designing iec 61850 systems

8/4/2019 Designing IEC 61850 Systems

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46

PAC.SPRING.2008

IEC61850

Engineering

communication services GOOSEand SMV (Sampled Values) allownew substation functionality orexisting functionality with lessengineering effort and higherreliability, however introducemultiple sinks for certain signals,which might be concerned bya change at the signal source, asillustrated in Figure 1.

IEC 61850 object types and

data identification

IEC 61850-7 introduces IED andcommunication modelling concepts,and standardized data semantics

by standardized names. However,the concrete instance names areadditionally dependent on thephysical and logical structuring of thedata and therefore not a priori stablewhen replacing IEDs or changingthe architecture. What is long termstable (as least as long as the switchyard itself), is the functional meaningof the data in relation to the switchyard respective the power delivery

process. Further the substationautomation functionality relatedto the switchyard is normally longterm stable, although extensionsare not excluded. Therefore IEC61850-6 introduces a second way ofidentifying the same data, namely byfunctional designations as defined inIEC 61346.

IED related objects and

their identifications

IEC 61850 as a communicationstandard in first line addresses dataidentification at communicationlevel, i.e. at interface level between aserver or publisher IED and the datareceivers (clients, subscribers). Tomake this naming independent fromthe physical structure, the concept ofa logical device (LD) is introduced asa management unit for functionalparts. Figure 2 shows the resultinginternal structure of an IED.

The communication functionuses IED access points to connectclients with servers. In principleeach logical node can be a client toother logical nodes on some server.IEDs which only receive data, likethe OPC server AA1KA1 in Figure1, can also be pure clients without aserver.

To reach the goal of havingstandardized semantics, the DATAnames as well as the names of

DATA attributes are completelystandardized. Also the semantic ofthe logical nodes is standardized bymeans of a logical node class, whichis part of the logical node instancename. A real system needs instancesof logical node classes, which areassociated to different parts of theswitch gear; therefore the LN instance

Usage of names

Names are used at systemengineering time to establishrelations between the different partsof the system: Relations betweenthe switch yard (primary system)and the IED signals (secondarysystem), and data flow between IEDsfor communication engineeringrespective online communicationassociation establishment. A namechange at a data source thereforeleads to reengineering of all IEDsconnected to the changed onerespective replaced one. In formermaster slave architectures all dataflowed between the bay level IEDsand one single central place, onlythe IED to be replaced and thecentral IED were concerned. ForIEC 61850 however already foravailability reasons several stationlevel IEDs might be connected tothe same bay level IEDs, and the new

Designing IEC 61850 systems

for maintenance, retrofit and extensionThe goal of IEC 61850 is to support arbitrary system configurations with

centralized or decentralized architecture. The choice of a specific system architecturis beneath pure technical aspects determined by the existing products and provensolutions. As technology advances, other kinds of architectures may become usabland cost optimal, which lead to a different amount of IEDs and a different internastructure of them, which is reflected in the IED related identification of data. On thother hand, low effort long term maintenance needs identical names for identicaobjects. But even at the replacement of an IED by a functional equivalent IED fromanother manufacturer a different internal structuring and naming is most likely.

Wolfgang Wimmer works for ABB Switzerland in Baden. He

is principle engineer in the development of substation auto-

mation systems. He has a M. Sc. degree as well as a Ph.D. in

Computer Science from the University of Hamburg. After some

years developing Computer networks at the German Electron

Synchroton DESY in Hamburg he changed to ABB (former BBC)

for development of train control systems, later Network Con-

trol Systems. He has more than 20 years experience with deve-

lopment of substation automation systems. He is a member of

IEC TC57 WG 19 and WG 10, and editor of IEC 61850-6.

by Dr. Wolfgang Wimmer, ABB, Switzerland


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InterlockInterlockInterlock

Color code:

