21-06-2012, 04:38 PM
SIMULTANEOUS AC-DC POWETRANSMISSION
SIMULTANEOUS AC-DC.docx (Size: 367.87 KB / Downloads: 65)
Abstract
The advantage of parallel ac-dc power
transmission for the improvement of transient
and dynamic stability and damp out
oscillations have been established. Present
paper proposes a simultaneous ac-dc power
flow scheme through the same transmission
line to get the advantages of parallel ac-dc
transmission to improve stability and damping.
Introduction .
HVDC transmission lines in parallel with EHV
ac lines are recommended to improve transient
and dynamic stability as well as to damp out
oscillations in power system. Long EHV ac
lines can not be loaded to its thermal limit to
keep sufficient margin against transient
instability. But for optimum use of
transmission lines here is a need to load EHV
ac lines close to their thermal limits by using
flexible ac transmission system (FACTS)
components .
Proposed applications.
1.Long EHV ac lines can not be loaded to
their thermal limit to keep sufficient margin
against transient instability and to keep voltage
regulation within allowable limit, the
simultaneous power flow does not imposed
any extra burden on stability of the system,
rather it improves the stability. The resistive
drop due to dc current being very small in
comparison to impedance drop due to ac
current, thee is also no appreciable change in
voltage regulation due to superimposed dc
current.
Conclusions.
A simple scheme of simultaneousEHV ac-dc
power transmission through the same
transmission line has been presented.
Expressions of active and reactive powers
associated with ac and dc, conductor voltage
level and total power have been obtained for
steady state normal operating condition. The
possible applications of the proposed scheme
may be listed as: loading a line close to its
thermal limit, improvement of transient and
dynamic stability and damping of oscillations.