Current 3-Stage Setting

Set a non-directional overcurrent line protection in three stages: instantaneous stage I (ride through max end fault), time-delayed stage II (coordinate with the adjacent stage I), and time-overcurrent stage III (far backup from max load current with return and motor self-start factors).

Inputs

Max-end 3φ fault Iₖ₁_max A

Min-end adjacent 2φ fault Iₖ₂_min A

Min-end local 2φ fault Iₖ_min A

Adjacent stage-I setting I_op.adj A

Max load current I_L_max A

Stage-I K_rel —

Stage-II K_rel —

Stage-III K_rel —

Return factor K_re —

Self-start factor K_ss —

Adjacent trip time t_adj s

Time step Δt s

Results

Note — Stage I is instantaneous and rides through the maximum end fault (K_rel ≈ 1.2–1.3); stage II coordinates with the adjacent stage I (K_rel ≈ 1.1) and needs K_sen.II = Iₖ₂_min / I_op.II ≥ 1.3–1.5; stage III is the far backup from the maximum load current including the motor self-start factor (I_op.III = K_rel·K_ss·I_L_max / K_re) with K_sen.III ≥ 1.5 (near) / 1.2 (remote). Operating times step by Δt. Confirm the short-circuit currents, the load and self-start data against the coordination study.