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An-Najah National University

Faculty of Graduate Studies

Power Flow Analysis Using ETAP Software

By:

Tareq Foqha

Supervisor:

Dr. Maher Khammash

Nablus, Palestine

II

ABSTRACT

Load flow is an important tool used by power engineers for planning, to determine the best

operation for a power system and exchange of power between utility companies. In order to

have an efficient operating power system, it is necessary to determine which method is

suitable and efficient for the system’s load flow analysis. This research will introduce a load

flow study and analysis for 36 -bus power system using ETAP software to improve the power

factor and to reduce the electrical losses.

CHAPTER ONE INTRODUCTION

CHAPTER ONE INTRODUCTION 1.1 Power Flow Studies:

Power flow (or load flow) is the solution for the normal balanced three-phase steady-state

operating conditions of an electric power system. In general, power flow calculations are

performed for power system planning and operational planning, and in connection with system

operation and control.

The data obtained from power flow studies are used for the studies of normal operating mode,

contingency analysis, outage security assessment, and optimal dispatching and stability [1].

The main objective of the load flow analysis is to identify the potential problems, in terms of

unacceptable voltage conditions, overloading of facilities, decreasing reliability, or any failure

of the transmission system to meet performance criteria. After this analysis stage, the planner

develops alternative plans or scenarios that not only will prevent the foreseen problems but

also will best meet the long-term objectives of system reliability and economy.

The effectiveness of the alternative plans is determined by load-flow, or power-flow studies

under both normal and emergency operations. The load-flow programs now in use by the

utilities allow the calculation of currents, voltages, and real and reactive power flows, taking

into account the voltage-regulating capability of generators, transformers, synchronous

condensers, specified generation schedules, as well as net interchange among interconnected

systems, automatically. By changing the location, size, and number of transmission lines, the

planner can achieve to design an economical system that meets the operating and design

criteria [2].

1.2 Newton-Raphson Power Flow Solution:

It is an iterative method which approximates a set of non-linear simultaneous equations to a

set of linear simultaneous equations using Taylor’s series expansion and the terms are limited

to the first approximation. It is the most iterative method used for the load flow because its

convergence characteristics are relatively more powerful compared to other alternative

processes and the reliability of Newton-Raphson approach is comparatively good since it can

solve cases that lead to divergence with other popular processes. If the assumed value is near

the solution, then the result is obtained very quickly, but if the assumed value is farther away

from the solution then the method may take longer to converge. This is another iterative load

flow method which is widely used for solving nonlinear equation. The admittance matrix is

used to write equations for currents entering a power system.

Equation ( 1 ) is expressed in a polar form, in which j includes bus i

The real and reactive power at bus i is

Substituting for Ii in Equation ( 1 ) from Equation ( 2 )

The real and imaginary parts are separated:

The above Equation ( 4 ) and ( 5 ) constitute a set of non-linear algebraic equations in terms of

|V| in per unit and δ in radians. Equation (4) and (5) are expanded in Taylor’s series about the

initial estimate and neglecting all higher order terms, the following set of linear equations are

obtained.

In the above equation, the element of the slack bus variable voltage magnitude and angle are

omitted because they are already known. The element of the Jacobian matrix are obtained after

partial derivatives of Equations (15) and (16) are expressed which gives linearized relationship

between small changes in voltage magnitude and voltage angle. The equation can be written in

matrix form as:

J 1 , J 2 , J 3 , J 4 are the elements of the Jacobian matrix.

The difference between the schedule and calculated values known as power residuals for the

terms ∆Pi(k)^ and ∆Qi(k)^ is represented as:

Tap-changing and voltage-magnitude-regulating transformers are used to control bus voltages

as well as reactive power flows on lines to which they are connected. Similarly, phase-angle

regulating transformers are used to control bus angles as well as real power flows on lines to

which they are connected. Both tap-changing and regulating transformers are modeled by a

transformer with an off-nominal turns ratio c. A change in tap setting or voltage regulation

corresponds to a change in c. The power-flow program computes the changes in Ybus, bus

voltage magnitudes and angles, and branch flows [3].

1.4 ETAP:

Electrical Transient Analyzer Program (ETAP) is the foremost-integrated for electrical

systems allowing to have multiple representations of a power system for different analysis and

design purpose. This research will introduce the load flow studies for various conditions by

Electrical Transient Analyzer Program (ETAP) application software as a successful and

accurate tool to conduct load flow study of complex electrical power systems within the

minimum time period.

CHAPTER TWO LOAD FLOW ANALYSIS

Table (2)

Summary of total generation, loading and demand are shown in the following table:

MW Mvar MVA PF

Source (Swing Bus) 143.465 180.335 230.440 62.26 lagging

Table (3)

We conclude that all voltages are less than the nominal voltage. And there is a high voltage

Figure (1): 36 -bus power system.

