Monitoring power quality becomes increasingly imperative as the modern power grid changes with the addition of green energy sources and as coal-fired generating plants continue to be taken out of service.
“As loads increase, coupled with the intermittent nature of solar and wind energy, the voltage stability will suffer,” said Jason R. Huneycutt, P.Q. applications engineer at Megger, Valley Forge, Pa. “In addition, renewable-energy sources add more power quality (PQ) issues such as higher order harmonics, power reversals and voltage frequency synchronization. High-speed frequency inverters used in solar and wind must be able to convert the DC power to AC power and match the frequency of the power grid in order for the power to flow back to the power grid. These high-speed inverters cause higher order harmonics, which cause more heat.”
PQ testers are available with varying levels of sophistication. A standard multimeter measures voltage and current.
“Some lower-cost PQ testers will record limited data and power-quality events such as dips, swells, power, energy and harmonics. But these testers will not meet requirements established by numerous standards related to power quality,” Huneycutt said. “An advanced PQ analyzer, however, will record all rms, power, energy, power factor, frequency, flicker, unbalance, total harmonic distortion, total demand distortion, harmonics and inter-harmonics. It will record all power quality events including dips, swells, sub-cycle distortions, high speed transients, total harmonic distortion, rapid voltage change, phase angle shifts and mains signaling.”
“More advanced PQ analyzers today can record higher harmonics, inter-harmonics, DC voltages and phase-angle shifts that are caused by renewable sources. They can now also capture higher voltage transients down to one microsecond, usually caused by lightning. We have also seen an increased demand for indoor and outdoor use and the ability to be powered from phase voltage,” Huneycutt said.
For each event, raw waveform data needs to be recorded pre-event and post-event cycles, and it is essential to analyze the cause of the event.
“Today, analyzers need to go beyond power quality. Some advanced analyzers will perform as recording oscilloscopes, capturing waveforms for days, weeks or months. Along with advanced analysis software, it allows the operators to troubleshoot the issues encountered today,” Huneycutt said. “Modern power quality analyzers will record power quality as well as all energy parameters and perform as a recording oscilloscope simultaneously, saving time and providing a complete picture.”
High-quality PQ analyzer manufacturers, he added, have embraced the trend of multifunction testers. Technology has allowed them to include a number of additional features and test capabilities.
“Wireless communications, in general, have increased analyzer versatility and reduced user time. Using Wi-Fi, cellular and hotspots allow operators to monitor and communicate with the analyzers remotely. They can view the field data from their office. Bluetooth allows short distance communications, but for true remote communications, Wi-Fi and cellular are more valuable,” Huneycutt said.
Richard Wexler, director of marketing, instruments, for Flir Systems (manufacturer of Extech products), Wilsonville, Ore., said power quality testing is not a one-size-fits-all practice—different installations demand different test equipment.
“A range of power quality problems include noisy waveforms and harmonic frequencies in the grid. Harmonics not only manifest as an electrical issue but as a thermal issue with a temperature rise of equipment and conductors. Variable speed drives start to misfire, and motors suffer harmonic torque pulsations, resulting in uneven shaft rotation, vibration and premature wear,” Wexler said.
Despite an increase in sophisticated multifunction testers, Wexler said, dedicated power quality testers have not been relegated to the dustbin of test equipment history. The wide range of test functions on a PQ analyzer provides granular insights that are only available on a dedicated rig.
“Test equipment makers are offering added choices in terms of test leads and current probes to ensure power quality testing is done right, and that the test equipment itself isn’t a barrier to effective and accurate diagnostics,” Wexler said. “This is particularly apparent with the array of clamp probes now available. Flexible current probes—also called Rogowski coils—are available in different amp ratings, thicknesses and lengths. Similarly, rigid jaw-style clamps offer choices that can be tailored to a site’s needs. Test leads with a silicone jacket remain flexible and easy to use even after overnighting in a truck in winter.
“Smart electrical contractors make good use of their test equipment for general electrical testing as well as power quality work. In addition to power quality analyzers, data loggers for voltage and current are employed as well as power clamp meters and insulation resistance testers,” Wexler said.
