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					                                                                                                                             ISSN: 2277 – 9043
                                                    International Journal of Advanced Research in Computer Science and Electronics Engineering
                                                                                                                  Volume 1, Issue 2, April 2012




           A study on Angle Stability Solution Using
                 coordinated Facts Devices
              Dr. K.T. Chaturvedi, Assistant Professor Dept. of Electrical Engineering UIT RGPV Bhopal
                                    Kripashankar Pandeya UIT RGPV Bhopal


                                                                       this model an iterative linear stability analysis is
Abstract— This paper presents a Angle Stability Solution                performed. This      approach  analyzes    all possible
Using coordinated Facts Devices located in different                    combinations of loads and the sustainable electricity
areas of a power system. Analysis of initial conditions and             generations. Eventually, this method reveals the most
a contingency analysis to determine the voltage stability               vulner- able operating points of the system and
margin and voltage variations at different critical nodes               consequently can be used as an indicator of small
are held. The response is carried out by the coordination               disturbance angle stability.
of multiple-type FACTS devices due to which the reactive
power is compensated, improving the voltage stability
margin at the critical nodes.                                                            II.   PROBLEM FORMULATION


  Index Terms— FACTS Devices, Transmission                            Postfault rotor angle oscillations lead to power swings. Both
Loadability,Angle stability, Voltage Stability, Continuation          unstable and stable swings can induce distance relay tripping.
Power Flow, Tangent Vector Technique, Real Power Flow                 For unstable swings, a new computational procedure to
Performance Index Sensitivity Factor                                  locate all the electrical centers is developed. It simplifies the
                                                                      work associated with visual screening of all the R-X plots.
                                                                      For stable swings, a generic three tier hierarchy of stability
                        I. INTRODUCTION                               related norms defined by branch norm, fault norm and system
    Currently, electric power systems are experiencing struc-         norm is proposed. Ranking by branch norm leads to ranking
    tural changes due to the growing incorporation of renewable       of power swings. Ranking by fault norm leads to ranking of
    sources of energy. Another determinant factor in modifying        faults or contingencies. Magnitude and rate of change of
    the configuration of electric power systems is the                system norm can be used to detect an out-of-step condition.
    liberalization of electricity market and restructuring the        Results on a 10-machine system and a utility system with
    trade of energy. Also, in near future, the number of              detailed models are also presented. Voltage stability is
    interconnections in electric power systems will increase.         concerned with the ability of a power system to maintain
    Thus, the future electric power systems will operate closer       acceptable voltage at all nodes in the system under normal
    to their limits. Considering the aforesaid reasons, together      conditions or after being subjected to a disturbance [1]. In
    with the major switching actions concerning the connection        order to detect the system conditions and to predict voltage
    of renewable energy sources, the stability of future power        instability, it is necessary to conduct a voltage stability study
    systems is undertaking a more highlighted role. Being large       at all nodes. To prevent or correct voltage instability, solution
    scale and complex, are features of modern power                   methods based on the results of the power system study must
    systems. Also, because of deregulation, the configu- ration       be applied; these methods allow to improve the voltage
    of interconnected networks is routinely in a state of change.     stability margin and to avoid voltage collapse.
    Therefore, an indicator of stability, which covers the vast
    spectrum of states, is of interest. Such a methodology            Study of Voltage Stability
    should reconcile the stochastic behavior of the                   The methods for studying voltage stability are used to find
    renewable energy sources and the deterministic approach           the operation state, the voltage stability margins and limits
    of stability                                                      and to study the system variation and element responses. The
     analysis.                                                        voltage stability study can be conducted using analytical or
        A methodology to indicate the small disturbance angle         monitoring methods.
     stability in future power systems is to make use of an
                                                                      1) Analytical Methods: These methods allow a detailed study
     iterative- stochastic approach. By applying such an
                                                                      of the variables, parameters and elements behavior of the
     approach, the prob- abilistic nature of sustainable energy
                                                                      power system, in order to find design solutions and operation
     sources is modeled and subsequently, for each sample of
                                                                      criteria that allow the system to work far from the instability
                                                                      point. Each of these methods uses a mathematical technique,
                                                                      which is implemented in a computational tool with a great
                                                                      number of nodes, lines and loads. These methods arebased on

