availability, total cost of ownership and the possibility
ofmodification, extension or partial replacement ofcomponents.
Specification, design, configuration,training and documentation are
key elements whichcontribute to the ability of the utilities to
maintain aSubstation Automation Systems during its lifetime.The
Technical Brochure (TB)written by WG B5.06defines DSAS as
Substation Automation Systems usingdigital communications on
substation level where themain functions are implemented in
Intelligent ElectronicDevices (IEDs) such as bay controllers or
digital protec-tions. It intends to give some guidance for
utilities,which require an understanding of how to adapt
themaintenance of their SubstationAutomation Systems tothis new
context. The topics developed also concern theother stakeholders in
DSAS maintenance, in particularthe vendors.When deciding the life
cycle strategy of DSAS,utilities should take into account all
aspects, frominitialinvestment costs to decommissioning. The
maincontributing factors which have to be defined for
theirlife-cycle strategy are identified in the Technical
Brochure.These factors also formthe base for the definition of
theutilitys maintenancestrategy :SubstationAutomationSystems (SAS)
and associatedtechnologies have evolvedconsiderably over the
precedingdecades, with the aimto increase their overall
efficiencyand to decrease the ownership costs. Amongst
otherfactors, this trend is driven by the rapid evolution
ofcomputer and telecommunication technology.
TheSubstationAutomation Systems commissioned today aredigital and
more integrated. They are designed andconfigured with powerful
engineering tools by highlytrained staff.The maintenance of Digital
SAS (DSAS) is differentfromthat of conventional SAS under different
aspects:G Digital Substation Automation Systems pose newquestions
on how to ensure the effectiveness ofmaintenance over the whole
life of the system.G The professional profile of maintenance
special-ists has been changing according to the technolog-ical
evolution of substation automation devicesand systems. This has an
impact of maintenanceon existing and future DSAS.G This
newtechnology implies a change in the taskscarried out by the
traditional actors in themaintenance of DSAS and imposes
differentstrategies for their maintenance practice in orderto take
into consideration new constraints.The approach for the maintenance
of DSAS has totake into account several factors including
systemMaintenance Strategiesfor Digital Substation
AutomationSystemsWGB5.06464TECHNICAL BROCHURENo. 256-
June2011ELECTRA67Members:Volker Leitloff, Convener (FR), Michael
Eckl (AT),Peter Jenker (SE), Martin Herzig (CH), Frank Koers
(NL),Steven A. Kunsman (US), Ivan Lorencin (SL),Rannveig S. J. Lken
(NO), Alberto Lopez de Viaspre (ES),Mika Loukkalahti (FI), Iony
Patriota de Siqueira (BR),MarceloPaulino (BR), Massimo Petrini
(IT),JohnRobertson (CA), Ville Tiesmki (FI),Peter Wittlinger (DE),
John Wright (GB)1105-014
Electra256.qxp:0507-012Mep22130/05/119:26Page 67Level of
specifications and maintenance principlescan vary greatly between
large and small utilities, betweendifferent voltage levels and
depending on type andimportance of substations.As for the other
technical requirementsin the DSAS specification, the approval
andtest process of the utility has to includethe verification of
the respect of therequirements concerning maintenance.Maintenance
procedures and testprocedures after maintenance operationsshould be
included in the deliverables ofthe DSAS documentation.Maintenance
tests in conventional baysare organized on the base of one
equipment = onefunction. In a DSAS, one function can either
beimplemented together with other functions in the sameequipment
(Functional Integration) or it can bedistributedover several
equipments. The testing procedurehas thus to take into account the
implementation of thefunctions and cannot, in some cases, be
performed as analmost independent procedure for each
functionality.Attentionhas also to be paidto the maintenance
tools,which may experience similar constraints concerning
themaintenance of their hardware and software than theDSAS
itself.TheWGB5.06 establisheda questionnaire concerningthe practice
of maintenance of DSAS. This questionnairehad a restricted
circulation and was completed by 12utilities related to the WG. It
is thus not completelyrepresentative for the industry. It gives
however an insightinto the current practice of maintenance of DSAS.
Theresults of the questionnaire are discussed in more detailin the
TB. Some salient points are:G There still seems to be much
time-based mainte-nance on DSAS. The potential offered by the
self-supervision of DSAS to adopt a maintenancestrategy principally
based on corrective mainte-nance is thus not completely used by all
utilities.G The average period of configuration modificationgiven
by the survey is about 4 years, but there is asignificant amplitude
in the received answers (fromone per year to once every ten years).
