Motor maintenance in an IIoT world

In an industry driven toward higher levels of productivity, with the ultimate goal being minimal downtime, proper maintenance of rotating equipment such as electric motors is essential.

Establishing a healthy blend of traditional best practices and emerging Industrial Internet of Things (IIoT)-enabled technology is key in developing the most cost-effective motor maintenance program.

The content in this article provides an overview of emerging technologies within the IIoT, which work in tandem with traditional best practices to ensure your operation is always performing at its optimum level of productivity and providing the highest possible return on the investment you’ve made in a pit or quarry.

Start with the basics

Imagine the efficiencies that can be achieved by transforming a personal computer or mobile device into an operation command center. Photo courtesy of Regal Beloit America Inc.

The best place to begin a motor management program is before you buy it.

The performance of any asset is dependent upon its inherent reliability, operating conditions and maintenance strategy. No amount or manner of maintenance is going to improve the reliability of a poorly designed or manufactured motor. Select a motor from a reputable manufacturer who stands behind their product.

Because one of the common failure modes is bearing contamination, select a motor with adequate ingress protection. Bearing failures due to misalignment or excessive vibration can be reduced by specifying a motor with a precision-balanced rotor, as well as by utilizing best practices during installation, such as laser alignment techniques. A special insulation system and/or shaft grounding may be required if your motor is being powered by a variable frequency drive.

One other consideration is whether the motor will be stored for an extended time prior to, or between uses, as this may require specifying space heaters and other precautionary intervention such as manual rotation of the shaft every 30 days to redistribute the grease and prevent damage to the bearings.

“Right-sizing” a motor for its intended application means understanding what will be expected of it. Make sure it’s of a sufficient but not excessive horsepower rating; operation at reduced loading tends to result in lower efficiency.

Most manufacturers have an application checklist to help ensure you don’t miss any critical nuances, such as specification of roller bearings for certain belted loads. Also, beware of “motor creep,” the phenomenon that results from replacing original motors with an available stock of incorrect power ratings.

Maintenance strategies are best developed using reliability-centered maintenance practices. This begins with identifying critical equipment in the facility, determining applicable failure modes, and employing various methods to mitigate or eliminate those failure modes. Mission-critical motors deserve special attention; establish a spares inventory from which maintenance personnel can draw upon in an emergency.

Obtaining baseline performance data on new or rebuilt motors will provide useful information, which can be incorporated into the various predictive maintenance options offered in a traditional venue or via IIoT-enabled technologies that provide local and remote monitoring with advanced analytics.

Traditionally, time- or cycle-based maintenance strategies have been utilized to prevent failures. This typically incorporates periodic physical inspection using your senses to safely see, hear, touch and smell the many clues your motor is giving you to alert you to abnormalities – we recommend you avoid tasting your motor.

Unfortunately, human senses are not acute enough to detect failures early in their progression, requiring an extensive inventory of spare parts (and their associated carrying costs) to be available when equipment fails.

According to a frequently cited Electric Power Research Institute (EPRI) study, the relative cost of a proactive maintenance program is 77 percent less than a reactive program. Since downtime on a rock crusher in a typical quarry can be many thousands of dollars per hour, the benefit in establishing and maintaining a proactive maintenance program is obvious. In an ideal world, elimination of downtime through predictive techniques would save the average pit or quarry millions of dollars each year while improving worker productivity and safety.

Sophisticated, yet simple to deploy, IIoT-enabled systems gather and report operation conditions, identify fault progression through pattern recognition and trending, and calculate duty cycles via a cloud-based network.

As IIoT-based systems become more common, their smaller sensors and lower costs will make them more attractive to your operation. Imagine gathering and reporting operational conditions, duty cycles and trending of your valuable equipment’s lifecycle via a local or cloud-based network.

Operating parameters

Fundamentally, an electric motor converts electrical energy into mechanical energy, exchanging current for torque. In the process, many critical electromagnetic and mechanical forces come into play. Each element tells a story about the motor’s overall health. Effective motor maintenance programs should detect the following faults and conditions:
◾ Rotor circuit porosity or rotor faults
◾ Motor misalignment
◾ Rotor eccentricity
◾ Power quality issues
◾ Overload conditions
◾ Load imbalance and/or disturbances
◾ Foundation looseness
◾ Bearing faults

Whether traditional or more innovative methods are employed, the same operating parameters must be captured to provide useful signals to maintenance personnel. These include:

Operating temperature. What is the baseline versus manufacturer/rebuilder specifications? Is there a trend? Are application demands changing, impacting operating temperature? Has the motor been relocated to an application different from that which it was originally selected?

Simplistic measurements of the motor’s temperature, such as the infamous “calibrated hand,” should be avoided – for obvious reasons. Not only is this practice unsafe, but it’s terribly inaccurate. Temperature of the windings and bearings is the No. 1 clue as to a motor’s health, as most other anomalies manifest themselves as motor heating.

Vibration. Vibration levels outside specification can provide useful clues as to irregularities within and external to a motor, from defects in material or workmanship to misalignment or an inappropriate mounting arrangement with inadequate support structure.

Vibration is also used to detect bearing faults long before bearings actually fail. By tracking vibration over time, many mechanical faults can be detected well in advance before they become catastrophic failures.

Sound level. Excessive sound levels can be traced to electrical or mechanical issues. Mechanically induced sound is most often another symptom of vibration levels, while electrical noise can be attributed to issues within the motor or power supply. Good systems can discern the difference.

Voltage. Measurement of motor voltage – and equally important, the balance of voltage between each of the three phases – is a critical piece of data used to determine motor health.

Current. Because the motor’s output torque is directly related to input current, measuring this important parameter helps you understand whether the motor is operating within its specified limits. Measuring and plotting this data over time provides useful clues as to whether anything in the motor’s operation or within the application has changed, which could signal imminent failure.

With the use of motor current signature analysis, even more detailed data, such as failed windings or a broken rotor bar, can be gleaned from just the motor’s current.

Text alerts

Today, more than ever, data from numerous sources is available. This can aid in improving operations, performance and reliability. These continuous data streams exceed human capability to effectively analyze, interpret and act on this information.

Available IIoT-based systems run the spectrum from relatively simple motor sensors, which monitor vibration, temperature, current and voltage, to GPS-based remote monitoring equipment capable of transmitting operating conditions and trends anywhere in the world. More sophisticated systems offer predictive and adaptive functionality to sense trouble and command the system to reduce loading while maintenance personnel are dispatched to investigate the situation.

Imagine the downtime you can prevent when your monitoring system automatically sends you an email or text message alerting you to an equipment failure before it actually fails. Imagine no more, because the days when you can do all that are here.

Dan Phillips is the director of PTS lifecycle services at Regal Beloit America Inc.; Theresa Smigura is innovative development engineer in R&D and IIoT at the company; and Rick Munz is Regal Beloit’s product/marketing manager of general industries, commercial and industrial systems.