RCT Resistance in REF Vk Calculation

In Knee voltage calculation, it is mentioned that resitance of CT is to be considered, however in the REF - high impedance protection, in all there are 4 nos. of CTS atr used (one Neutral & 3 main CTs connected in residual or parallel) . so here how many ct or CTs are to be considered in Vk Calculation & thereby Stabilsing Voltage Calculation.

If only one CT is to be considered then why one? what @ other three CTs (Main) ?

Regards,

sanjay