www.bunsmcd.com Title: Case Study: Minnkota Powe s Milton R. Young Station Electical System Assessment Authos: M. Cales Mille, Buns & McDonnell M. Dan Matian, Minnkota Powe Coopeative M. Richad Mahaley, PE, Buns & McDonnell Date: Decembe 12, 2007 Pesented at: Powe-Gen Intenational 2007 ABSTRACT Minnkota Powe s Milton R. Young Station Unit 1 was put into sevice in 1970. The oiginal electical distibution equipment is appoaching 40 yeas of age. Ove the yeas, it has been expanded to suppot plant additions. Electical distibution equipment typically has a 20- to 30-yea eliable life, afte that peiod, life extension measues such as etofitting, efubishment, o equipment eplacement is necessay to maintain a eliable electical system. With the demand fo electic powe expected to incease by about 25%, ove the next 10 yeas. Minnkota Powe s Milton R. Young Station has begun majo effots to pefom life extension pojects of majo equipment such as the tubines and geneatos. In addition, ove the next few yeas Milton R. Young Station will install mandated ai quality contol equipment. Fo these types of pojects to be successful, the electical distibution equipment at Milton R. Young Station needed to be evaluated. The evaluation included a feasibility assessment to analyze altenatives anging fom eplacing the existing electical equipment with new equipment to continuing to pefom maintenance on the aging equipment until failue occus. This pape will discuss how Milton R. Young Station developed a stategic plan fo electical system eplacement pojects, by pefoming a feasibility study. The pape will detail how qualitative and quantitative assessments of existing electical equipment wee used to develop a maste plan fo electical equipment eplacement. This pape includes details on evaluating the mechanical integity of the equipment and discusses how load flow, shot cicuit, and ac fault studies wee used in evaluating the existing equipment. The concepts of eliable electical systems and the use of IEEE Std 493, IEEE Recommended Pactice fo the Design of Reliable Industial and Commecial Powe Systems ae detailed. The convesion of failue pobability to isk cost will also be discussed. Finally, this pape will cove the implementation pocess including pefoming equipment isk anking, and developing a geneic phased appoach fo completing the upgade pogam. INTRODUCTION This epot discusses effots Minnkota Powe Coopeative, Inc. (MPC) conducted to pefom a feasibility study of the Milton R. Young (MRY) Station Unit 1 electical system fom the 230-kV substation down to the 480V moto contol centes (MCCs), including the vital AC, essential AC and DC systems. The feasibility study was used to develop a business case fo eplacement of majo components of the electical system, and to develop a Maste Electical Plan that outlines what Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 1 of 14
www.bunsmcd.com modifications/eplacements/upgades ae equied fo the electical system to adequately and eliably supply the pesent and the futue needs of MRY Unit 1. This includes the addition of Ai Pollution Contol Compliance equipment. MRY Unit 1 is a 250-MW (goss) unit with a Babcock & Wilcox cyclone fied boile and Geneal Electical steam tubine/geneato set. Boile-elated equipment includes a two-pass tubula ai peheate, induced daft and foced daft fans, and feedwate pumps. Poducts of combustion gases ae cooled as they pass though the seconday supeheate, eheat supeheate, and pimay supeheate convection sections pio to the two-pass tubula ai peheate with boile feedwate economize in between the two ai peheate sections. Entained flyash in the cooled flue gases is contolled with a Reseach-Cottell electostatic pecipitato (ESP) to educe paticulate emissions. Electical output fom Unit 1 is distibuted to a substation nea Fago, N.D., at 345-kV altenating cuent. FEASIBILITY STUDY To detemine if modifications, eplacements, o upgades wee equied fo the electical system to adequately and eliably supply the pesent and the futue needs of the geneation station an assessment study was conducted. Duing the poject initiation phase of the assessment study the oveall study paametes wee defined and a detailed scope of wok, schedule, deliveables and cost fo pefoming the study wee appoved. These appoved documents helped to ensue a consistent undestanding of the poject, and set the expectations and identified the esouces necessay to complete the study. It was detemined that an assessment of the condition of the existing