Optimal Placing of FACTS Devices to Improve Power System Security

Optimal Placing of FACTS Devices to Improve Power System Security

Chetan W. Jadhao1, K. Vadirajacharya2

1M.Tech. II Yr. Electrical Engineering,

2Associate Professor, Electrical Engineering Department

Dr. Babasaheb Ambedkar Technological University, Lonere-402103.

Raigad, Maharashtra, India.

Abstract In electric power systems, system no remain in secure operating state due to increased power demand. On other hand, the power system stability has been recognized as an important problem for its secure operation. Several methods are being used conventionally to improve operating margins necessary for system stability. Many of these suffer with excessive response time and considerable amount of power loss. To overcome this difficulty, a rapid development of power electronic devices such as Flexible AC Transmission System (FACTS) devices are used, their primary application is to enhance power transfer capabilities, power system stability and allow more flexible control of power flows. By installing FACTS equipment at optimal sites, the overall system benefits are sought. But the location of these FACTS devices has been big challenge. This challenge is overcome by using Sensitivity Indices analysis method. Here two Sensitivity Indices analysis methods are used and these are; reduction of total system reactive power loss and real power flow performance index sensitivity indices. The MATLAB software is used here to write a programming code for finding out the sensitivity indices for both methods. IEEE-14 bus system is used here for the study purpose.

Keywordssensitivity analysis; sensitivity indices; power system security; PI; FACTS

1. INTRODUCTION

   With the ongoing expansion and growth of the electric utility industry, including deregulation in many countries, numerous changes are continuously being introduced to a once predictable business. Although electricity is a highly engineered product, it is increasingly being considered and handled as a commodity. Thus, transmission systems are being pushed closer to their stability and thermal limits while the focus on the quality of power delivered is greater than ever [2]. Power system is a network of electrical components used to supply, transmit and use electric power. An example of an electric power system is the network that supplies a region like homes and industry with power. For sizable regions, this power system is known as grid and can be broadly divided into the generator that supply the power, the transmission system that carries the power from the generating centre to the load centre and the distribution system that feeds the power to nearby homes and industries. The power system needs to be operationally secure, i.e. with minimal probability of blackout

   acceptable limits despite changes in load or available generation. From this perspective, security is the probability of a power systems operating point remaining in a viable state of operation [5].

   The system operation is governed by three sets of generic equations one differential and two algebraic (generally non- linear). Out of two sets of algebraic sets, one set comprises equality constraints (E) which express balance between the generation and load demand. The other set consists of inequality constraints (I) which express limitation of the physical equipment (such as current and voltages must not exceed maximum limits). The classification of the system states is based on the fulfillment or violation of one or both sets of these constraints, Fig. 1 shows the system operating state [6].

   1. Normal State

      Here all equality(E) and Inequality(I) constraints are satisfied.

   2. Alert State

      This state implies that there is a danger of violating some of the inequality (I) constraints when subjected to disturbances enables the transition from an alert state to secure state.

   3. Emergency State

      Here inequality (I) constraints are violated. The system, however, would still be intact, and emergency control action could be initiated to restore the system to alert state.

   4. In-Extremis State

      Here both equality(E) and inequality(I) constraints are violated.

   5. Restorative State

   From this state, the system can transit to either the alert or the normal state depending on the circumstances.

   NORMAL STATE

   RESTORATIVE STATE

   ALERT STATE

   IN-EXTREMIS STATE

   EMERGENCY STATE

   and equipment damage [3]. An important component of power

   SYSTEM NOT INTACT

   SYSTEM INTACT

   system security is the systems ability to withstand the effects of contingencies [4]. The power system operation is said to be normal when the power flows and the bus voltages are within

   Fig. 1. Power System Operating State

   In the present day scenario, transmission systems are becoming increasingly stressed, more difficult to operate, and more insecure with unscheduled power flows and greater

   The real (Pij) and reactive (Qij) power flows from bus-i to bus-j can be written as;

   losses because of growing demand for electricity and

   Pij = V2 g

   V V ( g Cos

   + b Sin

   ) (1)

   restriction on the construction of new lines. However, many

   i ij

   i j ij

   ij ij ij

   high-voltage transmission systems are operating below their

   Qij = – V2 ( b + B /2 ) V V (g Sin

   • b Cos ) (2)

     thermal ratings due to constraints, such as voltage and stability limits. Now, more advanced technology is used for

     i ij sh

     Where,

     1. j ij

        ij ij ij

        reliable operation of transmission and distribution in power system. To achieve both reliable and benefit economically, it has become clearer that more efficient utilization and control of the existing transmission system infrastructure is required. Improved utilization of the existing power system is provided through the application of advanced control technologies.

