controllingmonitoringsubstationautomationnbkrinst

8/7/2019 controllingmonitoringsubstationautomationnbkrinst

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PROTECTION AND SUBSTATION AUTOMATION

N.B.K.R.I.S.T VIDYANAGAR 1

A

TECHNICAL PAPERONCONTROLLING AND MONITORING

OF

SUBSTATION AUTOMATION

AUTHORS:

N.VENKATESWARLU, N.KEERTHI KISHORE,

II/IV B.Tech, II/IV B.Tech,

Branch: EEE, Branch: EEE,

Vidyanagar. Vidyanagar.

Email:[email protected] Email:[email protected]

N.B.K.R.INSTITUTE OF

SCIENCE AND TECHNOLOGY

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Summary:

Protection and substation control have

Under gone dramatic changes since the

advent of powerful micro-processing and

digital communication. Smart multi

functional and communicative feeder

units, so called IEDs(Intelligent

Electronic Devices) have replaced

traditional conglomerations of

mechanical and static panel

instrumentation. Combined protection,

monitoring and control devices and LAN

based integrated substation automation

systems are now state of the art.Modern

communication technologies including

the Internet are used for remote

monitoring, setting and retrieval of load

and faultdata. Higher performance at

lower cost hasresulted in a fast

acceptance of the new technology.

The trend of system integration will

continue, driven by the cost pressure of

competition and technological progress.

The ongoing development towards

totally integrated substations is expected

to pick up speed with the approval of the

open communication standard IEC61850

in the next years.

Introduction:

Increased competition has forced utilities

to go into cost-saving asset management

with new risk strategy:

Plants and lines are higher loaded up

to thermal and stability limits.

Existing plants are operated to the

end of their life-time and not replaced

earlier by higher rated types.

Redundancy and back-up for system

security are provided only with critical

industrial load.

Corrective event based repair has

replaced preventive maintenance.

Considering this changed environment,

Power system protection and control

face new technical and economical

challenges:

Modern secondary systems shall enable

higher system loading at lower

investment and operation cost without

compromising system reliability.

Users widely dispense with special

custom-built solutions but aim at cost

reduction by accepting standard products

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of global vendors. Manufacturers had to

compensate the world-wide price drop

by cost saving. This has mainly been

achieved by right-sizing of product

ranges, standardisation of products,

rationalisation of manufacturing and

expansion to global markets.In this

regard, the introduction of the

digital technology has played a decisive

role because the price reduction at a

comparable function range could only be

achieved with the new generation of

smart highly integrated IEDs.Besides the

lower investment cost, theuser gets a

reduction of the operation cost

due to the inherent self-monitoring

capability(corrective instead of

preventive maintenance)and the possible

remote operationand diagnosis.

In the relay business, these advantages

were obvious for the user. Therefore, the

transition to the new digital technology

occurred within a decade (1985-1995).

FIGURE 1 - Current relay design trend

In the case of substation control, cost

comparison between electromechanical

anddigital technology has often been

discussedcontroversially.The recently

practised assessmentof total life cycle

cost, however, seemsto confirm

economic use in most cases. Decisive

is the possibility to rationalise and

automatesubstation operation and to save

operatingstaff on site. This pays off in

particularin industrialised countries with

high personnelcost.Relaying and control

IEDs also serve asdata acquisition units

for power system controland power

quality monitoring. By usingwide area

information systems, the data can

be made available to all involved

partners.This is becoming more and

more importantin order to satisfy the

information demandin the deregulated

power supply market withfree network

access.

Recent development

of protection and substation

automation:After more than 20 years ofdevelopment,

digital protection and substation control

have reached a mature product state.

In the mean time, some 100.000 digital

relaysand some 1000 digital substation



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control systemsare in service.As a rule, a

common IED hardwareplatform is used

today for relays and baycontrol units

(figure 1). Its modular designallows

adaptation of the input/output interface

to the individual application. Separate

processing modules are dedicated to the

communication interfaces to cope with

theincreased data rates and complex

transmissionprocedures. GPS time

synchronisationof microsecond accuracy

is optionallyoffered with the latest

device generations.Global products

designed for the worldmarket meet

relevant IEC as well asANSI/IEEE

standard requirements and can

be adapted to the communication

standardsused in Europe and USA. The

informationinterface of relays can for

examplebe delivered to IEC60870-5-103

as wellas to DNP3.0 or Modbus.

Windows compatible PC programs allow

comfortable local or remote operation of

IEDs. Unfortunately,there is no common

operatingstandard, so that the user must

changebetween vendor dependent

program versionsto address relays of

different make.This also concerns

communication interfacesand protocols.

