04-06-2012, 12:27 PM
Improvement of Power System Stability by Simultaneous AC-DC Power Transmission
Improvement of Power System Stability by Simultaneous AC-DC Power Transmission.pdf (Size: 350.34 KB / Downloads: 71)
1 INTRODUCTION
VDC 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 .Very fast control
of SCRs in FACTS devices like state VAR system (SVS),
controlled series capacitor (CSC), static phase shiftier
(SPS) and controlled braking resistors oscillations as
well as to control the voltage profile of the line by controlling
the total reactive power flow. Only the basic
idea is proposed along with the feasibility study using
elementary laboratory model. The main object is to
emphasize the possibility of simultaneous ac-dc
transmission with its inherent advantage of power
flow control improves stability and damps out oscillations
in power system.
EHV ac line may be loaded to a very high value
if the conductors are allowed to carry superimposed
dc current along with ac current. The added dc power
flow does not cause any transient instability.
This paper presents a simple scheme of simultaneous
EHV ac-dc power flow through the same
transmission line with an object to achieve the advantages
of parallel ac-dc transmission. Simultaneous acdc
transmission may also claim advantages in some
specific applications LV (low voltage) and MV (Medium
voltage) system.
The flexible ac transmission system (FACTS) concepts,
based on applying state-of-the-art power electronic
technology to existing ac transmission system,
improve stability to achieve power transmission close
to its thermal limit. Another way to achieve the same
goal is simultaneous ac–dc power transmission in
which the conductors are allowed to carry superimposed
dc current along with ac current. Ac and dc
power flow independently, and the added dc power
flow does not cause any transient instability.
2 COCEPT OF SIMULTANEOUS AC-DC TRANSMISSION
The circuit diagram in Figure1 shows the basic
scheme for simultaneous ac-dc transmission. The dc
power is obtained through the rectifier bridge and in-
H
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