Calculation
i0 = I0/IN · 100%
A small no-load current ratio indicates a well-designed, lightly saturated iron core.
Busch 2006, Abschnitt 8.3.3.2 Leerlaufversuch (Gl. 8.42–8.44); i0-Richtwerte nach Leerlaufversuch-Literatur
Transformer no-load current ratio
A small no-load current ratio indicates a well-designed, lightly saturated iron core.
MINTSI
02
Result
Select a target and calculate.
Understand the inputs
- No-load current ratio i0 in % — No-load current relative to rated current, in percent.
- No-load current I0 — Current measured in the no-load test at rated voltage.
- Rated current IN — Rated current of the transformer on the same side as I0.
Example
I0=0.5 A and IN=10 A give i0=5%.
Assumptions and limits
No-load test at rated voltage and frequency; partial-voltage tests and voltage-dependent saturation are excluded.
Understand Transformer no-load current ratio
This calculator relates a transformer's no-load test current to its rated current, one of the two classic factory tests alongside the short-circuit test.
What does this quantity describe?
In the no-load test, rated voltage is applied to the primary winding with the secondary open. The resulting current I0, mostly needed for magnetisation, is related to rated current IN: i0=I0/IN·100%.
Formula and variables
i0 = I0/IN · 100%
i0 = I0/IN · 100%I0 = i0/100 · IN
| Symbol / input | Meaning |
|---|---|
| No-load current ratio i0 in % | No-load current relative to rated current, in percent. |
| No-load current I0 | Current measured in the no-load test at rated voltage. |
| Rated current IN | Rated current of the transformer on the same side as I0. |
Choose the inputs correctly
I0 is the current measured in the no-load test at rated voltage, IN the transformer's rated current on the same side.
How to use the calculator
Take I0 from the no-load test (secondary open, rated voltage on the primary); take IN from the nameplate.
Worked example
I0=0.5 A and IN=10 A give i0=5%.
Understand the result and units
Smaller transformers and those with a more saturated core have higher i0; typical values are a few percent.
I0 and IN are currents. i0 is output as a percentage.
Typical applications
Evaluating test-bench results, comparing transformer designs, and estimating the magnetising current share.
Assumptions, limits and common mistakes
No-load test at rated voltage and frequency; voltage-dependent saturation and partial-voltage tests are not captured separately.
Common mistake: Do not confuse the short-circuit current with the no-load current; both come from different tests with opposite boundary conditions.
Frequently asked questions
What is “Transformer no-load current ratio” used for?
Evaluating test-bench results, comparing transformer designs, and estimating the magnetising current share.
Where do the input values come from?
I0 is the current measured in the no-load test at rated voltage, IN the transformer's rated current on the same side.
What does the result not cover?
No-load test at rated voltage and frequency; voltage-dependent saturation and partial-voltage tests are not captured separately.