Everything comes with an expiry date and so the transformer oil! Though your transformer oil doesn’t expire like other things, but it ages and wears with time. Therefore, experts recommend running routine transformer oil purification process to eliminate all contaminants that dilute the purity of the oil and make it unfit for the machine. When a transformer oil ages, it oxidizes and starts to break down. Degradation of oil release acids, peroxides, and aldehydes in the sludge form. This formed sludge affects clellulose insulation, traps heat, and restricts oil flow inside the transformer and causes transformer failure.