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The why and how of a power quality survey

By Randy Barnett

June 2012

Panelboards make ideal locations for many power quality measurements with the handheld power quality analyzer.

Panelboards make ideal locations for many power quality measurements with the handheld power quality analyzer.

With one estimate describing power quality problems costing the US economy 6.7 billion dollars per year, you would think it should be time to pay more attention to the voltage and current in our distribution system. Unfortunately, not all facilities are able to do so. Troubleshooting power quality problems requires specific electrical distribution system knowledge. Test equipment can be costly and requires some training and expertise to use. Maintenance and engineering staffs are often busy addressing seemingly more pressing production issues. Yet, with studies placing 30 to 40 percent of all business downtime related to power quality problems, there are more and more reasons to survey the power in plant distribution systems.

What is a "power quality survey"?

Electrical power delivered to a load must be of sufficient quality to allow the load to function properly. Waveforms must be relatively distortion free and of the proper magnitudes with no intermittent aberrations. Ideally, there should be little or no current flowing at frequencies other than 60 hertz. Unless all of these conditions are met, and depending upon the severity of problems and the length of occurrences, equipment malfunctions may result. Lost data, machine downtime, and even facility fires are possibilities. Thus, there is a need to monitor, observe, and analyze the electrical voltages and the currents that flow through our distribution systems. Such an analytical process is simply called a "power quality survey."

Utility or facility?

Power companies produce nearly perfect power. The three-phase sinusoidal voltage waveform is distortion-free as it leaves the utility's generator. However, events occur as the power makes its way along the distribution system: utility reclosers operate, power is switched by utilities at their substations, capacitor banks are switched, occasionally Mother Nature interferes with electrical distribution, and the many consumers along the distribution system operate equipment that has adverse effects on distribution voltages. The result is a distorted waveform, supplied by a utility, that may not be the best for supplying a plant's electrical equipment. Despite these distribution issues, it is not the utility supply that generally causes most facility electrical problems. It is estimated that 80 percent of all power quality problems come from within a facility. While it is important to contact and discuss any utility power quality issues with a utility representative when conducting a power quality survey, it is imperative that equipment within the facility be examined.

Understanding that there can be several sources of power quality problems will help you determine where to begin the power quality survey. It makes sense to first monitor the supply to the building for any abnormalities, then monitor further and further into the electrical distribution system to identify and isolate any power quality problems. In fact, since the majority of the problems are being created within the facility, it makes good sense to follow a logistical, systematic plan for observing the quality of the power throughout the plant electrical distribution system. Use a one-line diagram as the electrical drawing to provide the roadmap for following the distribution system.

You can measure and record deviations from the ideal voltage and current produced at the utility generator with a power quality analyzer. While permanently installed monitors provide on-going data, the handheld power quality analyzer allows for troubleshooting and performing routine surveys. Trained technicians or engineers using these test tools measure, record, and analyze parameters under varying equipment conditions, then make decisions as to problem severity and whether or not corrective action is warranted.

Different types of power quality problems

Modern handheld power quality analyzer usage becomes intuitive to the technician who understands the different types of power quality problems. Analyzer screens show voltage and current waveforms, freeze and magnify waveforms for close examination, trigger alarms when specified values are exceeded, graphically represent the various harmonic currents flowing in the systems, and indicate the percentage of voltage and current distortion created. Functions also display the many parameters monitored, including voltages and currents on each phase and the neutral, frequencies, unbalance values, and many other key parameters. Since many power quality problems (such as transients, voltage sags and swells, intermittent power losses) occur only for a very brief period of time, it is necessary for power quality analyzers to record data for hours or even days in order to capture problems. Data is then downloaded to software where it can be studied, analyzed, and saved for future reference. While anyone with an electrical background can be trained to use the power quality analyzer, the technician or engineer who is passionate about technology and enjoys the highly technical side of his or her business makes the best power quality technician.

There can be any number of reasons for performing a power quality survey. However, troubleshooting existing problems is one of the most obvious. A typical manufacturing problem may be a high-temperature shutdown on a vital piece of equipment, such as an injection molding machine. If a quick check of the screen display temperatures indicates normal barrel temperatures, a faulty thermocouple might be suspected. However, if replacing the thermocouple yields no difference and the machine continues to have alarm and shutdown problems, it is reasonable to suspect PLC control problems. The quality of the power delivered to the PLC needs examination as part of the investigative process. A power quality survey can be conducted at the machine incoming power and along the distribution system supplying the unit. It is not unreasonable to suspect harmonics, sags, transients and electrical noise from nearby automation equipment affecting the voltage sine wave delivered to the PLC.

Any significant nonlinear loads should have a power quality survey conducted at the equipment. Nonlinear loads account for the harmonics and resulting voltage sine wave distortion in a plant distribution system. In studying power quality problems, it is not uncommon to find that equipment that is sensitive to power quality problems is also the very equipment that is producing power quality problems. Therefore, conduct surveys at large nonlinear loads, such as variable speed drives, variable speed chillers and air compressors, battery chargers, and ac inputs to UPS systems, for example.

Baseline data and energy usage

Power quality surveys also provide baseline data. By keeping good records, data obtained while troubleshooting can be compared to data when the system was functioning normally. It is important to keep data up to date and conduct a survey before and after equipment is relocated or new equipment is installed. Generally, power quality surveys should be conducted throughout the year as plant conditions change. For example, chiller operations will be much more prevalent during summer months, production runs for certain parts may only occur for specified periods of time, or winter may mean changes in heating and even lighting requirements in office areas.

An important yet often overlooked reason for conducting a power quality survey is to monitor and help control energy usage. Power quality analyzers record kilowatt usage over time. By knowing the kilowatt hours of energy utilized and the cost per kilowatt hour a facility is being charged, it becomes easy to calculate the cost of operating a specific piece of equipment. Data collected during the survey can help eliminate utility penalties for poor power factor, reduce demand charges, and find system inefficiencies.

Conducting the power quality survey

Begin the power quality survey with careful planning; set survey goals, review plant drawings, use trained personnel, and coordinate the survey with plant operations. Since it makes sense to first check utility power, start at the service entrance and work your way down through the distribution system. Monitor at the source of each separately derived system, such as transformers and uninterruptible power supply (UPS) systems. Monitor at both the input and output sides of UPS systems. Monitor emergency and standby power sources when in use. Monitor at potential problem sources, including supplies to servers, fluorescent lighting panelboards, and panelboards supplying office equipment.

Carefully connect and set up the analyzer following the manufacturer's instructions. Verify that the analyzer is recording and is plugged into ac power before leaving the area. Once recording is completed, download data to a computer for analysis. Look for problems that occur shortly before or when equipment is known to malfunction.

Conducting a power quality survey does not happen without commitment. Equipment operational problems and downtime, lost data, and overheating of equipment and conductors are just a few of the issues that make the benefits of power quality surveys obvious. Train dedicated personnel, use the right power quality tools, set goals and begin a routine survey program. And, in return, expect a more efficient plant operation.