What does the X/R ratio tell us?
In one of our previous posts we have talked about “purely inductive grid”. That is certainly a special case of oversimplification. Keeping it still very simple we may use “resistive-inductive grid”. The relationship between the resistive and reactive component is particularly interesting. What does the X/R ratio tell us? After reading this article you will have an idea.
The X/R ratio tells about the character of the grid impedance. Here we model the grid in a simplified way by series connected reactance (X) and resistance (R). Large X/R means that inductive portion is far more dominant over the resistive part. Vice versa, small X/R ratio points to a significant resistive component. Small resistance means little damping and long time constant.
X/R ratio impacts the frequency characteristic of the grid. The inductive reactance increases linearly with the frequency while the resistance is normally kept constant (of course this is a simplification neglecting the skin effect). Therefore, X/R ratio has certain impact on harmonic distortion. To be fair, in a normal range of X/R between 5.0 and 30.0 the impact on harmonic distortion is almost negligible.
IEC standard uses factor κ (kappa) that is a function of R/X ratio. κ influences the peak short circuit current and therefore the dynamic forces relevant for dimensioning.
How does the short circuit current waveform look like depending on X/R ratio? What does this ratio mean for grid harmonic distortion? How does the X/R ratio impact the drive system dimensioning? What other implications does the X/R ratio have?
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References
[1] What does purely inductive network actually mean? https://mb-drive-services.com/what-does-purely-inductive-network-actually-mean/
[2] How strong is a strong grid? https://mb-drive-services.com/how-strong-is-a-strong-grid/
