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  • Users: prc
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  1. prc

    3-winding transformer impedance at extreme taps.

    Maximum tap means the highest voltage tap (usually No1 tap), i.e., 483.8/230 kV
  2. prc

    Transformer test report - zero sequence values

    Agree, dpc. When it is not measured, best way to judge Z0 is IEC 60076-8 where all possible connections are covered with approximate Z0 for each case.
  3. prc

    Transformer test report - zero sequence values

    1) When we have test report of Z0 measurement, why we go for assumptions? 2) Zo=8.11 % 3) To me 0.393 seems R0 in %. With 0.393 ohms, I2 R loss will be very high, much more than typical copper loss of such a transformer. 4) So X0= Square root( 8.11 square-0.393 square) = 8.1 % 5) X/R =...
  4. prc

    The floating star neutral to earth voltage in transformer.

    Thank you, Waross and Stevenal. When we say capacitive coupling is the reason for the ghost voltages, can you elaborate a bit more. As I understand, this is power frequency voltage transfer from primary. Being PF why it is not getting adding up at neutral? How the impedance of voltmeter acting...
  5. prc

    The floating star neutral to earth voltage in transformer.

    Thank you waross. What is a Wigginton Voltage tester? Moving Iron meter?
  6. prc

    The floating star neutral to earth voltage in transformer.

    How to explain the capacitive coupling and the reported results? L-E and L-N voltages are almost the same, meaning N and E are at the same potential. Then, how was a more than phase voltage measured between N&E? Since phase voltages are equal, a neutral inversion is ruled out.
  7. prc

    The floating star neutral to earth voltage in transformer.

    In a 131/11.5 kV three-phase Dyn Transformer, a balanced 10 kV was applied to the primary, with the secondary neutral floating. The voltages measured on the LV secondary were equal in all phases. The line to neutral voltages were 504 V, the line to earth voltages were 505 V, and the line to...
  8. prc

    Offshore power transformer YNd1 vs YNd11

    As already mentioned, the US follows a Yd1 generator step-up transformer + Dy1 distribution transformer at the consumer end. IEC world follows Yd11 + Dy11 transformers. This is just a practice with no other issues. The voltage vector at the generator and the consumer will be in the same...
  9. prc

    Two winding transformer equivalent from a three winding transformer

    Please refer to IEC 60076-8,, Transformer Application Guide, or the Transformer Book by L.F. Blume for Theory of Multi circuit Transformers
  10. prc

    Fault Current Distribution in a ZNyn1 (22kV/0.440kV) Transformer

    If you are loading a ZNyn transformer with a single-phase load, a stabilising tertiary is a must. Please see the attached link for details. ( last sections) How do Zig-Zag Earthing Transformers work? - Applications - Confluence (atlassian.net) https://rhconsult.tiny.us/2aew4ypn
  11. prc

    Transformer Winding Temperature Indication CT Ratios

    The CT ratio depends on the type of WTI you are using. A popular brand has a secondary rating of 2 A. The transformer manufacturer has taken the rated current of the winding as the primary current of CT. It is not necessary, and typically, a higher CT ratio is used. The same CT is used for all...
  12. prc

    110/33 kV transformer and REFCL for metro line

    What is REFCL ?
  13. prc

    Earthing of neutral point of power transformer

    In MV systems, NGR also reduces the risk from arc flashovers consequent to LG faults.
  14. prc

    Two Winding vs. Three Winding Transformer

    Yes. You can have two secondary windings with equal percentage impedances. In India, we have several 315 and 400 kV transformers with 400/33-33 kV YNynyn units at Solar firms. Some of them have 5-limbed core construction without a stabilising delta winding, In 2021, the Central Electricity...
  15. prc

    Transformer MVA rating IEEE vs. IEC

    1) Transformer overloading standards have changed significantly during the past 30 years. The relevant standards today are IEC 60076-7 ed2.0-2017 & IEEE C57.91-2011 for oil-filled transformers and IEC 60076-12-2008 & C57.96-2013 for dry-type transformers. 2) Manufacturers design transformers for...
  16. prc

    Power Transformer 300/150/150MVA cooling type.

    It is ODAF only without any ONAN. Each cooler of 20-25 % rating will be provided with a standby spare cooler.
  17. prc

    Transformer MVA rating IEEE vs. IEC

    Cucky, as someone who has designed large power transformers according to IEC and IEEE standards for more than half a century, let me confirm that I was making the same cooling circuit regardless of the standard. The temperature rises (oil/winding/ hotspot ) are the same in both standards...
  18. prc

    Transformer MVA rating IEEE vs. IEC

    cuky, as per my under standing, the temperature rise difference between IEC and IEEE is only 2C. The reference ambient temperatures are same. IEC 20 C is the yearly average and not stipulated in IEEE. As per IEC60076-2, the maximum permissible winding hot spot temperature rise is 78 C, over a...
  19. prc

    Power Transformer 300/150/150MVA cooling type.

    The ideal arrangement is ONAN/ ONAF . In case you have any restrictions in foot print, go for ODAF cooled compact coolers.
  20. prc

    Transformer MVA rating IEEE vs. IEC

    Let me disagree. IEC specifies Temperature rises based on max ambient air temp of 40C, monthly average of 30C and annual average of 20C. In case any one or more of the parameters differs from above, temperature rises can be modified as specified in IEC std clause 6.3.2 and table 2. As per...

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