IEC
IEC 60255
Measuring Relays and Protection Equipment
The series that defines how protection relays are specified and tested, including the standard inverse, very inverse and extremely inverse time-current characteristics that grading curves are drawn from. An integrity engineer meets it when verifying that the settings in a relay match the protection study, when injection testing a relay against its published characteristic, and when a numerical relay replaces an electromechanical one and the nominally equivalent curve behaves differently at low multiples of setting.
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