Abstract
This paper presents an electromagnetic transient analysis of lightning-initiated overvoltage stresses of the step-up transformers installed inside a nacelle of onshore, multi-megawatt, new-generation wind turbines. The increase in the wind turbine (WT) nominal power output, necessitated introducing the step-up transformer into the nacelle. A transformer installed inside a nacelle is subjected to completely different overvoltage stresses from those present if it were installed at the base of the WT tower. This has serious repercussions on its overvoltage protection (i.e., selection and installation of surge arresters) and insulation coordination. Furthermore, the overvoltage protection of medium-voltage cables (inside the tower) is also problematic when considering their length, proximity to the tower wall, and their screen grounding practices, and needs to be tackled in conjunction with that of the step-up transformer. This paper presents detailed models for the various components of the latest-generation WTs, intended for fast-front transient analysis and assembled within the EMTP software package. We further present the comprehensive results of the lightning-transient numerical simulations, covering both upward and downward (first and subsequent) strikes, their analysis, and recommendations for the optimal selection of medium-voltage surge arresters for the step-up transformers installed inside a nacelle.
Highlights
The continued growth of the wind energy sector worldwide, partially fueled by government subsidies and policy directions, is not showing any signs of abating
The intention of this study was to assist with closing this gap by presenting a rigorous numerical analysis using the electromagnetic transients (EMTP) simulations of the lightning-initiated overvoltage stresses of a step-up transformer installed in a nacelle of the most-recently developed new-generation wind turbines
A direct lightning strike to the wind turbine (WT) blade was modeled in the EMTPtype software packages with a special kind of current source, which can be of different types [25,26]
Summary
The continued growth of the wind energy sector worldwide, partially fueled by government subsidies and policy directions, is not showing any signs of abating. There is a clear and evident need for addressing the mentioned problems of lightning overvoltage stresses of the step-up transformer inside a nacelle These issues are current, pressing, and prevalent with the newest-generation multimegawatt wind turbines, and have not yet been fully studied to the best of our knowledge. The contribution of this paper is twofold: (1) introducing original improvements in the domain of the modeling of WT components for the lightning surge (i.e., fast-front transients) analysis, and (2) providing novel analysis and recommendations for the optimal selection of medium-voltage (MV) surge arresters for the step-up transformer inside a nacelle of the most-recently developed onshore WTs. The rest of the paper is organized as follows: Section 2 introduces a detailed model of the WT with all the pertinent component parts for the fast-front transient analysis.
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