ML20043F666
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| Issue date: | 02/12/2020 |
| From: | Office of the Chief Human Capital Officer, Woodard Corp |
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| Gary Callaway | |
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Emergency Diesel Generator EDG Performance Monitoring and Maintenance
- 12. EDG PERFORMANCE MONITORING Table 11-2 of the previous Chapter. Other AND MAINTENANCE data are needed for a complete, effective monitoring and trending program, including Learning Objectives analyses of fuel oil, lubricating oil, etc.
In the early stages of nuclear power in the Upon completion of this lesson you will be US, more regulatory attention was paid to familiar with the wide range of EDG the design and engineering of the plants monitoring and maintenance techniques than to the requirements for long-term that help assure reliable operation and you maintenance of plant systems. Once a will have a working knowledge of:
plant was placed in service the licensees then put varying degrees of attention on 1. The difference between Prescriptive system maintenance. (periodic) and Predictive (condition-based) EDG maintenance, and how Due to the complexity of EDGs and the licensees have benefited from the trend critical nature of their safety function as the to a Predictive approach.
onsite emergency power supply, they have attracted much attention. As a result, they 2. An overview of the key regulatory were one of the first major NPP systems to requirements for maintenance, including have regulated maintenance, primarily the "NRC Maintenance Rule."
requirements in Technical Specifications to follow the manufacturer's recommended 3. Monitoring, trending, and analysis of intervals for maintenance. That caused a key EDG parameters, including specific number of problems because the guidance engine and support system values from most EDG manufacturers was based during runs, as well as the fuel oil, on set intervals designed for units in year- lubricating oil, cooling water, etc.
around commercial service (e.g., marine propulsion, stationary power, locomotives). 4. The importance of baseline data, Unfortunately, those maintenance parameter trending, competent analysis, instructions simply were not appropriate for and follow-up to assure effectiveness.
nuclear applications, which typically involved intermittent standby service with 5. The necessity for observations before, very short run durations during and after EDG runs, and also in conjunction with any maintenance on In response, the maintenance philosophy at (or even in the vicinity of) the EDG.
many nuclear plants today has evolved toward a hybrid condition-based program 6. Some applications of EDG monitoring relying on extensive engine parameter systemsincluding the human senses.
monitoring. In recognition of the need for that approach, IEEE 387-1995 requires that 7. Information on the contribution of each licensee's monitor and track a number of EDG subsystem to the failure rate, and important EDG parameters, those listed in some observations regarding that.
Rev 9/19 12-1 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance 12.1 EDG Maintenance and the Critical many licensees were also testing EDGs by Need for Condition Monitoring fast starting, with immediate application of design loads. (Some still are.) It has been The two basic approaches to maintenance estimated that one such start causes wear of EDG systems will be briefly discussed equal to 35-50 hours run time! A number of and compared. failures have resulted from this practice.
Prescriptive (Calendar-Based) Method Predictive (Condition-Based) Method One reason diesel engines were selected An increasing number of licensees have to power on-site emergency power systems adopted much more effective maintenance is their very long history of reliable service practices based on equipment condition, as in diverse, demanding applications such as determined by comprehensive monitoring, locomotives, trawlers, tugboats and oilfield trending, and competent analysis of EDG equipment, mostly continuous-duty uses, system parameters. This method can head where equipment may provide power for off failure by detecting early warning signs more than 8000 hour0.0926 days <br />2.222 hours <br />0.0132 weeks <br />0.00304 months <br />s/year. such as abnormal temperature, pressure, vibration, wear products, etc.
Manufacturers had published maintenance schedules with daily, weekly, monthly, The condition monitoring program typically semi-annual, and annual frequencies. includes a wide range of techniques, from These schedules were acceptable for simple observation and logging of data by "continuous service" but inappropriate for the operator, to chemical analyses of the nuclear service, where engines are shut fuel oil, lube oil, and cooling water, to the down most of the time and typically ran for use of infra-red (IR) thermal scanning and infrequent, short intervals. Prescriptive various types of engine analyzers. All of maintenance schedules resulted in many these techniques require a commitment to unnecessary, and intrusive inspections, more than mere collection of data. It has to disassembly for parts replacement, etc. be trended and analyzed by competent Those operations were not only individuals who can assess the results, unnecessary (and costly) but each one make decisions, and get things done. Data gave an opportunity to make errors that sits in a file or a computerno matter detrimental to engine reliability. Actual how accurate and comprehensiveis of no examples include cleaning rags and other value without human action to make foreign objects left inside engines, use of effective use of it.
improper gaskets, over / under-torque of engine components upon reassembly, etc. A well-executed program of predictive, An uneducated (yet wise) mechanic might condition-based maintenance will increase have dryly observed regarding this practice, EDG reliability, reduce unscheduled down-
"If it ain't broke, don't fix it." time, and can reduce maintenance cost as well. It may also prevent a plant outage, an An additional factor in this equation is that event that could cost $1,000,000 / day.
Rev 9/19 12-2 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance 12.2 Overview of Regulatory Criteria 12.3 EDG Parameter Monitoring and Pertaining to System Maintenance Trending Fundamentals 10 CFR 50.65: "Requirements for A predictive maintenance program requires Monitoring Effectiveness of Maintenance at a clear understanding of present diesel Nuclear Power Plants." Known unofficially generator conditions for each parameter, as the "NRC Maintenance Rule," this including the optimum range or value, and requires the licensee to monitor the what represents unacceptable conditions.
performance of their structures, systems, It further requires systematic trending of and components against preset each parameter during successive EDG performance goals or criteria they operating cycles or time periods. When a establish, commensurate with safety parameter trend begins to deviate significance. For EDGs, this document significantly toward the unacceptable level compliments the licensee's FSAR, Tech during successive monitoring periods, it Specs, and other commitments to must trigger an alert for investigation of the maintenance. underlying cause, to determine what action is required to head off the adverse trend.
