Technology effects in repowering wind turbines

This research investigates, analyses, and quantifies the technological effects of wind turbine repowering (ie, where old turbines are removed and new turbines are installed at the same or a very close location, including the enhanced performance in energy production). In these cases, it is assumed that both old and new turbines are subject to the same wind regime, other than because of technological elements, such as hub height, and thus it is possible to isolate the effects of new technology from the effect of changing local wind conditions. This research is based on the analysis of empirical data on repowering turbines in Denmark and Germany, and on historical production data available for the Danish component of the data set. Technological innovations are expected to enable new wind turbines to capture more energy at the repowering site, mostly through larger rotors and higher hub heights, and this is what this study has analysed. The results show that new turbines in repowering projects are twice as high, have three times the rotor diameter, nine times the swept area, six times the nominal power, and nine times as much electricity as the old turbines. However, the most significant improvement is probably the increase of capacity factor of 7.1% on a per-turbine basis, or 9.7% on a per-production basis

A customer oriented approach to the classification of voltage dips

Voltage dips are an important cause for electrical equipment malfunctions. To obtain a better picture of power quality performance and the possibilities for standardization and regulation, the Dutch government initiated a research project to quantify, standardize and classify voltage dips. This article presents a new method that has been developed for predicting voltage dip magnitude, duration and annual occurrence rates at arbitrary locations. This method enables an accurate prediction of voltage sag performance. Secondly, a transparent and consistent framework for a dip quality standard and a dip classification method is proposed. This framework introduces a dip costs table and a meaningful dip performance indicator. The dip costs, based on equipment sensitivity, economic costs and inconvenience experienced by the customer, is the principal guidance data for establishing a dip standard and a dip classification

Harmonic interaction between large numbers of photovoltaic inverters and the distribution network

The dominating mechanisms of interaction between large populations of PV inverters and the electrical distribution network are investigated. Some demonstration projects with large number of small PV-inverters in a low voltage network, show high levels of voltage distortion, although the emission level of an individual PV inverter satisfy the PQ standards. The main object of this paper is to analyse the observed phenomena of harmonic interference of large populations of inverters and provide some explanation of the resonance between existing network components and the PV inverters. These resonances may lie typically between the 5th and 40th harmonic number. The resonance phenomenon is investigated using extensive laboratory experiments on two inverter topologies, as well as computer modelling of different inverter topologies and network simulation studies on the Vroonermeer-Zuid network

Harmonic interaction between large numbers of photovoltaic inverters and the distribution network

\u3cp\u3eThe dominating mechanisms of interaction between large populations of PV inverters and the electrical distribution network are investigated. Some demonstration projects with large number of small PV-inverters in a low voltage network, show high levels of voltage distortion, although the emission level of an individual PV inverter satisfy the PQ standards. The main object of this paper is to analyse the observed phenomena of harmonic interference of large populations of inverters and provide some explanation of the resonance between existing network components and the PV inverters. These resonances may lie typically between the 5th and 40th harmonic number. The resonance phenomenon is investigated using extensive laboratory experiments on two inverter topologies, as well as computer modelling of different inverter topologies and network simulation studies on the Vroonermeer-Zuid network.\u3c/p\u3