SEMINAR REPORT

On

FACTS CONTROLLERS

Submitted by

Name: DEBAYON SAHA

Roll: 10300512028 (12/EI/28)

Reg.: 121030110360

Department of Applied Electronics & Instrumentation Engineering

Haldia Institute of Technology

ICARE COMPLEX, HIT CAMPUS, P.O- HIT, HALDIA, PURBA MEDINIPUR,

PIN-721657

May, 2015

ACKNOWLEDGEMENT

Apart from the efforts of myself, the success of any project depends largely on the encouragement

and guidelines of many others. I take this opportunity to express my gratitude to the people who

have been helpful in the successful completion of this report. I want to express my gratitude to all

the people who have given their heart whelming support to finish this report. First of all I would

like to express my thanks and deep regards to my mentor prof. Ashim Halder for his exemplary

guidance and encouragement throughout the course of this report. I would express my thanks to

prof. Soumya Roy & prof. Monodipon Sahoo. I would like to thanks whole Applied Electronics &

Instrumentation Department for their support. I would like to express my thanks to my parents for

their financial as well as moral support. The guidance and support received from all the members

who contributed in this report, was vital for the successful completion of this report. I am grateful

for their constant support and help. My thanks and appreciations also go to my colleague in

developing the report and people who have willingly helped me out with their abilities.

------------------------------------

Name: DEBAYON SAHA

Roll No.: 10300512028 (12/EI/28)

Reg. No.: 121030110360

1

ABSTRACT

Modern power systems are highly complex and are expected to fulfill the growing demands of

power wherever required, with acceptable quality and costs. The economic and environmental

factors necessitate the location of generation at places away from load centres. The restructuring of

power utilities has increased the uncertainties in system operation. The regulatory constraints on

the expansion of the transmission network has resulted in reduction of stability margins and

increased the risks of cascading outages and blackouts. This problem can be effectively tackled by

the introduction of high power electronic controllers for the regulation of power flows and

voltages in AC transmission networks. This allows 'flexible' operation of AC transmission systems

whereby the changes can be accommodated easily without stressing the system. Power electronic

based systems and other static equipment that provide controllability of power flow and voltage

are termed as FACTS Controllers.

2

TABLE OF CONTENTS

SL NO TOPIC PAGE NO

1. ACKNOWLEDGEMENT 1.

2. ABSTRACT 2.

3. TABLE OF CONTENTS 3.

4. INTRODUCTION 4.

5. WHAT IS FACTS 5.

6. FACTS CONTROLLERS 5.

7. WHY FACTS CONTROLLERS 5.

8. TYPES OF FACTS CONTROLLERS 5.

9. STATIC VARIABLE COMPENSATOR (SVC) 6.

10. VOLTAGE SOURCE CONVERTER (VSC) 8.

11. STATIC SYNCHRONOUS COMPENSATOR (STATCOM) 9.

12. THYRISTOR CONTROLLED SERIES COMPENSATOR (TCSC) 10.

13. STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC) 11.

14. UNIFIED POWER FLOW CONTROLLER (UPFC) 12.

15. OTHERS FACTS DEVICES 13.

16. BENEFITS OF FACTS CONTROLLERS 13.

17. CONCLUSION 14.

18. REFERENCES 15.

19. BIBLIOGRAPHY 16.

3

INTRODUCTION

Modern power systems are designed to operate efficiently to supply power on demand to various

load centres with high reliability. The generating stations are often located at distant locations for

economic, environmental and safety reasons. For example, it may be cheaper to locate a thermal

power station at pithead instead of transporting coal to load centres. Hydropower is generally

available in remote areas. A nuclear plant may be located at a place away from urban areas. Thus,

a grid of transmission lines operating at high or extra high voltages is required to transmit power

from the generating stations to the load centres. In addition to transmission lines that carry power

from the sources to loads, modern power systems are also highly interconnected for economic

reasons. The interconnected systems benefit by (a) exploiting load diversity, (b) sharing of

generation reserves and (c) economy gained from the use of large efficient units without

sacrificing reliability. However, there is also a downside to ac system interconnection- the security

can be adversely affected as the disturbances initiated in a particular area can spread and

propagate over the entire system resulting in major blackouts caused by cascading outages.

FACTS devices incorporating power electronics based devices can control the parameters of an AC

transmission system to control reactive power and enhance the load capability. FACTS devices are

also very reliable than other devices. Now let’s see about the FACTS devices.

4

WHAT IS FACTS

A flexible alternating current transmission system (FACTS) is a system composed of static

equipment used for the AC transmission of electrical energy. It is meant to enhance controllability

and increase power transfer capability of the network. It is generally a power electronics-based

system.

