Abstract: Refurbished or newly constructed utility-scale turbo-generator rotors requires stringent acceptance testing before commissioning and subsequent operation thereof. Conventional methods of testing are inadequate in detecting and locating thermally induced problems. This paper presents a thermographic method for carrying out thermal instability testing of generator rotors. An experimental setup is used to map the thermal distribution of the generator rotor. Implementation and testing of the method is carried out in a laboratory setting using a down-scaled turbo-generator rotor