Differences Between Dry Transformers and Oil Immersed ...

The main differences between dry type transformers and oil immersed transformers are as follows:

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Applicable Locations

• Dry Transformers: Commonly used in environments requiring fire and explosion prevention, such as large buildings and high-rise structures.
• Oil Immersed Transformers: Typically used outdoors; some installations feature "accident oil pools" to manage oil spray or leakage in case of a malfunction, reducing fire risk.

Capacities and Voltages

• Dry Transformers: Generally used for power distribution with capacities below kVA and voltage levels below 15 kV, although some can handle up to 35 kV.
• Oil Immersed Transformers: Capable of handling a wide range of capacities from small to large, with voltage levels reaching up to kV.

Appearance and Shape

• Dry Type Transformers: The core and coil are visible, as they do not have an outer tank filled with oil.
• Oil Immersed Transformers: Encased within a sealed tank, only the transformer shell is visible.

Lead Wire Form

• Dry Type Transformers: Utilize silicone rubber bushings.
• Oil Immersed Transformers: Use porcelain bushings.

Insulation and Heat Dissipation

• Dry Transformers: Insulated with resin and cooled by natural air. Larger units use fans for additional cooling.
• Oil Immersed Transformers: Insulated with oil. The oil circulates to dissipate heat generated by the coil to the transformer's heat sinks or radiators.

Load Capacity

• Dry Type Transformers: Generally operated at rated capacity.
• Oil Immersed Transformers: Have better overload capacity, allowing them to handle higher loads more effectively.

Costs

• Dry Type Transformers: More expensive to purchase than oil-immersed transformers of the same capacity.

Models of Dry ype Transformers

• Common models include SC (epoxy resin casting), SCR (non-epoxy resin solid insulation), and SG (open type).

Most power transformers are oil-immersed for several reasons, and the use of oil as a cooling and insulation medium has proven to be effective in the electrical industry. Here are the main reasons for using oil in power transformers:

Cooling: Oil has excellent cooling properties. It helps dissipate heat generated during the operation of the transformer. As electrical currents pass through the transformer windings, some energy is converted into heat. The oil absorbs this heat and transfers it away from the core and windings, preventing the transformer from overheating.

Insulation: Oil provides effective insulation, helping to prevent electrical breakdown and arcing between the transformer's high-voltage and low-voltage windings. Insulating oil has high dielectric strength, which means it can withstand high electric field stresses without breaking down.

Dielectric Properties: The dielectric properties of oil make it an ideal insulating medium. It can withstand high voltages without conducting electricity, preventing short circuits and ensuring the reliable operation of the transformer.

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Chemical Stability: Transformer oil is chemically stable, which means it does not easily degrade or break down over time. This stability is crucial for maintaining the insulating properties of the oil and ensuring the long-term reliability of the transformer.

Arc Quenching: In the event of a fault or internal arcing in the transformer, the oil can act as a medium to quench the arc and extinguish it. This helps prevent further damage to the transformer.

Ease of Maintenance: Oil-immersed transformers are relatively easy to maintain. The oil can be tested for its dielectric strength and other properties, and if necessary, the oil can be replaced or treated to restore its performance.

Cost-Effectiveness: Compared to alternative cooling and insulating mediums, such as air or gas, transformer oil is often more cost-effective. It provides a good balance between performance and cost.

While oil-immersed transformers have proven to be reliable and efficient, there is ongoing research to explore alternative insulation and cooling methods, such as dry-type transformers that use solid insulation materials. These alternatives may be preferred in certain applications where oil may pose environmental or safety concerns.