1. Stop the transformer in operation and take safety measures such as power outage and locking; 2. The transformer oil used must meet the standards and should be checked for quality assurance; 3. Electrical test reports should be reviewed; 4. After refueling, it is necessary to let it sit for a period of time before putting it into operation, and observe for a period of time after putting it into operation.

Regarding the issue of mixed oil in transformer oil, the national standard GB/T14542-2017 shall prevail, and the excerpts are as follows:

When electrical equipment needs to be refilled due to insufficient oil filling, oil products of the same oil base, brand, and additive type should be added. Unused transformer oil that meets the GB2536 standard or used transformer oil that meets the GB/T7595 operating oil quality standard should be selected, and the characteristic indicators of the refueling product should not be lower than the oil inside the equipment. When there is a large amount of oil replenishment (greater than 5%), a sludge precipitation test of the mixed oil should be conducted before refueling to confirm that there is no sludge precipitation, acid value, and medium loss factor lower than the oil in the equipment before refueling.

3. Oils with different oil bases, grades, and additive types should not be mixed in principle. In special circumstances, if different grades of new oil need to be mixed for use, the suitability for use in the region should be determined based on the measured pour point of the mixed oil (the pour point should refer to the pour point index of GB2536 New Transformer Oil), and then an open cup aging test should be conducted according to the DL/T429.6 method. After aging, the mixed oil should have no oil sludge precipitation, and the acid value and dielectric loss factor of the mixed oil should not be worse than the worst single oil sample.

4. If different grades of new oil or used oil are mixed into the operating oil, in addition to measuring the pour point of the mixed oil in advance (the pour point should refer to the pour point index of GB2536 New Transformer Oil), the following requirements should also be met:

b) Open cup aging test should be conducted for operating oil, supplementary oil, and mixed oil according to DL/T429.6 method. After aging, the mixed oil should have no oil sludge precipitation, and the acid value and medium loss factor of the mixed oil and supplementary oil should not be greater than the measured results after aging of the operating oil.

When conducting a mixing test, the mixing ratio of the oil sample should be the same as the actual proportion used; If the oil to oil ratio cannot be determined, a 1:1 mass ratio mixture is used for testing

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Data sheet N degree 2-A: Transformer H61 33 kV/400V of 160 kVA