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| Transformer phase angle error |
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| Kleinstein:
There can be a valid point in using a transformer to couple the line signal. One is if one wants to keep it isolated from the grid and does current measurement with a current transformer or Rogowski coil anyway. The 0.4 degree measurend phase angle sounds perfectly plausible for a EI core transformer. Using the 230 V windings helps to keep the magnetizing current low. With a ring core type transformer one can expect even better values, though usually at a higher price. It might still be worth looking at, as the ring core type could be lower power rating (e.g. 3 VA instead of 5 VA). How stable the phase shift is, likely depends on the magnetizing current, as the resistance would not change much. The magnetizing current could change with mechanical stress on the transformer core and if the small residual air gap in an EI core changes. Another possible factor could be DC on the grid, that shifts the magnetization out of center. Even if the winding number it not accurate between transformers, it is stable over time. |
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