Dielectric type tests of insulator sets have been performed for decades to ensure satisfactory electrical performance when these are installed on distribution and transmission lines. Recently, four fully accredited high voltage test laboratories performed a Round Robin Test (RRT) on a 400 kV double suspension polymeric insulator set according to standard procedures given in IEC 60383-2 and 60060-1. Standard dielectric type tests were conducted. The same insulator set was circulated and the participating laboratories performed dielectric tests between 2015 and 2016. Maximum differences in measured values obtained by these laboratories were calculated for each test and these allow reproducibility of measurements to be investigated. Furthermore, one of the HV laboratories performed some of the dielectric tests several times to study repeatability of measurements.
There are several methods to statistically calculate repeatability and reproducibility of measurements, including Range & Average Method or Analysis of Variance Method. In this case, the number of measurements carried out as part of the RRT did not allow those methods to be utilized. Rather, relative differences and standard deviations of measurements were calculated.
Test results were evaluated according to ISO/IEC 17043 – a method generally based on comparing assigned values, considered as reference, with actual measured values. In this case, since none of the participating laboratories could be considered as a reference, assigned reference values were calculated as arithmetic means from each of the measurements at participating HV Laboratories.
Attend the 2017 INMR WORLD CONGRESS in Barcelona-Sitges from November 5 to 8 to hear a paper by Jan Lachman of EGU HV Laboratory. He will outline how the main goal of this testing was not simply to quantify differences in measurements but to analyze some of the main aspects that affect measured values – from test set-up, to rain parameters for testing under wet conditions. to voltage source parameters, to correction factors.