In this paper, a detailed spectral analysis of an offshore wind farm, based on AC submarine cables is carried out. It is well known that due to the capacitive character of the AC submarine cables, it is very common to find resonance problems in the transmitted power, associated to this issue. For that reason, this paper first analyzes which is the proper “π” electric equivalent circuit to model the AC submarine cable in a given frequency range. Then, a detailed model and a spectral analysis of the entire transmission system is developed, deriving how factors such as submarine cable parameters, static reactive compensation, etc… affect to the amplitude and location of the resonances of the system. After that, a solution to mitigate the negative effect of these resonances is proposed, based on a passive filter design procedure. Finally, simulation results validate the performance of the offshore wind park under the proposed approach.

Spectral analysis of a transmission system based on AC submarine cables for an offshore wind farm

This paper proposes an analytical method to calculate the earth fault factor (EFF) in power systems, under different neutral earthed possibilities. The magnitude of the EFF depends on the way the neutrals of a system are earthed and influences some important aspects in power systems as the sensitivity and selectivity of relays, the value of short-circuit currents, the overvoltage between lines and earth, the determination of arrester rating and the system insulation level. The obtained results are compared with the values of EFF referred in International Standards.

Determination of the Earth Fault Factor in Power Systems for Different Earthed Neutrals

Nowadays, the state of the distribution grids is significantly different in comparison with the state of two decades ago. One important reason for that is the existence of non-lineal loads. These non-lineal loads can provoke disturbances, like a high level harmonics in current and voltages (Pigazo, 2004). In the same way, there is consolidating a distributed generation system for the distribution grids. This kind of grids contain a combination of many types of generation plants, like cogeneration, combined cycle, wind farms, photovoltaic...Thus, if the distribution grid is made up with many small and medium generation plants, the waveform of the voltage may be distorted. In conclusion, the electric transmission and distribution system is evolving to a scenario with multiple harmonic sources. So, the frequency analysis of the electric grids is becoming an important tool, because can help to improve their efficiency reducing the power associated to these disturbances. As regards to AC offshore wind farms, the interaction between the offshore installations and the onshore grid can cause harmonic amplifications. This aspect is not trivial, because as a result of this harmonic amplification, the harmonic level in the point of common coupling of the wind farm can be unacceptable for the grid code requirements. Offshore wind farms are connected through a widespread medium voltage submarine cable network and connected to the transmission system by long high voltage cables. Submarine power cables, unlike underground land cables need to be heavily armored and are consequently complicated structures. So, in particular this type of power cables have a relatively larger shunt capacitance compared to overhead lines which make them able to participate more in resonant scenarios (Kocewiak et al., 2010). The present chapter evaluates the frequency behavior of the offshore wind farms at normal operation (steady state), in function of design procedure parameters like: the cable length / characteristics, transformers connection and leakage inductance or inter-turbine grids configuration. The analysis is performed from the point of view of the wind turbines, considering them as potential harmonic sources. Thus, the knowledge of the frequency behavior of the offshore wind farm can help to avoid as much a possible the harmonic amplification, at the design stage of the wind farm. This presents new challenges in relation to understanding the nature, propagation and effects of the harmonics.

/pdf/evaluation-of-the-frequency-response-of-ac-transmission-1w4ne5s66f.pdf

Evaluation of the Frequency Response of AC Transmission Based Offshore Wind Farms

This chapter concludes this book and further discusses future work. In Section 8.1, we summarize the main themes of our research and the current state-of-the-art in V3DOR. In Section 8.2, we discuss future work in V3DOR, including the issues of large data sets, feature extraction, multiple-view matching, multimodal data problems, and geographical location-based applications.

Chapter 8 – Conclusions and Future Work

Basslink is a major Australian energy initiative that will allow the exchange of electricity between the island of Tasmania and the mainland of Australia. Basslink Pty Limited, a wholly owned subsidiary of the international transmission developer and operator National Grid Transco, was established to build and operate the link. The HVDC project will deliver to Australian electricity consumers the benefits of an interconnector that is economically viable, technically feasible and environmentally acceptable. Aspects such as rising demand for electricity, enhanced security of supply on both AC networks, enabled competition in Tasmania's electricity supply system, the export of renewable power from Tasmania to the mainland during periods of peak demand in the NEM and the two-way exchange of competitively priced power are addressed. The Basslink HVDC interconnector consists of a monopolar metallic return scheme, with a rated DC voltage of 400 kV, a rated DC current of 1250 A and a rated continuous power of 500 MW defined at the DC terminal of the rectifier converter station. Both HVDC converter stations, located at Loy Yang (Victoria) and George Town (Tasmania), are designed to transmit rated power in either direction. Additionally, the HVDC system has a dynamic power transfer capacity of up to 630 MW from Tasmania to Victoria to meet Victorian peak demands. The completion date for this project is December 2005. This paper highlights some key aspects of the project starting from design considerations for all vital components including DC cables, direct-light-triggered thyristor (LTT) valves, converter transformers and a state-of-the-art control and protection system. Furthermore, the paper introduces the design and performance criteria for the Basslink HVDC transmission system.

Basslink - Project Design Considerations

Large wind turbine/ wind park Installations are developing to an important alternative of renewable energy resources. Wind park installations with a rated capacity of several hundred Megawatts up to more than 1000 MW installations for future offshore applications are under investigation in different countries. This paper will give an overview on planning and applications studying such large applications. Both the transmission technologies and the Grid Code requirements are in discussion with the Power Grid Utilities to find the most economical and reliable technical solutions. Long distance underground and sea cable transmission may be used either in HVDC or HVAC technology for some of these applications: Also Power Quality and Reactive Power Compensation / FACTS devices may be used to improve transmission capacity and dynamic stability of such transmission systems. The presentation will provide a summary on the present technologies available and the necessary planning/design steps. The advantages of using both ACand/or HVDC transmission will be compared from technical and economical aspects. The presentation will include some examples to demonstrate some specific design principles, the basic arrangements of different technical solutions, which can be used to interconnect and transport the electrical energy from far remote located wind parks to the local consumer’s at large industrial or residential areas.

https://www.ptd.siemens.de/GWREF_Beijing_Chn_1006.pdf

Siemens Ag

Papers

Grid Access Solutions Interconnecting Large Bulk Power On- / Offshore Wind Park Installations to the Power Grid