Abstract
This paper elaborates on several important outstanding issues in the state-of-art of overvoltage protection selection for modern wind farms. The lack of experience with this still-new technology, together with the inherent complexity of wind farm electrical systems, entails several unresolved issues pertinent to the topic of overvoltage protection, particularly in relation to lightning-initiated surges. Firstly, several aspects of the wind turbine lightning incidence, along with the issues related to the selection of lightning current parameters (pertinent to the wind farm overvoltage protection), are addressed in this paper. Secondly, several issues in the state-of-art models of the wind farm electrical systems—for the lightning surge analysis—are addressed and discussed. Here, a well-known ElectroMagnetic Transients Program (EMTP) software package is often employed, with all of its benefits and some limitations. Thirdly, the metal-oxide surge arrester energy capability and the issues related to the selection of the surge arrester rated energy—in relation to the direct lightning strikes to wind turbines—is addressed. Finally, some general considerations concerning the overvoltage protection selection for wind farm projects, particularly regarding the installation of the metal-oxide surge arresters, are provided as well.
Highlights
Wind farms are probably the single most significant contributors to the production of “green”renewable electrical energy, with additional capacity increases planned for the near-future
It has been mentioned in the Introduction that the main source of lightning-initiated overvoltages on electrical equipment (MV level) in wind farms comes from the so-called back-surge phenomenon, associated with direct lightning strikes on wind turbines (WT), e.g., [16,17,18,19,20]
In the instance of the lightning strike on the WT, a transient overvoltage rise of the WT grounding produces a back-surge, which travels—through the connected MO surge arrester—from the WT grounding system to the phase conductors of the associated equipment. This means that the surge arrester “brings” the overvoltage from the WT grounding onto the phase conductors
Summary
Wind farms are probably the single most significant contributors to the production of “green”. The main problems in lightning surge analysis of wind farms could be seen in the proper application of appropriate EMTP models for each of the individual components of the rather-complicated wind farm electrical system. There are several different arrangements of wind turbine systems: generators producing power at the medium voltage level, e.g., 12 kV, removing the need for the step-up transformer; generators producing power at low voltage level, e.g., 600 V, having a step-up transformer, which could be located in the wind turbine tower base or in the adjacent housing All these aspects need to be accounted for when analyzing the overvoltage protection for a wind farm, from the viewpoint of the lightning-associated surges, e.g., [16,18,19]. In the Conclusions and Discussion section of the paper, some general considerations about overvoltage protection selection for wind farm projects, and its analysis, are provided
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