Custom Brushless Excitation System
Calculate rotor field power and kinematics, then review what needs design-specific analysis.
Preliminary screening tool
Brushless Excitation Requirements Calculator
Calculate rotor field power and rotating-part kinematics.
No calculation yet
Enter the motor operating point and the rotating component radius, then calculate. If a value is unknown, use the inquiry link on the page to ask which measurements are needed before selecting a design.
Research evidence
What published brushless excitation work shows
Public studies support the feasibility of rotary-transformer excitation, but each result belongs to its own prototype, geometry, operating point and test setup. Use them as evidence of approaches, not as ratings for a new design.
| Study | Published result | How to use it |
|---|---|---|
| APEC 2026 laboratory prototype | Tested up to 20,000 RPM and 25 A rotor current; reported maximum efficiency of 96% at 7 kW output. | Evidence that a tested prototype reached those conditions. It does not establish a general speed, current or efficiency rating. |
| ORNL field-excitation modeling, 2019 | Analyzed a rotary-transformer system and series compensation, including sensitivity to field-winding resistance changes with temperature. | Use as a modeling reference; validate control and power transfer for the target motor. |
| DLR pot-core study, 2015 | Presented analytical and FEM work with a prototype tested in stationary and transient operation. | Supports a design workflow; it does not define a universal production envelope. |
- Rotary Transformer for Wound Rotor Synchronous Motors
Mohammad et al., Oak Ridge National Laboratory / APEC 2026
The publication reports a laboratory prototype tested up to 20,000 RPM and 25 A rotor current, with a maximum efficiency of 96% at 7 kW output. These are results for that prototype and operating point.
- Modeling and Steady-State Analysis of a Rotary Transformer-Based Field Excitation System for Wound Rotor Synchronous Machine
Haruna and Raminosoa, Oak Ridge National Laboratory / IEEE ITEC 2019
The study models a rotary-transformer field excitation system and reports that series compensation makes open-loop control robust to field-winding resistance variation with temperature in the studied system.
- Design of a brushless excitation system utilizing pot cores
Veitengruber, Rinderknecht and Friedrich, German Aerospace Center (DLR), 2015
The paper presents an analytical model, parameter studies, FEM calculations and a prototype tested in stationary and transient operation.
System architecture
Follow the power path across the rotating interface
This conceptual diagram shows the decisions that sit around the rotary transformer. It is a block-level view, not a component design or supplier capability claim.
Design review
Four areas need application-specific evidence
A screening calculation cannot establish a safe or manufacturable design. Ask a supplier to show the assumptions, analysis inputs and test acceptance criteria behind its proposal.
| Area | Key question | Evidence to request |
|---|---|---|
| Electrical | Can the link supply the full field operating map? | Current and voltage maps, winding resistance and inductance, compensation and control assumptions. |
| Magnetic | How do air gap and tolerances affect transfer? | Core and winding geometry, coupling analysis, leakage inductance and sensitivity study. |
| Mechanical | Can rotating parts withstand the intended duty? | Rotor stress and retention analysis, balance plan, temperature-dependent clearances and agreed overspeed test criteria. |
| Thermal + controls | Can losses be removed and field current controlled across the map? | Loss breakdown, thermal boundary conditions, fault response and measured validation data. |
Architecture choice
Contactless transfer changes the integration work
Compare the system around its requirements and evidence. Avoid selecting a topology from a generic efficiency, RPM or lifetime claim.
| Option | What it changes | Questions to resolve |
|---|---|---|
| Rotary transformer | Transfers power across an air gap and avoids sliding electrical contacts; adds an inverter, magnetic link and rotating rectifier/control decisions. | Package space, coupling sensitivity, field regulation, rotating-part retention, cooling and fault handling. |
| Slip rings | Provide a direct electrical connection to the rotor winding; retain contact interfaces that need maintenance and environmental review. | Contact environment, service access, wear monitoring, current rating and the application’s reliability targets. |
The comparison is qualitative. A DLR study describes contactless rotary-transformer excitation as a way to supply wound rotors without sliding contact wear, while noting that motor-specific compensation networks must be compared and validated. See the DLR study.
Validation path
Turn a screening brief into a testable design
Agree inputs and limits first, then progress through electrical, magnetic, thermal and rotor analysis. Prototype tests should use the intended assembly and pre-agreed acceptance criteria.
