Capacitive Current Estimation for Overhead and Cable Power Lines

The capacitive current is mainly determined by the length of the feeder, the cross-sectional area of the conductor, the dielectric constant, the height above the ground, and the rated voltage. The specific estimation methods are as follows:

• Estimation of capacitive current of overhead lines: For overhead lines of 3 - 35 kV, the capacitance per phase to ground is usually 5000 - 6000 pF/km. Based on this, the value of the single-phase grounding capacitive current per kilometer for lines of different voltage levels can be estimated.

• Estimation of capacitive current of cable lines: The capacitive current of cable lines is much larger than that of overhead lines and needs to be calculated separately. Its value is closely related to the cross-sectional area, structure, and rated voltage of the cable.

• Estimation of capacitive current of double-circuit overhead lines on the same pole: The capacitive current of such lines is not twice that of a single-circuit line. When equivalently calculated as a single-circuit line, the formula is: Ic = (1.4 - 1.6)Id (where Id is the capacitive current corresponding to the length of a single circuit in the double-circuit lines). The constant values need to be distinguished by voltage level: 1.4 corresponds to 10 kV lines, and 1.6 corresponds to 35 kV lines.