Paper Information

Title: 

DEVELOPMENT OF ZNO VARISTORS WITH HIGH TEMPERATURE DIELECTRIC COATINGS

Type: PAPER
Author(s): BOLANDI M.,NEMATI Z.,MOHANDES M.,MARKAZI M.
 
 
 
Name of Seminar: INTERNATIONAL POWER SYSTEM CONFRENCE
Type of Seminar:  CONFERENCE
Sponsor:  SHERKATE TAVANIR
Date:  2004Volume 19
 
 
Abstract: 

ZINC OXIDE VARISTORS ARE SMART ELECTRO CERAMIC DEVICES, WHOSE PRIMARY FUNCTION IS TO PROTECT AN ELECTRICAL SYSTEM BY SENSING AND LIMITING TRANSIENT SURGES AND TO DO SO REPEATEDLY WITHOUT BEING DESTROYED. THESE VARISTORS ARE STRONGLY NON-LINEAR RESISTORS, USED AS SURGE ARRESTERS IN POWER TRANSMISSION AND FOR THE PROTECTION OF ELECTRONIC DEVICES. METAL OXIDE VARISTORS HAVE A DIELECTRIC COATING ON LATERAL SURFACE IN THE FORM OF THERMO SET, GLAZE OR OTHER CERAMIC COATINGS. IN CONVENTIONAL LEAD OXIDE BASE GLAZES THAT ARE APPLIED ON VARISTOR BODY AT TEMPERATURE BETWEEN 500-700OC, IN SPITE OF LOW SINTERING TEMPERATURE, TWO DISCRETE THERMAL CYCLES ARE NEEDED, ONE FOR SINTERING OF ZNO-BASED BODY AND THE OTHER FOR BAKING OF THE LATERAL COATING. ON THE OTHER HAND, SINCE THE LEAD OXIDE BASE COMPOUNDS ARE TOXIC AND ALSO BECAUSE OF FRITTING PROBLEMS, COMPLETE OR PARTIAL REPLACEMENT OF LEAD OXIDE FROM COATING HAVE EVER BEEN INTENDED. IN THIS PAPER, HIGH TEMPERATURE COATINGS ON THE BASIS OF SIO2 AND FE2O3 ARE PRESENTED. APPLICATION OF THESE COATINGS ON MOLDED MATERIAL, PROVIDES THE POSSIBILITY OF SIMULTANEOUS BAKING AND PROCESS OF PRODUCT THAT LEADS IN TIME AND ENERGY SAVING. ADDITION OF BI2O3, B2O3 AND AL2O3 IN THE COMPOSITION OF THE COATING, AND ITS INFLUENCE ON SOME PHYSICAL AND ELECTRICAL PROPERTIES, ARE DISCUSSED IN THIS PAPER THAT SHOWS THE IMPROVEMENT OF THESE PROPERTIES ESPECIALLY, DIELECTRIC STRENGTH IN ALL OF THE PREPARED COATINGS. PHASE AND MICROSTRUCTURE INVESTIGATION OF THE COATINGS WAS DONE BY X-RAY DIFFRACTOMETERY AND SCANNING ELECTRON MICROSCOPY.

 
Keyword(s): ZNO VARISTOR, HIGH TEMPERATURE DIELECTRIC COATINGS, SIMULTANEOUS SINTERING, SIO2
 
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