BREATHING NEW LIFE INTO A DC MOTOR

WEBB ELEC RECENTLY OVERHAULED and rebuilt a 287kw ABB DC motor for one of its metal processing customers. DC motors are the main workhorse for steel and metal-producing companies, where they often drive a drawbench which pulls the steel or metal that is being processed. These types of shunt wound DC motors are useful for this application as they provide constant torque and variable speed. The ABB DC motor overhaul was needed as, over time, carbon dust from the brushes builds up inside the motor along with other debris that, in a worstcase scenario, can cause the winding insulation to fail. The bearings in these motors also have to be replaced at the correct intervals taking into account the L10 bearing life.

Following dismantling and a full cleaning cycle of all the components, the motor underwent a Baker and surge test to the armature, field and interpole windings. This enabled the Webb Elec engineers to check the integrity of the winding insulation both to earth and between each individual conductor. The resistance of all the coils within the individual winding circuits was then measured, and the motor passed all of these static tests.

Following the tests, the motor components were stoved, and all windings were re-impregnated with anti-tracking varnish. The armature then went through to the company’s balancing department, where it was dynamically balanced to ensure efficient and smooth running and to maximise the bearing life. The bearing journals and housings were then checked for wear, and replacement bearings were fitted. The commutator was machined, undercut and polished to ensure the brushes had a smooth and even brushtrack which reduces wear and heat generation and keeps the machine running efficiently. The brushgear was then fully overhauled with new carbon brushes fitted.

Finally, the force ventilation blower was serviced and rebuilt with a new motor being fitted, and after assembly, the coupling was re-greased and refitted. The motor then underwent an extensive run test with the brushes being correctly bedded in before being painted and returned to the customer.