REVIEW Open Access

Protection coordination in distributionsystems with and without distributedenergy resources- a reviewManohar Singh

Abstract

Emission of greenhouse gases and depletion of fossil fuel reserves are two key drivers, which are forcing themankind to generate the future energy demand from the renewable energy resources. These resources aregenerally distributed in nature and are directly integrated at distribution levels. Increasing penetration of thedistributed energy resources in distribution power networks creates additional operational and control issues.These are mostly regulatory, economical load dispatching, power quality and protection issues.Generally power distribution systems are protected with the help of dedicated over current based protectionschemes. But increasing share of distributed energy resources penetration in electric utilities poses a seriousthreat to the existing protection coordination schemes of the distribution systems. Distributed energy resourcesconnected distribution networks become interconnected in nature and protection coordination schemes, which aredesigned for unidirectional flow of fault currents become ineffective/non-functional.Therefore, new protection coordination schemes are required for providing the adequate protection coordination fordistributed energy resources connected electric power networks. In the available literature, the protection coordinationschemes for radial distribution systems and developments in the area of protection coordination are discussed indetail. A thorough review for all these protection coordination schemes for distribution systems with and withoutdistributed energy resources is done in this review article. It includes the analytical and artificial intelligence basedtechniques application for coordination of protective relays in the distribution systems. The limitations and researchgaps in the area of protection coordination schemes are also presented in this review article.The aim of this research paper is to bring all the available research in the area of relay coordination on one platform, sothat it will help the emerging researcher to identify the future scope of relay coordination application for distributedenergy resources connected distribution systems.

Keywords: Relay coordination, Distributed energy resources, Artificial intelligence, Adaptive relaying, And renewableenergy resources

1 IntroductionRenewable energy resources (RES) are the promisingsources of energy for future energy demand in most ofthe countries in the world [1]. These resources are sitespecific and their size varies from few kilowatts to mega-watt depending upon the availability and location. Gener-ally power generated from them is not bulk, as compareto thermal and nuclear power houses. Therefore, they donot require long power transmission corridors for powerevacuation from generating units to the load centres. This

results in less investment in long transmission circuits andrequires low relatively cost local distribution circuits forsupply of power in the local areas.In a country like India, these are emerging as potential

sources of supply of electric energy for rural electrifica-tion, where atleast 30 million people are yet un- electri-fied in the remote rural areas [2]. The scenario is mostlytrue for other developing countries as well as for underdeveloped countries across the world. It is learned alsothat RES are emerging as major source of power in fewEuropean and other developed countries to cut the

Correspondence: manoharsingh.cpri@nic.inCentral Power Research Institute, Bangalore, India

Protection and Control ofModern Power Systems

© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made.

Singh Protection and Control of Modern Power Systems (2017) 2:27 DOI 10.1186/s41601-017-0061-1

greenhouse gases emission from the conventional powerplants [3].The RES are distributed in nature and generally inte-

grated in the distribution networks and are known asdistributed energy resources (DER) [1]. Depending uponthe size of DER, their penetrations in the distributionsystem can be classified as either large scale penetrationor small scale penetration. When they are of megawattin size, they are generally integrated with the nationalgrid. They may result in change of configurations oftransmission/distribution networks due to their inter-mittent nature. Direct connections of DERs in thedistribution systems have both merits and demeritsfrom power economics, operation and control pointof view. Operation, control and protection of distribu-tion system become very complicated and challengingfor the protection engineers, when DERs are directlyconnected with them [4].Protection schemes are provided for distribution sys-

tems for quick disconnection of faulty section from theremaining healthy portion of power system. Main aim ofprotection schemes is to restrict the fault spread. Nor-mally distribution lines and feeders are protected by overcurrent relays [5]. Over current relays are used as primaryas well as in backup protection relays for the distributionnetworks. However, their slow operating speed is not adesirable feature for their application as primary protec-tion schemes for sub transmission systems. For sub trans-mission systems, distance relays are ideal choice forprimary protection and over current relay are used in backup protection relays.For an interconnected power networks, for each fault

location on a line, relays are installed at near end busand far end bus. The relay which is supposed to clearthe fault first is known as primary relay. In over current

relay coordination studies, failure of one over currentrelay is backed with other over current relays. The relayswhich are operating when the main relay fails to operateare known as backup relays [6]. The time-inverse curvesof for an over current to over current relay coordinationare shown in Fig. 1 for near end (F1) and far end (F2)faults.For fault at F1 and F2, there should be sufficient

coordination time margin (CTI1) between primary relayand backup relay time inverse relay characteristics. Theoperating time equation of a standard time inverse overcurrent is given in (1) below.

toc ¼ α�TDSIfIp

� �β−1

ð1Þ

Where toc operating time of over current relay, TDS istime dial setting, If is fault current, Ip is relay pickupcurrent and α and β are relay parameters as IEC stan-dards [7].Injections of DER jeopardize the existing protection

coordination schemes for the distribution system. Impactdepends upon number, size, type and location of DER inthe distribution system. Moreover, as the location of DERin distribution system varies, the configuration of distribu-tion systems also changes. Generally, the distributionsystems are radial in nature and over current based pro-tection schemes are set for unidirectional flow of faultcurrents. Penetration of DER usually causes meshed con-figuration of distribution systems and on majority of dis-tribution feeders, fault current flows in both the directions[4]. The protection schemes which are designed for uni-directional flow of fault currents fails to provide theadequate protection coordination when DER power isinjected in the distribution systems. Moreover, there is a

Fig. 1 Over current to over current relay coordination

Singh Protection and Control of Modern Power Systems (2017) 2:27 Page 2 of 17

requirement of additional number of direction over currentrelays. The new settings of over current relays dependupon the location of new incoming DER in the distributionsystems. In addition to these requirements, the impact mayalso reach to upstream transmission lines connected withdownstream DER connected distribution systems. Undersuch operational conditions, the distance relays in-stalled on the transmission line may result in under-react operation [8].Generally, the distribution system operators are not

willing to change the relay settings for each new incom-ing DER or any change in network topology. But fromprotection point of view, each relay requires new relaysettings whenever the fault level changes in the network.The small scale penetration is also known as microgrid

operational mode [9]. These are small size of off gridDER, generally feeding power to the local distributionnetworks. The main sources of power in such systemsare photovoltaic based systems, which have limited faultfeeding capabilities. The discrimination of fault currentfrom load current is very complex in such distributionsystems. Protection coordination and fault detection fora microgrid mode of operation is a complex protectionjob. In this review paper, new relay coordination tech-niques are discussed for protection of distribution systemunder larger scale and small scale penetration of DER.The available literature in the field of protection coordin-ation studies is presented in different sections in thisarticle. At the end of this review paper, author has pro-posed various research gap and future scope of work forextending the research in the area of the power systemsprotection with renewable penetration.

2 Protection coordination studies for radialdistribution systemsThe different methods where developed for performingfor protection coordination for transmission and distri-bution systems. These are classified based on the tech-nique used in them, to solve the relay coordinationproblems. These can be broadly categorized as under.

2.1 Curve-fitting techniquesThe time inverse-relay characteristics of over currentrelays are mathematically modelled using curve-fittingtechniques. From these modelled time-inverse character-istics, time dial settings (TDS) and operating time of theover current relays are calculated. These methods beganwith a functional form such as polynomials function,which has the potential of approximating the publishedrelay curves. Thereafter, the functional coefficients aredetermined by using computer, which best fits to thecurves. Developmental work using these techniques upto 1989 are available in IEEE Committee report [10].

Curve-fitting techniques are simple techniques forsetting of the relays, but they are inaccurate for currentssetting less than 1.3 times pick-up current.

2.2 Graph theory techniquesExtensive research had been done on the application ofgraph theory for protection coordination studies [11–16].Network structures are analysed by determining the breakpoints for relay coordination studies [15]. In graph theoryapproach, the relay coordination starts from the certainset of relays known as break point relays (BPS). Properselection of BPS is very crucial for quick convergence ofrelay coordination problems. Graph theory was success-fully applied for formulation of relative sequence matrix(RSM) [16, 17] and RSM later on used for determining theminimum break point relays as well as primary/backup(B/P) relay pairs.More systematic approaches based on the graph the-

ory also are reported in [18, 19] to determine B/P relaysand RSM using only fundamental loop matrix and someother arbitrary matrices. In [20], a new graph theorybased approach for calculating the loop matrix is reported.This technique is quite simple, fast and requires only halfnumber of network the loops. Therefore, the need of gen-erating all loops were eliminated in this technique [21]and only fundamental circuit matrix is sufficient to gener-ate all the B/P as well as BPS. A method based on thebranches of the network was also reported in [22] for de-termining the minimum BPS. A heuristic based approachwas also reported in the literature for finding the mini-mum BPS [23]. To reduce the complexity, anothermethod has been presented in [24]. This method claimsthat, it gives the least number of break points and wholemulti-loop network become a radial network.Graph theory techniques are quite useful for solving

the relay coordination for interconnected distributionsystems, but computation times for solving the overcurrent relay coordination problem is being exponentialfunction of network dimensions and a lot of unutilisedintermediate data is generated.

