One challenge with going to one of America’s iconic eating establishments—the diner—is that the menu has so many choices that decisions can change a dozen times before the server takes the order. Electrical contractors face a similar challenge when deciding which power quality tool to purchase or rent. Advertisements for instruments with “power quality (PQ) capabilities” can encompass a vast array of functionality and price points.
To help with decision making, buyers should understand the different tool categories and their capabilities. At the lower-end price point are digital multimeters (DMMs) and clamp-on meters. DMMs typically perform one function at a time, and only a few of them have harmonic measuring capabilities. The user usually must watch the display to see what happens, though some have max-hold functions. However, they are good for checking for excessive voltage drops across contacts, breakers and other connections or neutral-to-ground voltages that are too high or the voltage unbalance is excessive.
Clamp-on meters can do voltage and current simultaneously on one circuit, allowing for power parameters to be displayed as well. Prices from companies such as Amprobe, Extech, Flir, Fluke and Ideal range from $400–$2,000.
The lines get a bit blurred in the next level up in performance (and price). The difference between power quality meters, loggers, monitors and analyzers is often a function of the manufacturers’ marketing departments. Meters are often panel meters, with three-line numerical displays, though some have color-graphic LCDs. Well-known manufacturers include Amprobe, AEMC, Dranetz, ElectroIndustries, Extech, Flir, Fluke and SATEC. Pricing depends on number of channels and communication options and ranges from $1,000–$3,000.
A logger typically records voltage and current periodically, along with a few additional parameters, such has harmonic distortion, power factor and unbalance. A PQ analyzer and a PQ monitor are often used interchangeably and are generally considered to be portable instruments, used at one location long enough to figure out what is causing the problem or to record benchmark survey data. Users can customize thresholds to record both cyclic rms data for voltage and current and voltage and current waveforms when the thresholds are crossed. Infrequently occurring events, such as a voltage sag, can be recorded in adequate detail to determine magnitude and duration and even find the direction (upstream or downstream) and likely cause of the disturbance with some monitors.
AEMC, Dranetz, Fluke, Hioki and Megger offer a wide range of instruments with multiple communication options, some with high frequency (1 megahertz or greater) transient detection, and gigabytes of data storage. Price and performance go hand in hand. A good tool starts around $3,500, and the top end exceeds $10,000 with a three-phase set of flexible 3,000-ampere current probes.
For facilities where high reliability is essential, as well as those wanting to be proactive rather than reactive with regard to process malfunctions or interruptions caused by power quality phenomena, the permanently installed power quality and energy management systems from Dranetz, ElectroIndustries, PMI, PSL and Schneider Electric are commonly installed at the service entrance and critical points throughout the facility. Often just a black box hidden inside a switchgear cabinet, these instruments are generally less expensive than their portable counterparts. However, nearly all function through ethernet or wireless to report the data from multiple monitoring points to a central server.
Like the portable meters, these have a wide range of performance capabilities, including outputs for alarming and recording other signals. Many of these products have revenue-certified power and energy-measurement capability as well.
Most manufacturers have PQ software that allows management of systemwide data retrieval, storage and analysis as well as real-time data collection from individual monitors. Real-time data, historical data and events as they happened can be reviewed on smartphones, tablets and PCs. In addition to the instrument manufacturers, some companies sell the software alone. One of most widely used products, especially with larger systems, is Electrotek Concepts’ PQView software, which can handle hundreds of monitoring points with a year’s worth of data. It also can pinpoint faults on circuits.
A valuable addition to the toolbox for quick, noncontact investigations of potential problems are infrared/thermal imaging cameras from Extech, Flir, Fluke, et al. Some PQ instruments can directly interface with the cameras so that the magnitude of the current harmonics of a transformer running hot can be recorded along with its thermal image. Some of the cameras are so small that they can connect to smartphones and cost less than $250.
The latest Profile of the Electrical Contractor shows that nearly 70 percent of electrical contractors are involved in power quality. The Profile found that 8 percent of ECs purchased thermal imaging tools in the previous year, while 46 percent bought electrical testers/meters.