Technology / Engineering guide
Wind Generator Losses & Efficiency Maps
A generator’s efficiency belongs to a defined operating point and measurement boundary. A single favourable percentage cannot describe every speed, current and thermal condition or the complete wind installation.
Keep losses and delivered power on one boundary record.
Identify the mechanical input and electrical output represented by a result. Then distinguish measured total loss from individually assessed loss categories.
01 / Boundary
Generator efficiency is a ratio of matched powers.
For a defined generating operating point, efficiency is the named electrical output divided by the corresponding mechanical input.
For a defined generating operating point, efficiency is the named electrical output divided by the corresponding mechanical input. Both need a common equipment state. A converter or auxiliary load included in one result but excluded from another changes the comparison.
The torque and power guide explains shaft-power meaning. This page asks how losses and efficiency are represented across operating points, rather than deriving a rated torque from the model’s kW label.
02 / Winding loss
Resistive heating depends on current and resistance.
For a defined resistive element, P_loss = I²R, using current in amperes and resistance in ohms to obtain watts.
For a defined resistive element, P_loss = I²R, using current in amperes and resistance in ohms to obtain watts. For changing current, the appropriate RMS or time-based definition matters. This element relation is not the complete generator’s loss calculation.
As a hypothetical illustration, 5 A through 0.4 Ω gives 10 W; 10 A at the same resistance gives 40 W. The example contains no MARSTON phase arrangement, current rating or winding resistance.
03 / Other categories
A loss schedule should explain its contents.
A machine report may separate winding, magnetic, mechanical and additional loss categories under its assessment method.
A machine report may separate winding, magnetic, mechanical and additional loss categories under its assessment method. Check how each category was obtained and whether it is measured, calculated or allocated. Do not assume a percentage distribution from another generator.
The public IEC 60034-2-1 listing concerns test methods for determining rotating-machine losses and efficiency. Referencing that subject does not claim that MARSTON was assessed to it or that a particular report used the complete method.
04 / Thermal state
Resistance belongs to a condition.
Keep the resistance basis and machine temperature with a winding-loss calculation.
Keep the resistance basis and machine temperature with a winding-loss calculation. Using a value from one condition to represent a different thermal state introduces an assumption. A wire’s temperature-class description does not supply the required resistance measurement.
Also identify cooling and test duration when interpreting an efficiency result. Two operating points with the same electrical output can involve different speed, current and thermal conditions; a result at one point should not silently represent the other.
05 / Map coverage
A maximum value is not an efficiency map.
A map should name its axes, represented loading, temperature basis and valid region.
A map should name its axes, represented loading, temperature basis and valid region. Speed and torque or current may define operating points, but the actual axes and measurements must be stated. Interpolated areas should remain distinguishable from tested points.
A missing region is not proof that efficiency there matches the published maximum. Compare coverage against the project’s expected operating range without creating an unverified MARSTON curve or assigning an efficiency to every wind speed.
06 / Comparison record
Keep absolute powers beside the percentage.
Retain input power, output power, total loss, method, uncertainty and configuration identity for each compared condition.
Retain input power, output power, total loss, method, uncertainty and configuration identity for each compared condition. A small input/output difference may need particularly careful uncertainty interpretation; a rounded percentage hides those absolute quantities.
The documented FD14-50KW direct-drive permanent-magnet design does not supply a numerical efficiency map. Nor is that internal design assigned to the other models. Compare evidence at the actual generator boundary before using it in a whole-project energy calculation.
Continue the review with Wind Generator Winding Temperature & Insulation Class.
Continue the review with Wind Generator Cogging Torque & Rotor Start-Up.
Continue the review with Direct Drive vs Geared Small Wind Drivetrains.
Extend the generator component review with winding skin and proximity effects and magnetic hysteresis and eddy-current losses. Review loaded torque ripple and cogging contributions as a separate operating-torque topic.
For an additional electromagnetic topic in the generator review, see magnetic saturation and flux density.
General background: OpenStax: Resistive power dissipation · IEC: Rotating-machine loss and efficiency test-method scope. These references explain industry concepts; they are separate from the applicable MARSTON product and project documents.
Prepare the information for this review.
Use the checklist to organise the project information. Mark unavailable items and retain document references.
| Review item | Information to provide | Purpose |
|---|---|---|
| Power boundary | Mechanical input and named electrical output | Define the ratio. |
| Winding basis | Current statistic, resistance and thermal condition | Interpret resistive heating. |
| Loss schedule | Categories, methods and included parts | Avoid an assumed breakdown. |
| Map axes | Speed/loading, valid region and test points | Identify coverage rather than a peak. |
| Result record | Absolute powers, revision and uncertainty | Keep the percentage checkable. |
Engineering questions.
Does direct drive establish an efficiency value?
No. Its mechanical arrangement does not supply measured input/output performance.
Does I²R give every generator loss?
No. It describes a defined resistive element; the complete loss method must identify other contributions.
Does double current always mean four times total loss?
Only the illustrative resistive term at unchanged resistance follows that relation. Total machine loss is different.
Can one maximum describe all operation?
No. Map coverage and actual operating conditions must be reviewed.
Is an IEC title a MARSTON test result?
No. The listing identifies a method’s subject, not assessed product conformity.
What should accompany efficiency?
Matched absolute input/output powers, equipment state, boundary, method and uncertainty.
Technical enquiry
Bring your project information to the discussion.
A generator’s efficiency belongs to a defined operating point and measurement boundary. Share the available information and the equipment scope you want reviewed in a technical quotation.