2.3 Analytic methodsIn [25, 26], analytical based methods for identification ofcritical fault points for solving the relay coordinationproblem were discussed. An approach based on the“interior point primal-dual algorithm” was discussed in[27] where additional constraints were imposed by distancerelays and breaker failure on relay coordination studies.Gradient search based technique was also applied success-fully for optimization of relay coordination problems formid line faults [28]. These techniques generally take largenumber iteration to compute the relay settings and fails to

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give the optimal relay setting for interconnected power net-work. However analytic methods are very effective for ra-dial systems.

2.4 Optimization techniquesThe relay coordination problems solution using analyticmethods was very time consuming for complex and bigsize power systems. However, proper selection of BPSrelay helped in reducing the convergence time of therelay coordination problem. Application of optimizationalgorithms for solving the relay coordination problemshad eliminated the need of BPS relays. However, graphtheory is still used for formulation of the RSM for identi-fication of B/P relay pairs. The optimization methodsused for relay coordination can be broadly classified intwo groups as under.

2.4.1 Mathematical based optimization methodsApplication of mathematical based optimization methodsfor relay coordination was first time proposed by A.T.Urdanta et al. in 1988 [6]. In that paper, two techniqueswere suggested for solving the time inverse over currentrelay coordination problem. First technique was applicablefor fixed network configuration and second one was for avariable network configuration. The optimization prob-lems were formulated as a minimax problem for multiplenetwork configurations. In [29] a methodology based onthe linear programming and considering the definite timebackup relays for optimal relay settings was presented.Linear programming methods were simple and easily con-verge to optimal solutions. But they were only helpful foroptimal selection of TDS of over current relays. Designerexperience was used for selection of plug settings (PSs) ofover current relays in relay coordination problems.Application of simplex, dual simplex, two phase sim-

plex and big-M (penalty) methods for relay coordinationwere also reported in [30]. Another technique wasproposed in [31], in which linear programming was usedto optimize the TDSs and PSs was optimized using non-linear programming. Linear programming approach basedon interval analysis concept was also used for solving thedirectional over current relays (DOCRs) coordination prob-lems. These techniques also considers the effect of networkuncertainty in defining the relay coordination problem[32, 33]. In [34–36], linear programming methodswere discussed in which constraints relaxation was alsoconsidered for optimal coordination of over current relaysfor interconnected power networks.Non-linear based optimization (NLP) techniques were

also applied successfully for optimal selection of TDSsand PSs in the relay coordination problems. Nonlinearoptimization based on General Algebraic modelling(GAMS) and sequential quadratic programming (SQP) [37]

are reported in the literature. Application of random searchtechnique (RST) for solving the relay coordination prob-lems are also discussed in [38]. In [39], an advanced relaycoordination method for over current relays using non-standard tripping characteristics was applied successfullyfor solving the relay coordination problems.

2.4.2 Artificial intelligence based optimization techniquesOptimization techniques based on artificial intelligenceare reported in literature. These techniques are used forsolving/obtaining the global optimal settings of relays forinterconnected power networks. Application of geneticalgorithm (GA) for relay coordination has been reportedin [40]. For interconnected power networks, large num-ber of selectivity constraints, may cause the infeasiblesolution of relay coordination problems. For such relayprotection coordination problems, pre-processing of theselectivity constraints is done to remove the least efficientselectivity constraints from the efficient selectivity con-straints [41]. The least effective selectivity constraints areidentified with the help of area called possible solutionarea (PSA) for each relay pair, i.e. primary and backuprelays. Continuous genetic algorithm (CGA) techniqueapplied for optimum coordination of DOCR in a ring feddistribution system [42].A hybrid GA-NLP based approach is also implemented

for determination of optimum values of TDSs and PS ofDOCRs [43]. Evolutionary programming is a stochasticmulti-point searching optimization algorithm and is cap-able to escape from local optimum solutions. A hybridGA based method, was introduced to solve the relay co-ordination problem for different network topologies[44]. Hybrid GA based solution is also used to improvethe convergence of the of relay optimization problems[45]. In the relay coordination studies, it is learned thatthere is no upper limit of the CTI and fitness function isoptimised without putting any upper limit of CTI [46].This is one of the limitations seen in the existing relaycoordination studies and a solution is proposed by theauthor in [47]. Additional selectivity constraints are cre-ated to put an upper limit on the CTI. Another methodusing GA applied for over current relays coordination,considering the priority for constraints is applied forsolving the optimal setting of DOCRs.Particle swarm optimization (PSO) algorithm was pro-

posed to calculate discrete values for the PSs [48]. A modi-fied form of PSO for the optimal coordination of DOCRswas also reported in [49]. Laplace Crossover particleswarm optimization (LXPSO) had been applied success-fully for optimal setting of over current relays [50–52].Modified differential evolution (DE) algorithm based tech-niques are also reported in [53–55] for optimal setting ofDOCRs. In [56], non-heuristic method, for solving relay

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coordination problem without formulation of objectivefunction was presented. While in [57], an efficient hybridalgorithm based on Shuffled Frog Leaping (SFL) algorithmand LP was applied for solving relay coordination prob-lems. In that paper, a hybrid approach based SFL and LPwas used as global and local optimizers respectively.Seeker algorithm which is based on the act of humansearching was also reported in [58] for relay coordinationapplications. In [59, 60], artificial bee’s colony (ABC) andant colony algorithms were traced for solving therelay coordination problems. It was claimed that thesealgorithm leads better convergence of relay coordinationproblems as compare to PSO. In [61] biogeography-basedoptimization (BBO) algorithm was applied for solving therelay coordination problem.Mathematical based optimization methods are suitable

for radial power networks. For meshed power networks,the number of relays and accordingly the combinationof relay coordination pairs are quite large. This results increation of large dimensional constrains matrix. Sincethe relay coordination problems are non-convexity infitness function and constrains. Since mathematical basedoptimization programming has tendency of trapping inlocal minima for non-convex problems. This limitationhad led the researchers to explore the application of artifi-cial intelligence based optimization algorithms for obtain-ing the global minima solution for relay coordinationproblems. The global optimal solution/setting are ob-tained after properly tuning the optimization parametersof artificial intelligence based algorithm.

2.5 Fuzzy and neural network based methodsApplications of few fuzzy and neutral network basedmethods were also traced in the literature. These methodswere used for modelling the over current relays operatingcurves [62]. The feed forward multi-layer perceptronneural networks were used for calculation of the operatingtimes of over current relays for various TDS. In [63], anautomated fault location method was discussed which wasdeveloped using a two stage radial basis function neuralnetwork (RBFNN). In this method, first RBFNN deter-mines the fault distance from each fault source and sec-ond RBFNN identifies the exact faulty line. Multi-layerperceptron (MLPs) neural networks were also used fordetermination of faults in the distribution networks. Ap-plications of neural network for protection of distributionnetworks in DER connected scenario were also discussedin the [64].

2.6 Adaptive relaying based methodsRelays are set for a predefined network configurations.Protection engineers select the settings of relays settingsafter analysing all the critical power system conditions.

In reality, it is not only difficult to identify and analyseall critical operating conditions of power system inadvance. But it is also difficult to determine relay settingsthat will be optimum for all power network operating con-ditions. However, with the development of micro-processor based relays, now scenario has been changed.Micro-processor relay can store, collect information,handle complex logic and communicate with other relaysand control devices. This feature of micro-processor basedrelays had made it possible to continuously monitor thestate of a power system, analyse it in real-time and changethe relay settings to as per the prevailing networkconditions. In [65, 66], an adaptive relaying conceptsfor protection of transmission lines were discussed indetails. In [66, 67] software based adaptive relayingimplementations for transmission line protection werediscussed. Figure 2, shows the various functional ele-ments of adaptive relaying.Continuous monitoring of network topology and line

loading are sensed in this protection scheme. The requiredsettings of over current relays are updated in onlinemanner as per variation in fault current levels seen byrelays during changing network conditions. In [68], design,implementation and few remedial measures for adaptiverelaying failures were demonstrated using a relay hard-ware model implementation for a power system in Re-search Laboratory of University of Saskatchewan. In thisdesigned scheme, the adaptive relaying scheme respondsreliably to change in load currents, expected fault currentschange and system topology changes. Adaptive relayingscheme takes into consideration that status of a powersystem changes in reality and thus the settings of relaysneed to be changed in on-line mode to accommodatethese network changes.An on-line relay coordination algorithm based on

linear programming technique was reported in [69]. In[69, 70], adaptive optimal methodology based on a modi-fied PSO technique were applied for selection of overcurrent relay settings during on line mode according asper the prevailing network topology. The pre-solution andfiltering simplification techniques were used prior to theapplication of linear programming algorithm for reducingthe size and complexity of system [27]. The interior pointbased approach reaches close to the vicinity of the finaloptimal result hardly in only one or two iteration. There-fore this protection scheme is very suitable for the onlineapplication in adaptive relaying protection.The adaptive protection coordination approaches have

promising future application for DER connected distri-bution systems. In these networks, the fault levels areintermittent and continuously changing as per connec-tion of DER in the network. The generalised summary ofdifferent techniques used for protection coordination ofdistribution systems are listed in Table 1.

