The main role of external resistor in high impedance REF circuit is expansion of available protection setting range for suitable setting selection and increasing of protection stability against out of zone earth fault which can be caused CT saturation regarding probability variation wide of used current transformers characteristics. Indeed the prime task in REF high impedance calculating settings is to calculate the value of the stabilizing resistor Rstab and stability factor K. A stabilizing resistor is required to ensure through fault stability when one of the secondary CT