Salient features of the DMI motors are their very high output and torque in relation to the frame size.
A number of new solutions - patents applied for several of them by ABB - have together given the DMI motors such a superior performance that they are in a class of their own in the DC market. The development work on the stator, for example, has provided more space for the windings and led to a more uniform temperature distribution due to a more compact coil design and improved manufacturing processes.
The biggest difference, however, has been achieved in the armature. Arranging the cooling ducts below the winding slots gives first and foremost a fully symmetrical distribution of the magnetic flux path in the armature (see picture). In addition, there is a minimal intrusion of the cooling ducts into the magnetic flux path.
The efficiency of the cooling ducts could consequently be strikingly improved as a result of them being moved closer to the winding slots. At the same time, their cooling area could be enlarged.
Combining in this way increased cooling with a simultaneous improvement of the magnetic flux circuit was impossible in the past. The improvement of the magnetic flux paths in the armature was also followed up with a careful optimization of the stator.