Tata Iron & Steel Co. Ltd. (TISCO)have used Intelligent MCCs at theirCoke Oven Plant #2. They havebeen supplied by L&T in 1997.Probably, this was the first materialhandling plant in India to useIntelligent MCC concept completely.The plant was commissioned inJuly 1998.

Sharing of experience has been anongoing process at TISCO andL&T. Adopting the innovativeconcept of Intelligent MCCs withindigenous know-how andsuccessful implementation of theconcept on schedule was a realachievement for TISCO.

Mr. Sharat C. Kumar of TISCO wasinvolved in the process all along. Inthis issue of L&T Current Trends,he shares his experience with thereaders.

In the month of October 2000,Bureau Veritas QualityInternational (BVQI) has awardedISO 9001 - 2000 certification(based on the FDIS) to L&T'sfollowing divisions:-

❖ Electrical Standard Products❖ Electrical Systems &

Equipment❖ Petrol Dispensing Units

The certification involves L&T -EBG's Powai, Madh, Ahmednagarand Faridabad works.

So far, many Indian companieshave been certified for ISO 9001 -1994 standard.

The new standard, i.e. the 2000version, focuses on customerinteraction, customer satisfaction,etc.

With this certification, L&T is thefirst Indian company and one ofthe few worldwide to get certifiedfor ISO 9001 - 2000 (FDIS).

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

Prospect / Retrospect

October - December 2000

IntelligentSwitchboards at work

ISO 9001 - 2000 (FDIS)for L&T - EBG

Visit us at www.LNTEBG.com

1. I

TataCoktonsCokTecof tTheovecomalre0.5 in i199com

In intemaj❖ ❖

❖

1.1 Coacrusprocovetechthe requthrocrusandBattcanblenthenhopcoacak

1.2 CoprodbattFurnevaplou

FEATURE

AN EXPERIENCE WITH INTELLIGENT MOTOR CONTROL CENTRESAT COKE OVENS IN AN INTEGRATED STEEL PLANT

- Sharat Ch. Kumar, Dy. Divisional Manager, The Tata Iron & Steel Co. Ltd., Jamshedpur

NTRODUCTION :

Steel has set up state-of-the-arte Ovens for producing 1 million of Blast Furnace Coke and Nute using Stamp Chargehnology. Coke plant # 2 consistswo batteries viz. Battery # 8 & 9.se two batteries consist of 70ns each. Battery # 8 wasmissioned in July 1998 and it hasady achieved its rated capacity ofmillion tonnes of Coke productionts first full year of operation i.e.9-2000. Battery # 9 wasmissioned in August 2000.

any typical Coke Oven in angrated steel plant, there are threeor processes : -Coal handling plant.Battery proper with ovensmachinesCoke handling plant.

Coal Handling Plant :l handling plant blends andhes coal of various types and thisessed coal is fed for use in Coke

n batteries using Stamp Chargednology. Coal is withdrawn fromblending bins as per the blendired through weigh feeders, taken

ugh conveyors to primaryhers; then to secondary crushers finally to coal towers for bothery # 8 and 9. Each coal tower store up to 2500 tonnes ofded and crushed coal. Coal is fed in to the SCP machinepers from gates provided in thel tower and finally charged as coale in to the battery oven.

Coke Handling Plant :ke Plant evacuates the cokeuced from the Coke Oven

eries and transports to the Blastaces or stockyard. Coke is

cuated from the wharf usinggh extractor and sent to surge

Hopper through conveyors. Usingvibratory feeders and screens theCoke is separated into Nut, Pearl,Breeze, and BF Coke. BF Coke isultimately sent to Blast Furnaces.Schematic of the process is shown inFig.1.

1.3 Power Supply Arrangement:Three 1600 KVA transformers feedpower to the 415V PCC at Coal plantand an identical system exists forPCC at Coke plant. PCCs in turn feedpower to Intelligent MCCs 2.1 & 2.2for Coal plant and MCCs 3.1 & 3.2 forCoke plant. Each MCC has 2incomers and several motor starters.All incomers use Feeder Vision relays(FVR) for protection, monitoring,measurement and control. All motorstarters use Motor Vision relays(MVR) for protection, measurement,monitoring and control. Between Coaland Coke Plant Optical Fiber is used

for data transfer.

2. SELECTION OF INTELLIGENTMCCs : WHY?It would be prudent to discuss theselection of Intelligent MCCs at thisstage.

Experience with the use ofconventional MCC is as follows :-❖ Failure of bimetallic O/L

protection system on severaloccasions since precisionsetting not possible.

❖ No real time trends of load. Itrequired additional CTs.

❖ No facilities to integrate withhigher level system likePLC/SCADA.

❖ If U/V, O/L, metering which formpart of metering & protectionwere to be used in a globalSCADA system, then each ofthese inputs need to behardwired using transducersand other digital inputs.

❖ Extensive control cabling andmore physical space is required.