        ij = i – j

        Similarly, the real (Pij) and reactive (Qij) power flows from bus-j to bus-I can be expressed as;

        Power electronics has developed the Flexible AC

        Pji = V2 g

        V V ( g Cos

   • b Sin

   ) (3)

   Transmission System (FACTS) devices. FACTS devices are

   1. ij

   i j ij

   ij ij ij

   effective and capable of increasing the power transfer

   Qji = – V2 ( b + B /2 ) + V V (g Sin

   + b Cos ) (4)

   capability of a line and support the power system to work with comfortable margins of stability and used to overcome

   j ij sh

   Where,

   i j ij

   ij ij ij

   the insecure problem of power system [7] [8].

   FACTS is defined by the IEEE as a power electronic based system and other static equipment that provide control of one or more AC transmission system and increase the capacity of power transfer [9].

   In this paper, the optimal location of FACTS devices is find out using sensitivity indices analysis method. The

   MATLAB software is used here to write a programming code for finding out the sensitivity indices for both methods. For the study purpose electrical IEEE-14 bus system is used here.

2. BENEFITS OF UTILIZING FACTS DEVICES

The advantages of utilizing FACTS devices in power system can be given as below;

• Existing transmission system can be utilize in better way with the help of FACTS devices.

• Reliability and availability of transmission system increases.

• Environmental friendly.

Bsh is full line charging impedance.

ol>

The result obtained from the MATLAB programming are shown in TABLE I by using reduction of total system reactive loss and real power flow performance index sensitivity indices analysis method. Column 3rd gives sensitivity indices by using total system reactive loss and it is denoted by aij whereas 4th column gives the sensitivity indices by using real power flow performance index sensitivity analysis method and it is denoted by bij. According to total system reactive loss method (column 3rd), the line no. 19 (aij

= 0.0048 )is more sensitive and line no. 19 is suitable for placing the FACTS device and according to real power flow performance index method (column 4th), line no. 6 (bij = – 56813.7 ) is more sensitive and line no. 6 is suitable for optimal placement of FACTS device. In this way to overcome the security problem of power system, optimal placement of FACTS devices can done with the help of sensitivity analysis indices method.

TABLE I. CALCULATED SENSITIVITY INDICES

6.1 MW

1.6 MVAr V12 = 1.2

12

6.1 MW

1.6 MVAr

13

0.22092+j0.19988

0.06615+j0.13027

V13 = 1.2

0.17093+j0.34802

3.5 MW

1.8 MVAr

V11=1.2

11

0.08205+j0.19207

9 MW

5.8 MVAr

14.9 MW

5.0 MVAr G

14 V14 = 1.2

C

0.12711+j0.27038

Generators

Synchronous Compensators

0.12291+j0.25581

0.09498+j0.19890

10 V10=1.2

G 23.2 MW

0.03181+j0.08450

29.5 MW

16.6 MVAr V8 = 1.09

11.2 MW 9 8

1 V1 = 1.06

0.01938+j0.05917

0.01938+j0.05917

C

7.6 MW

1.6 MVAr

7.5 MVAr V9 = 1.2

6 V6 = 1.07

V5 = 1.07

5 0.01335+j0.04211

0+j0.17615 C

7 V7 = 1.2

4 V4 = 1.2

47.8 MW

0.05695+j0.17388

0.06701+j0.17103

0.05811+j0.17632

V2 = 1.045 2

21.7 MW

12.7 MVAr 94.2 MW

G

40 MW

0.04699+j0.33654

V3 = 1.01

3

C

19 MVAr

Fig. 3. IEEE-14 bus system

CONCLUSION

The system security is the important thing in the power system. As per expected goal, in large power system, the finding of the optimal location of FACTS devices is important step. The optimal place of FACTS devices to improve power system security is find out by introducing some sensitivity indices analysis method, the analysis approach has been utilized to find the most sensitive line in power sytem network and on sensitive line FACTS devices are placed to improve the system stability and system security.

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