In order to achieve the accurate temperature measurement in transformer

the distributed optical fiber sensor was applied along the windings and iron core

which also meets the internal insulation requirements. On this basis

adopting the scheme of parallel winding of single mode fiber and multimode fiber

and adopting the Brillouin sweep analysis to monitor the strain variation in optical fiber winding in real time

we finally developed a 35 kV oil-immersed self-cooled transformer with built-in distributed optical fiber sensor

and passed the corresponding factory type tests.In the temperature-rise test

the internal temperature distribution was measured

then a three-segment linear correction model（high and low voltage winding hotspots appear at 90% and 80% of the winding height

respectively） and a general formula for hotspot temperature calculation were proposed

and the model was compared with the IEC standard model. This technology can give a certain reference for delicately guiding the transformer economic operation.