FACTS is defined by the IEEE as "a power electronic based system and other static equipment that

provide control of one or more AC transmission system parameters to enhance controllability and

increase power transfer capability."

According to Siemens "FACTS Increase the reliability of AC grids and reduce power delivery

costs. They improve transmission quality and efficiency of power transmission by supplying

inductive or reactive power to the grid.

FACTS contains the design of the different schemes and configurations of FACTS devices is based

on the combination of traditional power system components (such as transformers, reactors,

switches, and capacitors) with power electronics elements (such as various types of transistors and

thyristors).

FACTS CONTROLLERS

FACTS Controllers are the power electronics based circuits or devices which are used to control

the power flow of Flexible AC Transmission Systems.

The FACTS controller is defined as a power electronic based system and other static equipment

that provide control of one or more AC transmission system parameters.

WHY FACTS CONTROLLERS

Earlier days Mechanical Circuit Breakers like Relay, Contactors etc are used to control the power

flow of the transmission systems and for the security of AC transmission system.

Mechanical Circuit Breakers was not very reliable and they can not compensate the power loss due

to Reactive Power of the transmission systems which can be performed by FACTS Controllers.

FACTS Controllers are also very reliable.

TYPES OF FACTS CONTROLLERS

Depending on the power electronic devices used in the control, the FACTS controllers can be

classified as:

1. Variable impedance type

2. Voltage Source Converter (VSC) based.

5

Variable Impedance Type:

Static Variable Compensator (SVC)

Thyrister Controlled Series Compensator (TCSC)

Voltage Source Converter (VSC) Type:

Static Synchronous Compensator (STATCOM)

Static Synchronous Series Compensator (SSSC)

Unified Power Flow Controller (UPFC)

Facts Controllers can also be classified as follows depending on the connection of the controller:

1. Shunt Connected Controllers

2. Series Connected Controllers

3. Hybrid/Combined Controllers

Shunt Connected Controllers:

Static Variable Compensator (SVC)

Static Synchronous Compensator (STATCOM)

Series Connected Controllers:

Thyrister Controlled Series Compensator (TCSC)

Static Synchronous Series Compensator (SSSC)

Hybrid/Combined Controllers:

Dynamic Power Flow Controller (DPFC)

Unified Power Flow Controller (UPFC)

STATIC VARIABLE COMPENSATOR (SVC)

Static Variable Compensator is the first generation FACTS controllers. Basically, SVC is a variable

impedance device where the current through a reactor is controlled using back to back connected

thyristor valves.

A static VAR compensator is a set of electrical devices for providing fast-acting reactive power on

high-voltage electricity transmission networks. SVCs are part of the Flexible AC transmission

system device family, regulating voltage, power factor, harmonics and stabilizing the system.

Unlike a synchronous condenser which is a rotating electrical machine, a static VAR compensator

has no significant moving parts (other than internal switchgear). Prior to the invention of the SVC,

power factor compensation was the preserve of large rotating machines such as synchronous

condensers or switched capacitor banks.

6

The SVC is an automated impedance matching device, designed to bring the system closer to unity

power factor. SVCs are used in two main situations:

Connected to the power system, to regulate the transmission voltage ("Transmission

SVC")

Connected near large industrial loads, to improve power quality ("Industrial SVC")

In transmission applications, the SVC is used to regulate the grid voltage. If the power system's

reactive load is capacitive (leading), the SVC will use thyristor controlled reactors to consume

VARs from the system, lowering the system voltage. Under inductive (lagging) conditions, the

capacitor banks are automatically switched in, thus providing a higher system voltage. By

connecting the thyristor-controlled reactor, which is continuously variable, along with a capacitor

bank step, the net result is continuously variable leading or lagging power.

In industrial applications, SVCs are typically placed near high and rapidly varying loads, such as

arc furnaces, where they can smooth flicker voltage.

Principle: Typically, an SVC comprises one or more banks of fixed or switched shunt capacitors or

reactors, of which at least one bank is switched by thyristors. Elements which may be used to

make an SVC typically include:

7

Thyristor controlled reactor (TCR), where the reactor may be air- or iron-cored

Thyristor switched capacitor (TSC)

Harmonic filter(s)

Mechanically switched capacitors or reactors (switched by a circuit breaker)

By means of phase angle modulation switched by the thyristors, the reactor may be variably

switched into the circuit and so provide a continuously variable MVAR injection (or absorption) to

the electrical network. In this configuration, coarse voltage control is provided by the capacitors;

the thyristor-controlled reactor is to provide smooth control. Smoother control and more flexibility

can be provided with thyristor-controlled capacitor switching. The thyristors are electronically

controlled. Thyristors, like all semiconductors, generate heat and deionized water is commonly

used to cool them. Chopping reactive load into the circuit in this manner injects undesirable odd-

order harmonics and so banks of high-power filters are usually provided to smooth the waveform.

