Electrical Troubleshooting Quiz — Nov. 16, 2021

The plant was recently awarded a new contract to build the widgets for the XYZ Corp. Your company has been chasing XYZ for a long time because the potential upside is huge. If your company can provide these widgets at a high enough quantity and low enough defect rate, more widgets are to come.

What clinched the deal with them is that your company implemented a Six Sigma program a few months back. Part of the pitch to XYZ was that operators could stop the line at any time a quality issue arose. This meant reducing the percent of defects and thus raising both overall quality and total output.

However, the line dedicated to the XYZ widgets has been suffering from motor issues. In nearly all cases, one or more of the overload protection devices (typically heater strips) blows, and the line shuts down. The operators call for a maintenance tech. By the time the maintenance tech responds, does some basic testing, identifies those overloads as bad, and replaces the overloads, half an hour or more can pass. This has caused your company to fail to meet its unit per day promises to XYZ.

You have been tapped to solve this problem. How might you begin?

One of the problems with Six Sigma and similar programs is they are so complex that many companies implement them a la carte or as “homebrew” versions. A likely problem here is the operators, ever diligent for quality problems because management has made quality a big issue, are stopping the line too frequently. The production quotas mean these stops have to be quick. Restarts happen quickly, meaning the motors run hot. This leads to the opening of the overload devices.

Although you can’t just go in and blame production, you can get some data from them and the equipment. A qualified thermographer can provide a heat assay on the motors that blow overloads, but this information must be collected under normal operating conditions rather than after equipment has cooled.

If the motors run hot and there are several operator-initiated shutdowns during the day, you can advise operations that a 10-min. cooling period is required after each shutdown. This is less than the half-hour incurred by opened overload devices. And if they are faced with 10 min. of waiting to restart after each shutdown, they will adjust by making the policy a little less liberal. If they are consistently finding the operators are crying wolf, then they’ll devise some metric or other constraint to limit these to something more reasonable.

In parallel with this, you need to address other possible causes. For example:

• How much is your voltage imbalance on each motor branch circuit? Focus on the motors that have had the overload protection shutdowns. Various recommendations exist; for example, 5% is acceptable. But with other contributing factors, maybe you should consider a much lower value to be acceptable.
• Use a power analyzer to check the waveform for problems like flat-topping or excess harmonics.
• What is the power factor at each motor? Can it be corrected?
• Are any variable frequency drives (VFD) involved? If so, do they correct for power factor and harmonics, and is each one correctly tuned for its application?
• Do these motors have sufficient cooling air?
• Is each motor of the correct NEMA design and insulation temperature rating for the application?
• Do any of the overheated motors start across the line? If so, a soft starter or VFD is probably a good investment.
• Is each motor properly mounted and correctly aligned? Have you verified with vibration testing?
• Are the gearboxes properly lubricated? Simply changing the gear oil from paraffin-based to synthetic will reduce motor load significantly. Ensure it’s the correct viscosity and that it’s clean. This is an issue for the mechanical arm of maintenance, so make them aware that it needs to be addressed.
• Are the motors properly lubricated? The emphasis is on properly. Don’t guess, know the procedure. Hint: If the people doing the lubrication don’t mention the drain plug when describing how it’s done, they aren’t doing it properly.