Preventive Repair Research Articles

Accurate on-line fault location and PD activity location results obtained with SCG – a long-term utility experience

In recent years, Alliander (one of the largest network owners in the Netherlands with almost 40,000 km of medium-voltage (MV) cable (polymer insulated lead covered and cross-linked polyethylene) installed a number of smart cable guard (SCG) systems to verify its effectiveness in preventing failures or, if there is a breakdown, to reduce the repair time (outage time). Alliander concluded that SCG is indeed a very effective tool for on-line detection and location of (intermittent) faults and partial discharges in MV power cables. These phenomena are located with an inaccuracy better than 1%, based on travelling waves. On average, each SCG system could have prevented about 6150 customer minutes lost per year. Preventive repair also allows seeing the cause of degradation, helping to develop counter measures. SCG can be used in all types of MV cable networks and replaces fault passage indicators as well. Based on this, Alliander will implement more SCG systems in the upcoming years.

Intellectual technologies in the problems of thermal power engineering control: formalization of fuzzy information processing results using the artificial intelligence methodology

Exploitation conditions of power stations in variable modes and related changes of their technical state actualized problems of creating models for decision-making and state recognition basing on diagnostics using the fuzzy logic for identification their state and managing recovering processes. There is no unified methodological approach for obtaining the relevant information is a case of fuzziness and inhomogeneity of the raw information about the equipment state. The existing methods for extracting knowledge are usually unable to provide the correspondence between of the aggregates model parameters and the actual object state. The switchover of the power engineering from the preventive repair to the one, which is implemented according to the actual technical state, increased the responsibility of those who estimate the volume and the duration of the work. It may lead to inadequacy of the diagnostics and the decision-making models if corresponding methodological preparations do not take fuzziness into account, because the nature of the state information is of this kind. In this paper, we introduce a new model which formalizes the equipment state using not only exact information, but fuzzy as well. This model is more adequate to the actual state, than traditional analogs, and may be used in order to increase the efficiency and the service period of the power installations.

Delayed maintenance modelling considering speed restriction for a railway section

The deterioration of track geometry depends on several factors of which the speed of the train is one. Imposing a speed restriction can slow down the track deterioration and allows a longer survival time before a serious condition is achieved. Preventive maintenance delays can be authorized during the survival time. However, speed restrictions also reduce the system throughput. On the other hand, a longer interval between preventive maintenance activities has a lower maintenance action cost and it also enables grouping the maintenance activities to save set-up costs as well as system downtime. If the repair delay is too long, it may cause unacceptable conditions on the track and lead to higher maintenance costs and accidents. Therefore, it is interesting to assess the effect of a speed restriction on the delayed maintenance strategies for a railway track section. We want to solve a maintenance optimization problem to find the optimal tuning of the maintenance delay time and imposition of a speed restriction. To this aim, a delayed maintenance model is developed, in which track deterioration depends on the train speed and the number of passing trains. The model is used to determine an optimal speed restriction strategy and a preventive repair delay for the optimization of the system benefit and unavailability. Coloured Petri Nets are adopted to model the maintenance and operation of the railway track section. The Coloured Petri Net model describes the gradual track deterioration as a stochastic process. Different speed restriction policies and maintenance delay strategies are modelled and activated by the observed component states. Monte Carlo simulations are carried out to estimate the maintenance cost, the system benefit and the system downtime under different policies. Numerical results show the maintenance decision variable trade-off.

Generalized control-limit preventive repair policies for deteriorating cold and warm standby Markovian systems

ABSTRACTConsider a deteriorating repairable Markovian system with N stochastically independent identical units. The lifetime of each unit follows a discrete phase-type distribution. There is one online unit and the others are in standby status. In addition, there is a single repair facility and the repair time of a failed unit has a geometric distribution. The system is inspected at equally spaced points in time. After each inspection, either repair or a full replacement is possible. We consider state-dependent operating costs, repair costs that are dependent on the extent of the repair, and failure penalty costs. Applying dynamic programming, we show that under reasonable conditions on the system’s law of evolution and on the state-dependent costs, a generalized control-limit policy is optimal for the expected total discounted criterion for both cold standby and warm standby systems. Illustrative numerical examples are presented and insights are provided.

Preventive repair policy for a system with minor failure and catastrophic failure

The paper studies a preventive maintenance system with multiple failures. Assume that the system has two types of failure. One is minor failure that the system will be replaced after the Nth failure. The other is catastrophic failure that the system is removed by replacement. Assume that the preventive repair is performed when the operating time reaches a fixed time T. The preventive repair of the system is “as good as new” which means the system will be restored as the initial state after the completion of last failure. Based on these assumptions, a preventive repair policy about the fixed-length time and the number of minor failures will be built. An optimal replacement (T, N)* can be determined by minimizing the average cost rate. Finally, we give a numerical example to verify that the policy is effective.

