Grid Impedance Ratio and Short Circuit Ratio (SCR)
Normally the power grid or utility system consists of many machines and high-power renewables that are interconnected with transmission and distribution systems. Knowing the system strength is very important for the power grids when the high-power renewables (like wind or PV plants) are interconnected with the network to avoid stability related issues. The strength of the power grid can be defined by the short circuit ratio (SCR) and grid impedance (or X/R) ratio.
1. Grid Impedance (X/R) Ratio
The grid impedance or X/R ratio is the ratio of equivalent inductive reactance (XS) to the equivalent resistance (RS) of the system. The X/R ratio indicates the characteristics of the power grid. The impedance of the network (Zs) and X/R ratio are given by,