IEEE Std C57.32a:2020 pdf download.IEEE Standard for Requirements, Terminology, and Test Procedure for Neutral Grounding Devices-Amendment 1: Neutral Grounding Resistors Clause (AM).
NOTE— -The editing instructions contained in this amendment define how to merge the material contained therein into the existing base standard and its amendments to form the comprehensive standard.
The editing instructions are shown in bold italic. Four editing instructions are used: change, delete, insert, and replace. Change is used to make corrections in existing text or tables. The editing instruction specifies the location of the change and describes what is being changed by using trikethrough (to remove old material) and underscore (to add new material). Delete removes existing material, insert adds new material without disturbing the existing material. Insertions may require renumbering. If so, renumbering instructions are given in the editing instruction. Replace is used to make changes in figures or equations by removing the existing figure or equation and replacing it with a new one. Editing instructions, change markings, and this NOTE will not be carried over into future editions because the changes will be incorporated into the base standard.’
7. Grounding resistors
Insert new section 7.2:
7.2 Ratings
Change existing 7.2 to 7.2.1 as follows:
7.2.1 Rated voltage
Since the active material used in resistors has an appreciable temperature coefficient, the resistance is materially changed during the time of operation causing the current to decrease. When the product of the fault current and resistance at 30 °C exceeds 80% of the line-to-neutral voltage of the circuit, the resistor shall be rated for constant voltage and the rated voltage shall be taken equal to the line-to-neutral voltage.
Insert new suhelause 7.2.2, and renumber .suh.seqiieiit .suhcluuses:
7.2.2 Rated time
Rated time shall be 10 seconds, 1 minute, 10 minutes, extended time, or continuous (steady-state). Extended time shall not exceed an average of 90 days per year.
7.2.2.1 Ten-second and one-minute ratings
The rated-time temperature rise of a I 0-second and 1-minute neutral grounding resistor is a hot-spot rise. The rated-time temperature rise of 10-second and 1-minute devices shall be taken as the sum of the steady- state rise determined as in 7.7.12 if specified, otherwise 0 °C rise if not specified, and the additional rise caused by the application of rated voltage for rated time as in 7.7.2.
7.2.2.2 Ten-minute ratings
The rated-time temperature rise of a 10-minute neutral grounding resistor is a hot-spot rise. The rated-time temperature rise of 10-minute devices shall be taken as the sum of the steady-state rise determined as in 7.7.1, if specified, otherwise 0 °C rise if not specified, and the additional rise caused by the application of rated voltage for rated time as in 7.7.2.
7.2.2.3 Extended-time ratings
The rated-time temperature rise of an extended-time neutral grounding resistor is a hot-spot rise. The rated- time temperature rise of extended time devices shall be taken as the temperature rise above ambient resulting from application of rated voltage as determined in 7.7.1.IEEE Std C57.32a pdf download.