Power Quality And Automation: Why Problems Arise
EP Editorial Staff | February 20, 2019
Manufacturers are responsible for providing the power quality required by today’s automation equipment.
By Alan Ross, SD Myers
Robotics. Artificial intelligence (AI). Automation. Synaptic performance indicators (SPIs). Machine learning. What do these have in common? They require quality power. Without consistent, reliable, quality power, the complexities of new plant operations are
Low-quality power creates countless problems in industry, including in sophisticated automation systems. What’s worse, as plants increasingly—and rapidly—move toward full digitization and automated control methods, the greater the impact that poor power quality will have on equipment and process reliability.
Globalization, hyper-competition, improvements in automation design, and the ever-present pressure to produce more at lower costs and higher quality mean plant-design, operations, reliability, and maintenance professionals can’t rest on yesterday’s advancements. The pressure becomes even greater on Reliability, E&I (Electrical & Instrumentation), and Electrical Engineering departments as the need for quality power will challenge them as soon as current flows from a primary substation into production floor.
THE RELIABILITY ANGLE
One of the more important changes taking place in the reliability world is the emphasis on “system reliability.” Consider that any production facility is made up of a series of assets, operated by people, within a designed set of operating parameters, and you can see how system reliability is more than the sum of its parts. In a complex manufacturing or process system, a disruption at any point affects the entire system.
Any variation that causes the voltage to drop below system requirements or causes voltage to spike, is a disruption due to power quality. Harmonics and waveform fluctuations create their own distinct set of problems that are different from sags or spikes. The devices or equipment being powered will fail, malfunction, or operate inefficiently.
Imagine the tighter parameters required as more robotics, automation, and sophisticated processes are incorporated into a production system. Surges, sags, transients, and momentary disruptions cause interruption or distortion of the ideal 60-Hz waveform. While an event that interrupts or distorts power may cause a slight flickering of the lights in an office, it can severely damage a plasma-TV production line or an automated-chip manufacturing process. These types of production systems require more-stringent power quality.
WHEN VOLUME MATTERS
Let’s step back and look at what has been happening to the power-supply side, i.e., the generating utility world. Most industrialized countries developed a step-down system. Power was generated from large generation facilities such as hydro, coal, nuclear, and gas. That power was then stepped up in voltage to large transmission lines crisscrossing the country, and then stepped down to cities, towns, communities and, ultimately, to the industrial and residential marketplaces. Providing the right volume of power to the end user was the requirement. In the industrial world, large mechanical machinery powered the assembly lines or the processing systems. Paper, steel, chemical, and other process operations needed substantial power to heat raw materials for processing into finished goods. Quantity and continuity of power was what mattered most. In the generation world, life was simple. Make more. Get it to the end user as safely and as cost effectively as possible.
Today, though, things such as distributed-energy resources, microgrids, and renewables are changing us from a step-down system to a “step everywhere” system. Consider what happens when a solar array that serves part of a plant begins sending power back into a grid that was designed to step down power but now must also step it up? The entire grid is negatively affected because of the way it was designed, which causes utilities to primarily focus on their side of the fence rather than that of the industrial customer. As one transmission-and-distribution engineer has described it, “In essence, everything on your side of the fence is your problem.”
The utilities basically leave the power-quality issue up to those of us on the demand side. Their job is to feed the main substation, while ours is to make sure that the feed from there is adequate to meet the needs of the system. And here’s where plenty of problems may arise.
Poor power quality can be responsible for automatic resets, data errors, complete equipment failure, circuit-board failure, memory loss, power-supply problems, UPS alarms, software corruption, and overheating of electrical-distribution systems. Because of the sophistication of automated systems, any one of those problems can be catastrophic.
Research by the Electric Power Research Institute, Palo Alto, CA (epri.com), has found that power-quality issues cost the U. S. economy about $15 billion annually, and that 80% of all power-quality problems originate from the customer’s side of the meter. Such problems grow exponentially as more power-quality parameters are added through automation, robotics, sensors, and micro-processing.
It’s important to note that without proper conditioning, sags, momentary interruptions, or transients could adversely affect the performance of your sensitive equipment. The Institute of Electrical and Electronics Engineers (IEEE), Piscataway, NJ (ieee.org), and the International Electrotechnical Commission (IEC), Geneva, Switzerland (iec.ch), have conducted extensive research and the development of standards in the area of power quality for industrial applications. Several of the most applicable to industrial and commercial facilities include:
• IEEE 1100-2005, Recommended Practice for Powering and Grounding Electronic Equipment. “This document presents recommended design, installation and maintenance practices for electrical power and grounding (including safety and noise control) and protection of electronic loads such as industrial and controllers, computers, and other information technology equipment (ITE) used in commercial and industrial applications.”
• IEEE 519-2014, Recommended Practice and Requirements for Harmonic Control in Electric Power Systems. “This recommended practice is to be used for guidance in the design of power systems with nonlinear loads. The limits set are for steady-state operation and are recommended for worse case conditions.”
