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Abstract – Dependability rating has been loosely used for power system planning and operations [ 1 ] , since they are capable of integrating assorted system uncertainnesss such as equipment failures every bit good as random fluctuations in coevals capacity or load demand. Meanwhile, power systems are going more complicated, which leads to extremely nonlinear jobs in their dependability rating. The intent of delegating the dependability of a composite power system is to gauge the ability of the system to execute its map of transporting the energy provided to the majority supply points. This paper gives an debut to dependability rating of composite power system. Paper besides includes description of dependability rating parametric quantities at different degrees and different methods for dependability rating of power system.

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Keywords-Reliability, Power System, Monto Carlo Simulation

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For system analyzers, system contrivers and interior decorators the system dependability is really important key point for analysis. It is because of increasing complexness of systems, cost fight, to hold alternate designs of system, cost benefit analysis and to analyze effects of operations and care processs As in today ‘s scenario the power system is acquiring more complex either dye to grid connexions or because of smart grids hence it is more complex to measure dependability. The degree of satisfactory dependability or unsatisfactory dependability of system is may be the consequence of single constituent or it may be the consequence of the whole system. The map or public presentation of single constituent and of whole system and its failure frequence decides the dependability of system. The basic definition of dependability besides says that “ Reliability is the characteristic of any device which shows its capableness to execute its equal map under given conditions ” . From the definition once more it is clear that dependability is a map of public presentation characterstic of a device. The failure of even a individual device may impact the dependability. So, there are two chief factors which affect the dependability.

System Reliability

System Capability


System Adequacy

System Security

System capableness is about to fulfill the burden demand and to make this it is required to hold presence of sufficient resource at bring forthing Stationss. For this the bring forthing capacity of station is ever maintained above extremum burden demand and is done by calculating the burden by system interior decorators. The system adequateness besides must includes the planned or unplanned outages of bring forthing units or other equipments which forms the system.

The system security is besides a map of system dependability. Here the security term stands for the capableness to last under any status. The fluctuation in normal runing status may be at that place because of fluctuation in lading conditions, either it may be due to over lading or under lading. There may be other parametric quantities which can impact the dependability of system viz. current fluctuation, frequence fluctuation etc. For a secure system all these parametric quantities must stay within allowable bounds.

Time period is besides one of the standards to mensurate the dependability. Reliability decreases as clip move towards t = a?z i.e. dependability is a diminishing map of clip. It is because after a clip period the aging consequence after ruling over the public presentation of device.

As we all know that the complete power system consist of three chief divisions i.e. coevals, transmittal and distribution. For dependability rating of system it ‘s rather hard to measure dependability of each and every device ( as dependability is related to equal public presentation of device ) separately. To avoid this complication, dependability rating is done for complete sytem by several methods. Now yearss the dependability rating is started on big graduated table i.e. for composite power system. In this method the dependability rating of each division i.e. coevals transmittal, and distribution is performed normally for complete system. .

Reliability rating for bring forthing Stationss: the dependability at bring forthing station can be the affect of independent outage of device/ bring forthing unit or may be the consequence of fluctuation or inaccessibility of resources. The dependability at bring forthing station varies harmonizing to mechanism applied for electricity coevals. The attack to to bring forth electricity can be thermic, hydel, air current, solar, atomic or it may be intercrossed attack to bring forth electricity. Karki et Al. [ 1.A ] has done the dependability rating for a intercrossed bring forthing station by using Monte Carlo simulation ( MCS ) . In this the dependability was evaluated utilizing IEEE RTS & A ; as a intercrossed combination they use combination of air current and hydro power station. Familial algorithm is one of the competent methods to measure dependability which gives out the optimum dependability consequence. Wang et Al. [ 2A ] find outs most common ground for failure and hence evaluates dependability. The work was carried out by using Genetic Algorithm engineering. Another fact associated with fluctuation in dependability is system economic sciences. The less dependable system effects more on the economic sciences of the system every bit good as on the consumer besides. R. Billinton, W. Zhang [ 5A ] discussed about dependability indices which was holding relation with cost so as to better economic sciences of system with maximal optimized dependability consequence. . As discussed earlier that aging consequence is besides one of the major ground which is involved in changing the dependability of system. Wenyuan Li [ 19 ] and Hagkwen Kim, Chanan Singh [ 20 ] has discussed the consequence of aging standards of reliability.. In this paper subsequently there is treatment about one of the dependability rating index which is chance of failure and in this dependability index the engagement of the failure protective devices are considered. The same was done by Xingbin Yu [ 22 ] . In this the system dependability was evaluated by sing the failure of the protection system which is considered to be one of the biggest grounds for failure of the system.