There has been a sharp increase in on-site solar installations at large commercial and industrial sites driven by local, state and federal incentives and subsidies to adopt solar. High schools, hospitals, malls, manufacturing, parking lots and garages are increasingly covered with raised solar panels. Larger-scale installations can make a substantive impact on electrical costs and power quality, for better and worse.
“One area where test equipment have evolved is with solar industry test leads,” Wexler said. “These ensure safe, snug connections to panels and inverters for faster, easier and more accurate diagnostics.”
Tester data logging capabilities have increased with availability of low-cost SD card storage.
“Dedicated current and voltage data loggers with multiple channels of input can store upwards of 2.7 million records on a 4-gigabyte card,” Wexler said. “This can be useful for high-frequency data logging as well as long-term logging. For added versatility there are PQ analyzers that record directly to Microsoft Excel files, helping to sidestep cumbersome importing and formatting.”
George Vlachos, AEMC regional sales manager, Dover, N.H., said PQ testers have more memory, better quality displays, greater range of CTs, smaller size, faster sampling and easier access of remote data. Basic testers should be three-phase 1,000V instruments with TRMS reading, memory, transient detection and alarm/event triggers.
“There is a trend toward multifunction testers that perform all tests,” Vlachos said. “Multifunction testers perform all tests and eliminate the need for individual volt and current meters, phase rotation meters and others. Harmonics issues have been on the rise, and newer PQ testers detect higher order harmonics and can provide information about the source.”
Data storage is important.
“Today, most testers can store 30 days or more data,” Vlachos said. “Memories of megabytes to gigabytes are available. Smart recording modes eliminate the need for huge amounts of memory. USB, ethernet, Bluetooth and Wi-Fi, as well as removable memory cards, are available. Bluetooth allows monitoring and downloading to perform without opening enclosures and reducing electrical hazards.”
Vlachos added that the best-equipped testers still require training and technical knowledge to know where to make connections, what to look for and how to understand data collected.
Fluke Corp., Everett, Wash., power quality product marketing manager Frank Healy said dip and swell, followed by harmonic distortion, are the most common PQ issues. Harmonic distortion is increasing as more distorting loads are installed (such as motor drives and vehicle charging systems).
“At the simplest level, a device that plugs in to a wall outlet can measure and monitor single-phase voltage dips and swells and monitor the level of voltage distortion present,” Healy said. “For more industrial application connections, three-phase equipment panels are required. Multifunction devices tend to do the basics well enough but don’t provide the complete picture required for detailed troubleshooting. Dedicated loggers have the measurement and time accuracy required for the difficult issues that are common in industrial electrical systems.”
Recent changes in PQ testers have not been that significant, Healy said, adding that he expects that this will change where higher frequency harmonics will be measured as the effects of different types of generation that includes solar, wind, microgrids, etc., become more prevalent.
“Bluetooth has made life easier for setting up power quality measuring equipment to use with equipment that is safely installed inside equipment panels,” Healy said. “Bluetooth is not suitable for downloading data as its too slow to be efficient.”
One of the most important considerations for PQ tester users, Healy said, is how they can take advantage of power quality measurement equipment’s performance. Returning to a logger after days or weeks of monitoring to discover the equipment was not set up correctly can be a nightmare for users.
The time wasted and cost incurred can be devastating in terms of reputation and lost opportunity cost. Check and double-check connections before leaving the equipment and hopefully choose a product that highlights and easily corrects errors before it’s too late. Having equipment that is easy to setup and offers guidance of how to connect can be a very serious benefit.
“Sometimes users mistakenly believe the more volume of data the more complete picture provided,” Healy said. “It’s possible to capture many gigabits of data if very short-duration average intervals are chosen and logged for a long time. If the user wants to log many parameters over a very long time, data streaming to the cloud is a better bet.
“This is not always helpful; it’s more important to have gapless measurement. With this type of measurement, the power system is sampled at a frequency that can provide very accurate half-cycle RMS values, which are used to trigger cycle by cycle data to give the user a fast RMS profile along with waveform data. By measuring in this way, compact useful data sets are created,” Healy said.