electical system fom the 230-kV substation down to the 480V MCCs, including the vital AC, essential AC and DC systems was needed. To pefom the Assessment Study, the mechanical integity of the equipment was evaluated. Also, load flow, shot cicuit, and ac fault studies on the existing equipment wee pefomed. Duing the assessment, eview of maintenance pocedues, maintenance ecods, and inteviews with maintenance and opeations pesonnel wee conducted. As well as, gatheing of infomation on availability of spae pats, system opeation, futue plans fo system gowth, and equipment ating data. The electical equipment was inspected fo signs of maintenance neglects and fo evidence elated to equipment deteioation. In addition, infomation on the condition of the location of the electical equipment, manufactue and type of equipment, yea of manufactue, date of installation, voltage ating, cuent ating, fault ating, details of any modifications o epais, and type of electical potection was also collected. The plant maintenance pactices and equipment condition wee compaed to typical maintenance pactices and failue modes fo majo equipment that make up a plant electical system. NFPA 70B Recommended Pactice fo Electical Equipment Maintenance was used as a guide fo typical peventive maintenance pocedues that the facility should be pefoming. IEEE Standad 493 Design of Reliable Industial and Commecial Powe Systems, was used as a guide fo equipment eliability data, IEEE 493 contains industy aveage failue mode data gained by pefoming industy suveys. The plant electical distibution equipment condition assessment epot was oganized by majo distibution equipment categoies, the esults fo the majo equipment assessments ae detailed below. Tansfomes Appoximately evey thee yeas, the main tansfomes, statup tansfomes and auxiliay tansfomes ae inspected by Minnkota pesonnel. Oil samples ae taken and analyzed fo combustible gases, Doble testing is pefomed to check the condition of the insulation, and a physical inspection is pefomed. Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 2 of 14
www.bunsmcd.com Duing the infomation gatheing pocess it was detemined that Unit 1 s GSU tansfome has expeienced occasional oil pump o cooling fan bank poblems. Wate spays has been used to keep the tansfome fom oveheating. This has not been a fequent occuence, but oveheating can cause tansfome insulation to deteioate. Failue modes fo tansfomes ae; failues due to deteioation of the electical insulation, deteioation of the electical connections, and exteio coosion. Insulation beaks down ove time, due to aging, and by heat geneated by the opeation of the tansfomes. Oil filled tansfomes, can have deteioation of the oil insulation system due to heat. Moistue contamination will cause deteioation of the insulation in dy type tansfomes. Also tansfomes can fail due to loose connections, winding temination points and bushing connections. Hash ambient conditions can coode tansfome tanks, cooling fins, and attached accessoies such as contol panels and consevato tanks. The industy aveage fo tansfome failues is 30 yeas, with the leading cause of failue being winding insulation deteioation fom aging. Due to the age of the main, auxiliay, and statup tansfomes, it was ecommended that the fequency of pedictive maintenance inspections and test be inceased. Also, to help pedict failues it was ecommended that tests such as infaed themogaphy, oil testing insulation powe facto testing, and patial dischage testing should be pefomed on a moe fequent basis. The test data should be tended to identify failue pattens. It is not ecommend to un powe tansfomes to failue, if the powe tansfomes wee to fail, it could take a month o longe to epai the tansfome, and a week o moe to make the necessay epais. Theefoe a tansfome eplacement schedule was developed fo the geneation station. Switchgea With the cuent switchgea configuation at MRY outine, peventative, o epai maintenance cannot always be done. The switchgea has to emain enegized even duing a plant outage including off hous. 480V busses cannot be woked on without de-enegizing the whole bus. Coss ties fom dual fed loads futhe complicate the poblems. Switchgea maintenance at MRY is pefomed duing cleaning outages which is on a thee-yea cycle. Duing each thee-yea maintenance cycle, beakes and elays ae emoved, cleaned, tested and any deficiencies addessed. The peventive/pedictive maintenance checks have found numeous poblems with beakes, including: main contacts not