| 摘要 |
<p>The system impedance ratio (SIR) is determined for the original zone 1 distance element reach (116) of a protective relay (132). The reduction in the original zone 1 reach is then determined (120), using the SIR value (118) and a known table of reduced values. When a fault is recognized the minimum reach (126) to just detect the fault is determined. A trip signal (130) is provided without any delay if the minimum reach (126) is less than or equal to the reduced reach (120). The trip is delayed (136) for a selected time if the minimum reach (126) is greater than the reduced reach (120) but not greater than the original reach (116).</p> |