PositionsPositions

GOOSE Unbuffered

Interlock

StatUrg

StatUrg

StatUrg

StatUrgC1 StatUrgC1

StatUrgM1

MeasFlt

AA1KA1OPC ServerP2WA1

P2Y1COM581***GW***

P2KA3Siprotec-7SJ6xxP2WA1

P2KA2C264P2WA1

P2KA1REC 670P2WA1

P2FA1REL 670P2WA1

P2KA4RED 670P2WA1

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PAC.SPRING.2008

identification has non standardizedparts. The logical device name asa manufacturer / organisationrelated structuring is completely

free within some syntactical limits.This is illustrated in table 1 with anexample designation for a switchposition value within the switchcontrol function:MyControl LD1/Q0CSWI3.Pos.stVal

A product manufacturer typicallyprovides IEDs as products withsome predefined functionality,however with no context to theproject specific usage. Therefore theLD relative name and some parts ofthe LN instance identification needto be given by the manufacturerindependent of the unknownproject, and might be needed afterproject engineering to associate theproject specific data to the projectindependent preconfiguration ofthe IED. Therefore it is manufacturerdependent, which parts of theLN instance identification can beadapted specifically for a project.

Although this designation ismainly used for communicationestablishment, we might call it aproduct related designation in thesense of IEC 61346-1, especially ifthe IED designation is used as part ofthe LD name.

From this discussion we seehow the physical architectureinfluences the communicationlevel naming. Table 2 illustrates

this with two logical nodes forthe control function: the CSWIhandling control commandsfrom the operators and the XCBRexecuting these commands at thecircuit breaker. The architecturesreferenced in the table are illustratedin Figure 5.

Consequence: different physicalarchitectures by grouping on IEDsas well as different organisationalstructures by means of logicaldevices lead to different names, evenif an IED and its tool supports freenaming for the non standardizedparts. And the free naming is notmandatory according to IEC 61850,and naturally introduces additionalengineering and testing effort especially at LN instance level.

Function related objects

and identifications

According to IEC 61346 thefunctional designation is at least asimportant for operation of a processas the product related naming formaintenance. IEC 61850-6 thereforeintroduces application relatednames of data by typically followingthe functions of the switch yard,however allowing additionally (with

Edition 2 practically at all places)functions which are not directlyswitch yard related, like protection,control and automation functions,

but also supervision functionsoutside the substation function itselflike fire supervision, or functions

belonging to power generation. Thefunctional names are completelyproject / customer specific withinthe structural restrictions given byIEC 61346-1. The transition object,i.e. the place where product relatedname and function / applicationrelated name matches the same

Usage of applicationoriented functional

names in parallel tomaintenancerelated IED names

with automatictranslation via

SCL files, enhanceslong term system

maintainability

For

interlock

reasons,

controlle

exchang

GOOSE

message

The

replacem

of IEDP2

influence

3 other I

The four

controlle

different

are send

reports t

station l

IEDs.

1Data flow between IEDs in the substationExample of a small system with an OPC server & a gateway as station level IEDs

Figure 1

an example

of a small

system


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Substation AA1

Voltage level E1 at 110kV

Bay Q3

Equipment QB1 : DIS

XSWI, Name /XSWI of Typem_XSWI

CSWI, Name /CSWI of TypeE3_CSWI

CILO, Name /CILO of Typem_CILO

Equipment QA1 : CBR

XCBR, Name /XCBR of TypeE_XCBR

CSWI, Name Q3QA1/CSWI of TypeE3_CSW

CILO, Name Q3QA1/CILO of Typem_CILO

Equipment BE5 : VTR

Function F1 : Protection

PTRC, Name /PTRC of TypeE3_PTRC

PSCH, Name /PSCH of TypeE3_PSCH

PTEF, Name /PTEF of Typem_PTEF

Subfunction Z1 : Distance zone 1

PDIS, Name /PDIS1 of Type E3_PDIS


PDIS, Name /PDIS2 of Type E3_PDIS


PDIS, Name /PDIS3 of TypeE3_PDIS

Subfunction Z1B :

PDIS, Name /BPDIS1 of TypeE3_PD

Function R1 : ProtRelated

RREC, Name /RREC of TypeE3_RREC

RFLO, Name /RFLO of TypeE_RFLO

Function M1 : Measurement

MMXU, Name /MMXU of Type E3_MMXU

Process bus access point (can be same as above)

