SURVEY OF TRANSFORMERTECHNO- ECONOMIC ANALYSIS
1Shalini Vaishya,
Research Scholar Electrical Engineering
2Prof. Dr. S.R. Nigam
3Prof. Dr. Smita Shrivastava
123AISECT University Bhopal , Madhya Pradesh , India
Abstract- Electricity is the prime mover of a modern society. It is regarded as the lifeblood of economic activities. Electricity is an essential requirement for all facets of our life. It has been recognized as a basic human need. It is a critical infrastructure on which the socio-economic development of the country depends.
Supply of electricity at reasonable rate to rural India is essential for its overall development. In the first hundred years of its commercialization, electricity was supplied to consumers by vertically integrated monopolies. It was generally felt that this was the only feasible option due to complexity as commodity and its natural monopoly aspects.It is one of the major infrastructural facilities required for setting up manufacturing industries in the country. Transformer Insulation aging assessment appraisal and life expectation more sensible, we will try to simulate a MTALAB / Simulink model for insulation life transformer assessment display in light of the working burden, ecological factors, the electrical qualities of the trial and oil chromatographic attributes for techno economic evaluation of the transformer. This paper is related to all literature survey for the proposed research.
Index Terms— Techno Economic, Transformers, Intelligent System, Review.
1. BACK GROUND
Introduction to Economic Life of Transformer Generally, transformer life can be divided into technical life, physical life and economic life and other forms [10]. 2.1. Economic Life of Transformer Physical life of transformer generally refers to the life determined by the physical wear and tear, which is also the life of the transformer from the time put into service until retired due to physical wear and tear. Physical life of transformer is mainly determined by tangible wear also related to self-quality status, the use of technology and maintenance quality. But, technical life of transformer commonly means that with the development of science and technology, existing transformer will be replaced by more advanced transformer before its physical or economic life is ended. Therefore, technical life of transformer mainly indicates the time from transformer investment to its loss of use value due to technological progress. Because of the impact by the intangible wear, technical life of transformer is generally shorter than the natural life. Based on the above, transformer physical life and technical life are defined from the use of the transformer itself.
Economic life of transformer generally refers to the life determined by operation and maintenance costs
of transformer. Because of transformer worn out in its late use, operation and maintenance costs of transformer is increasing. Under that circumstances, there will have a service cycle which is economic life of transformer when the
average running cost is below a certain limit.
Economic life is often used to analyze and determine the best life and the best update time of the transformer [11]. Therefore, we can determine the best life and the best update time of the transformer when the economic life is certain.
Based on the above, there will be a year that the average running cost is minimum and the year can be considered the economic life of transformer.
2. REVIEW OF LITERATURE
Power transformer windings are insulated with multiple layers of Kraft paper and immersed in mineral oil. This paper insulation is required to withstand both electrical and mechanical stresses.
The paper and oil insulation degrades over time at a rate depending on the moisture level, oxygen present and the operating temperature of the oil.
The degradation of original properties and the production of by-products are insulated in the deterioration process. The quantity of by-product derivatives and the degree of changes in properties are used to gauge the insulation condition in the power system. The methods to assess the condition of transformer insulation are generally classified into electrical and chemical analysis. They are available as standard guidelines published by American Society for Testing and Materials (ASTM) and International Electro technical Commission (IEC) organizations. These organizations have made significant contributions in the advancement of technology and skills for diagnostic techniques. Their standards are revised and updated from time to time to keep in touch
with the current situation. Researchers and engineers around the globe are constantly searching, modifying and developing new methods for diagnosis of condition of electrical equipment‘s.
The purpose is to seek advancements in technology in order to provide better, more effective, accurate, and economic approaches or inventions in condition monitoring and diagnostic methods.
Ahmed E.B. Abu-Elanien∗, et. al. [1] presented the transformer asset management was highlighted in this paper. The general classification of the asset management activities was illustrated. The three major activities of the transformer asset management are the application of CM techniques in the transformer operation, performing maintenance plans and investigating new less-cost maintenance methods, and assessing the health and end of life of the transformer. A detailed explanation of each transformer asset management activity was investigated in this paper.
J. P. van Bolhuis, et.al. [2] presented to solid insulation condition estimation, there currently are eight often used (mentioned) techniques, each with its own area of application and applicability. The techniques, their use, development, and applicability are mentioned in Table II. Because of developments in micro technology some methods are undergoing development that most certainly will improve the measurement and the corresponding interpretation of the insulation system behavior. For successful application of measurement results toward condition based maintenance, further research is needed, in coronation with practical experience.
