Special protection class Current Transformer

[Dhruv_vyas]

PX/ PS class CTs are use for REF protection system. I wan to know that why "Minimum" value for Knee Point Voltage and "Max" value for Magnetizing current is rated / Required for PX class CTs. 

What happen if Rated Imag < 30mA @ Vk/2, and All 3 Line CTs and 1 Ground CT are with different Imag, i.e. 10mA, 15mA, 25mA & 28mA respectively. (Though all CTs Imag value is within rated limit). Is there any effect in application to detect earth fault for Restricted Earth Fault relay?

Same Question for Min value of Knee point Voltage. Why it is minimum value and not fixed.