Modelling of multi-megawatt wind turbines for EMI and EMS investigations by a topological approach
Todays installed multi-megawatt wind turbines (WT) form highly diverse system due to very complex control devices. Thus, special attention has to be paid to the electromagnetic compatibility (EMC) of the wind turbine. This contribution deals with different electromagnetic interference (EMI) and susceptibility (EMS) effects within the wind turbine. A well-known susceptibility problem of constructions and buildings with large vertical dimensions is the threat situation due to lightning phenomena. On the one hand, the high amplitude of the lightning current effects destructions of infrastructure directly. On the other hand, the transient electromagnetic fields caused by this lightning current could lead to disturbances as well as destructions of electronic devices inside the wind turbine. Furthermore, common-mode currents ¡cm on the power lines between the generator and the frequency converter will cause EMI effects during the normal operation mode. These I cms lead to radiated emissions to the WT's environment as well as to transient disturbing fields inside the WT, which might interfere with the control unit (CU) and the condition monitoring system (CMS). These issues will be investigated in this contribution. Therefore, the electromagnetic topology (EMT) will be applied to the wind turbine. The EMT delivers useful information in order to increase the WT's susceptibility and ensure a high degree of availability.
Far Field Region of Radiated Emissions from Wind Energy Conversion Systems
Wind energy conversion systems (WECS) or wind turbines (WTs), respectively, radiate electromagnetic (EM) emissions unintentionally. In order to ensure that radio broadcasting services or terrestrial navigation systems are not disturbed by WTs, the radiated EM emissions have to be measured and assessed in the CISPR Bands A to D (from 9 kHz to 1 GHz) according to the corresponding standards. Due to the enormous size of a WT, it seem to be reasonable to evaluate, whether the emission measurement is be carried out in the far field region. For this reason, numerical field calculations are carried out by means of an simplified WT model. It points out, that far field region of the radiated emissions is not located in the standardized measurement distance of 30 m, but a distance of more than 3 km with respect to the WT. Assuming that a real world WT behaves similarly than simulation model used for the numerical field calculations, the measuring locations defined in the corresponding standards are only conditionally suitable for electrical large radiators like wind turbines.
Design and Development of an In Vitro Tear Replenishment System
Understanding the cellular and molecular mechanisms of the corneal tissue and translating them into effective therapies requires organotypic culture systems that can better model the physiological conditions of the front of the eye. Human corneal in vitro models currently exist, however, the lack of tear replenishment limits corneal in vitro models’ ability to accurately simulate the physiological environment of the human cornea. The tear replenishment system (TRS), a micro-fluidic device, was developed to mimic the in vivo tear replenishment in the human eye in an in vitro corneal model. The TRS is capable of generating adjustable intermittent flow from 0.1 µL in every cycle. The TRS is a sterilizable device that is designed to fit standard 6-well cell culture plates. Experiments with the corneal models demonstrated that exposure to the TRS did not damage the integrity of the stratified cell culture. Contact lenses “worn” by the in vitro corneal model also remained moist at all times and the cytotoxicity of BAK could also be verified using this model. These in vitro results confirmed that the TRS presents novel avenues to assess lens-solution biocompatibility and drug delivery systems in a physiologically relevant milieu.