Regulatory Guide 1.160, "Monitoring the Effectiveness of Maintenance at Nuclear This methodology allows for planned, need-Power Plants" provides NRC guidance for based maintenance rather than reactionary implementation of the "Maintenance Rule" corrective maintenance, or the previously (discussed above). discussed prescriptive, "one size fits all" scheduled maintenance. The data from NRC Inspection Manual, Chapter 0609, such parameter monitoring can be used to Appendix K is the "Maintenance Risk extend the frequency of what scheduled Assessment and Risk Management maintenance is still felt to be necessary.
Significance Determination Process." It incorporates a method to evaluate licensee Parameter monitoring will not guarantee maintenance program effectiveness using elimination of unplanned maintenance on the Significance Determination Process EDGs but the effective application of this (SDP) plus Inspection Procedure 71111.13, approach can minimize the frequency of "Maintenance Risk Assessment and such events. That fact alone will improve Emergent Work Control." equipment readiness time and resource allocation, which will ultimately reduce the NUMARC 93-01, Rev 1 (now NEI 1996a) cost of plant operations.
Originally the Nuclear Management and Resource Council, now the Nuclear Energy The preferred predictive monitoring Institute "Industry Guideline for Monitoring applications are those that can be Effectiveness of Maintenance at Nuclear implemented with the engine in service.
Power Plants" was prepared to provide The various monitoring methods and types guidance (for licensees) on 10 CFR 50.65 of equipment available provide different "Maintenance Rule" implementation. indications which may be used for Rev 9/19 12-3 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance determining diesel engine performance and 12.4 Monitoring Prerequisites predicting problem trends. For instance, one engine analysis technique may look at Equipment Calibration phased cylinder pressure characteristics, another at oil condition and contaminants Data measurements obtained from gauges, (including wear products), and yet another meters, or monitoring systems is useless at vibration signatures or other operating unless its accuracy is verified, meaning a parameters. system of equipment calibration is in place.
All measurements need to be "traceable" to The information from monitoring techniques reference standards maintained by NIST, may overlap, providing different indications the National Institute of Standards and of the same condition(s). In these cases, Technology (formerly NBS, the National integrated analysis of the information can Bureau of Standards), an arm of the US help to confirm adverse trends and isolate Department of Commerce. The licensee problem areas. With dieselsor any type should have an equipment calibration of enginegenerally no one symptom or system that is certified for compliance to an test can tell the whole story. Furthermore, acceptable standard such as ISO 170125 all parameter monitoring technology is or MIL-STD-45662A (1985), "Calibration useless without the resulting data being Systems Requirements," the successor analyzed competently and used effectively. document to MIL-C-45662, itself still widely The effective application of this technology used and referenced by industry.
is somewhat engine-specific and with some newer, complex engine analyzers the ability Ambient Conditions Data to draw specific conclusions about engine condition from the output is still a work in The temperature of engine intake air and progress. Even so, the data will still serve cooling air or water (as applicable) can to raise a flag indicating some change has have a substantial engine performance occurred in the engine. impact. Atmospheric pressure, especially as determined by altitude, is also a factor.
The main focus of this Chapter is to review Even humidity can be significant to engine application of the more proven monitoring operation. Therefore, ambient conditions technologies / techniques, and to introduce are an important part of engine some others that may not be as mature or performance data.
widely accepted. An approach for the integration and systematic analysis of data Fuel Oil (Diesel Fuel) Characteristics obtained using these applications will be provided in the summary. Although only Although not a direct engine parameter, partially implemented by the nuclear power diesel fuel qualities can have a profound industry, integration and analysis of data impact on engine performance and even from monitoring parameters has already service lifetime. Accordingly, principal improved the success rate for predicting diesel fuel qualities will be reviewed before needed maintenance or design changes. discussing EDG parameter monitoring:
Rev 9/19 12-4 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance 12.5 Fuel Oil Quality Monitoring at 10.0 for water where the lighter diesel fuels have a higher API gravity number.
The EDG manufacturer's qualified output ratings are based upon use of a specific Pour point (oF): This is the temperature of fuel oil having the characteristics needed the fuel at which it ceases to flow.
for proper operation. To ensure that fuel qualities and properties are maintained, the Cloud point (oF): This test determines the licensee is required to implement a fuel oil fuel temperature at which wax present in monitoring program. The primary standard the fuel will start to form crystals. The governing fuel oil monitoring at nuclear name is derived from the fact that the fuel power plants is ASTM D-975, Limiting begins to have a cloudy appearance as the Requirements for Diesel Fuel Oils. Criteria effect begins. This characteristic can have for diesel fuel oil quality and property limits a large impact on the performance of filters in ASTM D-975 are incorporated into a and injection equipment because the wax plant-specific fuel oil monitoring program. crystals will cause clogging / plugging in these components.
Licensee failure to maintain appropriate fuel quality and required characteristics can NOTE: The manufacturer's qualification result in the inability of the EDG to perform rating fuel oil specification may not fit site-its design safety function when called upon. specific conditions, particularly those for the Important fuel oil characteristics monitored temperature sensitive requirements of pour by the program, and their significance, are point and cloud point. If the specific discussed below, reinforcing Chapter 4: licensee's fuel storage temperatures can drop below the temperature specified by Flash point (°F): This is the lowest fuel oil the manufacturer for these properties, it temperature at which continuous vapor puts the EDG in an unanalyzed condition generation will sustain flame at a free for operation. Temperatures below that surface exposed to an oxygen source in the specified for pour point cause the fuel oil to presence of an ignition source. This become viscous (gel). There may be property is of interest more from a fire problems in transporting fuel oil from the protection standpoint than it is for engine storage tanks to the engine cylinders.
performance, although fuels with lower Temperatures below that specified for flash points will also typically have lower cloud point will cause wax crystals to ignition points. Fire protection codes often precipitate within the fuel and cloud it.
encourage fuels with flash points of 65°C These wax crystals plate out within the fuel (150°F) or above. oil system including on the critical components such as the fuel injector Specific Gravity or API Gravity @ 60°F: nozzle tips / orifices. There is considerable Relates the weight of fuel to water. Diesel increased resistance to flow of the fuel from fuels are lighter than water, with specific the increased viscosity and wax crystals gravity's under 1.0. However, the API particularly through the fuel filters. (Refer gravity index uses an inverse scale starting to Chapter 13 case studies and IN 94-19.)
