An inverse‐time low‐impedance protection design for feeders in active distribution networks

Abstract

One of the major issues associated with active distribution networks (ADNs) is to devise an appropriate protection scheme that works successfully in different operation modes. This paper describes the design of an inverse-time low-impedance (ITLI) protection scheme with the aid of the advanced measurement technologies in ADNs. The scheme detects faults and calculates tripping time by using the magnitude ratio of the maximum load impedance to the measured impedance. ITLI protection is immune to varying fault current caused by the flexible operation modes and able to automatically adjust fault-tripping time according to the fault severity. With the existing communication infrastructures, an event-triggered adaptive setting scheme updates the settings of ITLI relays in real time. The setting method not only enhances the detecting capability but also provides higher reliability and sensitivity before, during, and after events in ADNs, such as tap position adjustment, DGs fluctuation, and network structure change. Besides, an acceleration method based on the definite-time grading technique is presented to reduce the impact of infeeds and fault resistance. The effectiveness of the proposed protection scheme is demonstrated in a 12.47-kV active distribution network established by PSCAD/EMTDC.