What do robotics, artificial intelligence (AI), automation, synaptic performance indicators (SPI), and machine learning (ML) have in common? In addition to being buzzwords for the reliability professional to throw around, the reliability world uses these terms to get practitioners to spend a lot of money on the shiny new thing. Sadly, too much of that money will be wasted by well-meaning managers trying to impress their C-level bosses as we all adapt to the rapid move into the digital age.
Sophisticated systems all require quality power — not just bulk power, but quality power. Without clean, quality power, complex automated operations are meaningless and potentially even harmful.
While poor power quality can create a myriad of problems, this article focuses on the issue of power quality as it affects sophisticated automated systems from a reliability professional’s perspective. The more we rely on automation to operate plants, the greater the impact of poor power quality, and in turn, the greater the impact on the reliability of those plants.
In the world of the NETA professional, constantly increasing change affects the manufacturing world as we fully embrace digitization and automated control systems. Globalization, hyper-competition, advanced automation design, and the ever-present pressure to produce more at lower cost and higher quality means plant design, operations, maintenance, and reliability professionals cannot rest on yesterday’s advancements. The pressure is even greater on reliability, electrical and instrumentation (E&I), and electrical engineering departments, as the need for quality power challenges them the most.
Power Quality Defined
Poor power quality is defined by IEEE as “any power problem manifested in voltage, current, or frequency deviations that results in failure or mis-operation of customer equipment.” Thus, good power quality is best described as voltage that adequately feeds its load within proscribed parameters. For the most part, changing proscribed parameters creates the problem as the requirements of automated systems in industry decrease the margin of error for power quality. Adding uninterruptible power supply (UPS) equipment and back-up generation can also add fluctuations in power quality, so as these back-up systems for power availability become more important, they might not solve a power quality problem; in some cases, they could increase or create a problem.
Asset Reliability: When an asset performs its required designed function, without failure, over the course of its design life.
Let’s look at this definition in more detail given that most electrical systems, unless we are dealing with totally new installations, are full of assets that are well beyond their designed life. Power transformers, for instance, average over 38 years of life in the United States. The same is true of assets from cables to switchgear in a substation. To make this aging system more functional, we add relays, capacitance, and back-up systems that have been built within different design parameters. Assets designed using microtechnology and electro-mechanical technology can and do work well together, but their reliance on quality power varies.
When a steady supply of voltage within the proscribed parameters of the load is maintained such that the equipment using the load can operate effectively under normal conditions, we have power quality. Consider the premise that asset reliability is defined as an asset that performs its required design function over the course of its design life, and it is clear that one important factor for asset reliability is the power required to ensure the asset performs to its design standard. As design parameters for equipment power requirements get tighter — with little or no room for disruptions of any kind — making sure we maintain power quality requires greater emphasis on system design, not just the design of individual productive assets in that system. System design is paramount when changing assets within that system.
One important change 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 the reliability of the system is more than the sum of the parts. A disruption at any point in a complex manufacturing or process system affects the entire system.
Any variation that causes voltage to drop below the requirements of the system or causes voltage to spike severely is a disruption due to lack of power quality. Harmonics and wave-form fluctuations create their own distinct set of problems different from sags or spikes. The devices or equipment being powered will fail, malfunction, or operate inefficiently.
Imagine the tighter parameters required as we add more robotics, automation, and sophisticated processes into the production system. Surges, sags, transients, and momentary disruptions interrupt or distort the ideal 60-hertz wave form. And while it may cause a slight flickering of lights in the 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 happened to the power supply side — the generating utility world. Most industrial countries developed a step-down system where power was generated from large generation facilities such as hydro, coal, nuclear, and gas. It was 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. Getting the right volume of power to the end user was the requirement.
In the industrial world, large mechanical machinery powered assembly lines or processing systems. Paper, steel, and chemical facilities needed a lot of power to heat their raw materials as they were processed 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 cost effectively as possible.
But today, things like 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 powers part of a plant begins sending power back into a grid that was designed to step down power, but now it must also step up that power. The entire grid is negatively impacted because of the way it was designed, which causes utilities to put their primary focus onto their side of the fence, not on the industrial customers’ side of the fence. “In essence, everything on your side of the fence is your problem,” is how one transmission and distribution engineer described it to me.
Using micro-technology to measure and monitor systems as we automate production makes them more sophisticated and more reliant on the quality of the required power. But power suppliers are grappling with their own challenges of a similar nature, so for the most part, they leave the power quality issue up to others. Their job is to feed the main substation, and users are left to make sure the feed is adequate to meet the needs of the system.
Power Quality Problems
The results of poor power quality include 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. It’s enough to keep a reliability engineer up at night and give a plant manager nightmares.