                                              All Rights Reserved © 2012 IJARCSEE
                                                                                                                                            60
                                                                                                                             ISSN: 2277 – 9043
                                                    International Journal of Advanced Research in Computer Science and Electronics Engineering
                                                                                                                  Volume 1, Issue 2, April 2012

conventional power flows, progressive power flows and
dynamic analyses. Conventional power flow techniques are              2) Control of Elements: these techniques are used to avoid
based on mathematical calculations made for each load                 voltage instabilities and collapses in the power system by
condition of the power system and represent voltage variation         controlling elements that change the operation conditions as
at all nodes due to the change of the active and reactive power       protection relays [14], current limiters [15] and TAP
of the load. These techniques allow the calculation of the            changers.
system operation state and the voltage stability limits and
margins, in normal operation conditions and after                     3) System Changes: these techniques are based on the
contingencies. Some of these techniques are: sensitivity              entrance of elements or the shedding of loads to avoid
analysis [4], reduction of the Jacobian matrix (matrix                voltage instability in the system. They are used to increase the
singularity [5] and modal analysis [6]), network equivalent,          power transmission capacity and to alleviate the power
vectorial difference [7] and energy-based techniques.                 system overloads. These methods are divided in undervoltage
Progressive flow techniques are static analysis methods               load shedding [16], and system configuration changes [17].
based on consecutive power flow results used to find the
voltage stability margins and limits of the nodes with higher         4) Mixed: this is a technique based on the combination of the
numerical accuracy [8]; they use a prediction tangent vector          above mentioned techniques to create a voltage stability
to estimate a solution to another load value, which is then           prevention and correction scheme using different elements
corrected [9]. These methods have been widely used because            [18].
of their precision in the voltage stability limit
calculation.Dynamic analysis techniques are based on the
solution ofalgebraic equations in time-domain [1] and they
are used for transient and small signal stability events                             IV. VOLTAGE STABILITY PROBLEM
analysis. These techniques allow to create different scenarios
                                                                      Each node of a power system initially operates with a voltage
that include contingencies or normal operation states in order
                                                                      stability margin as shown in Fig. 1(a). Once a contingency
to determine the variables behavior and response of power
                                                                      occurs, voltage decreases to a stable point as shown in Fig.
system elements in the occurrence of an event [10].
                                                                      1(b) or it becomes unstable as shown in Fig. 1(c). Also when
                                                                      the node operates near the voltage stability limit, Fig. 1(b), a
 2) Monitoring Methods: these methods are based on data               voltage collapse can occur after other events or operations
 measurements of the power system variables such as                   that decrease the reactive transfer capacity to the critical
 voltages, current, active power, reactive power and vector           nodes; therefore it is necessary a prompt response to increase
 angles, to find the operation state, voltage stability limit and     the voltage stability margins as shown in Fig. 1(d).
 margin as well as the critical nodes of the system. They can
 be used as a tool for the on-line and off-line voltage
 stability detection and prediction

           III. SOLUTION OF VOLTAGE STABILITY
The methods used for the solution of the voltage stability are
based on the prevention and correction of the problem.
Prevention methods are aimed at maintaining voltage
stability at all nodes, avoiding them to get close to the limit;
correction methods are aimed at restoring the unstable
conditions to return voltage stability to the nodes. These
methods are divided in: reactive compensation, control of
elements and power system changes. Control actions can be
automatic or manual and must be used according to the time
of response to improve in a short, middle or long-term
stability.