О надежности технических устройств, прошедших ремонт

Article purpose – to offer and investigate expressions for definition of average failure rate and a time between failures of the repaired technical devices, the non-failure operation restitutions differing in depth.Value of average failure rate with decrease of frequency and number of repairs decreases to replacement of technical devices, and with decrease of depth of restitution of non-failure operation increases. Varying depth of restitution of non-failure operation or frequency and the number of preventive repairs for endurance, it is possible to provide practically any preset value of average failure rate of technical devices. The time between failures of technical devices significantly depends on depth of restitution of non-failure operation when carrying out their preventive repair. There are boundary values of frequency and depth of restitution of non-failure operation at which carrying out preventive repairs is inexpedient as the time between failures of technical devices in these cases becomes lower, than in the absence of such repair. There are limiting values of depth of restitution of non-failure operation at which carrying out preventive repairs with any frequency reduces a time between failures of technical devices and carrying out such repairs is inexpedient. The received results show that under operating conditions due to change of frequency of carrying out preventive repairs and depth of restitution of non-failure operation it is possible to provide a desired value of a time between failures of technical devices. For technical devices, with obviously expressed processes of an aging and wear, effectiveness of carrying out preventive repair increases. In this case with other things being equal at the technical devices having distribution of a time between failures with smaller value of a variation factor, average failure rate is lower.

Use of an analytical method for calculating reliability of elements of electric power systems based on probabilistic models

Today, we no longer have to prove the need for numerical evaluation of reliability of in-plant power supply systems. There have been established generally accepted reliability indices in the form of frequency of various accidents and mathematical expectation of undersupply of electricity to consumers, or decrease of power generation by plants. Factors are revealed factors that must be considered at analysis of reliability of power supply systems: availability of repair of switching circuits and duration of repair of the main equipment and switching equipment, failures of switching devices and devices of relay protection and automatics, routine switching, seasonal variations in damage to overhead lines and outdoor equipment. Here, one should take into account a possible lack of reliable initial information about the reliability of elements at the consideration of a specific installation. The paper formulates models of the analytical method of calculation of reliability parameters of elements of power supply systems in the Matlab software. Reliability models are considered for power units, which involve restoration and prevention activities. Three states of a system are considered: operable state; emergency downtime and recovery, scheduled downtime for preventive maintenance or repair subject to intensities of emergency and planned outages, intensities, recovery and completion of scheduled maintenance and repair. It is shown that, at present, targeted screening and quantification of contributions to unreliability of power supply systems by failures of elements of the system, its states and modes, as well as effectiveness of various measures, allow to identify weak links of the power supply systems and to work out specific ways for improvement in the process of human-machine synthesis of the power supply system. This approach to design involves searching for new circuit solutions, and changes in the structure of the circuit and layout solutions of its equipment mitigation of weaknesses, elimination of excessive equipment, or, on the contrary, using more reliable equipment, as well as its modernization.

Dental Caries and Treatment Needs in Adolescents Aged 15 to 19 Years Old and their Relationship with Dental Services: A Systematic Review

Objective: To systematically review the prevalence and the need for treatment of dental caries in adolescents. Materials and methods: References consulted: Cochrane Library, PubMed, Embase, SCOPUS, Web of Science, BVS-BIREME and Google scholar, in the period between July 2016 and September 2016. Titles and abstracts were evaluated according to criteria of inclusion and exclusion. The selected manuscripts had their methodological quality evaluated. Results: From a total of 877 studies, 11 articles were included in the review after the application of the methodological filters. The cross-sectional study was the most used design in the articles. Brazil stands out as the country with more published studies on this subject. The prevalence ranged from 59% to 90.4%, whereas the DMFT index ranged from 1.4 to 7.1. Most of the studies presented differences between genders and locations. The need for caries treatment varied from 42.3% to 62.3%. Locations committed to the use of preventive measures in oral health presented better indicators or decreased chance of individuals having an untreated caries. Conclusion: There is an evident and wide range in the average prevalence of caries among adolescents, although DMFT index averages have been declining over the past few years. Well-organized dental services guided by the preventive values of Evidence-Based Dentistry seem to contribute to reduce the damages caused to adolescents in their oral health and their subjective experiences of life. Clinical Relevance: The Access to dental services proved to be important for the control of caries, with preventive actions or clinical repair of the damages.