W Young, et. al. [3] showed level of condition monitoring employed is likely to increase as experience is gainedof the various systems available. In general, the initial cost of condition monitoring equipment is more than offset by the potential improvement in operating efficiency and extended life of the transformer. The complexity of monitoring equipment now being employed more frequently requires that the sensors are factory fitted and consequently have to be specified from the onset.
C. Myers, et. al. [4] examine practical aspects of maintenance of transformers. Condition monitoring is a powerful and reliable diagnostic tool to protect large, expensive transformers and can be applied at reasonable cost to all sizes and types of oil insulated plant. A minimal approach is to do nothing and in the current economic climate it is a dangerous method. Simply inspecting the color of
silica gel breathers and replacing when necessary at least gives some protection to small plant.
Ahmed E. B. et. al. [8] presented the transformer condition monitoring was defined and its importance as a first step to condition based maintenance was highlighted. The different techniques of the transformer condition monitoring were classified and their implementation was discussed. It is found, based on the literature survey, that CM using DGA is the classical transformer condition monitoring technique and it is found that it is well defined, well understood and no more enhancement expected in this field of transformer condition monitoring.
Jouni K. Pylvänäinen, et. al. [9] revealed input information could be adapted from different data sources. The precision of the evaluation depends on the input data and the calculation method utilized.
To evaluate temperature values for a transformer supplying loads with severe harmonics, the effects of current harmonics could be taken into account.
In the selected approach, the methods adapted from have been used. In the case of harmonics, the information of the amplitudes of predominant current harmonics must be available in order to evaluate the excess losses caused by the harmonics.
W.H. Tang, et. al. [10] presented power transformer thermal model has been developed based on the analogy between thermal dynamics and electric circuits. The proposed thermal model can calculate continuously temperatures of the main parts of an cooled power transformer under various ambient and load conditions. The model parameters can be obtained by the GA search only based on the on-site measurements, instead of the experimental methods and off-line tests. From the responses of the constructed thermal model, it can be seen that the thermal model analogous to an electric circuit has the potential for representing the real transformer thermal dynamics accurately. The improved knowledge of transformer characteristics can allow enhanced load ratings and reduce the risk associated with the emergency post-fault operations. Both the model parameters and responses can be used for predicting thermal distribution and monitoring the service condition of power transformers.
I. Q. Feng, et. al. [11] showed transformer temperature monitoring system based on an equivalent heat circuit thermal model is presented.
This system not only provides efficient, accurate prediction and analysis results, but also incorporates a convenient user interface, in which users can access the real-time monitoring data, prediction results and transformer load ability results remotely through a web browser. We have
been undertaking off line trial runs of the proposed system for several months. The results of these suggest that all functions of the system, including real-time data monitoring, data transmission (local remote), thermal model and HTTP services cooperate efficiently. The system will be tested in a substation of the National Grid Company plc in the near future, to verify its performance and reliability under real conditions, and moreover, to provide valuable information for its further development.
Roizman, V. Davydovet. al. [12] demonstrate that ANN and fuzzy logic technologies are found to be highly useful for transformer monitoring and diagnostics. Along with the problems described it can be concluded that most of the other monitoring and diagnostic tasks can also be tackled with the help of neuro-fuzzy computing.
JiShengchang, et. al [13] proposed transformer tank successfully extracted using the measuring system. The characteristics are in accordance with theoretical analysis. Future studies should be concentrated in the modeling of power transformer tank vibration, simulation of core deformation, pattern recognition of winding vibration due to load current and extracting of the failure characteristic vector. Most importantly, more work must be done to set up a database of signals, which represent a variety of transformer designs, sizes and degrees of failure. Only in this way can a true correlation between varying degrees of deformation and various vibration signal characteristics be established.
Pengju Kang et. al. [15] demonstrated in more than 3 yr field experiences that vibration monitoring is an effective tool for assessing the condition of tap changers. The overall condition indicator , the deviation of auto-correlation vector of the newly acquired envelope signature from the reference auto-correlation patterns, was used to provide a single index to detect faults automatically in the OLTC. This index can be directly sent to the asset management system to trigger alarms such that maintenance staff can examine the signatures closely and make decisions on the true condition of the tap changer. For the type of OLTC under our investigation, we used signatures of 50 operations at each tap position to establish the reference patterns.
Abbas Zargari Trevor R. Black bum et. al [17]
showed a good performance for partial discharge detection occurring inside the high voltage apparatus compared to piezo-electric detector.
