Static Synchronous Compensator (STATCOM) for Voltage Compensation of AC Transmission Lines

STATIC SYNCHRONOUS COMPENSATOR (STATCOM)
Voltage compensation of ac transmission lines.
In the transmission of electrical energy to the distribution system from the
generating station, AC power transmission is mainly used. The transmission of AC
power over a extensive distance is faces significant power losses due to the fact
that transmission line traversing over large distance is characterized by inductive
voltage loss. Voltage drop ( EL) caused by line inductor has a magnitude equivalent
to the product of line I Lcurrent and line inductive reactance X L. The receiving end
load voltage would thus be generating station voltage less voltage across line
inductor (E¿¿ Load=EGen−EL)¿. It can therefore seen that when line current and line
inductive reactance are large, then voltage drop along the transmission line would
be greater. A summary representation of the transmission line is as shown below.
To maintain equilibrium voltage level of sending and receiving end, compensation
of the voltage drops along the transmission line need to be compensated.
Traditionally, this can be achieved by incorporating a shunting capacitor at the
receiving end. For long transmission lines, shunt capacitor method becomes
complex as the system would require shunt capacitor banks placed at particular
interval leading to difficult coordination. Finding the appropriate combination of
capacitive reactance along transmission line segments is a task-hill whose most
resultant effect is voltage fluctuation at the receiver end. Voltage fluctuation is an
undesired condition that should be suppressed as much as possible so as to protect
vulnerable sensitive electrical equipment from voltage surge. Also, it is a drawback
for shunt capacitive method as receiver end load voltage fluctuates making
compensator coordination difficult to achieve.
Introduction of STATCOM
To mitigate against shortcomings of shunt capacitance, solutions have been
developed in the
flexible ac Transmission system (FACTS
) family. FACTS
technologies strives to improve steady state nature and improve ac power
transmission capacity. With respect to transmission line voltage compensation and
FACTS, Static Synchronous compensators (STATCOMs) have been developed to pay
off for the transmission voltage loss. STATCOMs’ architecture has a 3-phase PMW
rectifier/ inverter which stabilizes systems voltages dynamically when shunted into
the network. STATCOM converts dc voltage to ac voltage of desired phase angle
and amplitude. With ability of STATCOM to output desired voltage conditions
dynamically, the specific quantity of reactive power ensures that the ac voltage of
the scheme is maintained stable besides maintaining unity power factor of large