Which of the following is NOT a method used to cool transformers?

Transformers are essential components in electrical systems, and proper cooling methods are vital for maintaining their efficiency and longevity. The correct choice identifies that gas is not a standard method used for cooling transformers. Transformers typically generate heat during operation due to electrical losses, and maintaining optimal operating temperatures is key to performance and preventing damage.

Oil is a common coolant for transformers; mineral oil, for example, provides effective heat dissipation and can also serve as an insulator. Air cooling is another widely used method, particularly in smaller transformers or when ambient temperatures are adequate for temperature regulation. Water cooling can be effective as well, especially in larger installations, as it can absorb a significant amount of heat.

Gas, while theoretically usable, is not typically implemented as a cooling medium for transformers in practice. This is largely due to logistical challenges and the efficiencies associated with other conventional cooling methods. Hence, understanding the standard cooling methods helps in recognizing the importance of maintaining transformer health through proper thermal management.