Technical Development of the IEEE Guide for Visual Corona Testing of Insulator Assemblies and Line Hardware and its Application in the Testing of 765-kV Transmission Line Insulator Assemblies

Traditionally corona testing has been performed in laboratories by mounting a single phase mock-up of the conductor/hardware/insulator assembly at a given height above the ground and applying 110% of the rated line-to-ground operating voltage. If the test setup is shown to be free of corona by this test, then it is considered that the assembly will be free of corona under operating conditions. This method does not appear in any standards, but is used as a generally accepted test method. In spite of its general acceptance, this test method can give erroneous results. This is due to the fact that the inception of corona occurs at a given electric field gradient rather than a given absolute voltage. Under actual operating conditions, the electric field gradient at the conductor/hardware/insulator assembly is a function of phase spacing, the local geometry, and the applied 3-phase voltage. In order to correctly perform such a test in a laboratory, it is essential that the maximum gradients occurring on the conductors in the field be reproduced in the laboratory test. To address this shortcoming in test procedures, the IEEE PES Transmission and Distribution Committee´s Lightning and insulator and corona and field effects working groups are engaged in the development of a guide for the performance of visual corona and RIV testing on insulator assemblies and line hardware.This paper describes the theoretical and experimental background upon which the technical development of the guide is based, and the application of the procedures in the guide as used in testing insulator assemblies and hardware for a new design 6-conductor bundle 765 kV transmission system.