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Gerdau is one of the largest steel producers and recyclers in North America, with a production capacity of approximately 10 million metric tons of steel products per year. The company’s operations in Midlothian, Texas, maintain an inventory of approximately 70 vehicles, varying in size and usage across its steel mills and recycling facilities. An on-site predictive maintenance team inspects the overhead cranes quarterly. When the predictive maintenance team is alerted by the ALL-TEST PRO 5™ motor tester to a potential problem due to a lack of power, technicians take action to determine the cause of the issue.

 

What is Motor Circuit Analysis™?

A non-destructive low-voltage AC signal is passed through the motor windings to measure their response to these signals. The phase angle (Fi), current/frequency response (I/F), impedance (Z), resistance (R), and inductance (L) of each winding are measured, and the asymmetry of these measurements is compared. Winding malfunctions are identified by variations in the response to the signal supplied through the windings. These variations cause asymmetry in the measured response to the applied signal. Therefore, when testing three-phase equipment such as motors, generators, or transformers, the response of each phase is compared to the other two phases. Phase impedance is evaluated to identify coupling problems. Inductance is evaluated for possible rotor problems. Impedance and inductance matching are used to detect contamination or overheating of the windings. Insulation to ground testing detects problems with the conductor-to-ground connection.

 

Quarterly testing indicated motor deterioration (but more detailed testing found otherwise!).

The scrap crane trolley motor for recycling material #4 is scheduled for inspection in the first week of March 2017. The AT5™ unpowered motor tester will be used for Motor Circuit Analysis (MCA™) , which allows reliability/maintenance technicians to identify the condition of electric motor windings. The AT5™ was purchased in 2016 as a more portable handheld tool than the steel mill’s dedicated 60-pound weighing tester, which required a 110-volt power source.

The AT5™ connected to the motor control panel and performed a motor circuit analysis on a 20 HP trolley motor in just minutes. The test results showed an insulation-to-ground reading of 10.1 megaohms (see Figure 1). This ‘practically new’ motor, installed on a crane in October 2016, was tested at the time of initial installation. That initial test showed readings greater than >999 megaohms. This discrepancy in test results raised a red flag for the predictive maintenance team. Given that the motor had only been in use for six months, it was clear that it was unlikely to degrade that quickly.

Find the real problem.

The predictive maintenance team scheduled another test of the same motor the following week. However, this time the AT5™ would be directly connected to the motor. Within minutes of the second test, the AT5™ reported an insulation reading of >999 megaohms (see Figure 2). At this point, the predictive maintenance team realized the problem wasn’t with the motor itself, but with the tassel wiring from the motor control cabinet to the trolley motor. The cable from the drive to the tassel trolley junction box was inspected for damage and replaced immediately.

Learn from this predictive maintenance team!

They tested the new motor during installation.

It is crucial to test new motors at the point of installation. If a ‘new’ motor is installed after being stored for a period of time, testing confirms that it will function as promised. On-site testing can help identify problems that can be resolved within the warranty period. From a long-term perspective, motor testing also generates baseline data that may be useful for future maintenance reviews and decision-making.

Instead of replacing the motor immediately, they continued testing!

This predictive maintenance team doesn’t waste time trying to replace motors that are in perfect condition. They know how much time and resources are required to replace a motor: an overhead crane, multiple technicians, more people, and more working hours—all of which add up! By getting to the source of the problem, they save time and money.

They use reliable testing tools.

The AT5™ motor tester has proven to be an invaluable tool for motor diagnosis. It’s lightweight, portable, and provides instant results. This allows predictive maintenance teams to identify root problems immediately and resolve them quickly, enabling them to move on to other projects.

 

About ALL-TEST Pro, LLC

ALL-TEST Pro delivers true commitment to motor maintenance and troubleshooting with innovative diagnostic tools, software, and support to help you keep your business running smoothly.

 

About Gerdau

Gerdau, a 110-year-old steel company, is a leading American manufacturer of long steel products and one of the world’s largest suppliers of extra-long steel products.