The version with tube cooling covers the upper power range for flameproof motors and extends up to 6500 kW. Here, the stainless steel cooling tubes - concentrically arranged around the active part of the motor - act as an air-to-air heat exchanger. The special inner cooling system with X ventilation, axial and radial cooling slots ensure a consistent temperature level. The rugged version allows safe, reliable and straightforward operation in Zone 1 both for line and converter operation.