The past two articles covered how to get started with a power quality Job, including safety, connections and setup. For someone who doesn’t do PQ measurement and monitoring tasks often, a PQ meter, monitor, analyzer, instrument, software and systems might be a bit confusing. Even more puzzling is what piece of equipment from which vendor should be used. Let’s take a look at these issues before delving into what to do with the data once it’s collected.

Editor's Note: You can catch up on this series by reading part 1 and part 2.

Definition and terms used 

As in a number of other articles, the NJATC Power Quality Handbook and IEEE Std 1159, Recommended Practice for Monitoring Electric Power Quality, are a great starting point for beginners and as a refresher for those more experienced. 

From IEEE 1159 comes this definition: “The term power quality refers to a wide variety of electromagnetic phenomena that characterize the voltage and current at a given time and at a given location on the power system.” 

The definition I’ve used in hundreds of seminars and other presentations is, “any occurrence manifested in voltage, current or frequency deviations that results in failure or misoperation of end-use equipment.” 

If everything works as it should in the electrical environment, then it’s not really a power quality problem for that equipment at that time. My toaster can make perfect toast with 15% Vthd, voltage fluctuations with a Pst of 4 and voltage sags to 70% of nominal for 10 cycles. Some adjustable speed drives, desktop computers, extrusion machines and other equipment may not be so lucky. For them, this would be a power quality problem.

Equally confusing can be the use of the terms to describe an instrument that can be used for power quality measurements and monitoring programs. A measurement can be rms voltage, voltage total harmonic distortion, true power factor and hundreds of other parameters measured over a prescribed time with a process defined in the PQ standards. Making these measurements continually over a period of time and saving the relevant data is what we call a monitoring program or session. 

Portable instruments can move. Systems instruments are permanently mounted in panels or enclosures. Handheld instruments are a subset of portable instruments, which are obviously smaller, lighter and—to no surprise—able to be held in the hand. Of course, there are lots of crossovers, which the marketing departments of instrument manufacturers use to further confuse things. A number of PQ instrument manufacturers have product offerings in all three categories. This article will follow those guidelines in describing some of the PQ instruments out there.

PQ instrument guidelines

Handheld PQ instruments are generally characterized by single-phase connections, as getting all the voltage leads and current probe connections into a handheld package makes it a bit unwieldy. They are sort of like digital multimeters on steroids. They will calculate PQ parameters such as harmonic distortion, and some have logging capabilities to save data on a timed interval. Companies such as AEMC, Amprobe, Elspec and Fluke have products under $2,000 that are good tools for an initial analysis of what’s happening to the voltage and current.

The portable instruments are generally three-phase instruments rated for most in-facility voltage levels and with a variety of current probes to measure from 1A to 3,000A. Graphic displays provide oscilloscope-­like displays and time plots of stored parameters. These are the go-to instrument for troubleshooting and can be left on-site to monitor for weeks or months. Some have weatherproof enclosures. Companies such as, Dranetz, Fluke, Hioki, Megger, PowerSight and PSL have instruments with quite extensive monitoring capabilities in the $4,000–$10,000 range. If this price range is beyond your capital equipment budget, instrument rental companies such as Electrorent, RenTelco, Trancat and TRS carry many of these products.

Though electrical contractors are less likely to be buying and installing the permanent or fixed-system PQ instruments, they may already be in the facility of interest. These are an extremely valuable asset that should not be overlooked. Eaton, EIectro Industries, Dranetz, PSL and Schneider Electric are often found in facilities where downtime isn’t an option. Having an instrument already there collecting the necessary data can make the task much easier. It’s like a doctor having an EKG machine on a patient before the heart attack.

It’s not uncommon for PQ consultants and electric utility engineers to have instruments from multiple vendors. Standards on data formats and communications have made it possible to combine data from a variety of sources to get a much more complete picture. Though there is the analysis-paralysis potential from “big data,” most vendors’ software programs can take gigabytes of data and provide the simple answers, for example: this is what caused the equipment to malfunction, or the parameters are within limits now but the trends indicate there is likely a problem in the near future. 

Next month we’ll look at which tool makes sense for the particular task.

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