I. Comparison of Dry-Type and Oil-Immersed Transformers:
1. Price: Dry-type transformers are more expensive than oil-immersed transformers.
2. Capacity: Larger capacity oil-immersed transformers are more common than dry-type transformers.
3. Dry-type transformers are used in multi-purpose buildings (basements, floors, rooftops, etc.) and densely populated areas.
4. Oil-immersed transformers are used in independent substations.
5. Transformers inside prefabricated substations are generally dry-type.
6. Temporary outdoor power supply generally uses oil-immersed transformers.
7. The choice between dry-type and oil-immersed transformers should be based on available space during construction. Oil-immersed transformers are preferable for larger spaces, while dry-type transformers are preferred for more confined spaces.
8. Oil-immersed transformers are more suitable for areas with humid and hot climates. If dry-type transformers are used, forced air cooling equipment is essential. II. Differences between Dry-Type and Oil-Immersed Transformers:
1. Appearance: The encapsulation methods differ. Dry-type transformers allow direct viewing of the core and coils, while oil-immersed transformers only allow viewing of the outer casing.
2. Lead Type: Dry-type transformers mostly use silicone rubber bushings, while oil-immersed transformers mostly use porcelain bushings.
3. Capacity and Voltage: Dry-type transformers are generally suitable for power distribution, with capacities mostly below 1600KVA and voltages below 10KV, although some reach 35KV. Oil-immersed transformers, on the other hand, can be produced in all capacities and voltage levels. The 1000KV ultra-high voltage test line currently under construction in my country will definitely use oil-immersed transformers.
4. Insulation and Heat Dissipation: Dry-type transformers generally use resin insulation and rely on natural air cooling, with larger capacities cooled by fans. Oil-immersed transformers, however, rely on insulating oil for insulation. The circulation of the insulating oil within the transformer transfers the heat generated by the coils to the transformer's heat sink (plates) for heat dissipation. 5. Applicable Locations: Dry-type transformers are mostly used in locations requiring fire and explosion protection, such as large buildings and high-rise buildings. Oil-type transformers, on the other hand, are mostly used outdoors in locations with available space for an emergency oil tank, as oil spills or leaks can cause fires.
6. Different Load Capacities: Dry-type transformers should generally operate at their rated capacity, while oil-type transformers have better overload capacity.
7. Different Costs: For transformers of the same capacity, dry-type transformers are significantly more expensive than oil-type transformers.
III. Load Losses: Because SCB-type products use oxygen-free copper foil in their low-voltage foil structure, they have a high copper content and very few impurities, resulting in very low copper losses. Oil-type transformers have higher copper losses than SCB-type transformers.
For transformers of the same voltage level and specifications, SCB-type products have an average 5% lower additional loss than oil-type products due to the skin effect. IV. Insulation Performance
The SCB type product adopts a low-voltage foil structure, resulting in a very low voltage gradient between layers within the low-voltage winding. Compared to oil-type products, the SCB type product has higher insulation strength. Its larger inter-turn capacitance improves its resistance to overvoltage and lightning strikes.
V. Differences also exist in resistance to sudden short-circuit accidents.
The SCB type product uses a copper foil structure for the low-voltage winding, 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 in the transformer. Furthermore, because the entire winding uses a single wide and thin foil, it has strong resistance to axial tensile failure.
Oil-type products, due to their multiple parallel windings and extremely large end helix angles, generate a very strong end leakage magnetic field. Under sudden short-circuit conditions, this produces a very large short-circuit force, and if the structure is not sufficiently reinforced, axial damage can easily occur.
