Complex sentence: The new converter stations were to be commissioned by April 2012,, but in May 2011, Transpower announced that commissioning was delayed until December 2012 because of difficulties being experienced by the manufacturer.
Split into simpler sentences: The new converter stations were to be commissioned by April 2012. In May 2011, Transpower announced that commissioning was delayed until December 2012 because of difficulties being experienced by the manufacturer.