Porcelain is not a good material for acoustic transmission, however it was chosen to examine
the sensitivity of optical fibre sensor in an undesirable situation. With the results obtained in the laboratory, it shows a promising alternative for PD detection in inverted type current transformers and CTs with out DLA link. It can be used as a non invasive sensor with the flexibility of having various geometry and shape suitable for the particular application. The advantages such as immunity to electromagnetic interferences, non conducting, small weight and being chemically inert make it a desirable candidate as a sensor or data transmission line in high voltage applications.
Stephen D. J. et. al [18] presented the design of a multi-agent condition monitoring system for online transformer monitoring, using UHF PD analysis.
This research has explored the viability and benefits of a multi-agent approach to transformer monitoring. The next stage of the research is to extend the system in terms of its coverage.
Therefore, future research will prove the COMMAS architecture for the monitoring of multiple transformers in a substation. In addition, it will be extended for application at a number of different substations, allowing all the transformers‘
health assessments to be available through a single engineering assistant agent. Currently, plant lifetime models are being developed for integration into the system.
J. S. Fool et. al. [20] proposedthe ability of the ANN to recognize the condition of the transformer insulating oil basing on the PD parameters have been established. With the use of the optimized ANN parameters, a prediction accuracy with a
%MAE of 0.88% was achieved.
Ashraf I. Megahed, et. al. [21] revealed the wavelet transform in the protection of series- compensated transmission lines has been presented.
The algorithm for detecting the fault and its zone has been proposed. A single modal signal that covers all types of faults is obtained by combining the three-phase currents of the fault. Wavelet analysis, with db4 as a mother wavelet, is performed for the modal signal where detail 1 and detail 6 are obtained. The spectral energy of each detail is obtained and the ratio of the two energies determines whether the fault is internal or external.
Moreover, a threshold level for the high-frequency energy differentiates between external faults and switching operations. The purpose of fault classification wavelet analysis, with Haar as the mother wavelet, is for the three-phase and ground currents.
Ahmed E. B. Abu-Elanienet. al. [22]
presentedthe DWT integrated with FFANN is used for locating the switched capacitor in the
distribution systems. A single modal signal produced from the combination of the three-phase currents at the customer load side is used for monitoring the switched capacitor transient. The proposed algorithm uses the contained spectral energy in the first two details produced from the DWT decomposition of the modal signal and the number of samples from the beginning of the switching transient to its end for the first two details of the DWT as inputs to an FFANN to identify the switched capacitor. Although an 18-bus power system is used for testing the applicability of the proposed algorithm, it will operate successfully for any system size. The reason for that is the transient signature of the switching event for any given capacitor is never going to be the same for any two capacitor switching cases. The simulation study proved that the algorithm gives reliable results for locating the switched capacitor.
Hao Zhang, et. al. [23] proposed the ability of detecting PD from noisy environment can be greatly improved with WT. Several popular WT de-noising methods have been reviewed to find a better solution. A novel WT de-noising method has been developed based on continuously modeling noise Characteristic, and working out the threshold value to modify WT coefficients. The de-noised PD signal is then recovered by reconstructing those modified coefficients. On site PD measurement noise might be one or sum of white noise, DSI, pulse-like noise, etc. This novel method has been proved to be very effective in rejecting those noises. It was also shown that other existing methods did not yield satisfactory results. This may be due to several reasons. IShim proposed a threshold value selection rule as expressed in equation .
P. Werle', et. al. [25] presentedOnly the simultaneous detection of the apparent charge and the PD origin can lead to a precise diagnosis of the insulation condition and therefore to an optimization of the transformer maintenance resulting finally in a prolongation of its lifetime.
Wideband electrical measured PD signals offer information about the apparent charge as well as the PD source, which can be determined using a new approach that is based on neural classifiers.
DrEklund' et. al. [28] presented transformer evaluation Althoughno detectable furfural was measured up to temperature of 1 4 0 T in the aged samples, hut the degree of polymerization of paper starts decreasing at a temperature of 120 "C. This decrease of DP is temperature dependent and faster with increase of temperature, reaching the value characteristic of the end of life of paper, at a
temperature of 180 "C. The correlation between ZFAL and SHMF concentration in oil, and the corresponding DP value of the paper indicates that once DP value reached 450, production of ZFAL and SHMF starts. However, concentration of furfural absorbed by paper can be related to DP of less than 900, which means that detecting uranic compounds absorbed by the paper, is a better indication of DP depreciation. On the other hand, the concentrations of uranic compounds in paper, are about 150 times greater than the corresponding concentration in the oil, which suggest, that the partition coefficient of these compounds, between paper and oil, are much more favorable to the paper, than to the oil.
