What is mean by compensated and uncompensated power transmission line?

Answer 1

Power transmissions lines are inductive by nature. Power in AC systems is transmitted by varying the phase angle between source and receiving end following the below equation:

Vsource * Vrecieve * sin (phi) / (Zsource + Zrecieve + Zline)

V = the voltage

phi = angle between source and receiving end voltage

Z = impedance, Zsource = the impedance behind the source end

Series compensating lines is accomplished by adding capacitors in series on a line, which reduces the Zline term in the above equation. This allows more power to be transmitted from one end to the other.

Answer 2

Power is transmitted to loads/consumers via transmission lines. And the transmitted power is aparrant power ( i.e. it's the sum of active power and reactive power). Generally ,some load (inductive loads) consumes reactive power along with active power. Which leads to voltage fluctuations at consumer's side. To provide the reactive power needed by the load, Capacitors (Gives reactive power) are connected in series/parallel to the transmission line. This process is called Compensation of power transmission line. Without compensation the voltage at the recieving end would change alot. Compensation increases efficiency of the transmission. In short.. =>Compensated line-->Line with capacitors connected in series/parallel. =>Uncompensated line-->Line without any reactive power providers. NOTE: for compesation we can use any component that has ability to provide reactive power (ex. capacitors, synchronous machines etc.)