Differences between SCB and SC series transformers

Both SCB and SC series are three-phase resin-cast dry-type transformers, but they differ in the following ways:

I. Coil Winding

This is the biggest difference between the two.

The low-voltage coil of the SCB type is wound with copper foil:

(1) Winding structure: Single-layer copper foil winding, with epoxy resin containing latent curing agent and F-grade composite foil as the interlayer material. The copper foil is a copper plate with a thickness of less than 0.1mm, very thin.

(2) Winding material: Oxygen-free copper with excellent conductivity, containing 99.99% copper.

The low-voltage coil of the SC type is wound with wire:

(1) Winding structure: Cylindrical coil

(2) Multiple ordinary glass fiber wrapped flat copper wire.

II. Temperature Rise

Because the low-voltage winding is close to the iron core, heat dissipation is difficult. The SCB type uses a single-layer copper foil winding structure. Due to the thinness of the copper foil, heat dissipation is easy, allowing for convenient setting of heat dissipation surfaces and increased ventilation, thus ensuring timely dissipation of the heat generated by the coil. The SC type, employing a cylindrical wire-wound structure, faces greater challenges in achieving the aforementioned objectives.

The SCB type transformer, with its foil-wound structure, experiences an average reduction of 5-7K compared to the wire-wound structure. This improves the transformer's overload capacity and lifespan.

III. Load Losses: Because the SCB type uses oxygen-free copper foil in its low-voltage foil structure, it boasts a high copper content and minimal impurities, resulting in very low copper loss. The SC type uses flat copper wire, specifically No. 1 electrolytic copper with a copper content of 99.96%, leading to higher copper losses compared to the SCB type.

For transformers of the same voltage rating and specifications, the SCB type exhibits an average 5% reduction in additional losses due to the skin effect compared to the SC type.

IV. Insulation Performance: The SCB type, with its low-voltage foil structure, exhibits a very low voltage gradient between layers within the low-voltage winding, resulting in higher insulation strength compared to the SC type. Its larger inter-turn capacitance enhances its resistance to overvoltage and lightning strikes.

V. Differences also exist in resistance to sudden short-circuit accidents.

SCB-type transformers employ a copper foil structure for low-voltage operation, with the reactance height being the same as the winding height, identical to the high-voltage coil. This results in a smaller axial short-circuit force under sudden short-circuit conditions. Furthermore, the use of a single, wide, and thin foil for the entire winding provides strong resistance to axial tensile failure.

SC-type transformers, however, utilize multiple parallel windings with extremely large end helix angles, generating a strong end leakage magnetic field. Under sudden short-circuit conditions, this produces a very large short-circuit force, making them prone to axial damage if the structure is not adequately reinforced.

SCB-type transformers use copper foil, resulting in a large current-carrying area, fewer turns, and higher capacity. They also possess strong overload capacity and high insulation levels. Comparatively, SCB-type transformers are smaller and lighter.

SCB-type transformers are generally specialized, such as magnetizing transformers, but this winding structure is increasingly being adopted in ordinary transformers, representing a future development trend.