Application of Epoxy Resin Cast Dry-Type Transformers in Coal Mine Shafts

Coal mining is a crucial source of energy supply in China, and the requirements for mine-used transformers are exceptionally high. These transformers must not only provide essential power for mining operations but also ensure that their operation does not compromise mine safety. Considering current coal mine production demands in China, epoxy resin cast dry-type transformers are typically used as the core component, with appropriate modifications in external structural design.

Internal Transformer Design

The enclosure of mine-used transformers must be explosion-proof. The structural design of such transformers is based on electromagnetic calculations, focusing on reducing losses, enhancing insulation strength, and controlling temperature rise. Due to the constraints of underground environments, transformers must be compact and easy to transport and install. This can be achieved by optimizing the design of the core and high- and low-voltage windings.

Core Selection

The core should be made of cold-rolled silicon steel sheets with high magnetic permeability. The core surface is coated with epoxy resin and cured to improve moisture and corrosion resistance. The entire core assembly is clamped with low-magnetic steel plates and straps to reduce noise. In addition to noise reduction, the design must also address temperature rise and energy consumption. The core should be designed with low magnetic flux density to avoid the hysteresis expansion zone, thereby reducing no-load energy losses.

High- and Low-Voltage Winding Design

The high-voltage winding adopts a cylindrical structure, reinforced with fiberglass between layers, and encapsulated in epoxy resin to form a solid, robust assembly. The winding should be cast in sections to reduce internal electric field intensity. Longitudinal ventilation ducts are provided on both sides of the winding to enhance heat dissipation. The low-voltage winding is made of copper foil and similarly encapsulated with epoxy resin.

Transformer Enclosure Design

The transformer enclosure must withstand internal explosion pressures and prevent the release of explosive gases that could trigger mine-wide explosions or fires. The enclosure material must have exceptional mechanical strength and good heat dissipation properties.

Key Design Considerations

• Epoxy resin material must be strictly controlled, typically using H-class insulation. Additives such as promoters and curing agents should be included to match the thermal expansion coefficient of the resin with that of copper wire, improving thermal conductivity, mechanical strength, and electrical performance.
• Windings should be cast in a high-temperature, vacuum environment to ensure no moisture remains during the casting process.
• Cooling devices, typically ventilation ducts, should be integrated near the core and windings during design. Under extreme conditions, oil or water cooling methods may be employed to enhance internal heat dissipation.
• The explosion-proof enclosure should also be designed with heat dissipation in mind. A corrugated design can be used to increase surface area, enabling faster dissipation of internal heat.