We have one Seperately Excited DC Machine of 60 KW, 440 Volt Armature Voltage, 220 Volt Field Voltage, RPM 1500.
we have observed sparking beneath the Brushes, we have done Neutral setting by Centre Zero Galv Meter, removed all carbon from the Motor also done undercutting of commutator segments manually, winding resistance and insulation resistance of all Coils of Main Pole, Interpole are ok, even the armature resistance and Insulation resistance is alo ok.
Unfortunately the above efforts has not reduced the Sparking..
Please let me know, what is to be checked
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