IEEE C62.82.1-2010 pdf download IEEE Standard for Insulation Coordination—Definitions, Principles, and Rules
3.22 nominal system voltage: The rms phase-to-phase voltage by which the system is designated and towhich certain operating characteristics of the system are related.
NOTE–The nominal system voltage is near the voltage level at which the system norally operates. To allow foioperating contingencies,systems generally operate at voltage levels about 5% to 10% below the maximum svstemvoltage for which systemns components are designed.
3.23 non-self-restoring insulation: An insulation that loses its insulating properties or does not recoverthem completely, after a disruptive discharge caused by the application of a test voltage; insulation of thiskind is generally, but not necessarily, internal insulation.
3.24 overvoltage: Voltage, between one phase and ground or between two phases, having a crest valueexceeding the corresponding crest of the maximum system voltage. Overvoltage may be classified by shapeand duration as either temporary or transient.
NOTE 1–Unless otherwise indicated, such as for surge arresters, overvoltages are expressed in per unit with relerenceto peak phase-to-ground voltage at maximum system voltage, Vm x (2) / (V3).NOTE 2-A general distinction ay be made between highly damped overvoltages of relatively short duration(transient overvoltages) and undamped or only slightly damped overvoltages of relatively long duration (temporaryovervoltages). The transition between these two groups cannot be clearly defined.
3.25 performance criterion: The criterion upon which the insulation strength or withstand voltages andclearances are selected.The performance criterion is based on an acceptable probability of insulation failurcand is determined by the consequence of failure, required level of reliability, expected life of equipment.economics, and operational requirements. The criterion is usually expressed in terms of an acceptable failurerate (number of failures per year, years between failures, risk of failure, etc.) of the insulation configuration.
3.26 phase-to-ground insulation configuration: An insulation configuration between a phase and theneutral or ground.
3.27 phase-to-phase insulation configuration: An insulation configuration between two different phases
3.28 protective margin (PM): The value of the protective ratio (PR), minus one, expressed as apercentage.PM =(PR -1)x 100.
3.29 protective ratio (PR): The ratio of the insulation strength of the protected equipment to theovervoltages appearing across the insulation
3.30 resonant grounded neutral system: A system in which one or more neutral points are connected toground through reactors that approximately compensate the capacitive component of a single-phase-to-ground-fault current.
NOTE–With resonant grounding of a system, the fault current is limited such that an arc fault in air will be self
extinguishing.
3.31 self-restoring insulation: Insulation that completely recovers its insulating properties after adisruptive discharge caused by the application of a test voltage, insulation of this kind is generally, but notnecessarily,external insulation.
3.32 standard chopped wave impulse voltage shape: A standard lightning impulse that is intentionallyinterrupted on the tail by sparkover of a gap or other equivalent chopping device. Usually the time to chopis 2 us to 3 us.