2025-06-17
The core difference between oil-type (liquid-immersed) and dry-type transformers lies in their cooling/insulation medium and construction, leading to distinct advantages, limitations, and applications.
| Feature | Oil-Type (Liquid-Immersed) Transformers | Dry-Type Transformers |
|---|---|---|
| Insulation/Cooling | Mineral oil, silicone fluid, or ester oil. Acts as both insulator and coolant. | Air (ambient or forced) combined with solid insulation (e.g., epoxy resin, VPI varnish, Nomex). |
| Fire Safety | ❌ Flammable (mineral/silicone oil). Fire risk, requires containment systems, firewalls. Bio-esters less flammable. | ✅ Non-flammable (no liquid fuel). Self-extinguishing materials. Ideal for fire-sensitive areas (buildings, tunnels). |
| Environmental Risk | ❌ Oil leaks/pollution risk (soil/water contamination). Requires spill containment (bunds). | ✅ No toxic fluids - minimal environmental risk. No containment needed. |
| Cooling Efficiency | ✅ Superior (oil has higher thermal capacity/conductivity). Handles higher overloads/peak loads better. | ❌ Limited (air is less efficient). Lower overload capacity. May need forced air (AN/AF ratings). |
| Size & Weight | ❌ Generally larger & heavier for same rating (due to tank, oil, radiators). | ✅ Typically smaller & lighter (no oil tank). Easier indoor installation. |
| Maintenance | ❌ Higher (oil level/quality checks, filtration, leak detection, DGA testing). | ✅ Very low (visual inspections, cleaning). No oil management. |
| Initial Cost | ✅ Lower for medium/high power ratings. | ❌ Higher (especially epoxy cast resin). Cost gap narrows at lower kVA. |
| Lifespan | ✅ Longer (30+ years) if maintained properly. | ❌ Shorter (20-25 years) - solid insulation degrades faster. |
| Voltage & Power Range | ✅ Wider (Up to ultra-high voltage, 1000+ MVA). Dominates high-power applications. | ❌ Limited (Typically ≤ 35kV, ≤ 20 MVA). Advances pushing limits. |
| Noise Level | ❌ Quieter (oil dampens core noise). | ✅ Louder (core noise radiates directly into air). |
| Installation Location | ❌ Outdoor/ventilated indoor rooms (fire/ventilation codes). Requires containment. | ✅ Indoor/confined spaces (hospitals, high-rises, basements). No special ventilation. |
| Sensitivity | ❌ Sensitive to moisture ingress (reduces oil dielectric strength). | ✅ Tolerant to moisture/dust (if proper IP enclosure). |
1.Insulation and Cooling:
Oil type: Electrical insulation and heat transfer are achieved using insulating oil (mineral oil, silicone oil, or eco-friendly ester oil). Heat is dissipated through radiators/heat sinks.
Dry type: Heat is dissipated using ambient air. Insulation is provided by solid materials (wound coils wrapped in epoxy resin, coils treated with VPI, high-temperature insulating materials such as Nomex).
2.Safety and Environmental Impact:
Oil type: There are significant fire hazards (easily flammable oil), and there is a risk of leakage/pollution. Fire-resistant structures, containment facilities (dams), and usually, site selection away from residential areas are required.
Dry type: It has natural fire resistance (no flammable liquids, using self-extinguishing materials). The environmental risk is minimal. It can be installed in buildings with people living in them.
3.Efficiency and Load Capacity:
Oil-cooled type: Excellent heat dissipation performance can better cope with short-term overload situations and has a higher continuous power density.
Dry type: The heat dissipation efficiency is lower, which limits its overload capacity and may require reducing power or using forced air cooling in high-load conditions.
4.Maintenance:
Oil type: Regular oil sampling (dissolved gas analysis - DGA), filtration, moisture control, leakage checks, and final oil replacement are required.
Dry type maintenance: The main tasks include cleaning dust and debris from the windings and inspecting connection points. This maintenance method is less intensive and has lower costs.
5.Application Focus:
Oil type: Mainly used in substations, factories (for large power equipment), renewable energy power plants (wind/solar inverters), and areas with controllable fire risks. Suitable for extremely high voltages/powers.
Dry type: Suitable for indoor/industrial uses: buildings (hospitals, schools, offices, shopping malls), tunnels, underground stations, mines, marine environments, food processing plants, and environmentally sensitive areas. Many building codes have mandatory requirements for indoor locations.
The oil-type products are suitable for: high power/high voltage, cost-effectiveness (large capacity), excellent heat dissipation/overload capacity, outdoor installation. Some compromises can be made: fire risk, environmental issues, maintenance work.
The dry-type products are suitable for: indoor/public spaces, fire safety, low maintenance cost, environmental safety, narrow spaces. Considerations need to be made: higher initial cost (as is usually the case), lower overload capacity, noise, voltage/power limitations.
