Power lock for a performer (7)
I believe the answer is:
actress
'a performer' is the definition.
(actress is a kind of performer)
'power lock' is the wordplay.
'power' becomes 'AC' (AC is an example).
'lock' becomes 'tress' (both can mean a piece of hair).
'ac'+'tress'='ACTRESS'
'for' acts as a link.
(Other definitions for actress that I've seen before include "Theatrical female" , "One on stage" , "Female in plays/films" , "Female thespian" , "Garland perhaps" .)