Analysis Method of Transformer Fatigue Life and Damage Under Multiple Short-Circuit Conditions

Transformer winding subjected to alternating stresses caused by multiple short circuits can fail by fatigue even though the stress is below the yield point. The effect of the mean stress of unidirectional impulse pulsating short-circuit force is not considered in previous studies. Therefore, this paper proposes a general method for assessing the stress fatigue life and damage of transformer winding under short-circuit conditions. Take a 110 kV transformer for an instance, the electromagnetic forces and stresses on the winding under short-circuit conditions were calculated based on electromagnetic-structural coupling. The dynamic measurement of short circuit force is realized by using the piezoelectric thin film polyvinylidene fluoride (PVDF) sensor to verify the accuracy of the simulation calculation. Based on finite element stress results, this paper proposes a five-step method for calculating stress fatigue life, the S-N curve of the copper winding is estimated, and the short-circuit force of the unidirectional impulse is corrected under the consideration of the mean stress effect. Both the fatigue life and damage of transformer winding is analyzed using the Palmgren-Miner model. The proposed methodology can evaluate the number of stress cycles leading to transformer winding failure as well as the weak link of winding fatigue life.