Currently i don’t have chance to make the CTs ratio the same, else the solution is to use “low impedance (biased type) differential relay” and my question is how can i change the high impedance restricted earth fault relay to low impedance (biased type) differential relay what is the idea behind? and is it permanent solution I mean how much the power transformer is protected by doing so? can you give me brief things on the difference and similarity of the two protections? thanks inadvance