EI Portal · Worked cases

Worked cases

Full proving walks with the numbers worked through — worked demonstrations of the EI Portal workspaces, not site installations. Every figure is produced by the tool it describes.

• Frequency Protection (ANSI 81) One Event, Two Failure Modes — Tuning ROCOF on a Low-Inertia Grid
  A worked case: the same ROCOF element nuisance-trips a benign event at 0.18 Hz/s and misses a genuine island at 8 Hz/s. The whole dilemma on one screen.
• Thermal Overload (Device 49) The Same 1.5× Overload, Cold vs Warm — Why a Thermal Relay Has Memory
  A worked case: the same 1.5× overload trips a cold machine in 20.2 min and a warm one in 2.6 min. Why a thermal relay (device 49 / IEC 60255-149) has memory.
• Transformer Differential (87T) Proving an 87T Scheme on the SEL-787 — Through-Load, Internal, External, Inrush, Over-Excitation, REF
  A full SEL-787 proving walk on one 87T scheme: through-load, internal, external, inrush, over-excitation and REF — with the dual-slope maths worked through.
• CT Secondary Burden The Copper Was the Load — One Burden Budget, One CT Within Rating, One Busted by Its Own Leads
  A worked case: the same lead-burden method reads a 400/5 feeder circuit as 'Within rating' at 62.6%, and an 800/5 long run as 'Over burden' at 123.4% — the 45 m of cable alone exceeding the 15 VA core. Then the 1 A rescue: exactly 25× less.
• UPS / Battery Autonomy Sizing The 3000 Wh Trap — One Energy Method, One Covered Bank, One That Falls Short
  A worked case: the same energy method reads a 60 Ah bank as 'Autonomy covered' at 236% of need, and a 150 Ah bank as 'Below autonomy' at 77%. Nameplate Ah is not usable energy.