BarsaliS, et. al. [29] presentedExperimental and theoretical investigations were carried out on HV disc winding of a 11 kV/433 V, 1 MVA transformer. Sweep frequency responses of the transformer were obtained experimentally. It was observed that magnitude and phase frequency response plots of outer phases were similar. Even the middle phase had similar results except at low frequency. From the results it can he inferred that the frequency responses of the differnt phases of the same transformer are comparable. Experimental investigations reveal that very minor changes are easily detectable. The frequency response variations are in the frequency range of 200 kHz to 650 kHz. Similar results are also obtained from theoretical studies.
Nazar AI - Khayat, et. al. [31] discussed of the modeling and testing of a large distribution type power transformer. The models developed show a close trend between the measured and predicted frequency response. The results are believed to be very encouraging for rather work in this area.
Furthermore, the method used in this paper is sufficiently general to be easily applied to other electromagnetic devices.
S. Birlasekaran, et. al. [32] proposed a novel and reliable on/off-line condition monitoring technique using low voltage frequency signals and a number of analysis methods has been developed. The method is very sensitive and can detect minor and major faults with sufficient selectivity. Three configuration methods like LVO, HVO, and TransfV, and the chosen frequency range play a great role in identifying faults with maximum sensitivity and selectivity. Another major advantage is that the proposed technique can monitor online faults, like increased L or C loading, with more sensitivity when the transformer is operating.
33. A. Kingsmill, et. al. [33] presentedthe above analyses, based on online monitoring data and incorporating other information as it becomes available, can be used to provide information on high voltage equipment that is valuable for its use and management. Because online monitoring is continuous, it is more likely to pick up serious problems before traditional diagnostics (which are carried out at regular intervals), and can be used to attain business benefits in the electricity industry.
Stephen D. J. et. al. [34] presented this reseach opened by posing two sets of questions surrounding multi-agent systems: broadly, ―what are they?‖ and
―how should they be used?‖ In this paper (Part I of II), the first question has been answered, by defining the key terminology and concepts associated with multi-agent systems, and identifying the important contributions that can be made in the field of electrical power systems.
Drivers and benefits have also been identified, and a survey of publications in IEEE and IEE journals and relevant conferences has been used to highlight the application areas for which MAS technology is currently being investigated. As well as the potential benefits of MAS technology, this part has also considered the technical challenges which must be overcome through further research if MAS technology is to be successfully employed and deployed in the power industry. Part II will tackle the second question, giving detailed technical recommendations of how MAS should be employed by those building systems for power engineering applications.
AlirezaSetayeshmehr, et. al. [37]
presentedCondition based diagnosis and maintenance are very important techniques in the field of power transformers. Reducing maintenance costs, lengthening transformer‘s life, enhancing safety of operation, minimizing accidental and sever failures can be available with this methodology. Research in recent years clearly shows that advanced intelligence computer programs are indispensable in developing diagnostic and maintenance methods.
38. Yongli Zhu, rt. al. [38] presentedelectric utilities are continually under pressure to supply electricity economically with high reliability to their customers. Because CBM is being paid much attention, all kind of off-line testing data and online monitoring data should be fully used to make more accurate condition assessment on many transformers in an electric utility, and sophisticated data management systems are required. The paper presents some general guidelines of developing an intelligent transformer condition assessment system
to help electric utilities optimize the maintenance activities. This proposed framework is open and flexible, so the objective system is easy to be developed and maintained. Data warehouse, multi- agent system and data mining techniques are used in the framework. A data warehouse has been used to integrate all kind of transformer condition parameters. Open Agent Architecture (OAA) is employed to compose the multi-agent system that is the main part of the proposed system. Seven application agents are designed to evaluate transformers‘ conditions synthetically. The Grey correlation method, grey theory prediction model GM(1,1), Bayesian network classifier and Bayesian network are employed in the agents. A Bayesian network for transformer condition assessment is proposed.
S. Costa, et. al. [40] presentedthe processing in realtime of the information determines the current and remaining conditions of the transformer. The description of occurrences that increase the cost of energy, network configurations and load forecasts allow the determination of the optimum life cycle.
The best load flow configuration and supply give subsidies to the maintenance sector for the programming of interventions, and eventually replace equipment‘s and where to direct the investments. The extension of the useful life of the equipment is one of the main objectives of the maintenance program. It becomes possible throughout combined actions of monitoring and interventions such as modifications in the system configuration for oil preservation, checking the insulation between active part and OLTC, the reconditioning of the insulating fluid and the dielectric properties. However, the implementation of these actions is conditioned to the amount of available resources, consequence of the global and individual accepted failure rates and reliability.
