To earn money from a wind turbine, it has to be connected to a national grid. Obtaining permission for that connection is dependent on electrical measurements that prove the turbine operator has satisfied the grid's requirements.
DNV GL checks and measures the grid parameters occurring during normal operations, e.g. harmonics, flicker and power switching, and during abnormal conditions such as a grid fault. The grid code in question may require a turbine to have a grid protection system installed (where the release values have to be checked) or a specifically defined behaviour during grid failure. This so-called fault ride-through behaviour, which ensures the turbine stays connected during a grid fault, also has to be checked and certified. In many grids, e.g. Germany or Spain, a certificate of compliance with the required fault ride-through levels guarantees the wind farm owner or operator a higher tariff for the electricity generated.
DNV GL employs the following methods to obtain the required grid data:
- Power quality measurement: The data on harmonics, flicker, power switching and power peaks are obtained through remotely controlled, long-term measurements of 3-phase voltage and current in combination with a wind speed signal. We have offices with experienced measurement staff in Seattle (US), Shanghai (CN), Madrid (ES) and Kaiser-Wilhelm-Koog (GER), which can be supported by staff from one of our local offices around the world.
- Grid protection measurement: The grid protection system can be checked at the turbine itself or on a test bench with a test procedure run to obtain reaction times and values, e.g. under-voltage or over-frequency.
- Fault ride-through: A voltage dip unit and a system to measure voltage and current at different points inside the voltage dip unit, grid and turbine are installed at the turbine to measure the turbine’s reaction to a grid fault.
- Working safety: HSE regulations require a short-term manned measurement to be conducted to determine electromagnetic levels inside the nacelle and the tower.
- Electromagnetic compatibility: EMC regulations require a short-term manned measurement to be conducted to determine electromagnetic levels that can disturb other electrical devices.
- Grid monitoring: A small grid surveillance device installed in the wind farm substation to monitor the farm’s correct behaviour in the event of grid failure is regularly checked by DNV GL staff and details of high frequency data occurring during a grid failure reported to the client.
- Small wind turbines: Electrical measurements similar to those for utility-scale turbines can be conducted either in the field or on a test bench.