Client associations

Inter bay bus Access point1 logical, several physical

Client association

IEDServer

LN

DO

LN

DO

Logical DeviceLogical Device

LN

DODO

LN

DO

I / O

The server access point allows

access to data structured as

follows: logical devices contain

logical nodes (LN) containing

DATA respective data objects

(DO). Logical nodes on other IED

can access the data as clients

IEC61850

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PAC.SPRING.2008

Engineering

object, is the logical node instance.From here on all DATA and attributenames are completely semanticallydefined in IEC 61850. If we look

into the functional names of figure3 for the same control functionhandled by the IED related names oftable 2, these are:

AA1E1Q3QA1CSWI.PosAA1E1Q3QA1XCBR.PosThe protection related name of

the operation of distance protectionfor Zone 1 is:

AA1E1Q3F1Z1PDIS.OpAll these names are completely

independent from the distributionof logical nodes and logical devicesto IEDs, and also from the LD andLN instance names.

A complete SCL file for asubstation automation system,called an SCD file, includes thefunctional name, the IED relatedname, the communication related(LD) name, and the relations

between them thus serving as adata base for translation betweenthe different designations for thesame LN respective DATA object.This is shown in Figure 4 for theabove example, illustrating theindependence of the functional namefrom the IED related name up to thepoint where IEC 61850 providescomplete semantic standardization.

Communication engineering

IEC 61850 MMS based servicesallow an interactive browsing ofthe IED data model to retrieve all

communication related names. Dueto the unique LD name these can betranslated into IED related names aswell as functional names by meansof the SCD file. However, normallyoperational traffic is based onpreconfigured data flow for servicesallowing spontaneous sending.These are typically:

Reporting service for statusupdate and time stamped events tostation level IEDs like HMI, orgateways to network controlcentres.

GOOSE real time service forreal time functions typically between

bay level IEDs, or down to processlevel IEDs, e.g. interlocking relateddata or protection trips and

blockings.SMV services, if analogue

samples are needed directly from theprocess, e.g. for protection,synchrocheck and measurementfunctions.

To evaluate the importance ofthe DATA names for these services,we have to look a bit into theirdefinition:

All services are configured bymeans of a data set, defining the

IEC 61850

MMS based

services allow

interactive

browsing of

the IED data

model.

2 IED related object model structure

3 Example of a functionhierarchy


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Functional name:

AA1E1Q3QA1CSWI.Pos.stVal

Substation: AA1

IED related name:

Ctrl9LD1/QA1CSWI 1.Pos.stVal

Voltage level: E1

Bay: Q3

Switch: QA1

LN (class) : CSWI

Attribute: stVal

LD: LD1

IED: Ctrl9

DATA: Pos

LN: QA1CSWI 1

The structuring and naming

of the functional identifi-

cation (left) down to the

LN class are completely

independent from the IED

related name (right)

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PAC.SPRING.2008

data to be spontaneously sent, anda control block, defining when andhow it shall be sent, as illustrated inFigure 6.

The reporting service onlysends the changed data values. A bitpattern in each report identifies theplace of the data set to which the sentdata values belong.

For GOOSE and SMV servicesalways all values of the whole dataset are sent. The order of values in themessage corresponds to the order ofthe data items in the data setdefinition.

This means, that essentiallythe values sent on the wire do notcontain any of the names consideredearlier, just the relation between thesent values and their place in the dataset definition. For correct messageinterpretation the receivers onlyhave to know, to which data set themessage belongs, and how this dataset looks like. For reports this can beestablished dynamically by meansof the browsing services or data setcreation services, however also bystatic configuration with a commonSCD file as base. The relation

between the online message and thedata set definition then is establishedas follows:

Reports are MMS based andMMS associations must be

dynamically established. A reportclient either builds its own data setsdynamically (if the servers supportthis), or uses preconfigured data sets.

If he relies on preconfigured datasets, he can check at start-up thecontrol block revision number onany discrepancies between staticdefinition and actual definition onthe IED.

