Monitoring transformer for its fitness is inevitable toacquire uninterrupted power supply. Maintaining the good working condition oftransformer oil protects the equipment from tripping and other failures.
The wellbeing of the transformer is obsolete, if itstransformer oil is contaminated, lest the apparatus would bulge or burst in theworst cases.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 andanimal fats are not used in transformers since the fatty acids attack fibrouselements used in winding insulation.
When transformer oil comes in contact with atmosphericoxygen it goes through chemical reaction which results in sludge or acidformation and settles in windings of the transformer. The oil deterioration that occursdeprives the insulating liquid of its cooling attributes and leads to expensive repairs.
Oxidation and contamination take a toll on the transformeroil 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 faultslike arcing, corona and overheated conditions so that transformer oil acidity removal isexercised.
The transformer oil deterioration is averted by inspecting the oil twice a year withfocus 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 formcarbon compounds. Besides this, silica gel turns to pink colour from itsoriginal 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 isconducted once in two years for five years since installation of transformer todetect transformer oil deterioration.
Transformer oil acidity removal isconducted by processes including transformer oil regeneration which involvedegasification, dehydration and filtration. The transformer oil deterioration ismitigated 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 onsiteand the transformer need not be relieved for purification purposes.
The sludge and acid content settled in the windings attackthe cellulose and hamper oil circulation in the transformer and affects heattransfer. Transfromer oil acidity removal averts these events.
Besides these, transformer oil deterioration isalso prevented by the following maintenance tests that should be conductedevery day.
The oil levels in the Magnetic Oil Gauge or MOG of main tankand conservative tank must be maintained in prescribed levels. The silica gelmust 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 canbe avoided when transformer has additional film of nitrogen coated on theexpansion 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 extendslifespan of the oil and accentuates its insulating attributes.
