Converting a feeder's peak load and load factor into an annual energy-loss estimate — without needing a full year of interval load data.
| Peak load (individual, pre-diversity) | 500 kW |
| Diversity factor | 1.2 |
| Load factor | 60% |
| Line resistance (per phase) | 0.5 Ω |
| System voltage | 11 kV |
| Power factor | 0.9 |
| Energy cost | $0.12 / kWh |
Loss factor estimates how loss (which scales with current squared) averages over time, given only the load factor (which is a simple linear average) — using the widely referenced empirical approximation.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| Peak I²R loss | n/a (informational) | 0.886 kW | ✓ PASS |
| Annual energy loss | n/a (informational) | 3352 kWh/year | ✓ PASS |
| Annual loss cost | n/a (informational) | $402.20/year | ✓ PASS |
Key insight: Loss factor (0.432) is always less than load factor (0.6) whenever load factor is below 1.0, because loss scales with the square of current — a feeder that runs at partial load most of the time wastes proportionally less energy to resistive loss than one that runs flat-out constantly, even at the same average load factor.
Every input in this example is editable in the live calculator — free, no signup.
Open Distribution Line Technical Losses calculator →Because I²R loss is proportional to the square of current, not current itself, so simply averaging loss using the linear load factor would overstate annual losses whenever load varies over time — the loss-factor approximation exists specifically to correct for this squaring effect without requiring a full year of interval (load-duration) data, which most sites don't have readily available.
It's a widely cited empirical fit, not an exact relationship — the true loss factor for a given load factor depends on the actual shape of the load curve over time, which this approximation doesn't know. Where real interval/AMI data is available, computing loss factor directly from the actual load curve will always be more accurate than this formula.