M. E. Beehleret. al. [41] presentedthe fundamental goal of Reliability Centered Maintenance is to preserve the function or operation of a system. Specifically, the function that must be preserved for transmission systems is the delivery of safe, reliable electric power to customers. With careful and thoughtful implementation, the application of the concepts of Reliability Centered Maintenance to transmission systems is a viable and effective maintenance approach that proactively addresses the challenges of controlling costs and improving customer service in an increasingly competitive market.
B.Handley,et. al. [42] presentedThe maintenance periods of on-load tap-changers have traditionally been chosen based on a conservative estimate of
given practice. The opportunity to monitor the duties of a tap-changer have enabled an intelligent system to be introduced for assessing when a unit is ready for maintenance. This is related to the duties performed by the tap changer, and a crisp value of standardized operation has been introduced to highlight when a unit is ready for maintenance. The introduction of this monitoring system has resulted in a reduction of maintenance visits and hence a reduction in costs for the company. These cost reductions have not been insignificant. The new system has not led to any reduction in the quality of supply standards, and system security has been enhanced by a reduction in plant outages.
G. Theilet. al. [43] presentedTo overcome the restriction of Markov-theory to constant Energyewerschat, Technics Universidad Wien.
transition rates, a multi-stage outage and maintenance model is proposed in which each stage of system degradation is characterized by an individual outage and maintenance rate. By that way the increase of outage rate with operation time Gerhard Theil was born in Vienna, Austria can be simulated. The model can be applied in maintenance on 28.1.1948.Studies of Electrical planning to check the efficiency of different maintenance Engineering at the Technical University of Computation results obtained by application of the proposed electrical power systems. model are sensitive with respect to model parameter Employment: Technical University of variations.
Na Liu WenshengGaoet. al. [44] presentedA simulated model for the calculation of maintenance period is developed in this paper, which is suitable to power transformers. data by Monte Carlo Methodist for the system of high reliability, like power transformer. Moreover, with a Fault Tree representing the logic of the complex system, maintenance crew can know how the components affect the performance of the overall system, and then decide when the maintenance downtime should be, which fitting for the Condition Based Maintenance of transformers.
Iony P. Siqueiraet. al. [45] presentedThis paper has shown general requirements for Reliability- Centered Maintenance software application. A statistical model of equipment defects and failures, and an approach to optimization of maintenance frequency is used as a way to After its testing in an extensible electrical transmission network, with more then 80 high voltage installations operated by CHESF, it is now being used by Cigré-Brazil Task- Force SC-B3.01, to define an RCM Guide for Substation equipment‘s. A research project to
standardize these requirements among several companies is under way, supported by ANEEL and CHESF, and conducted by CESAR, the Advanced Studies and Systems Center of Recife, Brazil.
Wenyuan Li EbrahimVaahedi, et. al. [47]
presentedequipment aging is a fact of life in power systems. Dealing with aged equipment has been a challenge in the utility industry for years. This article discussed the issues around power system equipment aging, including concepts of equipment lifetime, approaches to estimating the mean life and age, and Weibull and normal-distribution-based models to assess the end-of-life failure probability.
The relationship between aging and maintenance activities, limitations of maintenance in extending equipment life, and determination of timing of retirement were also discussed. A few examples showing actual data of transformers, cables, and reactors at BCTC have been presented.
Maintenance activities can extend the life of equipment but could be very costly for equipment at their end-of-life stage. A compromise between maintenance and replacement must be carefully considered. RCM and probabilistic analysis approaches are available for utilities to guide maintenance activities and manage aged assets in a more efficient and economic manner.
M. Arshad, S.M. Islamet. al. [49] provides better maintenance framework for the transformer and its reliability issue can be met effectively. The residual life can be extended and maximum return on the investment can be achieved. It will limit the failure surprises. It allows planned shutdowns, minimizing the forced outages. The flexible budget and procurement polices can be implemented to arrange spares on competitive rates as well as the work force. Successful life management and life extension in power transformers produce financial benefits with increased reliability. It maximizes the transformer availability resulting in minimization of capital investment. It also facilitates failure analysis to predict the causes and their impact on the over all system. Diagnostics and monitoring techniques provide useful information for developing and implementing asset management strategies. The advance asset management strategies will allow the transformer to serve beyond its expected design age. It also provides an acceptable life time before a failure can be concluded or a criticality ranking among a group of transformer can be established.
H Herman, et. al. [50] demonstrated that spectroscopy and chemo metrics may be used to rapidly and nondestructively measure the condition of both insulation paper and mineral oil in
Transformers. For paper, DP and mechanical property data ‗that were previously only available after lengthy analysis‘ can now be measured within a few tens of seconds once chemo metric models have been developed. In the case of mineral oil, this approach has highlighted the underestimation of aromatic content when it is measured in the mid- IR region according to IEC standard 590. However, despite this, the current models still provide a reasonable estimation of the aromatic content and excellent data for the refractive index of the oil.
