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  1. Lucas_Sterquino

    Transformer impedance

    Hi mate, Every design is unique and has to be addressed on its own terms. My advice is to observe the power system distribution topology and its impedances, and ensure that the fault levels at the load terminals are within acceptable levels - which depends on the load: motors, IT racks, general...
  2. Lucas_Sterquino

    Questions regarding transformer's percent impedance in other than nominal voltages

    Hey mate, two things to consider: 1) I think there are CT testers in the market that you could use to confirm polarity and CT ratings. Generally, the differential protection could be triggered and tested through secondary injection or use a proper tester and running the cables through the CTs...
  3. Lucas_Sterquino

    Per Unit Impedance 3 Winding Transformer for simple fault current calculation

    Hi @Wfg42438, The impedances Zps, Zst, and Zpt are obtained though a short-circuit test as you explained: - Zps: Voltage applied on primary, secondary is shorted, tertiary is open. Therefore, Zps is the impedance between primary and secondary. - Zst: Voltage applied on secondary, tertiary is...
  4. Lucas_Sterquino

    Transformer impedance indexed to k-rating

    Hi @electricuwe and all, after debate with manufacturer I find out the issue. In order to deal with the additional heat coming from the harmonics, the transformer was oversized. The manufacturer then used the transformer oversized power to calculate the impedance at k=8. This approach was...
  5. Lucas_Sterquino

    Transformer impedance indexed to k-rating

    Hi Waross, You are right, but in this case the impedance is specified to be on the AN mode (from right to left - second column is the project requirement, first column is the manufacturer answer). I honestly don't understand this answer from the manufacturer. Constructively speaking, if the...
  6. Lucas_Sterquino

    Transformer impedance indexed to k-rating

    Thank you for the reply, @Gr8blu. The change in the impedance from 7.5% to 6.6% is really impacting the fault levels downstream. Despite theoretically possible as you explained, when I look at the specification (6.6% @ K=1, 7.5% @ K=8), constructively speaking, I see two different transformers...
  7. Lucas_Sterquino

    Transformer impedance indexed to k-rating

    Hi everyone, I have specified a transformer to have 7.5% impedance and k=8. I received a datasheet from the manufacturer with following information: Transformer impedance - 6.6% @ K=1; 7.5% @ K=8 It is the first time I see a transformer impedance indexed to the k-rating factor. Have some of...

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