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by Dr Stan Zurek

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loss_angle

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loss_angle [2021/10/19 23:50]
stanzurek [1. Set dummy model] 		loss_angle [2021/12/20 23:16] (current)
stanzurek [1. Set dummy model]
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 === 1. Set dummy model === === 1. Set dummy model ===
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 Set up a simulation, in which a block of this material is magnetised in a uniform way, in the whole volume (e.g. thin sheet in a closed yoke). For ferrites this is easier, because eddy currents can be mostly neglected and the conductivity can be set to zero, so almost any shape will do. For conductive materials this is more difficult, because the sample has to be very thin so that the eddy currents are negligible. It is advised to set this up as a very thin lamination, for instance with the thickness less than 10x the skin depth (see also: https://www.e-magnetica.pl/skin_depth) Set up a simulation, in which a block of this material is magnetised in a uniform way, in the whole volume (e.g. thin sheet in a closed yoke). For ferrites this is easier, because eddy currents can be mostly neglected and the conductivity can be set to zero, so almost any shape will do. For conductive materials this is more difficult, because the sample has to be very thin so that the eddy currents are negligible. It is advised to set this up as a very thin lamination, for instance with the thickness less than 10x the skin depth (see also: https://www.e-magnetica.pl/skin_depth)
  
-A good geometry is a very thin cylinder (toroid), excited with a single turn of primary winding, inside the cylinder. A ratio of outer diameter to inner diameter OD/ID < 1.1 (like a pipe with a fairly thin wall) guarantees uniform magnetisation, which is important.+A good geometry is a very thin cylinder (toroid), excited with a single turn of primary winding, inside the cylinder. A ratio of outer diameter to inner diameter OD/ID < 1.1 (like a pipe with a fairly thin wall) guarantees uniform magnetisation, which is important. 
  
-=== 2. Run dummy model === +^  Download  ^ 
-Set this dummy model such that the flux density in the material is close to the operating point in question, obviously at the required frequency.+|  **You can download a FEM example here: {{loss_angle_example.zip}}**  |
  
-Use the block integral, and calculate ''Total loss density'' which will give a numerical value in W/m<sup>3</sup>. +The dummy model should be set such that the flux density is uniform. As shown in Fig. 3 this can be done with the toroidal sample, with the magnetising winding positioned exactly at the centre. There is no need for the returning wire of the coil.
  
-Even if conductivity is set to some non zero value, this number should come very low (see next points).+{{loss_angle_example.png?500}} Fig. 3. Dummy model of a "thin toroid"  
 +=== 2. Run dummy model === 
 +Set this dummy model such that the flux density in the material is close to the operating point in question, obviously at the required frequency. In this example, we assume B = 1.0 T and P = 1.5 W/kg
  
-=== 3. Loss value ===+== 2a. Loss value ==
 Get the real loss value (e.g. from the manufacturer's datasheet) and convert it to a value in W/m<sup>3</sup>. If the value is specified in W/kg this can be converted to W/m<sup>3</sup> by using the density //D// of material which is given in kg/m<sup>3</sup>:  Get the real loss value (e.g. from the manufacturer's datasheet) and convert it to a value in W/m<sup>3</sup>. If the value is specified in W/kg this can be converted to W/m<sup>3</sup> by using the density //D// of material which is given in kg/m<sup>3</sup>: 
  
 $$ P_{W/m^3} = P_{W/kg} · D_{kg/m^3}$$ $$ P_{W/m^3} = P_{W/kg} · D_{kg/m^3}$$
  
-=== 4. Check for eddy currents ===+For example, if the target loss is 1.5 W/kg and the material density is 7650 kg/m<sup>3</sup>. Therefore, the **loss density** is 1.5 * 7650 = **11775 W/m<sup>3</sup>**. This is the target value to be achieved in the dummy simulation. 
 + 
 +== 2b. Set B  == 
 +Adjust the current (by trial and error, or better by scaling of the current by the error in B) in the magnetising wire until B is exactly 1.0 T. The value of B is to be measured (left mouse click, with the grid snapping disabled) at the point indicated by the black arrow in Fig. 3. 
 + 
 +== 2c. Set loss == 
 + 
 +Use the block integral, and calculate ''Total loss density'' of the dummy sample which will give a numerical value in W/m<sup>3</sup>.  
 + 
 +Adjust the value of loss angle (trial and error, etc. starting for example with a value of 1 deg) until the loss density is the same as the calculated target value (11475 W/m<sup>3</sup> in this case). 
 + 
 +Check the value of B, because it could change slightly. If it does, then just repeat the steps in another iteration (first adjust the current to set the B, then adjust the angle to set the loss). 
 + 
 + 
 +  * Note, if conductivity is set to some non zero value, the loss value should be very low (if eddy currents are negligible). With the conductivity enabled, it is likely to see B changing with added loss angle. If this is the case, just go through several iterations of setting current and loss angle until B = B<sub>target</sub> and P = P<sub>target</sub>.  
 + 
 + 
 +=== 3. Eddy currents in non-laminated materials ===
 Use the values of loss in W/m<sup>3</sup>. Use the values of loss in W/m<sup>3</sup>.
  
 With the loss angle set to zero, for very thin sample the loss should be very small compared to the real value (e.g. less than 5%). If it is not then the sample must be made thinner, to further reduce the eddy currents. With the loss angle set to zero, for very thin sample the loss should be very small compared to the real value (e.g. less than 5%). If it is not then the sample must be made thinner, to further reduce the eddy currents.
  
-=== 5. Compare losses === +The exception is if the material is set as laminated in its settings, because then they can be used with the default conductivity, with any thickness, because the "laminating" approach takes care of homogenisation of properties.  
-With the point above satisfied, set some arbitrary value of the ''loss angle'', e.g. 1 degree. Run the dummy model, extract the loss density, and compare with the target real value. + 
 +=== 4. Additional comments ===
  
 If the simulated loss is smaller than the target value, then increase the loss angle.  If the simulated loss is smaller than the target value, then increase the loss angle. 
loss_angle.1634680200.txt.gz · Last modified: 2021/10/19 23:50 by stanzurek

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