Supplier evaluation + engineering screening
Screen rotor loading, compare architectures, and prepare an RFQ. Results are preliminary.
Published scope: EESM/wound-rotor assemblies and project-scoped excitation-interface review.
Published 2026-10-17 - Reviewed 2026-10-17
Screen rotor motion and prepare an RFQ. Results are preliminary.
Example inputs; speed, radius, and balance grade drive results.
Use the specified maximum operating speed; state overspeed separately.
Measure from the shaft axis to the rotating feature being screened.
Captured in the RFQ summary only; include the rating basis and duty cycle in the supplier specification.
Captured in the RFQ summary only; state peak and continuous values separately if both matter.
Used in the RFQ summary only; the tool does not infer a required standard.
Ask the supplier to quote tooling, capacity, and lead time against your actual forecast.
Confirm the customer requirement and verify certificate scope, site, and validity.
This records your current option; it is not a recommendation.
A discussion value only. Confirm rotor behaviour, mass, application, and acceptance criteria with the balancing specialist.
These values follow from the entered speed and radius. They do not predict stress, temperature, fatigue life, air-gap clearance, or supplier capability.
Engineering boundary: acceleration uses a rigid-body kinematic relation, a = omega^2 * r. The balance value is the specific-unbalance reference e = G/omega, not a total residual unbalance or a grade recommendation. To express total residual unbalance, multiply the specific value in um by rotor mass in kg to obtain g*mm. Confirm whether ISO 21940-11 applies to the rotor behaviour and agree acceptance criteria with the responsible engineer.
Start with your operating envelope, keep calculation outputs in their proper scope, and request evidence for the exact design and production site.
Compare inductive rotary transformers, rotating AC exciters, and slip rings against standstill operation, speed, field power, package, cooling, service life, and control requirements. Published prototypes show feasibility for particular designs; they do not establish a universal best option or qualify a supplier.
ORNL 2026 prototype studyCentrifugal acceleration scales with angular speed squared and radius. Use the tool for a first calculation, then ask the supplier to validate the complete rotor geometry, materials, temperature range, overspeed profile, and assembly process.
Calculation method and limitsA certificate or a generic balance grade does not establish application suitability. Review the relevant certificate scope, balancing report, test definition, traceability, and acceptance criteria for the actual production site and assembly.
ISO 21940-11 scopeManufacturer scope
Magnet-Free Motor's published scope includes EESM and wound-rotor assemblies, hairpin stators, lamination stacks, and OEM motor components. Brushless excitation interface review is project scoped. Confirm standalone exciter, rotating rectifier, rotor, and complete-motor responsibilities against the drawing and operating map before quotation.
Review the company's stated factory positioning, product coverage, and engineering services before deciding whether your RFQ is component-level or for a complete motor program.
Read manufacturing capabilitiesFor speed n in revolutions per minute and radius r in metres, angular speed is omega = 2 * pi * n / 60. Peripheral speed is v = omega * r; radial acceleration is a = omega^2 * r. The displayed multiple of standard gravity is a/9.80665.
For a selected balance quality value G in mm/s, the tool shows e = G/omega as a specific-unbalance reference. Multiply e in um by rotor mass in kg to express residual unbalance in g*mm. The tool omits mass, rotor behaviour, geometry, material properties, temperature, joints, and boundary conditions, so it cannot calculate a design safety factor.
These options solve the same field-supply problem in different ways. A supplier proposal should make its system boundary and trade-offs explicit.
| Architecture | Transfer approach | Questions to resolve | Evidence to request |
|---|---|---|---|
| Inductive rotary transformer | Power crosses an air gap through magnetic coupling. | Check transfer power across the full speed and load map, converter/control behaviour at standstill, thermal path, rotor retention, and electrical clearances. | Prototype test data, efficiency and temperature maps, speed/overspeed reports, insulation test plan. |
| Brushless AC exciter | A rotating exciter and rectifier supply the main rotor field. | Check starting and low-speed excitation needs, rotating rectifier serviceability, speed envelope, field response, and cooling. | Exciter and rectifier drawings, operating/starting sequence, dynamic response test, overspeed and thermal validation. |
| Brushes and slip rings | Stationary DC is transferred through sliding electrical contacts. | Check access, wear management, contamination, brush current density, maintenance interval, and the system-level reason for retaining contacts. | Contact design, environmental tests, inspection and replacement procedure, service-life assumptions. |
Standstill performance, response, speed, efficiency, and service claims depend on the complete design and controls. Ask for results at comparable operating points rather than relying on architecture labels.