A proper put to deathing system may acquire perverts and losingss dependability even because of failure of a individual device. A constituent or device is considered to be on outage when it is unavailable to execute its proposed map. A component outage, nevertheless, may or may non do burden break. Independent outage events including the outage of two or more constituents are referred to as overlapping outages. The basic constituent theoretical account used in these applications is the two-state representation shown in Figure 2, in which the constituent is assumed to be either up or down. The rate of going from the constituent up province to its down province is the component failure rate I» . The Restoration of the constituent to its operating province is denoted by another passage rate, termed as the component fix rate I?.. The two parametric quantities, I» and I? can be expressed in footings of Mean Time To Failure ( MTTF ) and Average Time To Repair ( MTTR ) severally, where, MTTF is the reciprocal of I» and MTTR is the reciprocal of I? .

Reliability rating for transmittal system: The industry for conveying the electrical energy besides plays an of import function in accomplishing he dependability of system. In this peculiar portion the quality of equipment like music directors, dielectrics, and their withstanding capacities for perturbation decides the dependability of system. Sometimes weather or natural catastrophes besides are few parametric quantities which may impact the dependability.

As really normally multiple circuit transmittal lines are used over worldwide for transmittal of electrical energy. Lie et Al. [ 3A ] evaluated dependability for same construction utilizing analytical method followed by MCS. Choudhary et al. [ 4A ] has done a quantitative dependability appraisal of transmittal system. Its a necessary pre measure of system planning. The another technique to find dependability is deterministic standards but it lacks behind quantitative standards in footings of truth. Apart from this, sometimes dependability has consequence of and on reactive power besides. The reactive power is besides necessary in power system. Failure or mis-operation of reactive power beginning may take to either extra or deficit of reactive power which straight affects the dependability of power system. The consequence fluctuation in dependability may non be in the signifier of power outage but may be in the signifier of extra losingss or hapless power factor or hapless power evaluation. Peng Wang and et al [ 21 ] discussed about new dependability indices which are used to cipher reactive power deficit.

So, in a nut shell manner we can state that in today ‘s clip tonss of stairss are taken to do the system capable with an increased rate of security. One of the methods to better dependability is grid connexion and as a promotion in this the latest technique is smart grid. Other so this although there are many techniques to measure the dependability ( few of them are discussed shortly after this ) but in all the methods on the basic side we need to cipher the dependability indices. There are many dependability indices which can be evaluated for dependability rating. For illustration these are like loss of load chance i.e. [ LOLP ] loss of load outlook ( LOLE ) & A ; expected energy non supplied ( EENS ) etc.

II. Reliability Indices

Under wide section the dependability indices can be classified under two classs: [ 24 ]

I ) Deterministic indices

two ) Probabilistic indices

Deterministic indices show the postulated conditions. They do non demo the system dependability and are besides non responsible for system dependability. Hence for be aftering these systems are holding really limited usage.

Different deterministic dependability indices are:

Percent modesty border: This shows the surplus of installed bring forthing capacity over one-year peak burden.

Reserve border in footings of largest unit.

These parametric quantities do non reflect informations like unit size and outage rate etc.

Probabilistic indices show the dependability of system and are necessary portion for dependability rating. These parametric quantities can besides impact the system dependability.

Different probabilistic indices are:

Loss of burden chance ( LOLP ) : This LOLP may be defined as chance of loss of burden transcending the available coevals capacity.

Loss of load outlook ( LOLE ) : This dependability index shows the clip when insufficient bring forthing capacity is at that place to function peak burden.

Expected unserved energy or Expected energy non supplied ( EENS ) : This index measures the expected sum of energy which is failed to function or provide to consumer because of deficit in basic energy supply.

For composite power system dependability indices are categorized into system based indices and burden point indices. These dependability indices find outs their application at unlike topographic points. System based indices provide an grasp of planetary system adequateness and can be used by contrivers and directors for comparing the adequatenesss of different systems. However, these indices can non be used to measure the adequateness of peculiar system burden points. Therefore, burden point indices are required to measure the dependability of burden points, which is utile for benchmarking burden points and placing weak countries in the system. Load point indices can be used to place the part of each burden point to bulk system undependability.

