Removing or minimizing acidity content of transformer oil isimportant because acidity hampers the longevity of the oil and causes ageing.Acidity accentuates formation of insoluble deposits or x waves and generates colloids, which mitigate dielectric strength of the insulating material. Controlling acidity improves efficiency and reliability of the transformer oil. Insoluble suspensions caused by acidity mitigates cooling efficiency of the transformer.
When transformer ages, carboxylic acids are formed and theseacids are absorbed by the paper insulation thus initiating the degradation ofthe entire system. Ageing may be divided into three types Pyrolysis (due to heat), hydrolysis (due to water) and oxidation, which are all accelerated by heat, by products, contamination, work overload and voltage waves.
Transformer oil deteriorationoccurs due to overheating, electrical stress, contamination and oxidation. Tinywater droplets and water settled in the bottom of the transformer causes oil deterioration.
When acid content increases its quantity enough to become asludge and oxidation is developed. Oxidation produces low molecular weightacids which hamper or degrade the entire insulation system. High molecular weight acids do not dissolve in the oil and are not that aggressive in oil degradation. As a result, the electric and chemical properties of the insulating oil suffer a setback. To mitigate oxidation, oxygen must be removed.
Oil deterioration is detected byBDV of the transformer oil. The BDV or breakdown voltage of the transformerthrows light on the dielectric attributes which in turn show the moisture content in the oil.
Potassium hydroxide, also known as caustic potash, isemployed for transformer oil acidity removal.When added in transformer oil, it neutralizes the acidity effect. 0.3 milligramof potassium hydroxide is sufficient to neutralize one gram of transformer oil.
When a given amount of alkali is added to the transformeroil, the oil becomes acidic, neutral or alkaline based on the pH valuepreviously existing in the oil.
Transformer oil deterioration isaverted by removal of dissolved gases and moisture in the transformer oil. Adegassing and dehydration chamber is employed for this purpose and oil deterioration is eradicatedwith the help of vacuum pumps which purify contaminated oil which is passed three to five times in the filtration chamber.
Dehydration of transformer oil also removes solid particlesand sludge deposited. The transformer oil acidity removalprocess is complete only when the transformer oil meets standards including OEMand IEC among other equivalent standards.
Transformer oil deterioration isalso mitigated by centrifuging, where centrifuges are used to discriminate dirtfrom the oil. Centrifugation is applied in voltages more than 35 kV.
Oil deterioration is also curbed by employing mineral andartificial adsorbents, which remove water and impurities in the oil. Single useFullers Earth regeneration and multiple use reactivation regeneration enables to restore the ‘new’ or ‘better than new’ status of the transformer oil.
On a concluding note, preventive maintenance, by regular oilsampling and analysis and electrical measurements are important routine whileusing transformers. Such caution averts losses and repairs which could be translated as a part of the profits.
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