Zero sequence voltage-polarized directional element for protective relays

摘要

The directional element produces a quantity related to the zero sequence source impedance of the power system relative to the location of the directional element, from values of zero sequence current and an adjusted value of zero sequence voltage. The impedance quantity is then compared against first and second threshold quantities to identify the direction of a fault. Further, the zero sequence voltage-polarized directional element can be combined with other individual directional elements, including a zero sequence current-polarized directional element and a negative sequence voltage-polarized directional element to form a universal directional element for unbalanced faults, in which the individual directional elements operate in a particular sequence, with the other directional elements being blocked from operating if a prior directional element in the sequence provides a direction indication.