Fast-front overvoltages arising at or transferred to the medium-voltage and low-voltage terminals of a 20/0.4 kV distribution transformer are evaluated with the aid of ATP-EMTP simulations. The effects of lightning crest current and of the transformer and load grounding resistances on the computed overvoltages are investigated. The protection against lightning surges offered by surge protective devices installed close to the low-voltage terminals of the distribution transformer is evaluated. The peak of the overvoltage arising at the medium-voltage terminals of the distribution transformer may exceed the corresponding insulation level even when surge arresters are operating close to the latter. The peak of the overvoltage arising at or transferred to the lowvoltage terminals of the distribution transformer may exceed the corresponding insulation level when surge protective devices are not installed. When surge protective devices are installed, the overvoltages are significantly reduced and practically unaffected by transformer and/or load grounding resistances.
the aim of this paper is to present a theoretical approach of the hypothesis of electrostatic charging of rotor blades during storms and its effects on the lightning protection and overvoltage protection systems; taking into consideration the dimensions of multi-megawatt wind turbines and a particular electrical topology. Overvoltage and overcurrent in form of surges may be the result of electromagnetic traveling waves caused by lightning strikes, especially if the earthing (grounding) system of the wind turbines (WTs) is galvanic connected between each other in order to ensure a common earth potential in the wind park (WP). These effects may impose additional requirements for the reliable operation of the low voltage and medium voltage protection against surges.In Fig. 1 an example of extended electric discharges on a rotor blade root is depicted.
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