Transformer oil serves dual critical roles as dielectric insulation and heattransfer medium inside power transformers. Over longterm field operation, moisture ingress, dissolved gas accumulation, solid particle pollution and oxidation will degrade oil performance, raising risks of partial discharge, flashover and premature transformer failure. Transformer oil purification is the core maintenance solution to restore oil performance, and it relies on coordinated operation of a vacuum transformer oil dehydrator, transformer oil filtration machine, and supporting testing equipment such as a transformer oil bdv tester to finish standardized oil treatment workflows.
The whole purification procedure starts with oil sampling and baseline testing. Maintenance technicians extract representative oil samples from transformers and run tests with a transformer oil bdv tester following IEC 60156 standards. This device measures dielectric breakdown voltage by gradually raising AC voltage across standard 2.5 mm spherical electrodes until electric breakdown occurs, delivering intuitive data reflecting oil insulation quality. Low BDV readings directly warn operators about hidden moisture, carbon soot or microparticle contamination, confirming whether transformer oil purification is required.
After confirming the necessity of treatment, a transformer oil filtration machine takes charge of multistage physical purification. Take ZJAseries doublestage models as an example: contaminated oil first passes coarse filters to trap largesize rust, metal debris and cellulose fibers. Heaters heat oil to 4565 ℃ to cut viscosity and boost separation efficiency. Then oil flows into the core unit of a vacuum transformer oil dehydrator. Under highvacuum conditions below 80 Pa, both dissolved and emulsified water evaporate into vapor, while dissolved combustible gases including hydrogen and acetylene flash out from oil liquid films. Multigroup fine filter cartridges with 1μm precision further capture microcarbon particles and fine sludge residues. After full circulation processing, treated oil can reach technical indexes: moisture ≤5 ppm, gas content ≤0.3 %, and theoretical breakdown voltage above 70 kV.
Purification work is never completed without posttreatment verification. Processed oil must be retested with the transformer oil bdv tester. Only when repeated test results stably meet project acceptance standards can the purified oil flow back into transformer tanks. Operators should also record vacuum degree, working temperature, filter status and full sets of test data into equipment maintenance files.
Many maintenance teams make the mistake of running filtration cycles without posttest confirmation. Even if the vacuum transformer oil dehydrator and transformer oil filtration machine run normally, saturated filter cartridges or tiny vacuum leaks may leave residual contaminants. Without crosschecking by the transformer oil bdv tester, hidden defects will remain and shorten transformer service life. In modern power asset management, transformer oil purification is not merely equipment operation, but a closedloop system combining mechanical processing and accurate dielectric testing, protecting highvalue transformer assets for power grids, industrial plants and renewableenergy stations.
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