INTRODUCTION OF FACTS DEVICES

FACTS (Flexible AC Transmission System)

Introduction:

FACTS devices are used in AC transmission system. These devices are used to improve the stability and controllability of the transmission network. The FACTS is a static device, which is based on the power electronics. The power transfer capacity is fixed for any transmission network. If we transfer power beyond this limit, equipment may get damage. We can increase power transfer capacity by changing the layout of the power system but this is not a feasible way. So, in the actual power system, we use FACTS devices to increase power transfer capacity.

In simple word, FACTS is a variable impedance device like inductors and capacitors. In an ideal transmission system, the active power is equal to the apparent power. It means that the Power factor is unity. The power factor is defined as the ratio of the active power to the apparent power. This is the main role of FACTS devices, it is trying to keep power factor as near as possible to unity.

The active power is known as true power and it is useful for work in the system. The reactive power is not useful for the load. The reactive power is caused by the energy storage equipment. If we want to achieve the maximum power transfer capacity, we have to reduce the amount of reactive power. The reactive power reduces the power transfer capacity. The techniques used to reduce reactive power is known as the compensation technique.

In order to improve the efficiency of the power system, the compensation technique is supplying the inductive and reactive power to the power system. By these techniques, we can improve the quality of power, stability, voltage regulation, power factor.

Classification:

According to the type of connection; series compensation, shunt compensation.

Series compensation:

This type of compensation technique, FACTS devices are connected in series with the power system network. By series compensation, we can improve the stability and dynamic response of the system. Generally, the capacitors are connected in series with the transmission network. The amount of compensation is controlled by power electronics switches. For better control, more than one capacitor (capacitor bank) is connected.

                Example of series compensation:

                                Thyristor Controlled Switched Capacitor (TCSC)

                                Static Synchronous Series Compensator (SSSC)

                                Fixed Series Capacitor (FSC)

                                Thyristor Switched Series Capacitor (TSSC)

                                Thyristor Switched Series Reactor (TSSR)

Shunt compensation:

in this type of compensation technique, FACTS devices are connected in parallel or shunt with the transmission network. In this technique, the current is injected into the system from the FACTS devices and by this way the reactive component is reduced. This technique is used to improve voltage regulation and reduce losses of the power system. There are two types of shunt compensation; shunt capacitive compensation and shunt inductive compensation. The shunt capacitive compensation technique is used to improve the power factor. The shunt inductive compensation technique is used to charging the transmission line in low load condition or no-load condition.

                Example of Shunt compensation:

                                STATic Synchronous COMpensator (STATCOM)

                                Static VAR Compensator (SVC)

                                                Thyristor Controlled Reactor (TCR)

                                                Thyristor Switched Reactor (TSR)

                                                Thyristor Switched Capacitor (TSC)

In the next article, we will discuss briefly on all types of compensation device.

Please review this article, at the bottom of this page.