高志遠，曹陽，朱力鵬

（中國電力科學研究院，江蘇南京 210003）

In charge of the tasks of electric power transmission and distribution,the numerous substations are important supporting nodes in the power grid,and the investment is huge[1].Future development of smart substation is of great significance for the construction of smart grid.

From the traditional substation to ordinary integrated automation substation,and then to digital substation,until now widely studied smart substation，the research and construction of power substation has experienced a long-term development[2-6].In refs[7-9]some standardized descriptions and specifications were given for the digital and smart substation,which defined smart substation as“whole substation information digitization,communication platform networking,information sharing and standardization”.

How will smart substations develop in the future?Especially,under the construction environment of smart grid,what kind of features will next generation smart substations have in the aspects of technology,device,standard and so on?Regarding this issue,a large number of researches have been carried out at home and abroad.Refs[10-12]analyzed the integrated,high compact and low-cost development trends of modern substation technology and design.Refs[13-14]analyzed and showed the multi-levelsafetyand reliability connotation of substation.Refs[15-16]carried on some substation design and empirical research related to environment protection issues.From the economic perspective,refs[17-18]made the quantitative analysis of substation construction,maintenance and life cycle cost.Refs[19-20]discussed the supporting of smart substation for renewable energy development.By modularized and typical design,Refs.[21-22]presented aschemetoreducethecostand improvethe reliability of substation.Ref[23]actually proposed a principle to realize the coordination of reliability and economy by combined consideration of the risks and economic factors.To implement the“resource-saving,environment-friendly,industrialization”concept,typical designs of the new substation were given in ref[24].Ref[25]prospected the application of the solid-state power electronic technology in the future substation.By analyzing the key technologies involved in the smart devices of substation,ref[26]put forward that“it will be a long-standing problem in improving the body and increasing the attachments of two research lines．”

As can be seen from the above analysis,the future development of smart substation is all-around and multi-angle.At present,the key problem of the research on the future development direction of smart substation is: Carrying out a systematic and comprehensive framework research and avoiding constrained by a few specific professions and directions.This paper attempts to answer such a question:How to systematically study the future development of smart substation.Ref[27]presented a post-assessment method to evaluate and guide the development of smart substation by a series of interactive,comprehensive and advanced evaluation indexes.Starting from the intrinsic mechanism of substation development,based on the analysis of the extrinsic demands from socioeconomicenvironment,thispaperputforward a systematic method to analyze the development status,vision and trend of smart substation.

1 Substation Development Mechanism

To grasp the future development trend of smart substation,we need to clarify its developing mechanism from internal and external two aspects.The basic substation model is the fundamental factor in its development,as for reliability,energy-saving,environment protection,economical efficiency,high power quality and other extrinsic drives they take effects through the basic substation model.Finally the internal and external factors contribute jointly to the development of smart substation.

1.1 Basic Substation Model

As detailed structure,functions and technologies of substation are in the process of dynamic changing,this paper,taking those factors of stability,constructs a basic substation model with widely applicable scope as shown in fig.1.It includes:1）High-voltage power flow network of primary devices.It implements the basic electric power aggregation,transformation and distribution functions of substation and consists of such primary devices as power transformer,bus,incoming line,outgoing line,circuit breaker,disconnector,reactive power compensation devices,etc.2）Substation workers.3）Substation automation systems.It consists ofsuch low-voltage secondary devicesasrelay protecting devices,measure and controldevices,metering devices,fault recorders,merging units,etc.It also includes communication facilities, backend SCADA and advanced application systems,and such auxiliary production systems as fire alarm devices,video surveillance devices,etc.For smart primary devices,the intelligent components which work under low voltage also belong to thispart.4）Other infrastructure,such as buildings and HVAC systems.

Fig.1 The basic model of power substation

In theory,the basic problems of substation,including the development of smart substation,can ultimately be solved by the analysis of the basic substation model.Of course the basic model in fig.1 needs to be refined when considering a specific problem.For example,as to high-voltage networks of primary devices, there are various main bus connection modes,various primary devices selections,various requirements and design for different primary devices.As to automation systems,there are various hardware and software platforms,varioussystem structures,various human-machine interface styles,various function characteristics and various communication modes.It is likewise for buildings and substation workers etc.

1.2 Extrinsic Drives for Substation Development

The extrinsic drives of substation development are from the demands for whole smart grid development.These demands are all-round and multi-angle,some of them may become common keys,and some will become the development trends in certain situations.Sometimes we have to weigh the options among different development directions of mutual restrictions.

Considering the specific circumstances of substation,we think that the core extrinsic drives for substation development include:1）Basic functions,which realize the power aggregation,transformation and distribution.2）Reliability,that provides reliable power supply.3）High electric power quality.4）Environment protection,which includes the advanced treatment of noise, electromagnetic interference,sewage,emission and etc.5）Cost reduction,refers to the whole life cycle cost reduction.6）Reduction in covering area.7）Supporting the development of clean energy.These 7 core drives have certain correlations and influences between each other.

Almostallothertypesofdemandscan be attributed to the above 7 core drives.For example,improving the degree of automation through a variety of information and communications technologies can be attributed to improving reliability and saving human resources,and saving human resources ultimately means cost reduction.Energy-saving actually means reducing the operation cost of substation.The electricity load has been growing rapidly with the socio-economicdevelopment,so we need more substations in the power grid,so we have to face the demands of reduction in cost and covering area.Of course,we must take into account of the specific circumstances of transmission grid in the analysis.

2 Analysis Method for the Present Status of Smart Substation

We think that the analysis on the present status of smart substations is actually to analyze how current smart substations meet the demands of those core development requirements, based on the basic substations model.The detailed method as shown in tab.1 is given to clarify how the specific requirements to be met in the above 7 aspects,their strengths and weaknesses,etc.

