29-05-2012, 04:48 PM
OVERVIEW OF FLEXIBLE AC TRANSMISSION SYSTEMS
[attachment=23402]
Introduction
The term ”FACTS” (Flexible AC Transmission Systems) covers several power electronics based systems used
for AC power transmission and distribution. Given the nature of power electronics equipment, FACTS solutions
will be particularly justifiable in applications requiring one or more of the following qualities:
-Rapid dynamic response
-Ability for frequent variations in output
-Smoothly adjustable output.
FACTS are a family of devices which can be inserted into power grids in series, in shunt, and in some cases, both
in shunt and series. Important applications in power transmission and distribution involve devices such as SVC
(Static Var Compensators), Fixed Series Capacitors (SC) as well as Thyristor-Controlled Series Capacitors
(TCSC) and STATCOM.
SVC and SC have been utilized for a long time. The first SC installations came on line in the early 1950s.
Among the pioneering countries are USA and Sweden. SVCs have been available for commercial purposes since
the 1970s. Over the years, more than a thousand SVCs and SCs have been installed all over the world.
FACTS mainly find applications in the following areas:
• Power transmission
• Power quality
• Railway grid connection
• Wind power grid connection
• Cable systems
With FACTS, the following benefits can be attained in AC systems:
• Improved power transmission capability
• Improved system stability and availability
• Improved power quality
• Minimized environmental impact
• Minimized transmission losses
Power transmission under optimum conditions
A frequently occurring situation in a power system is the need to transmit more power over the system than it
was originally designed for. In cases where there is a need to transmit more power, it is often a safe way out
simply to build new transmission lines. This, however, may not at all be the best solution. Adding new lines may
be too costly and time-consuming. Concessions for right-of-ways may be hard or impossible to come by. And
last but not least, environmental aspects are much more important now than they used to be, and need to be
properly addressed in conjunction with transmission development.
There are two typical cases in this discussion:
1) Greenfield projects: a need to build new infrastructure, and then do it as economically as possible, both from
an investment point of view, and from an environmental point of view. This means as few transmission lines as
we can possibly get away with, without compromising our transmission goals.
2) Alleviation of transmission congestion: we need to build away bottlenecks in existing transmission systems.
This is very much on the EU agenda now, with the Energy Directive, which stipulates that each EU country
should have the capacity to transmit at least 10% of its installed power to its neighbour countries (and even 20%
in a certain perspective), to pave the way for the EU goal of free exchange of services and commodities inside
the EU. In this discussion, of course, electric energy is treated as a commodity among others.
In either case, there is a lot to be gained, in economical terms just as well as environmental, if we can minimize
the amount of transmission lines running through the countryside. This is exactly where FACTS is coming in.
Availability
With FACTS, availability and efficiency of power grids are improved, for existing just as well as new grids.
When we say availability, of course, one comes to think of the several large and more or less dramatic
blackouts in various parts of the world in recent years. The obvious question to be asked then is: can FACTS
help to prevent similar things to happen in the future? The answer is that it will definitely play a role, and an
important one, at that. And for sure, since blackouts in the majority of cases are caused by a deficit of reactive
power, FACTS comes into the picture as a remedy in a natural way.
Power quality
Getting as much active power as possible over the grid with a minimum of transmission lines, and a minimum of
losses, are crucial tasks, of course. There are other things that need to be looked after, as well, however: the
power which eventually reaches the consumer must also be of sufficient quality. With this we mean that when
we turn on the light at home, the voltage coming out of the socket should be fluctuation-free and free from
harmonics, to make the flow of light smooth and comfortable, and free from intensity fluctuations. This, too, is a
key task for FACTS to maintain. It is particularly important for residents living more or less close to heavy
industrial plants such as steel works, because such plants emit a lot of disturbances which spread over the
electrical grid, unless, as said, remedied by FACTS.
FACTS and Reactive Power
FACTS has a lot to do with reactive power compensation, and indeed, that used to be the term utilized for the
technology in the old days. Reactive power appears in all electric power systems, due to the laws of nature.
Contrary to active power, which is what we really want to transmit over our power system, and which performs
real work, such as keeping a lamp lit or a motor running, reactive power does not perform any such work.
Consequently, in a way one can say that the presence of reactive power in a grid makes it heavier for it to
perform its task, i.e. transmit power from A to B (Figure 1), and consequently less efficient than would otherwise
be possible. We can also refer to Lenz´ law, formulated already in the nineteenth century: Every change in an
electrical system induces a counter-reaction opposing its origin.
