The Problem In Detail
Banks Group wanted to avoid using a STATCOM but still needed a reactive compensation system that could comply with Grid Code connection condition CC.A.22.214.171.124, a condition that requires the reactive compensation to be switched a number of times at 15 second intervals. This is not possible using standard capacitor banks.
Finding the Solution
Through the use of SynchroTeq Point-on-Wave switching relays and high performance individual pole operated vacuum circuit breakers, Enspec designed two 33kV capacitor banks that could satisfy the requirement. The banks can be re-energised within seconds on de-energisation as Point-on-Wave technology matches the closing point with the capacitor trapped charge.
Making it all Work
Initial studies also highlighted a 7th order harmonic resonance when the standard capacitors were switched into circuit. Enspec mitigated this issue through the design of custom de-tuning reactors to shift the resonant frequency of the banks.
What that means for the project now
The site achieved full reactive power compliance and the Enspec solution delivered dynamic reactive power compensation capability at a fraction of the cost of an electronic STATCOM solution. The banks continue to provide transient free energisations with inrush currents maintained to below 2pu versus typical capacitor bank inrush in excess of 20pu.
What Banks Group say.....
"Banks Group have two innovative Enspec Point-on-Wave switched capacitor banks installed at our Kype Muir wind farm. Following a request Enspec adapted their installation to include de-tuning reactors to manage harmonics. I have appreciated working with Enspec, they have been innovative, flexible and responsive." Dan Thomas, Operations and Grid Director.