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Undersökning av intermittenta och transienta jordfelsfunktioner för reläskydd
University West, Department of Engineering Science, Division of Computer and Electrical Engineering.
University West, Department of Engineering Science, Division of Computer and Electrical Engineering.
2014 (Swedish)Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesisAlternative title
Investigation of intermittent and transient earth fault functions (English)
Abstract [sv]

Efter stormen Gudruns åverkan där stora delar av Sveriges elnät slogs ut infördes lagkrav på avbrottstider, detta har medfört att luftledning till stor del ersattes med markkabel. Följdeffekter med kablifiering är ökad generering av kapacitiva jordfelsströmmar samt uppkomsten av intermittenta och transienta felförlopp. Dessa förlopp infinner sig vanligtvis i kabelskarvar eller andra isolationsdefekter i kablaget. Det har visat sig att vissa skydd har haft problem med detektering av intermittenta och transienta jordfel, detta har i sin tur orsakat frånkoppling av krafttransformatorn vilket ger onödigt långa strömavbrott. Denna rapport har utförts på Göteborg Energi Nät AB, avdelning Nät/drift. Syftet med arbetet är att för uppdragsgivaren undersöka hur fem jordfelsskydd hanterar och detekterar intermittenta och transienta felförlopp. Studien påvisar att feldetekteringen försvåras vid ökad generering av kapacitiva jordfelsströmmar. Anledningen är att den resistiva delen blir för liten jämfört med den kapacitiva delen. För att minimera den kapacitiva genereringen i nätet har Petersénspolens kompensering fått stor betydelse. Studien konstaterar endast mindre teoretiska avvikelser mellan skyddens intermittenta och transienta feldetektering. En avvikelse är att MiCOM P132 mäter med en analog detekteringskrets. Resterande skydd mäter med digital teknik, den stora skillnaden mellan dessa skydd är samplingshastigheten. Slutsatsen är att Petersénspolens avstämning mot nätet är av stor betydelse. En adekvat kompensering förenklar feldetekteringen vilket medför att enklare skydd uppfyller detekteringskraven hos företaget. För att få ett helt rättvisande resultat behövs skarpa tester genomföras på berörda skydd

Abstract [en]

The hurricane Gudrun in 2005 left major damages on the Swedish grid. Therefore new grid regulations concerning downtime were implemented in Sweden. Resulting overhead lines were replaced with underground cables. The first well known effect of underground cables during a fault is the generation of capacitive earth fault current in the grid. The second well known effects are intermittent and transient earth faults in the underground cables. These faults usually occur in cable joints or other insulation defects in cables. It has been found that the recent earth fault protections have problems with detecting intermittent and transient earth fault, this in turn causes disconnection of the power transformer which yields a non-selective disconnection at the distribution system. This work has been carried out at Göteborg Energi Nät AB. The purpose of this work is to study and examine how some of the most common earth fault relays on market detects and manages intermittent and transient earth faults. The study shows that the fault detection became more complex by increased generation of capacitive earth fault currents. The main reason is that the resistive part of the fault current is too small in comparison to the capacitive part. Therefore the Petersen coil compensation calibration is vital in order to minimize the generation of capacitive earth fault currents. The study finds only minor theoretical differences between the intermittent and transient fault detection. One deviation found was in the protection MiCOM P132 which is designed and constructed with an analogue detection circuit in order to enhance the protection functionality. The remaining earth fault relays are designed and constructed with digital technology. The major difference between the digital technique relays is that the sampling rate is different in different models. A well calibrated compensation simplifies fault detection which results in simpler earth fault protection relays meet the detection requirements of the represented company. To achieve accurate results, live tests are highly recommended

Place, publisher, year, edition, pages
2014. , 31 p.
Keyword [en]
Directional earth-fault functions, intermittent, transient, electric grid, admittance
Keyword [sv]
Intermittent, transient, jordfel, admittansmätning, grundtonsmätning, distributionsnät
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:hv:diva-6833Local ID: EXH300OAI: oai:DiVA.org:hv-6833DiVA: diva2:755245
Subject / course
Electrotechnology
Educational program
Elkraft
Supervisors
Examiners
Available from: 2014-10-14 Created: 2014-10-14 Last updated: 2015-12-22Bibliographically approved

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