ASSESSMENT OF TECHNICAL CONDITION OF POWER EQUIPMENT IN CONDITIONS OF DIGITAL ECONOMY

The article outlines the conceptual provisions for new approaches to assessing the technical condition of assets. Here, an approach through weight coeffi cients of the values of groups of parameters of functional equipment units is taken as the basis of expert defi nition. The methodology of determining weight coeffi cients based on the method of analyzing the hierarchies of T. Saaty is described in suffi cient detail. Based on the calculation of technical condition indices of individual functional units, in accordance with the solution of the problem of fi nding optimized values under fuzzy conditions and constraints, the integral indicator of equipment (equipment group) is determined by the minimum value. The author, in accordance with the method of assessing the technical condition of the main technological equipment and power transmission lines of electric power stations and electric grids and developing the optimal type, composition and cost of the technical impact on equipment (equipment group), develops concepts of the state of the equipment, correlating them with specifi c measures of technical impact. This allows us to objectify the assessment process and create an information base for making managerial decisions on the use of assets. The given example of calculation of the technical condition index allows to visually demonstrate the practical importance of the proposed approaches and methods for assessing production assets. The approaches defi ned in the article create an information and methodological basis for the transition from planned preventive repair of electrical power facilities equipment to condition-based repair. The article outlines the problem of comprehensive assessment of the technical and economic effi ciency of energy system assets, which includes numerous energy facilities. Formation of the methodological and technological basis of the production assets management system and ensuring its functioning determines the scientifi c value and innovative approach to solving the identifi ed problems mentioned in the article.

Strategy of Russian Coal Mining Enterprises’ Excavator Park Technical State Correction

Coal extraction in Russian Federation increases by 3…4 %. This tendency will remain in the nearest 10…15 years. Opencast mining makes (70…72)% from the total extraction in the country. Though analysis shows that investments in coal mining within the last 25 years were insig-nificant. In these conditions the priority area for coal production cost re-duction and increasing productivity of opencast coal mines is optimization of the main technological equipment (excavator park) maintenance system. The article shows that current system of scheduled preventive repair is not efficient and requires to be changed to the system of repair works due to actual state of the equipment.

Improving the Repair Planning System for Mining Equipment on the Basis of Non-destructive Evaluation Data

The article tells about forming a new concept of scheduled preventive repair system of the equipment at coal mining enterprises, based on the use of modem non-destructive evaluation methods. The approach to the solution for this task is based on the system-oriented analysis of the regulatory documentation, non-destructive evaluation methods and means, experimental studies with compilation of statistics and subsequent grapho-analytical analysis. The main result of the work is a feasible explanation of using non-destructive evaluation methods within the current scheduled preventive repair system, their high efficiency and the potential of gradual transition to condition-based maintenance. In practice wide use of nondestructive evaluation means w;ill allow to reduce significantly the number of equipment failures and to repair only the nodes in pre-accident condition. Considering the import phase-out policy, the solution for this task will allow to adapt the SPR system to Russian market economy conditions and give the opportunity of commercial move by reducing the expenses for maintenance of Russian-made and imported equipment.

Возможность применения инфракрасных световодов для измерения температуры в труднодоступных зонах энергооборудования

Акифьева Наталья Николаевна, старший преподаватель кафедры «Атомные станции и возобновляемые источники энергии», Уральский федеральный университет им. первого Президента Б.Н. Ельцина, г. Екатеринбург; nna_1@mail.ru. Жукова Лия Васильевна, профессор, д-р техн. наук, зав. кафедрой «Физической и коллоиднойт химии», Уральский федеральный университет им. первого Президента Б.Н. Ельцина, г. Екатеринбург; l.v.zhukova@ustu.ru. Глухов Алексей Евгеньевич, магистрант кафедры «Автоматика», Уральский федеральный университет им. первого Президента Б.Н. Ельцина, г. Екатеринбург; gluxoff.aleksey@yandex.ru. Краснов Дмитрий Алексеевич, магистрант кафедры «Организация машиностроительного производства», Уральский федеральный университет им. первого Президента Б.Н. Ельцина, г. Екатеринбург; houston8@ mail.ru. Овчарников Александр Олегович, магистрант кафедры «Тепловых электрических станций», Уральский федеральный университет им. первого Президента Б.Н. Ельцина, г. Екатеринбург; strogg300@yandex.ru. Шмыгалев Александр Сергеевич, младший научный сотрудник, ИВЦ «Центр инфракрасных волоконных технологий», Уральский федеральный университет им. первого Президента Б.Н. Ельцина, г. Екатеринбург; a.s.shmygalev@urfu.ru. N.N. Akifeva, nna_1@mail.ru, L.V. Zhukova, l.v.zhukova@ustu.ru, A.E. Glukhov, gluxoff.aleksey@yandex.ru, D.A. Krasnov, houston8@mail.ru, A.O. Ovcharnikov, strogg300@yandex.ru, A.S. Shmygalev, a.s.shmygalev@urfu.ru Ural Federal University named after the First President of Russia B.N. Yeltsin, Ekaterinburg, Russian Federation

