Would You Believe? Some Oft-Repeated PQ 'Facts'

Published On
Oct 17, 2018

With the unprecedented amount of unregulated information available on the internet, one can find a wealth of facts and fiction on a given subject. Power quality is no exception. Even those skilled in the art can be misled by information that turns out to be posted by a proponent of a particular cause, rather than scientifically vetted facts.

In the ‘80s, the president of a large conglomerate company told a group of power quality monitoring equipment designers, including myself, that there would be no need for monitors within a decade, as manufacturers of equipment would make the equipment immune to PQ phenomena. Nearly four decades later, one could develop a case to say that many industries are even more vulnerable to power quality phenomena than back then. In order to increase speed of processors, the voltage that they operate on has decreased from 12 volts (V) to 1.3V or less. Noise on the reference ground signal lines that would be ignored by older CPUs can cause be perceived as false clock transitions or data. Couple that with increased interconnection to vulnerable communication circuits and you have a system with more opportunities for failure.

Another favorite misinformation is that the newer lighting types will eliminate flicker. The theory is because LED lighting uses direct current (DC) instead of alternating current (AC) voltage, the lamps aren’t susceptible to the voltage variations that result in light flicker. I have responded to more complaints of light flickering in past 3 years than in the prior 30. The majority have been LED lighting systems, especially on circuits with dimmer switches. The results have been discomfort in restaurant patrons to reduced egg production in chicken farms.

What the foreseers did unknowingly predict is that the flicker parameter used in the standards, perceptibility short term (Pst), often doesn’t show a problem. The intense mathematics that produce Pst are based on an algorithm developed for 60-watt (W) incandescent light bulbs. No significant variation in the input voltage to the dimmer circuit has been found in many locations, with the Pst being under 0.3 (where 1.0 is considered the threshold of perception). The flicker is there; we need a photon meter rather than a PQ meter to measure it.

Along those same lines is the often- repeated idea that running all computer facilities on DC voltage versus AC voltage also will eliminate PQ problems with computers and other IT equipment. Electronic equipment almost exclusively runs off DC voltage. The charger of your laptop turns the AC voltage into DC voltage. The rectified input switch mode power supplies in printers and PCs do the same. That doesn’t mean immunity. The electric utility distribution system is and will still be AC voltage in the near future, as the arguments that led Westinghouse to win out over Edison still hold.

As with CPUs, there are a multitude of paths for disturbances to make their way in to data centers even if the entire facility is run on a 380V DC bus. Improper grounding techniques, unprotected communication circuits, and HVAC harmonics generated from the newer high-order power supplies and the computer equipment themselves can contribute to continued susceptibilities to PQ phenomena.

Then there is my current favorite—the “smart grid” will raise the power-quality levels so there won’t be any related problems anymore. Electric utilities are installing billions of smart meters, often referred to as revenue meters with power quality. If one does some digging into how those meters are actually used, one will quickly see that it is revenue-based. It allows for time-of-use billing, the ability to charge more for energy when the demand is high. It also can provide outage information, which allows utilities to improve their SAIFI and CAIDI numbers. Those are numbers that the Public Utility Commissions look at, especially when the utility is going for a rate increase. This doesn’t imply in the least that getting customers’ service restored faster when there is sustained interruption isn’t a very good thing. But it didn’t prevent the process interruption. It didn’t improve the quality of the supply; it just helped reduce the pain (or cost).

We wouldn’t even get into the unsupported claims of mitigation equipment by some manufacturers selling on the internet to improve the quality of your electric supply and save you energy. For that, I suggest getting a copy of the recently balloted IEEE Std 1889, Draft Guide for Evaluating and Testing the Electrical Performance of Energy Saving Devices, and giving it a careful read.

I am not quite as pessimistic as this quote attributed to Edgar Allan Poe: “Believe nothing you hear, and only one half that you see.” However, I do suggest caution in believing that it must be true because it is posted on the internet from a seemingly reputable source. Do your homework and research thoroughly before investing in any solution that seems a bit too good to be true.

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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