# Transformer Protection Settings Report
**Generated:** 01/08/2026, 10:19:24

## Transformer Parameters
| Parameter | Value |
|---|---|
| Rating S_tr | 630 kVA |
| Primary voltage | 20 kV |
| Secondary voltage | 0.4 kV |
| Impedance Z_t | 6% |
| Fault level I_sc | 25 kA |

## CT Parameters
| Parameter | Value |
|---|---|
| CT secondary | 5 A |
| CT accuracy class | C |
| CT burden | 5 VA |
| CT ratio tolerance | ±10% |

## Protection Settings
| Setting | Value |
|---|---|
| CT ratio (secondary side) | 182:5 |
| CT ratio (primary side) | 4:5 |
| Knee-point voltage V_k | 7.5 V |
| Minimum V_k required | 8000 V |
| V_k check | ❌ FAIL |
| Bias slope 1 (unrestrained) | 0.5 |
| Bias slope 2 (restrained) | 0.2 |
| Pickup I_pu | 30% of I_nom = 272.8 A |
| Inrush peak | 7274.64 A (8× I_nom) |
| Inrush stability | ⚠️ May mis-operate |
| 2nd harmonic minimum | 15% |
| Bias increase @ harmonic min | 6% |
| **Overall** | **❌ FAIL** |

## Recommendations
- ❌ **ERROR** CT knee-point V_k=7.5 V < minimum 8000.0 V required. Upgrade to higher class (KM or X) or increase CT ratio.
- ⚠️ **WARNING** Differential pickup I_pu=273 A is below inrush peak I_inrush=7275 A. Increase pickup to 1.2× inrush or increase harmonic restraint threshold.
- ℹ️ **INFO** Unrestrained bias slope 0.5 is low — may be sensitive to CT saturation during deep faults. IEC 60255-151 recommends slope 1 ≥ 0.6 for transformer's internal fault sensitivity.

## Standards
- IEC 60255-151: Protection relays — numerical differential protection
- IEC 60076-1 §5.3: Transformer tap changer range
- IEEE C37.109: Guide for the Protection of Power Transformers
- Formula: CT ratio = I_nom_sec / I_sec_rated
- V_k ≥ 1.6 × I_fault × R_ct (IEEE C37.109)
- Inrush peak ≈ K × I_nom (K = 8, typical 8–12)