Research On Grounding-Fault Analysis And Protection Scheme For Petal-Shaped Distribution Network With Inverter-Interfaced Distributed Generation

The petal-shaped distribution network has high power supply reliability,and it can provide reliable grid connection conditions for the access of the inverterinterfaced distributed generation(IIDG).Therefore,the petal-shaped distribution network has been widely concerned.However,the closed-loop operation mode and the access of the IIDG make the distribution network have complex fault characteristics,and bring great challenges to the protection schemes.In this paper,the grounding fault characteristics of the petal-shaped distribution network with the IIDG are analyzed.In the meantime,the protection method and the fault location method for the petal-shaped distribution network with the IIDG are put forward.The following works are investigated in this paper.(1)The grounding fault characteristics of the petal-shaped distribution network with the IIDG are analyzed.According to the composite sequence network,the formulas for grounding current at fault location,fault phase current and sequence current are derived.Correspondingly,the variation trends of the above current are revealed.The results show that when the grounding fault occurs in the petal-shaped distribution network,the current at both sides of the fault line has special symmetry and correlation.In addition,the access of the IIDG can increase the fault current at both sides of the fault position,and leads to a ‘tick’ trend of some current.(2)A current differential protection method based on the steady-state positivesequence current and a centralized backup protection method based on multiple current information are proposed.The proposed current differential protection makes full use of the fault characteristics of the positive-sequence current and its fault components at both ends of the protected line.It can adapt to both closed-loop and open-loop distribution networks,and it is not affected by the fault type,position,resistance,or capacity of the IIDG.The proposed backup protection method can quickly remove the faults on the loop line,feeders and switch station buses only based on the current information measured at each protection.(3)A fault location method for the petal-shaped distribution network with the IIDG is proposed.For the asymmetrical fault,the closed-loop structure and the output characteristics of the IIDG are fully exploited,and the fault position can be calculated according to the amplitude and phase difference of negative-sequence current at both ends of the line.For the symmetrical fault,the influence of the IIDG access is considered.In order to locate the symmetrical fault position,the positive-sequence current at multiple positions is utilized based on the Kirchhoff Voltage Laws.The method can locate the fault position with high accuracy,which can effectively shorten the time of manual inspection and improve the power supply reliability.