Tips for improving the efficiency and reliability of your motor-driven systems
Balancing plant maintenance costs and activities with the need to achieve production goals is a daily challenge for most maintenance professionals. Since the motor-driven system is often a critical component in this dynamic, let’s look at some best practices to help it achieve those goals and meet customer demands.
Figure 1: Motor-driven system.
To plant maintenance pros in most industries, these are familiar questions: “How do we improve reliability within our plant?”
“How can we reduce unplanned downtime, so our production stays more consistent?”
“How can we decrease our total cost of ownership of our equipment?”
They phrase it differently, but ultimately each of these questions is about improving the efficiency and reliability of the motor-driven system. Although that encompasses a wide range of components including fans, pumps and drives, here we’ll focus on the electric motors.
As a class, motors are among the most efficient and reliable machines in most plants. But when one fails, especially if it fails unexpectedly, plant reliability obviously suffers.
The resulting downtime can slow or halt production, sometimes ruining raw materials and components or even damaging finished product. If you’re seeking answers to the questions about plant reliability and unplanned downtime, solutions that make motors last longer and prevent premature failures are good places to start. Such solutions will likely decrease your total cost of equipment ownership as well.
Failure analysis
Since motor failures often are a call to action, let’s start there. The mean time between failures can vary widely, so determining the root cause is the first step toward improving the motor-driven system’s reliability. Was there a maintenance issue or a previous failure? Was the motor well suited for the application load, torque, start-stop and environmental requirements? Was it installed and aligned properly, or did the process change after the motor was installed?
Some maintenance pros have the experience to analyze motor failures, but usually it’s a task for a qualified service center. A qualified service center can also help you determine what to do next, weighing such factors as the type of repair/rewind, the cost and availability of new equipment, the application requirements, and the efficiency of the repaired motor versus that of a new one.
Once identified, many causes of failure are easily remedied. For example, studies have shown that the most common motor failure involves the bearings, which can be a simple, cost-effective repair. Other solutions may include improved maintenance, condition monitoring, a motor rewind, or a replacement motor. Unless you determine the cause of failure, though, neither efficiency nor reliability will improve–even with a new motor.
Figure 2. Quality motor repairs ensure efficiency and reliability.
Is there a standard for repair of rotating equipment?
If repair turns out to be the best option, it’s logical to ask how you can be sure the work will be done correctly. Fortunately, the motor repair standard approved by the American National Standards Institute (ANSI), ANSI/EASA Standard AR100-2020: Recommended Practice for the Repair of Rotating Electrical Apparatus defines the performance criteria for a quality repair. It also cites best practices from widely accepted industry standards organizations, such as ANSI, ABMA, CSA, IEC, IEEE, ISO, NEMA and NFPA. To be assured of the highest quality repairs, specify that they be made in accordance with ANSI/EASA Std. AR100-2020.
Speaking of motor repair/rewinding, it’s important to note that even the most energy-efficient motors can be repaired with no loss of efficiency, if the repairs are in accordance with the best practices in ANSI/EASA Std. AR100. This was proven in a recent study by EASA and the UK-based Association of Electrical & Mechanical Trades (AEMT Ltd.): The Effect of Repair/Rewinding on Premium Efficiency/IE3 Motors. Based on that study, EASA and AEMT also published the Good Practice Guide to Maintain Motor Efficiency (see sidebar).
Why consider an EASA-Accredited service center?
