Whenever a fault occurs in theelectrical system of a plant, analarm is generated and audio-visually annunciated in the centralcontrol room. Generally, thecontrol room is manned by atleast two persons in all the shiftswho need to act now. One personwalks down to the sub-station.Now his job is to physically locatewhich feeder has generated thealarm/trip and then go ahead andtry to find out the cause of thefault. In case of a transient fault,the relay might have got resetted(in case set for "auto-reset"). Fora "manual-reset" option, he willhave to reset the fault and restartthe process.

In any case, the time and effortstaken to put the system back into

Mobile Control Station

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Issued by : EBG - Electrical Systems & Equipment, LARSEN & TOUBRO LIMITED, Powai Works, Mumbai 400 072

Visit us at www.LNTEBG.com

operation is enormous, speciallyin case of plants that are locatedin remote areas and are wellspread out.

In modern times, with more andmore automation, the cost of suchundesired shutdowns is notaffordable. It is also not desirableto restrict the information on theplant status within the boundariesof the control room. Specially, forimportant events/decisions, seniorplant officials need to be keptinformed wherever they are, forrapid decisions.

With advancements in the field oftelecommunication, it is very muchpossible to go beyond theboundaries of the control room.

Larsen & Toubro Limited hasdeveloped and supplied a HumanMachine Interface (HMI) softwarewhich gives all the metering / faultdata on the serial link. The fault/alarm annunciation by the HMI isprovided in the form of visualindication, pop-up on the computerscreen as well as audioannunciation.

With the help of telecommunicationnetworks, it can also give faultannunciation, reset facility for faultsand control of feeders from eithera land line telephone or a mobilephone. The same informationflows through other modes ofcommunication like E-mail / SMSand fax too. This issue gives moretechnical details.

Prospect / Retrospect

Integration of Telecommunication with HMI- Mr. Gagan Kapoor

Introduction

Introduction of microprocessorbased intelligent relays in electricalpower system has increased theefficiency of the system. Theseintelligent relays arecomprehensive devices whichprovide control, monitoring,protection and serialcommunication feature forextensive exchange of data. All thisresults in easy and user friendlyaccess to the necessaryinformation. The serialcommunication facility on a openprotocol envisages the user tohave Human Machine Interface(HMI) or an Engineering PC or anEngineering workstation and otherhigher level automatic system e.g.DCS, ECS, SCADA etc. Any userseeks for continuous interrogationof metering data from a feeder forevent logging, consumption ofpower, apart from the meteringdata. These intelligent relays giveall the control related data (start/stop and reset signal),maintenance related data, fault/alarm annunciation & logging andstatus of the particular feeder onserial link.

Conventional Control Room

In a conventional electricalsubstation, there areelectromechanical protectionrelays and remote metering CTs/PTs located in switchboards. Thecontrol room has large windowannunciator panels with hooters.Remote hardwired contacts areused for exercising controls and

taking feedback. Each feeder hasa auxiliary relay which operates incase of alarm in the respectivefeeder. Such alarm contacts of allfeeders are taken to the windowannunciator panel eitherindividually or looped together.Similar wiring of contacts isrequired for tripping. In case alarmoccurs in a feeder, the indicatorof the particular feeder blinks andthe hooter blows for visual andaudio indication respectively. Allthis requires constant monitoringof the annunciator panels. Aftergetting indication on theannunciator panel, the operatorgoes to the switchgear room andlocates the feeder/breaker that hasinitiated the alarm. This is followedby tracing the cause of the fault/alarm.

This entire process is very timeconsuming and requires at leasttwo persons in each shift; one atthe control room and one in thefield. It also has the followingdeficiencies:� Too many equipment in the

control room and switchgear� Large space requirement for

annunciator panels� Extensive cabling for auxiliary

contacts/relays� Resetting of faults only with

manual operation� Fault data not available, hence

analysis becomes difficult

PLC based Control System

In order to overcome some of thedeficiencies of the conventionalsystem, industry switched over to

PLC based data acquisition andcontrol system. The system getsanalog data from the feeders byusing transducers and AnalogInput cards of the PLC. Logic andsequence of operations is built inthe PLC. A Human MachineInterface software gets all the data(analog and digital) from thefeeders for continuous monitoring.Control can also be exercisedbased on the logic built in the PLC.

Advantages of the system over theconventional are as follows:� Log sheets can be generated

in the software and reportscan be printed for reference

� User friendly graphics enableoperator to view the data of allfeeders on one screen

� Complex logic of variousinterlocks can be developed inPLC reducing extensivecabling

� Individual fault/alarm data canbe seen on the PC

� High speed data availability andcontrol

� Saves premium space in thecontrol room

Deficiency of the system:� Extensive cabling required for

Analog and Digital Inputs toPLC

� Space required for interposingrelay panel for control

� Resetting of fault alarmcontacts in the switchgearpossible locally

� Too many interfacing devices� Continuous monitoring

required in the control room

FEATURE

Control & Data acquisitionSystem using IntelligentElectronic Devices (IEDs)

The microprocessor based IEDshave created revolution inelectrical control & monitoringsystem. Electromechanical relaysand meters are being replaced byIEDs capable of providing control,metering and protection functionsin a single device. These devicesalso have serial communicationfacility on “industry standard/openprotocols” for integration withHuman Machine Interface/Engineering Workstations/DCS/ECS/SCADA. The IEDs havingcontrol facility reduce extensivecabling and accessories. Only onetwisted pair cable can transmitdata from all the IEDs connectedon a multi-drop / daisy chain tothe higher level system. They alsohave built-in DIs/DOs and canrecord fault history as well astripping parameters.

