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Mobile High Vacuum Oil Purification

Wismer & Rawlings' Field Service Division has over 75 years combined experience in operating Mobile High Vacuum Oil Purification units. The unit effectively and economically reclaims transformer oil or preconditions EHV transformers prior to final in situ oil filling.

The Process

Transformer oil is passed through an inlet pump and heater into a 5 micron inlet filter / separator. From the 5 micron filter the oil passes into a vacuum chamber where water and gases contained in the oil are thoroughly exposed to vacuum by efficient dispersion and removed through a vacuum pumping system. This system consists of a vacuum booster and a back-up mechanical vacuum pump. Purified oil is then passed through a final 5 micron particulate filter by a discharge pump.

Mobile Unit Highlights

The unit was designed and built to ensure the highest degree of reliability and efficiency. Mounted within a 53 foot trailer, the oil purification unit has its own 280KVA on-board generator for complete independent operation in remote locations. It has its own laboratory for oil testing and a complete control room for instrumentation monitoring. A 3000 GPH portable booster pump and an on-board 6500 gallon storage tank rounds out the equipment needed to guarantee a "no-excuse" job on time and to specification.


An excellent application of this equipment is in dry-out and vacuum filling of modern sealed power and distribution transformers and reactors. This is mandatory for all EHV (Extra High Voltage) transformers.

Portable equipment is also used for maintenance of the quality of the insulating system in the older transformers.

The electrical industry uses this equipment in stationary applications for impregnation and vacuum filling of distribution transformers, bushings, and other oil filled apparatus.


The typical performance in a single pass through the Vacuum Purifier is as follows:

  1. Water Removal - from 100 PPM (Parts Per Million) down to less than 10 PPM or from 50 PPM down to less than 5 PPM at oil temperatures from 20-50 degrees C (77 - 100 degrees F) as measured by ASTM Method D-1533 and continuous panametrics hydrometer.
  2. Gas Removal - from fully saturated with air (10 - 12% by volume) down to less than 0.25% by volume as measured by ASTM Method D-2945
  3. Particulate Matter Removal - 99% of particles over 3 micrometers and 90% of particles over 0.5 micrometers to ensure dielectric breakdown value in excess of 40kV as measured by ASTM Method D-877, and 50kV by ASTM Method D-1816
  4. Acidity Correction - with addition of the optional clay filters, the neutralization from 0.3 down to 0.05 mg KOH/g oil as measured by ASTM Method D-974


Operating Flow Rate 1800 IGPH continuous rating, adjustable 0-100%
Heater Capacity 128kW in 160kW steps, Automatically controlled
Temperature Rise 30 to 60 degrees F per Pass through the Processor
Vacuum Pump 171 CFM
Booster Pump 1300 CFM
Mist Eliminator Refrigeration / Condenser unit to virtually eliminate vacuum pump exhaust fumes.
Vacuum Capabilities

500u Maximum during Vacuum Hold Time
1000u Maximum during Vacuum Oil Filling at Full Operating Flow Rate

Onboard Storage Tank 5500 Imperial gallons. Temporary storage during repairs or for off-loading Road tankers to reduce demurrages.
Onboard Generation 200kW Diesel Generator for remote site or plant outage type operations.
Continuous On-Line Instrumentation
  • Dewpoint
Doble HVD-10 moisture in oil sensor monitors dewpoint of incoming oil, outgoing dehydrated oil, and dewpoint of the vacuum in the transformer during vacuum hold time and vacuum oil filling procedures.
  • Vacuum
Hastings Model VT-4 monitors vacuum of the degasification chamber and the transformer tank during vacuum hold time and vacuum oil filling procedures.

Technical Electrical Field Service Support
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