A 10-step program for improved power quality
Have you ever noticed the lights in your plant blink slightly, and then some of your process or manufacturing equipment grinds to a halt? Sometimes this interruption occurs without the telltale flicker of the lights.
Have you ever noticed the lights in your plant blink slightly, and then some of your process or manufacturing equipment grinds to a halt? Sometimes this interruption occurs without the telltale flicker of the lights. What may have occurred is a slight electrical power disturbance; an event on the electric utility's system.
It could have been the result of a fault that was rapidly detected and cleared by the utility's protective system. It could also have been an unexpected utility breaker operation caused by a lightning strike, tree falling on a power line, vehicle accident involving a utility pole, or even the planned electrical switching that routinely takes place on the utility's grid.
The result is the same: A temporary, unplanned interruption of the manufacturing process, bringing losses in production, opportunity, and revenue. These situations can be controlled by establishing a Power Quality Program in cooperation with the electricity supplier. This article describes 10 specific steps toward implementing a Power Quality Program that reduces the production impacts associated with power disturbances and interruptions.
1. Secure a commitment. The first and most critical step is to obtain support for the program. Plant engineering, production, and management must be sufficiently convinced of the benefits to make modest commitments of precious resources.
2. Assemble the team. Secure the assignment of appropriate plant engineering, operations, maintenance, and production personnel.
3. Obtain participation and cooperation of the electric utility. This step is critical. Invite representatives of the electric utility to an initial meeting to discuss the business impacts of power interruptions, need to improve the situation, and role of the utility on the team that will help prevent future problems. The utility is likely to have knowledge in these areas and an interest in cooperating to help improve customer satisfaction.
4. Establish a power quality specification. The utility may have adopted a standard or specification for the quality of delivered electrical power. This information should be reviewed with the utility.
In the absence of an existing standard, consider adopting the Computer Business Equipment Manufacturers Association (CBEMA) curve, also published under the title of Federal Information Processing Standards Publications (FIPS) #94, and the IEEE Emerald Book, Powering and Grounding Sensitive Electronic Equipment . Agreeing to this curve (Fig. 1) as a power quality specification means that the utility will strive to design, build, operate, and maintain its electrical system to deliver measurable performance that falls within the envelope of the upper and lower parts of the curve.
The customer should design, build, operate, and maintain the facility and manufacturing process equipment such that it can withstand an electrical event that falls within the envelope of the curve. Simply stated, the customer is responsible for events which fall within the CBEMA curve, and the utility is responsible for events which fall outside.
5. Establish a communication process with the electric utility. Communication during and immediately following an electrical system event is of utmost importance. Prior to restarting equipment and systems, it is critical to know if the utility's system is stable or whether further disturbances are expected. If uncertainty exists, it may be prudent to delay the restart of facilities, equipment, and systems until normal utility operating conditions are established.
The electric utility has a continuously staffed control center (dispatcher). A communication process must be established between designated plant staff and the utility's control center. The communication process should span all plant operating shifts. Facilities having less than 21 operating shifts per week should consider the need for key employees to be contacted at home to respond. With a reliable communication process in place, critical impact and response data from both the facility and utility electrical system can be shared for future analysis.
6. Establish a process for measuring and recording event data. This step includes the ability to measure characteristics of the electrical event or incident, impact on business and production, conditions that preceded the event, responses by the facility and utility, and other data particular to the situation.
There are two important electrical event characteristics to obtain. One is the magnitude of a voltage drop that has occurred, usually expressed in percentage of nominal voltage. The other is the duration of the event, usually expressed in cycles. The combination of these two characteristics indicates event severity. (For a large facility served by high-voltage lines, swells or overvoltage conditions are unlikely.)
Depending on the point where the fault or event occurred and point where measurements are taken, these metrics can vary widely. Measurement equipment should be located close to the point of delivery from the utility and should be easily accessible. Measurements provide a means to relate event severity to production or business impact, which is an important relationship to establish. The necessary equipment is available in various levels of sophistication, and can include features such as wave form recording and remote alarm capabilities.
Data should be logged in, such as shown in the table on the previous page. It is also useful to record events on the CBEMA curve. This action provides a visual means of interpreting the relative severity of events. Fig. 2 shows data from the table plotted on the CBEMA curve.
Relating power interruptions to their impact on business also requires a meaningful measurement of production output. This measurement could be number of operations, number of parts output, amount of product scrap, or amount of product rework. Assign a measurable loss in production or a business impact to each event.
Events could include electrical storms, winter storms with ice or heavy snow, abnormal electric utility system configuration, abnormal plant electrical system configuration, operation under a condition of reduced electrical reliability, or other noteworthy weather or electrical operating conditions. Keep a record of actions and communications of the plant staff and utility for the event period until the utility's electrical system and the plant have resumed normal operation.
7. Establish a process for event analysis and root cause analysis. As soon after each event as practical, a review should take place. Schedule it promptly, before memories begin to fade and attention is drawn to other problems and issues. Both plant and utility representatives should attend this meeting. The need for plant management representation should be determined on a case-by-case basis, as circumstances dictate.
