Protection and Control ofModern Power Systems

Bo et al. Protection and Control of Modern Power Systems (2016) 1:7 DOI 10.1186/s41601-016-0012-2

REVIEW Open Access

Developments of power system protectionand control

Z. Q. Bo1*, X. N. Lin2, Q. P. Wang1, Y. H. Yi1 and F. Q. Zhou1

Abstract

Synchronized wide area communication has become a mature technology, which makes the real-time interactionbetween the substations and the wide area protection and control system possible. However, the presentprotection and control system to handle this real-time data has been recognized to be deficient. This paper beginsby reviewing the development history of power system protection, with special attention paid to the recentdevelopment in the field of wide-area and integrated protections, in order to look into the future development ofprotection and control systems. Then the concept of integrated wide area protection and control is introduced,where it can be shown that a hierarchical protection and control system provides the protection and control forwide area or regional power substations/plants and their associated power networks. The system is mainly dividedinto three levels: the local, the substation/plant, and the wide area/regional. The integrated functions at each levelare described in details with an aim to develop an optimal coordination mechanism between each level. The keyelement in the proposed system is the wide area real-time protection and control information platform, which notonly enables the merger of three lines of defence for power system protection and control, but also provides aperfect tool for the application of cloud computing in substations and power networks.

Keywords: Power system protection, Wide area protection, Integrated protection and control, Information platform

IntroductionPower system protection emerged at the beginning ofthe last century, with the application of the firstelectro-mechanical overcurrent relay. The majority ofthe protection principles currently employed in protec-tion relays were developed within the first threedecades of the last century, such as overcurrent, direc-tional, distance and differential protection, as shown inFig. 1. The development of modern science and tech-nology, especially electronic and computer technology,promoted the development of relay technology, such asmaterials, components and the manufacturing processof the hardware structure of relay protection device. Atthe same time, great theoretical progress had beenmade in the relay protection software, algorithms, etc.As shown in Fig. 1, the progress in modern technologystimulates the development in power system protection.In the last century from the emergence of protection tothe end of the 1990s, the relay protection had gone

* Correspondence: bozhiqian@263.net1XUJI Group Corporation, Xuchang, ChinaFull list of author information is available at the end of the article

© 2016 The Author(s). Open Access This articleInternational License (http://creativecommons.oreproduction in any medium, provided you givthe Creative Commons license, and indicate if

through a number of development stages, migratingfrom electro-mechanical to semiconductor, and subse-quently to integrated circuit and microprocessor tech-nologies. Today, microprocessor-based digital andnumeric relays are replacing conventional relays in allareas of power system protection. However, many ofthe same relaying principles of protection are still play-ing a dominant role to date. In the late 1960s, the appli-cation of a centralized substation protection systembased on a centralized computer system was proposed[1]. This constitutes an important milestone in the his-tory of power system protection. The idea fits well withthe concept of an overall integrated protection wherethe protection package would not only oversee indivi-dual units of a plant but also a section of the network.However, the idea has not been widely applied untilrecently, since there were no available computer hard-ware/software or communication technologies to sup-port such an idea. Since then, relay technology hasenjoyed successful developments based on the applica-tion of digital techniques. The introduction of micro-processors into protection in the 1980s generally

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1900 1970 1980 1990 2000 2010

ConventionalProtection

Modern Protection New development

Directional (1910)

Power line carrier(1927)

Differential (1908)

Overcurrent (1901)

Adaptive1980's

Travellingwave 1970's

Distance (1923)

ArtificialIntelligence

1990's

Wide area

Integrated

Integratewide area

P&C

transistorelectromechanical

communicationmicroprocessor

year

information

Transientbased

CloudBigdata

GPS(1990)

integrate circuit

rectifierTECHNOLOGY

PROGRESS

Computer(1970)