EASA has long encouraged motor users to require that service centers adhere to ANSI/EASA Std. AR100. Many users also require that each step in the supply chain comply with some quality assurance program. The EASA Accreditation Program fulfills this need–and beyond that, it has several components that are key to the efficiency and reliability of your motor fleet, including:
• Use of calibrated equipment with traceability (where required for precision measurements)
• 23 audited categories covering everything from initial inspection to completion of the repair
• More than 70 motor repair/rewind criteria are audited to ANSI/EASA Std. AR100–from terminal connections to core testing, from shafts and rotors to frames, housings, bearings and balancing
• Continual, documented employee training
• Internal and external auditing
EASA’s Accreditation Program requires annual internal audits and independent, third-party on-site audits initially and every three years to ensure compliance with ANSI/EASA Std. AR100-2020. Motor users can provide this accreditation to their customers to show that a critical part of their supply chain or process has a quality assurance program that meets the industry standard–ensuring efficiency and reliability. Partnering with an EASA-Accredited service center can help you confidently answer the questions posed earlier.
The “Big Four” factors impacting motor health
Earlier we looked at the importance of failure analysis. What we do with that information can have a major impact on equipment efficiency, reliability, and cost of ownership. Often the motor isn’t the root cause of the problem; it’s external factors from the application that I call the “big four”:
• Routine maintenance
• Environment surrounding the motor-driven system
• Alignment during installation
• Power supply for the motor-driven system
Failure to address the “big four” will likely result in the same failure of a new or newly repaired motor.
Maintenance. To prevent winding and bearing failures, keep the motor clean and follow the manufacturer’s recommended lubrication intervals. As a best practice, do not mix lubricants, many of which are incompatible and cause premature bearing failure. Over- or under-greasing a bearing can have the same result.
Environment. Key things to monitor in the motor-drive system’s immediate environment are ambient temperature and vibration, relative humidity, airborne contaminants, and potentially corrosive elements. Individually or collectively, these could hasten bearing and winding failures.
Also, make sure there’s sufficient airflow to cool the motor. If the motor has air filters, change them regularly. Dirty filters restrict airflow into the machine, causing it to run hotter and increasing the risk of bearing and winding failures.
Alignment. Something commonly overlooked during the installation process is proper alignment. Make sure the alignment of the motor-drive system is within tolerance, not just an individual component. For example, flexible couplings often function adequately with a fair amount of misalignment. However, a motor-driven system will generate less heat and lower vibration levels if it meets or exceeds the most stringent alignment specification for that system. This will lead to longer bearing life and a more efficient motor-driven system that can save money on utility and repair costs.
Power supply. The quality of the power supply is important for winding longevity. Common concerns include variation in supply voltage that is more than 10% of the nameplate voltage, voltage unbalance at the motor terminals that exceeds 1% of the average voltage, and transient peak voltages at the motor terminals. Voltage variation and unbalance can increase winding temperatures and cause premature failures. Transient peak voltages at the motor terminals can damage winding insulation, creating turn-to-turn or ground faults.
Condition monitoring
Once the motor-driven system is set up properly and you’ve handled the “big four” factors impacting motor health, condition-based monitoring can help prevent unplanned downtime. This could be as simple as having the service center check vibration, temperature, and insulation resistance on a prescribed timetable.
Remote condition monitoring with Industrial Internet of Things (IIoT) devices is the next step. These devices detect and record step changes in certain inputs and then prompt you to investigate. Some of them even use machine learning to reduce false positives, by getting “smarter” as they see more anomalies and receive feedback from users.
The key to success with either method is to evaluate and act accordingly when there is a step change in a monitored trend.
This may prompt you to send a motor out for reconditioning before it fails, keeping your productivity up and your repair costs down. If you need help during the evaluation and action phase, rely on a service center that adheres to ANSI/EASA Std. AR100.
The Effect of Repair/Rewinding on Premium Efficiency/IE3 Motors validated through third-party testing that ANSI/EASA Std.
AR100 repair best practices will maintain the efficiency of the repaired motor–whether it’s a mechanical repair or a full rewind.
A supplemental document called the Good Practice Guide to Maintain Motor Efficiency explains why these best practices are important and how they should be implemented.
It’s useful not only to service centers but also to end users who want to educate themselves about repair/rewind processes they receive.
Text: Matthew Conville, MBA, P.E. EASA Technical Support Specialist
