Hindustan Power Exchange (HPX) on Tuesday said it has reached the milestone of one billion units of power traded within six months of its launch. With more than 360 market participants, HPX has also raced to register participants comprising 80 per cent buy volume of overall Day Ahead Market (DAM); 90 per cent sell volume of Green DAM and 70 per cent buy of Real-Time Market (RTM), an HPX statement said.