Race Bank Offshore Wind Farm DRCs

Managing low frequency resonances and UK Grid Code compliance.

As one of the world’s most experienced developers of offshore wind projects DONG Energy has extensive experience of integrating its projects into the host transmission grids in the countries where it operates.

In June 2015 DONG Energy made its Final Investment Decision to build the Race Bank Offshore Wind Farm supported by UK's Renewables Obligation Certificate (ROC) scheme

The project uses 91 6MW Siemens Wind Power wind turbines, with a total capacity of 580MW.

Challenge

The turbines of the Race Bank OWF are connected to the UK’s National Electricity transmission System by 220kV cables with a route length of approximately 83 km (~71km offshore and ~12km onshore). These long HVAC cables can introduce significant low-frequency resonances, including when the offshore transformer is energised.

Additionally all forms of generation connected to the UK Electricity Transmission System must comply with the UK Grid Code. Specific requirements apply to renewable generation such as offshore wind turbines, specifically in relation to reactive power delivery and Low Voltage Ride Through.

Modern wind turbines are designed to address these requirements however in some cases their performance requires additional support from Dynamic Reactive Power Compensation equipment such as STATCOM technology.

In April 2015 DONG Energy contracted RXHK (then part of RXPE) to design, supply, install and commission two off STATCOM technology based ±120Mvar dynamic reactive compensation systems. Each system consists of the STATCOM valve, built into pre-fabricated modules within the factory, cooling water system, phase arm reactors, MV switchgear and a 120MVA step up transformer to connect each DRC system to the onshore substation 220kV busbar  All equipment supplied by RXHK is located at the onshore substation near Walpole in Lincolnshire, UK.

Solution

The STATCOM systems operate to ensure UK Grid Code reactive power and voltage control compliance. They must also manage the effects of offshore transformer energisation and the low frequency resonance. All equipment was extensively tested using an RTDS prior to arriving at site to ensure the required performance was achieved.

The project was project managed and engineered from RXHK’s offices in the UK.

Current status

The first Maxivar™ STATCOM has been in operation since January 2017. The second system has been in operation since April 2017. Together they have supported the commissioning and ongoing operation of the Race Bank Offshore Wind Farm

The ongoing success of this project underlines the capability, reliability and benefits of RXHK’s voltage source converter STATCOMs.