New Delhi, April 28 -- Last week's rupee-for-dollar swap auction carried out by the Reserve Bank of India (RBI) has reportedly been an even greater success than its first such exchange last month. As many as 255 bidders offered to place $18.65 billion (around Rs.1.3 trillion) with the central bank, more than three times the $5 billion it had said it would accept. The premium that winning bidders offered for the 3-year currency swap rose to Rs.8.38 from Rs.7.76 in the March auction. Clearly, currency swap as a tool to inject liquidity into the system has found favour with banks and companies. Robust demand has established it as a new arrow in RBI's quiver to ensure there is enough money to go around. But while market participants starved of cash are pleased and keen on further auctions of this kind, RBI needs to be careful that it doesn't rely too much on this seldom-used instrument, given the risks it bears on such transactions....