IEEE Std 1427:2006 pdf free download

IEEE Std 1427:2006 pdf free download.IEEE Guide for Recommended Electrical Clearances and Insulation Levels in Air-Insulated Electrical Power Substations.
a) Conventional BIL: 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, which is applicable specifically to non—self-restoring insulations.
b) Statistical HIL: The crest values of a standard lightning impulse for which the insulation exhibits a 90% probability of withstand (or a 10% probability of failure) under specified conditions, which is applicable specifically to self-restoring insulations.
The basic switching impulse level may be either a conventional BSL or a statistical BSL. classified as follows:
— Conventional IISL: The crest value of a standard switching impulse lbr which the insulation does not exhibit disruptive discharge when subjected to a specific number of impulses under specified conditions, which is applicable to non—self-restoring insulations.
— Statistical BSI.: The crest value of a standard switching impul for which the insulation exhibits a 90% probability of withstand (or a 10% probability of failure), under specitied conditions, which is applicable to self-restoring insulations.
Switching impulses often represent the more severe air insulation withstand condition at system voltages 362 kV and over.
5.2.2 Standard Insulation levels
Based on many years of historically successful operating experience, standard BIL and BSL have been established for given maximum system voltage levels. Table I and Table 2 (from IEEE Std 1313.1-1996) show several possible withstand voltages for a given maximum rated voltage. The withstand voltage selected should be based on the results of the user’s insulation coordination analysis.
For example, in Table 1, 650 kV BIL has been established as the historical, conservative insulation level at 145 kV. With improvements in surge protection, and for other reasons, successful operation at a HI L of 550 kV or 450 kV is possible. depending on user criteria and the desired protective margin. When other considerations arc incorporated (see Clause X). even further reductions in BIL may be possible.
The withstand voltages in Table I and Table 2 are phase-to-ground voltages. To establish the phase-to- phase withstand voltage, and associated clearances, it is necessary to continue the insulation coordination analysis. With some equipment, the phase-to-phase withstand voltage (based on test voltages) can be the same as the phase-to-ground withstand voltage (for example. three-phase transformers). With other equipment, the phase-to-phase insulation level is undefined (for example. support insulators) and the withstand voltage is dictated by the design of the assembly (i.e., air clearances between phases and from phase-to-ground).