- Dry-Type Transformers: Windings are cast or impregnated with epoxy resin, or wrapped in special insulating paper. They rely on air as the cooling medium, dissipating heat through natural convection or forced air circulation via fans. Being oil-free, they eliminate leakage risks.
- Oil-Immersed Transformers: Windings are immersed in transformer oil, which serves both as an insulating medium and a cooling medium. The oil transfers heat to the tank wall through thermal convection, and the heat is then dissipated into the air via radiators or cooling fins.
- Dry-Type: One of its key advantages. It uses non-combustible or flame-retardant materials; even if the windings overheat, it will not cause oil fires. Suitable for indoor locations with dense populations (e.g., commercial centers, hospitals, schools, tunnels, underground mines).
- Oil-Immersed: Transformer oil is a flammable liquid, which may cause fires or even explosions in case of faults. Fire-fighting facilities such as firewalls, oil pits, and emergency oil drainage systems must be equipped.
- Dry-Type: Oil-free, with no risk of leakage pollution.
- Oil-Immersed: Presents potential risks of environmental pollution due to oil leakage. Traditional mineral oil is difficult to degrade, while new synthetic ester oils (e.g., silicone oil, natural esters) offer better biodegradability.
- Indoor installations: Locations with high fire safety requirements.
- Special environments: Such as ships, offshore platforms, and chemical plants (dusty, humid environments without explosion risks, requiring enclosures with high protection levels).
- Building power distribution: Basements, floor-level electrical distribution rooms.
- Outdoor substations: Hub facilities for power transmission and distribution in power systems, such as power plants and substations.
- Occasions with high cost and overload requirements: Rural power grids, large industrial workshops (independent substations).
- High-capacity and high-voltage needs: Almost all high-voltage and ultra-high-voltage power transformers are oil-immersed.
- Dry-Type: Simple maintenance, mainly involving dust cleaning, inspection of ventilation and winding surface conditions, and tightening of connections.
- Oil-Immersed: Complex maintenance. Regular oil sampling for Dissolved Gas Analysis (DGA) is required to monitor internal faults; oil level, oil temperature, and sealing performance must be inspected, and oil filtration or replacement may be necessary when needed.
- Oil-Immersed: Transformer oil has a large heat capacity, enabling it to withstand short-term overloads.
- Dry-Type: Poor heat dissipation results in weak overload capacity; close monitoring of temperature rise is required during overload operation.
- Dry-Type: Windings are susceptible to moisture and chemical pollutants, requiring a good environment or protective enclosures. Service life is affected by the thermal aging of insulating materials.
- Oil-Immersed: The oil-paper insulation system is highly mature. With proper sealing and stable oil quality, the service life can reach several decades. However, oil aging (oxidation, moisture absorption) is the main influencing factor.
- Initial Investment: For the same capacity, dry-type transformers are usually more expensive.
- Installation Cost: Dry-type transformers are lightweight and do not require oil pits or complex fire-fighting facilities, with lower requirements for installation foundations, thus saving part of the civil engineering costs.
- Operating Cost: Oil-immersed transformers may incur ongoing oil treatment and maintenance expenses.
- Life-Cycle Cost: Comprehensive calculation is required. In indoor environments with high fire safety requirements, the total cost of dry-type transformers may be lower (eliminating the need for fire protection systems); in outdoor high-capacity scenarios, oil-immersed transformers have obvious economic advantages.
The key to selection lies in balancing safety, environment, cost, and technical requirements:
- Prioritize safety and environment: Must it be installed indoors or in fire-restricted areas? If yes, dry-type transformers are preferred.
- Consider capacity and voltage level: For high capacity (>10 MVA) or high voltage (>35 kV), oil-immersed transformers are a more economical choice.
- Evaluate total cost: Comprehensively consider equipment, installation, fire protection, maintenance, and potential risk costs.
- Assess reliability requirements: Oil-immersed transformers have a longer technical history and a proven track record of reliability in large power grids; dry-type technology is also highly mature and widely used in power distribution.
- Dry-Type Transformers: A safe, clean, and easy-to-maintain option, suitable for indoor power distribution scenarios with strict fire safety requirements.
- Oil-Immersed Transformers: An efficient, economical, and high-overload-capacity option, serving as the mainstay of high-capacity, high-voltage outdoor power systems.
