The Problem in Detail
Enspec were retained to carry out extensive site and background network modelling for a UK Wind Farm which was to be connected to the 33kV network. Initial analysis had shown the site may exceed G5/4 limits and so Enspec were tasked with accurately modelling the site and network, and then carrying out a harmonic filter design to ensure G5/4 compliance.
Finding the Solution
Enspec modelled the background network back to the 400kV level to ensure that the harmonic, impedance and resonance changes caused by the Wind Farm were as accurate as possible and closely represented the real world implementation.
Making it all Work
The Wind Farm developers provided harmonic information from the Point of Common Coupling (PCC). Enspec included a current source within the harmonic model that was tuned to give the required voltage harmonics at the modelled 33kV PCC. This allows for the resultant harmonics to be calculated after connection of the Wind Farm to allows for an assessment against the G5/4 limits.
What that means for the project now
The simulation showed once the Wind Farm was connected the PCC harmonic voltages would exceed the G5/4 limits. Enspec carried out an iterative process to design a 33kV passive harmonic filter that would mitigate these harmonic levels. The final design significantly lowered the voltage harmonics and ensured all order were fully compliant.