Understanding and Solving Power Quality Problems

Teresa Hansen, Associate Editor

Power quality disturbances, such as sags, swells, interruptions and other occurrences that do not allow equipment to function properly, are costing the U.S. economy more than $6.7 billion annually. This is according to a study sponsored by EPRI’s Consortium for Electric Infrastructure to Support a Digital Society (CEIDS). The recently released study titled “The Cost of Power Disturbances to Industrial & Digital Economy Companies,” highlights several industries’ growing need for so-called “digital quality” electricity.

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One EPRI source reports that the United States has invested more than $1 trillion in information technology (IT) equipment in the past 5 years. According to the National Coalition for Advanced Manufacturers, computers are fundamental in today’s manufacturing processes and to the nation’s economic health. The coalition reports that in the past 50 years, computer operations in manufacturing environments have advanced from being virtually non-existent to being responsible for more than 40 percent of all manufacturing processes (Figure 1). Virtually all of these computer driven operations require pure electricity and will not tolerate sags or surges, and they certainly won’t tolerate power outages, no matter how short lived.

To complicate matters even more, most highly sensitive IT devices contribute to the power quality problem by producing electrical distortions called harmonics. Computers, fax machines and much of the electronic equipment being used contain devices that convert 120V ac to as low as 5V dc. Each of these conversions slightly alters electricity’s frequency, causing distortion. With hundreds of thousands of these devices in service, the cumulative effect can cause severe problems.

Until recently, end-users have had the biggest burden when it comes to solving power quality problems. It is commonly reported that at least 80 percent of all power quality problems occur inside end-users’ facilities, thus utilities have typically left it up to these customers to diagnose their problems and find a solution. The increasing requirements and expectations of many of their best and largest commercial and industrial customers, however, have given utilities incentive to take more interest in their customers’ power quality problems. In addition, in states where electric competition exists, the possibility of losing large customers to other providers has prompted utilities to become more involved in solving power quality problems.

Equipment manufacturers are also joining utilities and end-users in the search for solutions to power quality problems. It is becoming clear that it will take cooperation and innovation from many industry players to improve and solve this growing problem.

Changing Times

“Reliability has always been how utilities’ performance was judged,” said Tom Blooming, P.E., a power systems engineer with Eaton Corp.’s Cutler-Hammer business unit. “Now, however, even though a utility is providing electricity more than 99.9999 percent of the time, if the power quality is poor, the utility’s performance may not be good enough for some customers.” A sensitive device might react to a sag just as it would to an interruption and shut down the equipment, he added.

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This increased need for power quality comes at a time of unprecedented change for the U.S. electric power industry. The Banc of America Securities Energy Technology Industry Overview illustrates what those delivering electricity are facing. The report indicates that digital related demand for power represented 8 percent to 13 percent of the electricity consumed in the United States in 1999. According to the report, this translates to approximately 385 billion kilowatt-hours, an increase of 670 percent since 1993. The same report predicts that by 2010, one-half of U.S. electricity consumption will be related to digital devices in some way (Figure 2).

If that isn’t challenge enough, much of the nation’s transmission and distribution infrastructure is in need of serious maintenance and upgrade. The uncertainty and chaos surrounding deregulation and competition has caused many utilities to tighten the purse strings, resulting in reduced manpower, lower maintenance and capital budgets. The nation’s power grids have been hard hit by these budget constraints. In many cases, utilities have failed to adequately maintain their existing infrastructure, and even more common is the failure by utilities to expand their transmission and distribution infrastructure to adequately meet demand. For example, according to a report from New York’s Attorney General, between 1988 and 1998 capital improvements to the state’s transmission system dropped from more than $307 million per year to about $90 million per year. This reduction in investment is common throughout the country.

Identifying Problems

Most energy providers and users understand the time has come to attack power quality problems. Several organizations have been formed to address these problems. One of the most notable is the IEEE Standards Working Group 1159. The working group has identified seven types of power quality disturbances-voltage imbalances, power frequency variations, long-duration variations (sustained interruptions, overvoltages, undervoltages), short-duration variations (sags, swells, interruptions), waveform distortion (harmonics, notching, noise), voltage fluctuations (flicker) and transients (impulsive, oscillatory). The ultimate goal of this group and other more targeted working groups is to find effective ways to mitigate and eliminate these disturbances.

According to Blooming, two of the most common power quality disturbances are long-duration variations and short-duration variations. Both of these disturbances have similar effects (shutting down equipment), but vastly different causes. Thus, different engineering approaches are required to diagnose and solve the problems.

Long-duration variation events often result from system design flaws or operating errors. Because the disruptions are long, power quality engineers usually have time to set up monitoring and diagnostic equipment and identify the root cause.

Short-duration variation events on the other hand, are not nearly as easy to identify. These events are often caused by things such as lightning strikes, small animals coming in contact with transformers or other equipment, or tree limbs being blown into wires. Since such events are transitory, it is very difficult to diagnose and prevent resulting disturbances. In many cases, these short-term disturbances are hardly noticed by most customers, but for those customers with sensitive equipment, even the slightest interruption can mean big problems.

