5 Amps is correct. Probably someone considered the system capacitive charging current around 1,7 A/per phase. So, considered 03 single phase transformers 11000/110 V (ratio 100). Secondary current during bolted ground fault would be 170A under 190V(3 x 11000 /sq3 x100) It means a 1,12 Ohms resistor Safe values for transformers would be 18kVA and 32kW for resistor. Voltage protection relay if installed at broken delta terminals must consider percentage of 190V for alarm and tripping. Limiting the ground fault current to a value slightly greater than capacitive charging current avoids dangerous overvoltages. Max system ground current would be 3 x 1,7A = 5,1 A(remember zero sequence).