I'm working on power system simulations with a 1 MW transformer (20 kV / 400 V). I'm having difficulty accurately determining the appropriate grid rated power and short-circuit power, which significantly influence my short-circuit analysis results. Could you share how you typically estimate these parameters and what the main challenges are in representing these values accurately in your simulations?
The short-circuit power indicates the grid's fault current capability at the point of connection. In contrast, the grid-rated power in ETAP power system simulations is usually the nominal power of the utility or upstream source supplying your system. For your 1 MW (1 MVA) transformer (20 kV/400 V), if utility data is not available, you can estimate short-circuit power using standard assumptions: a strong grid might have S_sc=100MVA or more at 20 kV. Using the formula Z_TH V^2/S_SC= 4 ohms. This impedance can then be entered as the equivalent source impedance in ETAP. As an alternative, utilize ETAP's "Short Circuit MVA" setting at the utility bus or define the Thevenin impedance explicitly. The primary issue is that even little variations in the anticipated short-circuit MVA can have a significant impact on fault current estimates. To ensure resilient system design, conduct a sensitivity analysis using varying short-circuit levels (e.g., 20–100 MVA) if precise utility data is not available.
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