Common causes of electric motor failure

Louise Smyth

Motor failure can cause downtime, an inconvenience for all manufacturers. Martin McGuffie explains three common causes of electric motor failure: weakened insulation, contamination and lack of maintenance

Modern electric motors may be more efficient and reliable than their ancestors, but they can still fail sometimes.

How long do electric motors actually last before they break down? The answer is often disputed, with some manufacturers stating 30,000 hours and others suggesting they can power through for up to 40,000 hours.

However, most manufacturers are in agreement that electric motors last much longer when maintained properly.

 Understanding the state of an electric motor’s health requires a range of tools and techniques, as well as thorough record keeping and regular maintenance. This allows the engineer to identify trends or weak points more easily.

Carry out an electric motor failure analysis


Electric motor failure symptoms start with weakened insulation

Nearly half of electrical failures in motors begin with weakening of the insulation around individual wires in the motor coils. This is often caused by thermal stress, contamination and movement of the winding due to the magnetic forces during start-up and shut-down of the motor.

Overheating can also cause the winding insulation to deteriorate quickly — for every ten centigrade rise in temperature, the insulation life is cut in half.

Overheating can occur when the power quality is poor or when an electric motor is forced to operate in a high-temperature environment.

Contamination causes electric motor failure

Contamination is another one of the leading causes of electric motor failure. Contaminants include airborne dust, dirt or any abrasive substance that finds its way into the motor. When they come into contact with the motor, foreign bodies can cause denting of the bearing raceways and balls resulting in high vibration and wear.

Luckily, preventing contamination is fairly easy. Main sources of contamination include dirty tools, work areas and hands. Motors can also be contaminated by foreign matter in lubricants and cleaning solutions.

Engineers should keep work areas, tools and fixtures clean to help reduce contamination failures. Also, when laying out the space, companies should try to keep motor assemblies and operation areas away from grinding machines to reduce the amount of foreign bodies that might contaminate the motors.

Lack of maintenance is a common cause of electric motor failure

A well-planned preventative maintenance programme is the key to dependable, long-life operation of motors and generators. It also helps reduce unscheduled production stoppages or long repair shutdowns.

The first step towards preventative maintenance is understanding how often tests need to be carried out on the motor. This varies, depending on the age, condition and quality of the machine, as well as the environment it operates in.

Static tests are an easy method of identifying weaknesses within the motor winding. The tests focus on winding and insulation resistance, as well as turn-to-turn and phase-to-phase insulation condition.

With the right equipment, these tests can be performed without taking the motor off site, thus minimising downtime.

Motor testing and analysis equipment, such as Euroserv’s SKF Static Motor Analyzer Baker DX, can survey all insulation and windings in AC and DC motors, coils and generators.

During a site visit, Euroserv attends with the all-in-one tester, providing customers’ maintenance staff an analysis of the condition of the impedance, capacitance, phase angle, resistance, insulation and step voltage.

Electric Motor failure can cause downtime, meaning companies can lose thousands of pounds every minute when operations are stopped.

Instead of exposing themselves to downtime, customers should request regular motor testing and analysis, ideally every six months, to ensure their electric motors are healthy, efficient and reliable.

Martin McGuffie is with Euroserv and CP Automation.