Stress control on polymeric outdoor insulators using Zinc oxide microvaristor composites

R. Abd-Rahman, A. Haddad, N. Harid, H. Griffiths

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88 Scopus citations


An approach to high field control, particularly in the areas near the high voltage (HV) and ground terminals of an outdoor insulator, is proposed using a nonlinear grading material; Zinc Oxide (ZnO) microvaristors compounded with other polymeric materials to obtain the required properties and allow easy application. The electrical properties of the microvaristor compounds are characterised by a nonlinear fielddependent conductivity. This paper describes the principles of the proposed fieldcontrol solution and demonstrates the effectiveness of the proposed approach in controlling the electric field along insulator profiles. A case study is carried out for a typical 11 kV polymeric insulator design to highlight the merits of the grading approach. Analysis of electric potential and field distributions on the insulator surface is described under dry clean and uniformly contaminated surface conditions for both standard and microvaristor-graded insulators. The grading and optimisation principles to allow better performance are investigated to improve the performance of the insulator both under steady state operation and under surge conditions. Furthermore, the dissipated power and associated heat are derived to examine surface heating and losses in the grading regions and for the complete insulator. Preliminary tests on inhouse prototype insulators have confirmed better flashover performance of the proposed graded insulator with a 21 % increase in flashover voltage.

Original languageBritish English
Article number6180266
Pages (from-to)705-713
Number of pages9
JournalIEEE Transactions on Dielectrics and Electrical Insulation
Issue number2
StatePublished - Apr 2012


  • electric field
  • Microvaristors
  • nonlinear grading material
  • polymeric outdoor insulators
  • stress control


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