What Factors Determine How Much and How Often?

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1 Testing of Electrical Power System Components: Feature What Factors Determine How Much and How Often? by Ron Widup Shermco Industries Almost all modern (and not so modern) electrical power systems have the same issue: how often should I test the critical components to assure continued serviceability and/or to assess remaining service life? While this question has many facets that need to be considered, this article looks at ten critical factors that come into play when trying to make informed judgments on this very critical aspect of electrical power system reliability. In the Beginning The Test Data If the system components were initially installed to all applicable codes and standards, and if the system tested and commissioned per NETA acceptance testing guidelines, then the owner is ahead of the game on determining the continued serviceability and remaining useful life of his power system. A critical component in the determination of a power system s reliability is past testing data and information. Manufacturing data from the factory, baseline NETA acceptance test data immediately after installation, and NETA maintenance test data during the life of the equipment are all important pieces of information for determining how much testing should be performed and how often. It is the trends that are imbedded in the data that tell us much about how the equipment is holding up in its environment and particular operating conditions. Anyone with responsibilities for electrical power systems should put into place a system and means for archiving all the relevant manufacturing and field test data for the equipment, as this becomes a valuable resource for system reliability assessment. What Factors Determine Maintenance Frequency? There are many factors affecting maintenance frequency and intervals. The goal of the maintenance activity is to determine the equipment condition and to identify any trends that indicate the degradation or impending failure of that particular piece of equipment. When considering your overall maintenance plan and frequency of test intervals, the following ten factors should be included in that decision-making process: 1. Equipment Criticality and Device Significance 2. Current Condition 3. Lubrication Life 4. Maintenance History 5. Operational History 6. Industry Experience 7. Maintenance Philosophy 8. Operating Environment 9. Time Allowed for Maintenance 10. Manufacturer s Recommendations Having an understanding of these ten factors, and using them as critical decision points, can greatly enhance your ability to accurately judge the frequency at which you maintain your equipment. So in looking at them further: Factor 1 Equipment Criticality and Device Significance How important is the device under consideration? The importance of the device and its relevance to your operation weigh heavily on factoring the type, frequency, and magnitude of the testing. Questions to ask about the device significance are: How important is this to my operations? Does it have safety significance?

2 What is the economic impact of the device? Will this affect other areas of the operation? How critical a device is to your operation should play a significant role in the overall assessment of maintenance needs. This factor should be placed high on the relevance scale. Figure 2 Figure 1 Figure 1 illustrates a generator step-up transformer at a power plant. This device is very critical to the operation of the power plant and has a high level of importance, economic impact, and relevance. Factor 2 Current Condition What condition the equipment is currently in has obvious implications as to both the frequency at which it should be tested as well as the remaining useful life. Electrical equipment begins to deteriorate from the time of manufacture until being removed from service. The current condition of that equipment, determined through as-found testing and evaluation, provides critical data points to consider. For example, if you have a situation where an electric motor shows signs of decreasing insulation resistance, this current condition factor of declining insulation health would have a greater impact to your maintenance decision process than some of the other listed factors that would weigh in as less relevant. Another, related factor is the rate of decline. If a sudden decrease in insulation resistance (or decrease in insulation power factor) is recorded during maintenance testing, that device may be in danger of imminent failure. Even though the test value is satisfactory, the rate of decline may be such that the device fails before the next scheduled test interval. Upon initiating a maintenance assessment at a facility, Figure 2 illustrates the current condition of 25 kv power cables that are in a less than desirable state, with obvious environmental problems as well as the presence of tracking across the insulation system. The cable s current condition factors into the overall needs assessment of the testing frequency as well as the overall expected service life. Factor 3 Lubrication Life Lubrication, especially as it applies to power circuit breakers, is a huge consideration when determining overall reliability and equipment health. The type of lubrication used at the time of manufacture and the expected service life of the lubrication must be taken into account when determining maintenance frequencies. You cannot expect a grease to function properly 20 years after being applied in a factory, and as such you cannot expect an electrical device to operate properly when called upon if the original grease specifications are not met. The greases used in the current path of circuit breakers will often last just three to five years before needing replacement. This is due to the heat generated by the current flow through the breaker (I 2 R losses). This is true even though the breaker is rarely operated. In fact, breakers that sit for extended periods of time without operating are more prone to lubrication issues than those that are operated frequently. Grease compatibility is another significant area of concern and is part of the overall lubrication assessment. Has the original grease been replaced, and if so was it replaced with grease that is compatible to the original? Also, has technician in a can, or penetrating greases such as WD-40 or LPS-1 been used on critical mechanical and electrical components that are now faced with grease compatibility and gumming up of the component? The use of such spray penetrating lubricants actually speeds the deterioration of breakers. If there were any original lubricant remaining, it would be flushed out by the spray. Also, these spray lubricants will only last a few weeks at best, then it s metal-tometal wear. In addition to the electrically-operated devices that have lubrication concerns, mechanical components must be evaluated as well. Components such as cell interlocks, racking mechanisms, jack screws, bearings, hinges, etc., must all be evaluated for their lubrication effectiveness. NETA WORLD Spring

