Second Harmonic Restraint Equation

[appunni]

Sir,
For calculating percentage second harmonic restraint of a transformer differential relay the following equation is used:
%HR = 47.1Idc / (Iac+1.11Idc)
Can anybody give me complete derivation of this equation?

 

[jbartos]

Suggestion: Visit

http://pm.geindustrial.com/FAQ/Documents/T60/GER-3989.pdf

and references therein for more info on the derivation.