Refinement of the aromatic model is on-going with aromatic data measured by alternative approaches.
In summary, the models are in place to enable a portable analyzer for measuring the condition of Kraft insulation paper and mineral oil within offline transformers to be developed.
M. Ali, et. al. [53] presented Furan-based aldehydes are typical degradation products of cellulose and can potentially be used to monitor the degradation of paper by analysis of the oil by HPLC. Normal levels of 2-furaldehyde are in the range 100 to 1000 ppb, but levels of about 1 ppm have been measured in a ―normal)) transformer, rising to 5 ppm in a transformer running hot and to over 10 ppm in a transformer that overheated after a cooler failure. The rate of change of concentration is as important as the absolute value.The DP of paper is difficult to measure reproducibly, We have developed a systematic approach, which gives results to a known accuracy, but even then the DP only gives a crude average of the molecular chain size and is a very coarse measure of degradation.Size exclusion chromatography (SEC) has the potential to give a far more detailed analysis of molecular weight distribution changes during cellulose ageing.
Coupled with computer modeling, SEC could provide the basis of more sophisticated degradation models than are currently available from the statistical analysis of chain scission, because more complex situations can be accommodated.In future studies, we hope to develop correlations of tensile strength to molecular weight distribution changes and the concentrations of key degradation products in the transformer oil, with the long-term objective of generating a more comprehensive model of insulation degradation.
M. Mirzaieet. al. [54] we measured paper tensile strength and oil gas chromatography under different thermal stresses. Paper tensile strength has decreased by temperature increasing. Also increase of ageing time and temperature remarkably boosted carbon dioxide and carbon dioxide concentration dissolved in oil. We studied paper tensile strength variations versus oil insulation properties too and
we observed a noticeable correlation between paper tensile strength and carbon monoxide, carbon dioxide to carbon monoxide concentration ratio in oil. Also the new life time model has been presented based on accepted tensile strength criteria (0/O50 of original tensile strength). This model has good accuracy.
Tapan K. Saha, et. al. [57] reviewed modern chemical and electrical diagnostic methods. Firstly traditional chemical methods have been discussed with currently available interpretation schemes.
Among chemical methods DGA is the most widely used method for investigating incipient faults. A number of interpretation techniques are available to analyses fault types. IEEE and IEC have appropriate Standards for the interpretation schemes. The next widely used method for analyzing cellulose ageing is furan measurements by the HPLC technique. Although no standard is available for the interpretation of ageing phenomena, some good literature is available on the technique. DP measurement has been widely used for monitoring cellulose mechanical strength.
The cellulose ageing phenomena and its relation to DP are reasonably well understood. Most of the currently used techniques have some drawbacks as well. When transformer oil is replaced or refurbished, the analysis of gases and furans in the refurbished oil may not show any trace of degradation although the cellulose may have degraded significantly. DP estimation is not possible without collecting cellulose samples from the operating transformers.
A.M. Emsley, et. al. [60] presented(i) The life expectancy of transformer paper insulation, at normal operating temperatures, can be calculated from laboratory ageing experiments with statistical errors, which are, at best, +20% of the estimated life.
(ii) Such an accuracy requires that: the initial degree of polymerization (DP) of the paper is accurately known; a satisfactory assumption is made about the final DP value
limiting useful life; the operational history and environmental condition of the transformer are known and invariant.
(iii) The systematic use of furfural and related compounds to monitor paper insulation condition promises a useful complementary technique to dissolved gas analysis and other monitoring techniques.
(iv) Measurement of phenol, m-cresol and xylene in the oil may indicate that electrical and thermal degradation of phenol formaldehyde resin insulation is occurring.
Kshira T. Muthanna, et. al. [63] presented the load and ambient temperature history for a power transformer is available over a time window, the modeling techniques discussed in this paper can be used to simulate the load and ambient conditions over the required time period. These load and ambient profiles enable quantitative assessment of the consumed life of insulation. The end of life can be obtained through the full simulation approach or a renewal process approach. The full simulation approach is computationally intensive but it is easier to implement the long-term variation effects in the operating profile of the transformer.
P.K. Sen, et. al. [64] presented workFor several reasons, overloading of power transformers beyond their nameplate rating has been routinely practiced by the utilities. However, in order to achieve greater profit (mainly in the form of deferred capital cost), more and more utilities now are aggressively pursuing overloading the power transformers. Overloading can take place in different forms, such as, continuous, intermittent, planned, short or emergency. Depending on the application considerations, some form of overloading of transformers may not cause any damage and hence, reduced life expectancy and may be acceptable. In other applications, overloading may cause severe damages. In order to find the optimum most cost effective operation, it is essential for the utilities to be able to predict with reasonable accuracy the transformer remaining life under certain overloading conditions.