An improvement can be expected when

relays will be equipped with their own

Internetserver and the operator-relay

dialoguecan be performed in a simple

way by usingstandard browsers. First

Internet enabledIEDs are already

available.

Protective relaying:

The number of functions integrated in

relays has been steadily expanded in

parallelwith the increasing processing

power andstorage capacity. Table 1

shows a typicalexample of relay

hardware evolution.



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TABLE 1: Development of digital relay

HW performance (example)

Protection relays have developed into

multi-functional universal devices,

generallydesignated as IEDs (Intelligent

ElectronicDevices). Non-protection

tasks, such asmetering,monitoring,

control and automation,occupy an ever

increasing share of thescope of

functions.Complete protection of a

power systemcomponent (transformer,

line, etc.) can nowbe provided by only a

few highly integratedrelays. For

example, the protection of a larger

generating unit only needs two or three

relays, each with about 15 protection

functions.At the time of traditional

relaying, severalpanels or cubicles full of

black-box relayswere necessary for the

same protection scope.Protection

functionsBasic digital protection

functions havepassed innumerable lab

and field tests andare well-established in

practice. In the lastyears, they could be

further improved byapplying intelligent

algorithms.Examples forthis are: higher

accuracy and stability in case of

disturbed measuring values (e.g. during

c.t. saturation), and better load versus

faultdiscrimination by adaptive

measuring principlesand flexible shaping

of characteristics.The offer of integrated

functions coversthe world-wide practice

(global relay). Theuser can for example

choose between definiteand various

inverse over-current timecurves or

between quadrilateral and MHO

type impedance characteristics. He has

thefreedom to configure the relay for his

particularapplication case by software

parameterisation.This trend will surely

contribute to aglobal convergence of

relaying practices.Additional functions

Metering and event/fault recording are

now offered as standard even with

smallestrelays.An accuracy of about 1%

for meteringof current and voltage and

of about 2% for active and reactive

power are usually specifiedfor relays.

For the total accuracy, theerrors of c.t.s

and v.t.s (up to 3% with protectioncores)

have to be added.The storage time for

fault records is nowin general at least

10s with a resolution of 600to 2 400 Hz

dependent on the type of relay.Power

quality monitoring is partly covered

by protection relays. The offered

registrationof voltage dips greater than

10 msand harmonics up to the 5th or

10th order issufficient in mostapplication

cases.Monitoringof fast transients and

higher harmonics(e.g. up to the 50th)



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would requirehigher sampling rates and

extended relaymemories. The ongoing

technical improvementand price

reduction of hardware components

will however favour a trend towards

the integration of full scale PQ

monitoringin protection relays.

Combined protection and control

IEDOver the years, there has been a

globaltrend towards combined units for

protectionand control on basis of IEDs

(Intelligent Electronic Devices, Figure

2). The main application:

Areas are distribution systems and

industrial networks. These universal

devicesintegrate all substation secondary

functionswith the exception of revenue

metering.Full scale versions include a

full graphicmimic display and a key pad

for supervisory

FIGURE 2 - Combined Protection and

Control IED

control. The devices can be used stand-

aloneor serially connected to an RTU or

a centralcontrol unit.Automation

functions can comfortablybe designed

and implemented by means ofa graphic

PC tool (CFC: continuous function

chart).Computer controlled testing

Simulation techniques have advanced to

a degree of virtual reality. This goes in

particularfor real-time digital simulation

systems(RTDS) which enable absolute

practicecompatible lab testing.However,

even PC-controlled portabletest sets

allow for dynamic testing under real

conditions.Among other features,

programadditions are offered for

extended relay testing,for example under

the condition of c.t.saturation.

This new quality of testing hasdecisively

contributed to the upgraded performance

and reliability of digital protection

systems.



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Maintenance Based on the nearly

complete self-monitoringof modern

IEDs, event controlled maintenance is

propagated world-wide asa decisive

contribution to cost reduction.

Theoretical studies have shown that the

availability of digital protection is even

comparableto a redundant analogue

protectionscheme providing at the same

time significantlyhigher security against

false operation.Complete abolition of

testing, however, ismostly not accepted

as even the best selfmonitoringconcept

cannot cover 100% ofthe protection

scheme.In the few publications about the

currentpractice, maintenance intervals of

four(Germany) to six years (Japan,

Sweden) wererecommended.

Newersurveys indicate atrend to longer

intervals, even up to 10 years.