Hold a constructive discussion and analysis of the available information. For the session to be fruitful all (or nearly all) event data should be available. Additional data or analysis may be necessary and should be completed promptly. The result should be clear identification of the root cause of the event. The purpose of this process is not to assign blame, but to constructively and clearly determine the cause or causes.
8. Establish a corrective action process. After all data and measureables are assessed and the root cause determined, the next step is to jointly determine actions to prevent the event from recurring, or to reduce or mitigate the impact in cases where prevention is not possible. This process may require some level of compromise by both parties. Prudent judgment should be applied. Some events are truly isolated incidents and should be declared as such. In these cases perhaps little or no further action may be required.
However, most root causes result in corrective actions. Human nature may sometimes lead to each participant believing that the solution lies with the other party. This belief can inspire lively debate, but should not discourage or deter the process, because the established power quality specification can help lead to the solution. Utilizing the CBEMA curve as a power quality specification is a good way to define responsibilities. Of course, common sense should prevail on both sides of the meter.
Technical and financial merits of any solution should be evaluated. It makes no sense to spend $10,000 to resolve a one-time event that causes a loss of $500. At the other end of the spectrum, making sound operational or procedural changes can lead to improved power quality performance, reduced plant impact, and improved customer satisfaction with minimal expense.
Another situation to consider is when the solution clearly resides with the utility, but the most cost-effective remedy lies on the customer side of the meter. Supplier investment on the customer side may be a logical solution and should be considered as a possibility. Needless to say, open and frank communication between supplier and customer is important for the program to succeed.
9. Set improvement targets. After a period of time, accumulated data reveal trends and patterns. An improvement goal emerges that can provide meaningful reduction in business losses. Establish improvement targets, identify and evaluate the possible improvement actions and activities, and put them into place.
10. Establish a process to evaluate the program. Measure and evaluate results and reset targets as needed. Principles of continuous improvement apply nicely to this process. At this point, the task of establishing a program is over, and the effort should begin to bring better performance, reduced impact, and an improved bottom line.
What lies ahead as electric utilities restructure and move into a more competitive environment?
This program and processes will continue to be valid in the future. The "wires" business -- where most utility system events originate -- will continue to be a regulated monopoly.
Many states are evaluating the benefits of implementing performance-based regulation (PBR). One PBR attribute valued by many business customers is improvement in electrical power quality performance. In the future, utility shareholders could be economically rewarded, in part, for delivering continuously improving customer value, as indicated by a measurable and verifiable reduction in customer facility impact and improved customer satisfaction.
Superior performance in this area could make a utility competitive in attributes other than cost alone, and put it in a position to attract and retain high-tech customers that have sensitive electronic equipment and continuous manufacturing operations. As competition in the electric utility industry unfolds, utilities will look for ways other than price to distinguish themselves. Cooperating with customers and improving power quality performance for customers will lead to the enviable "win-win" result.
The author gratefully acknowledges the ongoing support of Kevin Wortman, IBM High Voltage Operations and Maintenance Team Leader; Keith Thomas, IBM High Voltage Engineering Team Leader; Terry Cecchini, Green Mountain Power Manager of System Operations; and Mike Arthur, Green Mountain Power Operations and Maintenance Supervisor.
-- Edited by Gary Weidner, Senior Editor, 630-320-7143, firstname.lastname@example.org
The importance of power quality (PQ) issues is widely recognized.
PQ problems are too often approached with scatter-shot, band-aid fixes.
PQ issues need to be defined and addressed on a plantwide basis.
The PQP Co.1998 electrical power disturbances with business impact
Start End Voltage Event Business
Date time time drop duration impact Root cause Corrective action
Jan 12 0805 0805 13% 12 cycles 12 widgets scrapped Heavy wet snow frequency
of line inspections
Mar 3 1425 1425 38% 17 cycles 125 widgets scrapped Failed insulator Update insulator PM
scope & schedule
June 17 2315 2315 95% 71 cycles 500 widgets scrapped Electrical storm Isolated incident
Aug 29 1520 1520 35% 42 cycles 200 widgets scrapped Tree limb Improve tree
Sept 13 1445 1445 18% 6 cycles 10 widgets scrapped Electrical storm Isolated incident
Oct 19 2230 2230 33% 10 cycles 50 widgets scrapped Animal contact Install animal
at key locations
Dec 1 1035 1035 48% 123 cycles 450 widgets scrapped Ice storm Adjust timing of
Dec 23 0415 0415 29% 23 cycles 60 widgets scrapped Failed insulator Inspect similar type
insulators & replace
Elements of a power quality program
1. Secure a commitment
2. Assemble the team
3. Obtain participation and cooperation of the electric utility
4. Establish a power quality specification
5. Establish a communication process with the electric utility
6. Establish a process for measuring and recording event data
7. Establish a process for event analysis and root cause analysis
8. Establish a corrective action process
9. Set improvement targets
10. Establish a process to evaluate the program
The author is willing to answer questions concerning this article. Mr. Lang is available at 802-769-4966; e-mail: email@example.com
Related articles previously published include "Defining Power Quality in the Age of Solid-State Electronics" (PE, July 1997, p 81, File 0501) and "Instrumentation for Accurate Harmonics Measurement" (PE, December 1997, p 122, File 8520).
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