Investigation and Preventive Repair Strategy for North Breakwater Dome at Wakkanai Port

Investigation and Preventive Repair Strategy for North Breakwater Dome at Wakkanai Port

A geometric process model for deteriorating operating system with periodic and random inspections

In this paper, we consider a deteriorating operating system which executes a job with random working times. It is assumed that the working times form a geometric process. In Model 1, the system is checked at periodic times and also at every completion of working times to detect the failures. In Model 2, we extend Model 1 by further assuming that a preventive repair is taken when the failure is not found by periodic inspection. For both models, the explicit expressions of the total expected cost until the detection of the failure are obtained. The optimal periodic inspection policies are computed numerically.

Optimization of Paper Making System using Genetic Algorithm

Objectives: In the current work, a paper making system has been under consideration for its availability and optimisation. The objective of this paper is to optimize input variables of the paper making system, to maximize system availability. Methods/Analysis: Paper making system consists of mainly, six subsystems connected in series configuration. For analysis, Repair rates, failure rates, Transition rates and PM rates of each subsystem is taken from maintenance history sheets. Markov process with probabilistic approach is used to model the system for availability with ideal PM and faulty PM. Steady state availability is obtained by using normalizing condition. The optimization of a system availability is executed by genetic algorithms. Findings: Findings present in paper show a significant improvement in the system availability. With ideal PM the availability has been increase upto 93.43% whereas in case of faulty PM the availability has been increase upto 91.89%. Novelty/Improvement: The optimization would help the analysts to design and planning more effective preventive maintenance and repair rate policies.

Optimal maintenance policy for a system with preventive repair and two types of failures

Maintenance policy is one of the most critical issues in operations management. In reality, the proper functioning of productive systems is affected by so many complicated factors that even preventive repair cannot eliminate the possibility of system failures of different types. A cost-effective maintenance strategy is usually desired. In this paper, a geometric process maintenance model with preventive repair and two types of failures (repairable failure and unrepairable failure) is studied. A maintenance policy (T,N) is proposed, where preventive repair will be conducted when the successive operating time reaches T, and the system will be replaced by a new one when an unrepairable failure or the Nth repairable failure occurs. The optimal policy (T∗,N∗) is obtained such that the average cost rate (i.e., the long-run average cost per unit time) is minimized. The model is generalized to reflect three different types of maintenance systems. An algorithm is proposed to obtain the optimal policy (T∗,N∗). Numerical experiments are conducted to examine the impacts of system parameters on the optimal maintenance policy.

Optimising spare parts provision and inspection intervals for an aircraft fleet undergoing cannibalisation

This paper studies the problem of determining the optimal initial stock level of recoverable components and the aircraft preventive maintenance inspection interval for an aircraft fleet. Demand for spare components arises from both corrective and preventive maintenance tasks. An aircraft that experiences failures while performing a mission is maintained by replacing failed components with working spares. In order to reduce the amount of this unplanned, corrective maintenance that is performed, aircraft are usually inspected periodically and components found to be in poor condition replaced preventively. The supply of spares is critical to maintaining fleet operational requirements but determining the stock required while considering critical fleet operational requirements and budget limitations is a complex task. When spares are unavailable, inoperative aircraft must wait for failed components to be repaired. In such situations, cannibalisation may be performed, where working components are removed from inoperative aircraft in order to replace failed components of the same type in other aircraft. Cannibalisation is beneficial in maintaining fleet readiness and reducing spare part demands since is it allows any shortage of spares to be consolidated into a small number of inoperative aircraft. In this paper a coloured Petri net (CPN) model is used to model the fleet maintenance process. The model accounts for fleet operation, aircraft preventive maintenance, repair, spares and cannibalisation. A genetic algorithm (GA) based simulation-optimisation approach is employed to find the optimal solutions of fleet spare provisioning and the aircraft periodic inspection interval to minimise the cost.

