The study of the protection revision method based on the DG effect to protection sensitivity

This paper carries on the deep research to the influence of distributed generation (DG) introduction in distribution system to over-current protection sensitivity, and proposes the protection revision method. In this paper, it presented the unit-current method to analyze influence characteristic on current protection with DG. It is proved both in theory and by simulation: (1) the single DG influence characteristic is a quadratic curve, which is determined by the DG short-circuit impedance and the DG injection position; (2) the multi-DG influence characteristic curve is superimposition of each DG influence characteristic curve approximately; (3) The DG arrangement which has the minimum influence to the protection is: DGs are connected in the order of the capacity from small to large at both sides of the central point of the system short-circuit impedance. According to analyzing results, it is proposed the inverse time current protection curve revision method for the downstream fault and the reverse verification for the upstream fault to keep the protection coordination relationship and coordination margin, in this way it eliminates the influence of DG to the protection.