Feeder Overcurrent
→Inverse-time grading on a radial feeder — the first instinct of protection.
50 / 51Beginner · 45 min
Module 01 — Protection Relaying
A studio for the engineers who commission protection. Phasor diagrams, impedance planes and trip characteristics — drawn with the care of a technical plate, and learned the way a craft is learned.
Inverse-time grading on a radial feeder — the first instinct of protection.
Reading the residual current 3I₀ to catch the faults phase elements miss.
Polarising the element so it only looks the way the fault current flows.
Stacking time–current curves so the nearest device clears, and only it.
Telling a true internal fault from magnetising inrush by its harmonics.
A high-impedance boundary that stays stable through external faults.
Drawing reach as impedance — the mho circle on the R–X plane.
Holding a whole bus inside one high-impedance differential zone.
Proving the eyes of the scheme — ratio, polarity, and the knee-point on the excitation curve.
The reference every element trusts — ratio, polarity, and the accuracy class box.
The device that must interrupt — contact timing, pole discrepancy, and coil health.
Proving the machine before load — turns ratio at every tap, winding balance, vector group, and insulation.
The nerves behind the steel — point-to-point signals and GOOSE trips inside their transfer-time class.
The signature that energizes a station — one register, one gate, no open critical or major defects.
The buried kilometre you can't see — insulation resistance, a VLF withstand, the sheath, and TDR length.
The isolation you bet your life on — contact resistance, operation, and the interlock that must never let it break load.