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Table 1 Summary of different techniques used for protection coordination of distribution systems without DER penetration

Technique Main feature Merits Demerits

Curve fitting [1] Time inverse operating characteristicsare generated for various types of linear& non-liner functions relay timeoperating curves.

Only method was available at that time. Poor accuracy

Graph theory [3, 5, 7] Break point relays are identified Proper selection of break point lead toconverged solution of relay coordinationproblems.

Selection of break point is critical

Analytical method [16–19] Gradient, lagrange multiplier and otherclassical problem formulation areformulating relay coordinationproblems.

Mostly applicable for radial distributionsystems.

Requires large no. of iteration andinitial guess is essential forconvergence of the solution ofproblem.

Linear optimizationBased Techniques [22, 23]

Relay coordination problem isformulated as linear programmingproblem.

Helpful for optimizing only TDS PS are selected based on theexperience of the designer/operator

Non-Linear optimizationBased Techniques [30]

Relay coordination problem isformulated as non-linear programmingproblem

Both TDS and PS are selected optimally. Since relay coordination problemare non-convex, therefore there ischance of local minima trap.

Hybrid optimizationtechniques [38, 40].

Both analytic and optimization methodare applied.

Capable to solve the relay coordinationproblem for big interconnected systemsand global optimal solution can be easilyachieved.

Works for fixed network topology.

Fuzzy & neuro basedoptimization [55]

Concept of fuzzy and training ofneurons is extended for protectioncoordination problems.

Effective protection coordination fordifferent network pre-identified networktopologies.

Fails for respond when newnetwork topology comes inexistence during operationalconditions.

Fig. 2 Adaptive relaying scheme

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3 Protection coordination schemes forsub-transmission systemsSluggish operating speed of over current relays does notfavour their application in main protection for sub-transmission power networks [71]. In such power net-works, the distance relays are used as main protectionrelays and over current relays are used as backup protec-tion relays. The time inverse over current relay charac-teristics and different zones settings of distance relaysare shown in the Fig. 3.Critical points F2, F4 and F5 correspond at which the

selectivity margins (CTI2 and CTI3) between distancerelays and over current relays are at minimum. Theliterature reported research work done for combinedistance and over current relay coordination is discussedas under.In [72], an algorithm for distance and over current

relays coordination is discussed which uses GA as solver.In this article, the fitness function for optimal combinedistance relays to over current relays coordination is for-mulated by adding new terms to the time inverse overcurrent relay coordination fitness function as discussedin [6]. Additional terms in fitness function of time inverseover current relay coordination problem, results in opti-mal selection of zone-2 for distance relays. The varioustime-inverse over current relay characteristics are consid-ered for each back up over current relay and the best ofthem are selected using GA as a solver. In [73], anothermethod was also discussed for optimization of zone-2operational time of distance relays. This method providesbetter backup protection and higher line protection cover-age as compare to other methods.Another method for automatically determining the

optimum timing for Zone-2 of distance relays with

directional over current relays had been discussed in [74].In [74], optimal coordination between distance relays anddirectional over current relays for a series compensatedlines had been discussed. In order to solve this non-linearand non-convex combine distance and over current relaycoordination problem, a modified adaptive particle swarmoptimization (MAPSO) was used in [75].The downstream penetration of DER from distribution

systems may affect the coordination between distanceand over current relays at sub-transmission level. Theabove discussed techniques mainly considers the fixedzone-2 operating time of distance relays and standardtime-inverse characteristics for backup over currentrelays. These fixed type of relay characterises for distanceand over current relays may fail to maintain the propercoordination between distance and over current relaysduring downstream in-feed from DER at distributionsystems. The brief review of main points of otherprotection coordination for sub-transmission systemsare given in Table 2.

4 Protection coordination for distribution systemswith DEROne of major problem associated with DER connecteddistribution systems is the design of proper protectioncoordination schemes. It has been observed that, clas-sical protection schemes of radial distribution systemwill not work reliably for DER connected distributionsystems. Therefore, new protection schemes are requiredfor protection of DER connected distribution systems,which will provide reliable protection during grid con-nected and islanding mode of network operation.The protection coordination problem in DER connected

distribution systems may be classified as large scale and

Fig. 3 Distance to over current relay coordination

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small scale penetration protection impacts. The large scaleimpact is distributed and may spread to upstream trans-mission network. The impact may be observable in termof change in short circuit currents in upstream transmis-sion networks. This will require new relay settings for pro-tection of distribution system as well as sub-transmissionsystems. This requirement also may arise when the net-work topology changes due to incoming of new DERs.Proper combination of primary/backup relays pairs areidentified for each new incomer DER in the distributionsystem. Moreover, additional numbers of directional overcurrent relays are required for new DERs in the distribu-tion systems and they will results in new combination ofprimary/backup over current relay pairs. Identification ofcorrect combination of primary/backup relay pairs isa tedious task for interconnected distribution net-works. A network topology processor algorithm is utilizedfor identification of correct combination of primary/backup relay pairs under different location of DERs in thedistribution networks.The new protection schemes must be equipped efficient

data monitoring, communication and intelligence and areknown as wide area measurement protection and control.In the literature, few such type of protection schemes arediscussed which uses multi-agent system (MAS) and artifi-cial intelligence (AI) based technology with distributedcontrol for protection of such power networks. Thesetechniques are superior to the local protection schemes interms of distributed control, speed, reliability and are alsoequipped have artificial intelligence feature. These types ofprotection coordination schemes has potential applicationfor protection of future distribution system where theshare of DER will be quite high as compare to presentstatus of DER penetration [76]. Presently in India, injec-tion of DER is around 12% of total power demand. Insome western countries this injection level is higher ascompare of Indian scenario. Although with present DERpenetration level in India, the protection coordination isnot much effected. But by 2020, India is expectingaround 100GW (25% of total demand) DER injectionin the distribution networks [77]. This future bulk in-jection of DER may cause more challenges for the

protection of distribution systems with existing pro-tection coordination methods.The effects of DER on existing relay coordination in

mainly depend on size, type, and placement of DERs inthe distribution systems. Apart from these factors, theimpact also depends on the characteristics of the distri-bution network and type of connected DER. Short-circuit faults currents from a wind farms mainly dependson wind turbine generator type and network configur-ation [78]. On the other hand, synchronous generatorsare able to feed large sustained fault current irrespectiveto the network configurations. While in case of inverterbased DER systems, short circuit currents are very lowequivalent to their rated current. Recently few researchershad published few articles on impact on relay coordin-ation for DER connected distribution. Brief summary ofthese papers is discussed in this review paper as under.

4.1 General protection schemesA. Girgis et al. [4] discussed about the effect of highpenetration of DER on coordination of protective deviceand suggested an adaptive protection scheme as a solu-tion for maintain the protection coordination in DERconnected distribution systems. When DER connected, apart of the distribution system may lose its radial natureand subsequently coordination among the protectiverelays may be lost. As a general practice in utilities, DERsare disconnected from the distribution system duringfaults and distribution system becomes radial in nature.However this results in losing the support of DER duringthe fault conditions. To solve the problem of discon-necting all downstream DERs during faults, a system-independent adaptive protection scheme was discussed in[79] to achieve the stable fuse-relay coordination. Othertechniques are also discussed in [80–82], in which theimpact of DER on classical protection is first analysed. Inthese papers, a novel adaptive non-pilot over current pro-tection scheme is presented, which utilizes the steady statefault currents for maintain the sable protection coordin-ation. In [83], a non-adaptive relaying scheme is discussed,which utilised the fault current limiter (FCL) to locallylimit the DER fault current during fault conditions and

Table 2 Summary of different techniques used for protection coordination of sub-transmission systems

Technique Main feature Merits Demerits

Intelligent distance to over currentrelay coordination [62, 64]

Performs the coordination operationof distance and over current relays

Utilizes the different standardtime inverse over current relayand optimized zone-2settingof distance relays for coordination.

No hardware implementationreported.