3. Current protection

practice:

A world wide survey on reasons for

blackouts and experienced protection

performance[1] showed the following:

thejudgement of protection was in

general reasonablygood. There was,

however, a numberof maloperations of

feeder protection.More attention should

be paid to relay settingand co-ordination

with overload capabilitiesof the

protected plants.The survey confirms

that fast clearanceof fault, in particular

on busbars, is vital toa systems ability

to ride through disturbances.Duplication

of protection and

POWER SYSTEM FAULT (LIGHTNING

STRIKES AN OVERHEAD LINE).

the installation of breaker fail provision

isessential on crucial busbars and on

highvoltagelines since back-up operation

times often result in system splitting and

cascading.The following developmenttrends canbe observed in the individual

protectionareas:

3.1 Transmission system

protection:

On higher voltage levels, redundant

protectionconcepts with stand alone

relays havebeen kept also with thechangeover to digitaltechnology. Relays

with dissimilar measuringprinciples (e.g.

differential and distance)or relays of

different make are stillpreferred.Control

functions are provided byindependent



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feeder units.Line protection With the

advent of digital wide-band

communication more differential

protectionhas been applied at overhead

lines of evenup to some 100 km length.

Phase segregateddesign guarantees zone

and phase selectivityfor all kind of short-

circuits. The use isadvantageous in

particular with complex line

configurations such as multi circuit,

multi terminal or tapped lines.

Differential and distance protection are

now considered as ideal combination for

high voltage lines. The transfer of

protectiondata via communication

networks, however,requires careful

planning. GPS synchronisation

may be necessary in critical cases.

With short lines up to some 30 km, a

direct back-to-back connection of the

relaysat line ends is possible provided

that dedicatedoptic fibres are available.

Fault locationUpgrading of fault location

is a preferredsubject of ongoing studies

and numerouspublications. In most

cases, new or improvedmethods are

discussed and proposed to compensate

influencing factors such as fault

resistance, load transfer, parallel line

coupling,series compensation and line

chargingcurrent.Fault location based on

reactance measurementas integral

function of distance relays has an

accuracy of about one percent linelength

under favourable conditions. Larger

errors will however occur with higher

fault resistances. Improvement can be

expected inthe future by GPS based

synchronisation ofdata acquisition and

processing of the informationfrom both

line ends.High accuracy is achieved by

travellingwave based fault locators.

ESKOM, SouthAfrica reports about +/-

150 m on EHV lines[2]. Fault location is

in this case estimatedby measuring the

time difference of travellingwave

propagation from the fault to bothline

ends. Transformer protectionThe use of

digital filtering and intelligentalgorithms

has dramatically upgraded transformer

differential protection performance.

Stability against c.t. saturation, inrush-

currentsand overfluxing is now much

more reliable.Integrated numerical ratio

and vectorgroup adaptation belong to the

standard.Relays with up to five

stabilizing inputs are offered which

allow to protect all kind of transformer

connections. Integrated add-on functions

now reachfrom overload and overcurrent

back-up toearth-fault and over excitation

protection. OLTC control and



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transformer monitoringare also

integrated in some combined devices.

Busbar protection State-of-the-art is

decentralized digital design and sub-

cycle operating time. Bayunits are

connected to the central unit viafast

optical fibre links. Sophisticated

algorithms guarantee far reaching

independence of c.t. saturation. The

isolator replica is softwarebased and can

each be adapted to evencomplex bus

configurations by means of thesetting

program. Digital low impedance

protection is now offered even in

traditionally high impedanceminded

regions because high impedance

protection can by principle not be

transferred to digital technology.

Protection of generating units Function

integration has further proceeded. Even

larger generating units can now be

protected by two or three relays with

each about 15 protection functions

(protection of auxiliaries nor

considered).The quality (sensitivity and

accuracy of measurement, replica reality,

etc.) of individual protection functions

has been further improved. In principle,

however, the longtime established

protection principles are further used

Wide Area System Protection Schemes

(SPS)A more recent development

concerns System Protection Schemes

(SPS) [3, 4].They operate on the basis of

system wide acquired information and

try to avoid power system collapse

which can occur during unstable active

or reactive power conditions as a

consequence of voltage and frequency

drop or loss of synchronism. Normally

one tries to achieve stable partial

networks by purposeful system splitting,

GIS

load shedding and forced control of

power generation. The SPSs are

intended to operate already in the initial

state of instability before system control

can intervene. Recent developments

include GPS-based synchrophasor

measurement for on-line systemstate

monitoring. A number of SPS systems

are already in service, mainly in Japan

[3]



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3.2 Distribution System

Protection:

The current trend is towards combined

protection and control IEDs. Driving

forceis the need for cost cutting.The

reduction of the former conglomeration

of black box devices to only one

multifunctional relay saves on space and

wiring. Highly integrated switchgear

panels using small scale CTs and VTs

are gaining increasing market share.

