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Behavior of Eight Bus System with TC-IPC
« on: August 20, 2011, 06:16:39 am »
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Author : V.V.Satyanarayana Rao.R, S.Rama Reddy
International Journal of Scientific & Engineering Research, Volume 2, Issue 5, May-2011
ISSN 2229-5518
Download Full Paper : PDF

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

1   INTRODUCTION                                                                     
The  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 oscillation),  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).  According  to  equal-area  criteria transient stability  of a  power  system  is maintained if the accelerating area equals the decelerating area during  the  first  rotor  swing  fol-lowing  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-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  (Flexible  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 power 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.

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 difficult 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 another method to overcome the fault duty problem . Depending on voltage levels, the number of circuit breakers involved and desired new rating for the breakers, the replacement of breakers can be expensive. In addition, 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 devices.
The IPC does not have a fixed configuration, being more a technology for creating different and innovative 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 impedances 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.

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