etuning to full open pivot ams sticking tipping mechanisms sticking beake not able to be electically opeated boken ac chutes puffes boken and not opeating boken pats in ac chutes ac contacts boken silve platting on bus deteioating loose bus connections These types of deficiencies can cause faults on equipment and/o can allow high acing cuents and an ac blast to develop duing a fault condition. These deficiencies will also cause the cleaing time of beakes to be extended duing a fault. The unintentional delay, caused by these deficiencies duing a fault condition, can esult in catastophic damage to equipment, seious injuy to pesonnel, and cause loss of geneation fo seveal months. Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 3 of 14
www.bunsmcd.com The plant has minimal spae pats, and a limited numbe of 5-kV, and 480V spae beakes on hand. In addition, eplacement pats fo the medium voltage and low voltage switchgea ae becoming difficult to obtain. Pats ae being efubished, beakes ae being etofitted, and outside sevice pesonnel, when needed, ae fabicating eplacement pats. Lead times can be two months to a yea. In addition to the poblems listed above, MRY Unit 1 medium voltage beakes do not have though-thedoo acking means o wom scew acking mechanisms. To ack these beakes into the opeating position the switchgea must be open, and pesonnel must leveage the beakes on the bus by the use of a acking ba exposing plant pesonnel to high tempeatues and pessue if an ac fault would occu It was ecommended that the fequency of pedictive maintenance checks be inceased on the medium and low voltage switchgea until the switchgea is eplaced. The pedictive maintenance checks should include online patial dischage inspection to seach fo low level acing that might be occuing in the switchgea. Low level acing may not be detected by infaed inspection due to the low level of heat geneated. Howeve it will apidly deteioate bus insulation. Relays and metes MRY s medium voltage and low voltage electo-mechanical potective elays ae tested yealy at the plant. Some elays have gasket failues and ae getting dust inside of the cases that may cause elay misopeation. The plant also has micopocesso elays that ae cuently not being tested duing outages. Duing inspection, technicians have found contacts welded togethe on some elays. The plant has had chonic poblems with 480V Powe Shield SS5 tip units. Numeous units have failed and been eplaced but failues continue. Electo-mechanical elays usually malfunction by initiating tipping too slowly o by not tipping when called to opeate. The leading cause of this type of failue is the tipping mechanism being hung up mechanically. Micopocesso elays do not have mechanical mechanisms that may hang up o close too slowly when needed. Micopocesso based elays usually fail due to intenal o extenal loose connections, o powe supply failues. It was ecommended that the 40-yea-old electo-mechanical elays be tested yealy. Micopocesso based elays should be set up on a egula testing schedule evey two to thee yeas. Potective elays should be functionally checked by using pimay injection testing, o othe manufactue ecommended testing, and test voltage to assue that elay is functioning popely. All potection, meteing, input, and output functions should be checked on the elays duing testing. In addition it was ecommended that MRY eplace the 40-yea-old electo-mechanical elays with micopocesso based elays. Moto contol centes, switch boads and panel boads MRY Unit 1 has 17 moto contol centes (MCC) distibuted thoughout the plant. 15 MCCs ae elatively new having been installed since 1997. These ae Allen Badley Centeline 2100 with a 1200A bus ating and 65kA shot cicuit ating. The othe two MCCs, MCC 1M and MCC 1N, ae simila but have cuent limiting eactos, to limit the fault cuent. It was ecommended that MCC 1M and 1N be eplaced with popely ated MCCs. The majoity of low voltage MCCs fo MRY Unit 2 ae obsolete Clake-Sylvania MCCs. The plant has been eplacing these MCCs with 480V, 1200A, 65kA MCCs. The MCCs ae distibuted thoughout the plant and outlying aeas. Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 4 of 14
