TABLE OF CONTENTS This section is a general summary of important aspects of the existing international standards (IEC60099 and IEEE/ANSI C62.110).
The following standard definitions are used for both the testing and selection of zinc oxide surge arresters.
U c is the maximum permissible value of a sinusoidal power frequency voltage which may be continuously applied across the arrester terminals. The normal system voltage should not exceed this value. Some manufacturers use the terms maximum continuous operating voltage (MCOV) and continuous operating voltage (COV), the former being an upper limit for the arrester permissible continuous voltage.
I c is the continuous r.m.s. or peak magnitude current which flows through the arrester when the continuous operating voltage, U c is applied across its terminals.
U r is the maximum permissible short duration r.m.s. value of power frequency voltage between the arrester terminals. In IEC60099-4:1991 [77], the rated voltage is defined as the 10 s power frequency voltage used in the operating duty test involving high current and long duration impulses. However, it should be noted that some national standards use a number of impulses at nominal current with superimposed power frequency voltage in order to determine the rated voltage which may produce different values from those recommended by IEC. The standards bodies are now considering these discrepancies.
