Answer / shyamkr

symmetrical components are just the way of representing a
set of unbalanced phasors.whenever any fault occurs in any
phase,unbalanced set of vectors result,to analyse these
unbalanced set of vectors we require symmetrical components
i.e positive,negative and zero seq. currents or voltages.
as the question here ask about only negative sequence
faults,so the nagative faults result whenever there is any
asymmetrical faults in the system.it does not result
whenever 3 phase fault occurs in the system.

Answer / sanju

whenever there is a fault in the systm negative current
flows.

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