Effect of non-standard operating frequencies on the economic cost of offshore AC networks

The effect of choosing a non-standard operating frequency on the equipment and infrastructure costs of an offshore AC network is investigated. The offshore AC network considered is similar in design to the European SuperGrid “SuperNode”. It is designed to connect several large wind arrays to multiple HVDC converters through which power may be transmitted to shore. As the offshore AC network is isolated from onshore networks by the use of HVDC links, it may be operated unsynchronised at any desired frequency. The cost associated with operating the network at a fixed frequency in the range 20–120 Hz is investigated, focusing on the frequency-cost scalings of electrical devices (such as cables, transformers and reactive compensation) and offshore infrastructures. A case study is presented based upon Tranche A area of Dogger Bank, UK, where a minimum point in the total cost of the offshore network is found at 93 Hz.