Fast protection against islanding and unwanted tripping of distributed generation caused by ground faults
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Ground faults (GF) in a feeder with interconnected distributed generation (DG) might lead to overvoltages in healthy phases even after feeder disconnection from a substation, obstacles for reclosing schemes, and safety hazards. It requires urgent disconnection of DG to prevent islanding. On the other hand, fast location of GF in compensated networks is a difficult task and finding of the correct fault location is necessary in order to decrease a number of undesirable DG decoupling. The current paper proposes a communication–based scheme preventing islanding forming in a system. The scheme utilizes a new fast and universal indicator revealing fault positions. A locating algorithm is also applied to restrict unwanted disconnection of DG. The method is tested on a model in PSCAD/EMTDC of an actual 22 kV multiterminal grid grounded by a Petersen coil and including DG. The results show that the new indicator can reliably discriminate faults in the system. It has been found that precision of the locator utilizing two–point measurements is not sufficient and might lead to nuisance tripping of the DG. Using of multi–point measurements and the proposed indicator helps to solve this problem for a complex feeder topology. Finally, the same signals can be applied to enhance accuracy of the locator.