Fig. 1 History of power system protection

Bo et al. Protection and Control of Modern Power Systems (2016) 1:7 Page 2 of 8

followed the conventional approach with the implementa-tion of distributed processing platforms that concentratedon protecting individual units of the system. Limited inte-grated protection was provided in the form of back-upprotection and thus remained a secondary function.Developments in the 1980s and 1990s provided new

means to advance power system protection, especiallythe ‘Adaptive Protection’ and the Artificial Intelligence(AI)-based protection techniques proposed in the 1980sand 1990s. The adaptive protection started with the ap-plication of Inverse Definite Minimum Time Overcur-rent (IDMT) protection in the early time of protectionhistory. The concept played an important role in the1980s with the progress of computing technology andassociated control theory. It can be defined as a newtype of relay protection which can change the perform-ance, characteristics or set value according to the oper-ation mode and fault condition of the power system.The basic idea of adaptive relay protection is to protectthe power system as much as possible to improve theperformance of the protection. Adaptive relay protectionhas the advantages of improving the response of thesystem, enhancing the reliability and improving theeconomic benefits. It has a wide application prospect inthe field of distance protection, transformer protection,generator protection, autoreclosure and so on. Researchhas discovered that, to achieve the protection of thesystem adaptive to the operation mode and fault status,more detailed system operation and fault informationare required through communication network.The 1990s witnessed the rapid development of elec-

tronic and computer technology, the artificial intelligencetechnology such as artificial neural networks, geneticalgorithms, evolutionary algorithm, fuzzy logic and other

research applications, which have been applied to thefield of relay protection. For example, artificial neuralnetwork (ANN) is used to achieve fault type identification,fault distance measurement, direction protection, and soon. Artificial neural network has the characteristics of dis-tributed storage, parallel processing, self-organization andself-learning. The application of artificial intelligence willimprove the speed and accuracy of fault detection andanalysis, which represents the future development of anintelligent diagnosis system.As a result of these developments, the performance of

the protection relays has been improved. However, thesedevelopments have concentrated on the improvement ofconventional relaying techniques, and no significant newrelaying principles have been derived from the applica-tion of the Adaptive and AI techniques. At the sametime in the 1990s, with the continuous expansion of thepower network, the demand for fast fault clearance toimprove system stability encouraged research into non-power system frequency fault detection techniques to in-crease the speed of the relay response. This led to thedevelopment of the so-called ‘transient based protection’relays based on travelling wave and superimposed com-ponents, which utilizes the fault generated transients fortransmission system protection. Studies have found thatthe fault generated high frequency transients can be de-tected and quantified, creating the possibility for devel-oping new protection principles and techniques [2].Considerable effort has now been devoted to researchon high frequency transient detection. Another import-ant milestone is the application of novel communicationtechnique, the utilization of global positioning system(GPS) in power system protection as shown in Fig. 1. Inthis respect, a number of new techniques has been

Bo et al. Protection and Control of Modern Power Systems (2016) 1:7 Page 3 of 8

proposed. In particular, the new proposed protectionrelay principle is able to provide protection for wide areapower network [3, 4]. Following the development, theconcept of wide area protection focusing on control as-pect has been presented [5].In recent years, the dramatic growth in signal process-

ing capability of relay platforms, and the availability ofsuitable communications schemes, have provided a newopportunity to revisit the concept of centralized protec-tion. Research [6] on the concept of ‘Integrated Protec-tion’ shows that information obtained from multiplepower plants and components can be used to derive newprotection principles and schemes, which could have sig-nificant advantages over the existing protection tech-niques based on the individual plant or component. Inthis respect, the substation area protection [7] has quicklybecome a practical development and application area.Furthermore, the development of information technologyhas resulted in the interests in utilizing cloud computing[8] and big data techniques, as shown in Fig. 1, to improvethe performance of power system protection and control.On the other front, the developments in the field of

substation integrated automation technology provide thetechnical basis for optimizing the combination and sys-tem integration of monitoring, control, protection andmeasurement device and system. The implementation ofrelay protection and integrated automation reflects inthe integration and resource sharing, remote control andinformation sharing. Taking the remote terminal unitand microcomputer protection device as the core, thecontrol, signal, measurement, billing and other circuitsare integrated into the computer system to replace thetraditional control protection cabinet, which can reducethe area and equipment investment and improve the re-liability of the secondary system. With the advancedcomputer and communication network, the relay protec-tion device is actually a high performance and multi-function computer, which is an intelligent terminal ofthe whole power system computer network. It can obtainany information about the operation and fault of the powersystem from the network, and can transmit any informa-tion of the protected components to the network controlcenter or any terminal. Therefore, each microcomputerprotection device can complete not only the relay protec-tion function, but also the measurement, control, datacommunication and other functions under normal oper-ation condition, and can also realize the integration of pro-tection, control, measurement and data communication.

