Shunt wound DC motors are used where speed must remain constant regardless of load, such as on:

Shunt wound DC motors feature a field winding that is connected in parallel with the armature winding, allowing for a strong and consistent magnetic field. This design enables the motor to maintain a relatively constant speed under varying load conditions, making it particularly suitable for applications that require precise speed control.

Lathes are an ideal application for shunt wound DC motors because they often need to maintain a consistent rotational speed to ensure the accuracy and quality of the machining process. The ability to keep the speed constant despite changes in the load (for example, when cutting different materials or when the cutting tool encounters varying resistance) is critical in achieving the desired finish and tolerances in machining operations.

In contrast, other options may not necessarily require the same level of speed consistency under load. For example, traction engines or automobile starters may involve more variable loading conditions and operational demands, where speed can fluctuate according to the load on the motor. Elevators, while they do require speed control, often use different types of systems incorporating safety features and control mechanisms designed specifically for vertical lifting.

In summary, the application of shunt wound DC motors in lathes is due to the necessity of maintaining a stable and consistent speed during machining, which is essential for precision and efficiency in manufacturing processes