Since the filters themselves are capacitive, they also export MVARs to the power system.

More complex arrangements are practical where precise voltage regulation is required. Voltage

regulation is provided by means of a closed-loop controller. Remote supervisory control and

manual adjustment of the voltage set-point are also common.

Generally, static VAR compensation is not done at line voltage; a bank of transformers steps the

transmission voltage (for example, 230 kV) down to a much lower level (for example, 9.5 kV). This

reduces the size and number of components needed in the SVC, although the conductors must be

very large to handle the high currents associated with the lower voltage. In some static VAR

compensators for industrial applications such as electric arc furnaces, where there may be an

existing medium-voltage busbar present (for example at 33kV or 34.5kV),the static VAR

compensator may be directly connected in order to save the cost of the transformer.

Another common connection point for SVC is on the delta tertiary winding of Y-connected auto-

transformers used to connect one transmission voltage to another voltage.

The dynamic nature of the SVC lies in the use of thyristors connected in series and inverse-

parallel, forming "thyristor valves"). The disc-shaped semiconductors, usually several inches in

diameter, are usually located indoors in a "valve house".

VOLTAGE SOURCE CONVERTER (VSC)

VSCs’ are the power electronics based devices made of thyristor which can control the reactive

power of the transmission system.

Basically VSC ideal bi-directional switches. It converts voltage and currents from DC to AC while

the exchange of power can be in both directions

From AC to DC (rectifier mode)

From DC to AC (inverter mode)

8

A typical Voltage Source Converter (VSC)

STATIC SYNCHRONOUS COMPENSATOR (STATCOM)

A static synchronous compensator (STATCOM), also known as a "static synchronous condenser"

("STATCON"), is a regulating device used on alternating current electricity transmission networks.

It is based on a power electronics voltage-source converter and can act as either a source or sink of

reactive AC power to an electricity network. If connected to a source of power it can also provide

active AC power. It is a member of the FACTS family of devices. It is inherently modular and

electable.

Usually a STATCOM is installed to support electricity networks that have a poor power factor and

often poor voltage regulation. There are however, other uses, the most common use is for voltage

stability. A STATCOM is a voltage source converter (VSC)-based device, with the voltage source

behind a reactor. The voltage source is created from a DC capacitor and therefore a STATCOM has

very little active power capability. However, its active power capability can be increased if a

suitable energy storage device is connected across the DC capacitor. The reactive power at the

terminals of the STATCOM depends on the amplitude of the voltage source. For example, if the

terminal voltage of the VSC is higher than the AC voltage at the point of connection, the

STATCOM generates reactive current; on the other hand, when the amplitude of the voltage

source is lower than the AC voltage, it absorbs reactive power. The response time of a STATCOM

9

is shorter than that of an SVC, mainly due to the fast switching times provided by the IGBTs of the

voltage source converter. The STATCOM also provides better reactive power support at low AC

voltages than an SVC, since the reactive power from a STATCOM decreases linearly with the AC

voltage (as the current can be maintained at the rated value even down to low AC voltage).

The strategy of STATCOM controller is to keep the DC capacitor voltage constant while

controlling the modulation index to keep the voltage constant during the disturbance interval.

THYRISTOR CONTROLLED SERIES COMPENSATORE (TCSC)

TCSC comprised of a series capacitor bank, shunted by a Thyristor Controlled Reactor (TCR), to

provide a smoothly variable series capacitive reactance. It is a one-port circuit in series with

transmission line. It uses natural commutation. Its switching frequency is low; it contains

insignificant energy storage and has no DC-port. Insertion of a capacitive reactance in series with

the line’s inherent inductive reactance lowers the total effective impedance of the line and thus

virtually reduces its length. As a result, both angular and voltage stability gets improved.

Furthermore, in contrast to capacitors switched by circuit breakers, TCSC will be more effective

because thyristors can offer flexible adjustment, and more advanced control theories can be easily

applied.

10

STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC)

Static Synchronous Series Compensator (SSSC) is a series compensator of FACTS family. It injects

an almost sinusoidal voltage with variable amplitude. It is equivalent to an inductive or a

capacitive reactance in series with the transmission line. The heart of SSSC is a VSI (voltage source

inverter) that is supplied by a DC storage capacitor. With no external DC link, the injected voltage

has two parts: the main part is in quadrature with the line current and emulates an inductive or

capacitive reactance in series with the transmission line, and a small part of the injected voltage is

in phase with the line current to cover the losses of the inverter. When the injected voltage is

leading the line current, it will emulate a capacitive reactance in series with the line, causing the

line current as well as power flow through the line to increase. When the injected voltage is

lagging the line current, it will emulate an inductive reactance in series with the line, causing the

line current as well as power flow through the line to decrease.