The answer to the above problemlies in the use of Intelligent MCCs.

We, at Coke Plant # 2 in Tata Steel,studied the option of using IntelligentMCCs in place of conventionalMCCs. The offer was mainly fromL&T (in collaboration with P&BEngineering, U.K. for Supervisionseries of Relays) and some otherswitchgear suppliers.

Fig.1

The advantages foreseen in usingL&T's Intelligent switchgear wereobvious. Some of the benefits were: -❖ Additional hardware for O/L, E/F,

U/V, O/V, current metering andassociated wiring not required.

❖ Most of the protection, meteringand control data could betransmitted on serial link to higherlevel system like PLC andthereafter to the MMI forindication and informationfeedback as graphical or textdisplays. Operators andengineers as per theirrequirement could subsequentlyuse this information.

❖ Inputs for interlocking and safetycould be wired directly to theintelligent device instead of wiringin the PLC. By doing so, the MVRcould switch off on its own if anyinterlock fails and at the sametime this data (interlock failuredata) could be used by the PLCfor back-up action (trip/alarmetc.).

❖ An MVR could beprogrammed/configured as peruser's requirement out of theseveral options available formotor starters.

❖ Configuration or parameterizationwas extremely user friendly.

❖ Very good diagnostic facilitieswere available for pre and post-fault conditions.

❖ Use of twisted pair cable insteadof Optic Fiber for communicationbetween devices and Xcellsystem lead to lower cost andsimple connectivity.

Several other features were availablewhich sere convincing enough for usto decide in favour of IntelligentMCCs.

3. ELECTRICS :Electrics for Coal and Coke plantswere given as a turnkey project toLarsen & Toubro Limited (L&T), India.The following devices were used: -❖ Intelligent MCCs using Feeder

Vision Relay (for feeders) andMotor Vision Relay (for Motors).

❖ Data Concentrator XCell -Communication betweensupervision Relays and PLCs

❖ Modicon PLC and remote I/Os❖ IC2000 SCADA system running

on Modbus Plus protocol

❖ Connectivity between Coal andCoke plant using fibre optic cable.

❖ Use of Remote I/Os at blendingbins for easy interface betweenPLC and J&N Weighfeeders, Beltweighers and Bin level sensors.

❖ BM-85 protocol conSee Fig. 2 for ElectricalTata Steel (Coke Plant

4. OUR EXPERIENCEAfter the Coal and Cocommissioned, seveproblems and shortcomthe Intelligent systemHowever, these were ojoint effort by L&T and problems experiencedarrived at are given bel

4.1 Problems encountThe initial probcommissioning were quality and voltageincorporating surge replacing dielectric captype capacitors the pbrought under control.

4.2 Zero speed sensway sensing :Zero Speed Sensing (Sway Sensing (BSS)used as protection forsystem. These inputs w

as external digital inputs to MVR.External inputs have a finite time delayelement built into it. Additionalhardware was also provided to bypassthe ZSS during starting. On startingof the Plant, these inputs started

MCC 2.1 RS485

FeederSpecific

I/Os

PCC 2

RS232MBBM

MB+

CENTRAL

MAN MACHINE

verter modules being used at# 2).

ke Plants wereral teethingings arose in

and its use.vercome with aTata Steel. The and solutionsow : -

ered initially:lems duringdue to power spikes. By

suppressors,acitors with dryroblems were

sing and belt

ZSS) and Belt feedback are any conveyorere configured

misbehafinite ti"healthyto remato deteThese Eto run difficult being fo

Subseqwere redisablin"trip". Athese inthe PLCXcell). incorpothe drivwith arequiredtrippinginputs forcing belts aforcingsHardwasystem redunda

4.3 SerAs timecame ubecame@ 15Enginee

MCC 2.2

ProcessCommon

I/Os

OpticalFibreH/W

Xcell DataConcentrator

85

STP Cable

Prog. Stn.

INTERFACEBM85

Optical Fibre Cableto Coke Plant (1.5km)

DCS

C

PLC

PU

I/O Bus

PLCI/Os

ving since ZSS required ame part to get the final" condition and BSS hadin faulty for a finite periodct "unhealthy" condition.xternal inputs were forcedthe plant but it becameto keep a record of inputsrced (ZSS and BSS).

uently, these two inputsmoved as interlocks by

g them on the MVR fort the same time, status ofputs were being read by on serial link (through

These were additionallyrated in the interlocks fore in the PLC ladder logic time delay, which is for starting for ZSS and

due to BSS. Also thesebecame available for

OFF/ON during trailing ofnd motor trial and the could be monitored.re provided in the existing

for ZSS becament.

ial Communication : passed, one problemp. "Serial time out trip" a nuisance tripping-20 times per shift.r from P&B visited the

Fig.2

Plant, discussed and studied theproblem.

