Commissioning and Reliable Operation of Inter Array Cables in Offshore Windfarms: Testing and Monitoring

Abstract:
Invisible parts are most likely critical for the big picture. In an offshore windfarm this is true for the inter array cables (IAC) connecting the wind turbines to strings and those strings to the Offshore Switchgear Substation Platform (OSS). Due to the increasing generated power of the wind turbines, the nominal voltage for state-of-the-art designs is at 66 kV. Based on first system studies [1] the next generation of wind turbines with up to 20 MW will aim for 132 kV cables. The challenges of such installations arise mainly from the demand for highest quality and precision during installation and commissioning. Any failure will lead to tremendous costs by lost generation hours on one hand, and the necessary high effort to locate the failure and to repair it offshore. Based on weather conditions, the time between failure and suc-cessful repair can be between several weeks up to months. To improve availability after installation and reliability during operation, the paper will give first answers to the following questions: How can inter array cables be tested to prove the quality of the installation work? How can these high voltage tests be done most efficiently under offshore conditions? Can critical components be supervised during commissioning testing by partial discharge (PD)-measuring? What monitoring concepts improve reliability during operation and could enable condition-based maintenance?