Based on the characteristic of negative- sequence equivalent electric circuit under the unbalanced faults of power system,the unbalanced fault on transm ission line can be located.

Application on the quick acting phase relay protection of unsymmetrical fault and double loop-lines;

However,when unbalanced fault occurs in the AC system,negative-sequence components existing in AC system will lead to a lot of non-characteristic harmonics under the action of pulse width modulation(PWM),so the control performance of VSC-HVDC system will be deteriorated.

Transient unbalanced short circuits of induction machine;