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Algorithm of Load Flow Simulation and Fault Analysis using MiPower Software

Akshay Sharma

Scholar M.E., Department of Electrical and Electronics Engineering, NITTTR, Bhopal, India

akshaysharmagwl@gmail.com

Abstract - This paper focuses on load flow analysis in an electrical power system. A load flow analysis program using MiPower software has been developed using a fast decoupled load flow algorithm based on a Ybus admittance matrix to determine operating parameters of system bus. A network of 6 bus system is considered as a test case. The Simulink model developed using MiPower software results in fast iterative process. GUI (Graphical user interface) will be provided with the program as the component of the tool box. Fault analysis is carried out on one of the transmission line of 6 bus systems for frequently occurring single line to ground fault to observe the operating parameters of the system under consideration in terms of AC voltage, AC current and AC power waveform at the grid before and after the occurrence of Single line to ground fault.

Key Words: Load flow analysis, MiPower, Single line to ground fault, Fault analysis, operating parameters

I. INTRODUCTION

Load flow studies are used to ensure that electrical power transfer from generators to consumers through the grid system is stable, reliable and economic. It deals with the flow of electrical power from one or more sources to loads consuming energy through available paths. Unlike the traditional circuit analysis, a load flow study usually uses simplified notation such as a one-line diagram and per-unit system. Considerable research has already been carried out in the development of computer programs for load flow analysis of large power systems. However, these general purpose programs may encounter convergence difficulties. There are many solution techniques for load flow analysis. The solution procedures and formulations can be precise or approximate.In this paper we have attempted Fast decoupled load flow analysis to build a power system using the random data taking care of all the parameters required for the simulation and analysis. We have modeled an 11kv generation, 110kV transmission 6 bus grid using MiPower software. We begin with description of 6 bus system under section 1.1 and data collection and methodology required for modeling is discussed in section 3 and in section 4, Load flow study is carried out using Fast decoupled load flow analysis and voltage profile of buses are analyzed. In addition to load flow analysis, Our attention is on unbalanced (asymmetrical) fault analysis is carried out on one of the

Laxmikant Nagar

Scholar M.E., Department of Electrical and Electronics Engineering, NITTTR, Bhopal, India

lk.nagar063@gmail.com

transmission line of 6 bus systems for frequently occurring single line to ground fault. The simulation results and reports are analyzed in section 5.

1.1SYSTEM DESCRIPTION

Figure1 shows a single line diagram of a 6-bus system with two identical generating units, five transmission lines and two transformers. Per-unit transmission line series impedances and shunt susceptances are given on 100 MVA base, generator's transient impedance and transformer leakage reactances are given in the accompanying table1.1

Figure 1 “6 Bus” System model

Table-1.1

Bus Codep – q

ImpedanceZpq

Line ChargingY'pq/2

3 – 4 0.00 + j0.15 03 – 5 0.00 + j0.10 03 – 6 0.00 + j0.20 05 – 6 0.00 + j0.15 04 – 6 0.00 + j0.10 0

Generator Data:G1 = G2 =100 MVA, 11 kV with X'd =10 %Transformer Data:T1 = T2 = 11/110 kV, 100 MVA, leakage reactance = 5 %

All impedances are on 100 MVA base

2

II. DATA INTERPRETATION

In transmission line data, elements 3-4 & 5-6 have common parameters. Elements 3-5 & 4-6 have common parameters. Therefore 3 libraries are required for transmission line. As generators G1 and G2 have same parameters, only one generator library is required. The same applies for transformers also. Procedure to enter the data for performing studies using MiPower is discussed below.

2.1 MiPower-DATABASE CONFIGURATION

Power System Network Editor is used to select menu option Database Configure. Configure Database dialog is popped up. Browse the desired directory and specify the name of the database to be associated with the single line diagram. Uncheck the Power System Libraries and Standard Relay Libraries. For this example these standard libraries are not needed, because all the data is given on pu for power system libraries (like transformer, line\cable, generator), and relay libraries are required only for relay co-ordination studies. If Libraries are selected, standard libraries will be loaded along with the database. Since the impedances are given on 100 MVA base, check the pu status in Electrical Information tab. Specify the Base MVA and Base frequency. If the data is furnished, modify the breaker ratings for required voltage levels in Breaker Ratings tab otherwise accept the default values and create the database to return to Network Editor.