Low resistance earthed radial networks

are generally protected by inverse-time

OCrelays.Meshed Peterson coil earthed

networks which occur mostly in Europe

are also equipped with distance relays.

Urban cable networks traditionally use

differential protection. New digital

relays must be suitable for the existing

pilot wires. Therefore, proven analogue

current comparison principles are

maintained, however, upgraded to digital

relaying standards. For short cable

connections also relays with digital

wire communication can be applied. Inthe more seldom case where optic fibre

connections exist, relays with direct

relay-torelay OF connection can be used

for distances up to about 30 km.

The growing share of distributed

generation requires reconsideration of

distribution protection. In many cases

changeover to directional OC relays may

be necessary to cope with the backfeed

of distributed generators. A particular

problem provides the loss-of-mains

protection because traditional frequency

and voltage relays may be too slow or

insensitive and vector jump relays tend

tooverfunction.

OPEN AIR SWITCHYARD

Siemens (Germany)

A number of new principles

have been proposed but no satisfying

solution is yet available. Fast fault

finding and system restoration to

upgrade power supply quality is getting

more and more important. For this

purpose, the state of earth-fault and



11/16



shortcircuitindicators are evaluated

together with the distance-to-fault

calculation ofrelays.Modern fault

management includes automatic

acquisition and processing of these data.

The results are then indicated in the

graphic information system of the

control centre. [5, 6]In many countries,

fault clearing by distributedreclosers and

sectionalizes is stillpractised. Protection

and control functions of these devices

are now also provided bydigital devices.

In combination with poletopRTUs and

radio connections, fast faultclearing and

load restoration is also achievedin this

case. [7]Detection of high resistance

faults(downed conductors) has been

studied fora long time. Proposed

algorithms are basedon wave shape

analysis and recognition oftypical arc

characteristics.

A recent survey comes to the conclusion

that an algorithmsuitable for practical

application has so farnot been found

despite costly developmentefforts. [8]

4. State and trends of substation

automation Integrated protection and

control firstappeared in the mid

eighties and has sincethen matured to

full scale substation automation.

4.1 Recent practice:

Simple systems for distribution or

industrialnetworks mostly use feeder

dedicatedcombined protection and

control IEDs anda PC-based central unit.

Alternatively,enhanced RTUs with

decentralised I/Operipherals are applied.

FIGURE 3 - Communication world of

substation automation.

Ethernet is generally accepted as

substationLAN. Industry standards such

asProfibus and LON are successfully

used inEurope while DNP3.0 and

Modbus are preferredin USA. Recently,



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Ethernet withTCP/IP has also been

introduced. Larger systems typically use

a specialcentral unit (server) and

separate bay units for control.

Independent protection relays are usually

connected to the bay control unitsin this

case.The remote control function is

emulatedeach in the central unit. The

standard IEC60870-5-101 has in the

mean time beengenerally adopted for

communication between substation and

control centre.Time accurate GPS based

synchronisingis available as an option.

Direct peer-to-peer communication

between bay units is offered in some

cases.It can be used for control (e.g.

interlocking),however not for protection

because of therelatively long reaction

time (some 100 ms).Figure 3 shows the

complex communication world of

protection and substationautomation.The

upcoming standard IEC61850 foropen

communication in substations is stillin

the test phase and not generally

availablefor application. [9]Some

vendors in USA already offerUCA2-

compatible devices according to

thepreliminary standard draft. A few

pilot systemsare in operation using

standard 10Mbit/s Ethernet. It is also

reported on a successfulimplementation

of peer-to-peer communicationwith

quarter cycle reaction time.

4.2 Internet technology:

The latest trend goes to using Internet

technology in an Intranet or the Internet

itself.Several vendors already offer

substationautomation systems with

integratedInternet server. In this way, the

acquireddata can be exchanged in a cost

savingwayin an Intranet and distributed

to a widercircle of users. Classic

workstations can bereplaced by normal

Internet browsers.Maintenance work, for

example implementationof new

functions, must thenonly be performed at

the central applicationserver. [10]

In Japan, some systems have been in

servicewhere mini-servers are

implemented inrelays and bay controlunits on basis ofJavaVM (Java Virtual

Machine) [11]Also NGC in England has

been testingapplication servers in

substations.



13/16



Relays and other devices are in this case

connected tothe server via an Ethernet

information bus.Information gathered onthe SQL data bank of the server can be

accessed through standardbrowsers

using ASP (Active ServerPage)

procedures. [12]An American vendor is

even a step aheadand offers a monitoring

system where spaceand administration of

data is provided onthe vendors own

server. The user must onlyinstall the

Internet enabled relays and devicesin his

substation and connect them to the

Internet via the local service provider.

