This thesis examines using simultaneous AC-DC power transmission to improve power system stability. Simulation results show stability is enhanced when compared to only AC transmission. The thesis aims to emphasize the advantages of simultaneous transmission for improving stability and damping oscillations. FACTS devices allow flexible control of AC and DC power flows to achieve benefits like better transmission asset utilization and increased grid stability. Results demonstrate substantial gains in power transfer capability and reliability when converting dual AC lines to simultaneous AC-DC transmission.

1. M. TechM. Tech
ThesisThesis
OnOn
POWER SYSTEM STABILITY ENHANCEMENT BY SIMULTANEOUS
AC-DC POWER TRANSMISSION
Submitted By:
ABHISHEK
CHATURVEDI
ID No. : 11MTEEEPS019
Advisor:
Er. Vinay Kumar Tripathi
(Asst. Professor)
Department of Electrical and Electronics Engineering
Shepherd School of Engineering and Technology
Sam Higginbottom Institute of Agriculture, Technology and
Sciences
(Deemed-To-Be-University)
Allahabad-211007, Uttar Pradesh

2. INTRODUCTION

3.  The concept of simultaneous ac-dc power transmission.Long
extra high voltage (EHV) ac lines cannot be loaded to their
thermal limits due to this instability occurs in the power
system
 It is possible to load these lines very close to their thermal
limits.
 The conductors are allowed to carry usual ac along dc
superimposed on it.

4. The advantage of parallel ac-dc transmission for
improvement of transient stability and dynamic stability and
damp out oscillations have been established.
Simulation study is carried out in MATLAB software
package. The results shows the stability of power system
when compared with only ac transmission.

5. OBJECTIVE OF THE THESIS

6. 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.
To achieve the advantages of parallel ac-dc transmission in
some specific applications LV (low voltage) and MV (Medium
voltage) system.

7. METHODS
AND
METHODOLOGY

8. 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.
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.

9. BASIC BLOCK DIAGRAM

10.  Simulation Model

12.  Result’s and Discussion

13. Sending end Voltage, receiving end voltageSending end Voltage, receiving end voltage

14. Sending end current, receiving end current

15. Sub system 4, Active & reactive power

16. Combined AC DC Current

17. Ac current to Zig- Zag Transformer

18. Rectifier dc side Voltage

19. Inverter sending, receiving end
Voltage

20. FFT analysis of combined ac-dc
power transmission

21. TABLE I
COMPUTED RESULTS
 Power Angle 30 45 60 75
 AC Current(kA) 0.416 0.612 0.80 0.98
 DC Current(kA) 5.25 5.07 4.80 4.50
 AC Power(MW) 290 410 502 560
 DC Power(MW) 1685 1625 1545 1150
 Total Power(MW) 1970 2035 2047 1710

22. TABLE II
SIMULATION RESULTS
 Power Angle 30 45 60 75
 PS (MW) 2306 2370 2380 2342
 Pac (MW) 295 410 495 540
 Pdc (MW) 1715 1657 1585 1498
 Pac loss (MW) 12 30 54 82
 Pdc loss (MW) 280 265 241 217
 PR (MW) 1988 2050 2060 1995

23. Benefits of utilizing FACTS devices
 The benefits of utilizing FACTS devices in electrical transmission systems
can be summarized as follows
 Better utilization of existing transmission system assets
 Increased transmission system reliability and availability
 Increased dynamic and transient grid stability and reduction of loop flows
 Increased quality of supply for sensitive industries
 Environmental benefits Better utilization of existing transmission system
assets

24. CONCLUSION
 A simple scheme of simultaneous EHV ac-dc power
transmission through the same transmission line has been
presented.
 Active and reactive powers associated with ac and dc,
conductor voltage level and total power have been obtained
for steady state normal operating condition.
 Simulation studies are being made for the co-ordinated
control and also individually the control of ac and dc power
transmitted through the lines.

25.  There is substantial gain in the loading capability of the line
 The possibility of converting a dual circuit ac line into
simultaneous ac-dc power transmission block to improve
power transfer as well as to achieve reliability in the power
transfer.
 The added dc power flow is flawless and is not the cause of
any transient instability.

26. REFERENCES

27. [1] N. G. Hingorani, “FACTS—flexible A.C. transmission system,”
in Proc. Inst. Elect. Eng. 5th. Int. Conf. A.C. D.C. Power
Transmission,
[2] Padiyar.’HVDC Power Transmission System.’ Wiley Eastern,
New Delhi, 1993)
[3] H. Rahman and B H Khan “Stability Improvement of Power
Systemby Simultaneous AC-DC Power Transmission” Electric Power
System Research Journal, Elsevier, Paper Editorial ID No. EPSRD-
06-00732, Press Article No. EPSR-2560— Digital Object.