Buckling Strength Investigation for Power Transformer Winding under Short Circuit Impact
Power transformers are inevitably subjected to external short circuit impact during their service period. The electromagnetic force generated by the fault current may cause winding destabilization and collapse. The radial buckling of the inner winding accounts for a considerable proportion. Based on the effective contact of the sticks, the traditional analytical methods ignore the manufacturing deviation and operation impact (MDOI) characterized by assembly gaps and insulation shrinkage. To address the limitation of the contact-constrained approach, this paper proposes the equivalent support stiffness (ESS) analytical method. The ESS method can investigate the issues of support weakening and failure, which are affected mainly by assembly gaps and insulation shrinkage. Further, two transformers are implemented in the short-circuit tests to demonstrate the feasibility of the ESS method. Among them, the assembly gaps are investigated by the first and second windings of the newly manufactured transformer, and the influence of insulation shrinkage is researched through a 30-year-old transformer. Furthermore, the application of the ESS method is expressed based on the tests and the simulations. The research presents quantitative references for transformer design and operational reliability assessment. The ESS method can be an improvement and supplement to traditional methods.
The structure of this paper is organized as shown in Fig.2. Section Ⅱ proposes the ESS analytical method to investigate the radial buckling strength. Then, the vital characteristic quantities which affect the critical hoop stress are described theoretically, including the conductor, stick, MDOI, and defect. Based on the ESS method, Section Ⅲ investigates the buckling strength when the defect is ignored and considered, respectively. The short-circuit tests of two actual transformers are implemented in Section Ⅳ to demonstrate the ESS method. Further, the application of the ESS method is analyzed based on the tests and the simulations. Finally, the conclusion and further research plan are expressed in the last section.