The SS9 is a six-axle electric locomotive that was introduced in 1998 to accelerate passenger traffic. It was the last Chinese electric locomotive with DC traction motors and later gave way for the HXN series with three-phase AC motors. With a top speed of 170 km/h, they are being used to haul heavy trains at speeds of 160 km/h. Starting in 1998, 43 SS9 of the original variant were built. Between 2002 and 2006, 171 more were built of an improved variant that is also being called SS9G. These not only have a new exterior design, but also many improvements in the field of basic structure, ventilation and modular design. A part of the locomotives got electric train supply, others still need generator cars. 