Analiza varistorskega odziva na enosmerne prenapetosti

JAVORNIK, ŽAN (author), Pantoš, Miloš (mentor)

V tem diplomskem delu sem se posvetil časovnemu poteku električnega toka skozi energetski metaloksidni varistor (MOV) ob pojavu časnih prenapetosti, do katerih lahko pride v sistemu. Osredotočil sem se na enosmerne prenapetosti (DC), saj je te lažje ovrednotiti in simulirati. V začetku diplomskega dela sem opisal teorijo metaloksidnih varistorjev ter šest varistorskih tipov, ki so bili izbrani za testiranje in so najpogosteje uporabljeni v prenapetostnih odvodnikih podjetja Raycap. Nato sem opisal meritve varistorjev, kjer sem v začetku pridobil osnovne parametre vsakega vzorca. V drugem delu meritev se je vzorce varistorjev preobremenilo, dokler ti niso prebili. Iz oscilogramov prebojev se je nato ekstrapoliralo karakteristične parametre za vsakega izmed šestih varistorskih tipov, ki sem jih potreboval za simulacijo v programu LTspice. V zadnjem delu diplomske naloge pa sem opisal model za simuliranje preobremenitev DC, kjer se je simuliralo preobremenitev vseh šestih varistorskih tipov. Na koncu je sledila še ocena modela, kjer se je ocenilo napako v poteku ter napako karakterističnih parametrov. Izvajanje takih simulacij je lahko v veliko pomoč pri načrtovanju prenapetostne zaščite, saj lahko skrajšajo razvojne čase in zmanjšajo potrebne investicije, vendar le, če so dovolj natančne za naše potrebe. Po oceni simulacij se je izkazalo, da je predlagan model dovolj natančen za okvirno oceno, vendar ne dovolj za industrijske standarde. Težavo nekoliko predstavlja zadnji del simulacije, ko je varistor že globoko v termičnem pobegu. Kakor koli, potrebno je upoštevati tudi tolerance proizvajalcev energetskih varistorjev in povzeti, da je za prvi poizkus simuliranja model zadovoljiv.

• Language: Slovenian
• Keywords: prenapetostna zaščita, metaloksidni varistor, časne prenapetosti
• Work type: Bachelor thesis/paper
• Organization: FE - Faculty of Electrical Engineering
• Year: 2019
• PID: 20.500.12556/RUL-111715
• Publication date in RUL: 10.10.2019

Secondary language

• Language: English
• Title: Analysis of varistor behaviour under DC overvoltages

Abstract

In this thesis, I have analyzed the dynamic behavior of metal oxide varistor (MOV), under temporary DC overvoltages (TOV) The thesis begins with theory on metal oxide varistors, problematics of temporary overvoltages and it's effect on metal oxide varistor. In the second part, I described the measurements which provided me with the basic parameters for each MOV sample. In the second part of the measurements, each MOV sample was overloaded with such voltage that it caused a pin hole through MOV and it's destruction. From these measurements, I extrapolated basic characteristic parameters which I required for further simulation in LTspice software. In the last part, I have presented the simulations for all six MOV types and evaluated the model based on the measurements. Simulating overload behavior of MOV can be very time efficient as well as financially beneficial, but they have to be accurate enough so that we can rely on them. Evaluation of the model has proven that simulations were accurate enough, to gain a good perspective on how the current will flow through the MOV, however it still needs some work to get it up to industry standards. Most problematic is the last part of the simulation in which the MOV is deep in thermal runaway. It's also important to mention the tolerances of mass-produced MOV, as manufacturers have a +/- 10% tolerance. Overall the proposed model works well, however it still needs some more measurements and simulations to improve.

• Keywords: Surge protective device, metal-oxide varistor, temporary overvoltage