Power Quality Testers
Published: November 2004
Virtually everything we do at work, at home and at play
depends on an uninterrupted supply of “quality” electricity. Spikes, sags, line noise and harmonics are common power quality (PQ) problems that can cause damage or failure of
expensive electrical equipment and electronic devices, resulting in downtime, costly repairs and lost productivity. While recognizing the importance of electrical power quality is nothing new, advancing technologies are making power quality more complex while adding issues unknown a few years ago.
“Power quality has become an increasingly costly problem as a result of the dominance of microprocessor-based production equipment and computerized facility operations and the need for higher up-times for increased productivity,” commented Richard Bingham, director of product development at Dranetz-BMI. “This equipment is increasingly susceptible to power quality disturbances and often can no longer tolerate the typical impacts from standard utility-grade power.”
Protecting equipment from power quality issues requires gathering accurate power data relating specifically to the equipment being operated and assessing that information so that PQ problems can be corrected. Along with changing technologies, today's sophisticated portable PQ testers have evolved to monitor many variables.
Basic PQ testing instruments include multimeters, harmonic meters, oscilloscopes and power quality analyzers for recording the complete power quality spectrum. Software interfaces with computers to enter date, organize information for analysis and store it for future reference.
ELECTRICAL CONTRACTOR asked leading manufacturers of PQ testers to comment about changing PQ issues and the instruments to detect and analyze them. Here are summaries of their responses.
Amprobe-ATP, Jarek Bras, senior product manager: “With more and more powerful microprocessors, PQ meters nowadays can calculate more parameters and also perform other measurements such as phase rotation, insulation resistance (megohms) or ground resistance. High-end testers can measure and/or record more than 400 PQ parameters (just individual harmonics on each of the phases for voltage and current add up to 300, assuming 50 harmonics per phase per parameter). Fast microprocessors permit many large calculations to be processed simultaneously, allowing a single instrument to record several hundred parameters.
“Today's meters are equipped with memory from 1MB for lower-end meters up to several GB for higher-end units. Usually months of the recorded data can be stored in the instrument's internal memory. PC software has built-in analyzing capabilities to make the job easier for the end user. Data can be transferred via Internet or using wireless links.
“With all of these features, the cost of PQ meters is decreasing, and PQ testing equipment will continue to change with more sophisticated software and possibly with wireless technologies,” Bras said.
Dranetz-BMI, Rich Bingham, director of product development: “The most important features of today's instruments include [the] ability to simultaneously perform an ever-increasing range of power quality functions, including in-rush, flicker, inter harmonics, etc., on three-phase circuits. Today's instruments have the speed and capacity to perform in several modes simultaneously. For example, one product new to the market has six modes: power quality, in-rush, fault recording, data logging, energy monitoring and compliance monitoring in one unit.
“Processing speeds and memory capabilities have dramatically increased in the past year, allowing for more complex analysis. Color touch screens are user-friendly and take the guesswork out of setting up, collecting and analyzing data.
“Many three-phase handheld units have improved local displays and increased processing power through use of digital signal processors to compute thousands of parameters, many on a cycle-by-cycle basis, including additional indices for power quality as well as ones for energy and demand. Data cards up to 256MB are now standard and can be transferred within seconds to PCs and servers.
“As the loads change and the sources of separately derived power sources (UPS, motor-gen sets, etc.) evolve, so do measurement requirements. 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.
“Expect a continued trend toward more robust instrumentation and a greater reliance on the use of the Web for communications, as well as the integration of advanced processing algorithms to define the cause and source of disturbances and smaller units with more advanced processors,” Bingham said.
Fluke Corporation, David Pereles, marketing manager Fluke Power Quality:
“Today's testers can handle most relevant power measurements. Battery, processor and display technology make today's testers more portable and easier to use. High-speed transient capture capability varies among analyzers. The difference between analyzers is in how they fit a particular application-are you trying to solve a constant problem or optimize a decent system? Analyzers differ in ease-of-use features like displays and rechargeable batteries and differ in recording capability-some can record a couple of parameters for a couple of days, while others can record hundreds of parameters over months.
“Most of today's testers comply with EN61010 regulations for voltage ratings. These ratings provide the maximum working voltage of the tester and a category rating indicating its ability to handle spikes,” Pereles said.
Ideal Industries, Brian Blanchette, test and measurement team: “With changing loads coupled with deregulation of the power industry, power quality issues have changed dramatically. More so, the recognition by more energy consumers that power quality is real, that it affects everything, and failure to recognize this is becoming very expensive.
“Most of the older equipment used to measure power quality was designed to meet the needs of electrical distribution and transmission. Since the late '90s, many changes have occurred in the power quality market. It takes a different kind of power quality meter and training to measure and understand the issues of power quality on the load side of the revenue meter. It is a different challenge and requires a different approach to analysis.
“Most good analyzers will include all energy and power parameters as well as kilowatt-hour measurement so that the user will have all the needed information automatically. Basic testers must meet the needs of power quality measurement. With switching power supplies, variable speed drives and computers, the harmonic demand on many energy supply circuits has surpassed the demand for the fundamental, so ammeters need to be able to measure accurately up to the 50th harmonic or 3,000 cycles per second. Chances are that the current measuring equipment you own today cannot display above the sixth harmonic, around 400 Hz.
“Whether single-phase, three-phase delta or wye, it is necessary to record both voltage and current simultaneously on all three phases, measuring at both high speed and long term.
“Changes in power quality testers have been incremental, but the changes in the industry have been dramatic. The conundrum is that every 18 months or so, the feature set doubles and the price is reduced by half,” Blanchette said.
Megger, Fred Hensley, product manager, PQ instrumentation: “Most typical power quality issues today can be attributed to voltage sags and/or poor grounding practices. However, as the sophistication of measurements capabilities grow, both harmonics and flicker seem to be the least understood and/or reported criteria today.
“Because power quality measurement can mean so many different things, several of the newest handheld analyzers attempt to take advantage of other tests that can accomplished at the same time with a multi-purpose tester.
“Electrical testing equipment shares several similarities to the PC revolution of the past 15 years. Newer technologies tend to provide higher processing power via smaller footprints at a lower power consumption, just as we have seen in the personal computer revolution. This has resulted in the move away from proprietary embedded designs towards more PC-like operating systems and device support.
“Over the past several years the volume of data (as opposed to information) has experienced exponential growth.
“Analysis equipment today can store tens or hundreds of megabytes, sometimes even using the commercial, off-the-shelf non-volatile memory mediums designed for digital cameras and personal digital assistants. With high volumes of available data, either a high-speed connection or removable medium is preferable for transporting large files. Off-site network storage can maintain gigabytes of historical data for later review or calculation of historical indices.
“Life cycles for test and measurement equipment has shrunk, shortening the life and support available to devices that may be quickly orphaned in favor of the newer offerings. Manufacturers who continue to improve their products while continuing to support legacy products will be in the best position to offer comprehensive support to a rapidly changing marketplace.
“The most interesting thing I have noticed over the past few years is the effort to harmonize power quality standards between various international bodies for common terms and definitions as well as consistent measurement methodologies. It is hoped the results of this work will provide uniform PQ test results amongst equipment vendors, as well as common vocabularies for discussion amongst end-users,” said Hensley. EC
GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at 405.748.5256 or firstname.lastname@example.org.