1) Reactive Compensation: these techniques are based on the
compensation of reactive power to the system, from power
generation sources [11], transmission lines [12], transformers
                                                                      Fig. 1. PV curves and Voltage stability margins
[13] and load nodes. The line compensation can be carried
out with a constant value of reactive power, called static
                                                                      Line compensation using FACTS devices compared with
compensation, using switched elements to increase the
                                                                      other techniques, allows a fast response after disturbances,
voltages at the nodes; also, a variable compensation can be
                                                                      allows reactive power injection, does not change the system
carried out, controlled by power electronic devices as
                                                                      configuration or sheds loads, does not interfere with the
FACTS; this is called dynamic compensation and is used to
                                                                      availability of generators and can change the direction of the
respond during transitory and small signal variations that
                                                                      power flow from one area to another. These techniques can
occur in the power system due to disturbances.
                                                                      be used to respond to the events occurred after a contingency,

                                                                                                                                            61
                                              All Rights Reserved © 2012 IJARCSEE
                                                                                                                          ISSN: 2277 – 9043
                                                 International Journal of Advanced Research in Computer Science and Electronics Engineering
                                                                                                               Volume 1, Issue 2, April 2012

with a static or dynamic increasing of the voltage at the
nodes. Some methods seek to solve voltage instability by the          This methodology is based on a fast injection and the
optimal location of FACTS devices close or in the critical         direction of power through the transmission path of lower
nodes [19]; other methods are based on the coordination of         losses to increase the reactive power supply to the critical
FACTS devices, as in 1998, when a method to coordinate             nodes of a power system. This method avoids load shedding,
thyristor controlled series and shunt compensators (TCSC           increases the time for other slower reactive control elements
and SVC) was presented in order to improve angle and               to operate, can be applied to global power systems and does
voltage stability, using a disturbance response method based       not need to relocate FACTS devices so the costs are not
on the Disturbances Auto-Rejection Control (DARC) theory           increased. The coordination of FACTS devices to improve
[20]. In 2003, a secondary voltage control method was
                                                                   voltage stability is made in several stages: FACTS selection,
proposed to eliminate voltage violations at the nodes after a
                                                                   design and implementation.
contingency, using the coordination of SVC and STATCOM
devices to provide reactive power; the secondary voltage             A. FACTS Selection
control is implemented by a learning fuzzy logic controller        The FACTS controllers used in power systems are classified
[21]. In 2005, the development of a control system and             in: shunt controllers (SVC, STATCOM, BESS, SMESS,
control strategies capable of governing multiple flexible AC       SSG, TCBR, TCR, TSC, TSR, SVG, SVS), series controllers
transmission system (FACTS) devices in coordination with           (SSSC, TCSC, TSSC, TCSR, TSSR, TCPST), combined
load shedding was proposed to remove overloads caused by           shunt and series connected controllers (UPFC, TCPST, IPC)
lines outages in transmission networks, based on linearized        and other types (TCVL, TCVR) [23]. These devices allow
expressions in steady state [21]. In 2005, a method for            controlling power flow, increasing transmission line
coordination of FACTS devices as SVC, TCSC and TCPST               capacity, improving stability and reducing reactive losses.
was presented, based on the optimal power flow to avoid            The devices that should be used for voltage stability solution
congestion, to give greater security and to minimize the           are those that allow reactive power injection and power
active losses in transmission lines [22]. FACTS devices            transfer with lower losses.
location and coordination techniques mentioned above have
been based on the voltage stability improvement in an area
near the devices, improving voltages in steady state,                B. Design
preventing violations of the voltage limits, coordinating few      The design stage is based on the determination of the
quantity and types of FACTS devices, they do not allow to          coordinated control strategies of the FACTS devices. The
handle reactive power in the lines and aim at relocating the       steps to find the control strategies are shown in Fig. 3.
devices increasing the costs. Table I shows the comparison
among the techniques used for the solution of voltage
stability problems after a contingency. The rating of the
indexes was done with numbers that indicate the low (1),
middle (2) and high (3) levels of the objective functions of
the proposed method.

                       V. PROPOSAL
The proposed methodology consists on compensating the
reactive power in an interconnected power system of several
areas as shown in Fig. 2, by a coordinated control strategy of
a wide quantity of different FACTS devices located in
several parts of an interconnected power system in order to
increase the voltage stability margin during critical voltage
variations created by a contingency.




                                                                   1) Initial Conditions: the initial conditions of a system are
                                                                   calculated to determine the operation state and the voltage
                                                                   stability margin of each node.

