Ferranti Effect Calculator (Receiving-End Voltage Rise)

How to use the Ferranti effect calculator

Enter the sending-end voltage, the line length, the line’s inductance and capacitance per km and the frequency. The calculator returns the line’s electrical length, the open-circuit receiving-end voltage and the percentage rise. Typical overhead-line values are about 1.0 mH/km and 11–12 nF/km; cables have much higher capacitance.

Ferranti effect formula

β = 2πf √(LC)  ·  V_r = V_s ÷ cos(βl)

Worked example

A 400 kV, 300 km, 50 Hz overhead line with L = 1.0 mH/km and C = 11.5 nF/km, open at the far end:

• β = 2π × 50 × √(1.0×10⁻⁶ × 11.5×10⁻¹²) = 1.0654e-03 rad/km
• βl = 0.3196 rad (18.31°)
• V_r = 400 ÷ cos(0.3196) = 421.3 kV — a 5.33% rise

Ferranti rise vs line length (400 kV, 1.0 mH/km, 11.5 nF/km, 50 Hz)

Notes

• The lossless model slightly overstates the rise; line resistance and any load reduce it.
• Underground cables show the effect over much shorter distances because their capacitance is 20–50 times higher.

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