Monitoring transformer for its fitness is inevitable to acquire uninterrupted power supply. Maintaining the good working condition of transformer oil protects the equipment from tripping and other failures.
The wellbeing of the transformer is obsolete, if its transformer oil is contaminated, lest the apparatus would bulge or burst in the worst cases. Regular testing of the oil ensures safety and uninterrupted power supply while it serves insulation and cooling of the transformer.
Though all oils are good insulators, vegetable oils and animal fats are not used in transformers since the fatty acids attack fibrous elements used in winding insulation.
When transformer oil comes in contact with atmospheric oxygen it goes through chemical reaction which results in sludge or acid formation and settles in windings of the transformer. The oil deterioration that occurs deprives the insulating liquid of its cooling attributes and leads to expensive repairs.
Oxidation and contamination take a toll on the transformer oil and the sludge settles on the windings to cause more heat and more sludge. Increase in temperature and heat accelerates transformer oil deterioration.
Besides this Dissolved Gas Analysis (DGA) scans for faults like arcing, corona and overheated conditions so that transformer oil acidity removal is exercised.
The transformer oil deterioration is averted by inspecting the oil twice a year with focus on parameters such as dielectric strength, water content, colour, acidity, sludge, flash point, DDA, IFT (interfacial tension) and resistivity of the oil.
At higher temperatures, organic compounds breakdown to form carbon compounds. Besides this, silica gel turns to pink colour from its original blue colour, owing to saturation of moisture and when the gel is not renewed it contaminates the oil.
Besides the above mentioned general tests, Furan testing is conducted once in two years for five years since installation of transformer to detect transformer oil deterioration.
Transformer oil acidity removal is conducted by processes including transformer oil regeneration which involve degasification, dehydration and filtration. The transformer oil deterioration is mitigated by passing the oil through columns which contain Fullers Earth which removes impurities. The Fullers earth is used for approximately 500 times to purify the oil before its expiry. Oil deterioration is removed onsite and the transformer need not be relieved for purification purposes.
The sludge and acid content settled in the windings attack the cellulose and hamper oil circulation in the transformer and affects heat transfer. Transfromer oil acidity removal averts these events.
Besides these, transformer oil deterioration is also prevented by the following maintenance tests that should be conducted every day.
The oil levels in the Magnetic Oil Gauge or MOG of main tank and conservative tank must be maintained in prescribed levels. The silica gel must be monitored for change in colour and replaced when colour is changed. If any leakage is found, it must be promptly sealed.
Transformer oil deterioration can be avoided when transformer has additional film of nitrogen coated on the expansion tank. When the oil expands, the coating expands with it to avoid contact with external gases. In sealed transformers, excess nitrogen is ported to another tank.
Transformer regeneration extends lifespan of the oil and accentuates its insulating attributes.