José Antonio Jardini, et. al. [65] proposed a methodology is being implemented for distribution transformer management at EmpresaBandeirante de Energies Electrical. The diagram of Fig. 11 shows the main components of this methodology.
A. Naderian, et. al. [69] presentedhealth indexing quantifies equipment condition based on numerous condition criteria that are related to the long-term degradation factors that cumulatively lead to an asset' s end-oflife. This paper described a realistic Health Index method for power transformers using available data and considering IEEE and IEC recommendations for condition parameters. The calculation is based on weighting factors, condition ratings, and assigned scores for any specific parameter. By using a multi-criteria analysis approach, the various factors are combined into a condition-based Health Index. DGA, oil quality tests, furan, power factor, and load history are the parameters that have been used as quantitative data. The physical health condition of transformers was included using a count of corrective maintenance work orders. Some of the
important factors include bushing condition, oil leak, tank corrosion, cooling system, infra-red thermography, grounding, and foundation.
Ali NaderianJahromi, et. al. [70] presentedthe composite HI presented is a very useful tool for representing the overall health of a complex asset such as a power transformer. HI quantifies equipment condition based on numerous condition criteria that are related to long-term degradation factors that cumulatively lead to a power transformer‘s end-of-life. The method‘s multi- criteria analysis approach combines the various factors are combined into a condition-based HI. In addition to the regular test data that have been used in the past, a count of corrective maintenance work orders can be used to evaluate the physical health condition of transformers. Some of the important factors include bushing condition, oil leak, tank corrosion, cooling system, infrared thermography, grounding, and foundation. The relation between HI and probability of failure was developed based on available data and can be applied to similar analysis applications. HI can effectively be employed to provide justification for a capital plan which includes end-of-life asset replacement.
Nick Dominelli, et. al. [73] presentedA computer-based program has been developed to determine equipment health rating of power transformers. This has been used extensively by BC Hydro Generation for more than a year.
Ahmed E.B. Abu-Elanien, et. al. [75] presents a method of estimating the lifetime of transformer insulation based on the specific loading and location of the transformer. The drawbacks of the previous methods for estimating insulation lifetime are highlighted. The new approachincorporates the generation of two artificial histories for a transformer: one for the ambient temperature and the other one is for the load. The solar clearness index and average monthly temperatures are used to generate the artificial history of the ambient temperature. The uncertainties inherent in both the solar clearness index and the average monthly temperatures are considered when the ambient temperature is determined.
KorayUlgenet. al. [78] gives more information about the atmospheric characteristics of solar stations in addition to the degree of solar energy potential of stations and their surrounding areas (Sahin et al., 2001). The following conclusions may be drawn from the present study:
a) Solar radiation parameters (global and diffuse global radiation) were developed in terms of the clearness index in the 2 different polynomial forms
for Izmir (38° 240 N: 27° 100 E), located in the western part of Turkey.
b) The minimum and maximum values of the monthly average daily hours of bright sunshine (S) were recorded to be 3.54 and 12.28.
c) The values of the monthly average-daily clearness index (KT ) ranged from 0.45 to 0.66 averaged for a 5 year period from 1994 through 1998, with an annual average value of 0.55.
d) It was found that the monthly average daily total global solar radiation varies from 5964 kJ/m2 in December to 27154 kJ/m2 in June, while the monthly average daily total diffuse radiation ranges from 2684 kJ/m2 to 10313 kJ/m2 for the same months, respectively.
e) The 2 models presented here were found to be suitable and reasonably reliable for estimating or predicting the ratio Id =I and hence monthly average hourly diffuse radiation, Id , in terms of kT in this location and possibly elsewhere with similar climatic conditions.
Ahmed E. B., et. al. [85]presented the life expectancy of transformers has been proposed.
This method has the advantage of being based on both economic constraints and the technical parameters of the transformer. Transformer stresses are indirectly accounted for by the use of the bathtub model of the failure rate. The new method is, in essence, a reliability-based method that is supported by consideration of the economic factors in transformer operation; it yields the likely number of years remaining in the lifetime of a transformer before it is removed from service. The transformer costs used in the economic analysis are calculated based on the bathtub failure model, while a linear repair model is employed in order to calculate the repair costs.