                                                                   2) Contingency Analysis: a contingency analysis to determine
                                                                   nodes with voltage instability or near the limit is carried out.
                                                                   The selection of the




                                            All Rights Reserved © 2012 IJARCSEE
                                                                                                                                         62
                                                                                                                          ISSN: 2277 – 9043
                                                 International Journal of Advanced Research in Computer Science and Electronics Engineering
                                                                                                               Volume 1, Issue 2, April 2012

                                                                   determine the type of stability and the magnitude of the
                                                                   disturbance.

                                                                   2) Determination of Instability Type and Magnitude: one of
TABLE I                                                            the most important parts of the control strategy is the
COMPARISON OF THE TECHNIQUE FOR THE SOLUTION OF                    determination of the type of instability and the magnitude of a
VOLTAGE STABILITY                                                  disturbance occurred in the system, because it is necessary to
                                                                   establish the time for the operation of the devices and the
                                                                   reactive power quantity to be transferred to the critical nodes.

                                                                   3) Determination of the Coordinated Control: after
                                                                   determining the type and magnitude of the event, the
most critical contingencies and the nodes for the                  coordinated actions of the available devices are determined,
measurement of the entrance variables of the control strategy      transmitting through the transmission path of lower losses to
are carried out.                                                   reduce reactive losses and to allow a higher reactive supply to
                                                                   the nodes.
3) Voltage Analysis: based on the selection of the most
critical contingencies and the nodes for the variables             4) Sending Signals to Controllers: the operation signals for
measurement, a dynamic study of the voltages after the             FACTS controllers are sent according to the obtained control
contingency to determine the system response is carried out.       decisions; they control the operation of capacitors and
                                                                   inductors of each FACTS device, allowing the reactive
4) Coordination of FACTS: the control strategy of FACTS            injection and power flow direction to the critical nodes.
devices is developed to improve voltage stability at critical
nodes of the system. These devices should allow the reactive          5) Devices Operation: the devices operate based on the
power supply to the weak nodes and the directing of the            signals sent and inject reactive power or allow the pass of the
reactive power flow.                                               power flow to a specific node based on the transmission path
                                                                   of lower losses.
5) Operation Verification: after determining the control                                      REFERENCES
strategy, an appropriate response for the selected
contingencies should be verified and voltages must be              [1] P. Kundur, ―Power System Stability and Control,‖ Ed.
adjusted in order to comply with the system constraints.           New York: McGraw-Hill, 1994, pp. 17-39, 959-1020.
                                                                   [2] C.W. Taylor, ―Power System Voltage Stability,‖ Ed. New
                                                                   York: McGraw-Hill, 1994.
  C. Implementation                                                [3] J. Bucciero, and M. Terbrueggen ―Interconnected Power
The implementation stage is based on the operation form of         System Dynamics Tutorial: Dynamics of Interconnected
the coordinated control strategy of FACTS devices. The             Power Systems Tutorial,‖ Electric Power Reasearch Institute,
operation form of the control strategy is shown in Fig. 4.         EPRI, 3rd ed, Jan. 1998, pp. 6.1 – 6.55.
                                                                   [4] T.O. Berntsen, N. Flatabo, J.A. Foosnaes, and A.
                                                                   Johannesen, ―Sensitivity signals in detection of network
                                                                   condition and planning of control actions in a power system,‖
                                                                   CIGRE-Ib AC Symposium on Control Applications for
                                                                   Power System Security, 1983, Paper 208-03.
                                                                   [5] N. Flatabo, R. Ognedal, and T. Carlsen, ―Voltage stability
                                                                   condition in a power transmission system calculated by
                                                                   sensitivity methods,‖ IEEE Transaction on Power Systems,
                                                                   Vol. 5, No. 4, Nov. 1990, pp. 1286 – 1293.
                                                                   [6] N.T. Hawkins, G. Shackshaft, and M.J. Short, ―Online
                                                                   algorithms for the avoidance of voltage collapse: reactive
                                                                   power management and voltage collapse margin
                                                                   assessment,‖ Third International Conference on Power
                                                                   System Monitoring and Control, London, UK, 1991, pp.
                                                                   134-139.
                                                                   [7] T.A.M. Sharaf, and G.J. Berg, ―Probabilistic voltage
Fig. 4. Operation form of the voltage stability control            stability indexes,‖ IEEE Proceedings, Generation,
strategy.                                                          Transmission and Distribution, Vol. 138, No. 6, 1991, pp.
                                                                   499 – 504.
1) Measurement of System Signals: the measurements must            [8] V.A. Venikov, et al., ―Estimation of Electrical Power
be taken constantly at nodes identified as critical in the         System Steady- State Stability in Load flow Calculations,‖
contingency analysis; the obtained data is used as an input to     IEEE Transaction on PAS Vol. PAS-94, No. 3, May. 1975,
                                                                   pp. 1034 – 1041.

