Ioannis Naxakis

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.

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.

Effectiveness investigation of wind farm earthing system

Wind turbines are tall structures with heights that can exceed 80m. Their installation is usually done at high altitude and isolated areas causing these vulnerable to lightning strikes considering their total hub height and blade radius. The sites that wind farms are installed are usually of high lightning activity. Furthermore, in these areas the soil resistivity is high, leading to the design and construction of a reliable earthing system that shall ensure both lightning and earth fault current dissipation. Step and touch voltages shall be compatible with the safety limits as these are defined in IEEE80-2000. The earthing system is the main part of the wind turbine lightning protection system apart from the receptors and down conductors. It leads the lightning and the earth fault currents to the earth in a safe way both for the infrastructure and for the human beings. The earthing system of a wind turbine and thus the wind farm shall be designed on project specific conditions, considering the ground conditions, short-circuit analysis of the power plant collector system, international standards and also national requirements of the country that it shall operate if such exist. In the current paper will be discussed the effectiveness of a wind farm earthing system regarding the current dissipation. The evaluation will be executed based on project specific soil conditions which have been measured during a dry season and foundation earthing system of each wind turbine. The transient analysis will be performed via simulations in EMTP-ATP. The extracted results will be useful for other wind farms that are installed in similar soil and/or electrical conditions in order to reduce the project execution time by using a proven earthing solution.

Typical Lightning Protection System for Wind Turbines

Wind turbines are tall structures with heights exceeding 120m. They are usually installed on high altitudes or isolated areas. In these areas, lightning activity could be high and the installation conditions wind turbines are vulnerable to lightning strikes. Furthermore, these areas do not have ideal soil conditions and the efficiency of wind turbine lightning protection system (LPS) can be affected. Additionally, the LPS shall be compatible with IEC61400-24 as minimum; furthermore, the earthing system shall keep step and touch voltages within the limits defined in IEEE80-2000. Considering the high amounts of wind turbines installed annually and also the limited project time-schedules, it is needed to have a typical LPS for wind turbines that complies with the relevant standards; based on this, wind turbines are armoured against lightning strikes. In case of non-effective LPS, damages can be caused in vital wind turbine components like blades which can lead to downtime and loss of energy production. This paper will present a typical LPS for wind turbines. This system can be applied in every site condition up to a pre-defined level, provided that it respects local legislation and can protect the structure in a reliable way. This proposal does not replace the site specific design of LPS but can be used as basis for further adaption in local conditions. Sokratis Pastromas, Ioannis Naxakis, Elftheria Pyrgioti Typical Lightning Protection System for Wind Turbines 185

Dielectric strength measurements in photovoltaic modules

The purpose of this study is to determine the dielectric strength of a photovoltaic module through laboratory measurements. The measurements were taken using the standard impulse voltage, according to IEC 61730-2. Measurements were taken before and after the voltage stress in order to investigate in which way the module is affected. These results appear in the IV and PI characteristic curves. Subsequently, after a period of six months, the stressed module was compared to a similar non-stressed to find out whether the first regains some of its properties. In the same way the IV and PI curves are quoted. In conclusion the results obtained are evaluated and confirmed by the standards with a view to approach an optimal design of lightning and surge protection systems for photovoltaic installations (PVIs).

Surge arresters models for fast transients

In this paper is presented the performance of metal-oxide surge arresters, during fast transients. The simulations were carried out with the EMTP-ATP program. The equivalent circuits were those proposed by the IEEE and Pinceti-Giannettoni. The residual voltages of various rated voltages lightning arresters and for lightning currents with different peak values and front times were estimated. The results also been compared with the manufacturers data.