Safety against foreign access is claimed

to be guaranteed by passwords,

authenticationprocedures and firewalls.

FIGURE 4 - Structure of a highly

The integrated substation

offer aims at small users where an own

SCADA system is too expensive or not

yetinstalled.

4.3 Highly integrated

substations:

The use of electronic sensors instead of

traditional current and voltage

transformersin combination with digital

protectionand control allows to design

compact substations.In the distribution

area, there has beena long lasting trendto highly integratedswitchgear panels.

The current transformersare in this case

designed as Rogowski coilsor closed-

core low-signal transformers.Resistive or



14/16



capacitive voltage dividers areused as

voltage sensors. The low signal level

requires to use shielded cables for the

connectionof the combined protection

and controlIEDs. [13] This design

approach considersthe switchgear panel

as one totallyintegrated module.

In high voltage, the development goes to

optic-electronic current and voltage

transformers(acc. toFaraday and Pockels

principles)and data bus systems. (Figure

4).Currentand voltage sensors provided

withdigital output are connected to a fast

fieldbus (Fast Ethernet 100 Mbit/s or

even 1Gbit/s) in the switchgear bay.

Discussion at the CIGRE conference

2000 in Paris showed that the technicalproblemscan be mastered.A number of

pilot projectsare successful in operation.

[14, 15, 16]In general, a drastic cost

reduction isexpected with this novel

substation design.Broad application,

however, will only takeplace when

established standards (IEC61850)

for open communication are available.

5. Concluding remarks:

Modern media and cost pressure have

been the diving forces for system

integrationand automation in substations.

The furtherprogress in data acquisition

(synchronisedsampling, higher sampling

rate), processingand storage capability

(doubling every18 months as per

Moores Law) will allowfurther upgrade

of protection functionsandseamless

monitoring and recording of load,

fault events and switchgear state.Wide-

bandcommunication LANs and Internet

technology(relay integrated servers and

browserbased dialogue) will make the

informationavailable at any place of the

enterprise.Theproblem will however be

to select the usefulinformation from the

large amount of indicatedand stored

data. Expert systems willhave to take on

this task.Functionality, performance, and

operationcomfort of substation control

will beenhanced corresponding to the

current stateof media (colour graphics,

images, video,voice recognition,

etc.).Wireless hand helddevices may be

used for local operation andservices.

There will be cross-links throughfast



15/16



WAN to system control and there will

bea development towards totally

integratedover-all controlsystems.Access

for operationand diagnosis will be

possible from any place,even world wide

via mobile communication.Substation

automation and remote controlwill

increasingly extend to the distribution

level. The much discussed distribution

automation should become reality inthe

foreseeable future.The further fast

proceeding system integrationimplicates

however application issuesin particular

with reduced technical staffafter utility

privatisation and deregulation.Users

already complain about the complexityof

presently offered systems and ask

foreasy and vendor independent

configuration,parameterisation and

setting procedures.It remains to be seen

if applicable standardsand tools will be

available in the nearfuture and if the

promised plug and playcompatibility

can be achieved.Anyway, nomadic

knowledge workerswill be around to

provide adequate services.

6. Literature:

[1] Mackey, M.: Summary report on

surveyto establish protection

performance duringmajor disturbances,

ELECTRA No. 196,June/July 2001, pp.

19-29.

[2] Gale, P.F. et al: Travelling wave fault

locator experience in ESKOMs

transmissionnetwork. IEE DPSP

Conference, 9-12 April2001 in

Amsterdam, Conference manual

pp. 327-330.

[3] CIGRE Brochure.No. 187: System

protection schemes in Power Networks.

[4] CIGRE Brochure No. 200: Isolation

and restoration policies against power

systemcollapse.

[5] Lehtonen,M. et al: Automatic fault

management in distribution networks.,

CIRED 2001, Report 3.9.

[6] Roman H. und Hylla, H.: Fast fault

locating in rural MV distribution

networks.CIRED 2001, Report 3.6.

[7] Roth, P.D.: Communication

architecturein modern distribution

systems,CIRED 2001, Report 3.8.

[8] Redfern, M.A.: A review of

techniquesto detect downed conductors

in overheaddistribution systems. IEE

DPSP Conference,9-12 April 2001 in

Amsterdam,Conference manual pp. 169-

172.

[9] Shephard, B.; Janssen, M:C:;

Schubert,H.: Standardised



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communication insubstations. IEE DPSP

Conference, 9-12April 2001 in

Amsterdam,Conference manual

pp. 270-274.

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