Capacitance of 3 phase line with Equilateral Spacing:

Figure 3.5 shows a Capacitance of 3 phase line with Equilateral Spacing composed of three identical conductors of radius r placed in equilateral configuration.

Capacitance of 3 phase line with Equilateral Spacing

Using Eq. (3.2) we can write the expressions for V ab and Vac as

Adding Eqs. (3.8) and (3 9), we get

Since there are no other charges in the vicinity, the sum of charges on the three conductors is zero. Thus qb+ qc = – qa which when substituted in Eq. (3.10) yields

With balanced three-phase voltages applied to the line, it follows from the phasor diagram of Fig. 3.6 that

Substituting for (Vab + Vac) from Eq. (3.12) in Eq. (3.11), we get

The capacitance of line to neutral immediately follows as

For air medium (kr = 1),

Capacitance of 3 phase line with Equilateral Spacing

The line charging current of phase a is

Ia (line charging) = jωCnVan

Capacitance of 3 phase line with Equilateral Spacing