Because of the increasing share of renewable energies violations of the statuary voltage limits occur more and more often in the German distribution grids. Therefore, distribution system operators take advantage of reactive power support by dispersed generation units for voltage regulation. Commonly, only one standard cosφ(P)-profile is implemented as a controlmethod for all units to decrease voltage rises. This profile is independent of network characteristics and the point of common coupling. However, additional reactive power consumption causes additional reactive power unbalances in the networks which have to be compensated by the overlaid transmission grid. This becomes more difficult in times of a decreasing number of large conventional power plants. In order to reduce the additional reactive power demand caused by the improvement of statuary voltage stability this paper describes two methods to calculate optimized cosφ(P)-profiles for reactive power support. Beside the reduction of reactive power demand the optimized control-methods have also the positive effect of lower power losses in the distribution grids.Index Terms-Dispersed generation units, distribution network, reactive power balance, reactive power control, voltage stability I.

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Abstract. This paper presents a technical evaluation of two different methods to avoid the excessive voltage deviations caused by dispersed generation in distribution grids. Two voltage regulation methods, wide area voltage control of HV/MV transformer and inverters' reactive power support, are simulated in several real rural grids with different topologies located in Northern Germany. In all these analysed grids the high penetration of dispersed generation produces big power flow reversals during low load periods. The objective of implementing both voltage regulation methods is to reduce voltage deviations in such an extent that voltage band violations no longer act as the principal obstacle to host more dispersed generation in the distribution grid. We evaluate the effectiveness of these two methods through a power system analysis program and analyse the reciprocal effects caused by simultaneous use of both methods. Moreover, the concept of "voltage inhomogeneity" is introduced.

Reactive Power Compensation is becoming increasingly important, as more and more conventional generation is replaced by dispersed energy sources, which do not contribute to voltage stability in the transmission grid. The Mechanically Switched Capacitors with Damping Network (MSCDN) is a costefficient solution, combining reactive power compensation and harmonic mitigation. In this paper, the MSCDN is analysed with respect to its design parameters to determine the electrical stress on the components during energization. The analysis is done in Laplace and frequency domain, as well as through time-domain numeric simulation.

As well known, the increased share of renewable energies has led to new challenges for the electrical power system in Germany. Since the majority of renewable generation units are installed in the lower voltage levels, problems of congestion and voltage deviation occur more often. Commonly, the Distribution System Operators in Germany take advantage of a reactive power support by decentralised energy resources to ensure static voltage stability. The drawback of the support of reactive power for static voltage stability is the increasing demand for inductive reactive power by the distribution network which has to be compensated by the connected high voltage network. Besides, the power losses rise as well because of the additional reactive power flows. Therefore, other methods for voltage regulation like the use of compounding strategies at transformer stations could be advantageous to prevent the violation of voltage limits. This paper compares four different strategies of controlling the on-load tap-changer of the HV/MV-transformers in distribution networks and the effects on voltage deviation and power losses. A special focus is given to an advanced compounding strategy which adapts the control profiles of the compounding strategy dependent on the reactive power flow at the transformer as a second input parameter.

Due to the increasing amount of Dispersed Generation voltage stability is becoming a more and more critical issue especially in rural distribution grids where most of the generation capacity is installed. Characteristic for these types of grid topologies, which were not designed for a huge share of energy feed-in, are the long lines and the dispersion of consumers. Due to the expansion targets of the German Government regarding renewable energies, it is taken for granted that the voltage problems already appearing in the rural areas will be worsen. In numerous research projects different kinds of technical solutions for improving the voltage deviation have been tested in practice during the last years but often without performing an analytical study of network characteristics. Moreover in most of the projects the impact of only one innovative method was tested but research about the interaction of different technologies is seldom. Thus this paper tries to analyse the benefits of different kinds of innovative equipment and the reciprocal effect of these technologies in four real medium voltage networks in the northwestern part of Germany. Glance at the economic costs of their implementing is also provided.

Abstract. The power generation of isolated power systems is based on expensive oil-fired or diesel conventional power plants. The combination of wind/diesel hybrid power systems is one of the most common proposed and promising solution for stability problems. This paper deals with the definition of an optimal combination for diesel generators from a technical point of view. On the one hand the extreme case that the power infeed equals the power demand without power reserves is considered and on the other hand a high amount of wind power is taken into consideration. The main goal is to find out if in case of dynamic events which are related to frequency stability, the power system would collapse for the operating conditions of minimum load and high wind power penetration. The scope is both to ensure system stability for different combinations of conventional generation, as well as to verify grid code requirements for providing active power support from Renewable Energy Sources that is required for the power system of the island of Lesbos in Greece.

In this paper, the influence of the tolerances of the components on the steady-state electrical stresses of Mechanically Switched Capacitors with Damping Network (MSCDN) is assessed. For this purpose, a sensitivity analysis for 380-kVconnected MSCDNs with different quality factors and tuning frequencies is carried out. For the calculations, the level of harmonics defined in IEC 61000-3-6 has been considered. The calculations are based on simulations using ideal models of the MSCDN's components.