Proposed Revisions of American Standards C37.5 and C37.9 AIEE Committee Report

Specifying and determining the performance of circuit interrupting devices which interrupt short-circuit currents requires the measurement of the magnitude of transient alternating currents and voltages. Because direct components of current and alternating components of both current and voltage may be decreasing or increasing at the time for which measurement is desired, standards, e. g., C37.4, have defined the currents as rms values determined from the components at a given instant, and the recovery voltages as rms values measured from the envelope of the a-c component at the peak occurring during the interval of 1/ 2 to 1 cycle after final current interruption. These definitions eliminate the problem of decrements and simplify the measurement of the currents and voltages. Methods of measuring oscillograms to obtain these values are given in this section of standards for Alternating Current Power Circuit Breakers.