Abstract
This paper describes the result of measurement of residual dc charge decay in a 500kV transmission line, when the line is separated from power sources or other equipment by a circuit breaker. The measurement aims at obtaining data for calculating closing surges of circuit breaker, and appreciating the value and duration of dc voltage that affects the ac GIs insulation performances including inter-pole insulation of the circuit breaker. Since the measurement was performed in fine and dry days of winter season, the measured time constants are considered to be the largest among those of whole seasons. The measured decay curves indicate two parts; the rapid decrease part appears in the beginning stage of the phenomena and the following slowly decrease part. The time constant of the residual charge decay, which is defined as the time until the residual voltage decreases to l/e of the initial value, shows large scattering, but there appears clear polarity difference. Positive polarity gives 56-387 sec. from 38 measurements, and the average is 211 sec. Negative polarity gives 26-301 sec. from 24 measurements, and the average is 98sec.
