EI Portal · Engineering articles

Articles

Standards-grounded protection and power-system engineering, written from the tested engines behind the EI Portal tools — every worked number is produced by the tool it describes.

• Frequency Protection (ANSI 81) ROCOF & Loss-of-Mains Protection in a Low-Inertia Grid: The Nuisance-Trip vs Missed-Islanding Trade-off
  How ROCOF, underfrequency and loss-of-mains protection work, why GB raised RoCoF to 1 Hz/s, how inertia sets the nadir, and the settings dilemma.
• Transformer Differential (87T) Transformer Differential Protection (87T): Proving the Dual Slope, Inrush Restraint and REF on the Actual Relay
  How 87T differential stays stable through load and inrush yet trips internal faults — bias, dual slope, 2nd/5th-harmonic restraint, REF — proven on SEL-787, MiCOM, ABB, Siemens.
• Thermal Overload (Device 49) Thermal Overload Protection (ANSI 49): Why a Thermal Relay Has Memory — the IEC 60255-149 Replica Explained
  How thermal overload (ANSI 49) protection works: the IEC 60255-149 thermal replica, thermal state %, time-to-trip, and why a warm machine trips ~8× faster.
• CT Secondary Burden CT Burden Calculation: Why the Secondary Leads, Not the Relay, Decide the Verdict
  How a CT burden calculation works: total the connected device plus the two-wire lead burden, check utilisation against the rated VA, and see why 20 m of copper outweighs the relay — and why 1 A beats 5 A on long runs.
• UPS / Battery Autonomy Sizing UPS Battery Sizing Calculator: The Energy Method, and Why 3000 Wh of Load Needs 4076 Wh of Battery
  How a battery autonomy calculator sizes a UPS bank: the energy method, DOD and efficiency losses, recommended Ah with margin, runtime from a selected bank, and where verdicts flip.