Rev 9/19 12-5 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Water and Sediment (% volume), by is often used. Lighter, more volatile fuels centrifuge: This indicates fuel cleanliness. tend to have lower ignition points, which Water and sediment can result in serious can affect engine starting and running.
operational impact that may involve fuel injection components. Sediment can foul Viscosity @ 100°F (Saybolt Universal Sec, fuel filters but water also promotes the SUS): This relates to flow characteristics of growth of microbes in diesel fuel storage the oil. Oils with lower API gravity numbers tanks. In addition to bio-fouling, they can tend to be more viscous (thicker).
cause microbiologically-induced corrosion (MIC), especially of steel pipe and tanks. Sulfur (% by weight): Trace sulfur contaminates in the fuel can result in acid Color: Ranges from dark-amber to light- formation under engine post combustion golden. A fuels natural color (darker or conditions (i.e. in the presence of water lighter) is not as much concern as changes vapor at the required temperature). Lower in color during shipping and storage. sulfur fuels are typically preferred for this Changes in color, usually in the form of reason and are especially encouraged darkening, can indicate fuels with unstable under more recent emissions regulations.
properties subject to separation. Because sulfur serves as a lubricant, very low sulfur fuel have additives to provide Carbon Residue (% by weight): This lubricity. See Chapter 13 discussion of indicates the carbon depositing potential issues with ultra-low sulfur fuel characteristic of a fuel which can foul oil, including lube oil incompatibility.
injector tips , cylinder head exhaust valves, and piston rings. Copper strip corrosion test (comparative test): This test predicts the copper Ash (% by weight): Fuel ashes are non- corrosion characteristics of a fuel, which combustible trace minerals and metals in can be important for engines using copper fuels, such as silicon and vanadium. Most gaskets and components in fuel system are undesirable, as they tend to have an applications.
abrasive or corrosive effect on engine components or result in formation of engine Cetane number: An ignition quality test deposits. Vanadium in fuels is especially (comparative-qualitative rating). One of the troublesome because it forms Vanadium more critical properties of fuels relating to pentoxide, which can be highly corrosive smooth engine operation. The comparison under certain diesel operating conditions. is between cetane with a high ignition quality and heptamethylonane with a low Distillation temperatures (o F) at 90% and ignition quality. Ignition quality can effect end points, at STP: This relates to the diesel starting times and load acceptance volatility or the vaporization tendency of response time among other things. Fuels fuel during distillation. In lighter diesel with higher cetane numbers provide more fuels, such as those used in diesels at responsive start times, load acceptance.
nuclear facilities, the 90% distillation point The typical minimum value is 40.
Rev 9/19 12-6 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Heating value (BTU per lb.): One of the 12.6 Lube Oil Analysis and Trending more critical property of fuel. Diesels are heat engines (i.e. they convert stored Lubrication oil analysis can provide a good chemical energy into heat in the engine general indication of the engine's internal cylinder to produce work). Fuels with condition. To be representative, the oil higher heating values per pound tend to be samples should be taken downstream of the lighter fuels, but the lighter fuels have the supply pump and prior to the filter, with lower specific / API gravities. Although the the system at normal operating lighter fuels have a higher BTU content per temperature and pressure. Oil analysis will pound, the net effect is that they have a provide information relating to the following:
lower BTU content per gallon. Since diesel fuel storage and consumption data are Lubrication oil condition: Oil properties monitored in gallons, BTUs per gallon is the which indicate condition and age include critical parameter. As an example, diesels viscosity, oxidation, total base number /
used in nuclear applications frequently had total acid number (TBN /TAN), and the fuel consumption tests performed based on applicable additive concentrations. Typical a fuel oil with an API gravity of 28. If those values for new oil of the type being used are operated on a lighter fuel (i.e. API should be readily available from the oil gravity of 29 or above) than their initial fuel supplier or producer. Alert and action consumption tests were based on, they will values should be established which warn of have to burn more fuel to generate the pending end-of-useful-life for the oil.
equivalent heat required to produce the same power output. This would place into Contamination: Contamination of lube oil question the sufficiency of on-site fuel oil is usually due to the operating environment.
storage tanks for the EDG systems. Contaminants monitored may include water, glycol, TBN /TAN changes, SOx or The time to determine the acceptability of NOx level changes, fuel dilution, viscosity fuel oil shipments is before they are off- changes, and dirt (i.e. silicon, aluminum).
loaded into on-site storage tanks. Pro- Allowable concentrations of contaminants active licensees will subject samples of may be given by the engine manufacturer delivered fuel to appropriate quality tests or determined through use of accepted before accepting or permitting the fuel to be industry standards (e.g. ASTM, etc.). In the off-loaded. A program should also be in absence of these, engineering judgment place to periodically assess the quality of should be used to establish allowable diesel fuel in tanks, as it can be impacted contamination concentrations relative to a by moisture (condensation / infiltration), baseline sample of new oil. However, in tank deterioration (leaks / rusting), aging, the latter, the effect of each contaminant on and microbial growth. engine life and performance should also be considered independent of the baseline oil NOTE: Biodiesel is a particular concern contaminant concentration. This is to that will be discussed in Chapter 13. It has acknowledge that even baseline new oil potential to cause a number of problems. samples may contain higher levels of some Rev 9/19 12-7 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance contaminants than desired, depending on sampling procedure, technique, and the supplier's formulation and process accuracy but frequently lack the knowledge control. Alert and action values should be of engine detail and history, which are established which will allow recognition of essential for comprehensive evaluation of contaminated oil early enough to avoid the results. Major engine problems have engine damage. developed and been overlooked due to inappropriate alert limits or the fact that no Engine internal component condition: alert limits had been set at all. Similarly, Indications of engine internal mechanical oversights have occurred when the results condition and wear are based on metal were not reviewed in a timely manner by "wear" particle concentrations in the oil. experienced, qualified personnel.
