Variables affecting electric power quality haven’t changed significantly over the years, but the technological advances of electrical and electronic equipment make the equipment much more vulnerable to power quality events than in the past. Indeed, problems resulting from “dirty” power are multiplying.
Voltage spikes can range into the thousands of volts (V), even in low-voltage parts of a network, and can result in equipment failure or destruction, especially where electronic or microprocessor components are involved, said André Rebelo, who was global communications manager for Extech Instruments at the time of this interview. Insulators can be destroyed. In data centers, processes may fail, or data loss can occur. In plants where computers control automated manufacturing equipment, a power quality incident can shut down a facility’s production flow.
Rebelo said that, in addition, there is a global push for energy efficiency and reduced energy use, and an important element of that is to optimize electrical power for any given load.
“From a cost perspective,” he said, “there are global efforts to manage power quality in industrial and commercial applications because dirty electricity can add up to 30 percent of electrical costs in some cases. Now, power quality is not solely an issue of plant maintenance or electrical maintenance, but it has visibility in the CFO’s office as a cost center.”
Among the most common power quality issues are variations in voltage, brief interruptions in power, startup loads of equipment with large motors, and faulty insulation.
To identify and analyze power quality issues, there is a broad selection of testing equipment—including multimeters, harmonic meters, oscilloscopes, and power quality analyzers—for recording the full power quality spectrum. Manufacturers say there is a trend toward multifunction instruments and that memory in today’s models is greatly expanded at a relatively low cost.
Representatives of five test equipment manufacturers commented about current power quality testing.
John P. Olobri, AEMC’s director of sales and marketing, said: “Voltage surges and sags, overheating of neutral conductors are the most common power quality issues. Basic power quality tests include measuring and recording volts and amperes [A] and power with the ability to view and analyze to at least the 15th harmonic and measuring or, at least calculating, neutral current.
“High-end testers today can measure and record 20 to 30 different power quality variables as well as capture transients, display waveforms like an oscilloscope, log events and monitor demand. Today’s testers have more capability to capture and display inrush current, trigger alarm values to capture intermittent data, and to communicate wirelessly to the analysis station.
“Basic connections require direct voltage connection for each phase, usually via alligator clip or spade lug screw-down connection. Current measurement is accomplished using a split core ‘donut’ type CT, an iron-core current probe, or a flexible Rogowski coil. One sensor per phase is needed.
“Most, if not all, are safety rated to 600V CAT IV. Test connections for voltage and current have improved to eliminate the opportunity for the operator to come in contact with live voltages. Improved isolation between the tester and the computer protects the PC from harmful electrical signals should the tester be monitored in real time.
“The cost of memory has come down substantially. The use of SD card memory has made it common for testers to have two gigabytes or more of memory. In most cases, this is sufficient to capture and store one month’s worth of data at a 1-second rate,” Olobri said.
Extech’s Rebelo said: “There is no one-size-fits-all power quality tester solution. Different users will have different requirements. A modular approach to power quality testers offers customizable capabilities for power quality measurement and also data logging for analyzing trends in equipment loads and electrical supply quality. With several configurations, users are equipped with a truly custom and scalable power quality solution that grows with their needs and budgets.
“Two types of connections are made: invasive and non-invasive. Voltage leads with alligator clips or retractable plunger clips are used to connect directly to each phase. Flexible current probes are looped around conductors for noninvasive current measurements. Depending on the tests performed, either or both are used.
“Several new lines of three-phase power and harmonics analyzers have been introduced that can be customized more than ever with available current probes ranging from 100A to 3,000A ratings. Additionally, the added convenience of SD data card storage enables data logging that is preformatted in a Microsoft Excel-friendly format, making data imports easier.
“A couple of years ago, a study by market research firm Frost & Sullivan forecast a move towards more test and measurement capabilities in fewer devices. We see that with tools like a robust two-in-one insulation resistance tester/multimeter as well as power quality testers,” Rebelo said.
Wayne Thompson, power quality specialist for Fluke Corp., said: “Interest in power quality has increased substantially in the last several years but not because of an increased need for power reliability. Rather, the interest is in using three-phase power loggers and analyzers to capture true power consumption and identify wastes due to poor operational practices as well as poor power quality. Ironically, as facilities add more electronic controls to optimize power consumption, those introduce more harmonics into the system, reintroducing reliability concerns into the equation.
“A power quality tool differs from a regular multimeter in the number of simultaneous measurements it makes as well as the standards-based calculations it applies to the readings. A power quality meter will provide single- or three-phase V, A, Hz, kW as well as harmonics, peak demand, power factor and other power quality parameters. These readings are available in a variety of formats, from waveforms to bar graphs to phasor diagrams and numeric readouts. A single-phase power quality meter is more affordable and provides all of the parameters but, for a comprehensive reading, must be hooked up separately to all three phases of a system.
“More electricians are stepping up from using just current measurement to assess load—either consumption or system capacity—to using power quality tools to get the complete measure in kilowatts. Again, this is due mostly to the sustained interest in optimizing energy consumption. However, as our loads become more complex, factors—like unbalance—can cause inaccuracies in those single-phase measurements on a three-phase system,” Thompson said.
Charles Argenziano, Hioki’s director of technical support, said: “Power quality problems cause equipment to malfunction and can result in complete shutdowns and even worse. PLC and computer data errors that cause manufacturing defects can cost companies millions of dollars in waste and recalls. Harmonics cause heat buildup in transformers—both inside and outside the building—that can cause transformer failures. Circuit overloads can cause unbalanced loads and breaker failures.
“We have added new issues to the power quality analysis environment with the addition of VFD, CFLs, computers, and battery chargers—these units have added harmonics and now the high-order harmonics. New analyzers need to have the added sample speed and bandwidth to see these higher harmonics that can be in the 80-kilohertz range. Technicians need to read and understand the specifications of these units so they know what they are purchasing.
“Many of the newer units are smaller and run on batteries. USB ports have been added, and some have high-definition screens for better waveform viewing. There are testers that can see many different types of power anomalies. Many require turning off some features in order to see other features; others can capture all of them at once,” Argenziano said.
Brian Blanchette, test and measurement product development manager for Ideal Industries, said: “Simply put, power quality is voltage quality.
“Much has happened with straightforward power quality analyzers in the U.S. Analyzers are getting smaller and somewhat easier to use but still provide information based on the voltage events detected. More analyzers today incorporate load and power analysis, and those are important to most users. Basic voltage quality information provided as a simple envelope of cycle-by-cycle rms values is sufficient to document good or bad power quality. Needed for load are current; active, inductive and capacitive reactive power; apparent power; and power factor, plus the ability to integrate that into watt/hours and VAR/hours. This information should be available as three phase for revenue purposes and by phase for troubleshooting and evaluation. Harmonics information needs to be more than just total harmonic distortion to be able to interpret, understand and correct load distortion. Total demand distortion is best, and rms distortion also is useful.
“With the advent of inexpensive memory, there is virtually unlimited ability to store data locally. The newest, most advanced devices today incorporate communications for LAN, wireless, USB and many other communication protocols. The most important changes in analyzers will come with changes in the gathering and analysis of data.
“Anyone interested in power quality and the need to manage the cost of electrical energy should pay attention to the fast-moving changes in the industry. Lower costs of hardware and software as well as automated data gathering and analysis are important. Better quality, higher reliability and lower costs are well worth investigating new solutions,” Blanchette said.