How to calculate restraining quantity in Differential relay during testing

Here I'm providing the equation for calculate restraining quantity in differential relay.

%restrain= I diff setting + (I1 * CT1 error) + (I2 * CT2 error)

I diff setting=Differential setting in relay(ex. 0.2Amp)

I1=Current injected in CT for 1 end relay for testing

I2=Current injected in CT for 2 end relay for testing

Ct error=5%(if injected current <1) OR 15%(if Injected current >=1)

During testing we found Ij1=Ij2, because generally same current is seen during fault bay both end relay

Case-1

Injected current=1Amp,I differ setting=0.2( Assume CT error 15% when Injected current >=1)

%restrain= I diff setting + (I1 * CT1 error) + (I2 * CT2 error)

=0.2 +(1 * 0.15) + (1 * 0.15)

=0.50

%restrain =50%(around)

Case-2

Injected current=0.5Amp,I differ setting=0.2 ( Assume CT error 5% when Injected current <1)

%restrain= I diff setting + (I1 * CT1 error) + (j2 * CT2 error)

=0.2 +(0.5* 0.05) + (0.5 * 0.05)

=0.22

%restrain =22%(around)

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