Definite time based distance to overcurrent coordination [66]

Definite time based over current relaysare coordinated with distance

Simple in implement Over current relays havefixed operating time.

Optimized coordination for seriescompensation line [67]

Multiple relay settings are identified fordifferent level of series compensation

Applicable for varying degree ofseries compensation.

Real-time implementationchallenges

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thus restores the original coordination among the relays.In [84], the over current relay coordination in DER con-nected distribution systems are maintained by adaptiveand non-adaptive relaying schemes.In adaptive relaying scheme, the settings of the over

current relay are re-defined which are mal-operating dueto DER fault current contribution in the distribution sys-tem. In case of non-adaptive relaying scheme, FCLs are

placed in series with DERs to block the fault currentduring the fault conditions [84]. Figure 4 shows the algo-rithm, which is used to select the optimal size of FCL indistribution system to maintain the relay coordination inDERs connected distribution systems.In [85], a method based on online estimation of the

equivalent circuit parameters and application of theequivalent circuit to estimate the required short-circuit

Fig. 4 Non-adaptive relaying scheme

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currents for adaptive relaying setting has been discussed.This technique is used to resolve relay mis-coordinationproblems under DER penetration in distribution system.Another technique has been discussed in [86], in whichFCLs are connected in series with the DER and utilityinterconnection point to restore fault current levels tothe original values (without DER). The FCL sizing prob-lem is formulated as a non-linear programming problem,where the main objective is to minimize changes in faultcurrent levels due to the addition of DER in the distribu-tion systems. In [87, 88], multiple criteria such as thenumber of super conducting fault current limiter (SFCLs),fault current reduction and total operating time of therelays are considered for determining the optimal place-ment of SFCLs for protection coordination of relays in anelectric power system with DERs [89]. Fast switching timefeature of solid state fault current limiter (SSFCL) isalso utilised for quick blocking of fault current fromDER in the distribution systems. Moreover, SSFCLs arecost-efficient solution for minimizing the protection effectof DER on the distribution systems. In [90], GA is utilisedto determine the optimum number, location and size ofSSFCLs required in the network for blocking the DER faultimpact. Sung-Hun et al. [91] developed an experimen-tal model in which the application hybrid SFCL onprotection coordination among the protective relays isinvestigated.The effects of a resistive SFCL for determining the

optimal size with protection coordination constraints forwind-turbine generator system (WTGS) is discussed in [92]for a practical distribution system. In [93], an approach forrestoration of directional over-current relay coordinationusing different type FCL is discussed in details. Anothermethod is also discussed in [94, 95], for coordination ofover current relays by considering the transient behaviourof FCL on relay coordination for DER connected distribu-tion networks.In [5], a protection scheme based on the local infor-

mation are utilised for developing an adaptive protec-tion. In this protection scheme, trip characteristics ofthe relays are updated by detecting operating states ofDERs (grid connected or islanded) and faulted section.The FCL size and settings of DOCRs settings are optimallydetermined by taking into account both grid-connectedand islanded mode of operation of DERS. In [96], theapplication of evolutionary algorithms and linear pro-gramming solver are discussed for identifying the locationof FCL and size in DER connected distribution systemswithout violating the protection constraints. Protectioncoordination strategy for DER connected meshed distribu-tion systems is also analysed with the help of user-definedtime inverse characteristics of directional inverse timeovercurrent relays [97, 98]. In [99], another technique isproposed to maximize the penetration level of utility

owned inverter based DER into distribution system understandard harmonic limits and protection coordinationconstraints. In this article additional constraints such asnodal voltage limits, total and individual harmonicdistortion limits imposed by each DER units and relaycoordination constraints are all together consideredsolving the projection coordination problem with thehelp of evolution algorithm.In [100], another algorithm was published which

discusses about the maximum penetration level of DERpower in the distribution system under existing relay set-ting. In this algorithm, the DER locations are providedby the network operators, where the impacts of theDERs power is minimal for maximum penetration ofDER power in their distribution systems. If the DER arecustomer based, then size of the DER are optimised byDER owner so that it will not impact the existing relaysettings in the distribution systems. The algorithm formaximum DER penetration in the distribution systemwithout resulting in loss of coordination among theinstalled relays is discussed in the Fig. 5.In [101], dual relay characteristics are utilised for

maintaining the relay coordination in DER connecteddistribution systems. These dual setting will provide thedesired protection on forward and reverse fault currentdirections. As discussed above, implementation of thismethod requires the modern microprocessor based relayswhich can communicate among them self with the help ofIEC61850 communication protocol. Additional Cost ofcommunication infrastructure is main draw back inimplementation of this approach.

4.2 Multi-agent based protection schemesThe use of agent based technology is gaining popularityfor protection coordination application for power systems.In [102, 103], new protection coordination model, basedon agent technology is discussed for protection coordin-ation application for a DER connected distribution system.In [104], pair-to-pair agent based simulated communica-tion for relay coordination has been developed. Anothertechnique based on multi-agent which divides the networkinto different zones is discussed in [105]. This protectioncoordination scheme works on the principle of decentra-lized control for taking independent coordinated protec-tion decision.In [106], synchro phasor based communication tech-

niques are also discussed for protection coordinationapplication for DER based power systems. Islanding oper-ation of low voltage distribution system having inverterconnected (low short circuit capacity) renewable energysources, imposes addition problems for optimal setting ofover current relays [107, 108]. The protection coordin-ation for a strong distribution networks is normallydesigned for high fault current levels. But during micro

Singh Protection and Control of Modern Power Systems (2017) 2:27 Page 10 of 17

grid mode of operation, high fault-currents from the util-ity grid are absent. Since, most of the DER units will beconnected to the low voltage distribution systems andthese DER are photovoltaic in nature. The fault feedingcapabilities of these inverter based photovoltaic systemsare extremely and limited. Application of multi-agentbased protection coordination is also extended for suchsystem where speed of protection is very slow due to weakfault current. Figure 6 below shows the functional block ofmulti-agent based protection scheme used for relay coord-ination application discussed in [109].Multi-agent based protection coordination is reliable

solution for protection of isolated and grid confectedactive distribution systems. For such power systemsdecentralised control feature of multi-agent can be effect-ively utilised for protection application.

4.3 Expert system based protection schemesAn expert based system was used to provide rapidprototyping, friendly user interface, knowledge base

construction, knowledge inference and external programcapabilities features [110]. Expert system based protectionscheme can solve the complexity of the protection coord-ination problem caused by the connection of DER in thedistribution systems. It is quite helpful for utility engineers

Fig. 6 Multi-agent based protection scheme

Fig. 5 maximum DER penetration

Singh Protection and Control of Modern Power Systems (2017) 2:27 Page 11 of 17

to apply the expert system as a decision tool to investigatethe impact of DER connection on relay coordination andto modify the settings of protective devices in the existingprotection schemes [111]. Normal expert based systemssolve the protection coordination problem by using avail-able information in the knowledge base bank. An expertsystem provides an explanation of how and why it reachedits decision. This can be utilised by the users to check thevalidity of the decision as well as the knowledge and infer-ence procedures associated with it. This feature is crucialbecause it allows the users to update the knowledge baseand repeatedly improve the inference. Figure 7 shows theimportant block of expert system based protectionschemes.Load flow and short circuit are input for formulation

of rule base for implementation of relay coordinationscheme in such protection techniques. Decision regard-ing the operation of particular relay is done in decisionmaking unit of graphical user interface.Accurate possible identification of network operating

topologies is a challenge to create the data base forknowledge rule base.

4.4 Dual setting protection schemesIn some DER connected distribution systems, the backuprelays may operate after long time delay and this mayresult inadequate protection in case when primary relaysfails to trip. In [112], the bidirectional fault flow is utilisedfor tripping of near end reverse relays as backup relay.This protection coordination scheme is achieved by dualrelay setting for each relay. One set of relay settings willwork for forward fault current direction and other willwork for the reverse direction of fault current. The imple-mentation of protection scheme using dual relay setting isnot yet reported.

4.5 Voltage –current based protection schemesIn radial distribution systems, the main source of thefault current is substation, which is feeded from the

synchronous generators. The short circuit capacity of asynchronous generator is 6–8 times of the normal ratingand protection relay can easily discriminate between thenormal loading and fault condition due to this thickmargin between loading and fault conditions. Thedecentralised microgrid mostly consists of solar basedpower generating sources for which there is a very thinmargin between the normal loading and fault feedingcapability. This thin margin creates problem for overcurrent based relays to discriminate between fault andnormal loading conditions. In microgrid modes it isobserved that, there is small rise in load current from110 to 150% during fault condition and simultaneouslydecrease in voltage below 80% of system voltage. In[112–114], a method is discussed which utilises thevoltage and current signals for protection coordinationapplication in DER connected distribution systems. Theauthor has proposed a voltage-current time inverse pro-tection scheme which can discriminate normal and faultcondition in microgrid successfully. The operating timeof voltage-current inverse relay characterises is given in(2) below.

tvoc ¼ δ�TDSIfIp� Vp

Vn

� �γ−1

ð2Þ

Where, tvocoperating time of voltage current timeinverse relay, vp is pickup voltage, vn nominal voltage andδ and γ are user defined relay parameters in [108]. Theoperating zone of the voltage current time inverse relay isshown in Fig. 8. This protection scheme is also not yetimplemented in the field as per the available literature.The main above for distribution systems with DER

penetration are summarised in Table 3.

