Getting a Sense for Troubleshooting

Shutterstock/ Francescomoufotografo
Shutterstock/ Francescomoufotografo

I recently updated material I had originally written in 1995 for a forthcoming power quality seminar on the latest PQ measuring, monitoring and mitigating tools. Many of the tools are as necessary now as they were then, so here are my dusted-off tools you can use.

The following are the tools every electrical contractor should have at their disposal, as they are the minimum for troubleshooting PQ problems or performing periodic PQ audits:

  • Screwdriver: My very first slide highlights this basic complement, which is still one of the most important tools for fixing a number of PQ problems. Connections to equipment, breakers, switches and other devices can loosen over time from the heating and cooling cycles during load changes. As the gap increases, the impedance goes up, which results in more heat and in larger gaps, as well as larger voltage drop across the contact point. Eventually, the contact points may fail intermittently or catastrophically. Periodically check the tightness of connections with a properly insulated screwdriver. This also applies to torquing bolts on de-energized bus bars. Refer to guidelines in the NFPA 70B, Recommended Practice for Electrical Equipment Maintenance, and manufacturers’ maintenance instructions.
  • Digital volt meter (DVM): Often the first tool used, a DVM is good for the presence of sustained voltage levels, but it doesn’t have much use for intermittent or short- duration rms voltage variations. Likewise, it is not useful for detecting transients. The more advanced DVMs often have harmonic capability, though they may not follow the IEEE and IEC standards for measuring such, so the results may differ compared to a certified harmonic measuring device.
  • Clamp-on ammeter: Though voltage is often the parameter that deviates from normal in PQ disturbances, the current usually is the culprit in causing such. A significant current unbalance will result in a voltage unbalance. Harmonic currents from loads lead to the propagation of harmonic voltages. Like the shortcomings of a DVM, it often isn’t possible to detect the current change that resulted in the voltage sag or swell.
  • Infrared camera: The loose connection syndrome mentioned above can usually be detected efficiently using a thermal imaging camera. Many are available for under $100 that can connect to most cell phones to quickly detect hot spots in breaker panels, distribution systems and electrical equipment, such as motors.
  • Data logger: While a few DVMs have data logging capability, their memory isn’t adequate for longer term monitoring. This is where a data logger comes in. A monthlong survey of voltage and current can find problems before they escalate into major ones. Data loggers in weather resistant-packages that can power off the phase are especially versatile.
  • Portable PQ monitor: Whereas the price point of a dedicated power quality monitor used to be out of the realm of most small electrical contractor firms, the price has dropped significantly in the past 10 years. Of course, you get what you pay for, so don’t expect a $2,000 monitor to have the same capabilities for triggering and waveform capture as the $5,000 unit. Be sure that the current probes you use have the responsiveness and bandwidth that take advantage of the PQ monitors. Renting is a good option.

In addition to these portable PQ tools, here are some others that may be very helpful in certain applications:

  • Permanently installed system monitor: This is like having portable monitors throughout the facility on a 24/7 basis. Not only can potential problems be found early, but when something does occur, you can determine the source and extent of the effects at the click of a button.
  • Ground impedance tester: Good grounds are key to preventing many PQ problems and having an equipotential grounding system.
  • Spectrum analyzer: Not all extraneous signal issues are steady harmonics, or they may be above the bandwidth of the measuring instrument, including noise, which is what the spectrum analyzer is for.
  • Oscilloscope: Though most PQ monitors have built-in oscilloscope capabilities, the high-frequency o-scope can be useful in specialized cases.

There’s one more tool you’ll use that you always carry with you: your senses.

Here’s a still-relevant cautionary note from that original seminar. During my presentation, I would ask, “When conducting a PQ survey or study, use all of your senses but …” Someone in the audience usually would shout out “Touch!”

Your eyes can see wiring mistakes, “blinks” and flickering lights. You can usually hear transformers hum from harmonics and smell overheated electromagnetic devices, but touch should be thrown out as an option.

You’ll want to keep your PQ tools handy, but your hands off your work.

About the Author

Richard P. Bingham

Power Quality Columnist

Richard P. Bingham, a contributing editor for power quality, can be reached at 732.248.4393.

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