Use consistent questions for each bidder. Ask suppliers to distinguish measured results, simulation, proposed targets, and assumptions.
| Review area | Ask the supplier | Review evidence |
|---|---|---|
| System boundary | Confirm which parts are included: stationary supply/converter, coupler or exciter, rotating rectifier, rotor field interface, sensors, and cooling hardware. | A drawing or interface-control document with electrical, mechanical, and thermal interfaces. |
| Operating envelope | Provide continuous and peak speed, overspeed definition, field voltage/current/power map, duty cycle, ambient and component temperatures, cooling, and start/stop profile. | A requirement-to-test matrix with assumptions and unresolved inputs called out. |
| Mechanical validation | Ask how rotating parts are retained and balanced, what assembly is tested, and how temperature and speed limits are selected. | A design-specific analysis, balancing report, test procedure, calibrated records, and post-test inspection criteria. |
| Electrical and thermal validation | Ask for winding insulation, rectifier, thermal path, transient, and converter compatibility requirements relevant to the design. | Test scope, measured conditions, acceptance limits, instrumentation, and any deviations. |
| Quality and production | State customer-required quality systems, submission package, change control, sub-tier traceability, annual demand, and ramp profile. | Current certificates with site/scope, control plan, process capability evidence where agreed, capacity plan, and quotation assumptions. |
Agree the test article, configuration, limits, and acceptance evidence with the supplier and customer before testing begins. Test severity is design- and application-specific; there is no single overspeed percentage or dwell time that applies to every excitation rotor.
| Stage | Decision question | Evidence / output |
|---|---|---|
| Requirements review | Are interfaces, loads, environments, duty cycle, and acceptance criteria complete? | Signed requirements and open-item list. |
| Design review | Does the proposed architecture address the operating envelope and stated risks? | Drawings, analyses, materials, supplier assumptions, and verification plan. |
| Prototype validation | Did the defined test article pass the agreed electrical, thermal, mechanical, and environmental tests? | Traceable test reports with configuration, conditions, measured results, and deviations. |
| Production release | Can the production site repeat the validated design and control changes? | Approved production controls, capacity plan, traceability, and customer-specific submissions. |
Illustrative arithmetic only. The values below use a point radius and speed; they are not customer case studies, supplier test results, or design limits.
| Example | Speed | Radius | Peripheral speed | Centrifugal acceleration |
|---|---|---|---|---|
| A | 18,000 RPM | 70 mm | 131.9 m/s | 25,362 g |
| B | 6,500 RPM | 100 mm | 68.1 m/s | 4,725 g |
| C | 3,600 RPM | 200 mm | 75.4 m/s | 2,898 g |
Sources reviewed 2026-10-17. Standards are copyrighted documents; this summary describes their published scope and is not a substitute for reviewing the applicable edition and customer requirements.