GOOSE and SMV messageswork according to the subscriptionprinciple and are permanently sent.The message contains Ethernet levelidentifications like Multicast addressand application identification( A P P I D) , a n d t h e d a t a s et identification in the form /., which allows the subscribersto identify and filter the correctmessage fitting to the DATA theywant to use from their staticconfiguration based on the SCD file.A control block revision number,always sent in the message, allowsreceivers to detect any discrepanciesin data set layout configuration

between sender and receivers.This interpretation of messages

relative to a data set definition allowsto replace e.g. a GOOSE publisher

by any other IED without having toreconfigure the receivers, as long asthe new IED.

Contains the data of the oldGOOSE message with same datatypes and same semantics (functionalequivalence).

Contains or allows configuringa data set with the same type of datavalues in the same order and samesemantics related to the project asthe old IED.

Uses the same Ethernet leveladdressing (Multicast address,APPID, VLAN).

Has the same full data set name:same LD name (if freely configurableon the IED), same LN name (LLN0for all GOOSE and SMV messages),the same data set name (mostlyconfigurable at the IED for GOOSEand SMV data sets), and the sameconfiguration revision number(needs free setting by the toolcreating the data set, or some toolsupport for the replacement).

Different physicalstructures enforce

different IED relateddata identifications atIED/LD/LN level

4 Connection of functional and product related namingexample


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Ctrl 9

Station level

Bay level

Process level

Ctrl 1

Swg 8 SWg 9

Ctrl 9

Swg 8 SWg 9

Bay controller

+ Process bus

Central controller

+ Process bus

Bay controller

IEC 61850 offers solutions to

minimize the influence of main

tenance activities at applicatio

level, by introducing in parallel

to the IED related identification

a function oriented identifica-

tion of data according to the

concepts of IEC 61346.

IEC61850

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PAC.SPRING.2008

Engineering

This means that the replacing IED hasbeneath the requirements on compatiblesemantics and data types to fulfil someengineering related requirements, whichare not mandatory according to IEC 61850.Further it should be considered that errorsat the reconfiguration of the data set whenkeeping the old revision number and dataset identification can be safety critical,

because the receivers do not demand to benewly configured. So, a good tool supportor testing in a simulated environment isrecommended.

The problem of binding GOOSE orSMV receivers to the data set layout doesnot appear for reporting clients, becausethey can perform this binding dynamically.However, if the names have changed,the binding to the functional semantics,especially binding of LN instances toinstances of switch yard equipment andfunctions, is still a problem. One meansto solve this binding to the applicationfunction is to re-establishing the link

between functional names and IED relatednames also for the new IED(s). This is

supported in IEC 61850 better thain other protocols in so far, as th

binding is done on the level of logicnodes instead of signals, and will iall cases, where application specifLNs are used (e.g. no GAPC and nGGIO), reduce to a selection of Linstances with the same LN clasthus minimizing the amount owork as well as that of errors.

For good implementations ostation level clients, which internallwork with the functional names adefined above, it is then sufficiento reload them at driver level witthe SCD file resulting from thre-mapping of LN instances.

E v e n b e t t e r c l i e nimplementations allow to dthis reload per IED e.g. whecommunication with the (newIED is (re-) established. In any casthe probability of errors is restricteto the remapped IED, and th

Use functionanames as a key

between oldand new

configuration

5 Different architectures

Name differences caused by architectureTable 2

Architecture LD Name LN Name DATAName Remark

Single bay

controller

Ctr19LD1

Ctr19LD1Q0CSWI1Q0XCBR1

PosPos

LNs located in same LD

Process bus from

bay controller to

circuit breaker

interface

Ctr19LD1

SWg8LD1Q0CSWI1

QA1XCBR4PosPos

LD (IED) name at switch interface IED mustbe different to name in bay controller; LN

instance names are manufacturer specific.

Central controller

with process bus

to circuit breaker

interface

Ctrl11LD9

SWg8LD1Q0CSWI1

QA1XCBR4PosPos

Free LD naming would allow using centrallythe same LD names as de-centrally if the

central LD structure is the same.

