What are the specific features of transformers used in metro systems?

Transformers in metro systems are often designed for underground or enclosed environments, requiring enhanced fire safety features like the use of non-flammable or less-flammable insulating fluids (e.g., silicone oil or synthetic esters). They may be more compact to fit in limited spaces and designed for low noise operation to reduce acoustic impact. These transformers must handle frequent start-stop cycles and regenerative braking energy. Robustness against environmental factors like dust and vibration is also essential, along with high reliability to support continuous metro services.