| Reference | Issuer / publication | Relevant scope and limit | Link |
|---|---|---|---|
| Rotary Transformer for Wound Rotor Synchronous Motors | Oak Ridge National Laboratory / APEC 2026 | Reports a laboratory rotary-transformer prototype with an integrated rectifier, tested up to 20,000 rpm and 25 A rotor current; the study reports 96% maximum efficiency at 7 kW output. These are study results, not a general product rating or supplier capability guarantee. | Open source |
| Design of a Brushless Excitation System Utilizing Pot Cores | Veitengruber, Rinderknecht & Friedrich, DLR / COMPEL, 2015 | Describes an inductive power-transfer approach for supplying a wound-rotor field winding and compares compensation networks using analysis, measurements, and a prototype. | Open source |
| IEEE Std 421.1-2021, Definitions for Excitation Systems | IEEE Standards Association | Defines excitation-system elements and commonly used components, with typical system diagrams. It is a terminology reference; do not infer a universal field-forcing percentage or motor-specific design limit from the title alone. | Open source |
| IEEE 421.2, Guide for Testing and Evaluation of Dynamic Performance | IEEE Standards Association; P421.2 revision project status checked 2026-10-17 | The IEEE page describes the active P421.2 revision project and the 2014 edition it will supersede. The guide concerns dynamic performance evaluation of excitation control systems; it is not a source for fixed response times for rotary transformers. | Open source |
| IEC 60034-16-1:2011, Excitation Systems for Synchronous Machines - Definitions | International Electrotechnical Commission | Defines terms applicable to excitation systems of synchronous rotating electrical machines. Use the applicable product and test standards for requirements beyond definitions. | Open source |
| IEC 60034-18-41:2014 + AMD1:2019, Type I Insulation Systems | International Electrotechnical Commission | Sets qualification and quality-control test criteria for Type I insulation systems in converter-fed rotating AC machines. Confirm applicability to the specific winding, converter waveform, and machine design. | Open source |
| ISO 21940-11:2016 + Amd 1:2022, Rotor Balancing | International Organization for Standardization | The base standard specifies balancing procedures, permissible residual unbalance, correction planes, and allocation for rotors with rigid behaviour; flexible behaviour is covered by ISO 21940-12. The ISO catalogue lists Amendment 1:2022. It does not prescribe one grade for every rotor or establish a material speed limit. | Open source |
Answers focus on architecture choices, evidence, and procurement inputs. Requirements vary by machine and customer.
Scope varies. A supplier may provide a rotary transformer, a rotating AC exciter and rectifier, or a larger assembly. Define whether the RFQ includes stationary power electronics, rotating parts, rotor field connections, cooling, sensors, and validation.
There is no universal choice. Compare standstill and low-speed excitation, field power, rotor envelope, cooling, switching electronics, mechanical retention, efficiency, control response, service needs, and validation cost against the motor requirements.
Magnetic coupling itself does not require shaft rotation, but standstill capability depends on the complete source, converter, control strategy, and thermal design. Require a test or analysis for the actual system and operating point.
A prototype demonstrates a particular design under particular test conditions. Supplier qualification also examines production controls, repeatability, traceability, capacity, change management, and customer-specific requirements.
For rigid rotation, a = omega^2 * r, where omega = 2 * pi * RPM / 60 and r is the distance from the shaft axis. This is a kinematic value; it does not calculate stress, fatigue life, or structural safety.
No. It converts the selected G value into a specific-unbalance reference using e = G/omega. Rotor behaviour, mass, application, correction planes, and the agreed standard determine the actual acceptance requirement.
No such universal multiplier is established by the definitions scope cited here. Specify the excitation system performance required for the application and use the applicable IEEE guide and customer requirements to define tests.
It covers qualification and quality-control tests for Type I insulation systems used in converter-fed rotating AC machines. The responsible engineer should confirm that its scope fits the machine, winding, and converter conditions.
Share the speed and overspeed basis, rotor radius and envelope, field voltage/current/power map, duty cycle, temperatures, cooling, interfaces, annual demand, validation needs, and customer-required quality documents. Mark unknown values instead of guessing.
Flow down the requirements from your customer and sector. Verify certificate validity, covered legal entity, manufacturing site, product or process scope, and exclusions. A certificate alone is not evidence that a particular design passes its validation plan.
Ask suppliers to quote a schedule against the same input package, including design review, tooling, material procurement, prototype build, validation, customer approval, and production ramp. Record assumptions and long-lead items.
No. Papers can establish that a research team tested a particular prototype. They do not verify a supplier's current factory, production process, certification, or performance on your design.
Next step
Include the operating map, rotor interface and envelope, duty cycle, temperatures, cooling method, required evidence, annual volume, and target timing. The evaluator can prepare a preliminary summary; engineering should confirm the final requirements.
