The winding machine is formed by winding conductive wires. The conductive wires include copper wires and aluminum wires, and each layer of wires is covered with different types of insulating layers, meaning that the wires are directly combined with various insulating layers to form a whole. The role of these insulating layers is to constitute the inter-turn insulation of the winding. The coil we usually use is a single-layer pancake coil formed by continuously winding a single piece of paper-wrapped flat aluminum wire with a wire gauge of 2.2*2.5mm. The external dimensions, compactness, flatness, and other aspects of the pancake coil for traction transformers must meet technical requirements. When winding the coil, the wire gauge and inter-turn spacing of the conductive wires determine the dimensions of the coil. The prerequisite for controlling the coil dimensions is to identify the factors that affect the inter-turn spacing of the coil, which is also a necessary condition for controlling the coil dimensions.
1. Coil size issue
Recently, when using a vertical winding machine to wind a single pancake coil, the current value of the magnetic powder clutch, which controls the tension of the winding machine, was set at 0.45A. After the coil winding was completed, the size of the B end was consistently larger, exceeding the process requirement range.
2. Analysis of the causes of coil size issues
When the current value related to the tension of the winding machine is set to 0.45A, it was observed during the winding process that due to the excessively low tension, the wires on the wire reel were unevenly stressed. When the reel rotated, it exhibited a phenomenon of idling due to inertia, resulting in a significant amount of wire slipping out. Consequently, the wire between the reel and the wire gripper was not in an ideal state, but rather drooped with a certain curvature. Therefore, the wire was unevenly stressed during the winding process, and the compactness of the wound coil was insufficient, leading to the coil B size exceeding the technical requirement value.
3. Analysis of the relationship between the tension of the winding machine and the coil size
(1) The impact of appropriately increasing the tension of the winding machine on the coil. During the coil winding process, gradually increase the tension, adjust the tension-related current value of the vertical winding machine to 0.46A, and the coil becomes slack. The phenomenon of oversized dimensions has improved, but it still does not meet the requirements. Continue to increase the tension-related current value of the vertical winding machine to 0.47A, and the coil dimensions meet the requirements. The coil is tight, with no obvious gaps at ends A and B, and no tightening or upwarping at the four corners. The wire gauge change meets the requirements.
(2) The impact of excessive tension on the coil in the winding machine. When the current value related to the tension of the vertical winding machine is further increased to 0.51A, the four corners of the coil are subjected to excessive force during the winding process, resulting in an upward warping phenomenon. After winding is completed, there is no obvious gap between the wires, and the wire gauge does not decrease sharply. However, the four corners exhibit an upward warping phenomenon, which does not meet the technical requirements.
From the above, it can be seen that when the tension value of the vertical winding machine is too low, after the coil winding is completed, the coil is not tightly wound, there are gaps between the wires, and the size of the B end is larger than the technical requirement value. Increasing the tension of the vertical winding machine appropriately can reduce the size of the B end of the wire coil and have little impact on the wire gauge, thereby improving the problem of the B end being too large. However, when the tension of the vertical winding machine is too high, it can lead to the coil not meeting the technical requirements. Therefore, it can be seen that tension is closely related to coil size, and during coil winding, the tension of the winding machine should be adjusted to the corresponding matching value.