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                                            All Rights Reserved © 2012 IJARCSEE
                                                                                                                         ISSN: 2277 – 9043
                                                International Journal of Advanced Research in Computer Science and Electronics Engineering
                                                                                                              Volume 1, Issue 2, April 2012

[9] R.J. Thomas, et al, ―On the Dynamics of Voltage
Instabilities,‖ Proceedings - Bulk Power System Voltage
Phenomena- Voltage Stability and Security, EPRl EL-6183
PR 2473-21, Jan. 1989.
[10] P.-A. Lof, T. Smed, G. Andersson, and D.J. Hill, ―Fast
calculation of a voltage stability index,‖ IEEE Transactions
on Power Systems, Vol. 7, No. 1, Feb. 1992, pp. 54 – 64.
[11] P.-A. Lof, G. Andersson, D.J. Hill, ―Voltage stability
indices for stressed power systems,‖ IEEE Transactions on
Power Systems, Vol. 8, No. 1, Feb. 1993, pp. 326 – 335.
[12] B. Gao, G.K. Morison, and P. Kundur, ―Voltage stability
evaluation using modal analysis,‖ IEEE Transaction on
Power Systems, Vol. 7, No. 4, Nov. 1992, pp. 1529 – 1542.
[13] C.D. Vournas, ―Voltage stability and controllability
indices for multimachine power systems,‖ IEEE Transactions
on Power Systems, Vol. 10, No. 3, Aug. 1995, pp. 1183 –
1194.
[14]G. Papaefthymiou, ―Integration of Stochastic
Generation in Power Sys- tems‖, Ph.D. dissertation, Delft
University of Technology, ISBN 978-90-8570-186-6, 2007.
[15] P. Kundur, J. Paserba, V. Ajjarapu, G. Andersson, A.
Bose, C. Canizares,N. Hatziargyriou, D. Hill, A. Stankovic,
Taylor, Th. van Cutsem, V. Vittal, ―Definition and
Classification of Power System Stability‖, IEEE Trans. on
Power Systems, Vol. 16, No. 2, May 2004.
[16] A. M. Lyapunov, Stability of Motion: Academic Press,
Inc., 1967.
[17] P. A. Cook, Nonlinear Dynamical Systems, Second ed:
Prentice Hall, Inc.,2004.
[18] P. Kundur, Power System Stability and Control:
McGraw-Hill, 1994.
[19]      http://en.wikipedia.org/wiki/Normal   distribution
[online].
[20] N. Jenkins. et al., ―Embeded Generation‖, IEE Trans.
on Power and Energy, No. 31, 2000.
[21] J. G. Slootweg, ―Wind Power: Modelling and Impact
on Power System Dynamics‖, Ph.D. dissertation, Delft
University of Technology, ISBN 90-9017239-4, 2003.
[22]http://mathworld.wolfram.com/WeibullDistribution.html
[online].
[23] M. Ghandhari, ―Control Lyapunov Functions: A
control strategy for damping of power oscillations in large
power systems‖, Ph.D. dissertation, The Royal Institute of
Technology, TRITA-EES-0004, ISSN 1100-1607,2000.
[24] P. M. Anderson, A. A. Fouad, Power System Control
and Stability: The Iowa State University Press,1977.
[25] J. J. Grainger, W. D. Stevenson, Power System Analysis:
McGraw-Hill,1994.




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