Power Quality Testers
Published: October 2007
Among other problems, “bad” power quality (PQ) can cause loss of productivity from lockups and resets, premature equipment failure, overheating of components and corrupted data. It also can contribute to excessive energy costs.
“The ultimate cost of PQ event is in downtime, decreased productivity and very unhappy managers who are trying to meet operating budgets and schedules,” said Chuck Bowden, Fluke Corp. power quality product planner.
Most PQ problems, Bowden said, originate inside a facility due to undersized power distribution lines, equipment operated outside recommended parameters, improperly balanced or scheduled loads, old-style electronic power supplies without power factor correction, and deterioration of connections and cabling. Sometimes, problems can originate outside the facility in the power supply, often caused by a lightning strike.
Whether the result is a complete shutdown or poorly performing equipment over an extended period of time, poor power quality costs money.
“The quality of the energy supplied to a device will determine how well that device works,” said Brian Blanchette, test and measurement sales manager for Ideal Industries.
“If you are not getting the rated horsepower from a variable speed drive due to voltage unbalance or if you are getting reduced data throughput rates due to voltage events, then you can certainly determine a dollar value to these problems. Power quality may be the best place to look to find significant available cost reductions.”
Identifying and correctly analyzing PQ issues depends on correctly using PQ testing instruments, including multimeters, harmonic meters, oscilloscopes and power quality analyzers for recording the full power-quality spectrum.
According to Fluke’s Bowden, there are two distinct applications of PQ analyzers: live and recorded.
“Live troubleshooting,” Bowden said, “is valuable when you want to trace problems to their source and instantly test cause/effect with voltage and current waveforms and harmonic distortion readings. Recorded data is valuable when it is necessary to go back and examine the power quality at the exact moment a problem happened.”
Testers change with technology
While most PQ events are the same as they always have been, technology advances have made many types of electrical and electronic equipment more vulnerable than in the past.
For example, Charles Argenziano, Hioki national support manager, said advances in computers have increased speeds of CPUs and loads. “Older computers,” he said, “were slower, and power supplies were able to handle certain disturbances easier. Today’s high-speed CPUs with dual processing and high-speed busses are more sensitive to these high-speed disturbances, and PQ analyzers have to be able to see these higher-speed anomalies.”
The categories of PQ testers are familiar, but the capabilities of today’s testing equipment have advanced to meet changing needs.
Scott Black, Extech product manager, said there continues to be a trend toward multifunction testers. “A popular feature on many newer models are color screens, which can display color wavelengths. And the amount of storable varies greatly between one model and another depending on memory size. Each manufacturer has its own customer software to extract and display the collected data,” he said.
According to Bowden, in the past several years, options for three-phase power-quality analysis and monitoring have increased substantially, both in the handheld and small portable categories.
“The trend is toward streamlined tools designed for specific industries and applications,” he said. “For example, some PQ meters are designed to document the loading [power consumption] on a system, and discovering the PQ effects of the loading. Other PQ meters are better for comprehensively analyzing voltage stability and purity. Some meters are designed for fixed-mounting and can send their readings to a control panel or master device somewhere else in a facility.”
Most tools now connect to the PC via USB or offer data cards for easy retrieval.
“Some PQ recorders,” Bowden said, “come with a palm-type PDA device that connects using wireless communication to the recorder to view readings and check for correct voltage and current connections. Logging is now standard on most PQ meters, and model options have also increased on the lower end, with better tools for quick, successive testing. There is even a clamp meter that gives graphical and numeric results of all the parameters of interest to a PQ specialist.”
“Years ago, many PQ testers were designed to analyze only a certain type of disturbance, or some features had to be turned off to enable other functions; some only did sag, surges, transients while others did harmonics or power factor.” Hioki’s Argenziano said. “And some had to be programmed to enable two or three tests at a time. New higher-end units today capture all. Many new testers provide diagrams for hooking them up. Plus, many actually will tell the user if the unit is connected correctly before the study is actually started. Many have isolated inputs and cases that are insulated much better today than they were several years ago.”
Ideal’s Blanchette noted that while the same device can measure voltage to determine power quality, energy, harmonics and many other calculated parameters, many users may find the multiple functions confusing.
“The best advice,” he said, “is to purchase a unit that is completely automatic that allows you to look at just the information you need in a simple way. Be an informed consumer. Make sure tester features really add value to the measurement. Most important, in PQ analyzers, evaluate the software before purchase. Can you make copies? Are upgrades free? Is support available to use and interpret readings? Is the software simple and easy to use to share the data and make reports? The hardware is generally the least important in the long run, as long as it meets the basic requirement, which would be a simple 128-sample-per-cycle rate, all cycles measured simultaneously.”
Data storage and transfer
Blanchette emphasized that PQ analysis requires data acquisition.
“It is important to keep in mind that no power quality information ever comes from an instantaneous reading—multimeters, clamps, most panel meters have no power quality function. You need a good recorder, and today, that means data acquisition. And that is one criteria for selecting a recorder. To determine the quality of the energy on a branch circuit, you need to record for one business cycle, whatever that might be. Testers store a lot of data today, usually with multiple ways to download—via serial, Ethernet, phone line or wireless. Be sure you understand how to get the data out of the device. Simpler is better always.”
Fluke’s Bowden said a power quality investigator’s job is not complete until he or she has produced a textual and graphical explanatory report of test findings. Most PQ tools come with software for analyzing data and creating these reports.
“Most PQ recordings plot voltage, current and the different power units over time,” Bowden said. “They also read harmonic distortion (THD), watts, Hz, and power and energy parameters such as VA, VAR, kVAh, kWh, kVARh and power factor. More advanced PQ tools show you transient peaks and waveforms, motor start current inrush, and unbalance. The more advanced the tool, the more data it will log for longer periods of time.”
Argenziano pointed out that PQ tester memory capabilities vary greater by model.
“Many of the lower-end units have very limited memory, and depending how the memory is stored in a factor is how much data can be stored,” he said. “Units that store only screen shots have very short recording time, while those storing data in a binary format increase their recording time to weeks. The higher-level analyzers have a much deeper memory, and many of them use a compact flash card, which allows the units to collect data for months at a time without having to transfer data. Many use a USB connection to transfer the data, while the higher-end units may use a LAN connection or flash card, which plugs into a computer.”
Category safety ratings define the ability of a device to withstand accidental transient voltages, said Blanchette.
“Panels and service-entrance recording would generally require Cat 3 and Cat 4 respectively, while branch-circuit testing could be either Cat 2 or Cat 3,” he said. “Examine the location and safety rating before using any test equipment. Modern recorders and analyzers all have category safety markings. Respect and use them.” EC
GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at 405.748.5256 or firstname.lastname@example.org.