Typical engine wear metals of interest may include iron, copper, lead, tin, chromium, CASE EXAMPLE: Crankcase Explosions aluminum, and silver to name a few. The owner / operator should specify expected Engine failures occurred in which there wear metals of concern to the laboratory were wear metal trend precursors that performing lubrication oil sample tests to should have alerted the operators and ensure they are included for analysis. enabled them to head off the problem. The Engine component contributors to these crankcase explosion events involved the wear metals should be identified, and may Cooper-Bessemer KSV engines that power vary between engine models. Initial EDG units at several nuclear power plants.
guidelines for wear metal alert and action Figures 12-1 and 12-2 are photographs of concentrations should be obtained from the two pistons from an engine following an engine manufacturer, if available. In the explosion. Fig. 12-1 illustrates a piston with absence of recommendations from the a substantial amount of its tin coating wiped manufacturer, alert/action values should be off onto the cylinder liner. Figure 12 2 based on operating experience and illustrates a piston with virtually all of its tin engineering judgment, using know values coating wiped off, as well as piston and ring of metal concentrations in oil from the same damage. The piston was near a seizure engine or model when in good mechanical condition due to metal scuffing and there is condition. evidence of combustion blow-by.
The licensee is ultimately responsible for Even after the first crankcase explosion the evaluation and interpretation of oil there was a lack of understanding about analysis results and needs to stay very the failure mechanism(s) involved, as the engaged in the process, to maximize the situation was complex. Most agreed the value of this application. The success of oil failures were due to insufficient lubrication analysis is frequently disappointing of the surfaces between the piston and the whenever this responsibility is turned over cylinder liner. However, there were other to a laboratory or other organization without contributing factors, including fast starts, experience in diesel engine operations. cold intake combustion air, and the engine Laboratory personnel are familiar with design, which included an oil scraper ring Rev 9/19 12-8 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance (intended to reduce engine oil consumption 12.7 EDG /Support Systems Monitoring in typical "continuous-run" commercial service but not appropriate for intermittent By monitoring, trending, and analyzing duty applications such as EDGs). Before EDG operational data an engineer can effective corrective action was identified identify gradual changes in temperatures, and taken, a total of 13 crankcase pressures, and flows that may indicate a explosions occurred at nuclear plants! deteriorating condition or impending failure.
Changes were made to minimize fast This can head off problems likely to impact starts, to preheat intake combustion air, the availability, operational reliability, or and to provide better lubrication to the performance of the EDG in an emergency.
piston-to-cylinder liner interface. Following these design and procedural modifications, Engine and support system parameter no additional failures of this type occurred monitoring provides general indication of in the KSV engine. (For more information, mechanical condition and combustion see IN 92-78.) performance. For valid results, the EDG should be operated at repeatable baseline NOTE: When analyzing oil parameters conditions with the monitored parameters and characteristics, the rate of change is stabilized prior to the collection of data.
often a very important consideration for Progressive or step changes in engine or evaluating the significance of findings and support system parameter values should determining what action may be needed. be analyzed to determine cause. Some of Each engine and oil variation in use is the more important engine and support unique and must be monitored with that system parameters and conditions to fact in mind. Baseline concentrations of monitor are as follows:
contaminants must be used for reference and trended as part of the process. If NOTE: This list includes parameters from engine oil is changed, the prior values and IEEE 387-1995 Table 4 that are shown as trend data must continue to be part of the mandatory "during test" items. (Table 4 is analysis. Otherwise all of the accumulated reproduced in Chapter 11 of this Manual information from past testing and trend and discussed in 11.7). Of course, those.
analyses of that engine's lube oil is lost. NPP's licensed under older revisions of IEEE 387 and RG 1.9 have no obligation to A good lube oil monitoring program also monitor all of these parameters. However, samples for fuel oil dilution, as this is they are required to have an effective helpful in determining engine degradation system of monitoring the performance of of the type that can make it susceptible to their systems. The relevant items taken an engine crankcase explosion. Some sources of fuel in the engine crankcase are from Table 4 are followed by other EDG injectors with leaky or defective needles parameters that can help assess engine and seats, leaking fuel injector fittings, or a and generator condition, as part of the serious mechanical problem such as a licensee's maintenance program. They are cylinder that is badly worn or misfiring. identified with a unique bullet point ().
Rev 9/19 12-9 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Pressures Engine bearing temperatures.
- Lube Oil: Engine Inlet Ambient conditions (temperature, etc)
- Lube Oil: Turbo Inlet Engine hours (calendar time plot)
- Lube Oil: Engine, Filter Differential
- Lube Oil: Turbo, Filter Differential As discussed in 'Monitoring Prerequisites'
- Crankcase (Positive/Negative) essential for the results of monitoring to be Fuel Oil (Pressure and Flow) valid and useful. Modifications, repairs, Cylinder Combustion Air Inlet Manifold and replacement of equipment or devices Cylinder Inlet Manifold Boost Pressure should always be accompanied by a fresh calibration to assure continued accuracy.
The following case study illustrates this:
Temperatures
- Lube Oil: Engine Inlet and Outlet A generator outboard bearing oil level sight
- Jacket Water: Engine Inlet, Outlet gage was relocated such that the oil level
- Exhaust: Each Power Cylinder indication showed higher than the actual
- Exhaust: Turbo Outlet level. Subsequently, during an endurance
- Exhaust: Manifold (if applicable) run (24-hour), the bearing overheated and Cylinder Combustion Air Inlet Manifold caught fire from insufficient lube oil. Root Engine Bearings cause was failure to calibrate the oil level Generator Stator gage following a modification that could affect its accuracy. For more info see NRC Electrical violation Catastrophic Failure of Generator
- Frequency Outboard Bearing on Emergency Diesel
- Power (KW) Generator 14, dated 30 June 2001.
- Reactive (KVAR)
- Current: Generator, All Phases Engine parameter data may be collected
- Voltage: Generator, All Phases manually from hand written logs, hand held
- Current: Generator Field "data-loggers" or with monitoring systems Voltage: Generator Field having digital storage-retrieval capabilities.
