** Indian Energy Exchange IIAN.NS slumps 26% to 139 rupees, on track for seventh straight session of fall
** Stock logs steepest intraday single-day pct decline on record
** Bernstein says India's plan of overhauling electricity pricing will impact co's market share is "worse" than "what we have built in"
** Brokerage trims TP to 122 rupees from 160 rupees, maintains "market perform" call
** Avg rating of stock "buy", median TP 215 rupees - data compiled by LSEG
** Trading vols 21 mln shares vs 30-day avg of 7.1 mln shares
** YTD stock down 20%
(Reporting by Hritam Mukherjee in Bengaluru)
((Hritam.Mukherjee@thomsonreuters.com;))