The transformers on the substation platform will step up the 33 kV voltage from the wind turbines to a transmission voltage of 132 kV. High-voltage subsea cables will transport the power to the grid feed-in point, which is located at the Walpole 400 kV substation near King’s Lynn. In addition to the offshore substation, an onshore substation is to be supplied, which will be equipped with two 300 MVA power transformers (400/132/13.9 kV), Siemens will install two filters, 132 kV and 400 kV switchgear, and a reactive-power compensation system in order to meet the requirements of the UK power supply network on the quality of the power infeed (Grid Code).

Udo Niehage, CEO of the Power Transmission Division of Siemens Energy said: “We not only have the technology and know-how but also extensive project management experience with grid connections for offshore wind farms. Our recognized expertise in offshore connections is benefiting a number of international projects, especially in the UK, a fast growing market for renewables. In the UK, Siemens is the leading provider of integrated grid connection solutions for renewable energy, connecting 75 percent of the UK’s offshore wind farms to the UK grid. Our current projects will provide over 2.2 gigawatts of energy to homes and businesses across the UK.”

Siemens will use its new SVC Plus system for this purpose. SVC Plus operates with Siemens’ innovative voltage-sourced converter (VSC) technology and can be continuously controlled with the aid of insulated–gate bipolar transistors (IGBTs). The central feature of SVC Plus, a refined statcom (static synchronous compensator) is its modular multilevel converter technology. By contrast with other self-commutated converter topologies, the voltage waveshape produced by SVC Plus is practically sinusoidal by virtue of the multilevel technology. This makes existing low-frequency harmonic filters, found in current solutions unnecessary, and significantly reduces the space requirements for the overall system.

Siemens will also prepare the requisite design studies for all of the wind farm’s electrical components and the grid studies to provide evidence of fulfillment with grid connection requirements.

Energy-efficient grid connection of offshore wind farms is part of Siemens’ Environmental Portfolio. In fiscal 2009, revenue from the Portfolio totaled about EUR23 billion, making Siemens the world’s largest supplier of ecofriendly technologies. In the same period, the company’s products and solutions enabled customers to reduce their CO₂ emissions by 210 million tons. This amount equals the combined annual CO₂ emissions of New York, Tokyo, London and Berlin.