Power Quality Testers
Published: May 2003
There was a time when the quality of electrical power meant little more than whether the electricity was on or off. When power was on, lights worked and the radio played. When power failed, lights went off, and the radio was silent. Things are much different today. Businesses, government agencies, manufacturing plants and private residences must have dependable electric power suited to the electrical and electronic equipment being used. “Quality” of power can be as important as availability of power.
Any power outage, whatever its cause and duration, is disruptive, but sags and spikes, under- and over-voltages, line noise and harmonics issues are common power quality events that can cause equipment failures, damage to equipment requiring costly repairs, downtime and lost production. Newer PQ issues include flicker, inter-harmonics and the effects of distributed generation.
“Power quality [PQ] has become an increasingly costly problem with the dominance of microprocessor-based production equipment, computerized facility operations and the need for higher up-times for increased productivity,” observed Rich Bingham, director of engineering at Dranetz-BMI. “Equipment today is increasingly susceptible to power quality disturbances and often cannot tolerate typical impacts from standard utility-grade power.”
Within the same facility, a PQ solution for one problem may not address others because of the widely different requirements of equipment in use.
“The widespread use of high-tech electronic equipment within heavy commercial and industrial facilities has complicated every aspect of electrical power,” said Chad Reynolds, product manager, test and measurement division of Ideal Industries Inc. “These problems are coming to the forefront simply because of the increasing use of these devices and the rising costs associated with them.”
Protecting equipment from power quality issues requires gathering accurate data about power as it relates to the equipment being operated, assessing information collected and taking necessary steps to correct problems that are identified.
Portable PQ testers—connected by using voltage probes, or clips, or flexible current clamps—monitor various PQ variables; PQ software is used to analyze and store information collected by testing equipment.
Basic PQ testers include multimeters, harmonic meters, oscilloscopes and power quality analyzers for recording the full power quality spectrum. Information gathered by testers is entered into computers with PQ software to organize data for analysis by those who will make the decisions about correcting problems.
Which tester is used depends on circumstances and what information is needed, but most testers for power quality should at least be able to test for sags, surges and harmonics, according to Mel Hendrickson, application engineer, Amprobe Advanced Test Products.
“Power quality troubleshooters can make quick visual checks of a power system,” said David Pereles, electrical products marketing manager, Fluke Corp. “They are most often used when equipment failures have been experienced, and the name of the game is to diagnose the problem and get the system up and running.”
PQ analyzers perform comprehensive analysis of the power system. These are usually high-end instruments that can look at all aspects of a three-phase system and generate information for a complete report on the health of the power system.
“Power loggers,” continued Pereles, “are a good way to check a system’s loading before adding more equipment. Making sure a system has ample capacity ensures its ability to respond to intermittent current draws. Loggers are usually set up to log voltage, current, power, power factor and sometimes harmonics for a day, a week or longer. By monitoring the power over relatively long periods, it is possible to get a good sense of the system’s ability to handle more loads.”
Most portable testers incorporate the capability to measure and trend true RMS voltages and currents, whether single phase (1V/1I), split-phase (2V/2I), or three-phase (3+V/3+I), said Fred Hensley, Megger director of power quality sales.
“Some three-phase devices,” Hensley continued, “also allow for four differential voltage inputs to simultaneously measure voltages with differing/isolated neutrals, as well as five current inputs to simultaneously measure phase, neutral and ground currents. Other measurements simultaneously made by portable PQ testers might include harmonic analysis, fundamental power/energy, harmonic power flow (used to aid in determining the source of harmonics), waveform capture, trending of individual harmonics, total harmonic distortion (THD), total demand distortion (TDD) and out-of-limits events.”
Wayne Price, vice president of Hioki USA Corp., said the most common requested features for PQ analyzers are transient capture capability, 10 BaseT LAN capability to allow remote monitoring, internal and external memory capabilities, convenient size, ease of use, TFT color screen, a variety of clamp-on current probes and a quality software program.
PQ testers have quickly changed to meet changing demands, and today’s models are much more advanced than those available only a few years ago.
