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High power zinc oxide based varistors

Objective



Zinc oxide based ceramics possesses the remarkable property, following which its resistance decreases abruptly when the applied voltage exceeds a certain value called threshold voltage Vs. This property is used for the protection of electrical grids and electronic systems against overvoltage coming from lighting strokes. The component using this material (varistor) is used currently in the world and replaces SILICON Carbide based devices or gas spark gap. This activity generates in the world approximately 200 to 250 Millions Ecus per year.

Current research in the world concerns different points. It focuses on the utilization of others materials than the oxide of zinc, manufacturing processes (notably with the mixed powder obtained by chemical way), the improvement of the stability of their electrical characteristics during the aging, the reduction of the varistor volume of the in view to reduce its cost.

The proposed research project comprises two large parts, a research based on the ceramic material and two applications. On the material side, this project aims to increase the threshold voltage Vs of the varistor with the same characteristics concerning dimensions, the aging and the capacity of energy absorption in view to reduce the quantity of the raw material and the consumption of electrical energy needed for sintering.

With these new and improved varistors we undertake in this programme researches on :

the utilization of these new varistors in medium voltage arresters : dimensioning the arrestors, voltage repartition study of varistors mounted inside the arresters, behaviour of arresters in the electrical grids
the utilization of varistors in power electronic commutation circuits : thermal behaviour of varistors in high repetition frequency of overvoltage, dimensioning, method of varistor cooling.

There are 6 partners in the consortium geographically situated in the south part of Europe and of complementary competence. Two Laboratories, members of the EU, are Toulouse Electrical Engineering Laboratory (Fr, Coordinator and specialized in varistor research and electrical tests) and the High voltage Institute of the Technical University of Athens (Gr and specialized in High voltage testing). The two partners coming from Romania are an Institute of Research ICPE (Research and production of small quantities of varistors for national use) and a academic Laboratory, the Electrotechnic Department of The Technical University of Bucharest (Specialized in the power electronics). The last two members are in Slovenia: Iskra Varistors (a small size manufacturer and exporter of low voltage varistors) and the Josef Stefan Institute (specialized in the research on manufacturing processes and the analysis of the ceramics microstructure).

Advantages that one can take from this programme of research that last three years are the following :

From the knowledge point of view, the comprehension of the mechanism of the growth of Zinc oxide grains with a spinelle phase, the correlation between the ceramic microstructure and its electrical properties.
From the economic point of view, a reduction of the volume of the raw material and the quantity of energy needed to make a varistor.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

UNIVERSITE PAUL SABATIER DE TOULOUSE III
Address
Route De Narbonne 118
31062 Toulouse
France

Participants (5)

JOZEF STEFAN INSTITUTE
Slovenia
Address
39,Jamova 39
1001 Ljubljana
National Technical University of Athens
Greece
Address
42,28Th October Street 42
10682 Athens
Polytechnic University of Bucharest
Romania
Address
313,Splaiul Independentei, Sector 6
76206 Bucuresti
Research and Design Institute for Electrical Engineering
Romania
Address
313,Splaiul Unirii
74204 Bucuresti
VARSI D.O.O.
Slovenia
Address
35,Stegne 35
1000 Ljubljana