Vacuum oil treatment plants for the full transformer oil lifecycle.

Single- and double-stage vacuum oil treatment plants across five standard throughput classes: 500, 1,000, 2,000, 4,000, and 6,000 l/h, each infinitely variable through VFD control. Transformer oil handling from 2 m³ (500 l/h class) through 30 m³ (6,000 l/h class) per single pass, engineered for fully automatic, unsupervised operation.

Every unit is bespoke-engineered around the transformer condition, dielectric target, and site requirement. Heating capacity, vacuum system capacity, ultimate vacuum, filter fineness, degasser configuration, and process automation are scaled and specified to the application, whether that means a compact 500 l/h field unit for MV distribution transformers or a 20,000 l/h factory production system for extra-high-voltage transformer manufacturing. High-purity application-engineered systems reach residual moisture down to 1 ppm, residual gas down to 0.01 vol%, and breakdown voltage up to 100 kV for EHV production and commissioning.

Every unit is available in three physical configurations: movable (T: sturdy base frame for crane or fork-lift transport), mobile on rollers (R: workshop or plant-floor mobility), or mobile on trailer (H: road-licensed with aluminium casing or tarpaulin for public-road transit and field deployment).

Optional automatic Fuller's earth filtration and oxidation-inhibitor addition equipment (200 to 1,500 l/h throughput) for regeneration of aged transformer oils, integrated with the primary treatment plant.

Optional integrated quality-control devices for continuous on-line supervision: residual gas content meter (10 to 0.01 vol%), residual moisture meter (down to 1 ppm), and insulating oil testing apparatus (0 to 75 or 0 to 100 kV, programmable to VDE, IEC, ASTM, UTE, or CEI standards) with automatic release / interruption of oil supply based on measured dielectric strength.

Oil is heated and distributed across tower packings inside a vacuum degasser, presented in thin films so gas and moisture release efficiently under vacuum. This is the core purification mechanism across the AP range and delivers the specified residual gas and moisture values in the fewest passes.

Indirect electric hot-water heating raises oil temperature without direct contact with heating elements, eliminating the risk of thermal cracking, carbonisation, and premature oil ageing associated with direct-heater systems.

Two feeder pumps deliver defined supply and discharge, with throughput infinitely variable through frequency-controlled drives. Feeder rate matches the source and destination equipment without operator intervention.

Coarse filtration with magnetic separator inserts captures ferrous particles including tap-changer wear debris. Fine filtration to 1 μm with differential-pressure supervision generates a filter-change output signal before pressure loss compromises throughput.

Filtering and degassing the oil alone does not dry a wet transformer. Over 99% of the moisture in an in-service transformer sits in the solid cellulose insulation (paper and pressboard), not in the oil. A 300 MVA transformer at 3% moisture can hold approximately 300 litres of water in the solid insulation versus less than a litre in the oil itself. Removing that water is the actual dry-out job. Dry-out methodologies include hot-oil circulation, hot-oil-plus-vacuum, hot-oil-plus-vacuum-plus-hot-oil-spray, and low-frequency heating (LFH) with hot oil spray. Each requires sustained high oil temperature and vacuum capacity applied directly to the transformer tank, and each is bespoke-engineered to the tank volume, initial moisture, and dry-out target.

Drying a wet transformer from 3% down to 1% moisture in the solid insulation can extend transformer life by approximately 20 years, one of the highest-value maintenance actions available on an ageing transformer fleet. Reaching a vacuum of 1 mbar accelerates moisture diffusion by 10 to 20 times, and every 10 °C rise in drying temperature roughly doubles the diffusion rate; both drive how heating and vacuum systems are sized for a given transformer. Target end-of-drying moisture levels for our supplied units align with widely accepted industry criteria: 0.7 to 0.8% remaining moisture for critical applications (HVDC, GSU, grid transformers above 220 kV, rectifier and furnace duty) and 1.0 to 1.5% for standard grid applications.

Variable frequency drive control on the feeder pump delivers infinitely adjustable throughput across the full 1,000 to 6,000 l/h range. Siemens PLC and HMI touchscreen platforms provide fully automatic operation with anti-spray protection, low-liquid-level shutdown, leak detection through an oil-collecting tray with float switch, and remote diagnostics via VPN or Siemens SIMATIC connectivity for factory support without an on-site engineer.

Higher-specification units are provided with direct transformer tank vacuum drying capability, allowing the treatment plant to evacuate and dry the transformer tank during on-site commissioning without the need for a separate vacuum system.

Equipment supplied through Delstar can be specified with ISO 12944 C5 or C5M coating and SS316 external hardware for coastal, marine, and Pacific-island installations, matching the corrosion class used across our transformer and switchgear supply.

Plants are engineered for fully automatic, unsupervised operation with leakage alarms, luminous-circuit-diagram operating-state indication, and low-noise emission. Reduces on-site personnel requirements during oil filling, regeneration, and commissioning.