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Which of the following types of cooling is employed in small and medium distribution transformers?

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SSC JE Electrical 06 Jun 2024 Shift 2 Official Paper - 1
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  1. Water filled oil cooled
  2. Oil filled water cooled
  3. Water filled self-cooled
  4. Oil filled self-cooled

Answer (Detailed Solution Below)

Option 4 : Oil filled self-cooled
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Detailed Solution

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Explanation: In small and medium distribution transformers, oil-filled self-cooling (also known as ONAN – Oil Natural Air Natural) is the most common type of cooling method. 
  • The transformer is filled with transformer oil, which serves two purposes: insulating the internal components and acting as a coolant. The oil absorbs heat generated in the core and windings of the transformer.
  • The heat is then transferred to the tank walls, where it dissipates into the surrounding air. This process is passive and does not require any external cooling equipment.
  • The term "self-cooled" refers to the fact that the cooling relies on natural circulation of oil and air (no external pumps or fans are needed in this method).

    Additional Information 
  • Water filled oil cooled — This is not a typical cooling method used in transformers. Transformers do not use water as the primary coolant inside.
  • Oil filled water cooled — This method is sometimes used for large power transformers, where water is circulated around a cooling system to enhance heat dissipation, but it is not typical for small and medium distribution transformers. 
  • Water filled self-cooled — Water is not used as the primary coolant in transformer design, as oil provides both insulation and cooling properties.
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-> SSC JE Electrical 2025 Notification will be released on June 30 for the post of Junior Engineer Electrical/ Electrical & Mechanical.

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