3 Design Method for Development Vision of Smart Substation

The development vision of smart grid needs to be designed in different categories considering its internal and external environments.Vision is a proper development goal between extrinsic demands and realization possibility based on the basic substation model.The working environment of smart substation is various in geographical and geological conditions,amount of investment,socio-economic and technological environments,etc.As shown in Tab.2,we distinguish different types of substations from 3 dimensions:voltage grades,locations,and if it is an unmanned substation.The type numbers in Tab.2 are just some examples. Be noted that we can distinguish substations from different dimensions,such as junction substation,AVC monitoring substation,centralized control substation,terminal substation,etc.

Tab.3 is used to accurately design the development visions of various types of smart substation.For eachcore demand,firstly the detailed content of the demand need tobeconfirmed accordingtothe specific conditions,then we can use the basic substation model to design its vision based on the related technologies and devices.The specific content of table 3 is a sample vision design for type 213 of tab.2,which is a 500 kV underground or half underground substation.

Tab.1 Smart substation development status analysis table

Tab.2 Classification of smart substation

Tab.3 Definition of smart substation vision

4 Analysis Method for Development trends of Smart Substation

So far as the development of substation technologies can be illustrated as fig.2 according to the basic substation model.If taking no account of involved men and buildings,there are 2 main aspects:1)The progressofhigh-voltage powerflow network of primary devices.Development of high-voltage primary devices needs to adopt new principles,new designs,new technologies and new materials,the pace is slow,however itis fundamental.For example，power transformers have been slowly progressing in voltage level,capacity,cooling mode,Fe-core materials,winding materials and covering area,circuit breaker developed from the traditional oil circuit breaker to various vacuum circuit breaker,air circuit breaker,SF6circuit breaker,etc.Based on the progresses in basic units of primary devices and integration with automation systems ofsecondary devices,a new concept of smart components was put forward，which is the key for the fusion of primary devices and secondary devices.2)The development of automation systems.The development of automation technologies has a law that the progress of one phase is mainly around a core technology.The core technology of the progresses is the application of microcomputers from traditional substations to substations of integrated automation.The core technology is the application of network technologies from substations of integrated automation to digital substations,including all kinds of field bus and ethernet technology applications,and the research and application of IEC 61850 is its concentrated reflection.The core technology is intelligentization from digital substations to smart substations.We are on a new stage of deepening the application of network technologies and further intelligentization of smart substation at present.

The future development trend of smart substation is finally embodied in the related designs,technologies,devices,standards,etc.Which designs will become the mainstream of the future?That depends on how they meet the 7 core demands for smart substations.And we can analyze it based on the basic substation model.It is similar for the related technologies,devices and standards.

For each specific substation,the requirements in the above 7 main aspects are different,therefore the importance of same one key technology for various types of substations is different.In order to reflect the complicated situation of the core drives，which exert profound influences on the development of substation technologies，this paper designs the following analysis and judgment method.Assume that for each specific substation,the above 7 core extrinsic demands have different importance which we use weighting factors to represent,as shown in Table 4.

We use Cf,K1,K2,K3,K4,K5,and K6to represent the weighting factors ofthe 7 core demands respectively，and there are the following relationships among them:

Fig.2 Evolution schematic diagram of the substation technology

Tab.4 Demand weight table of smart substation

Cfmeans the importance of a function,for a needless or immature technology,we have:Cf=0，and for an optional function,we have:0

A rating scale is designed to evaluate accurately each demand satisfied degree,according to six of the above mentioned core demands excepting basic function demand.The full score of each individual item is 100,which is given according to the related indexes.Special attentions are paid to progressive effect,which means it should not be completely linear relationship between the related indexes and scoring.For the progresses of advanced and complicated functions,the scorings increase faster,and for those progresses easy to make,the scorings increase slowly.The following is an example of reliability.The reliability of devices and technologies themselves is included into the overall MTBF(Mean Time Between Failure).

Tab.5 the schematic table of reliability ratings

So we can get a comprehensive evaluation for each specific technology,device or standard according to the above method and rating scale.The value E of comprehensive evaluation can be expressed as:

The value of Cfcan be set according to the related national standards,enterprise standards and real working environment.Thus for most optional or compulsory technologies,devices,and standards,0≤E≤100;for a few ones we are advancing or in urgent need,E>100.The largest E value indicates the most possible future development direction of smart substations.

With the preliminary application of the above method and rating scale,we think that the most important development trends of smart substation include:1） Compact design.2） Large-scale energy storage.3） Environment protection.4） Automation system based on cloud computing technologies.5）New advanced primary devices based on the progresses of basic units of primary devices and reliability.6）Modularized design and typical design.7）Distributed integrated design.

5 Conclusion

On the basis of development mechanism analysis methodology of smart grid,starting from the analysis of intrinsic basic model of substation,combined with driving effects from the development of smart grid,a development mechanism model for substation is put forward.Furthermore by use of the mechanism model,the analysis methods for the development status,the future vision and the development trends of smart substation are designed.And as a preliminary application of the designed analysis methods,the future development of smart substation is prospected.

The future development of smart substation is a significant problem which involves the whole power grid operation and safety,as well as huge investments.Both the method and the conclusion proposed in this paperare justpreliminary research results.For example,the design of the analysis method has a certain degree of universality,but it needs further refining,the main indexes of rating scale are preset subjectively because of very limited information.We can carry out further research on the analysis method of basic substation model,the design of rating scale,operability of scoring method,application of cloud computing in substation automation systems,etc.We also need to carry out detailed research according to the different requirements of junction substations,AVC monitoring substations, centralized control substations,terminal substations,etc.

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