Figure 2: Configuration Information

2.2 BUS VOLTAGE CONFIGURATION

In the network editor, configure the base voltages for the single line diagram in menu option and again configure base voltage, if necessary change the Base-voltages, color, Bus width.

III. MODELLING OF COMPONENTS

The Simulink Models of various components of power system network are essential for the assessment of desired performance requirements, for the design and coordination of supplementary control and protective circuits, and for system stability studies related to planning and operation of power system. In this section, we begin with description of various components, and finally presents complete Simulink model for selected type of 6 bus system [1].

3.1 BUS SIMULINK MODEL

MiPower tool bar provide Bus icon. Draw a bus and a dialog appears prompting to give the Bus ID and Bus Name. Database manager with corresponding Bus Data form will appear. Modify the Area number, Zone number and Contingency weightage data if it is other than the default values. Usually the minimum and maximum voltage ratings are ± 5% of the rated voltage. Bus description field can be effectively used if the bus name is more than 8 characters. If bus name is more than 8 characters, then a short name is given in the bus name field and the bus description field can be used to abbreviate the bus name. For example let us say the bus name is northeast, then bus name can be given as NE and the bus description field can be North East [1]-[2].

Figure3 Bus Data Dialogue

Follow the same procedure for remaining buses. Following table 3.1 gives the data for other buses.

Table 3.1

Bus DataBus No. 1 2 3 4 5 6

Bus Name Bus 1

Bus 2

Bus 3

Bus 4

Bus 5

Bus 6

Nominal voltage

11 kV

11 kV

110 kV

110 kV

110 kV

110 kV

3.2 TRANSMISSION LINE SIMULINK

MODEL

Transmission Line icon provided on power system tool bar. To draw the line select the positions in between two buses and connect one bus to another bus by double clicking the mouse button.

Figure 4 Line Element ID

3Element ID number and the details of that line with corresponding Line\Cable Data is to be provided on database manager. The details of that line as shown in figure 5. Transmission line data for Line 3-4 in Line & Cable Library is shown in figure 6.

Figure 5 Line\Cable Data Figure 6 Line\ Cable Library

Data for remaining elements given in the following table 3.2 follow the same procedure for rest of the elements.

Table 3.2

3.3 TRANSFORMER SIMULINK MODEL

Two Winding Transformer icon is provided on power system tool bar. To draw the transformer, click in between two buses and to connect to the From bus, double click on the From Bus and joint it to another bus by double clicking the mouse button on the To Bus [5].

Figure 7 Transformer Element ID

Transformer Element Data form is shown in figure 7.Two Winding Transformer Data in the form is shown in figure 8. The data form table 3.3 entered in Transformer library form is shown in figure 9.

Figure 8 Two Winding Transformer DataIn the similar way enter other transformer details from table 3.3.

Figure 9 Two Winding Transformer Library

Table 3.32nd Transformer Detail

Transformer Number 2Transformer Name 2T2From Bus Number 6To Bus Number 2De Rated MVA 100

3.4 GENERATOR SIMULINK MODEL

Generator icon is provided on power system tool bar. Draw the generator by clicking on the Bus1. Element ID dialog is shown in figure 10.

Figure 10 Generator Element ID

Transmission Line Element/ Library DataLine Number 1 2 4 5 6

Line Name Lne 3-4

Line 3-5

Line 3-6

Line 4-6

Line5-6

De-Rated MVA

100 100 100 100 100

Positive Sequence Resistance

0 0 0 0 0

Positive Sequence Reactance

0.15 0.1 0.2 0.1 0.15

Thermal rating

100 100 100 100 100

4Enter Generator data in the form as shown in figure 11 below.

