facts analysis

7/28/2019 Facts Analysis

1/6

FACTS ANALYSIS

ABSTRACT:

The electric power generation-transmission-

distribution grid in developed countries constitutes a large system thatexhibits a range of dynamic phenomena. Stability of this system needs to

be maintained even when subjected to large low-probability disturbancesso that the electricity can be supplied to consumers with high reliability.

Various control methods and controllers have been developed over timethat has been used for this purpose. New technologies, however, in the

area of communications and power electronics, have raised the possibility

of developing much faster and wide-area stability control that can allowsafe operation of the grid closer to its limits.

For changing thenature of power transmission systems

themost important system and recent innovations isFACTS technology.This paper presents a conceptual picture of these FACTS technology and

overview of the existing FACTSdevices

WHAT IS FACTS ?

Flexible AC Transmission System (FACTS) is a concept basedon power-electronic controllers, which enhance the value of transmission

networks by increasing the use of their capacity and has been under

development for nearly twenty years and is now entering its third

generation. The first generation of FACTS devices used power electronicsto control large transmission circuit elements, such as capacitor banks, to

make them more responsive to changing system conditions. Second

generation FACTS devices were able to perform their functions, such asproviding voltage support to a long transmission line, without the need for

large, expensive external circuit elements. Both first and second-

generation FACTS controllers are currently operating on utilitytransmission networks. Demonstration of a third generation FACTS

1


2/6

device -- called the Unified Power Flow Controller (UPFC) -- is just now

getting under way

NEED OF FACT FOR STABILITY:

All around the world power system stability margins can be

observed decreasing. Among the many reasons for this, we point out threemain ones.

The inhibition of further transmission or generation

constructions by economical and environmental restrictions asa consequence, power systems must be operated with smaller

security margins.

The restructuring of the electric power industry. The

restructuring processes decrease the stability margins due to the

fact that power systems are not operated in a cooperative wayanymore

The multiplication of pathological characteristics when powersystem complexity increases. These include: large scale

oscillations originating from nonlinear phenomena, frequency

differences between weakly tied power system areas,interactions with saturated devices, interactions among power

system controls,

Beyond a certain level, the decrease of power

system stability margins can lead to unacceptable operating

conditions and to frequent power system collapses. One way toAvoid these phenomena i.e., to increase power system stability

Margins, is to control power systems more efficiently.

Flexible AC Transmission Systems (FACTS) is a

technology that responds to these needs. It significantly altersthe way transmission systems are developed and controlled

together with improvements in asset utilization, system

flexibility and system performance.

DIFFERENT MAIN TYPES OF FACTS DEVICES:

1 Static Shunt Compensators

Static Var Compensator (SVC):

2


3/6

A Static Synchronous Compensators (STATCOM).

Thyristor-Controlled and Thyristor-Switched Reactor (TCR

and TSR)

2 Static Series Compensators

Thyristor-Switched Series Capacitor (TSSC)

Thyristor-Controlled Series Capacitor (TCSC)

GTO Thyristor-Controlled Series Capacitor (GCSC)

Static Synchronous Series Compensator (SSSC

Phase Angle Regulator (PAR)

3 Combined Compensators

Unified Power Flow Controller (UPFC)

Interline Power Flow Controller (IPFC)

OPERATION OF FACTS DEVICES:

Facts devices are normally operated automatically. They can be

located in unmanned substations. Changing of set points or operation

modes can be done locally and remotely (e.g. from a substation controlroom, a regional control center, or a national control center).

USE OF FACTS:

3


4/6

Shunt compensators, series compensators as well as combinations

of these two types of compensators have been discussed. The application

of these devices depends on the problem, which has to be solved. In Table4, an overview of problems occurring in the grid and which FACTS to be

used to solve these problems are given.

Subject Problem Corrective action FACTS

Voltage

limits

Low voltage atHeavy load

Supply reactive powerSVC, STAT-

COM

Reduce line reactance TCSC

High voltage at low

LoadAbsorb reactive power

SVC, STAT-

COM

High voltage fol-Lowing an outage

Absorb reactive power,Prevent overload

SVC, STAT-COM

Low voltagefollow-

ing an outage

Supply reactive power,Prevent overload

SVC, STAT-COM

Thermal

limits

Transmission cir-

cuit overload

Increase transmission

capacity

TCSC, SSSC,

UPFC

Load flow Power distributionon parallel lines

Adjust line reactances

TCSC, SSSC,

UPFC

Adjust phase angleUPFC, SSSC,

PAR

Load flow reversal Adjust phase angleUPFC, SSSC,

PAR

Short

circuit

Power

High short circuit

Current

Limitation of short cir-

cuit currentTCSC, UPFC

StabilityLimited transmits-

sion powerDecrease line

reactanceTCSC, SSSC

4


5/6

ADVANTAGES IN FLEXIBLE AC TRANSMISSION

SYSTEMS (FACTS):

1) Increase in amount of power that can be improved over

existing transmission line

2) To provide dynamic reactive power support and voltage control3) Reduce the need for construction of the transmission line,

capacitor reactance etc.

Which

- Mitogate environmental and regulatory concerned

5


6/6

- Introducing atheistic by reducing the need for

construction of new facilities such as transmission line

4) Improve system stability5) Control real and reactive power flow

6) Mitigate potential sub-synchronous resonance problem

LIMITATIONS:

All FACTS controllers have two major drawbacks.

1) High installation costs

2) Operating costs.

CONCLUSSION:

From above paper FACTSare a well-proven technologyand itsdevices facilitate economy and efficiency in power transmission systems in anenvironmentally optimal manner

6

facts analysis

Documents