• IEC 62586-1 and 2 ED. 2.0 B:2017, Power Quality Measurement in Power Supply Systems and Parts 1 and 2; Power Quality Instruments (PQI). “Specifies product and performance requirements for instruments whose functions include measuring, recording, and possible monitoring power quality parameters in power supply systems.”
Guidelines and standards are available for various specific applications through IEEE, IEC, and the National Electrical Code (NEC or NFPA 70), from the National Fire Protection Association, Quincy, MA (nfpa.org/nec).
IMPACT ON RELIABLE SYSTEMS
What to do about the critical nature of power quality as it relates to reliability of a production system? Individual problems abound, and when investigated, there seems to be one common thread. Consider the following two real-world examples of problems that arose when newer, more sophisticated equipment was added to existing systems and the subsequent solutions to those problems.
• Ice-cream-storage facility. This operation added a series of new freezers with energy-efficient motors and compressors to save electricity, keep temperatures more constant, and create alarms that would directly alert the control system of any anomalies. The problem was that individual freezers would continue to shut down randomly. The freezer manufacturer checked them out and found all to be functioning properly and according to their operating parameters. An electrical contractor traced the feed and noticed sags in the power supply to these freezers that shut them down due to the sensitive parameters of the new equipment. The old freezers didn’t care if there was a sag in power, but the newer ones reacted as they were designed. Adding a small control transformer to even out the load and eliminate sags solved the problem.
• IEEE example. An IEEE case study involved monitoring power-quality disturbances at a plant and identifying the disturbances that disrupt production. The sensitivities of representative electronic-control equipment to the identified disturbances were measured and then projected to form a plant disturbance threshold. For the monitoring effort, six disturbance analyzers were installed at four voltage levels extending from the utility 40-kV station to 120-V control power in an individual machine tool. Voltage sags were the only disturbance to directly cause lost production and were the most common disturbance at 68% of the total number of events recorded. Two programmable-logiccontroller (PLC) transfer lines and a computerized numerically controlled (CNC) lathe were tested with a sag generator to determine the sensitivities of the equipment. The most sensitive components required the voltage during a sag to drop to less than 80% to 86% of rated to malfunction, whereas the least sensitive required the voltage to drop below 30% of rated. From the test results, the calculated sag threshold at the utility feed to the plant to disrupt production was 87% of the nominal voltage for more than 8.3 msec.
The common element in both cases, and to many others, is that of increased sensitivity to power quality from new equipment installed in an existing system. The prescribed parameters have changed and what was once adequate power quality is no longer sufficient. Mitigating the problem is often not all that difficult once the cause of the problem is determined.
THE PATH TO SUCCESS
These days, power-quality testing is much more cost-effective and common than it used to be. When adequate and appropriate power-conditioning equipment is installed between the main feed and the load requirements, the results are that automation and digitization of production and processing systems can continue to take advantage of new technologies and developments.
The first step is understanding that it is not the supplier of power or the new-equipment manufacturer who is responsible for power quality; it is the responsibility of the power user. The best time to address any potential power-quality problems is during the design phase of a line or system configuration where newer automated equipment is being deployed, not after it fails, because a failure may cause a catastrophic loss of the new equipment. Testing for power quality in alignment with the parameters required of the automated system, conditioning that power feed to meet the new parameters, and maintaining a vigilant monitoring program for power quality are the hallmarks of a good power-quality program. EP
Alan Ross is vice president of reliability at SDMyers LLC, Tallmadge, OH (sdmyers.com). An advocate of electric-power system reliability, Ross is a certified reliability leader, chair of the SMRP Smart Grid Working Group, and a member of the IEEE Reliability Society and the IEEE Power and Energy Society.
Power quality is best described as voltage that adequately feeds the load on it, within prescribed parameters. Problems arise because today’s automated systems have a relatively small power-quality margin of error. Adding uninterruptible power supply (UPS) equipment and back-up generation can also contribute to fluctuations in power quality. While essential equipment, they might not solve a power-quality problem, and in some cases they might increase or create a problem.
When a steady supply of voltage, within the prescribed load parameters, is maintained such that the equipment using the load can operate effectively under normal conditions, we have power quality. Consider that asset reliability is defined as an asset that performs its required design function over the course of its life. It is clear that one of the important factors for asset reliability is the power required to ensure that the asset performs to its design standard. As designed power parameters get tighter, with little or no room for disruptions of any kind, making sure we maintain power quality also requires a greater emphasis on the system design, not just each of the individual productive assets.
Ignatova, Vanya. “Why Poor Power Quality Costs Billions Annually and What Can Be Done About It.” Schneider Electric (blog), Oct. 16, 2015.
Wagner, V.E., A.A. Andreshak, and J.P. Staniak. “Power Quality and Factory Automation.” IEEE Transactions on Industry Applications 26, no. 4 (July/Aug. 1990): 620-26. doi:10.1109/28.55984.