Insulating Oil Treatment for Large Converter Stations, Application Case of Vacuum Oil Purifier Unit

Large converter stations, especially those serving high-voltage direct current transmission, contain dozens of converter transformers, smoothing reactors and auxiliary equipment, each filled with a considerable volume of insulating oil. These units operate under demanding electrical and thermal stress, and the insulating oil must maintain high dielectric strength and low gas content to ensure reliable conversion and transmission. During construction, commissioning and long-term service, however, the oil can take up moisture and gas from storage, handling, breathers and internal aging. If these contaminants are not removed before energization or during maintenance, dielectric strength falls and the risk of partial discharge and insulation failure rises. Rigorous oil treatment is therefore a core task at converter stations.

The vacuum oil purifier unit is the standard tool for this work. It draws oil through a heated circulation loop and passes it through a vacuum chamber, where moisture and dissolved gases are removed at controlled temperature and vacuum level. Multi-stage precision filtration then removes solid particles and oxidation sludge, and the treated oil returns to the equipment at the required dielectric, moisture, gas and cleanliness levels. The unit is sized to handle the large oil volumes found in converter stations, with sufficient flow rate to treat a full transformer charge within a practical schedule. Because the process is physical, the base oil and additive system remain intact, so the treated oil retains its service properties.

A typical application case follows a clear sequence. When converter transformers arrive on site, the purifier is used to condition the oil during oil filling and to circulate it through the unit until moisture and gas reach the levels specified for energization. Oil samples are taken at intervals and tested for breakdown voltage, water content, dissolved gas and particle counts, with the treatment continuing until every index passes. The same unit then serves routine maintenance, treating the oil of transformers and reactors during planned outages and after any water ingress or gas increase. This single-unit approach covers both commissioning and long-term care with the same equipment and procedures.

The benefit of this application is measurable reliability. Oil that meets moisture, gas and cleanliness targets provides the dielectric strength needed for stable converter operation, reducing the risk of partial discharge and unexpected insulation failure. Controlled dissolved gas levels also support dissolved gas analysis, the main diagnostic tool for detecting incipient faults, because the baseline gas content is known and low. By keeping all oil-filled equipment within specification, the station reduces unplanned outages and extends the service life of converter transformers and reactors, which are among the most expensive assets in the station.

From a maintenance management view, the vacuum oil purifier unit is practical and economical at station scale. A mobile or permanently installed unit can serve every transformer and reactor on site, shared across the fleet and scheduled around outages. Operation is straightforward for trained staff, and the treatment results are easy to verify through standard oil tests. Because the oil is restored rather than replaced, oil purchase and waste disposal costs stay low, and the station avoids the logistics of moving large oil volumes. The same unit also supports oil filling, hot oil circulation drying and emergency treatment, making it a versatile asset for converter station maintenance.

In summary, insulating oil treatment with a vacuum oil purifier unit is an established application at large converter stations. By conditioning and restoring the oil of converter transformers and reactors on site, it ensures the dielectric and diagnostic quality the station depends on, reduces the risk of insulation failure and lowers the long-term cost of oil and equipment maintenance.