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The method used for neutral point grounding is very important for power network operation. There are many ways of grounding, which are used in practice, and the decision on the method of neutral grounding depends on the situation in the network connected to the substation. When deciding on the method of neutral grounding it is necessary to thoroughly consider all the advantages and disadvantages of individual modes of neutral grounding, and then choose the best technical and economical solution. This paper analyzes the ways of neutral point grounding in medium voltage networks used in the current practice in Croatia which are isolated neutral point, low resistance earthing, partial compensation and resonant earthing. The use of shunt circuit-breaker is also described. Additionally, a survey of the relays used for the neutral point grounding system inside the substations was conducted and a brief analysis of the results is presented in the paper.

Zadatak ovog rada jest opisati pojam zemljospoja, što je on i kakav utjecaj ima na mrežu. Isto tako opisuje značajke svakog od četiri moguća načina uzemljenja neutralne točke koji se mogu pojaviti u distribucijskoj mreži. Prednosti i nedostatke izoliranog zvjezdišta, zvjezdišta uzemljenog otpornikom, zvjezdišta uzemljenog otpornikom i prigušnicom te zvjezdišta uzemljenog Petersenovom prigušnicom. Značajke ovih načina uzemljenja su detaljnije analizirane u simulaciji uzemljenja zvjezdišta srednjenaponske mreže 20kV Cerna. Simulacija je odrađena u programu NEPLAN, program za analiziranje, planiranje, optimiziranje i simuliranje energetskih mreža. Na temelju te simulacije određen je zadovoljavajući način uzemljenja te je svaki način potkrijepljen proračunima. The task of this paper is to describe the term ground fault, what it is and what impact it has on the network. It also describes the features of each of the four possible neutral point grounding methods that may occur in a distribution network. Advantages and disadvantages of an isolated starpoint, a resistor-grounded starpoint, a resistor-and-coil-grounded starpoint, and a Petersen coil-grounded starpoint. The features of these grounding methods are analyzed in more detail in the neutral point grounding simulation of a medium voltage network Cerna (20kV). The simulation was done in NEPLAN, a program for analysis, planning, optimization and simulation of energy networks. On the basis of this simulation, a satisfactory method of exclusion was determined, and each method was supported by calculations.

Način uzemljenja neutralne točke mreže veoma je važan za pogon mreže. Postoji mnogo načina uzemljenja koji se danas koriste u praksi, a odluka o načinu uzemljenja neutralne točke ovisi o situaciji u mreži priključenoj na transformatorsku stanicu. Pri donošenju odluke o načinu uzemljenja neutralne točke potrebno je dobro razmotriti sve prednosti i nedostatke pojedinih načina uzemljenja neutralne točke te odabrati tehnički i ekonomski najbolje rješenje. U ovome diplomskom radu analizirani su načini uzemljenja srednjenaponske mreže s obzirom na praksu u Hrvatskoj elektroprivredi, odnosno izolirano zvjezdište, maloohmsko uzemljenje, djelomična kompenzacija te rezonantno uzemljenje. Opisana je i upotreba shunt prekidača. Opisana je zemljospojna zaštita mreže ovisno o načinu uzemljenja i dan kratak pregled prakse načina uzemljenja u Europi i Hrvatskoj. The method used for neutral point grounding is very important for power network operation. There are many ways of grounding, which are used in practice, and the decision on the method of neutral grounding depends on the situation in the network connected to the substation. When deciding on the method of neutral grounding it is necessary to thoroughly consider all the advantages and disadvantages of individual modes of neutral grounding, and then choose the best technical and economical solution. This final paper analyzes the ways of neutral point grounding in medium voltage networks used in the current practice of ''Hrvatska elektroprivreda'' which are isolated neutral point, low resistance earthing, partial compensation and resonant earthing. The use of shunt circuit-breaker is also described. The paper describes the earth-fault protection of the network, depending on the method of neutral point earthing, and gives a short overview of the earthing methods in Europe and Croatia.

U ovom radu prikazana je problematika otklanjanja prolaznih jednopolnih kvarova u srednjenaponskim mrežama. Ti kvarovi imaju velik udio u ukupnom broju kvarova te bi njihovo uklanjanje značajno doprinijelo kvaliteti električne energije sa stajališta neprekidnosti napajanja potrošača. Otklanjanje se vrši pomoću sustava koji koristi tri jednopolna shunt prekidača koji u definiranom vremenskom intervalu uzemljuju srednjenaponsku sabirnicu faze u kojoj se dogodi jednopolni kvar i time gase struju kvara na izvornom mjestu kvara. Ako je kvar bio prolazan, uspostavit će se redovno pogonsko stanje, a krajnji potrošači električne energije neće doživjeti prekid napajanja. U radu je uvodno predstavljena predmetna problematika, a zatim su prikazana teoretska razmatranja jednopolnih kvarova u 10(20) kV-nim mrežama i s tim povezani različiti načini uzemljenja zvjezdišta. Nakon analize osnovnih parametara različitih načina uzemljenja zvjezdišta, dan je osvrt na praksu i utjecaj na isporuku električne energije. Definiran je sustav za otklanjanje prolaznih jednopolnih kvarova s opisanim zahtjevima na komponente tog sustava. Opisana je izvedba ugradnje predloženog sustava u 35/20 kV-nu transformatorsku stanicu, kao pilot-projekt u Hrvatskoj, s prikazom zahvata na primarnom i sekundarnim postrojenjima. Zatim je predstavljen rad sustava po ugradnji analizom dosad prikupljenih statističkih podataka, električkih prilika u jednom ciklusu rada i problematike prenapona pri sklapanju shunt prekidača. Opisani su utjecaji sustava na zaštitno uzemljenje transformatorske stanice. Izvršeno je vrednovanje sustava definiranjem mreža pogodnih za ugradnju sustava, navođenjem prednosti i nedostataka sustava te ekonomskim aspektom. Razrađene su mogućnosti usavršavanja predloženog sustava načinom priključka sustava, interakcijom sa zaštitom sustava i uklanjanjem definiranih nedostataka. Na kraju rada iznijeta su zaključna razmatranja predstavljene problematike. This thesis presents the problem of transient single-phase-to-earth faults elimination in medium voltage networks. These faults have a large share of the total number of errors and their removal would significantly improve power quality regarding uninterruptible consumer supply. Elimination is done with the system that uses three single pole shunt circuit breakers. It grounds the medium voltage sub phase in which fault occurred in a defined time interval and thus puts out the fault current on the original fault location. If the failure was transient, normal operating conditions will establish and the consumers will not experience interruption of power supply. The thesis presents introductory underlying problems. Theoretical considerations of single-phase-to-earth faults in medium voltage networks and different methods of neutral point grounding are shown. After analyzing the basic parameters of different types of neutral point grounding, a reference to the practice and impact on the power supply is given. The transient single-phase-to-earth faults elimination system and requirements for the system components are defined. The installation of the suggested system in a 35/20 kV substation, which was a pilot project in Croatia, is described, along with the representation of the operations on the primary and secondary facilities. The system operation is presented then, including analysis of previously collected statistical data, the electrical conditions in a cycle of work and overvoltage problems during shunt switching. The impacts of the system on substation protective earthing are presented. The evaluation of the system is given by defining the network suitable for the installation of the system, stating the advantages and disadvantages of the system and the economic aspect of implementation. Improving possibilities of the proposed system are elaborated, including system connection modus, interaction with the relay system and removal of defined deficiencies Final thoughts on the presented subject are given at the end of the thesis.