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Recent content by Alex68

  1. Alex68

    Generator Neutral Arrester

    During start up with SFC, Siemens usually isolated the neutral from grond to avoid harmonics flows and improper trip of protections. In this condition, the surge arrester protects against overvoltages Regards Alex
  2. Alex68

    Photovoltaic power plants: inverter controls

    Thanks Redfurry I asked several manufacturers in my country but I had only the possibility to speak with commercial people. It seems that nobody have made power system studies including PV systems and asked similar questions. Thank you
  3. Alex68

    Photovoltaic power plants: inverter controls

    Dear all, sorry for the long post. During the design of two big photovoltaic power plants, the first one connected to the national HV grid and the second one isolated, manufacturers of inverters were not able to give some answers about the behaviour of their devices in steady state conditions...
  4. Alex68

    CTs knee-point voltage for 6.6 kV motor feeder

    Every time a small motor is fed by Medium Voltage, the difference between the rated current and the fault current is huge. In case of fault, the saturation of the CT used for "normal" currents is required and desired to avoid the destruction of the protection by the extremely big secondary...
  5. Alex68

    Neplan

    Don't worry. You are welcome
  6. Alex68

    Neplan

    Neplan can import dxf drawings as background images and not as a first step of grid modeling. You can use this image to build over it your grid model. In this way you can obtain that your components have the same positions as in your drawing. DXFs are only graphical objects. That's all. Alex68
  7. Alex68

    Reverse power trip on a gas turbine

    What is the setting of the function 32? Maybe it was set to trip if the P is ... less than +5%_+10%? Maybe it was set like a heavy duty turbine, where if the produced active power is zero for a long time, then something is wrong. Alex68
  8. Alex68

    MV bus short circuit I

    I think that 35kA (for 1s or 3s) is the rated short-time withstand current of the switchgear Alex68
  9. Alex68

    GE Frame 9 Gas Turbine

    Typical impedances for IEC transformers are: 500 kVA Vsc = 4% 132 MVA Vsc = 12...13% So please review your calculation with these values. Alex
  10. Alex68

    Vector of an old transformer

    Thank you guys. You confirmed my suspects. I asked for the photo of the faceplate. Thank you again.
  11. Alex68

    Vector of an old transformer

    Dear Collegues, I'm dealing with an old transformer, dated 1970, whose ratio is 10 / 0.4 kV. The vector group is indicated as ynD11. This is new for me. Is it equal to Dyn11? What is the connection of the primary winding: yn or D? Thank you for you help. Cheers Alex
  12. Alex68

    Tap Changer and C37-13

    Thank you
  13. Alex68

    Tap Changer and C37-13

    Thank you, DPC. I suppose that 1.03 p.u. is your practise but it isn't imposed by the Std. What about the OLTC?
  14. Alex68

    Tap Changer and C37-13

    Dear all, this is my first time using ANSI C37-13 to calculate short circuit currents at generator terminals. I reading the std, the example of the annex A in particular, I noted that the calculation procedure does not consider the possibility that the tap changer of the step up transformer is...
  15. Alex68

    Active filter and cable sizing

    Thank you for your answers. Some data: Filter: Connection voltage is 600V. Rating is 4*900A rms. Harmonic current is mainly 5th but this can change and what we need is a general purpose rating method that can be adjusted to almost what ever combination of harmonic loads the operators dial up...
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