Research On The Mechanism Of The Cumulative Effect Of Power Transformers' Short-circuit Impact

Recently, frequent short circuit faults of power transformers have caused serious threat to the safe operation of power grid, which has attracted the attention of researchers. The damage of power transformer caused by short-circuit shock is often not caused by once or twice shorts, but the result of the cumulative short-circuit impact, which has lead to the serious economic losses for the safe and stable running of power system. The study on the mechanism of cumulative effect of transformers' short-circuit impact not only provided an important reference for withstanding transformer short, but also had a guiding significance for repairing and maintenance of power transformer so that the power system can be running in a safe and economical order.Firstly, based on short-circuit electrodynamics' force, various failure caused by short-circuit impact force was analyzed, including radial force, axial force and interaction of both. And then spiral deformation caused by the radial compressive stress was discussed emphatically.Secondly, this paper have explicitly illustrated the cumulative effect of transformers' short-circuit impact, and discussed the functional mechanism of t heat and force on short impact accumulation effect. At the same time, given the different design concepts of manufacturers and main structure of mainstream power transformers this paper has further analyzed the process of two accumulations by combining the source of accumulation effect function and starts from the aspects of windings, transformer oil, thermal reaction and degree of force of other components, and concludes that short impact force effect accumulation is the main type of accumulation effect.Finally, based on the finite element analysis software COMSOL, multi physical field coupling model with electric field, magnetic field and structure field of transformer shortcircuit impact cumulative effect has been established under a variety of short-circuit, based on which the relationship of maximum deformation of windings and short circuit impact times has been analyzed. According to the simulation results, it has been concluded that when the single short-circuit fault occurs, the displacement mutation of the transformer windings is most likely to occur in the case of low voltage symmetrical short circuit, and the phase-phase to ground fault is not easy relatively.