Ralph L. Hendriks

HVDC Connection of Offshore Wind Farms to the Transmission System

This paper presents a technical and economic analysis to evaluate the benefits and drawbacks of grid connecting offshore wind farms through a dc link. A first case, concerning a 100-MW wind farm, is thoroughly investigated and cases of larger wind farms (200 and 500 MW) are presented. Three different transmission solutions are compared: 150-kV ac, 400-kV ac, and high-voltage dc based on voltage sourced converters (VSC-HVDC). After a brief overview of the features of these connection solutions, the related operational aspects are evaluated. An economic assessment compares the dc connection option to the ac alternatives, taking into account the investment, operation, and maintenance costs, and the negative valorization of losses and energy not supplied. Economic assessment includes sensitivity analyses of parameters, which could impact the 100-MW wind farm: distance, component costs, dc converter reliability, and dc converter losses

Advanced transmission solutions for offshore wind farms

Future offshore wind farms will have large power ratings and will be situated much further offshore than current projects. The associated costs for grid connection will be high. This paper explores alternative methods of grid connection. By creating synergies with other applications for offshore power transmission, the total costs will be lower. Such synergies include the bundling of multiple wind farms, combination with offshore energy sources uncorrelated to wind, connection of oil and gas production platforms, and combination with interconnectors cables. High-voltage AC transmission through submarine cables has restricted application due to technical limitations. Alternative technologies are presented in this paper, such as high-voltage DC transmission, also in multi-terminal configurations, and gas- insulated transmission lines.

Combined stability and electro-magnetic transients simulation of offshore wind power connected through multi-terminal VSC-HVDC

Offshore wind energy has a high potential especially in Northern-Europe. Future wind power plants may be situated further from the shore and therefore a high-voltage direct current connection based on voltage sourced converters is most suitable for grid integration. Connection utilization can be improved by interconnecting several wind power plants leading to multiterminal schemes. This paper describes a modeling approach that facilitates the incorporation of such (offshore) dc-systems into transient stability simulations. It enables the possibility to use a different simulation approach for each side of the converters, i.e. to represent the acside by complex phasors and the dc-side by electro-magnetic transients. Coupling between the ac and dc-sides is obtained by the active power balance. To study the interaction between the multi-terminal scheme and the onshore network an illustrative test-network has been taken. A chopper-controlled braking resistor that protects the dc-circuit against overvoltages has been included and is expressed as a variable resistance. Methods to distribute the wind power among the onshore converters are explored and operation without a supervisory dispatch controller has been studied.

Fault ride-through requirements for onshore wind power plants in Europe: The needs of the power system

Wind power plants show different behavior than conventional (synchronous) generators. As the traditional power systems mainly consisted of centralized generation by synchronous machines feeding passive loads, it was well-understood how the system reacted in normal operation as well as during disturbances. As wind power plants are foreseen to increase in size and the amount of installed wind power will grow, the relative contribution of equipment not exhibiting this common behavior increases. At the same time power electronics offer opportunities for additional features to stabilize the power system. Transmission system operators impose requirements on the (dynamic) capabilities of connected new generation resources (including wind power plants) which are specified in grid codes. In this paper, the importance of such requirements is explained by looking at the needs of the power system and by showing simulation results for a test network. The paper facilitates a detailed understanding of the underlying phenomena related to grid code requirements with a focus on low-voltage ride-through and voltage support by reactive current boosting.

Twixt Land and Sea: Cost-Effective Grid Integration of Offshore Wind Plants

Offshore wind power is a relatively new market that has only really emerged on a commercial scale in the last decade. There are many technical and other challenges with the design, construction, operation, and maintenance of large offshore wind plants; this is especially true when, as is often the case today, they are built with capacities of hundreds of megawatts.

Implementation of wind power in the Dutch power system

We present the current status of wind power in the Netherlands and its future prospects, in particular for the development of offshore wind. An overview is given of the performance of the wind power on land. We briefly discuss the experience with OWEZ, the first offshore wind park commissioned April 2007, and the expectations for Q7, to be completed March 2008. The organization of the energy and imbalance markets in the Netherlands is described. Balancing requirements due to variability and limited predictability of wind energy are estimated, at system and market participant level. Next, we present the results of a wind power integration study performed in order to estimate the amount of wind curtailment due to the technical limitations of the conventional units in the Netherlands. It is found that due to must-run constraints on the combined heat and power units, which constitute over 50% of the Dutch production park, sufficient reserve is available to cover wind fluctuations and prediction errors for up to 8000 MW installed wind power. The only limiting factor is the minimum output of the conventional units, which may result in increasing curtailed wind starting around 4000 MW installed capacity. Changes in system operating costs, curtailed wind and total emissions due to the application of various large-scale storage technologies are described in the final section of the paper.

Developing a transnational electricity infrastructure offshore: Interdependence between technical and regulatory solutions

This paper aims at identifying the options for designing an offshore electricity grid and the legal instruments to create such a grid. It will make a first attempt at presenting the technical and legal considerations which coastal states, EU and national legislators and policy makers should take into account in the coming years when planning and weighing their grid design options. By contrast to the onshore system where the current grid is the result of many decades of local, regional, national and international developments, the situation offshore is different in the sense that currently there is more or less no grid. Moreover, the legal basis for developing such a grid is different offshore than onshore. Therefore designing a system which looks beyond national interests and concepts represents a major challenge. We will discuss whether such a new development as the construction of an offshore electricity grid should be a matter of national policy or should a multilateral or international approach be preferred.

Transmission and System Integration of Wind Power in the Netherlands

In this paper, an overview of wind power transmission and system integration aspects is presented for the Netherlands. Particular aspects regarding the Netherlands, such as the market organisation with respect to wind power, the technical characteristics of conventional generation units and grid connection of offshore wind power, are discussed in detail. Power system integration of wind power typically comprises local impacts (distribution level), grid connection aspects (perephery of the network), system wide impacts (power balancing), grid codes and market designs.