Recent development in power system protectionand controlWith the fast progress in high-speed communicationnetwork and information technology, there were sig-nificant developments in power system protection,

power system control and wide area control in recentyears, particularly in the wide-area and integratedprotection.

Recent developmentWide area protectionIn recent years, the fast development in communica-tion technologies makes the wide-area information ex-change possible. In this respect, the emergence of thewide area measurement system provides a new ideafor the design of power system protection systems.The first wide-area protection principle is derivedfrom the transient based protection in 1996 [2], inwhich GPS time synchronization played a major rolein the design [3]. This was immediately followed by asummary paper in 1997, which systematically outlinesthe concept of the so-called “wide area protection”[4], focusing principally on the control aspect of thearea. The wide area protection based on novel algo-rithms, which is derived from the measurements ofmultiple information points, is able to provide fast,reliable and accurate fault clearance, analyse the ef-fects on the system stability based on the fault systemanalysis and take necessary control measures to per-form the functions of relay protection, security, andstability control in order to prevent voltage collapse.Wide area relay protection has quickly become a hotresearch topic with many research results publishedparticularly in recent years.

Integrated protectionWith the development of digital technology, more andmore protection functions for any given apparatus (line,transformer, generator, etc.) have been implementedwithin one protective device to achieve a certain degreeof integration. For example, a numeric line protectionrelay may have distance or current differential functionas the main protection, and directional and overcurrentfunctions as the backup protection. The recent develop-ments in microprocessor and communication techniquesprovided new means to derive new protection principlesand schemes based on the information obtained frommultiple power plants and components, which couldhave significant advantages over the existing protectiontechniques based on the individual plant or component[5]. Unlike centralized protection (or substation areaprotection), the integrated protection does not simplycentralize the relay hardware/software, but concentrateson the developments of new concepts and algorithmsbased on multiple points of measurements; via thismeans it is hoped that the performance of protectioncan be improved significantly. There was also researchin the field of integrated wide area protection [9].

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Wide area controlThe increased deployment of wide-area measurementswill significantly enhance the power system wide-areapower system operation and control. They provide volt-age and current phasor information, synchronized withhigh precision to a common time reference provided byGPS. Therefore, a wide range of power system monitor-ing and control applications can be implemented in thesystem for improving system awareness and reliability,which includes enhanced state estimation based onmixed Remote Terminal Unit (RTU) and Phasor Meas-urement Unit (PMU) measurements [10], dynamicmodel online estimation and validation [11], real-timecongestion management, real-time stability estimation[12], detection and damping of inter-area oscillations[13]. However, the most important and challengeable ap-plications are the implementations of wide area stabilityreal-time detection and control to prevent blackouts[14]. There was also research in the integrated protec-tion and control [15].

New concept and developmentBased on the developments mentioned above, a newconcept of the integrated wide area protection and con-trol (IWAPC) has been proposed recently. The mainfocus of the concept [16, 17] is the integration betweenthe protection and control, particularly at the wide-areaor regional level, aimed to provide a number of benefitsto the future protection and control system, e.g., the po-tential to merge the three lines of defence system andon-line self-healing decision making, in order to preventcascading tripping of large area power network. Theconcept of integrated wide area protection and control isintroduced, in which a three-level hierarchically coordi-nated system, supported by the specially designed real-time synchronised wide-area communication network,provides the protection and control for wide area or re-gional power substations/plants and their associatedpower network. The key element in the system is the in-tegrated wide area protection and control informationplatform, which receives real-time synchronised datafrom the communication network to support the inte-gration of protection and control at the wide area/re-gional level.The information platform also supports the applica-

tion of a cloud computing system, which is specially de-signed to implement a number of secondary functionsfor substations and power networks. In addition to thebasic functions of relay protection, the platform shouldhave a large capacity of fault information and data stor-age, fast data processing functions, powerful communi-cation functions, and other protection, control devicesand scheduling network to share the whole system data,information and network resources, and can also carry

out remote monitoring with the computer monitoringsystem of substation communication. With the proposedplatform, the architecture of future substation equip-ment may be reshaped to provide a flexible frameworkfor building an interactive grid and subsequently im-prove the reliability and security of power grids.

