Investigation on the Application of IEC61850 in Smart Distribution Grid with Micro-grid

TAO Wei-qing

School of Electric Engineering and Automation

Anhui CSG Smart Grid Technology CO.,LTD Hefei,China.

YUAN Xin-xi School of Electric Engineering and Automation

Hefei University of Technology Hefei,China.

Abstract—New organizational unit of grid—the micro-grid

is an integral part of smart distribution network, with the

advantages of flexible and efficient use of new energy,

IEC61850 communication makes the electrical equipment

of different manufacturers interoperate in one system. In

this paper digital substation is divided into substation layer,

bay layer and process layer based on the IEC61850

communication ,this paper analyses the three-layered

structure of the digital substation communication systems

and the communication of smart distribution grid with

micro-gird,explores the information interactive when

there are faults in the grid and the feeder terminal

unit(FTU)for information modeling, discusses the

application of IEC61850 communication in smart

distribution grid containing micro-grid .

Key Words—Smart distribution grid;Smart micro-grid;

IEC61850;GOOSE;FTU

INTRODUCTION

The smart grid is considered to be a model for future grid development,starting the first major innovation reform in the power system.One functional of the smart grid is to support a large number of Distributed Energy Resources(DER)[1] integrated into. In order to reduce the impact of DER on the distribution grid, DER is integrating into grid through the form of micro-grid .

The nucleus of IEC61850 is to solve the problem that electrical equipment of different manufacturers can not be interoperability in one system. At present, the research based on the IEC61850 mainly focuses on the digital substation. Literature[2]introduced the first 220KV

digital substation— duerbot substation,and its implementation scheme in china.Literature[3] introduced the application of sampled value transmission based on IEC61850 standard. The IEC61850 standard is also expanding its scope of application. Literature[4~5] introduced a test platform of low power grid connected to the power grid of Catalonia Energy Research Institute,the platform is based on IEC61850 communication protocol.

This page discussed the application of IEC61850 communications in distribution automation system with multi-micro-grid,based on the research of distribution automation system with multi-micro-grid at home and abroad,and the application of IEC61850 standard in the digital substation.

THE INTELLIGENT DISTRIBUTION GRID AND

SMART MICRO-GRID

A. Smart distribution grid

Smart distribution grid is based on flexible network topology,highly integrated communication system,advanced sensor and measurement technology, advanced power electronic equipment,energy storage technology,advanced operational decision support software,these make smart distribution grid support lots of distributed generation and renewable energy into distribution grid,enhance the interactive between the power user and supplier,improve the operation efficiency of the distribution grid.

Figure 1 is a simple system of distribution grid with multi-micro-grid.

2012 International Conference on Control Engineering and Communication Technology

978-0-7695-4881-4/12 $26.00 © 2012 IEEE

DOI 10.1109/ICCECT.2012.146

847

2012 International Conference on Control Engineering and Communication Technology

978-0-7695-4881-4/12 $26.00 © 2012 IEEE

DOI 10.1109/ICCECT.2012.146

847

Figure 1. Distribution Network containing Multi-micro-grid architecture

This figure is the "hand in hand" distribution grid with multi-micro-grid.CB1 and CB2 are intelligent breakers, S2/S4/S5/S7 are intelligent isolation switches on line, S1/S3/S6/S8 are intelligent isolation switches for the micro-grid connecting to distribution grid, St is loop intelligent isolation switch.MGCC is micro-grid central controller. FTU is feeder terminal unit.

B. Smart mirco-grid

Smart micro-grid is the intellectualization of micro-grid.This paper holds that the realization of smart grid,must depend on strong power system, advanced communication system and advanced auxiliary equipment,to realize the information exchange of power generation unit,storage unit and load unit in micro-grid,and the information interactive of micro-grid with external power grid[6].The micro-grid information interactive is shown in figure 2.

Fig.2 Information exchange for smart micro-grid

THE APPLICATION OF IEC61850 IN THE

SMART DISTRIBUTION GRID WITH

MULTI-MICRO-GRID

A. IEC61850 in digital substation

According to the functions of controlling, monitoring and protecting in substation system, the system is divided into three layers based on IEC61850,namely the substation layer, bay layer and process layer[7].

The bay layer and the substation layer communi- cate by manufacturing message specification(MMS),as well as the substation layer internal;The bay layer and the process layer exchange the control and status information through the GOOSE,as well as the bay layer internal.The sample value information is transmitted by SMV signal of interval layer and the process layer[8].

B.IEC61850 in smart distribution grid with multi- micro-grid

1) The hierarchical structure of distribution grid with multi-micro-grid

Digital substation based on IEC61850 standard is divided into the substation layer,bay layer and process layer,the distribution grid with multi-micro- grid is divided into four layers:the master layer,the feeder layer,the terminal layer(FTU,DTU,MGCC, etc)and the process level(switch,the PT,CT)[9].

