This paper explains on how the replacement of the step-up grid transformers at Cruachan power station was achieved with the least impact to the supply. The approach taken was to address a safety issue and minimise the impact of the transformer fault on the overall generation production from Cruachan using a sound engineering assessment of the fault and risk of failure through routine monitoring of the fault through dissolved gas analysis. The result has been to leave the power station with a reduced risk of failure in the future given the ability to have one transformer out of service while generating through the other unit.