Stochastic Analysis of a Redundant System with Maximum Repair Time and Priority for Operation over Preventive Maintenance

The main goal of the present study is to analyze a redundant system by using the concept of priority to operation over Preventive Maintenance (PM) and Maximum Repair Time (MRT). For this purpose, two stochastic models are developed. The concept of MRTis studied in the second model in addition to the assumptions of first model. There is a single server who visits the system immediately as and when required. The server takes the unit under preventive maintenance after a maximum operation time at normal mode if one standby unit is available for operation. If the repair of the failed unit is not possible up to an MRT, failed unit is replaced by new one. The failure time, maximum operation time and MRT distributions of the unit are considered as exponentially distributed while repair and maintenance time distributions are considered as arbitrary. Various measures of system effectiveness are obtained by using the technique of semi-Markov process and RPT. To compare the performance of stochastic models graphs for several reliability measures are drawn.

EXAMINATION OF MEDIUM AND LONG TERM EXPRESSWAY MANAGEMENT POLICY FOR IMPLEMENTATION

In recent years, deterioration of expressways is the serious problem, and it is necessary to plan the medium and long term management policy. In this study, the authors examine the medium and long term management policy, using the accumulated enormous inspection data of road surface conditions. The future condition of road pavement is significantly different by the management system such as the budget, personal distribution or repair method, etc. The authors quantitatively evaluate the relation between the future condition of road pavement and the management system, of which the authors specially take up preventive repair by penetration repair agent. Then, the risk evaluation and the life cycle cost (hereinafter referred to as LCC) analysis can be conducted in deferent repair strategies by stochastic simulation. By using stochastic simulation as the method of these two evaluations, the comprehensive analysis can be conducted, considering the possible change of management surroundings in the medium and long term and various examinations for optimization.

Unfit for Repair After Screening for Abdominal Aortic Aneurysm: Do We Fail to Fulfil the Basic WHO Criterion of an Available Treatment?

In this edition of EJVES, the Gloucester group report that 18% of screen diagnosed cases of abdominal aortic aneurysms (AAAs) in need of preventive repair haven’t received repair after 3 months; 22% of these received repair later on with no 30 day post-operative deaths, so the final turn down rate was 13%. 1 The reasons are not given, but could be a sign of a kind of “intelligent waiting” where you take the chance of repair if progression is worrying, weak symptoms develop, or health conditions improve. However, “intelligent waiting” is a dangerous strategy because about 20% of patients in the current report experienced rupture. Clearly, earlier intervention seems more attractive. In addition, three major questions arise from this report if generalisation is possible. When we created a model to evaluate cost-effectiveness of screening for AAA in a modern context, we needed to know the proportion not repaired, and studied the four AAA screening randomised controlled trials; 15% didn’t receive repair. 2,3 However, these figures are mainly from the 1990s when the operative risk was 5% before endovascular aneurysm repair and the knowledge that treatment of screen detected cases carries a one third risk compared with incidentally detected cases. 4 However, initial results from the British National AAA screening programme (BNASP) reported that 26% of 417 referred patients weren’t yet repaired, and although probably biased by other factors, the proportion seems very high. 5 The first major question to be raised is whether screening is still beneficial and cost-effective. As mentioned, such rejection fractions for repair were also seen in the MASS and Viborg trials, both of which have reported efficient and cost-effective screening programmes. In order to evaluate the consequences in a modern context, 2 we ran sensitivity analyses of our modern model in which the originally used unfi tp roportion was exchanged with the proportions reported from Gloucester and the BNASP, respectively. It showed decreased efficacy from 32% to 30% and 23% reduced AAA specific mortality, respectively. Whether it remains cost-effective needs further time consuming calculations to clarify. A second major question to be raised is whether one of five or higher deemed unfit initially is acceptable according to the fundamental criteria for screening formulated by the WHO. Although some of them receive repair later, the initial refusal leaves the patients with the knowledge of having a life threatening condition with the obvious risk of losing life and quality of life. However, it seems to be correctable as the potentially maintained high rejection rate is combined with a tremendous decline in the operative risk from about 5% to about 1%. 4 We must not forget when the size criterion of 55 mm is met the condition is life threatening. If we assume the median size of referred AAAs is 6 cm and such an AAA carries an annual rupture risk of 10% with 75% overall mortality, 2,6 then survival curves of early surgery populations will cross those deemed unfit after just 1 year if the operative risk is as high as 7.5%. Modern public surveillance of results and risk of audits may have triggered this development, especially in Great Britain where individual surgeon outcomes are published. 7 Consequently, the third major question is whether we as vascular surgeons have failed by continuing to select people to repair using outdated criteria that are no longer balanced by the decreased risk of repair?