Method of high impedance groundfault detection for differential protection of overhead transmission lines

Abstract

The invention concerns a method of impedance groundfault detection for differential protection of an overhead transmission line in a three-phase high voltage electric power transmission system which comprises many lines (1,12) and many protection relays (2,4), which comprises the following steps: 1) in prefault condition: —measuring the differential current (I); —measuring the phase voltage (II) at the relay location; —measuring the phase current (III) the relay location; —calculating the differential admittance (IV), with the following equation: (formula (V)). With (VI): the positive sequence impedance of the line-protected. 2) In operating condition: —measuring the differential current (VII); —measuring the phase voltage (VIII) at the relay location; —measuring the phase current (IX) at the relay location; calculating the differential admittance (X), with the following equation: (formula (XI)); —detecting a high impedance groundfault detection, if the following formula is verified: (XII) with (XIII); B0=the total line admittance. I _ dph pre ( I ) U _ fph pre ( II ) I _ fph pre ( III ) Y _ d pre ( IV ) Y _ d pre = I _ dph pre U _ fph pre - 0.5  Z L   1  I _ fph pre ( V ) Z L   1 ( VI ) I _ dph ( VII ) U _ jph ( VIII ) I _ jph ( IX ) Y _ d ( X ) Y _ d - I _ dph U _ jph - 0.5  Z L   1  I _ jph ( XI ) abs  ( Y _ dN ) > 0.75  B d ( XII ) Y _ dR = Y _ d - Y _ d pre ( XIII )

Dependencies are inferred from the claim text.