Power cut - glad to have survived that! (4)
I believe the answer is:
phew
'glad to have survived that' is the definition.
('phew' is said when relieved)
'power cut' is the wordplay.
'power' becomes 'p'.
'cut' becomes 'hew' (I've seen this in another clue).
'p'+'hew'='PHEW'
(Other definitions for phew that I've seen before include "Gosh, I'm sweltering!" , "Recover unharmed" , "I'm overheating?" , "Exclamation of relief" , "Gosh, that's a relief!" .)