The calculation, without hidden assumptions
Model a distribution transformer across a daily duty cycle instead of judging it at one operating point. Enter up to four energized periods with different loading and power factor; MAXScanner totals delivered energy, fixed core-loss energy and load-dependent copper-loss energy.
How to use this calculator
Enter transformer rated kVA plus reliable no-load/core loss and full-load copper/load loss.
Describe up to four periods using hours, percent loading and power factor.
For energized no-load time, enter hours with 0% load and PF 0; omitted hours are treated as de-energized, not as no-load operation.
Keep total entered hours at or below 24.
Review delivered kWh, core and copper loss energy, input energy and all-day efficiency.
Where people use it
- •Distribution-transformer daily energy-loss studies.
- •Comparing duty cycles with the same transformer loss data.
- •Quantifying the effect of long energized no-load periods.
- •Separating fixed core-loss energy from load-dependent winding/load-loss energy.
Example: 100 kVA daily duty cycle
For 100 kVA, PF 0.8, 1.2 kW core loss and 2.0 kW full-load copper loss: 6 h at 100%, 10 h at 50%, and 8 h energized at no load gives 880 kWh output, 28.8 kWh core-loss energy, 17 kWh copper-loss energy, 925.8 kWh input and about 95.05% all-day efficiency.
What the result does not assume
- •This is energy efficiency over the entered duty cycle, not instantaneous operating efficiency or a regulatory certification calculation.
- •Core/no-load loss is modeled constant while energized at the applicable rated voltage/frequency. Full-load copper/load loss is scaled by load fraction squared.
- •Use manufacturer or test-certificate loss values. Temperature, harmonics, stray losses, voltage/frequency variation, tap position and cooling state can alter real losses.
- •A 0% load period still accumulates core loss when entered as energized time. Hours omitted from the profile are treated as de-energized.
- •The model limits entered loading to 100% because an energy-efficiency planner should not silently normalize overload operation.
Frequently asked questions
What is all-day efficiency of a transformer?+
It is total useful output energy divided by total input energy over a duty cycle, conventionally a 24-hour day. Unlike instantaneous efficiency, it captures varying load and energized no-load periods.
Why does core loss continue at no load?+
When an energized transformer is held near rated voltage and frequency, core loss remains even when the secondary supplies no useful load. Enter those hours as a 0% load period.
Why is copper loss multiplied by load fraction squared?+
The standard planning model treats winding/load loss as approximately proportional to current squared, so a 50% load period contributes about 25% of full-load copper loss per hour.
Can power factor vary by period?+
Yes. Each entered loaded period has its own power factor because useful kW output depends on both apparent loading and PF.
Is this the same as the Transformer Efficiency Calculator?+
No. The ordinary efficiency calculator evaluates one operating point. This owner integrates output and losses across a time-varying duty cycle.
Can this prove DOE or other regulatory efficiency compliance?+
No. Compliance requires the applicable prescribed test method and certified equipment data. This tool is for transparent engineering planning and energy studies.
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