Power Systems Lab · 18 modules · all computed in your browser
Distance · R-X
Mho and quad zones, k0, fault trajectory, load region.
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Power Systems Lab · 18 modules · all computed in your browser
Mho and quad zones, k0, fault trajectory, load region.
Loading module…
R-X diagram · distance zones and fault trajectory
Z seen (AG loop)
7.20 Ω ∠85.0°
Decision
Zone 1 · inst.
k0
0.669 ∠-7.5°
Shot test
75 % of Z1 reach
Learn it
A distance relay divides voltage by current. On a healthy line that ratio is a large, mostly resistive “load” impedance. On a fault it collapses toward the line impedance up to the fault, so it effectively measures how far away the fault is.
Zone 1 under-reaches (~80 %) so it never trips for faults on the next line, and trips instantly. Zone 2 over-reaches to cover the line end, with a delay. Zone 3 is remote backup. Fault resistance adds a resistive offset, which is why quadrilateral ground elements with a wide resistive reach exist.
Quiz · 0/3
1. Why is Zone 1 set to about 80 % rather than 100 %?
2. Fault resistance on a radial line moves the apparent impedance…
3. The load region is drawn so that…