3 Factor 4 Maintenance History How well the equipment has been maintained can have far-reaching effects on the overall health of the equipment. Just as a used car that has all service records is more desirable than one that does not; electrical equipment that has been properly maintained with a regular regimen of maintenance testing is a more desirable (and reliable) product. How much maintenance has been performed previously, what the lubrication practices were during that maintenance activity, the environment the maintenance activity was performed in, and the maintenance interval are all important points to consider when factoring in the maintenance history. Factor 5 Operational History When evaluating electrical equipment, the severity of service a piece of equipment has been subjected to is important when making maintenance decisions. Items to consider when looking at operational history are: Number of maintenance work orders (problems) Number of operations since the last maintenance activity Duty cycle (heavy load or light load) Number of faults seen by the device Severity of faults seen by the device Number of times the device has been racked in or out Exposure to transients or switching surges Applying these operational elements to your overall maintenance assessment will help to identify those components that are called upon to work harder, and as such will likely have a greater degree of wear and tear which ultimately affects overall reliability. Factor 6 Industry Experience Your experience with maintenance activities on equipment with similar design, age, lubrication, environment, maintenance, and operational history has invaluable benefit to assessing test frequency. Having experience with a particular type or model of equipment, including failure history, reliability, and overall performance can greatly increase ones ability to make sound judgments on maintenance activities. For example, if you have a 30-year old low-voltage power circuit breaker with series trip units, you can be fairly certain that the breaker will likely not operate properly when needed. History has shown a high failure rate of series trip units, and your experience with these types of breakers helps you make experience-based decisions about the device. Figure 3 Another example is shown in Figure 3. Would industry experience tell you certain things about the overall condition and needs of that particular device? Note the corrosion within the mechanism and obvious signs of neglect. Industry experience with this type of equipment will guide you in making smart and informed decisions on what to do next. Factor 7 Maintenance Philosophy Do you work in a facility that has a proactive and thorough maintenance philosophy, or do you work in a facility that has a run to failure maintenance mentality? Lack of maintenance or poor maintenance practices affect the overall health and condition of electrical power equipment. Just as it is detrimental to personal health not to see a physician on a regular basis for a health checkup, electrical equipment requires much of the same probing analysis as to overall health and physical condition. Look at Figure 4. When it is 2008 and there is a piece of masking tape with the words PM-ED , will this give you any indication as to the maintenance philosophy and likely skill set of the PM ers? It is probable and likely that this piece of equipment has not had proper maintenance in almost ten years, well beyond any recommendations of the manufacturer or of industry. As an additional note (under the Industry Experience factor), do you think it would be an issue that the 600-volt control wire on the transducer is hanging down below the front of the medium-voltage breaker the breaker that will be racked into the cell and likely pull the 600-volt wires with it?

