Mositure ingress in free breathing transformers

This paper determines the moisture ingress in free breathing transformers by analysis of on-line monitoring data and by laboratory measurements. A grid transformer, a transformer equipped with a heat recovery system and a generator step-up unit served as example transformers. Approximately 1,6 kg of water enter the large grid transformer having moderate temperature changes. The transformer with the heat recovery system suffers from rapid temperature changes, thus approximately around 16 kg/a increase its moisture concentration. The constant load of the generator step-up transformer let nearly no water contaminate it. Laboratory investigations on dehydrating breathers proofed the drying capability of these systems. They achieve at average volume flows a drying efficiency of 99 %. To conclude, the water mass entering transformers strictly depends on the operation mode and breather condition of the specific transformer.