"Transmission congestion continued to persist and affected volume traded on the exchange as almost 210 million units of power were curtailed in the month due to unavailability of inter-state transmission corridor," IEX said in a statement.
Several participants in the southern states refrained from bidding on the exchange due to unavailability of transmission corridor, the statement added.
IEX said Tamil Nadu and Kerala were the worst affected as power could reach them for only ten days in the entire month and that too an insignificant quantum.
On an overall basis, 2.35 billion units of power were traded on the exchange in May 2014, 6 per cent less than 2.5 billion units traded in the same month last year.
However, spot power market saw an increase in demand for electricity in May, especially in the North, West and Southern regions, the statement said.
"Considering the peak summer season, the volume traded in the spot market could have been much higher had it not been for transmission related constraints," IEX said.
As regards the price of power, the spot market continued to be lucrative in May 2014 with the average Market Clearing Price (MCP) at Rs 3.28 per unit, about 9 per cent lower than Rs 3.61 per unit in the previous month.
The market clearing price is where the supply and demand curves cross.