What are the main insulation and longitudinal insulation in a winding?

The main insulation in a winding includes components such as the paper cylinder, wooden cylinder, winding end insulation, and the insulation between the static ring and the ground. These elements collectively form the primary insulation system of the winding.

Longitudinal insulation in the winding comprises the insulation of the wire outer covering, circular simple winding layer, insulation between the static ring and line segments, and insulation between line segments (layers). These insulation components contribute to the longitudinal insulation system of the winding.

When using circular conductors to wind a cylindrical winding, it is necessary to use a rigid insulation cylinder to address processing challenges. However, due to the relatively low electrical strength of wooden insulation, designs for transformers with voltages above 60kV and capacities exceeding 8000kVA often employ windings on supporting structures. This involves first wrapping the paper layers and then enclosing the winding around the paper cylinder. In the case of extremely large-capacity transformers, the winding may be wound on a thick cardboard cylinder.

For cases where the end insulation level of the winding is lower than that of the first end, a graded insulation system is employed. In a graded insulation system, the distance from the first end to the iron yoke is greater than that from the last end when the voltage is high. The inner layers of a pancake winding usually do not use padding insulation, nor do they reinforce insulation or include static and angular rings. The use of graded insulation in high-voltage test transformer windings helps with heat dissipation and reduces capacitance.

Graded insulation aids in reducing the size of the winding, simplifying the structure, facilitating manufacturing, and saving materials. However, transformers employing graded insulation are generally limited to systems with a neutrally grounded neutral point where the voltage is ≥126kV.

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