Smart or expert system monitoring and Level controls have been developed in
- Jacket Water: Standpipe / Expansion conjunction with programmable logic Tank Level controllers (PLC's). Collected data may be Engine Lube Oil Sump Level stored, manipulated, and evaluated in Generator Bearing Oil Reservoir Level tables and graphs using a variety of available databases. Even in tabular form, Other Parameters step changes are usually obvious.
Engine speed However, trend graphs help to quickly Fuel rack settings. identify slower progressive changes. They All Alarmed Indications also provide visualization of the magnitude and rate of changes.
Rev 9/19 12-10 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Standard troubleshooting and response other applications, data collected for techniques should be developed for emissions analysis should be under operators to systematically identify and repeatable and comparable conditions.
correct the cause of commonly experienced Exhaust emissions analysis typically parameter deviations in excess of pre- includes the following parameters:
established limits.
Combustion Byproducts of Most 12.8 Jacket and Cooling Water Analysis Significance for the Engine:
Cooling water analysis can provide useful Carbon Monoxide (CO) - Possible rich information on cooling system condition fuel / air equivalence or high temperature and potential problems. Closed loop dissociation. CO concentration relates to cooling water testing commonly includes combustion efficiency.
Ph, conductivity, chloride titration, microbiological growth (bacteria count), and Unburned hydrocarbons (HC) - Possible additive concentrations. Open loop cooling crevice volume effect, flame quench, water sampling usually looks at Ph, total lubricating oil. Associated with engine dissolved solids, salt hardness, and condition and efficiency.
microbiological growth as a minimum. For both the main concerns are cooling system Particulate (soot) - Possible rich unburned fouling, scaling and component corrosion fuel spray / fuel-core zone or lubricating oil.
and wastage. Severe fouling, scaling or corrosion can degrade system integrity or Additional Combustion Byproducts:
heat transfer performance. Poor cooling system performance can ultimately result in Nitrogen Oxides (NOx) - Usually nitrogen degraded engine performance or failure. reaction with high temperature burned gases. Largely related to combustion 12.9 Exhaust Emissions Analysis temperature (i.e. thermal NOx), it can be associated with possible injection timing, Exhaust emissions analysis has developed spray pattern, or air temperature issues.
in more recent years, largely due to government influence through the Sulfur Oxides (SOx) - Usually associated Environmental Protection Agency (EPA). with fuel sulfur content. They have very Therefore, whether or not emissions testing little value for monitoring engine is performed and what is sampled for is performance, especially with Ultra-Low often viewed from a regulatory compliance Sulfur fuels.
standpoint. However, in a broader sense emissions testing can reveal useful Increases in emission levels from baseline information on engine combustion values can be caused by things such as performance and condition. This can be timing changes, degraded fuel system useful to identify an engine in need of performance or general engine / cylinder closer monitoring or adjustments. As with condition.
Rev 9/19 12-11 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance If exhaust emissions testing technology, cycles. (See Figures 12-3 through 12-6.)
and equipment costs continue to improve, Relative comparison of cylinders can this may become an increasingly valuable provide an indication of overall engine quick check to evaluate general engine performance and balance. This type of combustion performance and condition. equipment provides the following data:
12.10 The Use of "Engine Analyzers" Peak firing pressure spreads, deviation to Monitor EDG Performance Peak cylinder firing pressure angle (phased cylinder pressure)
Engine analyzers are available that monitor Rate of change in cylinder pressure cylinder pressures, temperatures, and (first derivative, psi / degree) vibration, integrating the resulting data with Mean effective pressure crankshaft angle and fuel rack position. Indicated horsepower Supplementary equipment can monitor lube Reference compression pressure oil parameters "on-line" (as the EDG runs), Reference exhaust terminal pressure providing additional real-time data. The Reference intake terminal pressure systems trend the data and compared it to baseline. Such comprehensive, whole- When this information is reviewed engine monitoring is costly but it gives EDG considering load, fuel rack position, air operators a potentially powerful tool to intake temperature, manifold pressure, and monitor engine performance and health. cylinder exhaust temperature, a picture of engine performance by cylinder is obtained.
As with any other monitoring scheme, the Pressure data is typically reviewed in key is to have competent analysis and tabular form and / or on pressure-time (PT, follow-up of the resulting data. The US often related to crankshaft angle) and Navy has done work in this area using their pressure-volume (PV) curves.
Integrated Condition Assessment System (ICAS). The lube oil analysis can either be The engine average cylinder peak pressure done on-line as indicated, or by the more and peak pressure spread are reliable common off-line method, where samples indicators to monitor for engine deviation are regularly sent to a laboratory for test. from baseline conditions. The magnitude This type of integrated monitoring can often of individual cylinder peak pressure can predict (and, thereby, prevent) many provide an indication of stress within that potential engine failures. A discussion of cylinder. Therefore, cylinders with some specific engine analyzers and engine excessive peak pressures should be monitoring equipment follows: considered for the possible effects on component integrity.
12.10.1 Phased Cylinder Pressure Type NOTE: Matching peak firing pressures Phased cylinder pressure data can provide between cylinders within a predetermined important information on individual cylinder band is the most accurate method of pressure characteristics through engine engine balancing (peak firing pressure Rev 9/19 12-12 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance balancing). However, high cylinder peak Valve train condition pressure can occur for a variety of reasons Main bearing condition and in some cases the cylinder with the Piston to cylinder interaction highest peak pressure is not the cylinder Injector nozzle characteristics actually carrying the highest load (although High pressure injection pump status the anomaly still warrants correction). Cylinder combustion characteristics Piston blow-by and cylinder-ring There are more accurate (and much more interaction complex) means to balance engine cylinder Magnitude and duration of the exhaust load but they are generally not considered blow-down event worth the effort, as they exceed industry Piston pin, articulated pin, or connecting expectations for overall engine balancing. rod bearing condition Therefore, peak pressure balancing is often Base/frame looseness or alignment.