The start command given by the hostPLC was a latched command. Thisled to the serial time outs. Startcommand was converted into a 4seconds pulse to reduce the numberof interrupt commands from PLC toXCell. This substantially reduced theserial time out. MVR ON commandwas also taken as an interlock bit.

4.4 Link between MV and XCell :On some occasions, communicationlink between XCell and MVRs failed;some drives tripped and some drivesremained ON leading to severespillage of material. On furtherinvestigation, we found that if seriallink fails, MVRs can stop the drive ifserial time out trip was enabled in theMVRs. Similarly, XCell couldrecognize or read serial link failurewith either one or all devices. Thiscommunication failure status wasread in the PLC system and providedas interlock bit in the ladder logic.Display of link failure was made onthe MMI using IC2000 system. Also afacility for serial fail reset from remote,which could be done on one click ofthe mouse, was disabled and resetenabled only through each MVR onthe MCC. This was required asoperators used to click the RESETicon on the MMI inadvertently as acommon icon is made for all RESET.In some cases AUTO RESET of seriallink failure of MVRs were enabled. Inthese cases as and when serial link isestablished fault resets automatically.The problem herein lies when anyconveyor trips in the circuit. As longas all conveyors are running and iflink fails and gets re-establishedwithin 120 seconds and resets onauto, then there is no problem as triptime were set at 120 seconds(programmable). But if a conveyortrips within these 120 sec, then

spillage would take place. thereforeboth AUTO and SERIAL RESET weredisabled through REMOTE and allowedonly through LOCAL mode.

4.5 Spillage in coke conveyors :Suppose conveyor A dischargesmaterial into conveyor B. If the twoconveyors are running and serialcommunication of conveyor B fails,conveyor B would trip on serialcommunication of conveyor B, the laststatus is conveyed to the PLC. The laststatus is ON when link has failed. Thisfeedback is motor on for B into A. Thusconveyor A doesn't know that conveyorB has tripped. This resulted in spillage.To prevent this, status of conveyor Bwas put in the starting interlock ofconveyor A.

4.6 Spillage between non - MVR andMVR conveyors:In the coke plant CK - 01A (a non-MVRconveyor) discharged coke into CK -03 (a MVR conveyor). A looseconnection at the RS485 port of theXCell concentrator had caused this.Two things happenedsimultaneously :-

❖ The motor vision relays connectedto the XCell tripped on serialtimeout.

❖ The XMIT block, a loadable functionblock used for mapping the XCelladdresses with those of the PLC,went into a fault state.

Thus with the failure of communicationbetween PLC and XCell, the last statuswas retained by the PLC. Thus thecurrent f/b, communication status,contactor A ON, remained highalthough CK - 03 had actually tripped.This led to spillage of coke from CK -01A over CK - 03. To avoid this, anadditional interlock "XMIT transmissionerror" was incorporated in the startinglogic of CK - 01A.

4.7 Remote Input / Output head:A Remote Input / Output (RIO) headercard was used in the PLC forcommunication with all Input / Outputmodules on various racks. In Dec '99this RIO card failed and we had nospare card available. Complete CokePlant came to a halt as all ONcommands were issued through RIOcard for Non MVR drives andRemote/Local selection to the MVRcontrol inputs. However, the serial linkbetween the MVR and the PLC wasstill existing which was used for ONcommand directly. Switching ON thedrives through this serial link withcertain interlock modification was triedfor one conveyor and thensubsequently for all coke conveyors.Additional interlocks were provided forthe whole system to work on serial link.

5. VISION FOR FUTURE :

❖ Eliminate ZSS by incorporating ZSSinto MVR or through currentmeasurement.

❖ Remove most I/Os from PLC anduse only CPU for digitally receivingdata through serial link.

❖ Eliminate unnecessary interface.❖ Real time and history of data on a

higher level system.❖ Database for all data imported from

MVRs.❖ Parameterization of MVRs through

serial link from XCell. Both onlineand off-line, from SCADA.

❖ Forcing of inputs serially.

6. CONCLUSION :

It can be certainly concluded that useof Intelligent MCCs has beensuccessfully implemented and benefitshave accrued to Tata Steel because ofthis. It has been a continuos learningprocess for both Tata Steel and L&T.

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

Fax : 022-8581024 e-mail : nk-swtc@pgriii.ltindia.com

Printed by Printania Offset Pvt. Ltd.,D 20/21, Shalimar Industrial Estate, Matunga (east), Mumbai 400 019. Tel: 407 7996/8866/4540Fax: 402 4703 Email: pds6@bol.net.in Edited by Dr. Arun C. Vakil for larsen & toubro Limited, from L & T House, Narottam MorarjiMarg, Ballard Estate, Mumbai 400 001. The views expressed in this magazine are not necessarily those of the management of larsen& Toubro Limited. The contacts of this magazine should not be reproduced without the written permission of the Editor. Not for sale -only for Circulation among the customers. Associate Editor: Luis S. R. Vas