Typical causes of electric motor winding failures and how to prevent them

Electric motors serve as a critical component for any facility. However, electric motors can be prone to any number of issues that lead to motor faults and failures, which can disrupt business operations, decrease productivity and adversely impact a company’s bottom line.

Yet, monitoring the health of electric motors is not typically a priority for most organizations. The importance of implementing predictive maintenance programs can offer tremendous benefits in detecting, identifying and evaluating electric motor abnormalities. Without proper visibility, the chances of motor failures increase, leading to unexpected downtimes.

To keep operations running smoothly, implementing preventive maintenance programs to detect, identify and evaluate the areas of electric motors that are prone to failure is crucial. To do so, understanding the underlying causes of motor failures is critical to determine the best course of action should a failure occur. As part a regular maintenance program, next-generation diagnostic and maintenance tools that include connected tools, sensors and software offer the best way to monitor an electric motor’s health.

Causes of electric motor winding failures

What causes electric motors to fail? Unfavorable operating conditions — whether electrical, mechanical or environmental — can dramatically shorten the life of an electric motor. The Electro-Mechanical Authority (EASA) cites many causes of electric motor winding failures including:

• Electrical failures, including single-phased winding failures (wye- or delta-connected) caused by an opening from a blown fuse, open contactor, broken power line or bad connection, which disrupts the power supply to the motor.
• Insulation failures, including winding that is shorted phase-to-phase or turn-to-turn, has a shorted coil, is grounded at the edge of the slot or in the slot, or has a shorted connection — all of which are typically caused by contaminants, abrasion, vibration or voltage surge.
• Thermal deterioration of insulation in one phase of the stator winding, which can result from unequal voltage between phases due to unbalanced loads on the power source, a poor connection at the motor terminal, or high resistance contact; or thermal deterioration in all phases of the stator winding typically due to load demands exceeding the rating of the motor or by very high currents in the stator winding due to a locked rotor. It may also occur as a result of excessive starts or reversals.
• Looseness and bearing failures. Another common fault stems from mechanical rubs, which can be the result of looseness of the motor shaft and/or the motor bearings. The most common mechanical faults are shaft imbalance, looseness, misalignment, and bearings. Often these mechanical faults are related: shaft imbalance, looseness, or misalignment left uncorrected will cause increased forces on the bearings which leads to rapid wear of the bearings.

Preventive maintenance and diagnostics key to electric motor winding failure prevention

The rate of interest (ROI) and benefits of reliability and condition-based maintenance have been known for decades, but only recently come together to make predictive inspection methods, portable condition monitoring, remote control and monitoring and SaaS computerized maintenance management software (CMMS) available and cost-effective. These next-generation maintenance and reliability tools support the generation, collection and consolidation of data from sensors, tools, and existing systems with remote monitoring capabilities through connected devices including desktop, tablet or smartphone.

The benefits of these tools include:

• Cloud-based CMMS provides a flexible and easy-to-use method for delivering asset management, workflow management and reporting.
• Connected tools and sensors offer all key stakeholders with access to the data they need, including plant managers seeking to maintain motor uptime, engineers who rely on precise data to monitor asset health, and maintenance managers trying to stay a step ahead of motor failures.
• Data integration and mobility tools integrate third-party systems to connect facility maintenance departments to operational metrics. The combination of data integration, data management and mobile interface gives maintenance and operations staff the ability to cross reference process automation information with maintenance activity and inventory records.

Leveraging these tools and technologies can offer key insights into the health of electric motors. Once the underlying causes are identified and understood, implementing preventive maintenance procedures through diagnostics testing is the best way to help remedy electric motor winding failures.

To diagnose a problem, there are three steps within each category to help quickly and efficiently manage the repair workflow:

• Step 1: Screen your machines to find out which ones are healthy and which ones may have a problem. Use simple screening tools, such as vibration meters and thermal imagers that provide quick answers.
• Step 2: Perform troubleshooting to diagnose the root cause of a problem and screen the machine for faults with fault severity and a repair recommendation.  Vibration testers should be used for mechanical faults and motor analyzers for electrical faults.
• Step 3: Correct the root cause problem. Replace the bearings, balance the shaft, and/or align the shafts.

Before returning the machine to service, perform a quick screening to ensure the repairs are completed.

When you suspect an issue with your electric motor winding, there are three categories of measurements to help identify the likely source of failures — electrical, mechanical and thermal.

To get a complete picture, evaluate the likely failure­ modes and match the right maintenance technologies with the most likely failure mode. Maintenance software and data gathering devices that integrates with third-party solution providers are ideal to accomplish this.

Electrical issues

A ScopeMeter and power quality sensor can help troubleshoot problems in drive and the drive’s output, power distribution, to uncover energy losses, and improve efficiency. These tools can assess electronic harmonics, distortion and load studies.

The motor and insulation tester assure safe operation, prolongs the life of electrical systems and motors. This device checks motor speed, torque, power and efficiency, and also checks for motor insulation degradation.

Thermal issues

Infrared imagers are the best technology for finding electrical hot spots in switchgear and motor controllers, for screening process and mechanical assets. The imagers test faulty connections, overheated bearings and tank levels.

Mechanical issues

Vibration and alignment tools are the best technology for diagnosing mechanical faults in rotating machines. They can test correct shaft alignment, imbalances, looseness, misalignment and bearings.

Plant owners, operators, and managers can benefit from both integrated data and maintenance management with a single system. Maintenance teams can cost-effectively implement this technology platform to address their needs with ease, using their existing staff and scale as necessary without costly retrofitting and large IT infrastructure investments. Leveraging these tools offer facilities the greatest flexibility and power to manage the health of electric motor windings to keep all of the organization’s assets up and running without downtime.