Power transformers used in trains, known as traction transformers, are designed to be compact and lightweight to fit within the limited space of a locomotive. They must handle high power levels and frequent load variations due to starting and stopping. Key features include robust insulation to withstand high voltages, efficient cooling systems to manage heat from electrical losses, and mechanical strength to endure vibrations and shocks. They often use advanced materials and technologies to achieve high efficiency and reliability while minimizing maintenance requirements.