5 Review of methodologies used for formulationof fitness function in protection coordinationThere were different approaches adopted in the literaturefor formulation of fitness function for relay coordination

Fig. 7 Expert system based protection

Singh Protection and Control of Modern Power Systems (2017) 2:27 Page 12 of 17

studies. The overall objective of all approaches is to main-tain the desired coordination time margin betweenprimary and corresponding backup relays and tripping ofminimum relays. In [115], the fitness function is formu-lated as summation of operating time of all primary relaysin the distribution systems and while in [37], it is formu-lated as minimization of total operating time of all primaryrelays for near end and far end faults. In [28], the fitnessfunction is also defined minimization of operating time ofprimary relay as well as backup relays. However, fewresearcher proposed the fitness function as minimisationof time dial setting [33] of primary relays. In all above fit-ness function formulation techniques, it is observed that,relay coordination problem becomes highly nonlinear andnon-convex optimization problem. The fast optimizationalgorithms can be effectively applied for for solving therelay coordination problems.

6 Research gaps and future scope for protectioncoordination research workIn his review article, the author have identified the vari-ous visible research gap and challenging for protectioncoordination schemes with and without DER connecteddistribution systems. These are as under.

i) Integration of DER changes the network topologyand additional requirement of directional relaysarises for which identification of correct backuprelays becomes more complicated. However graphtheory based approaches are used in the literature[46], but more reliable techniques will be requiredfor highly complicated networks.

ii) Heavy interconnection of distribution networksresults in an adequate change in the fault levels and

some undesired relays may trip during the faults andthese trippings are known as sympathetic trippings.Elimination of sympathetic tripping in thedistribution systems during the network steady stateand transient fault conditions with integration ofDERs is an another unaddressed area [116].

iii) Integration of DER at distribution level may affectthe protection requirement at upstreamtransmission for lines. For large scale penetration ofDER, the reach setting of distance relays installed attransmission line may get effected [8].

iv) From the literature, it is also observed that, the relaycoordination problems are optimised without anyupper limit of CTI [21, 43]. This results in delayedoperation of backup over current relays particularlywhen the fault current contribution fromPhotovoltaic based DER is weak. Operating time ofover current relays for such systems is enhanced byoptimal selection of multiple time-inverse relaycharacterises during relay coordination studies [115].

v) It is observed that for small scale penetration ofDER, the protection coordination requirement arenot much effected. A hybrid protection coordinationalgorithm is proposed in [116] in which minimumnumber of over current relays and smaller size ofFCLs are utilised for maintaining the relaycoordination in the distribution system during DERpenetrations. However for large scale Megawattintegration from wind, effect is un-avoidable. Anadaptive relaying algorithm with multiple relay groupsetting may be suitable protection coordinationsolution. In [117], author(s) have presented anidea for addressing the protection coordinationissues with large scale penetration of DER in

Fig. 8 Voltage-current time inverse relay operating zone

Singh Protection and Control of Modern Power Systems (2017) 2:27 Page 13 of 17

power networks. The implementation of thisscheme using the advance communication protocolin multi agent decentralised adaptive way is a newchallenge for the protection engineers. Implementationof these relay coordination techniques in thedistribution systems under DER penetration, isone of promising future area for relay in relaycoordination studies.

vi)Weak fault current contribution for inverter basedphotovoltaic based generating system, makes thedesign of protection systems highly complicated.The design of sophisticated & accurate protectionis an emerging research area for the protectionengineers.

7 ConclusionIn this review article, a detailed literature review forprotection coordination for distribution systems withand without DER is discussed. This review article coversthe review of all the notable protection coordinationmethods starting from the initial curve fitting, graphtheory and application of exact optimization tools forsolving the protection coordination problem for radial/interconnected power systems. In these techniques, therelay coordination problem is formulated as linear andnon-linear optimization problem and then solved using thedifferent optimization techniques. These included, exactmethod and artificial intelligence based optimizationsmethods.

Table 3 Summary of protection schemes for distribution systems with DER Penetration

Technique Main feature Merits Demerits

Fault current limiterbased [68]

Suitable for wind mill based DERpenetration

Block the fault current during faults Costly

Harmonic restrainedProtection [93]

The DER power is penetrated inthe power utility until theallowed harmonic limit andprotection is maintained

This approach is highly suitable forinverter based DER.

Not applicable for non-invertorbased DER.

Optimal sizing of DER. [90] DER power is penetrated at safelocation where existingprotection is least effected.

Existing protection may hold good. Applicable for small penetration

Adaptive Relaying [25] The relay setting are adoptedbased on the changing networktopologies/configurations.

This method is applicable for largescale penetration from wind farms.

Communication and numericalrelays are essential for design ofprotection schemes.

Local adaptiveovercurrent based Protectionscheme [88].

It monitors local information(current & voltage) continuouslyand re-calculate the relay settingbased on network topology.

This technique is applicable forboth grid connected and islandedmode systems.

Fails during network dynamicconditions,

A Novel adaptiveover-current Protection [96]

DERs are considering as currentinjection sources. Steady statefault currents are calculated fromsteady state equivalent reductionof the system for design ofprotection

Capable to handle the networkdynamic changes.

The algorithm run time increasewith system size.

Adaptive–relay-recloser-fusecoordination.

In this scheme, the relay/recloserand fuse current are determined.Based on the ratio relay andfuse current

This method is applicable for bothsynchronous based DG andInverter based DG

Sometimes it is not desirablechange the complete fast curveof recloser [33].

Online-Adaptive Overcurrent Protection

Based on the network condition,it will calculate the fault levels &relay setting will be updated byusing HIL IEC 61850communication.

This protection scheme isapplicable for both gridconnected mode and Islandedmode.

Performance fails during networkchanges.

Expert/Fuzzy basedprotection scheme [104]

Monitor the status of the DERsource, voltage phasor basedDFT technique and update thepickup & TDS settings based onthe network changes.

This approach is suitable forlimited network topologies

The identification of all potentialnetwork topologies is difficult.

Group setting basedprotection scheme [106]

The multiple relay group settingare identified based on the faultlevel in network

This approach is suitable formultiple DER and seriescompensated lines

The identification of all potentialnetwork topologies is difficultand communication protocol areessential.

Multi-agent basedprotection [103]

Coordinated decentralizedprotection

Distributed protection control Requites the communicableagents like relay, breaker etc.

Singh Protection and Control of Modern Power Systems (2017) 2:27 Page 14 of 17

Penetration of DER in distribution systems createsnew protection coordination issues. Their impact on thenetwork protection mainly depends upon their size andlocation and impact may be classified as large scalepenetration or small scale penetration. Large scale pene-tration results in bidirectional flow of fault current overthe most feeder. The existing unidirectional designedprotection coordination schemes fail to clear the faultfor such fault conditions. In the available literature, theseproblems are addressed by localising the DER impactand updating the protection setting wherever required.Therefore this review article makes a compressive reviewof all the protection schemes which are discussed inliterature for maintaining the protection coordinationunder DER integration. Review is also extended protectionissues arising in limited penetration of DER in powernetwork and islanding mode of operation of powersystems.In this review article, visible research gaps and possible

future scope of research in protection coordination hasbeen also presented.

Competing interestsThe authors declare that they have no competing interests.

Received: 28 October 2016 Accepted: 5 July 2017

References1. Sudipta, G. S., Ghoshal, P., & Ghosh, S. (2010). Optimal sizing and placement

of distributed generation in a network system. International Journal ofElectrical Power & Energy Systems, 32(8), 849–856.

2. Central Electricity Authority (2016). Draft National Electricity. Ministry ofPower Government of India, Delhi, 1(6).

3. http://www.ieee.org/about/ieee_europe/june-july-august-sept_2015_energy_news_bulletin.pdf.

4. Girgis, A., & Brahma, S. (2004). Development of Adaptive protection schemefor distribution systems with high penetration of distributed generation.IEEE Transactions on Power Delivery, 19(1), 56–63.

5. Mahat, P., Chen, Z., Bak-Jensen, B., & Bak, C. L. (2011). A Simple adaptiveovercurrent protection of distribution systems with distributed generation.IEEE Transactions on Smart Grid, 2(3), 428–437.