www.bunsmcd.com It was ecommended that the plant continue its cuent campaign to eplace all of the obsolete Clake- Sylvania MCCs. Cae should be taken in the location of the new MCCs. It is pefeable that MCCs ae located in ooms o aeas that ae accessible by qualified pesonnel that ae awae of the hazads of woking aound electical equipment. In addition, MCCs need to be cleaned, teminals inspected, insulation tested, and infaed themogaph pefomed on an annual basis. Uninteuptible powe supply system The plant has SCI feoesonant invetes, which wee installed in 1980. The capacitos ae being eplaced evey five to six yeas and the cicuit boads evey 10 to 12 yeas. The cicuit boads fo these invetes ae obsolete and ae scace. The uninteuptible powe supply (UPS) systems ae citical systems that supply citical loads which cannot be without powe. Loss of the UPS systems could cause catastophic damage to equipment and injuy to pesonnel. The UPS and battey systems, installed in 1980 ae ove 20 yeas eplacement pats ae becoming had to find. MPC should schedule the UPS systems fo eplacement. It was ecommended that the UPS systems be put on an annual inspection cycle, until eplacement is completed. Battey system Plant battey systems ae extemely citical in situations when powe is lost to citical equipment. These systems ae designed to pevent sevee equipment damage that could occu duing powe failues o black plant conditions. Opeation, maintenance, and testing of these systems ae vey impotant and must be taken seiously. Faults and DC gounds must be taken cae of as quickly as possible. Batteies ove 20 yeas old should be load tested annually. Batteies less than 20 yeas old should be load tested at least evey five yeas. Load testing should also include infaed themogaphic scanning pefomed duing battey dischage. The load test should be pefomed with a minimum of 50% of the battey ated load. Each cell should be measued duing load test and if the battey has less than 80% of ated capacity, it should be eplaced. If individual batteies ae eplaced, they must be identical to the existing batteies. Due to the citical natue of the battey systems and thei age, it was ecommended that the plants olde battey banks be scheduled fo eplacement. Emegency diesel geneato MRY has one emegency diesel geneato ated at 250 KVA, which seves Unit 1 and 2. The geneato is tied to a 480 volt distibution panel that is set up to feed one battey chage in Unit 1 and one battey chage on each of two banks in Unit 2 and the UPS altenate souces in both Units 1 and 2. The emegency diesel geneato does not have auto stat. An opeato must go to the machine and manually stat it, then go to the distibution panel to manually switch the loads and manually synchonize and evese the pocedue when nomal powe is estoed. The geneato is pesently test un duing cleaning outages but is not loaded. Based on the design eview and site investigation of the emegency diesel geneation system it is ecommended that new individual systems be designed, puchased, and installed fo each Unit. SYSTEM STUDIES To assess the MRY electical systems fo expansion load flow studies, and shot cicuit studies wee pefomed. The pupose of these studies was to assue that the electical system has the capacity to safely accommodate new loads. These studies wee also used to veify that the existing equipment is coectly applied within the manufactues atings. Popely ated electical equipment minimizes the damage done to Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 5 of 14
www.bunsmcd.com the equipment and pesonnel duing a fault on the system. An ac flash analysis was also conducted to evaluate if the electical system complies with the latest OSHA and NFPA standads, concening ac flash potection. Load flow Load-flow studies fo nomal and abnomal system configuations, fo the existing electical system, and fo the poposed changes to the electical system wee pefomed. These studies wee pefomed to detemine electical loading of main feedes, tansfomes, and bus voltage unde diffeent opeating conditions and to study the effects of changes to the electical system. To detemine the plant nomal electical system loading, the highest load ecoded fo the MCCs wee used. The lagest moto loads wee deducted fom the load data and modeled on the MCCs as an individual load. It is assumed that all motos on the 480V system ae ated 460V. The individual 480V motos modeled ae assumed to have 0.8 load facto, 0.8pf, and 0.9 efficiency. 