The selection of the rated insulation level consists of the selection of the most economical set of standard rated withstand voltages (Uw) of the insulation sufficient to prove that all the required withstand voltages are met.
The highest voltage for equipment is then chosen as the next standard value of Um equal to or higher than the highest voltage of the system where the equipment will be installed.
For equipment to be installed under normal environmental conditions relevant to insulation, Um shall be at least equal to Us.
For equipment to be installed outside of the normal environmental conditions relevant to insulation, Um may be selected higher than the next standard value of Um equal to or higher than Us according to the special needs involved.
Standardization of tests, as well as the selection of the relevant test voltages, to prove the compliance with Um, are performed by the relevant apparatus committees (e.g. pollution tests, partial discharge voltage tests
he withstand voltages to prove that the required temporary, slow-front and fast-front withstand voltages are met, for phase-to-earth, phase-to-phase and longitudinal insulation, may be selected with the same shape as the required withstand voltage, or with a different shape, exploiting, for this last selection, the intrinsic characteristics of the insulation.
The value of the rated withstand voltage is then selected in the list of the standard rated withstand voltages reported in 5.6 and 5.7, as the next value equal to or higher than: – the required withstand voltage in the case of the same shape, – the required withstand voltage multiplied by the relevant test conversion factor in the case of a different shape.
For equipment to be used in normal environmental conditions, the rated insulation level should then preferably be selected from Table 2 and Table 3 corresponding to the applicable highest voltage for equipment such that these rated withstand voltages are met.
The selection of the standard rated withstand voltage to prove the compliance with the veryfast-front required withstand voltage shall be considered by the relevant apparatus committees.
For surge arresters the required withstand voltages of the insulating housing are based on the protective levels Upl and Ups with suitable safety factors applied as per the apparatus standard IEC 60099-4. In general, therefore, the withstand voltages shall not be selected from the lists of 5.6 and 5.7
The selection of the rated insulation level consists of the selection of the most economical set of standard rated withstand voltages (Uw) of the insulation sufficient to prove that all the required withstand voltages are met. The highest voltage for equipment is then chosen as the next standard value of Um equal to or higher than the highest voltage of the system where the equipment will be installed. For equipment to be installed under normal environmental conditions relevant to insulation, Um shall be at least equal to Us. For equipment to be installed outside of the normal environmental conditions relevant to insulation, Um may be selected higher than the next standard value of Um equal to or higher than Us according to the special needs involved.Standardization of tests, as well as the selection of the relevant test voltages, to prove the compliance with Um, are performed by the relevant apparatus committees (e.g. pollution tests, partial discharge voltage testshe withstand voltages to prove that the required temporary, slow-front and fast-front withstand voltages are met, for phase-to-earth, phase-to-phase and longitudinal insulation, may be selected with the same shape as the required withstand voltage, or with a different shape, exploiting, for this last selection, the intrinsic characteristics of the insulation. The value of the rated withstand voltage is then selected in the list of the standard rated withstand voltages reported in 5.6 and 5.7, as the next value equal to or higher than: – the required withstand voltage in the case of the same shape, – the required withstand voltage multiplied by the relevant test conversion factor in the case of a different shape. For equipment to be used in normal environmental conditions, the rated insulation level should then preferably be selected from Table 2 and Table 3 corresponding to the applicable highest voltage for equipment such that these rated withstand voltages are met. The selection of the standard rated withstand voltage to prove the compliance with the veryfast-front required withstand voltage shall be considered by the relevant apparatus committees. For surge arresters the required withstand voltages of the insulating housing are based on the protective levels Upl and Ups with suitable safety factors applied as per the apparatus standard IEC 60099-4. In general, therefore, the withstand voltages shall not be selected from the lists of 5.6 and 5.7
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