Lossless Lines

Consider a lossless line with a purely imaginary propagation constant, resistive characteristic impedance, and established ABCD parameters.

Its equivalent pi circuit has imaginary series impedance and shunt admittance. When the beta and length product is less than pi, it exhibits inductive series impedance and capacitive shunt admittance, making it lossless.

The wavelength, or distance required to change the voltage or current phase by 2-pi, is calculated using the velocity of propagation.

Surge impedance loading is the power delivered to a load resistance equal to the surge impedance.

Here, voltage remains constant along the line, and constant real power flows from the sending to the receiving end, with zero reactive power flow.

Real power delivered is determined using the rated voltage and surge impedance.

In reality, power lines are not terminated by their surge impedance, causing non-flat voltage profiles that vary depending on load conditions.

At no load, voltage increases from the sending to the receiving end, while for short circuits, it decreases to zero at the receiving end. The full-load profile is higher than the short-circuit profile.