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Shaft Current Protection
KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
2015 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Shaft current protection in hydro and turbo generators is an important generatorprotection issue. Currents owing in the generator shaft might damagegenerator bearings which, in turn, could reduce operating time and cause largenancial losses. Therefore, it is important to prevent operation of the generatorunder conditions of high shaft currents.In this project, task was to develop measurement and protection system thatis able to operate under certain conditions. Measurement device has to be ableto accurately measure currents lower than 1 A in a generator shaft that canvary in diameter from 16 cm up to 3 m. Also, those currents might appear infrequencies equal to multiples of line frequency. Device is to be located in alimited space and in a proximity of the generator. Thus, stray ux is expectedwhich might inuence measurements. Furthermore, since currents that haveto be measured are low, output of a measurement device is usually a low levelsignal. Such signal had to be catered for and adapted in a way that it can beused with numerical relay. After literature review and overview of possible solutions, Rogowski coil waschosen as the measurement device which will be further analysed. Two othercurrent transformers were considered which served as a good comparison withRogowski coil. Several dierent tests and measurements were made on mentionedmeasurement devices. Also, it was investigated how IEC61850-9-2 andMerging Unit (MU) could be used in this application. Upon this investigation,complete protection systems were assembled in the laboratory and they weretested. To asses the behaviour of dierent systems in the real environment, test installationwas built in the hydro power plant, Hallstahammar. This installationincluded traditional systems, with measurement signals connected to the relaya,and the one which utilized concepts of Process Bus and Merging Unit. Measurementsand tests that were made there served as a nal proof of successfulnessof protection systems. Results showed that Rogowski coil was a suitable choice for a measurementdevice due to its benecial mechanical and electrical properties. Also, tests madewith actual shaft current showed advantages of using Rogowski coil in pair withMerging Unit and process bus over traditional protection systems. Nevertheless,it was conrmed that both types of systems satisfy project requirements.

Abstract [sv]

Skydd mot axelstrommar i vattenkraft- och turbo-generatorer ar mycket viktiga. Strommar kan uppkomma i generatoraxeln beroende pamagnetisk osymmetri istatorkarnan. Denna osymmetri ger upphov till en inducerad spanning i axelnsom sedan kan ge en axel-strom vid kortslutning av isolationen som rotornslager vilar pa. Om axel-strommen gar genom generatorns lager, kan lagretskadas allvarligt. Detta kommer i sin tur minska drifttiden och orsaka storaekonomiska forluster vid produktionsbortfall. Darfor ar det viktigt att detekteraom det gar axelstrommar genom generatorns lager. Examensarbetets mal var att utveckla ett mat- och skyddssystem for att detekteraaxel-strommar. Den matande enheten maste kunna detektera strommarmindre an 1 A i generatoraxeln vilken kan variera i diameter fran 16 cm upp till3 m. Dessutom kan dessa strommar ha frekvenser lika med eller multiplar avkraftnatets frekvens (50 eller 60Hz). Den matande enheten skall vidare kunnamonteras i ett trangt utrymme och i narhet av generatorns stator. Lackodefran statorn kan forvantas vara stort, och detta kan antas ha stor paverkanpamatningarna. Eftersom axelstrommen som mats ar lag, ar utsignalen franden matande enheten vanligtvis en lagnivasignal. Denna laga signalnivamasteanpassas saatt den kan anvandas i ett numeriskt rela, vilka vanligtvis kraverhogre energinivaer paingangsignalerna.Efter genomford litteraturstudie och oversikt over mojliga losningar, konkluderadesdet att en losning med Rogowski spole som matanordning borde varaintressant, och denna analyserades ytterligare. Tvastromtransformatorer medkonventionell konstruktion med karna av elektroplat valdes som jamforelse medlosningen baserad paRogowski spole. Flera olika tester och matningar gjordes. Dessutom undersoktes hur en process-bus losning enligt IEC61850-9-2LE meden Merging Unit (MU) skulle kunna anvandas i denna tillampning. Vid alladessa undersokningar har kompletta system for matning och skydd monteratsoch testats i laboratoriemiljo.For att registrera funktionen for de olika systemlosningarna i en verkligmiljo, monterades det kompletta systemet fran laboratorietesterna in i ett vattenkraftverki Hallstahammar. I detta vattenkraftverk ingar traditionella skydd-, styrnings- och kontroll-system och aven en aldre losning for att skydda generatornmot axelstrommar. Darmed kunde man jamfora prestanda mellan deolika losningarna baserade pastromtransformatorer av konventionell konstruktionmed karna av elektroplat och losningen med Rogowski spole. Signalerfran bada givarna anslots till ett numeriskt rela, och anslutning av Rogowskispolen gjordes aven via en MU till det numeriska relat. Matningar och testersom gjordes i kraftstationen kunde tas som ett slutligt bevis paatt de olikalosningarna baserade pa Rogowski spole ar en framtida losning for ett valfungerande axel-stroms skydd for generatorer. Resultaten visar att Rogowskispolen ar ett lampligt val aven med avseendepadess fordelaktiga mekaniska och elektriska egenskaper. Testerna som gjordesmed en verklig axel-strom visade tydligt fordelarna med att anvanda Rogowskispolen i kombination med MU och process bus jamfort med traditionella skyddssystem. Det ska dock understrykas att bade systemet med och det utan MUuppfyllde projektets krav.

Place, publisher, year, edition, pages
2015. , 69 p.
Series
EES Examensarbete / Master Thesis, XR-EE-ICS 2015:009
Keyword [en]
shaft current, Rogowski coil, generator protection, Merging Unit, process bus
Keyword [sv]
axelströom, lagerströom, Rogowskispole, generatorskydd, Merging Unit, process bus
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-177353OAI: oai:DiVA.org:kth-177353DiVA: diva2:872371
Examiners
Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2015-11-18Bibliographically approved

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