B. Retterath a, et. al. [88] showed that time- varying failure rates do have an impact on the reliability of the entire distribution system. The failure pattern of each of the components is an important issue and one, which may vary quite differently from utility to utility. The historical information gathered on the failure of the components is a key issue if the failure pattern is going to be accurately predicted. The break-in time, wear-out time and average lifetime of the components have been shown to have an impact on the reliability of the system as well. Other important issues include replacement of aged components and maintenance activities. A reasonable approximation to the time-varying failure rate is the mean value of the failure rate.
However, when additional system conditions are incorporated into the problem, such as weather related events, time-varying repair rates and
maintenance, the time-varying failure rates may result in a more accurate representation of actual system reliability. In addition, to get an idea of the cost of interruption to the customer, time varying failure rates are important.
R. Billinton, et. al. [92] illustrates the application of a Monte Carlo simulation procedure to substation reliability evaluation. The reliability indices obtained by the simulation technique and those calculated by the approximate approach are compared. The reliability indices presented in this paper are the basic substation indices. Other relevant parameters [3] can be calculated from these indices. The relative error between the analytical and simulated indices is less than three percent and is within the basic tolerance associated with a simulation technique. The Monte Carlo simulation method can be used to evaluate reliability indices for substations with both Markov and non-Markova models.
P. J. Balducci, et. al. [93] indicated that an interruption in power supply can result in enormous costs to end-users in the industrial, commercial and transportation sectors. Direct costs include lost production, idle facilities and labor, damage to electronic data, damaged or spoiled product, damage to equipment or customer refunds. Indirect costs can include accidental injuries, looting, vandalism, legal costs, medical costs, insurance costs and loss of water supply. Further, residential customers may experience direct out-of-pocket expenses, including the purchase of wood for home heating, alternative light sources, food spoilage and damage to electrical equipment. The findings of this and all other studies of interruption costs conclude that outage costs vary significantly based on the demand characteristics of the end-user. The analysis presented in this report suggests that interruption costs are highest in the transportation sector at $16.42/kW for a 1-hour interruption, followed by the industrial sector ($13.93/kW) and the commercial sector ($12.87/kW), also for 1-hr.
interruption.
Roy Billinton, et. al. [94] presented the series of approximate methods to assess customer interruption costs due to specified outage events are described in this paper. These techniques require general data which usually are available from most utilities. These approaches are, therefore, more realistic for most utilities to use to estimate the customer interruption costs. The results obtained using the approximate event cost techniques show that the customer interruption costs are dependent on many factors, such as the customer types interrupted, the actual load demand at the time of
the outage, the duration of the outage, the time of day and the day in which the outage occurs. The developed concepts can also be used to estimate the costs associated with a widespread outage event, i.e., a whole city. A customer interruption cost evaluation for a widespread outage situation can be done by estimating the individual feeder outage costs. The aggregated cost then can be obtained from a summation of the costs of all the feeders in the outage area. The individual feeder outage durations in this case may be quite different, depending on the restoration procedure used.
A.A. Chowdhury, et. al. [95] revealed concepts and applications of the reliability cost/ reliability worth methodology in power system resource planning have been illustrated. Value based assessment provides a useful adjunct to testing system performance against planning criteria by verifying that planning decisions provide reasonable value to customers. Value based reliability planning is a valuable methodology for power system planning and design. There is a wide variety of applications using this approach to enhance service reliability. This procedure will help electric utilities to achieve their goal of providing reliable energy service at lowest possible cost that their customers value. The two casestudies considered in this paper are mere illustrative examples which do not represent any real system projects. The concepts, however, are still valid. The value-based reliability planing methodology presented in this paper clearly reveals the significant impact on the cost of consumer interruptions when changes to the supply of various groups of customers occur due to network configuration occurs. As an area network is partitioned into various feeder arrangements to serve groups of customers in which the type of customer being served is unique, the cost of interruptions to these customers can vary significantly between the consumer groups. One objective of utility planning is to minimize the cost of interruptions to a given area and at the same time minimize the cost of the utility providing the degree of system reliability to achieve this result.
Raymond F. Ghajar, et. al. [96] provided a consistent set of data for building cost of interruption models for a given service area and the individual load points of the IEEE-RTS. The utilization of these models in calculating the IEAR‘s at HLI and HLII is also illustrated in this paper. The calculated IEAR values can be used in expansion studies and cost/benefit analysis of generating and composite generation and transmission systems. The proposed cost model and methodology constitute a fundamental addition to
the basic IEEE-RTS data outlined in [1] and permit an analyst to conduct cost/benefit studies of the system. Hopefully, they will also stimulate the development of new applications of quantitative reliability methods.
3. CONCLUSION
This research paper is related to literature survey part for the proposed research to study about the ageing, Insulation properties and the different parameter of the transformer.
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