According to Blooming, more then 80 percent of utility-side disturbances fall into the short-term variation category. At facilities where standard kilowatt-hour meters are used to measure energy use, such events are never recorded. The use of widespread system monitoring, however, has helped both utilities and their customers identify and understand the cause of such disturbances.

Florida Power & Light (FP&L) is one utility that has seen big benefits from using Siemens power quality meters at commercial and industrial customer locations. The initial project started as a program to replace many of the utility’s old solid-state meters with more advanced digital meters. It was quickly realized, however, that the real benefit of the program comes from the ability to monitor power quality events. At the recent Automatic Meter Reading Association conference and exhibition held in Quebec City, Canada, Ed Malemezian, a former FP&L manager who was involved with the project, talked about the project. He said that once the meters were installed, the project quickly turned into a project to lessen and solve power quality events. “Customers love this service,” Malemezian said.

End-users are also becoming more interested in power quality monitoring devices because they have discovered that these devices can be used to not only identify problems within their facilities, but also to look up into the utility’s system. Some end-users see such technology as a way to ensure that utilities are being honest when it comes to power quality problems. “C&I customers are quick to blame utilities for their problems, but 80 percent to 90 percent of the problems are caused inside the users’ facility,” said Blooming.

Who’s Responsible?

When a customer encounters power quality problems, that customer most often contacts the utility. Customers typically believe that it is the utility’s responsibility to solve any power quality problem. While most customers expect the utility to solve their problems, these customers don’t believe they should pay for the solutions. “End-users want premium power, but most aren’t ready to pay for it,” said Ernst Camm, a power quality engineer with S&C Electric. Both Blooming and Camm said that most end-users don’t recognize that utilities are not solely responsible for providing whatever power quality they (the end-users) need. According to Blooming, most any power quality problem can be solved with enough money, but it isn’t always economically feasible to spend the amount of money it would take to solve a problem. Utilities are not in the position to correct all problems for free.

“Many customers have an event or problem and they say that it is costing them a lot of money. But when it comes to paying for a solution, they decide it isn’t worth it,” said Doug Staszesky, S&C Electric’s business development manager. It is important to determine how much the problem is costing and compare that cost with the cost of the solution, he added.

Solving Problems

Even though end-users are still often left to deal with their power quality problems, the trend is beginning to change. According to Camm, end-users are becoming more proactive in their demand for higher quality power, and utilities are becoming more open to offering higher quality power, but at a price.

CEIDS, the organization mentioned earlier that was formed to focus on power quality problems, is bringing utilities’ and end-users’ together to find solutions that are economically feasible for all parties. EPRI’s CEIDS, which is a national effort to ensure power for a digital society, includes members from utilities, equipment manufacturers and representatives of industrial groups, such as high-tech companies that are particularly sensitive to power interruptions. The effort, which officially began in January 2001, is the second phase of EPRI’s Power Delivery Reliability Initiative focused on determining the root causes of the nation’s reliability problems and on identifying ways to provide immediate improvement. CEIDS has a much broader membership than the first phase of the reliability initiative, and its main purpose is to determine which combination of technologies is likely to be most cost effective in optimizing reliability and power quality.

According to Don Von Dollen, CEIDS integration manager, the consortium is addressing power system technology needs holistically. It is considering the power system, distributed resources, power quality devices and the end use devices themselves.

Solutions

Currently, many utility customers’ power quality problems are handled by outside companies, such as Eaton Corp.’s Cutler-Hammer business, S&C Electric, Cooper Power Systems, General Electric, ABB and others, that specialize in designing, manufacturing and installing power quality improvement equipment. Surge protectors, uninterruptible power supplies (UPS) and static transfer switches are all common equipment that can improve an end-user’s power quality. In some extreme cases, on-site generation is installed at a user’s facility to improve power quality or avoid power disruptions, but this is an expensive solution for most end-users.

The technology selected to solve a problem is highly dependent on the individual situation. “You can look at the type of disturbance and determine how much of it you can economically cover,” Camm said. “A UPS usually covers 95 to 98 percent of typical utility disturbances.”

In almost every case, it is not economically feasible to provide high-quality power throughout the distribution system. “The only economically feasible way to fix the problem is at the load,” Staszesky said. Most experts agree. To install equipment necessary to meet one customer’s requirements on the entire system would mean that all customers would be charged for the improvements.

Blooming believes that better communications between utilities and their customers would bring about more cost effective solutions. “Knowing that the power system isn’t perfect and that it isn’t economically feasible to make it perfect, it is the responsibility of utilities, end-users and equipment manufacturers to work together to design facilities and equipment that will work in the current environment,” Blooming said.

Author

  • The Clarion Energy Content Team is made up of editors from various publications, including POWERGRID International, Power Engineering, Renewable Energy World, Hydro Review, Smart Energy International, and Power Engineering International. Contact the content lead for this publication at Jennifer.Runyon@ClarionEvents.com.

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The Clarion Energy Content Team is made up of editors from various publications, including POWERGRID International, Power Engineering, Renewable Energy World, Hydro Review, Smart Energy International, and Power Engineering International. Contact the content lead for this publication at Jennifer.Runyon@ClarionEvents.com.

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