Ground resistance meter

Diplomsko delo obravnava izdelavo merilnika ozemljitve, skupaj z opisom delovanja v skladu z mednarodnim standardom IEC 61775. V delu so predstavljene najbolj pogoste vrste ozemljil, skupaj z metodami, s katerimi je moč pomeriti njihovo ozemljitveno upornost. Merilnik ozemljitve je naprava, s katero je mogoče pomeriti ozemljitveno upornost ozemljitve. V teoriji je to upornost pomerjena med ozemljilom in neko zelo oddaljeno točko na zemlji. V praksi pa se izkaže, da se tej upornosti lahko približamo z eno od opisanih metod. V naši napravi sta podprti dve metodi: tripolna metoda in tripolna izbirna metoda. Obe metodi temeljita na principu merjenja padca napetosti na ozemljilu, ki se pojavi, ko skozi njega spustimo znan tok. Izbirna metoda je za razliko od običajne namenjena merjenju izbranega ozemljila v primeru več vzporedno vezanih ozemljil. Pri tem delež toka, ki teče po izbranem ozemljilu pomerimo s tokovnimi kleščami. Izdelana naprava je modul, ki ga bomo kasneje vključili v novejše merilne naprave za testiranje inštalacij, zato tudi nima svojega prikazovalnika in je izdelan kot prototip. Modul krmilimo s pomočjo računalniškega programa, v katerega se izpisujejo tudi izmerjeni rezultati in ostale informacije. Komunikacija med napravo in računalnikom poteka po serijskem vodilu RS-232. Na koncu je predstavljeno tudi preizkusno merjenje na terenu skupaj z dobljenimi rezultati. Čeprav dobljene rezultate še nismo primerjali z ostalimi tovrstnimi napravami ne dvomimo o njeni točnosti.This thesis deals with the design of ground resistance tester together with a description of its operation in accordance with International Standard IEC 61775. The present paper describes the most commonly used earth electrodes with methods for measuring their ground resistance. Ground resistance tester is a device capable of measuring earth resistance. In theory, earth resistance is the resistance existing between the electrically accessible part of a buried electrode and another point on the Earth, which is far away. In practice, it turns out that this resistance can be approached by one of the methods described in the present paper. In our device two methods are supported: 3-pole Fall of Potential test and 3-pole selective method. Both methods are based on the principle of measuring the voltage drop across the earth resistance, which appears when the known current flow passes through. The selective method, unlike the usual method, is aimed at measuring the resistance of certain earth resistance in case of multiple parallel earth resistances. Its current is measured with a clamp meter. The designed device is a module which will be later incorporated in new measuring devices for testing electrical installations. Therefore, it does not have its own display and is designed as a prototype. The module is controlled by a computer program. The measuring results together with other information is displayed in it. Communication between the device and the computer runs through RS-232 serial bus. At the end of the present paper, the results obtained from the field measurements are presented. Although the obtained results have not yet been compared to other such devices, we do not have doubts about its accuracy