Follow the Protection Suite's demo project from load to source: the grading check, the Suggest tool, and why the grid-intertie boundary needs a different fix than a bigger TMS.
| Project | Demo Project (▶ Demo Project on the start screen), plot reference 0.4 kV |
| Devices graded | MCB-45 (32 A type C) → MCCB-12 (LSIG, Ir 320 A) → REL-05 (33 kV feeder, IEC VI, 420 A, TMS 0.30) → REL-04 (33 kV incomer, IEC SI, 625 A, TMS 0.25) → REL-01 (400 kV intertie, IEEE EI, 900 A, TD 0.15) |
| Required margin (CTI) | 0.3 s, and 0.4 s at the grid intertie boundary |
Margins are checked at 2, 3, 5, 8, 12 and 20 times the downstream device's pickup. Hover a cell in the grading table to see the current and both operating times.
| Pair (upstream / downstream) | ×2 | ×3 | ×5 | ×8 | ×12 | ×20 | Result |
|---|---|---|---|---|---|---|---|
| MCCB-12 / MCB-45 | 25.84 | 28.18 | 28.93 | 14.21 | 6.31 | 2.27 | PASS |
| REL-05 / MCCB-12 | 19.16 | −0.59 | −0.03 | 0.88 | 0.62 | 0.35 | FAIL ×3, ×5 |
| REL-04 / REL-05 | 4.77 | 0.49 | 0.41 | 0.45 | 0.45 | 0.44 | PASS |
| REL-01 / REL-04 | 3.62 | −0.20 | −0.66 | −0.67 | −0.61 | −0.53 | FAIL ×3…×20 |
Margins in seconds. Differential REL-02 (87T) is unit protection and is not time-graded.
💡 Suggest on REL-05 / MCCB-12 proposes the smallest TMS that gives 0.3 s at every multiple.
REL-05 is now slower, so the incomer above it has less margin.
💡 Suggest on REL-04 / REL-05:
Suggest on REL-01 / REL-04 proposes TD 0.15 → 3.675 (24.5 ×). It would pass, but the margin would become 151.6 s at ×2 and 33.7 s at ×3 — REL-01 would take minutes to clear a fault just above the incomer's pickup. An extremely inverse curve cannot be made to track a standard inverse curve by time dial alone.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| MCCB-12 over MCB-45 | ≥ 0.3 s | Passes at all multiples | ✓ PASS |
| REL-05 over MCCB-12 | ≥ 0.3 s | After TMS 0.355: ≥ 0.34 s | ✓ PASS |
| REL-04 over REL-05 | ≥ 0.3 s | After TMS 0.272: ≥ 0.33 s | ✓ PASS |
| REL-01 over REL-04 | ≥ 0.4 s | Needs a curve/pickup change agreed with the grid operator | ✗ FAIL |
Key insight: Grading is a chain: every TMS increase restores one margin and takes it from the next device up. Accept a suggestion only after checking the pair above it and the resulting clearing time at the source.
Every input in this example is editable in the live calculator — no signup needed.
Open Protection Coordination Suite (full workbench) calculator →No. It only changes the TMS (or time dial) of the upstream device, keeping its curve family and pickup. Re-run it if you change either device afterwards.
Inverse curves of different shapes converge or cross, so a single fault level can hide a failure. The suite also checks the exact maximum fault level when you enter it for the pair.