The master layer is the core of the intelligent distribution grid,the feeder layer located in the substation which is responsible for connecting the feeder of all

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FTUs,the terminal layer is a intelligent device located in the specific line,including pole-mounted FTU,the monitoring terminal of switching stations DTU,link switch to the micro-grid FTU,MGCC,etc.The process layer device is the implementation layer of the specific equipment, including circuit breakers,isolating switches,TA,TV,etc.

Smart distribution grid described in this paper applies the IEC61850 communication protocol.If the distribution system in Figure 1 applies the traditional 101 and 103,the FTU do report the information of modification initiatively , but can not be used for point to multi-point communication.so the FTU can only transform collected operation and fault data point-to-point,and accept remote control signal.

IEC61850 communication is applied in the distribution grid with multi-micro-grid,its sub-station and master station are generally communicated by the client/server(C/S) communication with the core of manufacturing message specification(MMS),the substation and terminal layer communication generally use the generic object oriented substation event(GOOSE) message communication.GOOSE communication replaces hard links communication among the traditional intelligent electronic devices(IED), has provided a fast and efficient method of communication among the logical nodes.GOOSE communication makes that any of IEDs can connect other IEDs by Ethernet,GOOSE messages are sent in the form of broadcast, a heartbeat message is sent out when IED status does not change,the other IED can be received when the IED status changes, the GOOSE messages are sent quickly,the other IEDs can receive the messages of status variation,thus achieving the interoperability of equipments.

With the development of embedded technology, a large number of intelligent circuit breakers and IEC61850 communication are applied in the smart distribution grid, as a result, the faults processing time becomes shorter, and the range of failure interruption smaller.In Figure 1,during normal operation of distribution grid,the micro-grid is incorporated into the power grid,contact switch St is disconnected.When a permanent fault occurs in A, the intelligent circuit

breaker S2,S3 and intelligent circuit breaker CB1 will detect a fault current, they will send the message of state variable by GOOSE message,other intelligent circuit breakers will receive variable messages.Intelligent circuit breaker S4 does not detect a fault current, and will send the normal heartbeat message.The intelligent circuit breaker S2,S3,S4 disconnect. If S2 refuse, S2 will send failure information by the way of a heartbeat message,then S3,S4 send the message after disconnection,at this time CB1 is off,S1 disconnect,either.

When S3 detects a fault current, MGCC will send coordination of signals to internal micro-grid. The micro-source controller(MC),load controller(LC) and energy storage controller(SC) of micro-grid will send information to MGCC regularly.MGCC sends coordination of signals to the MC/SC/LC by GOOSE message while failure,according to the information of micro-sources, energy storage and load before the failure.

2) Information Modeling

Modeling of substation automation equipment based on IEC61850 is already quite mature now. The application of IEC61850 standard in the smart grid,we should use logical nodes provided by IEC61850 standard,to complete the information modeling of key equipment in the intelligent distribution grid with multi-micro-grid.For example,the information modeling of feeder terminal unit (FTU).

FTU modeling described in this paper is on the foundation of four information modules:telemetry, remote control,remote signaling and power management function. Telemetry information mainly includes measurement value of active power,reactive power, current,voltage and equipment state.Remote signal information includes information of relay protection, communication.Remote control information mainly include the division and control information of the circuit breaker and the isolating switch[10].Power management includes batteries and battery management.If each functional module is regarder as a logical device(LD),FTU can be divided into four logical devices(LD1,LD2, LD3, LD4).

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LD1 mainly accomplishes the function of telemetry;LD2 is mainly for the remote signal;LD3 is mainly for the remote controlling;LD4 is mainly used to complete the management of the intelligent power module.Each logical device contains LLN0 (including the related information of IED,control of IED selftest)and LPHD(public information module of the physical device).

The remote function module LD1,includes measurement (MMXU),harmonic and interharmonic(MHAI),phase sequence and unbalance(MSQI), current transformer(TCTR) and voltage transformer(TVTR). MMXU collect the current and voltage information of distribution lines by TCTR and TVTR. MHAI completes harmonic measurement, MSQI is used to measure the unbalanced current.

3 FTU information module

Remote signaling function module LD2,includes the universal process I/O(GGIO),instantaneous over-current protection(PIOC),time limit over-current protection (PTOC), sensitive direction of earth fault(PSDE),direction components (RDIR) and the fault location (RFLO).

LD3 is a remote control module, includes the switche controller(CSWI), load switche(XSWI) and breaker (XCBR).

The LD4 power management module, includes batteries (ZBAT) and battery charging management (ZBTC).

CONCLUSIONS

Smart grid,as a new concept,its connotation is constantly enrich with the deepening construction of smart grid.In this page,we discussed the application of IEC61850 in the distribution grid with micro- grid,based on the research of the distribution grid with micro-grid and the application of IEC61850 in the digital substation.Smart distribution grid based on IEC61850 communication is only in the research phase,and is seldom used in the practical power system.The research of smart distribution grid in China starts relatively late, in order to make contribution to our country of building a resource-saving and environment-friendly society, we should intensify the research of smart distribution grid in the future,and pay attention to the experience of other countries for reference.

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