In this work, a method is presented to ensure more regional use of the generated electric power in neighboring medium voltage grids, thus increasing their capacity to host renewable energy sources. The method consists of a grid topology optimization during operation, where load segments between two neighboring medium voltage grids are switched over. The considered grids should have different load and generation characteristics as well as an existing coupling possibility between them. The results of this concept applied to two real medium voltage grids in a southwestern region in Germany show that the yearly fed-up energy to the high voltage grid could be reduced by up to 19 %. In addition, a guaranteed free hosting capacity could be added to a grid depending on the base load of the switchable segment. It is also shown that loop-flow currents can occur during switching and can be critical to the grid if not well calculated.

Power system engineers and planners often consider high-voltage dc (HVdc) systems for bulk power transmission over long distances. There are two technologies within HVdc: line-commutated converters (LCC-HVdc) and voltage-source converters (VSC-HVdc). Each type has its own suitable range of applications. LCC-HVdc is a mature technology that has been available since the 1970s and uses thyristor valves. LCC-HVdc is commonly applied for high-capacity power transmission between two strong power systems (high short circuit ratio) over long distances with limited dynamic requirements (e.g., features such as fast power reversal, dynamic reactive power support, or black start are not available or are available only with limited performance). Currently installed systems reach ratings of 12 GW at a transmission voltage of ?1,100 kV and may cover distances beyond 3,000 km. The introduction of VSC-HVdc in the late 1990s initiated the use of self-commutated valves employing insulated-gate bipolar transistors with a significant improvement in dynamic performance. Presently, the ratings of VSC-HVdc a relower than those of LCC-HVdc. VSC-HVdc systems are now installed with a rating of 3,000 MW at a transmission voltage of ±525 kV, and higher ratings are under development. For special applications such as the connection of offshore wind power plants or connection to/between weak grids, VSC-HVdc often offers the only technoeconomically viable solution.

The traditional electrical power system and electricity markets have been designed to work with SGs, and so these have traditionally provided various 'inherent' capabilities to the system critical to ensure the stable operation of the power systems during severe faults and even basic system survival during rare system splits. Due to the potential total absence of SGs approaches during periods of high penetration (HP) of PEIPS infeed, the wider industry has engaged in a closer examination of the lack of these system capabilities [4], [17], [31], [32]. Traditionally, the focus in the context of PEIPS has been on steady state and a limited number of dynamic (faster) aspects recently expanded to include PEIPS contributing fast fault current during system faults and extended contribution to frequency management (although this latter capability has been required from RES for more than 10 years in some countries). Demand side contributions in these contexts are emerging and have significant potential.

A significant number of renewable energy sources are predominantly connected to the distribution grid level. The ratio of feed-in to load is very different in distribution systems so that the balancing between the grids usually takes place via the transmission grid. Thus, leads to additional bottlenecks in the related grid areas and is associated with curtailment of renewable energy generation. This contribution represents a new approach to power balancing at the distribution system level. The objective is to integrate several point-to-point direct current (DC) links into the distribution system operation so that additional power flow capacities and related ancillary services can be provided.

This paper presents a novel method to optimize the placement of a given number of HVDC links. An optimization criterion, based on the minimization of branch loading, is proposed as a valid alternative to other criteria widely used in the literature. To take into account the uncertainty given by the grid operating conditions, i.e. by load demand and generator dispatching, a double stage stochastic optimization is proposed. The validity of the proposed approach is demonstrated by different analysis performed on the IEEE39 test grid. Results show effectiveness of the method in improving grid security. Indirectly a more economic grid operation is achieved and interesting findings related to the use of the HVDC links in various grid operating conditions are drawn.

With the ongoing changes in the European electrical energy systems, redispatch measures are more often required to maintain system security. The introduction of HVDC transmission can potentially reduce necessary redispatch not only by providing additional transmission capacity but also with its inherent controllability. This work analyzes the effect of HVDC dispatch in regard to preventive and curative redispatch measures using a security constrained optimal power flow calculation. For this, a mixed ac/dc benchmark network with predefined contingencies is examined with different redispatch options for pre-and post-contingency operation. Results show, that the required redispatch measures can be reduced significantly by an adaptation of HVDC set points and even further, when post-contingency redispatch measures could be applied.

Large renewable energy sources are usually connected to a single transmission system. In the future, groups of renewable energy sources (RES) could link several asynchronous power systems through HVDC systems. This study implements a Master Control for a HVDC system to utilize the RES-grid between two asynchronous power systems to the maximum amount. Master Control of the HVDC system is based on an optimal power flow. Objective of the optimization is the adherence of a given power exchange with the external systems. A two-path transmission system with three wind farms and two asynchronous power systems is used, where one external system is connected through a HVDC system. Master Control of the HVDC system must guarantee a permissible system operation. The interaction between Master Control and local reactive power control is thus the main question of the study. Results show that Master Control is able to guarantee an optimized and permissible utilization for this type of system.

Condition based maintenance requires as in- put information about the condition of the equipment to be maintained. Such information has to be firstly obtained through a condition assessment procedure. Rating schemes for condition assessment are implemented by almost every power grid owner. In the present paper a proposal is made for utilisation of such rating schemes in order to give a fore- cast of equipment condition development in the future. In a further step a methodology is presented for the tran- sition from the condition assessment to a risk assessment pro- cedure (the failure probability is used here as the risk pa- rameter). Finally, the information obtained from both con- dition and risk assessment is integrated into a markov chain for reasons of better illustration as well as for a possible use in condition simulations.

Condition based maintenance requires as in- put information about the condition of the equipment to be maintained. Such information has to be firstly obtained through a condition assessment procedure. Rating schemes for condition assessment are implemented by almost every power grid owner. In the present paper a proposal is made for utilisation of such rating schemes in order to give a fore- cast of equipment condition development in the future. In a further step a methodology is presented for the tran- sition from the condition assessment to a risk assessment pro- cedure (the failure probability is used here as the risk pa- rameter). Finally, the information obtained from both con- dition and risk assessment is integrated into a markov chain for reasons of better illustration as well as for a possible use in condition simulations.