Integrated wide area/regional protection andcontrolArchitecture of integrated wide area protection andcontrolThe proposed integrated wide area or regional protec-tion and control system (IWAPC) is illustrated in Fig. 2.There have been fast developments in both power trans-mission and distribution networks, e.g., the series com-pensation in AC lines and high-voltage DC lines intransmission systems, distributed generation and energystorage in distribution systems, etc. These new develop-ments result in far more complicated characteristicsthan that of conventional systems. Consequently, theexisting protection and control system will no longer beeffective to cope with the new systems, and this has ledto the proposed IWAPC system. As is shown, theIWAPC system consists of different equipment at differ-ent layers: from bottom to top, there is the integratedmultiple-function intelligent equipment at the local level;the substation communication network and the inte-grated substation protection and control at the sub-station level; the wide area communication network, theintegrated wide area information platform and the inte-grated wide area (regional) protection and control atwide area level. The key parts of the system are thehigh-speed wide area communication network and thereal-time synchronisation information platform.The IWAPC is further extended to dispatching in

order to achieve the integration of dispatching automa-tion, protection and control of power grid, and accord-ing to the three-level dispatching (country, province,regional) architecture to implement the functions of re-gional protection, control and dispatching managements.

Multiple functions intelligent equipment at the local levelAs shown in Fig. 2, the Intelligent equipment at locallevel is an integrated multiple function secondary equip-ment in the substation, which mainly consists of theMU, intelligent terminal, metrology measurement, PMU& local protection. The equipment is responsible forsampling all real-time data and sending information tothe integrated substation P&C and wide area P&C. Italso receives and carries out the control commands fromthe integrated substation P&C and the IWAPC. Theequipment can be integrated into primary power appara-tuses and achieve local protection for 90 % of its associ-ated line sections. It has a redundant configuration to

Fig. 2 Integrated wide area protection and control

Bo et al. Protection and Control of Modern Power Systems (2016) 1:7 Page 5 of 8

ensure reliability, together with other integrated func-tions such as fault recorder, data storage and networkanalysis, etc.

Integrated substation protection and control at thesubstation/plant levelThe substation P&C integrates functions of line, bus,transformer protections, switch failure; autoreclosure,automatic bus transfer, UFLS, UVLS, overload inter-tripping and substation control function, etc. It utilizesinformation from the entire substation to achieve sub-station backup protection and safety automatic control,etc. The CBs are used as units to configure the adaptivebackup protection, and current differential protection isused to replace the stage overcurrent protection, breakerfailure protection and dead zone protection in the con-ventional protection system.

Integrated wide area/regional protection and controlThe IWAPC specially designed for the protection andcontrol of power network is able to offer fast protec-tion. In addition, they both integrate functions ofautomatic UFLS and UVLS, voltage and frequencycontrol, oscillation detection and out-of-step sepa-ration, etc. In addition, the IWAPC also incorporatesthe function of transmission cross-section safety P&C.

Unlike conventional protection and control, which areseparated in both design and operation, the IWAPCintegrates protection and control into one optimalcombined system, which effectively coordinates thewide area (regional) protection and control, in orderto achieve significant improvements in the protectionand control of power systems.

Synchronised high speed communication networkOne of the most important elements of the IWAPC sys-tem is the fast communication network. In this respect,the latest development in communication network, thePacket Transport Network (PTN) may be a better choiceto implement such a task. The present power communi-cation network is mainly used in multi-service transportplatform based on the Synchronous Digital Hierarchy(SDH). Its advantages lie in its high efficiency for carry-ing TDM services, low latency, high reliability, with endmanagement capabilities. However, with the new trendsin smart grid development, SDH technology graduallyrevealed its limitations, such as low bearing efficiencyand poor flexibility for data services. In contrast, PTNcan realise statistical multiplexing and efficient transferof packet service by using packet-switched core, whichcan overcome the weaknesses of SDH rigid bandwidth.In addition, it can provide good quality of service,

Bo et al. Protection and Control of Modern Power Systems (2016) 1:7 Page 6 of 8

operation, administration and maintenance. Self-healingfibre optical network is employed to connect a numberof substations in the region, to ensure full sharing of dy-namic and transient information for all electrical mea-surements, breaker status and protection operations;using high reliability IEEE-1588 technology to ensurethe synchronization timing of the sharing data, to provethe data for the integrated wide area protection and con-trol. However, SDH is still an option for the task since ithas been widely applied in power network.

