Coal mining is a crucial source of energy supply in China, and the requirements for transformers in coal mines are exceptionally high. These transformers must not only provide the necessary electrical power for mining operations but also ensure that their operation does not compromise the safety of the mine. Considering the current demands of coal mine production in China, epoxy resin cast transformers are employed as the main component, with appropriate external design modifications.
1. Internal Design of the Transformer
The housing of mine transformers must be designed with explosion-proof capabilities. The structural design of explosion-proof transformers is based on electromagnetic design calculations, focusing on reducing losses, enhancing insulation strength, and lowering temperature rise. Transformers used in underground mining operations must be easy to transport and install, so the overall size of the transformer needs to be minimized. This can be achieved by optimizing the iron core design and the high- and low-voltage winding coils.
2. Selection of the Iron Core
The iron core material should be cold-rolled silicon steel sheets with high magnetic permeability. The surface of the iron core is coated with epoxy resin and cured to provide superior moisture resistance and corrosion protection. The entire iron core assembly is secured with low-magnetic steel plates and steel straps to reduce noise levels. In addition to minimizing noise, the design must also account for temperature and energy consumption. The iron core should be designed with low magnetic flux density to avoid the hysteresis expansion zone, thereby reducing energy consumption under no-load conditions.
3. High- and Low-Voltage Coil Design
The high-voltage coil should adopt a cylindrical design, reinforced with fiberglass between layers, and cast in epoxy resin to form a solid assembly. The coil should be cast in sections to reduce the electric field intensity within the coil. Longitudinal ventilation ducts are incorporated on both sides of the coil to enhance heat dissipation. The low-voltage coil is wound using copper foil and similarly impregnated with epoxy resin.
4. Transformer Housing Design
The transformer's housing must withstand the pressure generated by internal explosions while preventing any internal explosive gases from causing mine-wide explosions or fires. The housing should be constructed from materials of exceptional strength and also feature good heat dissipation properties.
Key Considerations
1. The epoxy resin material must be strictly controlled, generally selecting H-class materials. To improve the thermal conductivity, mechanical properties, and electrical performance, additives such as promoters and curing agents should be included to match the thermal expansion coefficient of the epoxy resin with that of the copper wire.
2. The coils should be cast in high-temperature and vacuum environments, ensuring no moisture is present during casting.
3. Before design, additional cooling devices should be incorporated near the iron core and windings, typically using ventilation ducts. Under extreme conditions, oil cooling or water cooling methods can be employed to enhance the internal heat dissipation of the transformer.
4. The explosion-proof housing should also be designed with heat dissipation in mind. A corrugated housing design can be used, as the corrugations increase the surface area of the explosion-proof housing, allowing internal heat to dissipate more rapidly.