Here comes the question. Oil-immersed transformers rely on insulating oil for cooling and insulation. Since dry-type transformers do not have insulating oil, how do they achieve cooling and insulation?
Let's talk about cooling first. Dry-type transformers usually have two cooling methods. One is natural air cooling (AN). When the transformer is operating at its rated capacity, it mainly relies on natural air convection for heat dissipation. At this time, it can operate continuously for a long time without relying on additional cooling equipment. The other is forced air cooling (AF). When the working environment temperature of the transformer reaches 80 degrees Celsius, the temperature control system will automatically start the fan for forced air cooling. Through the forced air flow, the heat dissipation efficiency of the transformer can be significantly improved, enabling the transformer to maintain normal operation even under overload or high-temperature conditions. In simple terms, it is cooled through air flow, and if the temperature is too high, the fan is used to assist in heat dissipation.
Now let's talk about insulation. Dry-type transformers mainly use epoxy resin as the insulating material and ensure the insulation effect through various technological methods. The specific types include vacuum casting type of epoxy quartz sand mixture, vacuum pressure differential casting type of epoxy non-alkali glass fiber reinforced, and impregnation type of non-alkali glass fiber winding.
Advantages of Dry-type Transformers
High Safety: Dry-type transformers do not contain flammable and explosive oil products. Therefore, it is less likely to cause fire or explosion accidents during operation, greatly improving the safety of use. At the same time, dry-type transformers have good electrical insulation performance, which can effectively prevent the occurrence of electric leakage and short-circuit phenomena.
Good Environmental Friendliness: Since dry-type transformers do not use oil as the cooling and insulating medium, there will be no oil pollution, which is environmentally friendly.
High Efficiency and Energy Saving: During the design and manufacturing process of dry-type transformers, attention is paid to improving energy efficiency and reducing losses. By optimizing the coil structure, using high-efficiency insulating materials, and advanced manufacturing processes, dry-type transformers can maintain low energy consumption and high efficiency during operation.
High Reliability: Dry-type transformers adopt advanced manufacturing processes and materials, with a long service life and high reliability. Under normal operating conditions, the failure rate of dry-type transformers is relatively low, which can ensure the stable operation of the power system.
Disadvantages of Dry-type Transformers
Poor Moisture and Dust Resistance: Dry-type transformers have relatively weak protection against moisture and dust. When used in a humid or dusty environment, additional protective measures may be required, such as installing protective covers or building special distribution rooms, to protect their insulation performance.
Relatively Poor Resistance to Harsh Environments: Compared with oil-immersed transformers, dry-type transformers are generally more suitable for installation in indoor environments. When used outdoors, special attention needs to be paid to their protection and heat dissipation issues to ensure their normal operation and extend their service life.
High Requirements for Insulating Materials: Dry-type transformers have high requirements for insulating materials and need to use materials with good thermal conductivity and insulation properties, such as specially treated epoxy resin. This will also increase their manufacturing cost.
Difficult to Repair Once the Coil is Damaged: Once the coil of a dry-type transformer is damaged, it is usually difficult to carry out local repair and requires overall replacement. This increases the complexity and cost of maintenance.
Differences from Oil-immersed Transformers
Appearance: It is easy to distinguish between dry-type transformers and oil-immersed transformers in appearance. Oil-immersed transformers have a metal shell, while the iron core and windings of dry-type transformers can be directly seen.
Cooling and Insulation: As mentioned above, oil-immersed transformers use insulating oil for cooling and insulation, while dry-type transformers use air for insulation and cooling, which is the main difference between the two.
Structure: Since dry-type transformers do not have insulating oil, their volume and weight are smaller than those of oil-immersed transformers, making them easier to handle. At the same time, without being immersed in insulating oil, the windings and iron core are usually wrapped with multiple layers of insulating materials, and then a protective layer is added outside the insulating materials. The iron core is composed of layers of iron sheet chips, reducing the magnetic flux loss.
Application Sites: Due to their fireproof and oil-free pollution characteristics, dry-type transformers are particularly suitable for installation in indoor environments and are mostly used in "fireproof and explosion-proof" places. Oil-immersed transformers are more suitable for outdoor installation and are widely used in large-scale power systems, such as power grid transmission and substations, because of their good heat dissipation performance and the ability to withstand higher loads and voltages.
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