Structural stochastic reliability of testing transformers with impulse current under short-circuit condition based on the magnetic field-circuit coupling

Impulse current under short-circuit condition is the key factor for the structural reliability of the testing transformer. Therefore, the structural reliability analysis model of transformers was proposed based on the probability density evolution theory. Firstly, the basic principle of probability density evolution theory was introduced, and the analysis method of electromagnetic force field for windings was given considering the coupling effects of magnetic and electric fields. On the basis， the numerical analysis model of transformers structure was constructed by using the Abaqus software finite element analysis method. Taking an AGF 20 kV testing transformer as an example, the above model was validated. The longitudinal Mises stress of windings was chosen as the control variable, and the stress distribution and probability density evolution characteristics were given. Then, the structural reliability index was calculated, and the extreme mechanical response and the corresponding distribution zones of windings and iron cores were discussed. The results show that the stress of windings increases significantly under the action of short-circuit impulse current. The maximum value of windings’stress reaches 82% of the threshold, and plays the key role in structural reliability, the increase of impedance has obvious influence on the reliability of transformers.