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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

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

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...

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...

Don't worry. You are welcome

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

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

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

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

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

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

Thank you

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?

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...

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...

Dear Collegues, I must size the cable of an active filter. This cable has to carry a little 50 Hz harmonic but lots of harmonics in the range 150 Hz to 2.5 kHz. So I can't apply the usual sizing criteria based on the fondamental harmonic and the de-rating factors as indicated in the Red Book...

Dear mnewman, if you consider only the part 0 of the IEC 60909, you can't find an explanation of the correction factor K. Some indications seem to appear from the note at the end of point 3.3.3 but they are misleading. You can find the true explanation in the IEC 909-1 / 1991, even if it is...

Dear Radug, to size a switchgear you need two parameters: Ith = thermal equivalent short circuit current, described at point 4.8 of the IEC 60909-0 / 2001 and ip = peak short circuit current, described at point 4.3 of the same standard. Please don't use the Ik as Ith because they are very...

Thank you Slava

Thanks Alehman, I must do some load flow and short circuit calculations. My concern is about the reactances required by IEC 60909 for the short circuit calculations. At least I need the saturated values of Xd and X"d. Thank you in advance Alex