“Changing technologies have absolutely changed testers,” said Amprobe’s Hendrickson. “The introduction of faster microprocessors and digital signal processors has improved operation and accuracy of today’s testers. New tool designs allow for smaller, more portable products that incorporate greater accuracy, more measurement functions, are easier to use and meet safety standards for both product and user.”
As the loads change and the sources of separately derived power sources evolve, so do measurement requirements, said Bingham. “For example, 12- and 24-pulse power converters used in some newer adjustable speed drives generate higher harmonic currents than are seen in the common 6-pulse converter of today. As the internal components of electronic equipment use lower supply voltage and operate at higher speeds, new measurements may be needed to determine what phenomena adversely affects them.”
What should buyers consider when selecting equipment?
“The primary concern in choosing a tester is: ‘What do I want to do with it?’” said Fluke’s Pereles. “If the need is to perform comprehensive surveys of a power system, you’re not going to want a tool designed for troubleshooting. And if your main role is to troubleshoot problems, then a full-blown analyzer may slow you down. For troubleshooting tools, make sure they’re designed for use in your environment and look for a tool that gives quick results. If you want to carry just one tester, you’ll want a troubleshooter that can measure ohms, capacitance and perform diode checks.”
Look for simplicity, advised Megger’s Hensley: “Simplicity in installation, simplicity in configuration, simplicity in data presented for analysis.
“In areas where simplicity must be set aside in favor of flexibility,” he added, “basic elements of instrument operation must at least be straightforward and easily repeatable. Other most important features include a very rugged design for hard and outdoor environments, capabilities to self-power the instrument via the unregulated AC/DC voltage being monitored, and field-upgradeable functionality without requiring the instrument be returned for factory service.”
Portable instruments, Hensley continued, should have a complementary software package for configuring the instrument to a specific application; the ability to retrieve data recorded over the monitoring period; and have a charting, graphing and reporting mechanism to turn the raw data into useful information. Some instruments utilize monitoring software for remote connectivity, remote polling and proactive alarm registration from instruments recording in the field.
Ideal’s Reynolds believes the most significant trend in PQ tester equipment is ease of use. “For the most part, work is not done while walking around with the instrument, but with the product’s analysis software. The ability to easily create reports and graphical representation for the problems make it easier for the customer to identify a problem and apply its eventual solution.
“Another trend is for instruments that can measure more than one aspect of power quality,” he said. “While a worker may be interested primarily in power or power factor, he also may need to analyze the harmonics on the line. A tester that is multi-functional will lower overall costs in the long term.”
Technology has changed with regard to both hardware and PC software, said Bingham. “Today’s hardware is a smaller footprint with more computing power at a lower cost—customers get more for less. Windows- or PC-based software is more analytical, multi-functional, and easier to use.”
Pereles says that testers are becoming smaller with greater capabilities, displays and batteries have improved considerably in recent years, and computer interfaces and software support have gotten more sophisticated, extending analytical capabilities.
He adds that PQ software must communicate easily and quickly with analyzers. Most PQ software packages today allow data to be exported to spreadsheets, he explains, allowing easy export to word processing programs.
Bingham sees PQ testers of the future continuing a trend toward more “robust” instrumentation, a greater reliance on the use of the web for communications, and the integration of artificial intelligence to define the cause and source of disturbances.
New ways of measuring data, calculating methodologies, storage mediums and environmental considerations have already significantly improved monitoring equipment designs over the past 10 years, said Hensley.
For example, Hensley said, the advent of compact, removable flash memory for digital cameras has provided an obvious, off-the-shelf solution as a non-volatile mass data storage and data transfer container without the difficulties of moving parts or battery backup requirements. Digital signal processors have dramatically and inexpensively increased the processing power available to power quality measuring instruments, allowing mathematically intensive calculations to be economically and reliably added without hardware upgrades.
“Look for simplicity of instrument configuration, installation, removal, and confirmation of connectivity—preferably without requiring a computer,” he added. “The sophistication of reporting and after-the-fact analysis increases sharply by utilizing vendor-neutral power quality data file formats.” EC
GRIFFIN, an experienced construction and tools writer from Oklahoma City, can be reached at 405.748.5256 or firstname.lastname@example.org.