Transformer Loading % Formula
How to calculate transformer loading percentage and check for overloading.
The Formula
Apparent Load (kVA) = Active Load (kW) ÷ Power Factor
Loading % = (Apparent Load ÷ Transformer Rating) × 100%
Example
500 kVA transformer, 320 kW load, PF = 0.85:
Apparent Load = 320 ÷ 0.85 = 376.5 kVA
Loading % = (376.5 ÷ 500) × 100 = 75.3% ← Optimal range
Loading Ranges
| Loading % | Status | Action |
|---|---|---|
| < 40% | Underloaded | Consider right-sizing |
| 40–85% | Optimal | Normal operation |
| 85–100% | High | Plan capacity expansion |
| > 100% | Overloaded | Immediate action needed |