 The converter transformers are of the relatively unusual single-phase, four-winding arrangement, with a 38.5 kV filter winding on which the tuned filters are connected.Other high-pass filters are connected directly to the 330 kV or 400 kV AC busbars.With a total transmission rating of 1000 MW, Vyborg was the world's largest HVDC-back-to-back facility until the 1800 MW Al-Fadhili facility was completed in Saudi Arabia in 2009.