well i dont know about oem not a test person but ive done some testing the trip is selected to the know mismatch of the secondary currents and to diff relay plus a safety margin example 10 to 15% this helps offset a mistrip by normal inrush of everyday loads or error at normal current issues .lets say max at 3%at 20 times normal current at a ratio of 10% plus or miunis but our settings were given to us by a engineer from factory or spec for that diff relay and that switchboard so theres no set standard ,he makes adjustments and if test fails his settings for test he makes adjustments per test or that meaning that tested gear and test set used , example we inject current into each current input with test circuit and test set used star side of transformer to 1.73 times of ld1 on delta side its 1.0times ld2 but writing this out is a night mare , ther is some on this site who maybe able to help you better iam trying to help but theres not enough space on this page , most of our testing is new stuff but we do it under load and also we do a real injection current test with load high current injection bank transformer backfed / timed test / to check micro seconds of trip points , a b cof each phase its a lot of test explaining try and get a book on diff relay testing it would be much simpler to explain to you as i have done on most of your post but we never get a answer back , you must be a qualified electrician to just asked these questions, give me some input on a return post do i make sense let me know if this helps ,take care best to ya[ brain explain this for me]
Differential protection testing of a three phase Power T/F
Linear Mode
