I believe there is an error in this question, if you raise the LTC 10% how do you get a mismatch of 14.2%, if you do I am missing something completely. I come close when you Lower 10% (124.2 KV)
4. Calculate the percentage differential mismatch for an electromechanical relay protecting a 138kV-69kV Delta-Wye 50MVA LTC Transformer with 250:5 CTs on the primary and 500:5 CTs on the secondary, with CT ratio taps on the relay set to 5A on the high side and 9A on the low side, when the LTC is raised by 10%.