11-04-2014, 12:49 PM
An Overview of Flexible AC Transmission Systems
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INTRODUCTION
Long distance transmission of electric power permits serving loads
with lower cost energy than may be available locally. For such economic
reasons, most if not all of the world's electric power supply !systems are
widely .interconnected, involving interconnections inside utilities' own
territories. These interconnections extend to inter-utility and then to
inter-regional connections.
Due to a variety of environmental, land-use and regulatory
pressures, the growth of electric power transmission facilities in many
parts of the world is restricted, even though bulk power transfers and
access by third parties are on the increase. The result is transmission
bottlenecks, non-uniform utilization of facilities and unwanted parallel-
path or loop flows.
Often as power transfers grow, the power system beco:mes
increasingly more complex to operate, and the system can become more
insecure with large power flows with inadequate control. Th.e other aspect
of the problem then becomes the inability to utilize the full potential of
tran~mis~sion
interconnections.
EXPLOITATION OF HVDC TECHNOLOGIES
Over the past twenty years, high-current, high voltage power semi-
condul:tors and advanced control technologies have had a profound effect
on electric power generation and transmission systems. Many examples
can k
,cited, including very large High Voltage Current (HVC)
installations, Static Var Compensators (SVCs), thyristor-based high-speed
generator excitation systems and sophisticated region-wide relay and
protection systems. During this same period, similar advances in analytical
tools, (software and models), have enabled power system planners to
exploit the evolving hardware and control technologies. S.tudies conducted
show that these same advances can now be used to increase the capability
of existing ac transmission systems.
The revolution made possible by modern solid-state IIVDC systems
has resulted in more than 25 GW of installed capacity worldwide. These
systems make possible
precise control of large blocks of power between
points in existing ac systems. Projects in operation in North America are
shown on the map in Figure 1.2.
EXPLOITATIOTECHNOLOGIESN OF HVDC
Over the past twenty years, high-current, high voltage power semi-
condul:tors and advanced control technologies have had a profound effect
on electric power generation and transmission systems. Many examples
can k
,cited, including very large High Voltage Current (HVC)
installations, Static Var Compensators (SVCs), thyristor-based high-speed
generator excitation systems and sophisticated region-wide relay and
protection systems. During this same period, similar advances in analytical
tools, (software and models), have enabled power system planners to
exploit the evolving hardware and control technologies. S.tudies conducted
show that these same advances can now be used to increase the capability
of existing ac transmission systems.
The revolution made possible by modern solid-state IIVDC systems
has resulted in more than 25 GW of installed capacity worldwide. These
systems make possible
precise control of large blocks of power between
points in existing ac systems. Projects in operation in North America are
shown on the map in Figure 1.2.
SUMMARY OF RESULTS
Applying FACTS to the point-to-point system showed that rapid
control of series and shunt capacitor compensation can resu.lt in increased
loadability of the corridor, and that damping of dynamic swings can be
achieve:d by modulating the degree of compensation. Thylistor-controlled
high-speed phase shifters were also investigated as an alternative to series
capacitors, but since they do not provide VARS to compensate for line
reactivt: losses as do the capacitors, economically they were less attractive.
The corridor configuration proved to be even richer with possibilities
because: the control of flow along the corridor could be played off against
flow in. the parallel paths. Six basic FACTS options listed in Table 1 were
examined. The pre-FACTS base system as illustrated in Figiure 1.6a was
loaded to about 5000 MW, beyond which the loss of a circuit within the
corridor led to potential voltage collapse in the load area.