The system has followingadvantages:� Reduced cabling

� Reduced hardware in terms ofAI/DI/DO cards

� Elimination of interposingrelays

� Exhaustive analog and digitaldata available

� Controls possible by click of abutton in graphics of HMI

� Setting of IEDs possible fromHMI

� Integration of LT and HTswitchgear in the same HMIwith dynamic data/statusmonitoring

� Reduced equipment in thecontrol room and switchgear

� Annunciation available on HMI� Fault type, fault data and

location can be seen in controlroom facilitating furtheranalysis

� After corrective action,resetting of fault can be donefrom control room

� Different security levels can beconfigured in the HMI byassigning multi-level passwordfor effective control

� Metering of all instantaneous(viz. I, V, PF), integrated (viz.kW, kWH, kVA, kVAr) and

statistical parameters (viz. Noof operations, Total Hrs inservice) can be captured bythe IEDs and thiscomprehensive data can beviewed in the user defined formof HMI.

� The HMI can further eliminateneed of separate drawings likeGA, MBOM

� The HMI helps introubleshooting the scheme asthe IEDs have programmabledigital inputs and outputs thatcan be configured in the relay.The status of these inputs canbe seen in the HMI and thesame can be compared withthe desired state of the input/output for a scheme toperform. This eliminatesphysical checking of wires. Acontrol room operator candiagnose the fault and decidethe corrective action.

Deficiency:� Continuos monitoring required

in control room

Analog Card - Forseparate analog inputs

Digital Input CardProcess permissivesfrom a group of drives

ConnectionthroughModem

Satellite Connectivity

415V Swgr. 33 kV Swgr. 6.6/11/22kV Swgr.

EDMS

XCELLData

Concentrator

DCS Engg.PC

number. The message will containinformation about the faultlocation, type of fault and theaffected feeder description.

This facility can be used for furtherinterrogation. The user can inquireabout critical parameters likevoltage, current and some otherconfigurable parameters. Oncethe call is received by the HMI, arecorded message asks for therelay number. It then generates anaudible message giving the valuesof the required parameters.

A PC can be used as an ethernetgateway and can act as a serverwhile other PCs can work asclients on the LAN. This will enableavailability of data on LAN atdifferent locations over largedistances.

The on-line data acquired can bestored in the PC to facilitate theuser in generating customisedreports. These reports can beused for MIS effectively.

Mobile Control Stations

The integration of tele-communication with the HMI usingIEDs has introduced the conceptof Mobile Control Station. A mobiletelephone can be used as aremote monitor cum control stationfor the switchgear using IEDs anda Laptop with internet connectivitycan be used as an informationcentre.

The basic philosophy of thesystem is described below :

The IED transfers comprehensivedata on serial bus to HMI in a PC/Laptop. In case of any alarm orfault, the HMI initiates connectivitywith predefined telephonenumbers in the order of priority.Once a user picks up the call, aprerecorded voice message isheard. The message describes thetype of fault and the affectedfeeder. The message also givesthe user option for exercisingcontrols on the feeder, resettingof the fault or acknowledging thefault by using the keypad of thetelephone.

Different users can be givendifferent level of authority. Thus,only master can exercise controland others can only receiveinformation.

In case no user responds to thecall, the message about the fault/alarm is transmitted to the mobileusers on SMS or landline userson e-mails. If the email facility isnot available, the message canalso be faxed to a pre-defined fax

Conclusion

The technology of havingannunciation on mobile / fax /SMS / e-mail gives the advantageof information flow to variouslevels in an organisation withoutloss of time. This eliminates needof constant monitoring of plantelectricals sitting in a confinedlocation.

The advantages of such systemare:� Availability of information on

m o b i l e / S M S / e - m a i l / f a x .Therefore no need of a personspecifically for monitoring.

� Control possible from anylocation by authorisedpersonnel expands theboundaries of the control room.

� Data interrogation on a mobileenables user to get theinformation about a criticalfeeder even if he / she is outof the industry premises, asand when desired.

For further details on this subject, please contact:EBG - Electrical Systems & Equipment, Larsen & Toubro Limited, Saki-Vihar Road, P.O. Box 8901, Powai, Mumbai 400 072

Fax: 022-2858 1024 * E-mail: kotnisnd@Intebg.com

Printed by Printania Offset Pvt. Ltd.,D 20/21, Shalimar Industrial Estate, Matunga (East), Mumbai 400 019. Tel.: 2407 7996/8866/4540 Fax : 2402 4703 Email: pds6@bol.net.in Edited by Henry A. Karkada for Larsen & Toubro Limited, from L&THouse, Narottam Morarji Marg, Ballard Estate, Mumbai 400 001, The views expressed in this magazine are not necessarilythose of the management of Larsen & Toubro Limited. The contents of this magazine should not be reproduced without thewritten permission of the Editor. Not for sale-only for circulation among the customers. Associate Editors: SharmilaBanerjee. Editorial Coordinators : R. S. Mahajan, Neelam D. Kotnis, EBG-ESE, Powai .Member

ABCI

Typical architecture of Data availability over LAN