faster thermal response, lower dielectric losses (decreased dissipation factor: tan δ), and very high endurance during discharge stressing. The developed nanofluid was studied and compared with a similar system containing commercial iron oxide nanoparticles, the latter demonstrating extensive sedimentation. Herein, the dielectric properties of the nanofluids are analyzed at various concentrations by means of breakdown voltage and dissipation factor measurements. The characterization techniques unequivocally demonstrate the high performance reliability of the reported nanofluid, which constitutes a significant breakthrough in the field of high voltage insulation technologies.

Induced Voltage on a above-ground natural gas/oil pipeline due to lightning strike on a Transmission line

This paper studies the effect of a High Voltage transmission line on a nearby above-ground natural gas/oil pipeline, under lightning conditions affecting the transmission line itself. A detailed description of the models used to simulate the transmission line - natural gas/oil pipeline layout, is presented and specific information concerning the calculations of model parameters and their implementation in ATP-Draw of EMTP are given. Thereafter, the coupling between the 400kV transmission line and the nearby natural gas/oil pipeline is examined and simulated. Finally simulation results are presented and an attempt to deduce useful conclusions based on the overall study is carried out.

Analysis of lightning impacts in Greece

In this paper, data analysis concerning human and animal deaths and injuries from lightning in Greece, is presented, for a time period of eleven years, from 2000 to 2010. In addition lightning strikes in factory facilities, buildings, aircrafts and lightning-ignited fires are recorded and presented. Lightning death data have been distributed in years and months of occurrence, and an effort has been paid to connect the casualties with the places they occurred and the actions of the victims. Furthermore in this paper, the relative lightning death indicator Dr is calculated for different, places in Greece to express the relative number of lightning deaths in a country (or province) taking into account its population, its area and the lightning activity Ng. This indicator is useful for comparison purposes and could merely be a criterion for the effectiveness of lightning protection measures, and for the results of educational and informational campaigns about protection from lightning danger.

Classification of surface condition of polymer coated insulators using wavelet transform and neural networks

Polymer coated insulators are used to suppress the pollution phenomenon on high voltage insulators. In order to investigate surface activity, which is directly linked to insulation performance and lifecycle, leakage current waveforms are used. In this paper a pattern recognition system is proposed capable of identifying four different types of surface activity. Patterns are extracted from leakage current waveforms through wavelet analysis, and especially multi resolution signal decomposition technique. The identification process is automated using an artificial neural network.

Performance of an installed lightning protection system in a photovoltaic park

The subject of this paper is the evaluation of the performance of an installed lightning protection system in a photovoltaic park after a potential lightning strike event. The transient behavior of the grounding grid of an installed photovoltaic park in Cyprus was investigated, for several situations of lightning strikes, through its assimilation in the ATP — EMTP program taking into consideration the phenomenon of ionization of the soil.

Lightning protection of Airport Traffic Control Towers (ATCT)

In this paper effort has been made for improvement of the design of Lightning Protection Systems (LPS) for Airport Traffic Control Towers (ATCT) in Greece. The improvement was limited to the effective placement of down-conductors and grounding systems in order to increase the level of protection against direct lighting strike. Technical parameters for implementation of external lightning protection have been analyzed and constructional instructions for the proper installation of a LPS is presented according to the international norms and patterns. Additionally a simplified P-spice simulation is presented that indicates performance improvements.

Electromagnetic transient programs and the photovoltaic input

In this paper, a linearized equivalent electrical circuit of a photovoltaic generator is developed. The application of a linearization process, which differs from the well-known piecewise linear approximation and is based on Taylors series scheme, leads to uncoupling of the current and voltage quantities. This uncoupling is represented by a equivalent electrical circuit. Using the proposed equivalent photovoltaic generator circuit, the photovoltaic systems modeling is remarkably simplified. This is because one can develop a photovoltaic generator element in electromagnetic transient programs for photovoltaic power systems transient analysis.

Performance of surge arresters in a low voltage distribution system

This paper is about a simulation model developed in order to indicate the optimal choice and connection of Surge Protective Devices (SPDs) in a domestic electrical installation according to their performance when a direct lightning flash strikes the distribution system. The proposed real-time model which is implemented in Simulink represents a LV distribution system that includes two simplified households. The related benefits of this kind of work are highly significant, as such overvoltages are a threat not only for the household equipment but, most importantly, for the human residents.

Lightning impulse performance of a wind generator grounding grid considering soil ionization

In this paper the simulation of a wind turbine grounding grid and the study of its transient behavior when high impulse currents — such as lightning strokes — appear, including the phenomenon of the soil ionization, are presented. An efficient mathematical model to simulate this situation is one based on the circuit approach. The transient behavior of the grounding grid has been simulated with the numerical code ATP — EMTP.