IEEE 1312-1993 (R2004) pdf free.IEEE Standard Preferred Voltage Ratings for Alternating-Current Electrical Systems and Equipment Operating at Voltages Above 230 kVNominal.
IEEE 1312 This standard provides preferred voltage ratings above 230 kV nominal for alternating-current (ac) systemsand equipment.
NOTE—The definitions given in 2.1 through 2.5 for certain terms relating to voltage ratings for ac systems and equip-ment are intended to clarify the meaning and intent of this standard.
system voltage: A root-mean-square (rms) phase to-phase power frequency voltage on athreephase acelectrical system.
maximum system voltage:The highest rms phase-to-phase voltage that occurs on thesystem under nor-mal operating conditions, and the highest rmsphase-to-phase voltage for which equipment and other systemcomponents are designed for satisfactory continuous operation without derating of any kind.
When defining maximum system voltage, voltage transients and temporary overvoltages caused by abnor-ma system conditions such as faults load rejection, etc., are excluded. However, voltage transients and tem-porary overvoltages may affect equipment operating performance and are considered in equipmentapplication.
nominal system voltage: The system voltage by which the system may be designated and to which crtain operating characteristics of the system are related.
The nomina voltage of a system is near the voltage level at which the system normally operates. To alowfor operating contingencies, systems generally operate at voltage levels about 5-10% below the maximumsystem voltage for which system components are designed.
extra-high voltage (ehv): A maximum system voltage that is greater than242kV but less than 1000kV.IEEE 1312 pdf download.