Distance Protection Setting

Set a line impedance (distance) protection: Zone 1/2/3 reach from the line positive-sequence impedance, relay secondary impedance from CT/VT ratios, and remote-backup sensitivity (IEC 60255 / protection coordination practice).

Inputs

Positive-sequence impedance Z₁ Ω/km

Line length L km

Adjacent-line impedance Z_next Ω

CT ratio n_CT (prim/sec) —

VT ratio n_VT (prim/sec) —

Zone 1 reliability K_rel1 —

Zone 2 coordination K_rel2 —

Zone 3 sensitivity K_sen3 —

Measured impedance Z_m Ω

Results

Note — Zone 1 reach is K_rel1·Z_L (instantaneous, typically 80% of the protected line). Zone 2 reaches Z_L + K_rel2·Z_next to back up the adjacent line. Zone 3 covers the full Z_L + Z_next for remote backup; its sensitivity K_sen3 = Z_set3 / Z_L must be ≥ 1.2. Relay (secondary) impedance is Z_set · n_CT / n_VT. The element operates when the measured Z_m ≤ Z_set (for the instantaneous zone). Confirm the CT/VT ratios, the line impedance data and the load-avoidance reach against the supplier / utilityCoordination study.