The plant consists of four unconnected buildings, each with its own electrical service. In Building Three, production has fallen short of quota because of repeated downtime incidents. In the past six months, there have been:

• Over 20 incidents of motor overloads taking a motor offline.
• Six PLC modules that had to be replaced.
• Multiple reports of dry type transformers humming loudly and “radiating heat.”
• Multiple complaints of lights flickering.

The Operations Superintendent of Building Three has missed his performance bonus three months in a row now and has decided to provide what he calls “adult supervision” in the plant engineering department. He wrote a capital funding request for several power conditioners to be installed “to fix what is obviously a power quality problem.” He needs the Plant Manager to sign off on it before sending it to Corporate, and she won’t sign off before getting input from the Plant Engineer. The Plant Engineer came to you.

What are some steps you can take to get to the bottom of these various failures, and write your own list of recommendations?

Answer to Quiz

These problems are not necessarily related. Take them one at a time to see what is really going on.

It might surprise the Superintendant to know that the primary reason motor overloads open is the motor is overloaded. Start by identifying which motors have had open overloads and which, if any, are repeats. The responding electrician to any of these downtime calls should have looked for the cause, and put something down in the work order system. Look there for the causes. You may see things like dirty air intake, dirty oil in gearbox, alignment problems, and operator error. A power conditioner will not fix any of these.

PLC modules might fail due to problems with the PLC power supply, but that very power supply rules out most power quality issues. As with the motor overloads, consult the repair records and see what each responding tech wrote. Determine if human error might be involved, for example removing a module and zapping it with static discharge. Check any involved power supplies, to ensure the voltage is correct and there’s little or no AC ripple. Also check for proper bonding of metallic objects. Another issue is incorrect terminations. For example, terminating a 120V control circuit conductor to a thermocouple input terminal or mixing resistance thermal device (RTD) and thermocouple wiring.

A dry type transformer could emit a loud hum due to heavy loading, and that will also cause it to throw off more heat than usual. Ask which transformers are in question, then visually inspect for proper airflow around each, proper grounding connections, and proper bonding. If a given transformer is indeed humming loudly, go to the panel and measure the total load. You should also determine the power factor at each motor supplied by that transformer. If power factor is low at a few of the largest motors, adding power factor correction capacitors (or a power factor corrected variable drive) at each one will noticeably reduce the hum and the heat.

Lights flicker for many reasons, such as a bad ballast or a bad lamp. A possible cause in the afflicted area is lights were wired with a shared neutral but there is a lot of non-linear load on that particular panel so the neutral isn’t sufficient to handle the unbalanced current. Poor bonding to the Equipment Grounding Conductor is another possibility. A power conditioner won’t solve these problems. As with the other problems, look at the specific equipment involved.

A power conditioner does have its place. But it is not a first line of defense. It helps you cope with power quality problems; it does not solve them. Used incorrectly, power conditioners can make power quality problems even worse.

Once you’ve gathered enough information for a full picture, identify what the recommended fixes are and which ones Maintenance has already implemented. For example, it sounds like Maintenance is lazy because you did nothing about nearly two dozen motor overload incidents. But what if each had been a one-off because Maintenance fixed the root cause in each incident? For example, the first motor failed due to a dirty intake filter and a tweak on the PM schedule fixed that one. But the second motor got overloaded because the operator fed the machine too fast. A quick conversation with the operator, and that cause was solved.

If a power quality survey has not been completed at this facility in a few years, such a survey needs to be arranged. You’ll want to include the Building Three Superintendant in that process, since he made a stink about power quality. Yes, he may slow it down. But as with every major plant issue, there is always a political repair to do in addition to an equipment repair. Treating him as your ally and seeking his input should do the job nicely.