accepted as the best available method for Turbocharger and/or supercharger balancing. It enables adjustments to be status, including bearing condition made that improve engine balance, timing, and cycle efficiency (i.e. performance). These phased analyzers provide a means NOTE: Section 12.11 discusses a simpler to monitor for vibration and ultrasonic method of engine cylinder balancing, one frequency anomalies and changing that is frequently practiced in the field. conditions for the EDG components noted above. These signatures can be graphed 12.10.2 Phased Engine Vibration (VT) over a cylinder/engine cycle. Each graph and Ultrasonic (UT) Type has a VT5 trace which represents ultrasonic noise and a VT4 trace that Phased vibration and ultrasonic traces can represents vibration monitored at selected provide valuable insight to engine points for each cylinder. The cylinder's component mechanical condition and pressure trace can also be superimposed combustion events. Data is typically on the same graph. Intake and exhaust collected at the same time as cylinder valve opening and closure event anomalies pressures. Probes used to collect cylinder can often be identified. Of these vibration and ultrasonic traces should be anomalies, the most common is a placed in the same location each time, for collapsed valve hydraulic lifter. However, consistent and comparable data. When other valve anomalies detected have relocating probes to improve data included valve stem galling or separation of collection, be alert to potential differences chrome plating (resulting in sticking valves) in traces compared with earlier data. and defective valve roller tappets.
The phased VT and UT traces obtained This monitoring of injection pumps and from this equipment can provide an nozzles has detected leaking injector indication of engine mechanical needle valves and fuel pump delivery performance and condition, including the valves. Less frequently, degrading fuel following attributes: injection pump tappets may be detected.
Rev 9/19 12-13 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance 12.11 Practical Cylinder Balancing by the EDG at or close to full load. However, an Approximation Method this practice can result in fuel delivery and cylinder temperature biasing at other than Smooth and reliable engine operation full load. Cylinder temperatures can then depends on an even power balance vary widely (in excess of the recommended between the cylinders. This balance is 150ºF average) at less than full load determined from the temperatures and conditions. Rather than using cylinder pressures occurring in each cylinder. temperatures, the preferred method for Cylinder exhaust temperature is measured engine balancing is by cylinder firing by pyrometers located in the exhaust gas pressures, accomplished by adjusting the outlet elbows adjacent to the cylinder fuel racks.
exhaust ports. Cylinder pressures are frequently measured using special gauges 12.12 Crankcase Oil Mist Detection of connected to cylinder test ports with Engine Mechanical Distress passages connecting to the combustion space. Several companies offer crankcase oil mist detection systems that warn of engine Although cylinder pressures are the mechanical issues such as cylinder wall or preferred method of balancing an engine, piston scuffing, incipient bearing failure, the pyrometers remain connected to the etc. All depend on the fact these problems engine during operation whereas the are accompanied by localized hot spots cylinder test gauges are connected only that cause lube oil to boil, producing oil mist long enough to take the required readings in air samples aspirated from the engine.
and then removed (as they will not provide Although all engines have some oil mist in reliable service for long periods in that their crankcase area, the concentration in a harsh environment). Therefore, cylinder normal engine is typically below 2 mg / liter, temperatures are often used and are the while the lower explosive limit (LEL) for most convenient indicator of cylinder lube oil mist is 50 mg / liter. The better balance during routine operation. As a instruments provide calibrated oil mist rule of thumb, balanced engines will concentrations, likely using forward-scatter normally have these attributes: of an LED light beam into a photodiode receiver, much as a modern photoelectric Cylinders with exhaust temperature smoke detector. As the problem gets deviations < 150 F on the average.
worse, rising mist concentrations are logged Cylinders with cylinder firing pressure (with alarms at set levels). See Figure 12-7.
deviations < 150 PSI on the average.
12.13 Infrared (IR) Scanning -- An NOTE: In the past cylinder balance has Effective, Under-Utilized Tool often been done in the field by adjusting fuel control racks to increase or decrease Many operational anomalies and incipient fuel to individual cylinders until balanced failures in engines, generators, electrical temperature conditions are reached with systems, and support equipment result in Rev 9/19 12-14 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance pronounced temperature variations from Likewise, an EDG operator is required to the norm. Overheating is often the first visually check the system before run, to sign of impending failure in a generator verify it's configured properly and that no winding or bearing, an electrical circuit, anomalies are apparent. Following each transformer, or switchgear, a pump motor, run a repeat inspection is required, to etc. Large variations in cylinder loading check the equipment over for problems and may be seen as temperature differences to verify it has been configured for possible between those cylinders, where the automatic (emergency) use.
exhaust manifold connects.
The need for such systematic checks before Many such temperature anomalies can be and after each EDG run was demonstrated detected by an IR scan thats compared to by a number of failures that occurred simply a baseline scan. It is not unusual for the because a switch or valve or some other temperature gradient is so pronounced as control was inadvertently placed in or left in to not even require baseline data. Portable the wrong position. In many cases that equipment to take IR images of equipment occurred following some very routine EDG is very easy to use, readily available, and is check or maintenance procedure.
very cost-effective. Again, the item being observed should be stabilized at a steady- A simple walk-around inspection with a state load. check list provides a first-hand assessment of engine and support systems status.
12.14 Visual & Other Human Senses While such inspection is primarily visual, Have a Vital Role in Reliability other senses can provide valuable input. An overheating transformer or motor will often 12.14.1 The "Walk Around" Inspection manifest itself through unusual odor. An experienced hand on a generator bearing The emphasis thus far in this Chapter has housing may detect unusual heating as a been on the use of technology, some of it signal of distress and eventual failure. The high-tech and high-cost, for EDG condition protesting sound of a fuel oil pump or monitoring. However, visual observations engine room cooling fan, or unusual noise and other human senses can be extremely from a relay, etc. should trigger action.
effective in identifying anomalies.
