Transformer Differential Setting

Rated winding currents, CT secondary currents, balance factor, pickup, through-fault unbalance and inrush 2nd-harmonic blocking for a transformer differential relay.

Inputs

Transformer rating S kVA

HV voltage U_hv kV

LV voltage U_lv kV

HV CT ratio n1/n2 —

LV CT ratio n1/n2 —

Pickup (% of Iₛ) —

CT error ε %

OLTC range %

Vector-group angle °

2nd-harmonic I₂ₕ A

Differential I_d A

2nd-harmonic block %

Through-fault I (sec.) A

Restraint slope —

Results

Note — Simplified percentage-restraint model. Pickup 0.2–0.5 Iₛ and slope 0.3–0.5 are typical; confirm CT ratios, vector-group compensation and the relay's internal settings with the protective-coordination study and a certified engineer.