So, as a consequence, if we can minimize the flow of reactive power over the transmission system, we can make
the system more efficient and put it to better and more economical use.
[attachment=23402]
Introduction
The term ”FACTS” (Flexible AC Transmission Systems) covers several power electronics based systems used
for AC power transmission and distribution. Given the nature of power electronics equipment, FACTS solutions
will be particularly justifiable in applications requiring one or more of the following qualities:
-Rapid dynamic response
-Ability for frequent variations in output
-Smoothly adjustable output.
FACTS are a family of devices which can be inserted into power grids in series, in shunt, and in some cases, both
in shunt and series. Important applications in power transmission and distribution involve devices such as SVC
(Static Var Compensators), Fixed Series Capacitors (SC) as well as Thyristor-Controlled Series Capacitors
(TCSC) and STATCOM.
SVC and SC have been utilized for a long time. The first SC installations came on line in the early 1950s.
Among the pioneering countries are USA and Sweden. SVCs have been available for commercial purposes since
the 1970s. Over the years, more than a thousand SVCs and SCs have been installed all over the world.
FACTS mainly find applications in the following areas:
• Power transmission
• Power quality
• Railway grid connection
• Wind power grid connection
• Cable systems
With FACTS, the following benefits can be attained in AC systems:
• Improved power transmission capability
• Improved system stability and availability
• Improved power quality
• Minimized environmental impact
• Minimized transmission losses
Power transmission under optimum conditions
A frequently occurring situation in a power system is the need to transmit more power over the system than it
was originally designed for. In cases where there is a need to transmit more power, it is often a safe way out
simply to build new transmission lines. This, however, may not at all be the best solution. Adding new lines may
be too costly and time-consuming. Concessions for right-of-ways may be hard or impossible to come by. And
last but not least, environmental aspects are much more important now than they used to be, and need to be
properly addressed in conjunction with transmission development.
There are two typical cases in this discussion:
1) Greenfield projects: a need to build new infrastructure, and then do it as economically as possible, both from
an investment point of view, and from an environmental point of view. This means as few transmission lines as
we can possibly get away with, without compromising our transmission goals.
2) Alleviation of transmission congestion: we need to build away bottlenecks in existing transmission systems.
This is very much on the EU agenda now, with the Energy Directive, which stipulates that each EU country
should have the capacity to transmit at least 10% of its installed power to its neighbour countries (and even 20%
in a certain perspective), to pave the way for the EU goal of free exchange of services and commodities inside
the EU. In this discussion, of course, electric energy is treated as a commodity among others.
In either case, there is a lot to be gained, in economical terms just as well as environmental, if we can minimize
the amount of transmission lines running through the countryside. This is exactly where FACTS is coming in.
Availability
With FACTS, availability and efficiency of power grids are improved, for existing just as well as new grids.
When we say availability, of course, one comes to think of the several large and more or less dramatic
blackouts in various parts of the world in recent years. The obvious question to be asked then is: can FACTS
help to prevent similar things to happen in the future? The answer is that it will definitely play a role, and an
important one, at that. And for sure, since blackouts in the majority of cases are caused by a deficit of reactive
power, FACTS comes into the picture as a remedy in a natural way.
Power quality
Getting as much active power as possible over the grid with a minimum of transmission lines, and a minimum of
losses, are crucial tasks, of course. There are other things that need to be looked after, as well, however: the
power which eventually reaches the consumer must also be of sufficient quality. With this we mean that when
we turn on the light at home, the voltage coming out of the socket should be fluctuation-free and free from
harmonics, to make the flow of light smooth and comfortable, and free from intensity fluctuations. This, too, is a
key task for FACTS to maintain. It is particularly important for residents living more or less close to heavy
industrial plants such as steel works, because such plants emit a lot of disturbances which spread over the
electrical grid, unless, as said, remedied by FACTS.
FACTS and Reactive Power
FACTS has a lot to do with reactive power compensation, and indeed, that used to be the term utilized for the
technology in the old days. Reactive power appears in all electric power systems, due to the laws of nature.
Contrary to active power, which is what we really want to transmit over our power system, and which performs
real work, such as keeping a lamp lit or a motor running, reactive power does not perform any such work.
Consequently, in a way one can say that the presence of reactive power in a grid makes it heavier for it to
perform its task, i.e. transmit power from A to B (Figure 1), and consequently less efficient than would otherwise
be possible. We can also refer to Lenz´ law, formulated already in the nineteenth century: Every change in an
electrical system induces a counter-reaction opposing its origin.
So, as a consequence, if we can minimize the flow of reactive power over the transmission system, we can make
the system more efficient and put it to better and more economical use.