FACT Devices; Statcom & its working

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 -

  1. 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.
  2. 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:

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