NOTE: Knowledge of critical components Think of the aviation example, where a especially what is normal, versus marginal crewmember of a highly instrumented or abnormal, is vital to success.
aircraft costing perhaps 50 million dollars or more takes the time for a simple walk- Engine visual inspections often provide the around before flight, checking for tire most information regarding the condition of problems, leaking fluids, damaged (or gust specific components. They can discover locked) control surfacesanything that new conditions previously unidentified by could represent a potential problem to safe monitoring, or confirm indications from flight (often based on industry experience). engine monitoring systems. Regardless, Rev 9/19 12-15 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance suspect indications obtained from engine For either type of engine or component monitoring systems will generally require visual inspection, a clear roadmap for the some degree of inspection to determine the effort is essential. The following should be scope of corrective actions necessary. This planned and discussed with inspection is the pay line. An oversight at this stage personnel prior to commencing:
can negate the information gained from Areas to be inspected sophisticated engine monitoring equipment. Expected normal condition Any areas of special concern 12.14.2 Assembled Inspections Suspected abnormal condition(s).
Information on the availability of parts Assembled visual inspections are the least Preliminary action plan if an abnormal intrusive and frequently involve use of condition is confirmed by the inspection boroscopic / videoscopic equipment with tape or disk storage capabilities. Minimal Monitoring Summary disassembly and/or removal of engine access covers is usually all that is required. Engine and technology improvements have Since this is the least intrusive it is the most affected data collection and analysis for desirable form of visual inspection and may EDG systems. None of the described be scheduled periodically or as a condition- monitoring schemes or systems will provide based task. High resolution imaging complete, conclusive information on engine equipment can then be used to evaluate health and maintenance needs. However, potential component degradation. the integration and competent analysis of data from all the means employed will When using various imaging equipment greatly enhance system reliability and such as boroscopes, fiberscopes, or availability. A successful EDG predictive videoscopes, the inspection plan should monitoring program will have:
consider inspection equipment and engine access limitations. For example, upper or Access to monitored data collected mid piston skirt scuffing may go undetected under consistent and reproducible due to access limitations from an engine conditions, and compared to baseline lower end inspection. data.
Review by experienced personnel who 12.14.3 Disassembled Inspections are knowledgeable with engine design details and operations.
Disassembled inspections are the most intrusive form of visual inspection and may Whenever an alert limit is reached, two require extensive engine / component tear- things should immediately happen:
down. Disassembled inspections are the last resort in visual inspections. They are Confirm the alert by additional analysis only recommended if justified by checking or inspections.
analysis results from other monitoring Review other available data that may applications or by assembled inspections. either confirm or refute the indication.
Rev 9/19 12-16 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Analysis and corrective action are expected the inboard and outboard bearings of the for all confirmed EDG anomalies. generator for EDG 11. Low oil viscosity might cause bearing degeneration and 12.15 Selected Maintenance Concerns failure during EDG operation. From March and Observations for EDGs 3 until April 1, the plant was operated at various levels of power up to 97 percent.
Lubrication and Oil Changes The plant was shut down from April 2 to April 12 during which the bearing oil was Engine oil change interval is typically based replaced with the correct oil. Based upon on manufacturer recommendations. Due to the Significant Determination of Risk the large volume of engine oil used (1-2 Process, the EDG was considered gallons per hour), oil change frequently inoperable between the periods of March 3 involves monitoring engine oil analysis to April 12. The risk significance was results for degrading conditions which considered low because the other three would warrant oil change. EDG units were operable during this time.
(Refer to NRC NCV, May 19, 2000.)
Generator pedestal bearing oil changes are frequently conducted on some set Example 2: Formulation Changes of periodicity, such as 18 to 24 months, due to Engine Lube Oil the smaller quantities involved.
Recommended engine lube oils used in Governor oil changes are also frequently EMD engines contained a chlorinated conducted on some set periodicity, such as additive that made the waste oil 18 to 24 months, due to the smaller unacceptable for disposal. An oil was quantities involved. authorized which did not contain the chlorinated compound. This oil had been Exposed linkages and mechanisms such successfully used by the railroads in their as the fuel control linkages, racks, and EMD engines for several years. However, overspeed trip devices require occasional the operating conditions and demands on lubrication and frequent inspections to the lube oil are different. Railroad engines maintain them in an operational condition. start slowly and infrequently and run almost all the time. Nuclear plant engine start fast Improper lubrication or lubricants can lead and often and run infrequently.
to component damage or EDG inoperability. Consider the following case Three nuclear plants reported wrist pin study examples. bearing failures after the change in oil.
Consultant evaluations were made to Example 1: Improper Generator Bearing Oil determine root causes. They reported:
On March 3, 2000, while conducting 18- 1. The chlorinated additive in the previous month preventive maintenance, personnel oil was there specifically to increase the oil's added the incorrect oil (too low viscosity) to ability to cling to bearing surfaces during Rev 9/19 12-17 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance long periods of shutdown and to provide the approximate failure rate of each EDG extreme pressure lubrication capabilities. sub-system, based on many years of licensee event reports (LERs), refer to
- 2. The new oil did not provide the Figure 12-8 at the end of this Chapter.
equivalent extreme pressure capabilities or the adherence qualities of the former oil. Post-Maintenance Inspections Critical
- 3. The lubrication problem is aggravated Many EDG failures have been attributed to by frequent starts and long shutdown the lack of an effective post-maintenance procedures. inspection after any work is done on the EDG, any of its support systems, or just in
- 4. There is concern for the other bearings the vicinity of the EDG. Some examples will in the engine. be discussed in Chapter 13. These failures are completely preventable, which is what
- 5. Lube oil analysis wear metals alert level makes them so unnecessary, yet some of may be too high. them have occurred again and again. The most common involve maintenance work in For a detailed description of this problem, the vicinity of the EDG (but not on it), such refer to NRC IN 2002-22, "Degraded as painting the engine room, cleaning the Bearing Surfaces in GM/EMD Emergency floor, or plumbing problems a level above.
