Porast potencijala oklopa visokonaponskih postrojenja zbog sklapanja rastavljačem

scientific master's theses

• Title (english): Enclosure Voltage Rise in High-voltage Switchgear Due to Disconnector Switching
• Author: Srećko Bojić
• Mentor: Ivo Uglešić (mentor)
• Committee member: Sejid Tešnjak (predsjednik povjerenstva)
• Committee member: Ivo Uglešić (član povjerenstva)
• Committee member: Maks Babuder (član povjerenstva)
• Granter: University of Zagreb; Faculty of Electrical Engineering and Computing; (Department of Energy and Power Systems); Zagreb
• Defense date and country: 2002-01-15, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Electrical Engineering
• Universal decimal classification (UDC): 621.3 - Electrical engineering

Abstract

Porast potencijala oklopa plinom izoliranih visokonaponskih postrojenja posljedica je širenja i prijelaza unutarnjih vrlo brzih prenapona na vanjski oklop i uzemljene dijelove postrojenja. Pojava je najizraženija pri sklapanju rastavljačem malih kapacitivnih tereta pri čemu dolazi do višestrukih povratnih preskoka na kontaktima rastavljača. Pri svakom povratnom preskoku nastaje visokofrekvencijska slabo prigušena prijelazna pojava koja zbog valne prirode na točkama diskontinuiteta oklopa stvara vanjske prenapone i time privremeni porast potencijala oklopa. Zbog visokofrekvencijskih svojstava, porast potencijala znatno ovisi o načinu povezivanja oklopa sa uzemljivačem postrojenja. Na izraženom diskontinuitetu i nepovoljnim konfiguracijama spoja s uzemljivačem, porast potencijala može doseći nekoliko desetaka kV pri čemu su mogući nepoželjni preskoci na vanjskim dijelovima postrojenja. Najveći dio rada posvećen je eksperimentalnom načinu utvrđivanja prijelaznog porasta potencijala na jednom od izraženih mjesta diskontinuiteta, na spoju oklopa s energetskim kabelom, a sva istraživanja provedena su na jednom tipičnom 123 kV oklopljenom SF6 postrojenju. Zbog slučajnog nastanka inicijalne prijelazne pojave, u istraživanje je uveden statistički pristup. Višestrukim ponavljanjem pokusa sklapanja sekcijskog rastavljača i mjerenjem prijelaznog porasta potencijala na oklopu i platu kabela, na mjestu promatranog diskontinuiteta, dobiven je veći broj mjernih uzoraka za daljnje statističke obrade. Istražene su četiri različite konfiguracije spoja oklopa i plata kabela s uzemljivačem. Rezultati mjerenja i statističkih obrada pokazuju svrsishodnim, osim povezivanja oklopa i plata kabela s uzemljivačem, i potrebu premotenja kabelskih izolacionih prirubnica kratkospojnicima ili nelinearnim otpornicima. Time se višestruko i vrlo učinkovito smanjuju međusobne previsoke razlike potencijala i onemogučava vrlo vjerojatan vanjski preskok. Provedba mjerenja iziskuje opsežnu pripremu i korištenje suvremenog mjernog sustava, s visokom gornjom graničnom frekvencijom, velikom brzinom uzorkovanja i s vrlo "dubokom" radnom memorijom.

Abstract (english)

Enclosure voltage rise of the gas insulated high voltage switchgears is the result of the propagation and transition of internal very fast overvoltages on to the outside enclosure and grounded parts of the switchgears. The phenomenon is mostly evident at switching small capacitive loads by disconnector, when the multiple back flashovers on the disconnector contacts appear. The high frequency weakly damped transient phenomenon occurs at each back flashover, which, due to its wave character, creates the external overvoltages on the discontinuity points of the enclosure and as the result the temporary enclosure voltage rise. Due to the high frequency characteristics, the voltage rise significantly depends on the way the enclosure is connected to the switchgear grounding system. On the stressed discontinuity and inconvenient connection configurations, the voltage rise can be up to several times ten kV and the undesirable flashovers on the external part of the switchgear are possible. The greatest part of the dissertation is dedicated to the experimental method of determining the transient voltage rise on one of the stressed discontinuity points (at the connection of the enclosure and the power cable) and all the researches are done on a typical enclosed SF6 switchgear, voltage level 123 kV. The statistical approach has been implemented due to the random occurrence of the initial transient phenomenon. By multiple repetition of switching operation on the section disconnector and by measuring the transient voltage rise on the enclosure and cable sheath (on the observed discontinuity point), the greater number of the measuring samples for the further statistical elaboration has been obtained. Four different configurations of the connection of the enclosure and the cable sheath to the grounding system have been researched. The measuring results and statistical elaboration show that, beside connecting the enclosure and the cable sheath to the grounding system, it is useful to bridge over the cable insulating flange using the jumpers or non linear resistors. In such manner, too high voltage differences are significantly and efficiently decreased and very probable external flashover is prevented. The measurements require comprehensive preparation and modern measuring system, with high upper frequency limit, great sampling speed and very deep working memory.

• Keywords: Porast potencijala oklopa; vrlo brzi prenaponi; oklopljeno postrojenje; rastavljač; uzemljenje; mjerenje; statistički pristup
• Keywords (english): Enclosure voltage rise; very fast overvoltages; enclosed switchgear; disconnector; grounding; measuring; statistical approach
• Language: croatian
• URN:NBN: urn:nbn:hr:168:265446
• Study programme: Title: Postgraduate master programme in electrical engineering; Study programme type: university; Study level: postgraduate; Academic / professional title: Magistar znanosti elektrotehnike (Magistar znanosti elektrotehnike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Closed access
• Created on: 2019-04-25 12:27:21