6. Urdaneta, A. J., Ramon, N., & Jimenez, L. G. P. (1988). Optimal coordinationof directional relays in interconnected power system. IEEE Transactions onPower Delivery, 3(3), 903–911.

7. IEEE Std C37.90–1989 “IEEE Standard for Relays and Relay SystemsAssociated with Electric Power Apparatus,” (ANSI), 1994.

8. Dubey, R., Samantaray, S. R., & Panigrahi, B. K. (2014). Adaptive DistanceRelaying Scheme for Transmission Network Connecting Wind Farms.Electric Power systems and components, 42(11), 457–464.

9. Olivares, D. E., et al. (2014). Trends in microgrid control. IEEE Transactions onSmart Grid, 5(4), 1905–1919.

10. Zocholl, S. E., Akamine, J. K., Hughes, A. E., Sachdev, M. S., & Scharf, L. (1989). H.computer representations of overcurrent relay characteristics. IEEE Transactionson Power Delivery, 4(3), 1659–1667.

11. Whiting, J. P., & Lidgate, D. (1983). Computer predictions of IDMT relaysettings and performance for interconnected power systems. IEEE Generation,Transmission and Distribution, 130(3), 139–147.

12. Jenkins, L., Khincha, H. P., Shiva Kumar, S., & Dash, P. (1992). An applicationof functional dependencies to the topological analysis of protectionschemes. IEEE Transactions on Power Delivery, 7(1), 77–83.

13. Ramaswami, R., & Mc-Guire, P. F. (1992). Integrated coordination and shortcircuit analysis for system protection. IEEE Transactions on Power Delivery,7(3), 1112–1120.

14. Damborg, M. J., Ramaswami, R., Venkata, S. S., & Postforoosh, J. M. (1984).Computer aided transmission protection system design, Part – I, algorithms.IEEE Transactions on Power Apparatus and Systems, 103(1), 51–59.

15. Knable, A. H. (1967). Electrical Power Systems Engineering: Problems andSolutions. New York: McGraw–Hill.

16. Shah, K. R., Detjen, E. D., & Phadke, A. G. (1988). Feasibility of adaptivedistribution protection system using computer overcurrent relayingconcept. IEEE Transactions on Industry Applications, 24(5), 792–797.

17. Dwarkanath, M. H., & Nowitz, I. (1980). An application of linear graphtheory for coordination of directional overcurrent relays. Electric powerproblems–mathematical challenge, proceedings of the society for industrialand applied mathematics (SIAMS) conference Seattle, Washington;(pp. 104–114).

18. Damborg, M. J., Ramaswami, R., Jampala, A. K., & Venkata, S. S. (1986).Application of relational database to computer aided engineering oftransmission protection system. IEEE Transactions on Power Apparatus andSystems, 1(2), 187–193.

19. Damborg, M. J., Ramaswami, R., Venkata, S. S., & Postforoosh, J. M. (1984).Computer aided transmission protective system design, Part – II,implementation and results. IEEE Transactions on Power Apparatus andSystems, 103(1), 60–65.

20. Rao, V. V. B., & Rao, K. S. (1988). Computer aided coordination of directionalrelay: determination of break points. IEEE Transactions on Power Delivery,3(2), 545–548.

21. Prasad, V. C., Prakash Rao, K. S., & Subba Rao, A. (1991). Coordination ofdirectional relays without generating all circuits. IEEE Transactions onPower Delivery, 6(2), 584–590.

22. Jamali, S., & Shateri, H. (2004). A branch–based method to break–pointdetermination for coordination of over–current and distance relays.International Conference on Power System Technology POWERCON, 21–24,1857–1862.

23. Gajbhiye, RK, De, A, Helwade, R, Soman, SA (2005). A simple and efficientapproach to determination of minimum set of break point relays fortransmission protection system coordination. In procc. of Internationalconference on future power systems(pp. 1–5). Amsterdam.

24. Yue, Q. M., Lu, F., Yu, W. Y., & Wang, J. (2006). A novel algorithm todetermine minimum break point set for optimum cooperation ofdirectional protection relays in multi-loop networks. IEEE Transactions onPower Delivery, 21(3), 1114–1119.

25. Alkaran, D. S., Vatani, M. R., Sanjari, M. J., Gharehpetian, G. B., & Yatim, A. H.(2015). Overcurrent Relays Coordination in Interconnected Networks UsingAccurate Analytical Method and Based on Determination of Fault CriticalPoint. IEEE Transactions on Power Delivery, 30(2), 870–977.

26. Urdaneta, A. J., Jimenez, L. G. P., Gomez, J. F., Feijoo, B., & Gonzalez, M.(2000). Presolve analysis and interior point solutions of the linearprogramming coordination problem of directional overcurrent relay.Electrical Power and Energy System, 23, 819–825.

27. Mahari, A., & Seyedi, H. (2013). An analytic approach for optimalcoordination of overcurrent relays. IET Generation, Transmission andDistribution, 7(7), 674–680.

28. Pandi, VR, Zeineldin, HH, Xiao, W. Determining optimal location and size ofdistributed generation resources considering harmonic and protectioncoordination limits. IEEE Transactions on Power System, 28(2), 1245–1254.

29. Perez, L. G., & Urdaneta, A. J. (1996). Optimal coordination of directionalovercurrent relays considering definite time backup relaying.IEEE Transactions on Power Delivery, 14(4), 1276–1284.

30. Singh, M, Panigrahi, BK, Abhyankar, AR (2005). ptimal over currents relaycoordination in distribution system. In Procc. of IEEE Conference on Energy,Automation and Signal (ICEAS)(pp. 1–5). Bhubaneswar.

31. Bedekar, P. P., Bhide, S. R., & Kale, V. S. (2011). Determining optimum TDS andPS of overcurrent relays using linear programming technique. 8th InternationalConference on Electrical & Engineering/Electronics and Information Technology(ECTI-CON)(pp. 700–703).

32. Abyaneh, H. A., Al-Daddagh, M., Kamangar, H., Sadeghi, S. H. H., & Khan, R. A. J.(2003). A new optimal approach for coordination of overcurrent relays ininterconnected power system. IEEE Transactions on Power Delivery,15(2), 430–435.

33. Noghabi, A. S., Mashhadi, H. R., & Sadeh, J. (2010). Optimal coordination ofdirectional overcurrent relays considering different network topologiesusing interval linear programming. IEEE Transactions on Power Delivery,25(3), 1348–1354.

Singh Protection and Control of Modern Power Systems (2017) 2:27 Page 15 of 17

34. Laway, N. A., & Gupta, H. O. (1994). An efficient method for generation,storage and retrieval of data for the coordination of directional relays.Electric Power Systems Research, 29(2), 147–152.

35. Irving, M. R., & Elrafie, H. B. (1993). Linear programming for directionalovercurrent relay coordination in interconnected power systems withconstraint relaxation. Electric Power Systems Research, 27(3), 209–216.

36. Urdaneta, A. J., Perez, L. G., & Restrepo, H. (Oct 1997). Optimal coordinationof directional overcurrent relays considering dynamic changes in thenetwork topology. IEEE Transactions on Power Delivery, 12(4), 1458–1464.

37. Birla, D., Mahaeshwari, R. P., & Gupta, H. O. (2006). A new nonlineardirectional overcurrent relay coordination technique and banes and boonsof near end faults based approach. IEEE Transactions on Power Delivery, 21(3),1176–1182.

38. Birla, D., Mahaeshwari, R. P., Gupta, H. O., Deep, K., & Thakur, M. (2006).Applications of random search technique in directional overcurrent relaycoordination. International Journal of Emerging Electric Power Systems, 7(1),1–14.

39. Keil, T., & Jäger, J. (2008). Advanced coordination method for overcurrentprotection relays using nonstandard tripping characteristics. IEEETransactions on Power Delivery, 23(1), 52–57.

40. Razavi, F., Abyaneha, H. A., Al-Dabbaghb, M., Mohammadia, R., & Torkaman,H. (2008). A new comprehensive genetic algorithm method for optimalovercurrent relays coordination. Electric Power Systems Research, 78, 713–720.

41. Karegar, H. K., Abyaneh, H. A., & Al-Dabbagh, M. (2003). Flexible approachesfor overcurrent relay characteristics simulation. Electric Power SystemsResearch, 66, 233–239.

42. Bedekar, P. P., & Bhide, S. R. (2011). Optimum coordination of overcurrentrelay timing using continuous genetic algorithm. Expert Systems withApplications, 38, 11286–11292.

43. Bedekar, P. P., & Bhide, S. R. (2011). Optimum coordination of directionalovercurrent relays using the hybrid GA-NLP approach. IEEE Transactions onPower Delivery, 26(1), 109–119.

44. So, C. W., & Li, K. K. (2000). Overcurrent relay coordination by evolutionaryprogramming. Electric Power Systems Research, 53, 83–90.

