How we savved a Generat G tor (in fact f tw wo), agaain! Backgrround
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t was just anotheer day and d another morning of o January 2019, on which wee received a call from m a new Customer C in Metal Seector, from m Chhattissgarh. And d urgently, they t wanteed us to teest and com mmission an old 10 M MW, 11 kV Generatorr along with h its relayin ng, schemees and com mplete testing. On enquirring about such urgeency, we le earnt that their origiinal Generator rated d 12 MW, 11 1 kV got burnt (staator) and was w sent for f repairin ng, this 10 0 MW wass taken on rental basis and a temporaryy solution. As we aall know th hat in ourr industry, Generatorr failure is nothing le ess than an a air‐crash and thiss criticalityy warranted d extensivve and meethodical analysis a like an air‐‐crash inve estigation.. Hearing th his, the daay went intto a tizzy and a we im mmediatelyy started preparing a checklist (we’ll ( see it later in a diagram)) to find out the Roo ot Cause. And A unlesss we find th he Root Cause and so olve it, this rented Geenerator w was in danger and thee too! upcomingg repaired Generator G We immediately dispatched 2 of our enggineers alo ong with th he test setss required,, by the firsst flight avaailable and d were soo on on the jo ob. In less than a dayy, we weree up and wo orking.
Findinggs‐ at Site ‐
The initiall forensics were found from th he fault reecords of tthe Relay. We learntt that the Relay R (and d GCB eventually) was w tripped d on NPS protection n, which iss normally a time delayed prottection. It was a surprise, becaause norm mally when n such faultt occurs (sttator failurre), other protection ns take carre, NPS is something s g like last lin ne of defen nse.
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So, such a surprisingg observattion just att the start of the job b prompted us to bee extra vigilant. This warranted d us for in‐depth and thorou ugh checkiing of thee protection n system.
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And then came thee momentt of reckoning, and you know w from wh here? NCTT wiring waas the culp prit for thee Generator burn‐ou ut! Least eexpected fault f for a Protection n Engineerr so to speeak (It was found while w carryiing out Stator Earth h Fault scheeme checkiing).
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Following actual im mages cleaarly show the fault. So, 90 % Stator Earth Faultt Protection n (51S) did not operaate due to non‐wiring n g of NCT seecondary S2 2 to Relay.. Generatorr kept running on th his serious a fault wh hich finallyy led to he eating and d eventuallyy, NPS op peration operated o on o time delay. d Butt by the time NPSS operated, the damage was alreeady done.
Seen heree is S2 misssing (to Reelay)
Stator Burnt B
Co orrected byy new wirin ng
Disconneected Wind ding
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NCT, whicch is used for f Stator E/F E Protecttion, was wired w up to o TB in CRP P correctly.. But from TB to Relaay, wire S2 2 was misssing/not co onnected o on Relay. So S even in n case of Sttator E/F, Relay wou uldn’t have sensed nor operated nor trripped thee relevant breakers. b T fault was This w simplyy corrected d by conneecting a 2.5 sq. mm.. wire.
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Differentiaal Protectiion settingg was foun nd high, besides, b th he referencce for thee settings was w not available, a w recommended to we t furnish us the OEM O data,, compiled during com mmissionin ng and to carry out the t fresh SStudies on Relay Co‐‐ n, Power Syystem and Load Flow w. ordination
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Suppose both b the above proteections, Stator E/F and Differential, are alright a and d operate and generate alarm and a trip siggnals faithffully. And aas we all know, both h a must cut c the very source of the fault. Here in n these are Class A prrotection and nd? AVR could not be b tripped d this case, it’s AVR. And you know whaat we foun nter‐panel wiring was not done e. Corrected and now w stands rectified. because in
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Reverse Power P and Forward Power P Pro otections were w set but with wrrong logic.. Logic wass so wronggly set that neither Alarm A could be geneerated norr Tripping! With the set logic,, these prrotections were ren ndered useless. Corrrected byy t logic. changing the
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Similarly, this wrong logic error wass observeed in Und der Voltagge, Underr hese weree set alrigh ht, but thee Frequencyy and Over Frequency Protections. All th set logic didn’t let these pro otections generate g a Alarm or Trippin any ng signals,, ng the logic. imagine! Corrected by changin
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but as per the OEM LBB Proteection tripping was assigned to Outputt No. 3, b Manual of the Geneerator Prottection Re elay, this Output O No. 3 must be e used forr unctions and not thiis. Correctted by chaanging the logic and other dessignated fu wiring.
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Following Diagram will w help uss understan nd this critical event better.
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Conclu usion – How w our insigghtful actio ons helped d the Indusstry ‐
Not only our o team verified v thaat the new wly installeed Generattor of 10 MW M has alll the protecctions available, theyy verified that it opeerates, and d operatess correctly.. And geneerate a corrrect tripping sequen nce too. No N burningg of Generrator from m now onwaards, the way w a safe and a reliable protectio on system should be..
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By doing so, we also ensured complete e protectio on of 12 M MW Generaator which h will be put in place after a due repairs. r Setttings need d to be verrified/corre ected with h rewindingg data but more m or lesss, the macchine will be b protecteed.
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Generatorr is an expensive e asset itse elf, and the t loss o of producction in a continuou usly running plant du ue to failure e of a Gen nerator can n run in to crores. Alll our effortts are view wing the prroblems fro om custom mers’ pointt and resollving them m in totality. Testing, as a such, is an isolated d job, but when w it is done in a way w which h affects the end‐resu ults (produ uction/revenue), theen it’s profoundly meaningful. m . And that’ss what we delivered.
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And at last, we weere happy to “wow”” the custo omer, who o learnt at last, thee differencee between symptom‐‐solving‐aggents and proper p Docctors.
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The abovee are in fact the majjor problem ms found and a correccted. Though, duringg our very busy 3‐days (and nights too) at site, we w also ob bserved maany minorr a many as possible. Well, W to kn now more,, call/writee abnormalities and corrected as to us, we’ll be happyy to save your assets too! ng for a dedicated agency a wh ho understtands the direct linkk And if you’re lookin ur revenue e, we’ll be happy to assist you, anytime,, between your assetts and you anywheree.
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