## 3 Cushion Compression and Offset Test Based on Short-Circuit Force Simulation
### Analysis of Three-Point Bending Test  
In this section, an experiment platform for cushion block compression and offset was set up. Insulating cushion blocks measuring 77 mm in length, 39 mm in width, and 2 mm in thickness were used. Rectangular copper wires were cut into several small segments of the required length and flattened using pliers. These segments were then tightly bound together with adhesive tape in groups of five, and two sets of insulating cushion blocks were used as endpoints to form the main structure for the three-point bending test. The wire samples were secured at both ends with fixtures. The wire bending tests were conducted  
Figure 5: Cushion block tangent modulus–strain curve. Figure 6: Maximum unbalanced height calculation illustration. using an electronic universal testing machine with the model number ETM504D. During the testing process, a clamp moving speed of 2 mm/min was maintained, and a continuous bending force was applied to the rectangular specimens, with the force-deflection curve being automatically recorded. The test procedure is illustrated in Figure 7.  
Under the influence of axial forces, the winding can undergo compressive deformation, leading to a reduction in axial height, structural relaxation, and a lack of axial compressive force within the winding. Because the insulating cushion blocks between windings are continuously subjected to axial compression forces, the unbalanced heights of some cushion blocks may vary. Additionally, under the action of axial forces, the internal fibers of certain cushion blocks will gradually break, resulting in plastic deformation [36] and further compression. This leads to an increase in the unbalanced heights of adjacent cushion blocks and causes the support structure to become lax. When studying the impact of cushion block unbalanced heights on the mechanical properties of the wire, different numbers of cushion blocks (ranging from 2 to 5) were stacked to achieve varying unbalanced heights between adjacent cushion blocks. Specifically, the unbalanced heights of the cushion blocks at both ends were set at 0, 2, 4, and 6 mm, respectively. To investigate the effect of cushion block offset, six sets of experiments were conducted, involving single-end cushion block offset, two-end cushion block offset in the same direction, and two-end cushion block offset in opposite directions of 30\({}^{\circ}\) and 45\({}^{\circ}\). Taking 30\({}^{\circ}\) as an example, three different offset positions for the cushion blocks are explained, as shown in Figure 8. The simulation results yield axial bending stress cloud maps for the winding. A continuous bending force was applied to the center point of the rectangular specimens, and their force-deflection curves were recorded, respectively. Figure 7: Flow chart of cushion block compression offset test. For the purpose of comparative analysis, the bending elastic modulus of the wire under the three-point bending test was calculated in accordance with YB/T 5349-2006 [37]. Figure 9 illustrates the three-point bending test, where the wire is part of a beam-like structure composed of cushion blocks. The wire is placed transversely between the supports of the two end cushion blocks with a span length \(L\). In the middle of the wire, a concentrated force F acts downward, causing bending, and f represents the deflection in millimeters. With reference to YB/T 5349 2006, the force-deflection curve, as shown in Figure 10, was measured by the universal testing machine. On the force-deflection curve, starting from the intersection point O of the elastic straight-line segment with the deflection axis, a segment \(\overline{OC}\) corresponding to non-proportional bending strain is extracted and calculated according to Equation (26):  
\[\overline{OC}=\frac{nL^{2}}{6h} \tag{26}\]  
where \(n\) denotes the deflection magnification, \(L\) denotes the span of the wire, \(h\) denotes the height of the wire, and \(\epsilon_{pd}\) denotes the specified non-proportional bending strain.