Following the Curve

Instrumentation, software, and other tools available for measuring and monitoring power quality (PQ) continue to follow the curve found in consumer electronic products—“more for less.” The capabilities in a $3,000 PQ monitor equal or surpass those of the $15,000 analyzers that were available just five years ago. Advances in technology and the global economy have given PQ tool users a more powerful set of instrumentation options. Although some people categorize PQ instrumentation by handheld, portable, and permanently installed equipment, the usage of the equipment is a better way to look at the commonality among the troubleshooting and continual-monitoring PQ tools. Troubleshooting tools come in a multitude of sizes, functions, and prices. Some of the more recognized companies providing such equipment include AEMC, AVO, Dranetz-BMI, Fluke, Hioki, Summit Technology, and Yokagawa. Multimeters, once used for just single measurements, have improved accuracy, multiple-reading memory, and software programs for PCs. Prices generally range from $100 to $400. The size and weight of these rugged tools have been reduced in many new models by using more surface-mount-technology (SMT) components, and custom application-specific integrated circuits (ASIC). Nearly all of them calculate true root mean square (TRMS), which is critical with today’s distorted current waveforms. (Older products use multipliers to determine the RMS value that aren’t valid when any significant distortion is present.) Some of the meters can even provide harmonic analysis within the unit, or through separate software programs that run on PCs. Displays are primarily limited to four- or five-digit liquid crystal displays (LCDs). Monitors are distinguished from meters by their ability to run unattended for a day, week, or month, saving data automatically based on trigger conditions. The troubleshooting monitors continue to have increasing memory depths through the use of internal Flash memory or removable memory cards. Besides allowing for longer monitoring periods, this also provides the capability to capture more waveforms and other data during critical events throughout the monitoring period. The extra memory is also a necessity, given that these are generally three-phase monitors that calculate current, voltage, power factor, demand and energy, apparent/real/reactive power, individual and summary harmonic values, frequency, sags/swells/interruptions, transients, and more. Several of the PQ monitors can provide specialized information, such as inrush conditions and flicker analysis. Color graphic LCDs are becoming more prevalent, which helps in viewing the multiple waveform displays. Low-cost, flexible-core current transformers (CTs) of various sizes facilitate getting around the conductors to monitor the current. Prices for three-phase PQ monitors generally range from $4,000 to $10,000. The ground-resistance testers, megohmmeters, and circuit breaker identifiers are specialized tools for troubleshooting the improper grounding and wiring problems that are often listed as the source of 70 to 80 percent of the PQ problems. When using such tools, remember to follow instructions carefully. Though there have been advances in this area, some of the tools require disconnecting any signal sources from the conductors, which require taking safety precautions to maintain the safety-ground integrity. Since the data in an instrument by itself is often not enough to solve the problem or provide the end customer with proof of what happened, PC software programs for visualization of trends and analysis of the source of the fault source continue to provide more information from the measurements. Those with an automatic report-writing feature allow the user to generate a word-processing formatted document with relatively little effort. Care should be taken to review and customize such reports, as a generic program may not focus on the critical event that tripped the plant offline. The advances in the permanently installed, continual monitoring PQ systems also follow the curve for pricing versus functionality. However, the trends are a bit more noticeable. Among the more significant improvements from such companies as Cutler Hammer, Dranetz-BMI, ElectroIndustries, PMI, PML, RPM, and Square D are in the visualization and communication areas, and the development of the revenue-meter-with-PQ market at a lower cost of service. The $10,000 price point for three-phase monitoring is down $3,000 to $4,000 for the systems with more complete range of PQ phenomena monitoring, and $500 to $1,000 for the revenue meters with PQ. Internet-based technologies are increasingly used in PQ monitoring systems. In some products, this means that access to timely and critical information is just a click away from anywhere in the world. Data and information can be viewed using Web browsers, instead of proprietary software programs loaded on PCs. Some products offer interfaces that allow for increasing levels of detail to be examined through interactive features over the Web, such as zooming and hyperlinks Real-time meter displays can provide continually updated data, and e-mails and pagers notify users when critical events occur. The data produced from the continual-monitoring systems is often more extensive than the troubleshooting tools. These systems are often used for both PQ analysis and energy management. The ability to trend thousands of different parameters allows users to customize what is important for their particular applications. For example, voltage and current imbalance can be measured and trended using either the maximum-deviation-from-average method, or the negative-sequence-components-divided-by-positive-sequence-components computation. Recording the power factor (PF) coincident with peak demand helps facilities find ways to reduce electric bills. Both the individual spectrum and summary values of harmonics and interharmonics (frequency components between the harmonic frequencies) can be measured, triggered on, and waveforms associated with them can be captured to determine if the quality is getting worse, or to find the source of intermittent system failures. Choosing what to monitor can result in complicated setup procedures and analysis-paralysis from too much data. A trend in some of the monitors is to provide “answers, not just data.” In some instances, the answer may be a “Pass/Fail” output, such as “is the voltage regulation within the required equipment specifications powered from such?” In other cases, the answers are more specific, indicating the type, source, and direction of a PQ event, such as a sag or transient. Knowing what caused the event and if the origin was upstream or downstream from the monitoring location can help get the facility back up and running as quickly as possible, and prevent future occurrences. Many of the systems can now communicate using network-based technologies. This means that system installation requires working with the MIS staff and the plant electricians. Although some systems can plug directly into existing building LANs, some applications require installation and performance verification of Category 5 or other Ethernet-cabling. Wireless communication, either through cellular modems, RF, or infrared communication, is gaining in popularity. While this eliminates cabling installation costs, it can introduce new concerns, such as with interference-causing communications interruptions. Revenue meters with some PQ measurements are finding more applications, especially in the electric utility market. These meters are replacing the traditional “glass watt-hour” electromechanical meter, providing the users with precise measurements even in the presence of highly distorted current waveforms. In addition, remote access can provide automatic meter-reading capability. Within a facility, this can be used for energy cost-allocation to a product line. Since these meters employ measurement techniques that are similar to those in PQ monitors—harmonic data, and limited sag and swell information—is often available. Overall, the tools available continue to provide increased functionality at a reduced price. Often, these instruments have many more capabilities than necessary, but they are often used by various people with different needs. The susceptibility to PQ phenomena of equipment that has the need for improved reliability and uptime (in the high 9s) has increased awareness of the users, and the need for PQ troubleshooting tools and continuous monitoring systems. Trends towards providing better answers to the “what happened” and “how can I prevent it” questions are being found in many of those tools available today, and on the drawing board for tomorrow. BINGHAM, manager of products and technology for Dranetz-BMI in Edison, N.J., can be reached at (732) 287-3680.

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