Voltage Compensation for AC Transmission Lines

VOLTAGE COMPENSATION
Many electrical devices work efficiently under steady state voltage conditions close
to their rated voltage. Shunt capacitors are used to increase receiving end voltages
while resistive loads and line inductances reduce receiving end voltages. Therefore,
receiver voltage can be compensated by properly switching capacitive shunt
reactance. Shunt capacitance in case of excessive receiver voltage are removed
into the transmission line to reduce the line current. Phasor diagrams representing
ac uncompensated transmission line, shunt capacitor compensated transmission
line and increased line current when the transmission line is compensated more is
as shown below.
As in the first figure, the load is purely resistive and as a result, the line current
lags the sender voltage ES by a certain angle θ that is determined by line
inductance and load resistance. Also, the receiver end voltage ER lags the sending
end voltage Esby the same angle θ . Similarly, the transmission line voltage drop EL
leads line current by 900 . The scalar computation of these voltages is as shown
below