In general,modification of the configuration is more frequentfor
new DSAS developments (migration period,bugs).Fromthe utility point
of view, the life cycle of a DSAScan be broken down to several main
phases as shownin figure.The TB briefly describes the different
types of main-tenance. As far as DSAS is concerned, the
self-supervi-sion implemented in these systems allows a reduction
ofpreventive maintenance. The self-supervision results thusin a
shift of balance away from preventive maintenancetowards corrective
maintenance.Utilities can basically adoptthree different
strate-gies for doing the maintenance of DSAS :G Outsourcing of
this activity by subcontracting toa vendor or another service
provider.G Doing the maintenance of DSAS completely by itsown
staff.G A mixture between the two above mentionedpossibilities.The
TB identifies items that need to be consideredwhen developing a
maintenance strategy and describesthemin detail.Conservation of
knowledge and skills for the main-tenance of DSAS is a vital issue
for utilities. As comparedwith conventional SAS, maintenance of
DSAS globallyrequires a higher level of training and skills. The
TBdiscusses the different aspects to be taken into account.The DSAS
should be designed by the vendors withmaintenance inmind, not as
anafterthought. Concerningthe utilities, the specification of the
DSAS shouldcontain requirements related to the maintenancepolicy of
the utility. It has to be made sure that themaintenance operations
are feasible under theconditions defined by the utility. These
conditionsinclude the global availability of the DSAS,
safetyconditions and acceptable degraded operation, e.g. dueto
common modes. Often, a de-energising of theconcerned feeder is not
accepted for basic maintenanceoperation of the
DSAS.WGB5.06464TECHNICAL BROCHURENo. 256- June2011ELECTRA691105-014
Electra256.qxp:0507-012Mep22130/05/119:26Page 69DSAS (but not all).
IEC 61850 will also facilitatespare-part management due to
interoperability andstandard data models. But the reality of
hundreds oflegacy DSAS deployed by utilities must not beforgotten.
The main stakes of DSAS maintenance in thenear future concern these
systems.It has been demonstrated that the version manage-ment of
DSAS configuration, both for hard- andsoftware is of major
importance for the long-termmaintenance of these systems. In
practice, only theutilities are able to put into place version
managementsystems that properly reflect reality in the field.Remote
access is believed to play a more importantpart in the future, in
spite of security issues which haveto be addressed. It may be
possible to performon-lineupdates of centraliseddatabases of the
utilities containingsetting and configuration information using
standard-ised data models and remote access.Much work is clearly to
be done in the field ofmaintenance testing in order to obtain
adequate toolsand validated and standardised testing procedures.The
issues concerning life-time maintenance ofDSAS for utilities can be
summarised as follows:Utilities should not try to apply the
organisation andprocedures put into place for maintenance
ofconventional SAS. Maintenance of Digital SAS has to beadjusted
and adapted. IG About half of the utilities state that they use
acomprehensive asset management systemfor DSAS.G Almost all
interviewed utilities have trained staffwho can do maintenance.
Half of themstate thatthe part of the maintenance done by utility
staff isincreasing.Almost all utilities have a particular strategy
forspare-parts. Two thirds have their own spare-partstorage, and
about half of them also have an externalcontract for spare-part
storage. The model of a store atthe utility which belongs to a
vendor is not very common.A considerable number of Digital
SubstationAutomationSystems are already inoperation,
andutilitiesare concerned about the most efficient, cost effective
andsafe way of maintaining themduring their lifetime. Thereis a
general consensus within the industry that mainte-nance strategies
for DSAS cannot be the same as thoseemployed for conventional SAS
and would need to beadapted to meet the their needs. This is
related to theparticular characteristics and implemented
technologiesof DSAS.The organisation of the maintenance activity
ofutilities has to be adapted to this new context. Thisincludes
long-termmaintenance contracts and the reviewof the possibility of
outsourcing a part of this task to thirdparties.System
standardisation and optimisation of main-tenance is a continuous
task for all power utilities.It also appears that maintenance of
DSAS has to betaken into account at the systemdesign stage and
requiresspecific training, test methods and
procedures,documentation and skilled staff. The expression of
aparadigm change was recently employed to describethe amplitude of
this evolution.One key element is to acquire and to maintain
asufficient knowledge of the staff in charge of DSASmaintenance.
This requires adapting the content of thetraining courses and to
plan periodic updates. In thiscontext, the training courses for
maintenance staff shouldconcentrate more on howto solve the
problems than onhow to build the systems.These requirements also
apply to DSAS based on IEC61850. In addition, this standard may
help to make themaintenance for DSAS of different vendors more
homoge-nous. Its applicationsupports a self-documentationof
theconfiguration and of some other information of
theWGB5.06464TECHNICAL BROCHURENo. 256- June2011ELECTRA71Hardcopyin
English onlyOn sale at the Central OfficeMember Price :Non-Member
Price :e-mail : [email protected] tlcharger
http://www.e-cigre.orgor download at http:
//www.e-cigre.org(Membres uniquement / Members only)BROCHURE N
4641105-014 Electra256.qxp:0507-012Mep22130/05/119:26Page 71
