a) Line reactance.
b) Phase angle δ when it is not large which controls the active power flow.
c) Injecting voltage in series with line and at 90° phase with line current i.e.
Injection of reactive power in series. This will control active power flow.
d) Injecting voltage in series with line at variable phase angle. This will control
both active & reactive power flow.
e) Controlling the magnitude of either V1or V2.
f) Variation of line reactance with a series controller and regulating the voltage
with a shunt controller. This can control both active and reactive power.
Flow of Power in A.C Systems:
In AC power systems the electrical power at source and load must be balanced. To
some extent, the electrical system is self regulating. If generation power is less than
load requirement, the voltage and frequency drop. However there is only a few
percent of margin for such a self regulation .If voltage propped up with reactive
power support, then the load will go up and consequently frequency will drops and
system will collapse .If there is inadequate reactive power support, the system
voltage can be collapsed. When adequate power generation is available, active
power flows from the surplus generation areas to shortcoming areas through all
parallel paths available this frequently involves EHV (extra high voltage) and
medium voltage lines.
Power Flow in Parallel Paths:
Consider power flow through two parallel paths from a surplus generation area to a
deficit generation area as shown in Fig.2 (a). Without any control, power flow is
based on the inverse of various transmission line Impedances. As a result line