The main difference between oil and dry type transformers lies in their cooling methods and insulation materials. Oil transformers utilize mineral oil for cooling and act as both a coolant and an insulator, providing efficient heat dissipation and higher capacity for power transfer. This type of transformer is typically used in outdoor installations, offering advantages like improved thermal performance and moisture resistance. In contrast, dry type transformers use air or a solid insulation medium, such as epoxy, for cooling, making them suitable for indoor environments where fire safety is a concern. Dry type transformers are generally more compact and require less maintenance but have a lower power capacity compared to oil transformers. Each type serves specific applications depending on environmental and electrical requirements, with oil and dry type transformers tailored to different operational conditions and safety standards.

The IEEE guide for loading mineral oil immersed transformers provides comprehensive guidelines on the safe and efficient operation of these transformers, addressing aspects such as thermal ratings, loading capabilities, temperature limits, and cooling methods. It emphasizes the importance of maintaining proper thermal balance, considering ambient temperature effects, and ensuring adequate cooling for optimal performance. The guide also discusses equipment specifications, testing procedures, and maintenance practices to extend the life of transformers, ensuring reliability under various operating conditions. Additionally, it highlights the significance of monitoring and evaluating loading conditions to prevent overheating and potential failures, ultimately promoting safer operation in industrial applications.

To take an oil sample from a transformer, first ensure safety by wearing appropriate personal protective equipment and turning off the transformer if necessary. Locate the sampling valve or tap on the transformer, usually found at the bottom of the tank where sediment might settle. Clean the area around the sampling valve to prevent contamination. Prepare a clean, dry sampling container, preferably a glass or plastic bottle with a tight seal. Open the sampling valve slowly to avoid splashing and allow the oil to flow into the container, filling it to about two-thirds capacity. While sampling, ensure that no air bubbles are trapped in the oil sample as they can affect the analysis. Once the sample is taken, securely close the valve and seal the container tightly to avoid any leakage. Label the container with necessary information such as date, time, and location, and store it in a cool, dark place before sending it to a laboratory for analysis. Following these steps helps ensure the quality and reliability of your oil sample from the transformer.

The colour of transformer oil can signify several important factors related to its quality and condition. Generally, clear or pale yellow transformer oil indicates good quality and low levels of contaminants. As the oil ages or degrades, it may darken due to the presence of moisture, oxidation, and the accumulation of particulates, which can signify deterioration and the potential for reduced electrical insulation properties. A darker or cloudy appearance may suggest the presence of impurities, such as dissolved water or carbon, necessitating further analysis or treatment. Therefore, monitoring the colour of transformer oil is essential for assessing its health and performance in electrical systems.