International Journal of Scientific & Engineering Research Volume 2, Issue 5, May-2011 1

ISSN 2229-5518

Behavior of Eight Bus System with TC-IPC

V.V.Satyanarayana Rao.R, S.Rama Reddy

Abstract— Environmental, regulatory and economic constraints have restricted the growth of electric power transmission facilities, and the topologies to enlarge the levels of power transmission and enhance stability through existing transmission lines have become greatly needed. Many approaches have been proposed for solving the stability problems found in power system operations. Considering the diversity of both, the solutions and the problems, it is often difficult to identify the most suitable solution. The main purpose of this paper is to demonstrate the capability of Inter Phase Power Flow (IPC) Controller as a mean for stability improvement in power systems. In this paper 8 bus system is used as a test bed, the results are shown with and without TC-IPC. The results indicate the robustness of this Flexible AC Transmission System (FACTS) controller to the variation of system operating conditions.

Index Terms— Controlled Series Compensator (CSC), Eight Bus System, Flexiable ac transmission system (FACTS), Interphase power controller, Static phase shifting transformer, TC-IPC, UPFC

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1 INTRODUCTION

he basic operating requirements of an AC power system are that the synchronous generators must remain in synchronism and the voltages must be kept close to their rated values. The capability of a power system to meet these requirements in the face of possible disturbance is characterized by its transient (or first swing), dynamic (or power oscilla- tion), and voltage stability. Transient stability may be defined as the ability of an electric power system to remain in synchronism after being subjected to a major system disturbance (such as a short circuit). Accord- ing to equal-area criteria transient stability of a pow- er system is maintained if the accelerating area equals the decelerating area during the first rotor swing
following the fault clearance.
To avoid stability problems a fast power flow con- trol within the first swing of the generator is re- quired. This can be achieved by different means, such as high performance excitation systems and high ceiling voltage, breaking resistors usage, supercon-

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• V V Satyanarayana Rao.R received Masters Degree in Power Engineer- ing from JNT University, Hyderabad, India in 2007. He is pursing the Ph.D in Power Systems at SCSVMV University, Kanchipuram, Chen- nai, India. Presently he is working as Senior Assistant Professor in Sri Sarathi Institute of Engineering & technology, Nuzvid, India. His areas of interest are FACTS, Power Electronics and Deregulated Power Sys- tems. PH-09396677506. E-mail: rvvs_ssiet@yahoo.com

• Dr.S.Rama Reddy received his ME degree from college of Engineering, Anna University Chennai, India in 1987.He received his Ph.D degree in the area of Resonant Converters from College of Engineering, Anna University Chennai in 1995.Presently he is working as Dean in Elec- trical & Electronics Department , Jerusalem College of Engineering , Chennai. He has publish 30 research papers in reputed Journals. His re- search areas are power electronic converters, Drives and FACTS.

ducting magnetic energy storage systems and etc.
The recent availability of solid-state power switching devices with controlled turn off capability has made possible further advances in power con- version and control, leading to the development of a new generation of FACTS devices. FACTS (Flexi- ble AC Transmission Systems) devices, as discussed in references , are first of all, effective tools for dy- namic power flow control. On the other hand power flow is clearly related to a system‘s transient stability problems. As a result FACTS devices,
such as UPFC (Unified Power Flow Controller), SPS (Static Phase Shifting Transformers) , CSC (Controlled Series Compensator) , are presented as an effective tool to mitigate transient stability problems in electric power systems. These devices are power electronic based controllers, which can influence transmission system voltages, currents, influence transmission sys- tem voltages, currents, impedances and/or phase angle rapidly. Thus FACTS devices (or controllers) can improve both the security and flexibility of a pow- er system. This paper presents the capability of IPC (Interphase Power Controller) as a mean for power stability improvement. Concerning this matter, it is necessary to replace the conventional PST (Phase Shifting Transformer) with the static PST (SPS). The result of these changes is a new FACTS device, which is referenced to it as Thyristor Controlled IPC or TC-IPC.

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2 INTRODUCTION TO IPC

One of the problems for interconnected power sys- tems is overrating of circuit breakers and associated substation equipment due to short circuit level. Con- ventional options to decrease the short circuit levels are splitting existing bus into two or more sections, addition of series reactors in transmission lines and using transformers with high impedance or replacing over-duty substation circuit breakers and associated equipments. However, none of the above methods provide additional transmission capability or ability to control and redirect the power flow.
Splitting an existing bus into more than one section decreases the substation fault problem in a relatively costeffective manner, but operating flexibility and re- liability will be decreased. In practice, it may be diffi- cult to obtain permission to change the existing bus configuration. Series reactors can neither completely eliminate the fault current contributions nor efficiently reduce the transmission constraints. At normal condi- tions, series reactors absorb reactive power. Under heavy loading conditions, this solution can make more problems for voltage regulation. Replacing the under- rated circuit breakers and associated substation equipments with higher interrupting devices, is anoth- er method to overcome the fault duty problem . De- pending on voltage levels, the number of circuit break- ers involved and desired new rating for the breakers, the replacement of breakers can be expensive. In addi- tion, scheduling large number of circuit breaker re- placements imposes planning and engineering chal- lenges.
Some new techniques for fault limitation such as se- ries compensation, flexible alternative current trans- mission systems (FACTS), phase shifting transformer (PST) or Inter phase Power Controller (IPC) in an exist- ing substation can be very attractive options. In the present thesis, the role of IPC is discussed .