The system based dependability indices are:

Bulk power break index

Average figure of burden curtailment

Average energy curtailment

Average figure of electromotive force misdemeanor

Maximal system burden curtailed under eventuality status

Maximum energy non supplied under eventuality status.

The burden point indices include the rating of:

Probability of failure

Failure frequence

Average of electromotive force misdemeanor

Average burden curtailed

Expected energy non supplied

Average continuance of burden curtailment

With the aid of above available dependability indices the dependability of the composite power system is calculated, this computation will be done with the aid of any one of the method of dependability rating. To measure dependability there are few more dependability indices that are used to weigh up dependability. These dependability indices are:

SAIFI ( System Average Interruption Frequency Index ) ; Measures the mean frequence of breaks per client by holding a ratio of entire breaks to client to the figure of clients in system.

SAIDI ( System Average Interruption Duration Index ) ; Measures the mean clip that all clients are interrupted by holding ratio of client break entire period to the entire figure of client in systems.

CAIDI ( Customer Average Interruption Duration Index ) ; Represents the mean clip required to reconstruct service

CAIFI ( Customer Average Interruption Frequency Index ) ; It is the mean figure of breaks considered to hold a continuance, experienced by clients who had at least one break during the period.

MAIFI ( Fleeting Average Interruption Frequency Index ) ; Tracks the mean frequence of fleeting breaks, typically defined as less than five proceedingss.

The above discussed last five indices give information about the continuance and frequence of the system.

III. Reliability rating for composite power system:

As the subject of paper suggests we are concentrating on the dependability rating of composite power system So a composite power system can be divided in many runing provinces in footings of the capacity available to carry through demand topic to the satisfaction of security bounds ( line flows and voltage bound ) . Hence, the rating of a dependability index for a composite system is really much computationally demanding. The three basic functional zones are those of coevals, transmittal and distribution as shown in figure-1.

These functional zones can be combined to organize hierarchal degrees ( HL ) for carry oning system dependability analysis [ 4 ] . Reliability appraisal at HL I is concerned with the coevals installations [ 6 ] . Reliability appraisal at HL II considers the coevals and transmittal as a composite system. The consequence of burden growing, constellation alterations and installation add-ons can be studied and dependability indices can be evaluated for the overall system, every bit good as for the single coachs [ 7-10 ] . All three of the functional zones are involved in an HL III appraisal. The chief aim of an HL III survey is to carry on adequateness appraisal at consumer burden points [ 4 ] .

III.A Composite System Reliability Evaluation Methodology

There are two chief methods which are widely used for dependability rating i.e.

Analytic Methods

Computational or Simulation Methods

Both attacks are able to cipher dependability indices. Both methods use the adequateness & A ; security of a system province utilizing a power flow methods for ciphering dependability. AC burden flow or DC burden flow [ 8-9 ] may be used depending upon the demands of the survey.

1. Analytic Methods can be divided in to

Contingency Enumeration Methods ( CEM ) ,

State Enumeration Methods ( SEM ) and Markov Cut Set method. One more mistake analysis method is fault tree analysis method and minimum cut set method is one of the portion or we can state its the first measure of mistake tree analysis method to measure dependability. Based on the mathematical analysis in all analytical methods a mathematical theoretical account is prepared and by and large all theoretical accounts are based on Markov theoretical accounts. Yong Liu & A ; Singh, C [ 23 ] proposed a method to measure dependability of composite power system. In that they used Markov cut set method which was based on DC optimum power flow. The minimum cut set is analysed utilizing this DC optimum power flow which was limited upto a peculiar order and so they used Markov cut set metod to cipher dependability indices. Yong Liu & A ; Singh, C [ 26 ] once more use minimum cut set method attack as analytical methodological analysis to measure dependability of composite power system but for a short continuance of clip. Cost outage is besides one of consequence of dependability. Choi, J.S. and et Al [ 32 ] usage analytical attack to find the outage cost in a composite power system as a consequence of dependability. To measure this cost outage they use the analytical method utilizing effectual burden continuance curve.

2. Computational Methods can be divided in to

Monte Carlo Simulation ( MCS ) & A ; Artificial Intelligence ( AI ) based on the loop technique. Monte carlo method can be applied on clip changing burden to measure dependability. For demoing the clip changing burden burden continuance curve can be used. Monte carlo itself consist of consecutive technique and non consecutive methods such as province sampling and province passage sampling.