4160V motos ae modeled as 4000V motos with 0.8 load facto, 0.9pf, and 0.9 efficiency. The load flow study shows that the Unit 1 auxiliay tansfome and a few station sevice tansfomes could exceed thei nominal ating. Adding new AQCS equipment to Unit 1 will incease the load on the plant s auxiliay and statup tansfomes. The esults of the load flow study, eveals that the capacity of the auxiliay tansfome and the stat up tansfome would not suppot the new AQCS. The load flow study indicates that Stat up Tansfomes 2 and 3 can possibly exceed thee nominal ating. It was ecommended that new auxiliay tansfomes be installed, and the electical system be econfigued with geneato cicuit beakes to eliminate the need of Stat up Tansfomes. Shot cicuit Shot cicuit studies wee pefomed to veify that equipment withstand atings ae capable of handling the system available fault cuent. Switchgea, moto contol centes, safety switches, panel boads, moto states, and bus ba must be capable of withstanding available fault cuents. The studies wee based on the ANSI/IEEE C37 standad fo cicuit beakes, switchgea, substations, and fuses. ANSI Standad C37.13 is used fo calculating the fault duty at low voltage buses, wheeas ANSI Standad C37.5 and C37.010 ae used fo calculating the fault duty on medium and high voltage buses. The existing plant is studied with all loads connected to the system this yields the highest available fault cuent, and is used to veify that the existing plant equipment is ated popely. A study was then pefomed to detemine what the new available fault cuent will be with the new equipment added. The scenaios that wee pefomed include nomal loading conditions with the system connected to the auxiliay tansfome and then the stat up tansfome. All 4160V bus loads wee evaluated with the system connected to the auxiliay tansfome and then the stat up tansfome. Then all loads wee evaluated with the system connected to both tansfomes. The study evealed that thee wee seveal buses on the medium voltage and low voltage system that exceeded o wee at the maximum shot cicuit ating of the electical equipment. Exceeding the shot cicuit ating inceases the pobability of catastophic damage to equipment and seious injuy to pesonnel duing a fault. Ac flash analysis An ac flash analysis was pefomed on the electical system to detemine the existing ac flash condition of the plant. Studies wee based on IEEE 1584 and NFPA 70E calculations. NFPA 70E calculations ae based on voltages less than a 1000V while IEEE 1584 equations ae based on laboatoy expeiments of low voltage and medium voltage equipment. Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 6 of 14
www.bunsmcd.com The studies show that unde all conditions thee ae available incident enegy levels, fo which no potective clothing manufactued will offe adequate potection to employees. OSHA 1910.269 equies employes to assue that employees who ae exposed to electical acs, wea clothing that will not ignite when exposed to electical acs. It was ecommended that no hot wok be pemitted on buses that have dangeous levels of incident enegy. One of the detemining factos of the amount of incident enegy available is the cleaing times of potective devices. The vintage beakes cuently in use at the plant have 8 cycle cleaing times. Electo-mechanical elays of the vintage in use, usually have vey consevative settings to account fo elay eo, this adds exta time delay to the cleaing time. Also, epoted powe beake deficiencies such as pivot ams sticking, tipping mechanisms sticking, beakes not tipping, beake not able to be electically opeated, and elays not able to tip beake cause unintentional time delays that inceases the amount of incident enegy. It was ecommended that MPC eplace the medium voltage and low voltage switchgea with newe equipment that will have faste cleaing time. Also, it was ecommended that new medium and low voltage switchgea be ac esistance. CONCEPTUAL DEVELOPMENT Afte completing the mechanical integity assessment of the electical system and identifying the deficiencies, thee sepaate and distinct conceptual solutions fo upgading the electical system wee developed, and pesented to management. The conceptual solutions included peliminay oneline diagams, site plans, calculations, +/- 30% cost estimate, and outline in detail the conceptual solutions. In developing the conceptual solutions, eplacement, efubishment and/o etofitting stategies wee evaluated and incopoated into final epots. The mechanical integity assessment detemined that system expansion would incease the powe demand, available shot cicuit cuent, and ac flash incident enegy of the system. Theefoe to incease safety, eliability and decease maintenance cost of the electical system the eplacement of MRY s electical equipment with new highe ated and latest technology equipment was chosen. While developing the conceptual