Figure 11 Generator Data

The details of Generator 1 are provided on Generator Library as shown in figure 12. Connect another generator to Bus 2. In similar way enter its details as given in the following table 3.4

Figure 12 Generator Library

Table 3.4Generator 2 details

Bus Number 2De-Rated MVA 100

Specified Voltage 11Scheduled Power 80Reactive Power

Minimum0

Reactive power Maximum

60

Note: To neglect the transformer resistance, in the multiplication factor table give the X to R Ratio as 9999.

IV. SIMULINK MODEL OF 6 BUS SYSTEM

The Simulink model now incorporated into MiPower to

analyze and design of power systems. The simulated model

of 6 bus system is shown in figure 13.

Figure 13 Simulink ModelIV. LOAD FLOW ANALYSIS

Load flow analysis can be performed using menu option as Solve - Load flow studies. Following dialog will appear.

Figure 14 Load Flow Analysis

Study Info option provides following dialog. Select Fast Decoupled Load Flow and enable Optimal Load Flow Analysis [4].

Figure 15 Load Flow Studies

4.1 RESULT OF LOAD FLOW ANALYSIS

Load flow analysis is done by Fast Decoupled Load flow Method. The report of the simulation shows the specified MW generation as 160 MW, total minimum & maximum MVAR limit of Generator are 0 & 120 respectively. Part of the Report generated by MiPower is shown in Figure 16

5

Figure 16 Report of Load Flow Analysis

V. FAULT ANALYSIS (SINGLE LINE TO

GROUND)

To solve short circuit studies choose menu option Solve - Short Circuit Analysis or click on SCS button on the toolbar on the right side of the screen. Short circuit analysis screen appears [5]-[6].5.1 CASE STUDY INFORMATION

Figure 17 Short Circuit Studies

Afterwards click Execute. Short circuit study will be executed. Click on Report to view the report file.

Figure 18 Short Circuit Analysis

5.2 GRAPHICAL ANALYSIS

For the Graphical analysis of Short circuit studies, select Graph option of Short Circuit Analysis as shown by dialog

Box in Figure 18. Select Import Button of MiGraph Screen following Graphical representation will appear to understand the behavior of electric power systems under the occurrence of a short circuit as shown in Figure 19.

Figure 19 Graphical View

5.3 RESULT OF FAULT ANALYSIS

The result of Short Circuit Analysis is developed by creating a line to Ground Fault at Bus 5 using MiPower is shown in Figure 19.

Figure 19 Report on Short circuit analysis

VI. CONCLUSION

Load-flow studies are important for planning future expansion of power systems as well as in determining the best operation of existing systems. The principal information obtained from the load flow study is the magnitude and phase angle of the voltage at each bus, and the real and reactive power flowing in each line.A MiPower load flow simulation program has been developed using a Fast decoupled load flow algorithm to calculate and control the voltage, determine real and reactive power flows. The procedure is directly applicable to other unbalanced operating conditions of interest to the power system analyst for various short circuits such as three phase to ground fault, Line to line, Double line to ground, Single phase open fault, and Simultaneous faults.

REFERNCES

[1] K. Manohar, P. Sobha Rani, “Mppt and Simulation for a Grid-Connected Photovoltaic System and Fault Analysis,” The International Journal of Engineering and Science Vol.1, pp. 158-166, 2012.

[2] Vivek Raveendran, Sumit Tomar, “Modeling, Simulation, Analysis and Optimisation of a Power

6System Network- Case Study,” International Journal of Scientific & Engineering Research, Vol. 3, June 2012.

[3] S. Jovanovic, “Semi Newton Load Flow Algorithms in Transient Security Simulations.” IEEE Transaction on Power Systems, vol. 15, No. 2, May 2000.

[4] Khalid Mohamed Nor, Taufiq Abdul Gani, “Reusability Techniques in Load Flow Analysis Computer Program,” IEEE Transaction on Power Systems, vol. 19, No. 4, Nov. 2004.

[5] Prdcinfotech.com, India: Bangalore Center; 2013 [cited 08 Jan 2013]. Available from: www.prdcinfotech.com/products.html

[6] Prabha Kundur, “Power System Stability & Control,” 2nd ed. Electric Power Research Institute, McGraw-Hill, Jan 1994.