Monte Carlo simulation methods estimate the indices by imitating the existent procedure and random behavior of the system. The method, hence, treats the job as a series of experiments. In general, if complex operating conditions are non considered and/or the failure chances of constituents are little ( ie. , the system is really dependable ) , so analytical techniques are normally more efficient. When complex operating conditions are concerned and/or the figure of terrible events is comparatively big, Monte Carlo methods are frequently preferred [ 5 ] . The basic sampling process can be conducted by presuming that the behavior of each constituent can be categorized by a unvarying distribution under { 0,1 } . In the instance of a two-state constituent representation, the chance of outage is the constituent forced inaccessibility. It is besides assumed that constituent outages are independent events. The basic information obtained by this constituent outage is merely inaccessibility of constituent. The other information by this type of theoretical account is handiness of constituent. This gives merely mean informations information. If we increase the information by increasing the no of provinces than it is traveling to be rather complex. To take this complexness S. A. Khaparde, K. Bhattacharyya [ 30 ] gives the combination of fuzzed loagic and nervous web to measure dependability with more accurate power system theoretical account and more accurate dependability indices. A. R. Abdelaziz [ 31 ] besides evaluate dependability on fuzzy based power system. Jaeseok Choi et Al [ 27 ] nowadayss a construct of composite power system effectual burden continuance curves utilizing monte carlo method. This effectual burden continuance curve is of import for coevals and transmittal both. The dependability indices for composite power system are calculated utilizing this effectual burden continuance curve with monte carlo method. Sometimes the burden is wholly curtainless and for such type of jobs fuzzed logic can be used. J. Tome Saraiva et Al [ 28 ] see the uncertainness in burden and specify it by fuzzed Numberss utilizing monte carlo algorithm. This fuzzed engineering is specially used for long term planning where there is uncertainness in burden in future. J. He, Y. Sun, L. Cheng et Al used a intercrossed method to measure dependability. They use the combinable advantage of province numbering method and monte carlo simulation. The advantage of this combination is that SEM is used to work out lower order eventualities and MCS for higher order eventualities. As such there are tonss of computational methods but out of those computational methods familial algorithm is once more one of the good computational methods which makes the dependability rating easier and reduces the attempts as compared to analytical methodological analysis. Samaan, N. ; Singh, C. [ 33 ] used familial algorithm method to measure dependability. Familial algorithm is a computational method which gives the consequence holding resemblance with the existent system consequences. To better the truth we can increase the figure of algorithm coevalss. In this the existent dependability indices for complete system are calculated utilizing dependability indice informations for each burden individually. The GA method takes the failure position of each burden individually and so combined it to acquire the one-year consequence. Lingfeng Wang ; Singh, C. [ 34 ] used this GA method in analogue to rush up the computational procedure. All of the above described methods for dependability rating are used on different trial systems. Most of them are used on IEEE dependability trial system. The IEEE dependability trial system ( RTS ) is of two versions.RTS-79 which was the first trial system of IEEE. RTS-96 has introduced as an advanced version of dependability trial system from IEEE. In this there are some alterations with regard to rating methodological analysiss [ 35 ] . R. Billinton besides developed a dependability trial system which is known as RBTS i.e. Roy Billinton trial system. This trial system is besides used in many research works to measure the dependability of system.

IV. Recognition

Its quite hard to show thanks in words. I would wish to thanks all my well-thought-of modules for their cherished counsel and clip. I want to thank all net lovers who are continuously updating their work on cyberspace which works as a way demoing taper for us to take our work upto a new finish.

V. Conclusion

This paper summarizes the assorted facets for the dependability rating of composite power system. This introduces the assorted dependability indices used for dependability rating. The burden point indices like LOLP, EENS etc. play an of import function in dependability rating of composite power system. For dependability rating as trial systems we have IEEE RTS and RBTS. IEEE RTS 96 is one of the advanced trial system with different rating methods as compared to IEEE RTS 79. For rating Simulation and analytical methods are available. Simulation methods are considered to be superior because it reduces the computational clip as compared to analytical methods every bit good as it gives more accurate system. Monte carlo is one of the good simulation technique for big systems. GA is besides a good option for dependability rating. Fuzzy logic is besides in usage for dependability rating with unpredictable burden conditions.

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