solutions cuent and futue NFPA, OSHA and IEEE standads fo electical system was taken into consideation. The decisions of which solution was chosen was based on the following: Safety Reliability Oppotunities fo inceased system o load capacity Site modification, installation, and downtime costs Futue maintenance and taining equiements Availability and cost of eplacement pats Also duing the development of the conceptual solutions issues such as; downtime to emove the old and install the new equipment, site modifications to accept the new equipment, and elocation of powe and contol cables wee consideed. To povide MRY with an electical system that is safe, eliable, and has sufficient capacity to satisfy the needs of the plant yeas into the futue thee options wee developed. The goals of the options wee to: OPTION 1 Inceases capacity of the auxiliay electical system to seve all loads fom the main plant auxiliay busses. Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 7 of 14
www.bunsmcd.com OPTION 2 Replaces the deficient auxiliay busses in the plant and feeds the new scubbe loads fom new statup 2 and 3 tansfomes in the cente switchyad. OPTION 3 Replaces the deficient auxiliay busses in the plant and adds capacity fo one plant scubbe feed while the backup feed comes fom an existing tansfome in the cente switchyad. Afte developing poposed options and estimates fo the ecommended upgades, the options wee analyzed using data fom the eliability modeling pefomed. The pocedue fo developing a eliability model is discussed in the next section of this epot. Reliability modeling allowed the eliability, maintainability and monetay esults of each option to be compaed based on pobability of failue. The cost impact due to loss of geneation associated with the failue of the electical system was detemined and then calculated on an annual basis, the annualized cost aided in monetaily compaing the options. To convet failue pobability to isk cost, the decision tee method of analyzing eliability options was used. The decision tee method is a good tool fo assessing the chances fo failue vesus expected monetay esults fom an outcome of the poject. To pepae the decision tee model the plants availability was detemined. Availability of the plant is the pecentage of time the plant is not in a scheduled outage. The goss evenue fom the sell of electicity on a megawatt hou (MWH) was detemined. Also, the cost of a foced outage was detemined. The cost of the foced outage includes the cost of puchasing electicity, the cost of eplacement pats, and the cost of man hous equied to etun the plant to the poduction levels befoe the outage occued. Fo the MRY study it was assumed that the plant is available 92% of the yea, net evenue is $40/MWH, and downtime cost is $80 MWH. Next the expected net evenue value the plant will geneate with no foced outages was calculated. The plant is capable of geneating 285MWH, 92% of the yea, at a net evenue $40/MWH. Condition value = 285MWH x 0.92 x 8760Hs/yea x $40/MWH = $91,874,880 The condition value is multiplied by the electical system eliability. This calculated value is the expected condition value o the expected evenue the plant can ean with the cuent failue ate of the electical system, fo MRY the eliability (R) of the cuent electical system is 0.9637. Expected condition value = $91,874,880 x 0.9637 = $88,539,822 Next the cost of a majo failue of the plant electical system was detemined. A majo failue would include such things as powe tansfome failue, switchgea failue, o othe majo equipment failue. Majo failue cost is the downtime cost multiplied by the mean time to epai (MTTR) and MWH output of the plant, MTTR fo MRY s cuent electical system is 1128 hous. Majo failue cost = downtime cost x MTTR x MWH = $80MWH x 1128Hs x 285MWH = $25,718,400 The majo failue cost was then annualized by multiplying the value by 1 R, this yielded the annual expected failue cost. The annual expected failue cost is the yealy cost of a failue of the electical system and includes cost of equipment, lost cost of poduction, and man-hous to epai system. The expected condition value is the expected etuns and expected failue cost fo doing nothing. With the electical system at the end of its useful life, the pobability of the full cost of a majo failue on the system is inceased. Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 8 of 14
