FACT is an abbreviation for Flexible AC transmission system. It is a system composed of static equipment used for the alternating current (AC) transmission of electrical energy and is a power electronics based system.
Series compensation - In this we connect
the fact devices in series with power system. Here, the line impedance is
modified, that means net impedance is decreased and increasing the
transmittable active power.
Shunt compensation - It is used to
improve the power factor. In this we connect the fact devices in parallel with
power system. It also works as a controllable for the current source. Eg-
Statcom (Static synchronous Compensator) and SVC (Static VAR compensator). They
are further classified into two types -
- Shunt capacitive compensation: This method is used to
improve the power factor. Whenever an inductive load is connected to
the transmission line, power factor lags because of lagging load current.
To compensate, a shunt capacitor is connected, which draws the current
leading to the source voltage. The net result is an improvement in
power factor.
- Shunt inductive compensation: This method is used
either when charging the transmission line, or when there is a very
low load at the receiving end. Because of very low, or no load–very low current
flows through the transmission line. Shunt capacitance in the transmission
line causes voltage amplification (Ferranti effect). The receiving end
voltage may become double the sending end voltage (generally in case of
very long transmission lines). To compensate, shunt inductors are
connected across the transmission line.
A few advantages of FACT devices
are:
• Helps in improving power transfer capability
• Used for transient and dynamic stability improvement.
• Used for damping of power system oscillations.
• For better voltage regulation.
• For flexible operation and control of the system.
What
is a Statcom?
The STATCOM (or SSC) is a
shunt-connected reactive-power compensation device that can generate and/ or
absorbing reactive power and in which we can vary the output to control the
specific parameters of an electric power system. It is a solid-state switching
converter capable of generating or absorbing independently controllable real
and reactive power at its output terminals when it is fed from an energy source
or energy-storage device at its input terminals. Voltage-source converter that,
from an input of the voltage, produces a set of 3-phase AC-output voltages,
each in phase with and coupled to the corresponding AC system voltage through a
relatively small reactance.
How
does a statcom work?
Now suppose we have a load connected
to the grid; the load takes the power as P + jQ, where P is active power and Q
is reactive power. Now we have to make the Q= 0. So that the power factor is
always unity (PF = 1). For that, we connect statcom at the load, so that the
reactive power is supplied by the statcom and active power is given by the
Grid. This is how a statcom works for reactive power compensation.
The different softwares in which we
can simulate and analyze FACT devices are:
• MATLAB
• PSCAD
• ETAP
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