Synchronized information platformSubstation is installed with a wide range of electricalequipment with complex designs and is difficult tomaintain. With the continuing improvement in powersystem automation and the intelligence level, the sys-tem network has been expanding, along with the hugeamount of information in protection and control. Aseach piece of information is collected and stored by dif-ferent devices in each separate system, the interoper-ability of the internal power system data betweensystems is poor, whereas complex communication pro-tocols tend to create information islands. Consequently,the measurement data and protection control mechan-ism cannot be shared, which restricts the informationintegration. The protection and control of smart gridrequires dealing with the new situation demands of theapplication, in order to improve further the informationplatform capabilities for the future development of keytechnologies, and to make the information platformsystem more open.The real-time synchronized information platform ac-

curately collects wide area information and conductsdata mining to investigate the logic relation between thereal-time information to increase the sensitivity, reliabil-ity and fault tolerance capability. The data received fromthe platform includes static, dynamic, transient measure-ments and states of circuit breakers, etc. Valuable infor-mation is extracted from the data and allocated tovarious specially-designed computation algorithms inthe platform to perform advanced functions of protec-tion and control for the power network. In the platform,sets of data need to be transferred and their transferringspeed depends on the application, e.g., slow speed forcontingency analysis, near real time speed for monitor-ing, real time speed for control, and high speed for widearea protection,; in particular, time synchronization. Theinformation can also include other types of data, such asthe oil and ambient temperature of the transformer,wind speed and direction, sun intensity, etc. On theother hand, the information is stored in a hierarchicalmanner instead of a centralized one, which comprisesthe hierarchical protection and control system. Equippedwith the latest high-speed synchronised communication

technology, integrated with the advanced protectiontechniques and the latest developments in control sys-tem, the system offers not only fast protection, but alsocomplete control of entire power network.The advanced computing technology is introduced to

establish a synchronized information platform for widearea protection and control, to build a panoramic oper-ation and maintenance data collection network, provid-ing a standardized interface to the terminal device, toform a resource sharing, flexible and interactive, openand ordered information platform. In summary, ad-vanced computing technologies are used to build a dis-tributed collaborative intelligent information platform,simplifying terminal data collection equipment, andbreaking the barriers between protection and controlsystems at different substations through the specially de-signed synchronized information platform.

Wide area power cloudBased on the information platform mentioned above, adistributed cloud system is designed to implement func-tions at substation and regional levels, such as wide areafault location, fault line selection, power quality monitor-ing, protection settings, etc. The extended functions alsoinclude the equipment monitoring, life cycle and oper-ation management, as shown in Fig. 3.Currently, many kinds of secondary equipments

achieving different functions are installed in each sub-station, and an increasing number of distributed energyresources of small capacity added to the system greatlyincrease the number of equipments. To implementthese equipments, complex functions in a specially de-veloped distributed “cloud” system will greatly reducethe equipment investment. The cloud at substationlevel receives the data from process level, and the re-gional cloud receives the data from the informationplatform, which includes static, dynamic, transientmeasurements and states of circuit breakers, extractingvaluable information and allocating them to variousspecially-designed computation algorithms in the plat-form to perform advanced functions in order to identifythe faulted line, the accurate fault location and the con-tents of harmonics, etc.The cloud computing platform can make full use of

“processing ability of cloud” to reduce the burden of ter-minal secondary equipment. Based on big data tech-nique, the computing clouds enjoy strong processingpower based on demand. There is no need for endlessupgrades to improve the processing capacity of theequipment, and there is also no need to update the soft-ware to achieve a variety of task processing. There aremany more advantages which can be derived from thecloud system, such as the wide area information sharing,standardization of software and algorithm, reduction of

Fig. 3 Structure of distributed power cloud

Bo et al. Protection and Control of Modern Power Systems (2016) 1:7 Page 7 of 8

equipment investment, substation area occupation andwork load for operation and maintenance.

