IEEE C62.82.1-2010 pdf free download.IEEE Standard for Insulation Coordination—Definitions, Principles, and Rules.
3. Definitions For the purposes of this document, the following terms and definitions apply. The IEEE Standards Dictionary: Glossary of Terms & Definitions [B1] should be consulted for terms not defined in this clause. 7 3.1 atmospheric correction factor: A factor applied to account for the difference between the atmospheric conditions in service and the standard atmospheric conditions. NOTE—In terms of this standard, it applies to insulation exposed to the atmosphere only. 3.2 basic lightning impulse insulation level (BIL): The electrical strength of insulation expressed in terms of the crest value of a standard lightning impulse under standard atmospheric conditions. BIL may be expressed as either statistical or conventional. 3.3 basic switching impulse insulation level (BSL): The electrical strength of insulation expressed in terms of the crest value of a standard switching impulse. BSL may be expressed as either statistical or conventional. 3.4 conventional BIL (basic lightning impulse insulation level): The crest value of a standard lightning impulse for which the insulation shall not exhibit disruptive discharge when subjected to a specific number of applications of this impulse under specified conditions, applicable specifically to non-self-restoring insulations. 3.5 conventional BSL (basic switching impulse insulation level): The crest value of a standard switching impulse for which the insulation does not exhibit disruptive discharge when subjected to a specific number of impulses under specified conditions, applicable to non-self-restoring insulations. 3.6 conventional withstand voltage: The voltage that an insulation system is capable of withstanding without failure or disruptive discharge under specified test conditions. 3.7 crest value (peak value): The maximum absolute value of a function when such a maximum exists.
3.22 nominal system voltage: The rms phase-to-phase voltage by which the system is designated and to which certain operating characteristics of the system are related. NOTE—The nominal system voltage is near the voltage level at which the system normally operates. To allow for operating contingencies, systems generally operate at voltage levels about 5% to 10% below the maximum system voltage for which systems components are designed. 3.23 non-self-restoring insulation: An insulation that loses its insulating properties or does not recover them completely, after a disruptive discharge caused by the application of a test voltage; insulation of this kind is generally, but not necessarily, internal insulation. 3.24 overvoltage: Voltage, between one phase and ground or between two phases, having a crest value exceeding the corresponding crest of the maximum system voltage. Overvoltage may be classified by shape and duration as either temporary or transient. NOTE 1— Unless otherwise indicated, such as for surge arresters, overvoltages are expressed in per unit with reference to peak phase-to-ground voltage at maximum system voltage, Vm × (√2) / (√3). NOTE 2— A general distinction may be made between highly damped overvoltages of relatively short duration (transient overvoltages) and undamped or only slightly damped overvoltages of relatively long duration (temporary overvoltages). The transition between these two groups cannot be clearly defined. 3.25 performance criterion: The criterion upon which the insulation strength or withstand voltages and clearances are selected. The performance criterion is based on an acceptable probability of insulation failure and 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 failure rate (number of failures per year, years between failures, risk of failure, etc.) of the insulation configuration.
3.28 protective margin (PM): The value of the protective ratio (PR), minus one, expressed as a percentage. PM = (PR − 1) × 100. 3.29 protective ratio (PR): The ratio of the insulation strength of the protected equipment to the overvoltages appearing across the insulation. 3.30 resonant grounded neutral system: A system in which one or more neutral points are connected to ground 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 a disruptive discharge caused by the application of a test voltage; insulation of this kind is generally, but not necessarily, external insulation. 3.32 standard chopped wave impulse voltage shape: A standard lightning impulse that is intentionally interrupted on the tail by sparkover of a gap or other equivalent chopping device. Usually the time to chop is 2 µs to 3 µs. 3.33 standard lightning impulse voltage shape: An impulse that rises to crest value of voltage in 1.2 µs (virtual time) and drops to 0.5 crest value of voltage in 50 µs (virtual time), both times being measured from the same origin and in accordance with established standards of impulse testing techniques. It is described as a 1.2/50 impulse.