www.bunsmcd.com Configuation Annual expected failue cost = Majo failue cost x (1 0.9637) = $25,718,400 x 0.0363 = $933,578 Net condition value = Expected condition value Failue cost pe yea = $88,539,822 - $933,578 = $87,606,244 The steps above wee epeated fo each eliability option poposed. This allowed the cost of doing nothing to be compaed to the cost of the poposed options. To calculate the benefit o avoided isk of the option the net expected value of the cuent system was subtacted fom the net expected value of the option being consideed. As an example fom Table 1 below the benefit of Option 1 is: Benefit = Net expected value option - Net expected value cuent system = $89,930,735 - $87,606,244 = $2,324,491 To calculate a payback peiod the totaled installed cost fo the option is divided by the benefit fo the option. Payback = Totaled installed cost/benefit = $17,621,302/$2,324,491 = 7.6 yeas The esults of the quantitative analysis ae summaized in Table 1. This table summaizes the eliability data, the eliability cost data, and the cost of each option. This table is a summay of the pimay easons why the selected option was chosen ove the othe options identified. failues/y. () R (Reliability) MTBF Expected Cond. Value Failue Cost/y. Net Cond. Value Benefit Total Installed Cost Cuent System 0.0370 0.9637 27.03 $88,539,822 ($933,578) $87,606,244 OPTION 1 0.0210 0.9792 47.61 $89,963,882 ($33,147) $89,930,735 $2,324,491 $17,621,302 7.6 OPTION 2 0.0189 0.9813 52.90 $90,156,820 ($19,596) $90,137,224 $2,530,980 $19,504,680 7.7 OPTION 3 0.0187 0.9814 53.35 $90,166,007 ($10,563) $90,155,444 $2,549,200 $15,678,078 6.2 Table 1: Reliability Summay RELIABILITY The seies and paallel eliability methodology is a ecommended methodology found in IEEE 493 this method was used to detemine the eliability of the MRY electical powe systems. To use the seies and paallel method the electical system was sectioned into seies and paallel zones, o eliability blocks. By doing this the eliability of the electical system was easy to detemine. The eliability of the system depends on the eliability and maintainability of the components that make up the system. The system was sectioned into zones and the failue ates, mean time befoe failue (MTBF) and mean time to epai (MTTR) was assigned to each component and calculated fo the entie system. Reliability data compiled in IEEE Std 493 was used to pefom the evaluation. 1 The failue ate pe yea () is given by = (equation 1). MTBF ( )8760 Component eliability (R) fo one yea is given by (equation 2). R = e Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 9 of 14 Payback Peiod
www.bunsmcd.com Seies components of the system ae modeled by the following equations and should be modeled as shown in Figue 1. is mean time to epai (MTTR). n = + S 1 + 2 3 (equation 3) 1 1 2 2 3 3 + + 1 1 2 2 S = (equation 4) 1 2 Figue 1 Paallel components of the system ae modeled by the following equations and should be modeled as shown below. 1 2 P = (equation 5) 1 + 2 8760 P + 1 2 = (equation 6) 1 2 Figue 2 Figue 3 and Figue 4 below demonstate how to use the seies and paallel zone method to detemine eliability. 1 1 2 2 Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 10 of 14
www.bunsmcd.com Zone 1 TECHNICAL ZonePAPER 2 Utility Zone 1 Utility Zone 2 Zone 3 Zone 3 Utility Utility 2Bea ke 2Bea ke Utility Utility Bea ke Bea ke Zone 4 Cable Cable Zone 4 Zone 5 Zone 6 Bus Bus Fuse Fuse Fuse Fuse Zone 7 Figue 3 Zone 5 Zone 6 Cable Cable Cable Cable Zone 7 XFMR XFMR XFMR XFMR Using data fom IEEE Std 493 we will apply the following values to the model. Utility = 0.537000 Utility = 5.7 Beake = 0.017600 Beake = 10.6 Cable = 0.006170 Cable = 95.5 Bus = 0.001129 Bus = 128.0 Fuse = 0.006100 Fuse = 2.8 XFMR = 0.005900 Xfm = 356.0 Using equation 3 and equation 4 the values fo the seies components ae: Zone 1 = 0.5546 Zone 1 = 5.8 Zone 2 = 0.5546 Zone 2 = 5.8 Figue 4 Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 11 of 14
