Electrical calculations

Electrical design

The electrical design of standard machines based on magnetically equivalent circuits, know-how and measured values is fast and easy to perform. After a rough first dimensioning, the optimization can be carried out with the calculation of different geometry variants and operation points. Developers of large generators prefer to use their in-house program mostly written in Fortran or programmed with Simulink; these have been tuned with measurements results.

The magnetic field of new electrical machines should be calculated with the Finite-Elements Analysis. For the concept of a long motor, these calculations can be made in 2D; E-Cooling is well experienced with the software 2D-FEMM. For a more complex and detailed analysis, the calculations should be made in 3D using a commercial software.

 

 
     Magnetic field of an assynchronous motor
     (© Institute for energy and automation, technical university in Berlin)

Localization of the losses

Losses in electric machines are ohmic losses (winding copper losses), re-magnetization (iron losses) and mechanical losses (ventilation losses and bearing losses); the copper losses are for most designs the largest. The allocation of the electrical losses to the places of production is not a subject of focus during the concept phase; the project members are mostly interested in the values of the total losses and the corresponding efficiency. A good knowledge of the locations of production is however required for temperature calculation.

The copper losses of the stator winding and pole winding can be directly calculated based on the current and the voltage waveforms including skin effect. The magnetic field and iron losses can be analytically calculated based on the Steinmetz equation.

In order to localize the distribution of iron loss densities precisely. It is recommended that 2D calculations of the magnetic field be performed prior to a thermal calculation. If this is not possible then the supplementary losses can be located using formulas available from freely-available literature.

 
  Distribution of the flux density for a machine with pole salients

 

News:
Article about E-Cooling in the
periodical Engineering Edge
(issue 1, volume 2, pages 28-29)
 
SPS IPC Drives 2014
Fair for electrical Automation
2
5.-27 Nov. in Nuremberg, Germany
 

 

Offer untill September 2014 for motors and transformer up to 350 kW:
We offer one 2D magnetic calcaulation for only 900 Euro!

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