Five Ways to Prevent Poor Power Quality With Maintenance

Many causes of poor power quality are preventable with the right maintenance. Is that maintenance performed at your facility? Does your maintenance department address the issues below?

1. Bonding pathway and connections. Do you have any procedures for checking the bonding system for all of the equipment on a given circuit or in a given area? Over time, mechanical connections (e.g., bolted, threaded) of electrical systems tend to deteriorate and become high impedance points. When this happens to enough bonding system connections, especially in the equipment grounding conductor system, some undesired current begins to flow between metallic objects and some circulates within the electronics. A common maintenance practice is to simply tighten connections, but this actually makes them worse (especially if they are not actually loose or deteriorated to begin with). Use an impedance meter (not a DMM) to measure across suspect connections and identify bad ones. To repair a bad one, dissemble it, clean the contact faces, reassemble with new locking hardware, and tighten to the correct torque value.
2. Electronic motor drives. These can be sources of power quality problems. Consider, for example, a drive that is designed to be power-factor corrected and harmonics-corrected. Are those features still working, and how do you test to ensure they are? Capacitors go bad eventually, whether in a drive or not. Performing the recommended diagnostics and maintenance on each drive will keep you ahead of this particular 8 ball.
3. Transformer heat issues. Dry-type transformers don’t lend themselves to maintenance the way oil-filled transformers do. This doesn’t mean you can set one in place and forget about it. Even if it’s been properly sized and no additional loads have been added, a transformer can run hot for many reasons. The usual culprit is impaired ventilation. In a factory, the usual cause is stuff stacked up too close to the vent. Another less common cause is a new process or machine is installed near the transformer and it vents its waste heat into the same space. If a feeder from that transformer shows a distorted waveform, get out an infrared camera and see what’s going on thermally.
4. Motor insulation and general motor health. Big motors are big inductive loads, but so are many small motors on the same transformer. Part of motor maintenance is testing the insulation integrity. A good way to do this is to take baseline insulation resistance readings on the windings and then schedule subsequent readings at some regular interval. Over time, the readings will gradually drop as the insulation gradually degrades. If you plot these out and see a hockey stick when you add the latest readings, it’s time to replace or rewind that motor. An automatic insulation resistance monitor is an even better solution, if appropriate for the application. This way, you can see the hockey stick emerge much sooner. But you also get those windings dried out if they are starting to accumulate some moisture.
5. Power analyzer analysis. Who is monitoring the power monitor and who is analyzing the reports available in the power analyzer? A power monitor without a qualified analyst is about as useful as a taxicab without a driver. “Wall ornament syndrome” leaves the value of a power monitoring system unrealized. Make sure someone who knows what he’s doing is reading the story that power monitor is writing.

If you have only a rudimentary power analyzer or none at all, don’t rush out and buy the equipment. First, decide on whether to outsource the analysis or have your own expert on staff. Outsourcing has some huge advantages, such as the fact a firm that does this has ongoing experience with other facilities similar to yours. And they won’t get called off on side projects, becoming too busy to look at what the power monitor is reporting. Second, implement a power monitoring strategy that covers your service(s), critical feeders, and critical equipment. Then work with your analyst to specify what exact equipment needs to be purchased, installed, set up, and monitored.