45. So, C. W., & Li, K. K. (2000). Time coordination method for power systemprotection by evolutionary algorithm. IEEE Transactions on industrialApplications, 36(5), 1235–1240.

46. Saberi Noghabi, A., Sadeh, J., & Rajabi Mashhadi, H. (2009). Consideringdifferent network topologies in optimal overcurrent relay coordinationusing a hybrid GA. IEEE Transactions on Power Delivery, 24(4), 1857–1863.

47. Mohammadi, R., Abyaneh, H. A., Rudsari, H. M., Fathi, S. H., & Rastega, H.(2010). Overcurrent relays coordination considering the priority ofconstraints. IEEE Transactions on Power Delivery, 25(3), 1937–1948.

48. Zeineldin, H. H., El-Saadany, E. F., & Salama, M. M. A. (2006). Optimalcoordination of overcurrent relays using a modified particle swarmoptimization. Electric Power Systems Research, 76, 988–995.

49. Mohamed, M. (2007). Mansour, Said F. Mekhamer, Nehad El-Sherif El-Kharbawe.A modified particle swarm optimizer for the coordination of directionalovercurrent relays. IEEE Transactions on Power Delivery, 22(3), 1400–1410.

50. Deep, K, & Bansal, JC (2009). Optimization of directional overcurrent relaytimes using Laplace Crossover Particle Swarm Optimization (LXPSO). 2009World Congress on Nature & Biologically Inspired Computing (NaBIC), (pp.288–293). Coimbatore.

51. Liu, & Yang, M.-T. (2012). A New Hybrid Nelder-Mead Particle SwarmOptimization for Coordination Optimization of Directional OvercurrentRelays. Mathematical Problems in Engineering, 2012, 1–18.

52. Thangaraj, R., Pant, M., & Deep, K. (2010). Optimal coordination of over-current relays using modified differential evolution algorithms. EngineeringApplications of Artificial Intelligence, 23, 820–829.

53. Thangaraj, R., Pant, M., & Abraham, A. (2010). New mutation schemes fordifferential evolution algorithm and their application to the optimization ofdirectional over-current relay settings. Applied Mathematics and Computation,216, 532–544.

54. Moirangthem, J., Krishnanand, K. R., Dash, S. S., & Ramaswami, R. (2013).Adaptive differential evolution algorithm for solving non-linear coordinationproblem of directional overcurrent relays. IET Generation, Transmission andDistribution, 4(7), 329–336.

55. Chelliah, T. R., Thangaraj, R., Allamsetty, S., & Pant, M. (2014). Coordination ofdirectional over current relay using opposition based chaotic differentialevolution algorithm. International Journal of Electrical Power & EnergySystems, 55, 341–350.

56. Ezzeddine, M., Kaczmarek, R., & Iftikhar, M. U. (2011). Coordination ofdirectional overcurrent relays using GA novel method to select theirsettings. IET Generation, Transmission and Distribution, 5(7), 743–750.

57. Payam, M. S. B., Ehsan Abdollahi, M., & Dehkordi, A. S. (2011). Optimalcoordination of directional overcurrent relay for power delivery systemwith a hybrid shuffled frog leaping algorith. Australian Journal of Basic andApplied Sciences, 5(12), 1949–1957.

58. Amraee, T. (2012). Coordination of directional overcurrent relays usingseeker algorithm. IEEE Transactions on Power Delivery, 27(3), 1415–1422.

59. Barzegari, M., Bathaee, S. M. T., & Alizadeh, M. (2010). Optimal coordinationof directional overcurrent relays using harmony search algorithm. InProceedings of 9th Conference on Environment and Electrical Engineering, EEEIC.(pp. 321–324).

60. Shih, M. Y., Castillo Salazar, C. A., & Conde Enriquez, A. (2015). Adaptivedirectional over current coordination using ant colony optimization.IET Generation, Transmission and Distribution, 9(14), 1240–2049.

61. Albasri, F. A., Alroomi, A. R., & Talaq, J. H. (2015). Optimal Coordination ofDirectional Over current Relays Using Biogeography based OptimizationAlgorithms. IEEE Transactions on Power Delivery, 30(4), 1810–1820.

62. Javadian, S. A. M., Haghifam, M.-R., Bathaee, S. M. T., & Fotuhi Firoozabad, M.(2013). Adaptive centralized protection scheme for distribution systems withDG using risk analysis for protective devices placement. Electrical Power andEnergy Systems, 44, 337–345.

63. Rezaei, N., & Mr, H. (2008). Protection scheme for a distribution system withdistributed generation using neural networks. International Journal ofElectrical Power & Energy Systems, 30(4), 235–241.

64. Sanaye-Pasand, M., & Khorashadi-Zadeh, H. (2006). An Extended ANN-basedhigh speed accurate distance protection algorithm. International Journal ofElectrical Power & Energy Systems, 28(6), 387–395.

65. Shih, M. Y., Enríquez, A. C., & Trevi, L. M. T. (2014). On-line coordination ofdirectional overcurrent relays: Performance evaluation among optimizationalgorithms. Electric Power Systems Research, 110, 122–132.

66. Rockefeller, G. D., Wagner, C. L., & Linders, J. R. (1988). Adaptive transmissionrelaying concepts for improved performance. IEEE Transactions on PowerDelivery, 3(4), 1446–1458.

67. Jampala, A. K., Venkata, S. S., & Domborg, M. J. (1989). Adaptive transmissionprotection: Concepts and computational issues. IEEE Transactions on PowerDelivery, 4(1), 177–185.

68. Enriquez, A. C., Martinez, E. V., & Altuve-Ferrer, H. J. (2013). A TimeOvercurrent Adaptive Relay. International Journal of Electrical Power & EnergySystems, 25(10), 841–847.

69. Chattopadhyay, B., Sachdev, M. S., & Sidhu, T. S. (1996). An online relaycoordination algorithm for adaptive protection using linear programmingtechnique. IEEE Transactions on Power Delivery, 11(1), 165–173.

70. Mohammed, A., Haj-ahmed, & Mahesh, S. (2014). Intelligent coordinatedadaptive distance relaying. Electric Power Systems Research, 110, 163–171.

71. Calderaro, V., Galdi, V., Piccolo, A., & Siano, P. (2007). Adaptive Relays foroverhead line protection. Electric Power Systems Research, 77, 1552–1559.

72. Chabanloo, R. M., Abyaneh, H. A., Kamangar, S. S. H., & Razavi, F. (2011).Optimal combined overcurrent and distance relays coordinationincorporating intelligent overcurrent relay characteristics selection. IEEETransactions on Power Delivery, 26(3), 1381–1391.

73. Sidhu, T. S., Baltazar, D. S., Palomino, R. M., & Sachdev, M. S. (2004).A New approach for calculating zone-2 setting of distance relays andits use in an adaptive protection system. IEEE Transactions on Power Delivery,19(1), 70–78.

74. Perez, L. G., & J. (2001). Urdaneta. Optimal Computation of distance relayssecond zone timing in a mixed protection scheme with directionalovercurrent relays. IEEE Transactions on Power Delivery, 16(3), 385–388.

75. Moravej, Z., Jazaeri, M., & Gholamzadeh, M. (2012). Optimal coordination ofdistance and overcurrent relays in series compensated systems based onMAPSO. Energy Conversion and Management, 56, 140–151.

76. Basak, P., Chowdhury, S., Halderneedey, S., & Chowdhury, S. P. (2012).A literature review on integration of distributed energy resources in theperspective of control, protection and stability of microgrid. Renewable andSustainable Energy Reviews, 16, 5545–5556.

77. Central electricity authority ministry of power government of India. Annualreport, 2013–14.

78. Mohamed, A. E., & Zhao, Z. (2010). Grid-connected photovoltaic powersystems: technical and potential problems-a review. Renewable andSustainable Energy Reviews, 14, 112–129.

Singh Protection and Control of Modern Power Systems (2017) 2:27 Page 16 of 17

79. Ma, J., Wang, X., Zhang, Y., Yang, Q., & Phadke, A. G. (2012). A Noveladaptive current protection scheme for distribution systems withdistributed generation. Electrical Power and Energy Systems, 43, 1460–1466.

80. Barker, P. P., & De Mello, R. W. (2000). Determining the impact of distributedgeneration on power systems: part 1-radial distribution systems. IEEETransactions on Power Delivery, 15(2), 486–493.

81. Leelaruji, R., & Vanfretti, L. (2012). State-of-the-art in the industrialimplementation of protective relay functions, communication mechanismand synchronized phasor capabilities for electric power systems protection.Renewable and Sustainable Energy Reviews, 16, 4385–4395.

