Abstract
The lifetime of any device is limited by the aging of the insulation material due to temperature: the higher the activation energy of any material, the faster the aging proceeds. Iron and copper/aluminum have low activation energies and for this reason their aging is negligible. Insulation material – either of the organic or inorganic type - is most susceptible to aging caused by temperature. If a device is properly designed then the rated temperature results in the rated lifetime. Temperature rises above rated temperature result in a decrease of lifetime below its rated value. The presence of current and voltage harmonics in today's power systems causes additional losses in electromagnetic components and appliances, creating substantial elevated temperature rises and decreasing lifetime of machines and transformers. Therefore, estimating additional losses, temperature rises, and aging of power system components and loads has become an important issue for utilities and end users alike. The deterioration of the insulation caused by the elevated temperature rise is manifested by a reduction of the mechanical strength and/ or a change of the dielectric behavior of the insulation material. Three different phases are involved in the estimation (or determination) of the lifetime of magnetic devices: modeling and computation of the additional losses due to voltage or current harmonics; determination of the ensuing temperature rises; and estimation of the percentage decrease of lifetime as compared with rated lifetime.
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