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Transformer All-Day Efficiency Calculator — 24-Hour Load Profile

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Transformer rating (kVA) Nameplate apparent-power rating.Core / no-load loss (W) Reliable no-load test or manufacturer value.Full-load copper / load loss (W) Reliable full-load loss value.Period 1 hours Period 1 load (%) Period 1 power factor Use 0–1; use 0 only for a no-load period.Period 2 hours Period 2 load (%) Period 2 power factor Period 3 hours Period 3 load (%) Energized no-load period.Period 3 power factor PF is irrelevant at zero load.Period 4 hours Period 4 load (%) Period 4 power factor

Calculated result

95.053% all-day efficiency

Output energy: 880 kWh

Core-loss energy: 28.8 kWh

Copper/load-loss energy: 17 kWh

Total loss energy: 45.8 kWh

Input energy: 925.8 kWh

Time-weighted average loading: 45.83%

Entered energized profile: 24 h

Period 1: 6 h × 100% × PF 0.8 → 480 kWh output, 12 kWh copper loss

Period 2: 10 h × 50% × PF 0.8 → 400 kWh output, 5 kWh copper loss

Period 3: 8 h × 0% × PF 0 → 0 kWh output, 0 kWh copper loss

Model boundary: core loss accrues only for entered energized hours. Add a 0% load period for energized no-load time; omit hours only when the transformer is de-energized.

Show the working

1. Output energy = Σ(kVA × load fraction × PF × hours) = 880 kWh.
2. Core-loss energy = 1.2 kW × 24 h = 28.8 kWh.
3. Copper-loss energy = Σ(2 kW × load fraction² × hours) = 17 kWh.
4. Input energy = 880 + 45.8 = 925.8 kWh.
5. ηall-day = 880 ÷ 925.8 × 100 = 95.0529%.

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