Electric Motors -Technical Information

Information Source:

Installation and Maintenance Manual 

Troubleshooting Chart

Failure Probable Cause Corrective Measures

Motor fails to start

 1. No voltage supply - Check feed connections to control system and from control to motor.
2. Low voltage supply - Check voltage supply and ascertain that voltage remains within 10% of the rated voltage shown on the motor nameplate.
3. Wrong control connections - Compare connections with the wiring diagram on the motor nameplate.
4. Loose connection at some terminal lug - Tighten all connections.
5. Overload - Try to start motor under no-load conditions. If it starts there may be an overload condition or a blocking of the starting mechanism. Reduce load to rated load level and increase torque.
6. Brushes - Brushes may be worn, dirty or incorrectly fitted.

High Noise Level

 1. Unbalance - Vibrations can be eliminated by balancing rotor. If load is coupled directly to motor shaft, the load can be unbalanced.
2. Distorted shaft - Shaft can be bent; check rotor balance and eccentricity.
3. Incorrect alignment - Check motor alignment with machine running.
4. Uneven air gap - Check shaft for warping or bearing wear.
5. Dirt in the air gap - Dismantle motor and remove dirt or dust with jet of dry air.
6. Extraneous matter stuck between fan and motor casing. - Dismantle motor and clean. Remove trash or debris from motor vicinity.
7. Loose motor foundation - Tighten all foundation studs. If necessary, realign motor.
8. Worn bearings - Check lubrication. Replace bearing if noise is excessive and continuous.

Overheating of bearings

 1. Excessive grease - Remove grease bleeder plug and run motor until excess grease is expelled.
2. Excessive axial or radial strain on belt - Reduce belt tension.
3. Deformed shaft - Have shaft straightened and check rotor balance.
4. Rough bearing surface - Replace bearings before they damage shaft.
5. Loose or poorly fitted motor end shields - Check end shields for close fit around circumference and tightness.
6. Lack of grease - Add grease to bearing.
7. Hardened grease cause locking of balls - Replace bearings.
8. Foreign material in grease - Flush out housings and relubricate.

Intense Bearing Vibration

 1. Unbalanced rotor - Balance rotor statically and dynamically.
2. Dirty or worn bearing - If bearing rings are in perfect condition, clean relubricate the bearing, otherwise replace bearing.
3. Bearing rings too tight on shaft and/or bearing housing - Before altering shaft or housing dimensions, it is advisable to ascertain that bearing dimensions correspond to manufacturer's specifications.
4. Extraneous solid particles in bearing - Take bearing apart and clean. Reassemble only if rotating and support surfaces are unharmed.

Overheating of Motor

 1. Obstructed cooling system - Clean and dry motor; inspect air vents and windings periodically.
2. Overload - Check application, measuring voltage and current under normal running conditions.
3. Incorrect voltages and frequencies - Compare values on motor nameplate with those of mains supply. Also check voltage at motor terminals under full load.
4. Frequent inversions - Exchange motor for another that meets needs.
5. Rotor dragging on stator - Check bearing wear and shaft curvature.
6. Unbalanced electrical load (burnt fuse, incorrect control) - Check for unbalanced voltages or operation under single-phase condition.

Slip Ring Motor Operating at Low Speed with External Resistance Disconnected

 1. Control circuit conductors too light - Install heavier conductors on control circuit.
2. Control too far from motor - Bring control closer to motor.
3. Open circuit on rotor circuits (including connections with control apparatus) - Test circuit with a magneto, or other means, and undertake necessary repairs.
4. Dirt between brush and slip ring - Clean slip rings and insulation assembly.
5. Brushes gripe on brush holders - Select brushes of correct size.
6. Incorrect pressure on brushes - Check pressure on each brush and adjust it accordingly.
7. Rough surfaces on slip rings - File, sand and polish.
8. Eccentric rings - Machine on lathe or with portable tool without removing from machine.
9. High current density on brushes - Reduce load or replace brushes.
10. Poorly set brushes - Reset brushes correctly.

Brush Sparking

 1. Poorly set brushes with insufficient pressure - Check brush setting; adjust for correct pressure.
2. Overload - Reduce load or install motor with higher capacity.
3. Slip rings in poor condition - Clean rings and reset brushes.
4. Oval slip rings. Rough surfaces and scored rings. - Polish the slip rings with an emery and machine the same on lathe.
5. Excess of Vibration - Balance the rotor, check the brushes for free movement within holders.