METHOD OF HIGH IMPEDANCE GROUNDFAULT DETECTION FOR DIFFERENTIAL PROTECTION OF OVERHEAD TRANSMISSION LINES

摘要

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.