Cool Tools: Power Quality Testers
Published: October 2009
Poor power quality continues to be a costly problem. Basic power quality (PQ) issues are unchanged, but their impact appears to be increasing as more businesses and organizations embrace new technologies. These technologies include sensitive equipment that is more susceptible to a variety of problems caused by “bad” power.
While surges and sags may be the most common problems, power quality issues have changed in the sense that they are influenced by increasingly volatile energy prices coupled with adoption of fiscally attractive green policies by power intensive organizations, said Extech Instruments’ Andre Rebelo said.
He believes these and other factors have made power quality monitoring imperative.
“As the pressure mounts to control costs, it has become urgent to have a detailed picture of electrical usage as a key component of reduced or better distributed energy-usage strategies. Companies want more precise information about peak demand periods, and they want to identify inefficiencies that may be costing them,” Rebelo said.
Quality equipment to test and analyze power are essential to effectively addressing power issues, and manufacturers of PQ testing instruments say today’s product lines generally are more accurate than earlier models, offer more functions, are easier to use with enhanced graphical displays, and can accommodate more data.
AEMC Instruments, John Olobri, director of sales and marketing, said: “The number of companies and individuals affected by them have increased. In the production arena, poor power quality can cause premature failure of motors and pumps. In the office environment, they cause computer glitches and employee irritation due to lighting flicker. With more sensitive equipment installed today, these problems are more noticeable.
“PQ tester models being sold do all that their predecessors did with more user- friendly selections, as well as automated functions such as starting a recording at a future date and time or auto correcting for improper lead connection.
“Improvements include remote access to data retrieval, graphic displays on the instruments that allow real-time troubleshooting, and automatic recognition of probes in use.
“Quality testers tend to stay focused on power quality. Some instruments will also measure temperature and allow for DC measurements. Good instruments will simultaneously measure power, harmonics and event-triggered information. Data storage has increased in importance. More data needs to be analyzed and, therefore, storage capacity needed to increase. Capacities below a gigabyte are no longer considered very effective,” Olobri said.
Dranetz-BMI, Jerry Olechiw, vice president of international sales, said: “The basic types of power quality events remain the same with increased emphasis on harmonics and flicker. What has changed are the applications. From a generation standpoint, green initiatives, such as solar and wind raise new concerns about voltage stability, harmonic content, and flicker generation. In addition, much more emphasis is being placed on energy efficiency and the costs associated with poor power quality as it relates to equipment performance and overall operating reliability and efficiencies.
“At the most basic level, all instruments measure a number of parameters—voltage and current at the minimum. From these are extracted a number of parameters that can be used for applications. A typical instrument, in addition, records power quality events and trends, will do harmonics, interharmonics, flicker, and all the power parameters. In addition to power quality, load studies for demand and energy can be performed. Also, firmware that focuses on measuring motor parameters to trend motor performance has been added in firmware as well as compliance reporting.
“In software, the ability to post process data and to create mathematical functions specific to an application increases even further the versatility of the instrument. Managing databases has become more important, which is why software becomes so important. Being able to append files related to one monitoring point allows the user to look at long-term trends and perform an analysis on that location,” Olechiw said.
Extech Instruments, Andre Rebelo, global public relations manager, said: “Some of the biggest PQ issues come from contending with fluctuations from the power grid. In part, this involves identifying peak periods that can benefit from supplemental alternative energy.
“Newer PQ testers permit increased onboard testing with a graphical display to illustrate data being collected. For example, phase diagnostics and harmonics tracking can be performed not just with numerical data but also with a visual, graphical illustration. This signals a transition away from a display with numerical-only or basic graphical information whereby a download to a PC was required for graphing and analysis.
“Data logging has become much more sophisticated, permitting snapshots and transients and setting up a ‘work envelope’ or thresholds to more clearly identify transients, dips and swells.
“Newer products also offer higher accuracy and higher amp ranges coupled with flexible clamps for more versatile connection to circuits, around busbars for example.
“Data storage is a key limiting factor for effective long-term analysis, or short term, high-density data analysis. As PQ testers move to standardized memory card formats such as SD cards, they are limited only by the immense capacities of today’s cheap multi-gig memory cards.
“Looking ahead, market research firm Frost & Sullivan said in February 2009 that a key trend in test and measurement equipment will be a move to what was termed ‘combinational’ testers. Consistent with that, expect to see increased capabilities in PQ testers,” Rebelo said.
