Technology / Engineering guide
Wind Generator Cogging Torque & Rotor Start-Up
A rotor beginning to move and a generator delivering usable electricity are separate events. Cogging torque is one possible part of the mechanical behaviour; it is not a complete low-wind performance specification.
Distinguish the torque contribution before naming the cause.
A position-dependent magnetic effect, friction and electrical loading can all appear in a startup discussion. Their evidence and operating boundaries differ.
01 / Cogging
A magnetic preference can depend on rotor position.
In a relevant permanent-magnet machine design, cogging refers to position-dependent torque associated with magnetic interaction between rotor and stator geometry.
In a relevant permanent-magnet machine design, cogging refers to position-dependent torque associated with magnetic interaction between rotor and stator geometry. It can be present without winding current. maxon’s official explanation separates that effect from electrically produced torque ripple.
The definition does not establish a MARSTON cogging value, pole count, slot arrangement or compensation algorithm. Even the documented 50 kW permanent-magnet machine needs its own evidence before a quantitative cogging claim is made.
02 / Friction
Mechanical resistance is a separate contribution.
Bearings, seals and other mechanical interfaces can contribute friction in the actual assembly.
Bearings, seals and other mechanical interfaces can contribute friction in the actual assembly. A torque observation combining several effects is not automatically a cogging measurement. The assessed parts and method need to be stated.
Likewise, a preferred rotor position is not a complete diagnosis of startup resistance. Comparing machines requires separation of the represented mechanical assembly and electrical condition rather than assigning every variation to magnetic design.
03 / Electrical loading
Rotation can encounter a different load after connection.
A generator under a stated electrical loading condition is not the same test boundary as an unloaded machine.
A generator under a stated electrical loading condition is not the same test boundary as an unloaded machine. The connected devices and loading method must be identified when comparing torque or low-speed observations.
An unloaded voltage observation also does not prove usable power. Retain the output boundary, voltage and loading information needed to establish delivered electricity, rather than describing any rotor movement as electrical cut-in.
04 / Acceleration
Net torque and rotational response are linked.
The torque available to change rotation is distinct from an individual resisting contribution.
The torque available to change rotation is distinct from an individual resisting contribution. The assembly’s inertia affects the response to a net torque. A short observation of speed change cannot isolate cogging without the rest of that context.
Use the inertia guide for that separate physical relation. It supplies no actual MARSTON inertia or startup time, and does not suggest altering a rotor to change its response.
05 / Wind events
Low cogging does not establish a cut-in wind speed.
Wind-driven startup also depends on rotor aerodynamics and the state of the complete machine.
Wind-driven startup also depends on rotor aerodynamics and the state of the complete machine. A favourable cogging comparison cannot alone prove the wind speed at which sustained electrical output becomes available.
The documented FD14-50KW 2.5 m/s statement concerns rotor start-up only. It is not assigned to the other models and is not a verified electrical cut-in speed. Keep that distinction when describing a low-speed benefit.
06 / Evidence question
Compare the result that was actually assessed.
A torque record should identify the component, position or speed basis, connected state, temperature and measurement method.
A torque record should identify the component, position or speed basis, connected state, temperature and measurement method. A system-startup record instead needs the wind and equipment-state context. These records should not be presented as interchangeable tests.
No shaft-turning, unloading or controller-tuning procedure is provided here. Use existing authorised evidence and the operating-speed guide to define the claim under discussion.
Continue the review with Wind Rotor Inertia, Acceleration & Rotational Energy.
Continue the review with Wind Generator Losses & Efficiency Maps.
Continue the review with Wind Generator Bearings & the Mechanical Load Path.
General background: maxon: Distinct cogging and electrically produced torque effects. 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 |
|---|---|---|
| Effect identity | Cogging, friction or electrically produced torque | Name the quantity correctly. |
| Assembly scope | Component versus assembled rotor/generator | Avoid mixed measurement boundaries. |
| Electrical state | Connected devices and loading basis | Compare equivalent conditions. |
| Measurement basis | Position/speed, method and temperature | Interpret a quantitative claim. |
| Start-up event | Wind reference, motion and output observations | Keep motion distinct from delivered power. |
Engineering questions.
Is cogging the same as bearing friction?
No. Magnetic position effects and mechanical friction are different contributions.
Does no winding current mean no cogging?
Not in every relevant machine design; cogging can be present without current.
Does low cogging prove low-wind electrical output?
No. Rotor aerodynamics, machine state and electrical loading still matter.
Is every torque ripple caused by cogging?
No. Electrical production and other effects need separate identification.
Does 2.5 m/s apply to all models?
No. It is a documented 50 kW rotor-start-up statement only.
Can I use this guide to tune compensation?
No. No compensation capability or adjustment procedure is established.
Technical enquiry
Bring your project information to the discussion.
A rotor beginning to move and a generator delivering usable electricity are separate events. Share the available information and the equipment scope you want reviewed in a technical quotation.