27.6 : 정전용량: 단상 및 3상 라인

Consider a single-phase two-wire transmission line with equal phase spacing energized by a voltage source. One conductor carries a uniform charge, and its counterpart has an equal negative charge. Applying the formula for voltage between conductors and substituting cylinder radii, the capacitance for a one-meter line is calculated.

For lines supplied by a grounded center tap transformer, the voltage between each conductor and ground and the capacitance from either line to the grounded neutral are obtained.

These capacitances are represented in specific circuit representations.

Next, consider a three-phase line with equal phase spacing, neglecting earth and neutral conductor effects.

To determine the positive-sequence capacitance, the sum of positive-sequence charges is assumed to be zero.

Now, the voltage between the conductors is calculated, followed by substituting the radii.

Recalling the voltage equations for balanced positive-sequence voltages, adding them, substituting the voltage expressions, and the charge relation gives the capacitance-to-neutral per line length.

The same results apply for all three phases due to symmetry, but for a balanced three-phase operation, only one phase is considered.