Choosing between oil type and dry type transformers can be challenging for machinery industry professionals.
Making the wrong choice can lead to safety hazards, high maintenance costs, and reduced efficiency.
Understanding the key differences between these transformer types, from cooling mediums to applications, enables you to select the optimal solution for your specific needs and environment.
What Is Oil Type Transformer
An oil type transformer utilizes mineral oil or synthetic ester liquid as an insulating and cooling medium. The transformer core and windings are immersed in the oil, which circulates to dissipate heat generated during operation.
What Is Dry Type Transformer
Dry type transformers, as the name suggests, do not use any liquid insulation or cooling medium. Instead, they rely on air circulation and solid insulation materials like cast resin, vacuum pressure impregnated (VPI) resin, or epoxy. The transformer windings are encapsulated or coated with these insulating materials.
Difference Between Oil Type and Dry Type Transformer
Cooling Medium
Oil type transformers use mineral oil or synthetic esters for cooling and insulation.
Dry type transformers rely on air circulation and solid insulation materials for cooling.
Insulation
In oil type transformers, the mineral oil or synthetic ester liquid acts as both a coolant and an electrical insulator. The oil immerses the core and windings, preventing short circuits between conductors.
Dry type transformers use solid insulating materials like cast resin, fiberglass, and nomex to coat or encapsulate the windings.
Maintenance
Oil type transformers require regular monitoring and maintenance of oil levels, pressure, and purity. The oil needs to be sampled and tested periodically for contaminants and breakdown. Leaks must be repaired promptly.
Dry type transformers are relatively maintenance-free, only requiring occasional cleaning and inspection of terminations and insulators.
Safety
Dry type transformers are considered safer than oil type because they do not contain any flammable liquids. In the event of a fault or overheating, there is no risk of an oil fire or explosion. The solid insulation will smolder but not burn.
Oil type transformers have fire and environmental hazards due to the large volume of oil.
Environmental Impact
Oil leaks from oil type transformers can contaminate soil and water, harming the surrounding ecosystem. A ruptured tank can spill hundreds of gallons of oil.
Dry type transformers do not pose this environmental risk, as they do not contain any liquids. However, cast resin transformers can emit small amounts of fumes in high heat conditions.
Cost
Dry type transformers have a higher initial cost compared to oil type of the same rating, as the solid insulating materials are more expensive. However, they have lower lifetime ownership costs due to less maintenance and simpler installation.
Oil type transformers are more economical for larger power ratings above 10 MVA.
Efficiency
Oil type transformers have higher efficiency than dry type transformers. The oil circulation allows for better cooling, so they can be operated at higher power densities with lower losses.
Cast resin dry type transformers are limited by the heat dissipation capacity of the solid insulation, resulting in more no-load and load losses.
Load Capacity
For the same physical size and weight, an oil type transformer will have a higher load capacity than a dry type. This is because the oil cooling allows the windings to carry higher currents without overheating.
Dry type transformers are limited by the heat removal through air circulation and solid insulation, so more winding material is needed for the same kVA rating.
Lifespan
With regular maintenance and oil reconditioning, oil type transformers can have a service life exceeding 25-30 years.
Dry type transformers, especially cast resin, have a shorter average lifespan of 15-25 years. This is because the solid insulation deteriorates faster with repeated thermal cycling and can develop cracks. The windings are also exposed to moisture and contaminants.
Size and Weight
For the same kVA rating and voltage class, a dry type transformer will be larger and heavier than an oil type. This is because air is a less efficient cooling medium than oil, so more core and winding material is needed to prevent overheating. The solid insulation also adds to the volume and mass. Oil type transformers are smaller and more compact.
Noise Level
Dry type transformers typically have higher noise levels than oil type transformers. The noise comes from the core and winding vibration, which is dampened by the oil in liquid filled units. In dry type, the vibration is transmitted through the solid insulation and enclosure.
Applications
Oil type transformers are used in high-voltage and high-power applications, such as power generation, transmission, and distribution.
Dry type transformers are suitable for low to medium voltage applications, including buildings, industrial plants, and renewable energy systems.
