Oil-type and dry-type transformers: full analysis of the differences

Among the many devices in the power system, transformers play a key role in power conversion and transmission. Oil-type transformers and dry-type transformers are the two most common types, and they differ significantly in many aspects.

1. Insulating medium

Oil-type transformers  use mineral oil or other insulating oil as the insulating medium. This insulating oil fills the transformer's oil tank, completely immersing the windings and core. Insulating oil has good insulation properties and can effectively prevent electrical breakdown between windings and between windings and iron cores. For example, the insulating oil of oil-type transformers used in large substations can ensure the safety of the electrical insulation inside the transformer in high-voltage environments.

Dry-type transformers use solid insulating materials such as epoxy resin. The windings are tightly wrapped or molded in these solid insulating materials, which isolate the electrical circuits through the insulating properties of the solid materials. Like dry-type transformers used in high-rise buildings, shopping malls and other places in cities, solid insulation materials can avoid the risk of leakage caused by liquid media, greatly improving safety.

2. Heat dissipation method

Oil-type transformers mainly rely on the heat conduction and convection of insulating oil to dissipate heat. When the transformer is running, the heat generated by the windings and iron core increases the temperature of the insulating oil. The hot oil rises through the radiator or cooler, exchanges heat with external cold air, cools down, and then flows back inside the transformer to continue circulating heat dissipation. For example, in some oil-type transformers in industrial plants, the radiator will automatically adjust the fan speed according to the oil temperature to control heat dissipation efficiency.

There are two heat dissipation methods for dry-type transformers: natural air cooling and forced air cooling. Natural air cooling uses the natural flow of air around the transformer to take away heat; forced air cooling uses a fan installed on the transformer to accelerate the air flow to enhance the heat dissipation effect. However, compared with oil-type transformers, dry-type transformers have relatively weak heat dissipation capabilities, which also limits their use in large-capacity applications. For example, in power distribution rooms in residential areas, dry-type transformers generally use natural air cooling to meet daily operation needs.

3. Fire performance

Oil-type transformers use flammable insulating oil. Once a fault occurs and the insulating oil leaks and encounters a fire source, it can easily cause a fire and cause serious damage to the surrounding environment and equipment. In some past power accident cases, oil transformer fires have resulted in widespread power outages and significant property damage.

Because there is no flammable insulating oil, dry-type transformers have excellent fire protection performance and will not cause fires due to their own reasons. They are especially suitable for use in places with extremely high fire protection requirements, such as hospitals, libraries, schools, etc., where people are densely populated and there are no fire hazards. Fire safety sensitive areas.

4. Volume and weight

Oil-type transformers are bulky and heavy because they have oil tanks, a large amount of insulating oil, and matching radiators. This requires a large space for installation and has high requirements on the load-bearing capacity of the installation site. For example, in large power plants, the installation of oil-type transformers requires special infrastructure to support their weight and reserve sufficient space.

Dry-type transformers have a relatively compact structure, no oil tank and a large amount of liquid medium, are small in size and light in weight, and are more flexible and convenient to install. They can be installed in a relatively small space indoors and have lower installation site requirements. In some small substations or power distribution facilities inside buildings in urban centers, the advantages of small size of dry-type transformers are fully reflected.

5. Maintenance requirements

The maintenance of oil-type transformers is more complicated. It is necessary to regularly check the oil quality of the insulating oil, including the oil's voltage resistance value, water content, acid value and other indicators. If the oil quality drops, oil filtering or oil replacement is required; it is also necessary to check whether there is leakage in the oil tank and whether the radiator is Work normally etc. Maintenance work requires professional technicians and specialized oil treatment equipment.

Maintenance of dry-type transformers is relatively simple. The main inspection items include whether the appearance of the winding is damaged, whether the solid insulation material shows signs of aging, and whether the fan is operating normally. The daily maintenance workload is small and there is no need to deal with complex liquid medium-related issues. General electrical maintenance personnel can perform the operation.

6. Applicable places

Oil-type transformers are suitable for places with high capacity requirements, outdoor environments and not particularly strict fire protection requirements, such as large power plants, substations, industrial and mining enterprises, etc. It can meet the needs of large-capacity power conversion and long-distance transmission, and plays an important role in the backbone network of the power system.

Dry-type transformers are widely used in indoor places with strict requirements for fire protection and explosion protection, such as high-rise buildings, shopping malls, hospitals, data centers and other places with densely populated areas and high requirements for the safety and stability of power supply, as well as some places with limited space. In small substations or distribution facilities.

There are obvious differences between oil-type transformers and dry-type transformers in terms of insulation media, heat dissipation methods, fire protection performance, volume and weight, maintenance requirements and applicable locations. In the design and construction of power projects, it is necessary to select the appropriate transformer type based on comprehensive considerations such as specific application scenarios, power demand, safety requirements and other factors to ensure the safe, efficient and stable operation of the power system.