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Recent content by FPelec

  1. FPelec

    3-winding transformer impedance at extreme taps.

    Hello osizer, Given the voltage ratio, I'm guessing that the transformer is actually an autotransformer (400/230 kV) with a tertiary winding (YNad), and a regulating winding connected to the HV line side. Am I correct? If so, the variation of the short-circuit inductance strictly depends on the...
  2. FPelec

    100 Mvar shunt reactor total power losses

    Hello osizer, our standard 230 kV, 100 Mvar shunt reactors (three-phase units, gapped-core desing, ONAN cooling) have about 175 kW total losses @50 Hz. For 60 Hz units, you have slightly higher core losses per unit of weight, but these are generally compensated by the reduced core weight...
  3. FPelec

    Transmission Line Geometry and Impedance/Losses

    Exactly, bacon4life — that’s the phase arrangement. We call that type of tower “5-phase” because, in IEC overhead line terminology, “phase (of an AC line): designation of any conductor, or bundle of conductors, of a polyphase AC line which is intended to be energized under normal use”...
  4. FPelec

    Transmission Line Geometry and Impedance/Losses

    We have recently introduced a new class of low-impedance towers, called "5F" and characterized by high Surge Impedance Loading (SIL), low EMFs and reduced Right-of-Way (ROW) requirements. These towers are a specific type of split-phase structure that utilizes 5-conductor bundles. For a 230 kV...
  5. FPelec

    Dead tank high voltage circuit breakers in Europe

    I don't believe there are any constraints from the TSO, but in some cases there could be obstacles related to product certification and legal requirements. For instance in Italy, all circuit breakers that involve the use of compressed gas (air, SF6, alternative insulating gas mixtures) must be...
  6. FPelec

    Dead tank high voltage circuit breakers in Europe

    I agree with ema157. The so-called "Hybrid Switchgear" are in practice dead-tank CBS with integrated disconnector / earth switch (they can ALSO include VTs and CTs), and they are widely adopted by european TSOs See, f.i. Hitachi/ABB PASS (up to 420 kV)...
  7. FPelec

    The floating star neutral to earth voltage in transformer.

    As said by waross, I also believe that the star point to ground voltage is due to capacitive coupling between the primary and secondary.
  8. FPelec

    Offshore power transformer YNd1 vs YNd11

    We normally use autotransformers for 230 kV / 69 kV and 400 kV / 135 kV transformers as well. While the advantage is less significant than in 400 kV / 230 kV units, we still find it beneficial.
  9. FPelec

    Offshore power transformer YNd1 vs YNd11

    I agree, there is no difference between Dyn1 and Dyn11. On the other hand, it seems like a strange setup to me. Why not use 400/230 kV and 230kV/66kV autotransformers instead? It would reduce costs and losses, and provide solid neutral grounding for the 66 kV network — which, in turn, would...
  10. FPelec

    Issues with transformer ester oils

    We’ve been using autotransformers insulated with natural ester (from various suppliers) since 2016, with tens of units currently in operation, and we haven’t encountered any major issues. These are typically 400 kV, 250 MVA units. It’s important to note that these transformers were specifically...
  11. FPelec

    Transformer clearance from Oil containment

    Hello 082399, if I remember correctly, IEEE standard 980 recommends that the oil pit extends at least 1,500 mm beyond any part of the equipment filled with oil. IEC 61936-1 reccomends instead that the length and width of the oil pit be at least equal to the length and width of the oil-filled...
  12. FPelec

    GIS Circulating Shell and Grounding Current

    Hello, In GIS installations, currents of similar order of magnitude as those in the phase conductors are induced in the enclosures. These induced currents become larger as the enclosure thickness increases; consequently, they tend to be higher in EHV switchgear. When multiple grounding points of...
  13. FPelec

    Wait to reenergize following lightning?

    Yes, SPAR is Single Phase Auto Reclosing, here is widely adopted on 400 kV and 230 kV lines; it's instead much less common on 150 and 132 kV lines. Our network code prescribes the following: "Automatic Rapid Reclosing (RRA) and Automatic Slow Reclosing (RLA) of transmission lines Automatic...
  14. FPelec

    Wait to reenergize following lightning?

    We normally adopt SPAR, so that the delay for re-energizing a 230 kV line after a lighting / flash over is about 0.5 to 2 s
  15. FPelec

    Voltage given from the secondary of the capacitive voltage transformer

    Each CVT includes an Electromagnetic Unit (EMU) whose primary winding is connected to the capacitive divider and has an output voltage of a few kV. If a CVT is energized from the low-voltage side (i.e., from the secondary winding of the EMU), the CVT will behave as a voltage source with a no...
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