Portable Power Quality Testers
Published: August 2002
Growing numbers of electrical contractors are testing for power and power quality for their customers, looking to prevent or minimize unwanted consequences of harmonics and voltage transients. As businesses and the industry rely more heavily on information technology, they contribute to problems with power quality while desiring and benefiting from good power quality. Some of that power quality testing may use portable instrumentation.
Portable (including handheld) instruments are useful for on-site analysis where there is no permanent recording instrument in place or where the tester is not the same individual who will do the analysis. Portable power-quality instrumentation is increasingly sophisticated, often featuring streamlined methods for getting data out of the instruments, for results and analysis. For example, the instruments may use plug-in cards for downloading data, for real-time graphical input for on-site analysis, or for changing the configuration and setup of the measuring instrument on site, eliminating need to transport a computer to the project site.
“In most cases, a power-quality problem comes up as symptoms at a particular load,” said David Pereles, marketing manager for electrical products, Fluke Corporation. “For example, a programmable controller mysteriously resets, or a variable-speed drive keeps burning out. The trick is to trace back into the system, and a portable analyzer is designed for moving around in a system—the more portable, the better.”
“Handheld PQ monitors have evolved either from portable monitors, where technology, such as surface-mount components and programmable logic devices, has allowed a 15- to 20-pound instrument to be miniaturized to a 3- to 5-pound unit, or from combining technology of digital voltmeters and handheld oscilloscopes,” said Richard Bingham, director of product development, Dranetz-BMI. Some portable units have built-in printers and/or modems. Many products have graphical LCDs, including color, that display waveforms, metering data, timelines, event waveforms, harmonic spectrums and statistical information.
Power parameters—such as W, VA, VAR (volt, amps, reactive), PF and KWhr—are standard in most products, enabling energy audits at the same time as a power-quality study. Other capabilities sometimes included on portable instruments are: ability to enter rate structure for billing purposes, True RMS reading, Crest factor, K factor, Transformer Derating factor, Telephone Influence factor and sequencing components. Most units provide total harmonic distortion (THD) and individual harmonic spectrums of voltage, current and power harmonics.
Automatic tools and report generators, however, are only as good as the person using them. “When it comes to reports or even just the readings, the contents or results can be effectively meaningless unless the user has at least some elementary understanding of power quality principles, application and operations, in order to comprehend what it all means and its relevance to a particular investigation,” noted Fred Hensley, director of power-quality sales, AVO International.
If an electrician does not have enough depth of experience, when results are ambiguous or not readily interpretable, he or she can send the data file, along with background information, to an outside power-quality consultant for in-depth analysis. For educating users about how to set up instruments, take readings and retrieve data for diagnosis and analysis, many companies offer training, ranging from videotapes to on-site or off-site training for a day up to a week, often supplemented with technical phone support and/or a frequently asked questions (FAQs) page on a company Web site.
The cost of portable instrumentation varies greatly. Often, the instrument comes as part of a package, with other components necessary to conduct and interpret the tests. Features and accessories vary among kits. Roughly, a low-end recorder—for instance a basic updated data-logger, which measures voltage and current and some combination of them—could cost about $900 to $4,000 for a package. A middle-range kit consisting of a modestly empowered power-quality analyzer and related components could cost between $4,500 and $7,500. A high-end package of power and power-quality analyzers, sometimes also referred to as power line disturbance analyzers, could run $10,000 to $15,000 or more. (Some instruments may be available on lease-to-own programs or as rentals.)
In this increasingly deregulated marketplace, facilities are interested in monitoring not only for cost allocation but also for consumption. Some of today’s “smart” power-quality instrumentation provides consumption reporting as well as power-quality reference information. Sometimes, management would benefit from making more efficient use of the existing transformers and services, especially if a distribution system is loaded to the max. Use of appropriately accoutered power-analysis instruments can help facilities maximize existing incoming power. With certain target information, an industrial facility could, for example, reorient manufacturing processes both to take advantage of the capacity and to lower the overall energy bill by moving peak loads around so the facility is not billed for peak loading at the peak demand rate.
Many portable units work with vendor-furnished PC application software. Some packages support downloading of data into a spreadsheet program. Other applications provide detailed analysis tools that help find the source of the problem and/or automatic report-writing tools to provide a quick means of presenting collected data to facility management. Memory storage may be internal or may use removable Flash memory modules. Some power-quality monitors feature high-speed Ethernet connectivity (10/100 Base T), which enables fast transfer of logging data and waveform captures between the circuit monitor and the analysis software, and generous amounts of onboard nonvolatile memory, which (unlike more traditional methods such as thermal printers and floppy disks) has no moving parts and is maintenance free.
Monitoring and analyzing power can save a facility money in several ways. If it is possible to identify the causes of downtime, it may be possible to prevent those causes from recurring. Also, by increasing efficiency of each process, management can maximize return on equipment.
Portable instruments are suitable for both temporary power monitoring and for applications where switchgear prohibits or makes impractical permanent circuit monitor installation. Using portable instrumentation for monitoring, once a technician learns about a particular electrical system, in interests of reducing facility energy costs, it is possible to use the information to avoid misuse of equipment (e.g., HVAC equipment or illumination turned on after hours). “If a technician can identify the demand profile caused by the equipment and processes, it may be possible to sequence the loads to reduce demand peaks,” noted Marcelo Perez, senior product specialist, Square D. It may also be possible to analyze the costs and benefits of power system improvements, as well as document the changes, he added.
Power-quality monitoring equipment can help the electrician troubleshoot unexplained events in a facility, such as motor and drive failures, lockups, or a CNC machine misoperation, remarked Perez. With a portable power-quality analyzer, technicians can create a record of all the anomalies in an electrical system that could, undetected, cause destruction of costly equipment and downtime.