Degree of name standardizationTable 1

IED structurelevel

Degree of standardization Exampledesignation

Stan-dardized

Predefined na-me semantic

Logical device LD Syntactical (61850-7-2) MyControlLD1 --- ---

100 Kb/S Partly: LN class (61850-7-4) Q0CSWI3 CSWI Switch control

200 Kb/S Full: DATA name (61850-7-4) Pos Pos Switch position

Attribute Full: Attribute name (61850-7-3) stVal stVal Status value

For maintenance it is recommended to choose an IED related logical device name,

structured as IED name - LD relative name


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defned by data sets and control blocks

DO

LN

DO

LN

Logical Device

DO

LN

Logical Device

IED

DataSet

GOOSE or Report messages

trigge

rs

CB

51

PAC.SPRING.2008

probability is quite low, becausethe remapping is performed on therelatively high level of LN instances,supported in most cases by the

needed LN class. It should howeverbe considered that the new IEDshould contain at least the sameDATA per remapped LN instance asneeded by the application.

Impact on engineering and

used products

The following points areimportant to minimize the efforts incase of SA system retrofit:

Use functional naming forsystem engineering and the IEDrelated names, so that the SCD fileprovides a translation between themin a standardized format.

Use functional naming atapplication level, i.e. withinapplication functions. Let the (MMS

based) communication driverstranslate the IED names intofunctional names by means of SCDfile(s). In case of (station level) clientswhich do not support this, use a toolto create the new configuration fromthe SCD file, by using the functionalname as common key between oldand new configuration.

The safety of this approach canbe supported by a system tool whichsupports the IED replacement at thefunctional structure on LN level,with a check of the same respectivecorrect LN classes.

As we have seen, the replacementof GOOSE servers without havingto reconfigure all GOOSE receiversneeds some optional features fromthe IED respective its tool:

Support free LD namingSupport free data set naming, at

least for GOOSE and SMV data setsSupport free (guided) setting of

GOOSE confRev

To make this procedure safer,the tool should support remappingthe new IED to the functionalnames and, after this remapping,automatically (re-)create the GOOSE/ SMV data sets with identical layoutand name, set the LD name propertyidentical and take over all oldaddresses.

Unfortunately, all these featuresdo not help for the GOOSE / SMVcase, if a changed architecture leadsto another logical device structure,

so that the requirement onuniqueness of the LD name forbidsthe proposed LD renaming, or ifdue to a new physical structure theGOOSE messages have to be splitonto different IEDs.

Some impact on system

modelling principles

A relatively safe tool-supportedbinding of the LN instances of thenew IED to the functional names

by using the old IEDs binding astemplate is only assured, if GGIOand GAPC LN classes are avoidedas far as possible. This is also in thesense of IEC 61850, which demandsusing a fitting LN class whereverone is defined. Here also someimprovements of manufacturerIED tools might help, whichallow replacing a GGIO by a moreappropriate LN class at IED (pre-)engineering time.

However, if the old structuringinto logical devices does not fitto the new structuring, this doesnot help. Therefore, already at theinitial system design, the logicaldevice structure in relation to theused GOOSE and SMV messagesshould be set up to support themost distributed structure whichis intended to be used during theswitch yard life time. Further,GOOSE and SMV data sets shouldnot reference data outside the LD inwhich they are defined else thesemay later reside on different IEDs,and therefore force a redefinitionof the data sets with appropriatere-engineering of the receivers.

The general concept of a maximaldistributed system, even if it is

implemented centrally, also helpsin having a common behaviour ofdistributed and central systemsconcerning functionally connectedlogical nodes, because it makes thefunctional behaviour independentfrom the fact if internal functionalconnections between the LNimplementation are used or external

explicit communication connections.This has also been considered at themore detailed definitions of IEC61850 Edition 2 for the influenceof the test and block quality ofincoming signals, and should also beused when implementing test and

block modes on internally connectedlogical nodes.

If these additional systemstructuring rules are considered,then the consequent usage offunctional naming for applicationrelated functions in parallel to theusage of product related naming forautomation system maintenance, asforeseen in IEC61850-6, supportseasy retrofit and system extensionwith minimum engineering,modification and (re-)testing efforteven if the underlying physicalarchitecture is changed or IEDsof a different type or a differentmanufacturer are used.

Designing systemsfor the maximal

ever intendedphysical distribution,

eases futureretrofit

6 Communication model

Communi-

cation mode

with data set

and control

blocks

designing iec 61850 systems

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