The length of a transformer’s service life is determined by the service life of its insulation system. If the insulation fails, the transformer fails.
Transformer insulation is made up of two components: (1) a liquid insulator known as transformer insulating oil; and (2) a solid insulator made up of Kraft paper and other cellulose material. As much as 80% of a transformer’s insulation protection however, is provided by the insulating oil. The insulating oil can be either changed, purified, or regenerated, but the solid insulation must last the entire service life of the transformer. Transformer Preventive Maintenance therefore, is vitally important to the life of your transformer.
Industry statistics reveal that approximately 85% of transformer failures are caused by insulation system malfunctions and failures. Bad insulating oil will lead to degradation of the insulating paper and ultimately to catastrophic transformer failure.
Transformer oils are designed to maintain and increase the dielectric strength of the insulation material in the windings. This is possible as a result of the permeation of oil into the solid insulation materials such as the paper, fabric, and cardboard that make up the solid insulation section of the transformer.
Due to its low viscosity, transformer oil is able to enter and flow through the solid insulation and also serves to dissipate excess heat by transferring the heat to the cooling system as it flows in and out of the solid insulation.
Degradation of transformer oil performance is caused by aging due in part to a process called oxidation. This process occurs in transformer oil even in the most ideal of conditions. As soon as oxygen and water enter the oil, the oxidation process begins and is unavoidable. The insulating oil’s condition is also influenced by various solid particles known as particulate matter that enter into the transformer and become suspended in the oil. Reactions between hydrocarbons, water and oxygen are significantly accelerated in higher temperatures which causes oil to decay or oxidize. Oxidation cannot be stopped entirely, but it can be slowed significantly by oil treatment.
An annual oil check known as “Oil Analysis” is one the best tools for transformer preventive maintenance. Special analysis of the oil will alert the operator to the condition of the oil and will tell him when to service the transformer. Oil analysis can also indicate the overall health of the insulating paper. A well organized oil analysis program provides the best way to monitor the acid number of the insulating oil and enable the operator to perform preventive maintenance before the contaminates in the oil become overly aggressive against the insulating paper.
A good preventive maintenance program should include purification and regeneration of transformer oil as opposed to merely changing the oil. The main objective of preventive maintenance is the removal of oil aging products (contaminates) from the oil and the solid insulation before they cause damage to the insulation system.
When changing the transformer oil, it is usually replaced on site. First, the transformer is dried, then its top part is rinsed by naphthenic or regenerated oil to remove dirt deposits. Only then the transformer is re-filled with new or restored oil.
The best and most cost effective way to service a transformer is with the GlobeCore Process. Contaminated transformer oils are purified by the GlobeCore CMM-1A units. The GlobeCore CMM-1A units are designed for the purification and drying of transformer oils. The oil is dried by vacuum while the evaporating moisture is removed from the surface of the oil. The oil’s viscosity should not exceed 70 cSt at 50ºС/122ºF. GlobeCore’s CMM oil purification units offer purification of oil up to ISO4406 purity class 9.
Regeneration and purification of oil, using the GlobeCore Process, may be performed onsite and with the transformer energized or de-energized. First the oil is pumped out and heated and then is passed through the GlobeCore unit. The CMM unit degasses, filters and dries the oil and then returns the treated oil back into the transformer through the expansion tank. The process is repeated until the composition of the oil meets industry standards.
Its time to get with the Process, The GlobeCore Process!