(U) Effect of atmospheric conditions The sparkover voltage of a spark gap depends on the air density which varies with the changes in both temperature and pressure. If the sparkover voltage is under test conditions V of temperature and pressure torr and if the sparicover voltage is under standard T p VQ conditions of temperature » 2O0C and pressure = 760 torr, then T p The sparkover voltage increases with humidity. The increase is about 2 to 3% over normal humidity range of 8 g/m3 to 15 g/m3. The influence of humidity on sparkover voltage of a 25 cm sphere gap for 1 cm spacing is presented in Fig. 7.20. It can be seen that the increase in sparkover voltage is less than 3% and the variation between a.c. and d.c. breakdown voltages is negligible (< 0.5%). Hence, it may be concluded that the humidity effect increases with the size of spheres and is maximum for uniform field gaps, and (/O the sparicover voltage increases with the partial pressure of water vapour in air, and for a given humidity condition, the change increases with the gap length. As the change in sparkover voltage with humidity is within 3%, no correction is normally given for humidity.
(U) Effect of atmospheric conditions The sparkover voltage of a spark gap depends on the air density which varies with the changes in both temperature and pressure. If the sparkover voltage is V under test conditions of temperature T and pressure p torr and if the sparicover voltage is VQ under standard conditions of temperature T » 2O0C and pressure p = 760 torr, then The sparkover voltage increases with humidity. The increase is about 2 to 3% over normal humidity range of 8 g/m3 to 15 g/m3. The influence of humidity on sparkover voltage of a 25 cm sphere gap for 1 cm spacing is presented in Fig. 7.20. It can be seen that the increase in sparkover voltage is less than 3% and the variation between a.c. and d.c. breakdown voltages is negligible (< 0.5%). Hence, it may be concluded that the humidity effect increases with the size of spheres and is maximum for uniform field gaps, and (/O the sparicover voltage increases with the partial pressure of water vapour in air, and for a given humidity condition, the change increases with the gap length. As the change in sparkover voltage with humidity is within 3%, no correction is normally given for humidity.
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