Fluke Corp., Frank Healy, product marketing manager, Fluke power quality products, said: “Many more users of electricity experience power quality problems today as they implement control systems and other efficiency upgrades with sensitive electronics that also put harmonics back into the system. A risk is that facilities swallow the cost for an efficiency upgrade and are then faced with a whole new set of problems that require slightly more advanced troubleshooting than regular maintenance. Far more technicians are coming to us about power quality issues than in the past.
“One issue is sensitive electronic devices tripping out due to power interferences, and in some cases, motors burning out prematurely. One of the causes is harmonics added into the power system by the new variable frequency drives (VFDs), etc., and power loads not assessed before new additions, resulting in supply issues, unbalance, etc.
“New power quality tester models are substantially easier to use. They still fall into two primary categories: loggers or analyzers. Analyzers evaluate power parameters on the spot, but cost a little more. Loggers collect power data over longer periods of time and then download the information to a PC. The difference is a greater range of model options per category, with more units being introduced for beginners.
“All market segments have a need for tools that do more, more easily, primarily for efficiency’s sake. More technicians are cross training and facilities typically have fewer techs on staff—so the remaining heads have to do more, faster.
“Overall, the expectation of electricians that tools store great quantities of data has increased. The aptitude for tools graphing that data on-the-spot has also increased (even the newest digital multimeter graphs logged data on a screen, and it’s not as complex a tool as the power quality line).
“More important than quantity is quality of data and the ease of analysis—especially with technicians who are new to power quality. Making the data accessible and easy to comprehend is harder than simply storing great amounts of it. What is interesting is that so many more techs carry a laptop with them. Using the laptop for analysis and reporting makes life much easier and allows easy sharing of the data they collect. However, they do not want to leave a laptop behind if long term logging is required. For power quality logging applications, yes, tools should log for at least 30 days per NEC load-study standards,” Healy said.
Hioki USA, Charles Argenziano, director, technical support, said: “The most common issues we are seeing that concern end-users are voltage sags, load and demand studies, and harmonics. Voltage anomalies cause computer-drive equipment to become sluggish and cause problems when trying to perform their desired applications. Load/demand problems affect the equipment’s ability to perform to optimal performance. Harmonics cause many of the smaller IC and chips to run hot and finally fail.
“I believe the issues have changed since the introduction of VFD, many of the older PQA instruments have problems with these systems, and as these VFD become more popular, products have to change or get left behind. Other issues that have gained awareness are power usage or demand. With the green movement sweeping the country, power users are becoming very aware these issues.
“Many test units have not changed, but some companies have introduced units with very long battery life, larger memory capacities, and portability designs for the day-to-day troubleshooter. The way the power quality units connect have not changed all that much. It is necessary to connect to the voltage lines using a voltage input cable with some sort of clip. It still is necessary to clamp over the cable using a clamp-on device such as a current transformer to measure the current. Units today are more forgiving if they are hooked up incorrectly, and many have excellent isolation characteristics that help protect the users.
“PQ engineers and technicians look for different things in testers. Engineers want a system that can perform many PQA functions while day-to-day troubleshooters are looking for a simple and easy to use tester—they don’t mind having multiple units for varying tests. In addition, many customers give up superior monitoring capabilities for longer monitoring times. Some companies are introducing larger compact flash and SD cards to increase the monitoring times,” Argenziano said.
Megger, Andrew Sagl, product manager, said: “The most common PQ issues still seen are voltage sags, swells, transients, and harmonics, which can cause manufacturing equipment to trip out and equipment failures as well as UPS issues.
“In the past two years, there has been more of a push towards standardization of testing equipment with different class units for different applications. Class A units would be used for verifying compliance with standards and resolving disputes, while Class B units may be used for statistical surveys and troubleshooting applications. Many new PQ testers are now Class A or at least have some Class A functions. They also tend to have higher safety ratings. The new models tend to have more powerful processors and larger memories allowing them to record more data. New models tend to have Cat IV safety ratings. How they are connected to circuits has not changed drastically but how they communicate has changed, as wireless communications has been introduced to many new units.
“Today all new PQ analyzers can be considered multifunction, measuring and recording such parameters as rms voltage and current, unbalance, power and energy parameters, sags, swells, transients, THD, harmonic content, interharmonic content and flicker. With larger memory sizes leading to larger data files, data analysis becomes a more daunting task. To this end, advancements in the software used with these units is also critical in order to alleviate this issue,” Sagl said.