standards / manuals / guidelines for small hydro development - AHEC
standards / manuals / guidelines for small hydro development - AHEC
standards / manuals / guidelines for small hydro development - AHEC
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Spark gaps specified <strong>for</strong> fitting to the bushings of power trans<strong>for</strong>mers, potential andcurrent trans<strong>for</strong>mers, rated 66 kV and above.The spark gaps are to con<strong>for</strong>m to the following specification, to prevent any damage tothe bushing due to the flashover gazing the petticoats of the bushing:a) The rods are to be circular not less than 12 mm diameterb) The rods should overhang their supports at-least one half of the gap spacing.c) The rods should be mounted so as to give a height of 1.3 times the gap spacingplus 100 mm (4 inches) above the ground plane as shown in fig. 2.3.5.Fig. 2.3.5The gap setting furnished below are adopted <strong>for</strong> all stations whether lightning arrestersare provided or not.Spacing <strong>for</strong> standard rod-gaps is given in table 2.5 (TNEB Practice).Highest systemvoltage kV rmsU mTable 2.5Critical Flashovervoltage 1/50 microsecondmkV Peak 23 Spacing of Standard Rod GapU Positive Polarity Negative Polarity72.5 59.1 7.7 6.5123 100.4 12.4 10145 118.3 15.4 13245 200 28.0 23Note: - The spacing given above are <strong>for</strong> the standard atmospheric conditions viz:1-7
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