ConclusionsThis paper presents an integrated wide area protectionand control system based on a hierarchical structure,which integrates protection and control at local, sub-station and regional levels. Covering both transmissionand distribution networks, the system is supported bythe proposed high-speed synchronised communicationnetwork and the real-time protection and controlinformation platform. The system, which integrates theadvanced protection techniques and the latest develop-ments in control system, offers not only fast protec-tion, but also complete control of the entire powernetwork. It offers a potential for the merger of thethree lines of defence into a unified system to ensuremore effectively the reliable and safe operation ofpower grid. Based on the system information platform,a distributed power cloud system is also designed tosupport many advanced applications for the integratedwide area protection and control.With the continuous advances in measurement, com-

munication and information technologies, the systempresents a bright future for practical application. Overallimproved performance of protection and control can beexpected from the proposed system. However, for thesystem to become useful in power system application, itis equally important that its practical implementation bereadily manageable, user-friendly and cost-effective. The

authors hold that, to achieve these goals, the proposedintegrated protection and control at wide area level of-fers an appealing way forward.

Authors’ contributionsZB investigated the framework of integrated wide area protection andcontrol, and drafted the manuscript. XL summarized the history of powersystem protection. QW summarized recent development of power systemprotection. YY summarized the wide area power cloud. FZ participated intypesetting and revision of the manuscript. All authors read and approvedthe final manuscript.

Competing interestsThe authors declare that they have no competing interests.

About the authorsZhiqian Bo received his BSc degree from the Northeastern University, Chinain 1982 and PhD degree from The Queen's University of Belfast, UK in 1988respectively. From 1989 to 1997, he was with the Power and Energy Group,University of Bath, UK. He has been with ALSTOM Grid Automation andresponsible for new technology development and international researchcollaboration from 1998 to 2012. Recently he joined the XUJI Group of theState Grid Corporation of China (SGCC) as the Chief Expert on smart grid.Xiangning Lin (SM’08) received the M.S. and Ph.D. degree in school ofelectrical and electronic engineering of Huazhong University of Science andTechnology (HUST), Wuhan, China. Currently, he is a professor at HUST. Hisresearch interests are modern signal processing and its application in powersystems as well as power system protective relaying and control.Qingping Wang was born in Hebei Province, China, in 1975. He received hisPh.D in 2002 from the Department of Electrical Engineering, Tianjin University,China. At present, he has been employed as CTO of XJ Group CorporateResearch. His research interests include protection, substation & distributionautomation, power system simulation and micro-grid. He is author or co-authorof more than 40 journal papers and owner of more than 30 invention patents.Yonghui Yi, born in 1969, PhD in electrical engineering. Currently he works asthe Managing Director of Protection and Automation Company of XUJI Group,His main research areas are smart grid and power system protection.Fengquan Zhou, born in 1969, is the director of R&D Center, XJ Group,obtained his first Degree and graduate Degree from Tsinghua University,

Bo et al. Protection and Control of Modern Power Systems (2016) 1:7 Page 8 of 8

finished his PHD research in McGill University in Canada. His research areasinclude energy efficiency, power system automation protection, distributedgeneration, renewable energy, smart grid and other fields.

Author details1XUJI Group Corporation, Xuchang, China. 2Huazhong University of Scienceand Technology, Wuhan, China.

Received: 9 May 2016 Accepted: 9 May 2016

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AbstractIntroductionRecent development in power system protection and controlRecent developmentWide area protectionIntegrated protectionWide area control

New concept and development

Integrated wide area/regional protection and controlArchitecture of integrated wide area protection and controlMultiple functions intelligent equipment at the local levelIntegrated substation protection and control at the substation/plant levelIntegrated wide area/regional protection and control

Synchronised high speed communication networkSynchronized information platformWide area power cloud

ConclusionsAuthors’ contributionsCompeting interestsAbout the authorsAuthor detailsReferences