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Thermal issues in the design of permanent magnet based electrical motors - QuickField simulation example
36 poles brushless DC motor with NdFeB permanent magnets.
Engineering question
How to find rotor temperature rise in permanent-magnet motors?
Answer
Set up a plane-parallel QuickField Multiphysics problem for a permanent-magnet motor and evaluate rotor temperature rise from computed field results.
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Typical applications
permanent magnet motors, electric motor rotors, traction motor assemblies
Simulation problem
Problem Type
Plane-parallel problem of DC magnetics and heat transfer.
Geometry
Stator
| Name
| Parameter
| Value
|
| Stator internal diameter
| D
| 400 mm
|
| Stator tooth zone external diameter
| DS
| 430 mm
|
| Stator external diameter
| DE
| 446 mm
|
| Stator axial length
| LE
| 300 mm
|
| Rotor
| Name
| Parameter
| Value
|
| Rotor shaft diameter
| DH
| 355 mm
|
| Rotor core diameter
| DN
| 386 mm
|
| Rotor external diameter
| DR
| 398 mm
|
| Rotor axial length
| LX
| 300 mm
|
|
Given
DC motor power P = 12 kW
Voltage U = 600 V;
Speed Nn = 200 rpm;
Torque Mn = 573 N·m;
Insulation class: f (155°C);
Steel power loss (50 Hz, 1.6 T) pf = 5 W/kg;
Air temperature T = 40°C.
Task
Which temperature will afford the magnets under the following working conditions:
Cooling: natural / forced
Load: permanent / periodic (50%)
Results
Rotor final temperature.
|
| Natural convection
Periodic load
| Natural convection
Permanent load
| Forced convection
Periodic load
| Forced convection
Permanent load
|
| Winding
| 335°C
| 375°C
| 142°C
| 155°C
|
| Magnets
| 335°C
| 385°C
| 125°C
| 140°C
|
| Hub
| 342°C
| 395°C
| 133°C
| 147°C
|
One has to keep in mind the use of forced air circulation as a normal procedure. The controller could offer additional options to pose a limit to currents and/or temperatures.