How to Inspect Electric Motors

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Electric motors are the backbone of modern industry. Available statistics shows that they constitute the bulk of electrical machines in the industry. Electric motors use 70 % of the electricity consumed by industry and therefore deserve special attention and regular inspection.

What to Look for During Electric Motor Inspection
(1) Inadequate ventilation or air flow
(2) Unbalanced voltage or an overload
(3) Bearing failure
(4) Insulation failure
(5) Shaft misalignment
Item (1) – (5) above tend to results in
excessive temperature production leading to premature failure of electric motors. Hence excessive motor temperature is a possible indication of any of the above.

Effect of excessive Temperature on Motor Life
One of the most common causes of premature motor failure is excessive temperature. Each motor has a maximum operating temperature that usually appears on its nameplate and represents the maximum allowable rise in temperature of the motor above ambient.  Most motors are designed to operate in ambient temperatures that do not exceed 40 °C. Generally, each 10 °C rise above its rated temperature cuts a motor’s life in half. Excessive motor can easily be identified with thermal imaging technologies.

Regularly scheduled inspections of critical parts -the motor shaft coupling, shaft bearings, gearbox - of electric motors help to identify motors which are starting to overheat so that corrective action can be taken immediately.

Inspection of Electric Motors
Regular inspection of electric motors will ensure an excessively hot motor is  spotted and cause of overheating eliminated immediately. To inspect electric motors for possible overheating, see checklist in table below and possible remedies:

Checks Possible Cause Remedy
Inadequate air flow or poor ventilation Dirty motor air intake grills Minor or total cleaning of motor is required
Unbalanced voltage or overload High resistance connection in the switchgear or motor connection box Remove high resistance connection and restore motor supply
Bearing failure Ageing, vibration or misalignment Align, lubricate or replace
Insulation failure Ageing, Overload etc De-rate motor or replace
Shaft coupling misalignment Vibration Align