ONE-LINE GROUND PROTECTION SYSTEM FOR NON-GROUNDED SYSTEM TRANSMISSION/DISTRIBUTION LINE

摘要

PROBLEM TO BE SOLVED: To provide a ground protection system which can identify a fault circuit and a fault point, when a one-line ground occurs in a non-grounded neutral type power system transmission/distribution line. SOLUTION: If a one-line ground fault occurs at a relative position k (k=1 at an end) in an end concentrated load transmission line of a non-grounded system transmission/distribution line having a length of Lkm, respective phase voltages Vp of substation bus-bars, respective phase currents Ic of the transmission lien and a current Iz of a zero-phase CT (ZCT) are measured and, denoting impedances between phases and ground admittances of respective phases of the transmission/distribution line by Z and Y respectively, an equation (1) is established according to Kirchhoff's Second Law, concerning the fault phase (a) and a fault point current If is expressed by a formula (2), under the condition that a load current does not vary. Vp(a)=RfIf+ kVz (where Vz denotes a phase (a) component of LZIc) (1), If=Iz+LYVp (2). The complex equation (1) is decomposed into a real component (Re) and an imaginary component (Im). By obtaining solutions of simultaneous equations of the real components (Re) and the imaginary components (Im), the fault point k and a ground resistance Rf are obtained and, if the ground resistance Rf is not negative, it is decided that the fault exists on that circuit.