Power transformers can be classified into two types based on their structure: core-type transformers and shell-type transformers.

1.Core-Type Transformers:

The winding of a core-type power transformer is cylindrical, and the cross-section of the core column is approximately cylindrical. The high-voltage and low-voltage windings are concentrically arranged, and the body (core and winding) is vertically oriented. The winding structure can take various forms, such as circular, helical, continuous, layered, twisted, and internal shielded, depending on the voltage and current. The core column is approximately cylindrical in cross-section, and the shape of the yoke varies based on the design.

2.Shell-Type Transformers:

The winding of a shell-type transformer is flat rectangular, with high and low-voltage coil discs arranged vertically and interleaved. The core is horizontally oriented. Most manufacturers produce core-type transformers, while a few produce shell-type transformers. Generally, shell-type transformers are technically and economically superior for capacities greater than 120 MVA, whereas core-type transformer technology is more advantageous for capacities less than 120 MVA.

3.Structural Differences:

In shell-type transformers, the winding is surrounded by the core, while in core-type transformers, the winding surrounds the core.

The core in shell-type transformers is horizontally positioned with a rectangular cross-section, making it prone to shear; in core-type transformers, the core is vertically positioned with an approximately circular cross-section, resulting in a larger shearing workload.

The winding in shell-type transformers is rectangular and arranged in an interleaved manner, allowing for adjustable short-circuit impedance. The winding in core-type transformers is cylindrical and concentrically arranged, forming two separate high and low-voltage winding groups.

The coil discs in shell-type transformers are vertically oriented, facilitating heat dissipation. In core-type transformers, the coil discs are horizontally oriented, leading to poorer heat dissipation, often requiring directed cooling structures.

The coil discs in shell-type transformers are larger, resulting in larger series capacitance and uniform impulse distribution. In core-type transformers, the coil discs are smaller, leading to smaller series capacitance and uneven impulse distribution.

The gap between the oil tank and the body is small in shell-type transformers, suitable for compact oil tanks. In core-type transformers, a certain insulation distance is needed, and the oil tank supports the core, reducing the oil quantity.

The winding in shell-type transformers is supported by the core and oil tank, resulting in small electromagnetic forces. The winding in core-type transformers is supported by winding screens, leading to larger electromagnetic forces.

The leads in shell-type transformers are drawn from the upper part, facilitating arrangement. Core-type transformers have a longer production cycle, involve more manual operations, and require oil immersion or oil spraying treatment.

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