Feasibility of Impulse Voltage Puncture Test on Insulators in Air

The puncture withstand tests on insulators for overhead electric power lines should ensure that the insulators withstand the stresses caused by lightning overvoltages with a tolerable risk of puncture. Of the two alternatives given by IEC Standard 383 (Insulators for overhead lines) the impulse voltage puncture test on insulators in air (IPT) is considered more representative of service conditions than the alternative power frequency puncture test on insulators in oil (PFT). The aim of the research was to study the feasibility of the IPT, which mainly comprises the reproducibility and costs of the test. In addition, the reproducibility of the PFT is shown to be poor. The conditions of reproducibility of IPT are definition of test voltage, test procedure and accuracy of the measurement of the very fast front impulse voltages. These have been studied thoroughly. The test voltage should be defined by its peak value and not by the front steepness. In addition to peak value of the test impulse voltage, also the polarity, number of impulses, polarity reversal, sequence of impulses, time interval between consecutive impulses, any prestress and mounting arrangements can all influence the result of IPT. The measurement accuracy of the very fast front impulse voltage is critical, and special measuring systems for the purpose have been developed and analyzed. The costs of IPT can be reduced by compacting the test system and by automation. The main outcome of the research is the publication of IEC Report 1211 (1994).