82. Walid El-Khattam, T. S. (2008). Sidhu. Restoration Of directional overcurrentrelay coordination in distributed generation systems utilizing fault currentlimiter. IEEE Transactions on Power Delivery, 23(2), 576–585.

83. El-Khattam, W., & Sidhu, T. S. (2009). Resolving the impact of distributionrenewable generation on directional over current relay coordination: a casestudy. IET Renewable Power Generation, 3(4), 415–425.

84. Ojaghi, M., Sudi, Z., & Faiz, J. (2013). Implementation of full adaptivetechnique to optimal coordination of overcurrent relays. IEEE Transactionson Power Delivery, 28(1), 235–244.

85. Zeineldin, H. H., & Xiao, W. (2011). Optimal fault current limiter sizing fordistribution systems with DG, IEEE Power and Energy Society GeneralMeeting(pp. 1–5). San Diego, CA.

86. Jo, H.-C., Joo, S.-K., & Lee, K. (2013). Optimal placements of superconductingfault current limiters (SFCLs) for protection of electric power system withdistributed generations (DGs). IEEE Transactions on superconductivity,3(3), 5600–5604.

87. Kim, J.-S., Lim, S.-H., & Kim, J.-C. (2011). Study on protective coordination forapplication of superconducting FCL. IEEE Transactions on superconductivity,21(3), 2174–2177.

88. Kim, J.-S., Lim, S.-H., & Kim, J.-C. (2012). Study on application method ofsuperconducting fault current limiter for protective coordination ofprotective devices in a power distribution system. IEEE Transactions onApplied Superconductivity, 22(3), 1560–1564.

89. Ali, S., Shahriari, A., Varjani, A. Y., & Haghifam, M. R. (2012). Cost reduction ofdistribution network protection in presence of distributed generation usingoptimized fault current limiter allocation. Electrical Power and EnergySystems, 43, 1453–1459.

90. Lim, S.-H., Kim, J.-S., Kim, M.-H., & Kim, J.-C. (2012). Improvement ofprotection coordination of protective devices through application of a SFCLin a power distribution system with a dispersed generation. IEEETransactions on Applied Superconductivity, 22(3), 5601001–5601004.

91. Lee, H.-J., Son, G., & Park, J.-W. (2011). Study On Wind-turbine generatorsystem sizing considering voltage regulation and overcurrent relaycoordination. IEEE Transactions on Power Systems, 26(3), 1283–1293.

92. Lee, H.-J., Son, G., & Park, J.-W. (2011). A Study on wind-turbine generatorsystem sizing considering overcurrent relay coordination with SFCL. IEEETransactions on Applied Superconductivity, 3, 1240–1244.

93. Javadi, H., Ali Mousavi, S. M., & Khederzadeh, M. (2013). A Novel approach toincrease FCL application in preservation of over-current relays coordinationin presence of asynchronous DGs. Electrical Power and Energy Systems,44, 810–815.

94. Chabanloo, R. M., Abyaneh, H. A., Agheli, A., & Rastegar, H. (2011).Overcurrent relays coordination considering transient behaviour of faultcurrent limiter and distributed generation in distribution power network.IET Generation, Transmission and Distribution, 5(9), 903–911.

95. Najy, W., Zeineldin, H. H., & Woon, W. (2013). Optimal protectioncoordination for microgrid with grid-connected and islanded capability.IEEE Transactions on Industrial Electronics, 60(4), 456–461.

96. Sharaf, H. M., Zeineldin, H. H., Ibrahim, D. K., & Essam, E. L. (2015). Aproposed coordination strategy for meshed distribution systems with DGconsidering user-defined characteristics of directional inverse timeovercurrent relays. International Journal of Electrical Power & Energy Systems,65, 49–58.

97. Zayandehroodi, H., Mohamed, A., Shareef, H., & Farhoodnea, M. (2012).A novel neural network and backtracking based protection coordinationscheme for distribution system with distributed generation. Electrical Powerand Energy Systems, 43, 868–879.

98. Zeineldin, Mohamed, H. H., Khadkikar, Y. A., & Pandi, V. (2013). A ProtectionCoordination Index for Evaluating Distributed Generation Impacts onProtection for Meshed Distribution Systems. IEEE Transactions on Smart Grid,3(2), 1523–1532.

99. Singh, M, Panigrahi, BK, Abhyankar, AR, Mukherjee, R, & Kundu, R (2013).Optimal Location, Size and Protection Coordination of DistributedGeneration in Distribution Network. In PROCEEDINGS of IEEE Symposium andcomputational intelligence, (pp. 16–19). Singapore.

100. Zeineldin, H. H., Sharaf, H. M., Ibrahim, D. K., & El-Zahab, E. E.-D. A. (2015).Optimal Protection Coordination for Meshed Distribution Systems With DGUsing Dual Setting Directional Over-Current Relays. IEEE Transactions onSmart Grid, 6(1), 115–123.

101. Wan, H., Member, K., Li, K., & Wong, K. P. (2010). An Adaptive multiagentapproach to protection relay coordination with distributed generators inindustrial power distribution system. IEEE Transactions on IndustrialElectronics, 46(5), 2118–2124.

102. Zhu, Y., Shaoqun, S., & Wang, D. (2009). Multiagent-based wide areaprotection with best-effort adaptive strategy. Electrical Power and EnergySystems, 31, 94–99.

103. Laaksonen, H. J. (2010). Protection principles for future microgrids.IEEE Transactions on Power Electronics, 25(12), 2910–2919.

104. Chen, C.-R., Lee, C.-H., & Chang, C.-J. (2013). Optimal Overcurrent relaycoordination in power distribution system using a new approach.Electrical Power and Energy Systems, 45, 217–222.

105. Katiraei, F., Iravani, M. R., & Lehn, P. W. (2005). Micro-grid autonomousoperation during and subsequent to islanding process. IEEE Transactions onPower Delivery, 20(1), 284–292.

106. Sortomme, E., Venkata, S. S., & Mitra, J. (2010). Microgrid protection usingcommunication-assisted digital relays. IEEE Transactions on Power Delivery,25(4), 2789–2797.

107. Velasco, D., Trujillo, C. L., Garcera, G., & Figueres, E. (2010). Review ofanti-islanding techniques in distributed generators. Renewable andSustainable Energy Reviews, 14, 1608–1614.

108. Javadian, SAM, Haghifam, M-R, & Rezaei, N (2009). A fault location andprotection scheme for distribution systems in presence of DG using MLPneural networks. In: 2009 IEEE power engineering society general meeting,(pp. 1–8). Calgary, Alberta, Canada.

109. Wayne Hong, H., Chuen-Tsai, S., Mesa, V. M., & Ng, S. (1991). Protectivedevice coordination expert system. IEEE Transactions on Power Delivery,26(1), 359–365.

110. Tuitemwong, K. Expert system for protection coordination of distributionsystem with distributed generators. International Journal of Electrical Power &Energy Systems, 33(3), 466–471.

111. Zeineldin, H., Sharaf, H., Ibrahim, H. M., & Abou El-Zahab, E. E. D. (2014).Optimal protection coordination for meshed distribution systems with DGusing dual setting directional over-current relays. IEEE Transactions on Smart Grid,6(1), 115–123.

112. Saleh, K. A., Zeineldin, H. H., Al-Hinai, A., & El-Saadany, E. F. (2015). OptimalCoordination of Directional Overcurrent Relays Using a New Time–Current–Voltage Characteristic. IEEE Transactions on Power Delivery, 30(2), 537–544.

113. Saleh, K. A., Zeineldin, H. H., Al-Hinai, & El-Saanday, E. F. (2015). Dual-settingcharacteristic for directional overcurrent relays considering multiple faultlocations. IET Generation, Transmission and Distribution, 99(12), 1332–1340.

114. Manohar, S., Panigrahi, B. K., & Abhyankar, A. R. (2013). Optimal coordinationof Directional Over-current Relays Using Teaching Learning-BasedOptimization Algorithm. International Journal of Electrical Power & EnergySystems, 5, 33–41.

115. Singh, M., & Panigrahi, B. K. (2014). Minimization of operating time gapbetween primary relays at near and far ends in over current relay coordination.North American power symposium(pp. 7–9). USA: Washington StateUniversity.

116. Manohar Singh, B, Panigrahi, K, & Abhyankar, AR (2013). A Hybrid protectionscheme to mitigate the effect of distributed generation on relaycoordination in distribution system. In PROCEEDINGS of IEEE PES GeneralMeeting, (pp. 1–5). Vancouver, Canada.

117. Singh, M., Vishnuvarthan, T., & Srivani, S. G. (2016). adaptive protectioncoordination schemes for power network under penetration of distributedenergy resources. IET Generation, Transmission and Distribution, 10(15), 3919–3929.

Singh Protection and Control of Modern Power Systems (2017) 2:27 Page 17 of 17