Diesel Generators," including consultant reports. Engine "Air Roll" or "Bar" Check EDG Support Systems are Major Following engine maintenance the post-Contributors to Inoperability Incidents maintenance run begins with an air roll to verify freedom of movement. The air roll is Most long-term studies have attributed EDG performed with the cylinder test cocks open systems failures to engine-mechanical in and the fuel control racks in the no fuel only 5% to 10% of cases. This record is position. A start signal is generated to testimony to the durability and reliability of rotate the engine several times to clear out diesels. The logical question then is why any moisture trapped in the cylinders.
put so much emphasis on monitoring the Maintenance personnel observe the test engine if it causes so few failures? The cocks during the air roll for signs of water or answer, of course, is that such failures are other liquids present in the cylinder. A small usually catastrophic and very costly, while mist of water, sometimes mixed with oil problems with support systems can be emitted from the test cocks is acceptable.
addressed in much less time, at lower cost. Test cocks are then closed and the engine is placed in an operational mode.
This statistic points out the need for a comprehensive approach to EDG system NOTE: Failure to close the test cocks will reliability, one that puts adequate resources not prevent engine start but flames will on support system operability. For data on shoot out of each one, with much noise!
Rev 9/19 12-18 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Engine Owner Groups affecting the aging of EDG units at nuclear power plants are quite similar to those To pool the knowledge and experience imposed on EDG systems supplying gained by various nuclear facilities, owners hospitals, military facilities, and other critical groups have been formed. The common installations.
denominator in these groups is the model or brand of engine used. For example, in PNL-10717 further observes that An 1982 or 1983, those plants having installed important finding of these studies was that Enterprise model R&RV diesel engines the EDG fast-starting and fast-loading formed the TDI (Transamerica-DeLaval) testing program, undertaken in response to Owner's Group. Their effort lead to the the old Regulatory Guide 1.108 (U.S.
development of the Design Review Quality Nuclear Regulatory Agency 1977), was Revalidation (DRQR) program. Each TDI itself a major contributor to premature aging engine was disassembled, extensively of the EDG units. The current applicable inspected, modified, and reassembled to Regulatory Guide 1.9, Revision 3 has assure it could reliably perform its vital greatly reduced this source of aging safety function when called upon. stressors. (Ed note: Rev 4 now applies.)
However, not all licensees have embraced Currently, there are numerous active the new test procedures designed to lower nuclear EDG owners groups in operation. unnecessary engine stressing and wear.
Licensees should be encouraged to network with other owners on common, relevant Comprehensive Report on Diesel Engine EDG operational and performance issues. Analyzers, Their Use, and Limitations Long Term Aging Concerns, and NPP The subject of diesel engine analyzers is far Operating License Extensions too broad and complex for full treatment in this Manual. Those who wish to learn more These comments pertain to PNL-10717, A about the application of these system are Review of Information Useful for Managing encouraged to obtain and study the EPRI Aging in Nuclear Power Plants (Compiled 'Diesel Engine Analysis Guide' (TR-107135),
by W. C. Morgan and J. V. Livingston, Nov prepared in 1997 and made available to the 1997). In Section 9 Emergency Diesel public in December, 2006. This illustrated, Generator it addresses aging issues, now 143-page Guide is available for download at heightened by NPP license extensions. no cost from EPRI and other web sites. It includes a summary of the engine analysis The report states, Most of the EDG equipment offered by four manufacturers.
components were designed for continuous http://my.epri.com/portal/server.pt?space=C use, not for standby and intermittent service. ommunityPage&cached=true&parentname=
However, except for the periodic testing ObjMgr&parentid=2&control=SetCommunity requirements imposed under Regulatory &CommunityID=404&RaiseDocID=TR-Guide 1.108 (U.S. Nuclear Regulatory 107135&RaiseDocType=Abstract_id Agency 1977) (now withdrawn), stressors Rev 9/19 12-19 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Tin removed from side of piston, exposing the base metal (dark area).
Some scoring of piston base metal, plus indication of sticking rings.
The direct result of inadequate lubrication (multiple underlying causes).
Figure, 12-2 shows this effect on another piston with more severe damage.
Figure 12-1 Piston with Advanced Tin Smear Rev 9/19 12-20 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Essentially all tin removed from sides, exposing the base metal (dark area).
Scoring of piston base metal, entrapped rings, and evidence of blowby.
The direct result of inadequate lubrication (multiple underlying causes).
Figure 12-2 Failed Piston -- Tin Wiped Off Rev 9/19 12-21 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Figure 12-3 EDG Diagnostic Report - PFP vs. Crank Angle (Right Bank)
P S I Rev 9/19 12-22 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Figure 12-4 EDG Diagnostic Report - PFP vs. Crank Angle (16 Cylinders)
P S I Rev 9/19 12-23 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Figure 12-5 EDG Diagnostic Report - PFP vs. Crank Angle (& Swept Volume (4L)
P S I Rev 9/19 12-24 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Figure 12-6 EDG Diagnostic Report - PFP vs. Crank Angle (& Swept Volume (2R)
P S I Rev 9/19 12-25 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance Figure 12-7 Crankcase Oil Mist Monitoring System Rev 9/19 12-26 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance NOTES:
Idaho National Engineering Laboratory (INEL) data is for 353 LERs, 1987-1993.
Southwest Research Institute (SwRI) data is based on 689 LERs, 1968-1982.
US Navy data is skewed by piston-cylinder failures with one engine family, plus a high rate of cooling water problems. Their Instrumentation and Control data also does not correlate with the other sources.
Nuclear Plant Reliability Data System (by Institute of Nuclear Power Operations) includes many EDG event reports that are not in NRC's LER system due to being a non-demand situation and, therefore, not required to be reported.
Figure 12-8 EDG Failures by Responsible System Rev 9/19 12-27 of 28 USNRC HRTD
Emergency Diesel Generator EDG Performance Monitoring and Maintenance ORDINARY VISUAL INSPECTION IR THERMOGRAPH OF SAME EQUIPMENT FAILING ELECTRICAL TERMINATION FAILING LEG OF 3-PHASE FUSE BLOCK FAILING SHAFT BEARING Figure 12-9 IR Thermographs of Impending Failures Rev 9/19 12-28 of 28 USNRC HRTD