Short interturn faults and short circuits to ground in the rotor winding of turbo generators are crucial to detect because they can lead to significant operational problems. Identifying short interturn faults early allows for corrective action before the fault escalates to more severe damage. A case study of the QFSN-220-2 generator rotor showed severe short interturn fault between coils 5 and 6 or equal to 20 turns due to a conductive contaminant problem. Short interturn faults have caused localized heating on the rotor winding especially on the spacer block insulation. Conductive contaminants on the spacer block insulation have caused loop current to flow between coils 5 and 6. It has led to spacer block insulation and retaining ring insulation being burnt. This paper discusses a method to detect short interturn faults in the generator rotor through rotor winding temperature monitoring and to estimate the hot spot temperature of rotor insulation due to short interturn faults within a period of time. A rotor temperature rise of more than 10°C during a couple of months before the generator rotor experienced ground fault could be an indication of conductive contaminant existence that causes short interturn fault occurrence. Calculation of the heat absorbed by the spacer block insulation due to loop current within a period of time has proved that the hot spot temperature of the spacer block insulation exceeded the permissible value of the exposed temperature of G11 class F insulation. By this calculation, rotor winding temperature monitoring can be also used to estimate the permissible duration of generator rotor operation with short interturn fault condition. © 2025 IEEE.