Evidence limits
Do not transfer prototype numbers directly
Published values describe specific prototypes and test setups. This page does not claim a universal mass, coupling factor, efficiency, lifetime, thermal limit, speed rating or cost.
The cited public sources establish research methods and selected prototype results. They do not validate a particular commercial supplier, your motor envelope, production capability or application safety.
The acceleration calculation is based on the entered speed and radius. It is not a structural analysis. Obtain rotor stress, retention, thermal, balance and overspeed evidence for the assembled design before making a release decision.
Frequently asked questions
Engineering and sourcing questions
What does this calculator determine?
It calculates rotor field winding electrical power from current × voltage, the ratio of that power to the entered shaft power, and kinematic acceleration and peripheral speed at the entered radius. It does not size or rate an excitation system.
Is field current multiplied by field voltage the exciter input power?
No. It is the electrical power at the rotor field winding for the specified operating point. Supply-side input must also account for the transformer, rectifier, inverter and other conversion losses.
Does the acceleration result prove that a rotor is safe?
No. It is a kinematic value at the radius you enter. Rotor stress, retention, fatigue, balance, thermal expansion and overspeed acceptance require design-specific analysis and testing.
Can I use this tool to estimate mass, coupling or efficiency?
No. Those outputs depend on geometry, winding layout, magnetic materials, operating waveforms, cooling, manufacturing tolerances and measured component data. The tool intentionally does not guess them.
How should I choose the air gap and carrier frequency?
Treat both as design inputs for electromagnetic and mechanical analysis, not stand-alone targets. Published work uses different transformer geometries and compensation networks; its values cannot be transferred directly to another motor.
What should accompany an RFQ?
Provide continuous and transient field-current maps, field winding resistance and inductance over temperature, speed map, available envelope, air-gap and runout tolerances, cooling conditions, duty cycle, target volume and required validation evidence.
What does published prototype evidence establish?
It shows that rotary-transformer brushless excitation has been analyzed and prototyped. For example, an APEC 2026 paper reports one laboratory system tested up to 20,000 RPM and 25 A, with a maximum efficiency of 96% at 7 kW. It does not establish ratings for an unrelated design.
Does contactless excitation mean maintenance-free operation?
Removing sliding electrical contacts removes that contact wear mechanism, but bearings, insulation, rotating electronics, cooling paths and mechanical retention still need application-specific reliability and maintenance planning.
Why is resonant compensation discussed in the research?
Rotary-transformer leakage inductance and the rotor field load affect power transfer and control. Published studies analyze compensation as part of the system design; the appropriate network and controller depend on the motor and operating range.
What should be validated before production?
Agree the electrical operating map, thermal limits, mechanical retention and balance criteria, environmental conditions, fault response, test instrumentation and acceptance criteria. No single public prototype result replaces validation of the intended assembly.
Procurement next step
Prepare a useful custom excitation system inquiry
Include the field operating map, winding resistance and inductance, speed range, available envelope, air-gap and runout tolerances, cooling conditions, duty cycle, target volume and required test evidence. Ask the supplier to state assumptions and unresolved limits in its response.
Inquiry Email
Include target torque/speed, quantity, and delivery location.
Research sources
Sources checked on October 16, 2026. Reported results remain specific to the cited study and prototype.
- Rotary Transformer for Wound Rotor Synchronous Motors
Mohammad et al., Oak Ridge National Laboratory / APEC 2026
The publication reports a laboratory prototype tested up to 20,000 RPM and 25 A rotor current, with a maximum efficiency of 96% at 7 kW output. These are results for that prototype and operating point.
- Modeling and Steady-State Analysis of a Rotary Transformer-Based Field Excitation System for Wound Rotor Synchronous Machine
Haruna and Raminosoa, Oak Ridge National Laboratory / IEEE ITEC 2019
The study models a rotary-transformer field excitation system and reports that series compensation makes open-loop control robust to field-winding resistance variation with temperature in the studied system.
- Design of a brushless excitation system utilizing pot cores
Veitengruber, Rinderknecht and Friedrich, German Aerospace Center (DLR), 2015
The paper presents an analytical model, parameter studies, FEM calculations and a prototype tested in stationary and transient operation.
- Rotary transformer with ferrite core for brushless excitation of synchronous machines
Vip et al., Leibniz University Hannover / IEEE ICEM 2016
The publication discusses analytical and 2D FEM design, high-frequency winding effects and comparison of calculated results with prototype measurements.