4 At the onset of the equipment s life, the manufacturer most likely presented the owner with a plan for maintenance testing and frequency. While the manufacturer s data does not take into account the nine other factors presented in this article, they do typically offer up a conservative guide to maintenance needs. Another advantage to manufacturer s guidance is the fact that they quite often point out special needs or requirements for equipment specific to that particular piece of equipment, information that might otherwise not be known. Manufacturers also produce service advisories and product recalls. It is important to be aware of such advisories and recalls, as quite often they are linked to equipment performance and/or operation, most of which will affect the serviceability, or continued serviceability, of that particular device. Figure 4 Factor 8 Environment One of the quickest ways to cause failure of electrical equipment is to place the equipment in a poor environment. Whether it is due to moisture, corrosive atmosphere, physical abuse, or general dirt and debris, this is one area that has a high degree of relevance. When environmental conditions come into play on frequency of test assessment, the poor environment factor can weigh heavily on the assessment, especially with older equipment. Factor 9 Time Allowed for Maintenance The equipment is finally scheduled for maintenance but how long did you give the maintenance personnel to perform the critical maintenance activities? The amount of time made available for the equipment can greatly impact both the quality and the quantity of required maintenance. Outage schedules should be well thought out with regards to comprehensive maintenance tasks, especially if the equipment is critical to plant operations or has known issues affecting performance. Often times outside maintenance personnel must be hired in order to meet the time constraints of an outage and to bring in the required expertise for the equipment under test, and it makes economic sense to use personnel specifically trained and certified for these types of activities. Factor 10 Manufacturer s Recommendations An important aspect to any equipment maintenance schedule is the manufacturer s recommendations for service, even if the manufacturer is no longer in business. Frequency of Test: What Does NETA Say? There is a very useful tool for determining frequency of maintenance tests located within the standard ANSI/NETA MTS 2007 Standard for Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems. If you look at Appendix B in the standard, you will find guidance on frequency of test, whereby the following factors are taken into account through the use of a multiplier on preset maintenance intervals: Equipment Condition: Poor Average Good Equipment Reliability Requirement: Low Medium High Excerpt from the ANSI/NETA 2007 Maintenance Testing Specifications, Appendix B: APPENDIX B Frequency of Maintenance Tests NETA recognizes that the ideal maintenance program is reliability-based, unique to each plant and to each piece of equipment. In the absence of this information and in response to requests for a maintenance timetable, NETA s Standards Review Council presents the following time-based maintenance schedule and matrix. One should contact a NETA Accredited Company for a reliability-based evaluation. The following matrix is to be used in conjunction with NETA s Frequency of Maintenance Tests Table. Application of the matrix is recognized as a guide only. Specific condition, criticality, and reliability must be determined to correctly apply the matrix. Application of the matrix, along with the culmination of historical testing data and trending, should provide a quality electrical preventive maintenance program. NETA WORLD Spring

5 EQUIPMENT RELIABILITY REQUIREMENT MAINTENANCE FREQUENCY MATRIX EQUIPMENT CONDITION POOR AVERAGE GOOD LOW MEDIUM HIGH Figure 5 ANSI/NETA MTS 2007 Appendix B Maintenance Frequency Matrix Summary Maintenance Factors: How Can it Work for Me? So think about this: Say you take these ten maintenance factors and apply a relevance number to each factor from one to ten (or one to one hundred, or one to one thousand, etc.), with one being the least relevant and the highest number being most relevant. Score your most important factors the highest, and the lesser aspects at a lower numerical value. Then take the relevance factor and multiply it by a range, again with a weighted number from one to ten, with one being least weighted and ten being highest weighted. What you end up with is a number that takes into account ten factors associated with the device, and from that number you should be able to better establish a priority list of importance and relevance for maintenance testing and frequency. Using your best judgment and applying numerical values to these judgments, and using the NETA Maintenance Testing Specifications, this should help in your overall quest for power system reliability. And it ain t too bad for the safety stuff, either. Ron. A. Widup, Executive Vice President/General Manager of Shermco Industries, has over 20 years of experience in the low-, medium-, and high-voltage switchgear and substation market and is a NETA Level IV Senior Test Technician. Ron is a past president of NETA, and currently serves on NETA s Board of Directors and Standards Review Council. He also serves as chair of the Certification Exam Committee and Conference Committee. Ron is a principal member of the Technical Committee on Electrical Safety in the Workplace (NFPA 70E) and a principal member of the National Electrical Code (NFPA 70) Code Panel 11. He is also a member of the technical committee Recommended Practice for Electrical Equipment Maintenance (NFPA 70B).