SSSC is superior to other FACTS equipment and the benefits of using SSSC are:

� Elimination of bulky passive components -capacitors and reactors,

� Symmetric capability in both inductive and capacitive operating modes,

� Possibility of connecting an energy source on the DC side to exchange real power with the AC

network.

An SSSC comprises a voltage source inverter and a coupling transformer that is used to insert the

ac output voltage of the inverter in series with the transmission line. The magnitude and phase of

this inserted ac compensating voltage can be rapidly adjusted by the SSSC controls. The SSSC

injects the compensating voltage in series with the line irrespective of the line current. The

transmitted power Pq, therefore becomes a parametric function of the injected voltage. The SSSC,

therefore can increase the transmittable power, and also decrease it, simply by reversing the

polarity of the injected ac voltage.

11

UNIFIED POWER FLOW CONTROLLER (UPFC)

The UPFC can provide simultaneous control of all basic power system parameters (transmission

voltage, impedance and phase angle). The controller can fulfill functions of reactive shunt

compensation, series compensation and phase shifting meeting multiple control objectives. From a

functional perspective, the objectives are met by applying a boosting transformer injected voltage

and an exciting transformer reactive current. The injected voltage is inserted by a series

transformer. Besides transformers, the general structure of UPFC contains also a "back to back" AC

to DC voltage source converters operated from a common DC link capacitor.

UPFC is the combination of Static Synchronous Compensator (STATCOM) and Static Synchronous

Series Compensator (SSSC). It is a VSC type device. It impacts both active and reactive power flow

in transmission line.

The shunt converter (STATCOM) is primarily used to provide active power demand of the series

converter (SSSC) through a common DC link. STATCOM can also generate or absorb reactive

power and thereby provide independent shunt reactive compensation for the line.

SSSC provides the main function of the UPFC by injecting a voltage with controllable magnitude

and phase angle in series with the line via a voltage source.

12

OTHERS FACTS DEVICES

Others FACTS devices are as follows:

Thyristor Controlled Phase Shifting Transformer (TCPST)

Interline Power Flow Controller (IPFC)

Thyristor Controlled Braking Resistor (TCBR)

Thyristor Controlled Voltage Limiter (TCVL)

Thyristor Controlled Voltage Regulator (TCVR)

Interphase Power Controller (IPC)

Distributed Power Flow Controller (DPFC)

NGH-SSR damping

BENEFITS OF FACTS CONTROLLERS

Benefits of FACTS controllers are as follows:

To increase the power transfer capability of transmission networks.

To provide direct control of power flow over designated transmission routes.

Increase the loading capability of lines to their thermal capabilities.

Control of power flow as ordered so that it follows on the prescribed transmission

corridors.

To increase the reliability of transmission network.

To compensate the power loss due to reactive power of transmission system.

13

CONCLUSION

Use of FACTS controllers in the field of transmission system is a new topic. In this article

we have discussed about some of the FACTS Controllers, their types, their circuits, working

principal, advantages and disadvantages. Continuous research is going on worldwide on

this topic. We can tune or use different control algorithms to tune this FACTS systems like

PSO, Genetic algorithm, Fuzzy Logic etc.

The installation of FACTS devices is very important in the context of INDIA & CHINA.

Because the population of these two countries are increasing day by day; as a result the

demand of electricity and power also increasing. For this reason we have set a stable and

powerful power transmission system which have very low transmission loss. FACTS

devices can take this responsibility well & they are very reliable as well as perform well.

Using FACTS we can enhance the controllability and power transfer capability of a

transmission system. More research work is needed in this area for the improvement of

human needs.

14

REFERENCES

1. www.wikipedia.org

2. www.google.com

3. www.webopedia.org

4. www.ieeeexplore.org

5. www.projectmatter.com

15

BIBLIOGRAPHY

1. Book Power Generation Engineering. Author R.P AJWALIA (Atul Parakashan)

2. A. L’Abbate, G. Migliavacca, U. Häger x, C. Rehtanz x ERSE (ENEA - Ricerca sul Sistema

Elettrico) [former CESI RICERCA] Spa, Milan, Italy Technical University of Dortmund,

Dortmund, Germany

3. European Transmission System

4. V. Kakkar, Head of Deptt (EEE), and N. K. Agarwal, Assist. Prof. (EEE) VITS Ghaziabad.

5. L. Gyugyi, N.G. Hingorani, “Understanding FACTS,” IEEE Press, 1st Edition, December

1999.

6. M.H. Rashid, “Power Electronics,” Prentice Hall, 3rd Edition, 2004.

7. K.R. Padiyar, “FACTS Controllers in Power Transmission & Distribution”, New Age

International Publishers, 1st Edition, 2005

16