Because of the sophistication of automated systems, any one of these problems can be catastrophic. As Schneider Electric has found:
“Several studies estimate that power quality issues cost the U.S. economy about $15 billion each year. Because approximately 80 percent of all power-quality problems originate from the customer’s side of the meter, facility owners, managers, designers, and other high-tech equipment users need to understand and manage and avoid power quality issues.”
Schneider estimates 80% of power quality problems are the customer’s problems, and those problems grow exponentially when we add more power quality parameters through automation, robotics, sensors, and micro-processing. Without proper conditioning, sags, momentary interruptions, or transients can adversely affect the performance of sensitive equipment.
Power Conditioning Research and Standards
IEEE and IEC have conducted a great deal of research and developed standards in the area of power quality for industrial applications. The most applicable to industrial plants or commercial facilities include:
- IEEE Std. 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 both 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 Std. 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 Edition 2.0 b:2017, Power quality measurement in power supply systems – Part 1: Power quality instruments (PQI): “Specifies product and performance requirements for instruments whose functions include measuring, recording and possibly monitoring power quality parameters in power supply systems, and whose measuring methods (class A or class S) are defined in IEC 61000-4-30.”
- IEC 62586-2 Edition 2.0 b:2017: Power quality measurement in power supply systems – Part 2: Functional tests and uncertainty requirements: “Specifies functional tests and uncertainty requirements for instruments whose functions include measuring, recording, and possibly monitoring power quality parameters in power supply systems, and whose measuring methods (class A or class S) are defined in IEC 61000-4-30.”
Additional guidelines and standards for specific applications such as medical or specific industrial applications are available through IEEE, IEC, and NEC.
Power Quality Impact on a Reliable System
The critical nature of power quality as it relates to the reliability of a production system has been established, and now we are left with what to do about it. Individual problems abound, and there seems to be one common thread. Let’s consider a few cases where the problem was created when newer, more sophisticated equipment was added to an existing system.
- An ice cream storage facility added a series of new freezers with energy-efficient motors and compressors to save electricity, keep the temperature more constant, and create alarms that directly alerted the control system of any anomalies. The problem was that individual freezers continuously shut down randomly. The freezer company checked them out, and they were all 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. Old freezers did not care that there was a sag in power, but the newer ones reacted as they were designed. The solution to the problem was to add a small control transformer to even out the load.
- A more complicated but insightful 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 logic controller (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 80–86% 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 ms.”
Conclusion
The common element to these cases — and to most others we have researched — is increased sensitivity to power quality from new equipment installed in an existing system. The proscribed parameters have changed, and what was once adequate power quality is no longer adequate. Mitigating the problem is often not all that difficult once you determine the cause of the problem.
Power quality testing has become much more cost-effective and common. When adequate and appropriate power conditioning equipment is installed between the main feed and the load requirements, results show automation and digitization of production and processing systems can continue to take advantage of new technologies and developments.
The first step is to understand that it is not the supplier of power or the new equipment manufacturer that is responsible for power quality; it is the responsibility of the power user. The best time to address potential power quality problems is during the design phase of a line or system configuration where newer automated equipment is being deployed — not after a failure causes a catastrophic loss of the new equipment. Testing for power quality in alignment with the parameters required by the automated system, conditioning the 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.
References
Ignatova, Venya. “Why Poor Power Quality Costs Billions Annually and What Can Be Done About It,” Schneider Electric Blog, https://blog.se.com/power-management-metering-monitoring-power-quality/2015/10/16/why-poor-power-quality-costs-billions-annually-and-what-can-be-done-about-it/.
Wagner, VE; Andreshak, AA; and Staniak, JP. “Power Quality and Factory Automation,” IEEE Transactions on Industry Applications, Vol. 26, No. 4, pp. 620-626, July-Aug 1990. Access at: https://ieeexplore.ieee.org/abstract/document/55984.
Alan Ross is President of the Electric Power Reliability Alliance (EPRA) and is responsible for leading the alliance to build electric system reliability in the industrial and commercial marketplace. He often presents at industry conferences and has authored several trade publication articles on electric power reliability, including articles featured in Solutions and Uptime magazines and has written two books: Unconditional Excellence and Beyond World Class, and is currently Editor in Chief of Transformer Technology magazine. Alan earned a BS in mechanical engineering at Georgia Institute of Technology and an MBA in marketing from Georgia State University, graduating Magna Cum Laude. He is a Certified Reliability Leader (CRL), a Certified Maintenance and Reliability Professional (CMRP), a member of the IEEE Reliability and Power Energy Societies, and chairs the Smart Grid Reliability Alliance.