“We recommend technicians in facilities to pro-actively characterize their equipment performance. By establishing a baseline, it is possible to determine maintenance requirements or benchmark against similar processes,” Perez said.
Suitable for checking three-phase circuits, the AVO International PA-9 Plus is a comprehensive power and power quality analyzer sporting nine ph\ysical input channels, four for voltages and five for currents at 256 samples/cycle each, and an integrated graphical display. The PA-9 Plus self powers from the unregulated voltage being monitored (90-600AC/DC) and can verify power quality at the service entrance or monitored circuit to determine the degree and source of harmonics at play. The instrument can indicate the direction of harmonic power flow, an aid in tracing the location of harmonic sources. Capable of being fully controlled remotely, the unit features many vendor-neutral components such as voltage and communications cables. As an option, users can plug any standard Kodak compact flash-type memory module (64MB+) into the outside of the instrument and format the module for downloading data from internal memory, without requiring a computer on site or transfer new instrument configurations to the unit without a computer connection. Free Windows software incorporating all graphical and report evaluation capabilities of the instrument is downloadable from the company Web site.
The Square D portable CM4000T power-quality monitor offers the ability to simultaneously record electrical events in eight independent channels of voltages and currents with the additional capability of recording optional digital status (sometimes associated with events). Using four different waveform capture configurations (simultaneously if desired), the user can narrow down the time scale from minutes to microseconds. Depending on the type of waveform capture selected, the resolution can vary from 16 to 83,333 points/cycle. The unit features transient detection capability of less than one microsecond duration. The monitor also features optional Web-enabled technology allowing the user to connect to a high-speed Ethernet network and view instantaneous readings, harmonic power flows, historical trending and forecasting, SEMI/ITIC [Information Technology Industry Council] disturbance filtering, and IEC-based flicker trending through a standard Web browser. It is possible to get information from other Modbus compatible devices connected to the portable unit. The unit sports a minimum of 8 MB of nonvolatile memory (32 MB optional). System Manager Software is also available for viewing and analyzing the data and printing reports.
Featuring four differential voltage channels and four independent current channels, Dranetz-BMI Power Platform 4300 analyzes and records power quality, harmonics and energy data simultaneously and continuously on single- or three-phase systems. The software-enabled lightweight, handheld power analyzer monitors up to 16 parameters, including V, I, WQ, VA, VAR, power factor, demand and energy. The 4300 can trigger and capture both voltage and current high-frequency transients, as well as RMS variations and other parameter changes. With integrated PCMCIA technology, a two-hour UPS capacity and individual TASKCards for upgradeable operations, the instrument provides four modes of operation: scope modes, for real-time viewing of voltage and current waveforms and voltage and current phase or diagrams; meter mode, with values displayed by parameter or channel; event recorder; and time plot, for as many as 16 parameters and eight individual channels, to identify abnormalities before they become problems. The PP4300 can be equipped with up to 4MB of additional memory for collecting data, via removable memory cards. DRAN-VIEW 5.0 software allows users to scroll through event, timeline and waveform data simultaneously, zero in on captured disturbance waveforms, scan historical trends, evaluate statistics and perform harmonic and interharmonic analyses.
RPM Reliable Power Recorder is a portable three-phase instrument suitable for all power surveys including logging, consumption, harmonics and power-quality studies. It has four voltage and five current channels so all phase, neutral and ground currents can be monitored simultaneously. Internal hard disk storage and Ethernet connections are standard. The instrument’s Full Disclosure technology eliminates the need for manually setting triggers and time-bases and prevents wasted surveys resulting from incorrect programming. Data is captured automatically with virtually no setup—the user need only tell the instrument when to start and stop. Full Disclosure provides continuous measurements of all aspects of power on all channels so that all harmonics, consumption and power-quality data are recorded together with one-cycle resolution. Other features include display of events against the Computer and Business Equipment Manufacturers Association curve, single-ended safety connections, oscilloscope tools to correct wrong connections via software, and add and subtract waveform tools to identify ground loops and leakage currents. The Scenario software program allows Web-based monitoring of remote sites and the calculation of indices for predictive maintenance.
IDEAL’s new Model 61-805, a highly-portable power analyzer, includes key features such as an energy/harmonics program, an RS232 interface for fast downloading, and one MB of internal memory to allow for longer periods of testing. Surprisingly compact and versatile, it contains five testing programs, which comprehensively analyze the power-quality issues frequently faced in commercial and industrial environments. These programs can be uploaded in the field on the same unit and be programmed to run sequentially, saving the user time and money. The tool comes standard with three 1,000A clamp adapters, voltage leads with four alligator clips, power supply, power and RS232 cables, PowerVision software for in-depth analysis, and a hard protective carrying case with accessory storage.
AEMC Instruments portable Single-Phase Power Quality Logger PQL 100 measures, records and stores several power parameters, including W, VA, Var, Demand and Peak Demand, and power-quality parameters including harmonics, THD (rms and fundamentals) and K-factor. The unit records up to 12 data channels and stores 100 worst-case surge and sag events, including time, date and duration. The 20 worst of these events are also saved in high-resolution mode and can be displayed as waveforms. The user-programmable recording session can range from 15 minutes to eight weeks. Featuring 1 MB storage, the instrument, which plugs into a standard AC receptacle, enables the recorded information to be retrieved via a computer using an RS-232 serial link. DataView Lite software, which provides graphs, waveforms and pre-configured reports, is supplied with the logger. EC
THE FELDMANS write for various magazines and Web sites. They can be reached at email@example.com or 914.238.6272.