www.bunsmcd.com Zone 4 = 0.007299 Zone 4 = 18.7 Zone 5 = 0.0296 Zone 5 = 77.8 Zone 6 = 0.0296 Zone 6 = 77.8 Use equation 5 and equation 6 to combine Zone 1 and Zone 2 esults in Zone 3. Repeat the calculations to combine Zone 5 and Zone 6 esult in Zone 7. Zone 3 = 0.000408 Zone 3 = 2.9 Zone 7 = 0.000016 Zone 7 = 38.9 To calculate the failue ate and MTTR fo the combined system equation 3 and equation 4 ae used to combine Zone 3, Zone 4 and Zone 5 in seies. System = 0.007707 System = 17.9 Fom the failue ate and MTTR the eliability (R) and the mean time between failues (MTBF) can be calculated. Using equation 1 to solve fo MTBF yields 129.7 yeas. The eliability of the system can be solved by equation 2. Fo the example the is in tems of pe yea, so ( ) equation 2 is modified to R = e. The eliability of the system is 0.9923. The MTBF fo this example is a 129.7 yeas, edundancy calculations fequently lead to eliability numbes that ae outside the ealm of eason. In eality, even edundancy of components still leaves a chance that the paallel system will fail fom a common-mode. Examples of this include common electical connections, common alam wiing, o the envionment. These common modes can be epesented by placing a component in seies with the system. A common failue mode of olde systems is contol wie failue, inputting data fom IEEE Std 493 fo contol wie failue yields a MTBF of 17.6 yeas and a MTTR of 2.4 hous. UPGRADE PLAN Afte the appopiate option was selected, planning fo the equipment upgade was conducted. The equipment to be upgaded was evaluated based on safety, condition of, and impotance of the equipment; this helped pioitize the upgade pogam. Also, the schedule of planned outages was consideed. Duing the planning geneic phases and activities equied to complete the upgade pogam wee identified. Also, equipment with long lead times wee identified, and a pocuement plan was developed. Wok that could be done befoe an outage was identified, and a man-hou loading schedule was developed fo each phase of the poject. Also, duing this phase of the study any poject isk was identified and a contingency plan developed fo mitigation. Some othe consideations in the planning phase: Limited space in the plant pio to demolition of existing equipment. Limited time fame fo installing equipment duing outages. Escalating pices of majo equipment. Constuction contacting methods. The poject will equie close coodination between plant opeations and constuction, theefoe it was ecommended that a time and mateial contacting stategy be consideed CONCLUSION Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 12 of 14
www.bunsmcd.com Powe geneating companies ou cuently upgading thee aging assets fo continued safe and economic opeation fo the next 30 yeas and beyond. These companies will not only need to assess the condition of thei tubines and geneatos, but they will also need to poactively assess thei electical systems. The electical equipment in many geneating plants wee installed in the 1970s, ealy 80s and some as fo back as the mid 50s and 60s. It is impotant to emembe that if the equipment in electical system exceeds the equipment shot cicuit atings o full load ating, is obsolete, spae pats ae unavailable, o the condition of the equipment has deteioated to whee it is unsafe to opeate the equipment, the equipment should be upgaded. This pape has discussed methodologies that have been developed and efined ove the past 10 yeas fo effectively assessing electical equipment. Duing that time thee has been many papes witten and standads developed to simplify modeling techniques fo assessing the eliability of industial electical system. These eliability modeling techniques ae cuently not widely used in the powe geneation industy, it is the intent of this pape to demonstate the use of these eliability techniques in assessing and justifying electical system upgade pojects. REFERENCES Chau, N.H., Beach, Juno, Patel, Subhash C., David, Jonathan, 1998, Upgading and Enhancing the Geneato Potection System by Making Use of Digital Systems Stani, David, ABB Life Assessment Study Hovath, David A., Industy Appoach To Aging Assessment Updated Bainge, Paul, 2005, How To Justify Equipment Impovements Using Life Cycle Costs & Reliability Pinciples Bainge, Paul, 1998, How To Use Reliability Engineeing Pinciples Fo Business Issues Hung, Olive K., Gough, William A., Elements Of A Powe Systems Risk Analysis And Reliability Study Pospt, J.E., Giffin, T., Evaluating Aging Electical Systems And Equipment Hung, Olive, Klimache, Ben, Justifying Upgade Pojects in Existing Mills IEEE 141-1993, Recommended Pactice fo Electic Powe Distibution fo Industial Plants (Red Book) IEEE 463-1990 Recommended Pactice fo the Design of Reliable Industial and Commecial Powe Systems IEEE 493-1997 IEEE Recommended Pactice fo the Design of Reliable Industial and Commecial Powe Systems NFPA 70B-2002, Recommended Pactice fo Electical Equipment Maintenance Engineeing, Achitectue, Constuction, Envionmental and Consulting Solutions 2007 Buns & McDonnell aticles@bunsmcd.com Page 13 of 14
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