Define Charging Current formula

The charging current ($I_{ch}$) of a transmission line is directly proportional to the operating voltage and the shunt capacitance of the line.

$I_{ch} = V \times 2\pi f C$

Identify proportionality

Since the length of both lines is the same, the shunt capacitance ($C$) is approximately constant (assuming similar geometry). Therefore, the charging current is directly proportional to the line voltage ($V$).

$I_{ch} \propto V$

Compare the lines

Comparing the two lines, the 400 kV line has a higher operating voltage than the 220 kV line. Since $400 > 220$, the charging current of the 400 kV line will be higher.

$I_{ch(400 kV)} > I_{ch(220 kV)}$