3 IPC DESCRIPTION

The basic design goal in IPC technology is to find passive solutions to fundamental frequency problems. Power electronics modules can be added in situations where rapid control action is required to damp oscilla- tions or prevent excessive voltage variations. Hence, basic IPC solutions utilize only conventional equip-
ment, such as capacitors, inductors and phase-shifting
transformers. They generate no harmonics and have no commutation losses. Robustly built, they require much less maintenance than power electronics-based devic- es.
The IPC does not have a fixed configuration, being
more a technology for creating different and innova- tive power flow controllers with diverse characteristics and configurations. Generically, it is a seriesconnected device consisting of two parallel branches, each with an impedance in series with a phase-shifting element (Figure 1). The four design parameters (two imped- ances and two phase shifts) allow enormous design flexibility and make a wide variety of applications possible. Because of the different characteristics these IPC applications can have, they have their own specific names.

Fig 1: The Single diagram of Generic IPC

IPCs can be adapted to specific operating condi- tions. In general, the adaptation also results in an op- timization. For example, the removal of the phase shift in one of the two branches of the IPC reduces the amount of equipment and relocates the control charac- teristic to a more favorable position in the power-angle plane. The adaptability of the IPC technology is also demonstrated by the various ways in which the inter- nal phase shifts can be implemented. Conventional phase-shifting transformers (PST) are the first obvious choice, but the IPC characteristics can also be obtained using conventional transformers which have auxiliary windings added to create the desired internal phase shift by injecting series voltages from other phases.

4 THYRISTOR CONTROLLED INTERPHASE POWER

CONTROLLER (TC-IPC)

In this paper a 8 bus system is implemented with thyristor controlled interphase controller. Based on this model it is demonstrated that the TC-IPC can be very effective to damp power systems oscillations. Simulation results indicate the robustness of this Flexi-

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ble AC transmission system (FACTS) controller to the variation of system operating too, IPC system is shown in the fifure 2(a). Real and reactive powers with a=1440 and 1530 are shown in figure 2(b) & 2 (c) respectively.

Fig2 (a): Interphase controller with Thyristors

Fig 2(b) : Real and Reactive Power at Alpha =144 Degree

Fig 2(c) : Real and Reactive Power at Alpha =153 Degree

It have been shown that real and reactive power could be controlled by Varying "alpha" in Thy- ristor controlled-Inter phase power controller.

Eight bus system without TC-IPC is shown in figure 3(a). Real and reactive powers are shown in fig- ure 3(b), current and voltage at bus 3 is shown in fig- ure 3(c).

Fig 3(a): 8 Bus System without TCIPC

Fig 3(b): Real and reactive power across bus-3

Fig 3(c): Current and volatge across bus-3

Eight bus system with TC-IPC is shown in figure 4(a). Real

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and reactive power at busses 7,1,3 & 4 are shown in figure

4(b) to 4(e), voltage and current at bus 3 are shown in figure

4(f). Reactive power with and without TC-IPC are shown in

Table-1.

Fig 4(a): Bus System with TCIPC

Fig 4(b): Real and reactive power across bus-7

Fig 4(c): Real and reactive power across bus-1

Fig 4(d): Real and reactive power across bus-3

Fig 4(e): Real and reactive power across bus-4

Fig 4(f): Current and volatge across bus-3

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Table1: Reactive Power with and without TC-IPC

[8] H.F.Wang, F.J.Swith, “The Capability of Static VAR Compensator in Damping Power System Oscillations” IEEE Proc-Gener. Transm. Distrib.No4,1996.

[9] J.Brochu “Interphase Power Controller” book Polytechnics Inter- national Press 1999

6 CONCLUSION

This paper presents the simuation resuts of 8 bus system with and without TC-IPC, simuation resuts shows that TC-IPC can improve the system stabiity and mean while preserved the merits of conventiona IPC, simuation resuts indicate that TC-IPC as a FACTS controller can improve the dynamic performance of the system. Simuation results indicate that TC-IPC can increase the real and reactive powers in the line.

ACKNOWLEDGEMENT

We are thankful to Department of Electrical and Electonics Engineering of SCSVMV University and Jerusalem College of Engineering, Chennai, India with whom we had useful discussions regarding FACTS Performance of transmissions lines. Any suggestions for further improvement of this topic are most wel- come.

REFERENCES

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[3] Mohammadi, M.; Gharehpetian, “Thyristor controlled inter phase power controller modeling for power system dynamic studied” TENCON 2004. 2004 IEEE Region 10 Conference.

[4] “FACTS OVERVIEW” Joint IEEEKIGRE Special Publication No.95 TP 108 Sybille G, Haj- Maharsi Y , Morin G , Beeaure- gard.

[5] E.V. Larsen, J.J Sanchez-Gasca and J.H.Chow, “Concept for Design of FACTS Controllers to damp overswings”. IEEE Transactions on power systems Vol.10 1995

[6] R. Mohan Mathur, Rajiv K. Varma “Thyristor-based facts con- trollers for electrical transmission systems”.

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