In order to clarify the grounding conditions for protecting workers on the de-energized circuit from induction due to the live circuit and the required current capacity of grounding conductor for a 1, 000kV double-circuit power transmission line, the phenomena caused by the electrostatic induction resulting from the live circuit are first discussed. The results are as summarized below.
(1) Even though both ends of the de-energized circuit are grounded, the electrostatic induction voltage grows larger in parabolic form as the distance from the grounding point increases. As such, this voltage then determines the safe working zone, which determines the electrostatic induction current Ig flowing through a worker and the electrostatic induction current Ig0 flowing through the grounding conductor.
(2) The electrostatic induction current Ig and Ig0 are determined by the voltage applied to the live circuit, grounding intervals on the de-energized circuit conductor conditions of the circuit and the phase configurations at the line.
(3) If a worker has an electric resistance of 1kΩ and touches any portion of the de-energized circuit, the current Ig will not exceed 1mA as long as the grounding intervals are less than approximately 9km.
(4) The value of the current Ig0 is proportional to the grounding intervals surrounding the relevant grounding point, regardless of the location of this point. This Ig0 current reaches a maximum of 10 A if the intervals are 100km.
(5) The calculation formulas used in considering the above are now in practical use for verification purposes on an actual power line of 500kV.
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