Transformer Oil Maintenance

Energy transformers are critical components of the energy distribution grid and it is therefore important to have a monitoring and maintenance plan in place to preempt their failure. One of the critical components of an energy transformer is the transformer oil.
A transformer operates in a moisture free environment and even the slightest moisture can seriously reduce its life. Most companies have an oil maintenance schedule to monitor the condition of oil and detect a problem before it causes extensive damage. Oil testing during maintenance also helps detect problems like contact arcing, aging insulating paper and other latent faults.
Steps for Collecting Oil Sample for Transformer Oil Testing:
Oil testing is a critical process it can be done before the transformer start-up, during a routine transformer inspection or in any circumstances indicating possibility of damage to the transformer, particularly when a protective device is triggered.
To collect an oil sample a sampling valve located near the bottom of the tank is used. Transformer oil is a hygroscopic substance and must be protected from contact with moisture. It is therefore important to place the collected oil sample in a clean dry container.
Oil Treatment Guidelines
Following are the oil treatment guidelines which can prolong the life of transformer and save a company thousands of dollars:
  • Purify when the acid level is still low, i.e. <0.1 mg
  • Regenerate preferably from 0.1 mg KOH/g oil to avoid precipitation of sludge
  • Desludge when the acid level is >0.20 mg KOH/g oil
  • Dry-out when the solid insulation is wet >3.5 % MDW
Purification, a method of transformer oil maintenance
Purification is the process by which moisture and gasses are removed from the insulating oil. This process readily dries up the oil but not the insulation system, this is because the drying depends on the rate of diffusion of water through the paper into the oil, which is slow. Frequent processing is necessary to attain the degree of dryness desired in the cellulose insulation.
Even though the purification method is not the best, it is an effective moisture management tool. It is used widely in the industry to effectively reduce the moisture content and elevate the dielectric strength of the oil in wet core situations.
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