2.3 Load Flow Analysis For the 36-Bus System (Maximum Load Condition):

In this section maximum load state will be studied and we will see the optimization problems

and will search solution for this optimization problem; and obtain results and make

recommendations.

1. Increasing the swing bus voltage;

2. Tap changing Transformers;

3. Addition of a shunt capacitor bank to a load bus

2.3.1.1 Improvement by increasing the swing bus voltage:

For this network we assume that we can increase the voltage on the swing bus up to 5% from

the nominal voltage (220 kV), the new value of the swing bus voltage will be (231 kV), After

running the ETAP the load flow results obtained are shown in the tables 4 and 5, other results

are shown in the appendix B, Figure 3 shows the load flow analysis after increasing the swing

bus voltage by 5%.

Bus Number Bus Type Nominal Voltage PF % Angle 1 Load Bus 94.680 - 5.6 70. 2 Load Bus 92.246 - 4.7 70. 3 Load Bus 91.926 - 4.7 70. 4 Load Bus 91.926 - 4.7 75. 5 Load Bus 91.868 - 4.6 64. 6 Load Bus 91.8 38 - 4.7 74. 7 Load Bus 91.845 - 4.6 67. 8 Load Bus 91.935 - 4. 7 74. 9 Load Bus 92.049 - 4. 7 61. 10 Load Bus 91.905 - 4.6 68. 11 Load Bus 92.117 - 4. 7 71. 12 Load Bus 91.292 - 4. 5 67. 13 Load Bus 92.214 - 4.6 68. 14 Load Bus 91.322 - 4. 5 68. 15 Load Bus 91.763 - 4.6 68. 16 Load Bus 90.928 - 4. 4 68. 17 Load Bus 90.917 - 4. 4 67. 18 Load Bus 90.911 - 4. 4 71. 19 Load Bus 91.203 - 4. 4 62. 20 Load Bus 83.043 - 8. 3 67. 21 Load Bus 87.870 - 6. 1 70. 22 Load Bus 88.750 - 5. 2 75. 23 Load Bus 86.873 - 6. 5 65. 24 Load Bus 85.379 - 8. 2 78.

Table (4)

• CHAPTER 1 : INTRODUCTION …………………..….………………………..….……..... II
  • 1.1 Load Flow Studies …..….…….…………………..….……….……………..……..…..…..…
  • 1.2 Newton-Raphson Power Flow Solution ………………..….……………..….……….…
  • 1.3 Control of Power Flow …………………..…………………………………..…………....…
  • 1.4 ETAP ………………………………………..……………..….…………………………....….…
• CHAPTER 2 : LOAD FLOW ANALYSIS .…..…..………..…..…..…..…...…...……...
  • 2.1 Power System Description ……………….....….…………….……….…..……….….…….
  • 2.2 Load Flow Analysis for the 36-Bus System (normal condition) …...…….………
  • 2.3 Load Flow Analysis for the 36-Bus System (Maximum Load Condition) ….… - 2.3.1 The Maximum Load Improvement ….………….………….………….……………... - 2.3.1.1 Improvement by increasing the swing bus voltage ….……………..……… - 2.3.1.2 Improvement by Using Tap-Changing Transformers ….……………..…… - 2.3.1.3 Improvement by Using Shunt Capacitor Banks ….……………..…………. - 2.3.1.4 Comparison between the three cases ….……………..………….….………..
  • 2.4 Load Flow Analysis For the 36-Bus System (Minimum Load Condition) ….... - 2.4.1 The Minimum Load Improvement ….………….………….………….………….….. - 2.4.1.1 Improvement by increasing the swing bus voltage ….………….….……... - 2.4.1.2 Improvement by Using Tap-Changing Transformers ….……….….……...
    • 2.5 Load Flow Analysis For the 36-Bus System (Post Fault Condition) ..….……...….
      • 2.5.1 The Post Fault Condition Improvement ….……………..………...….……………..... - 2.5.1.1 Improvement by Using Shunt Capacitor Banks ….……………..………...
• CHAPTER 3: CONCLUSION …………..…..…..…..…..…..…..…..…..…...…..…..……...
  • 3.1 Conclusion …………………..….…………….……………....….…..……………….....………
• BIBLIOGRAPHY ………..….……...…………………..…………....….…..……..………….....…….
• APPENDICES …………..….……...………………………………....….…..……………….....……… - 7 Load Bus 86.106 - 5.1 66. - 8 Load Bus 86.202 - 5.1 74. - 9 Load Bus 86.321 - 5.1 60.
  • 10 Load Bus 86.170 - 5.1 68.
  • 11 Load Bus 86.393 - 5.1 71.
  • 12 Load Bus 85.526 - 5.0 67.
  • 13 Load Bus 86.495 - 5.1 68.
  • 14 Load Bus 85.558 - 4.9 68.
  • 15 Load Bus 86.007 - 5.0 67.
  • 16 Load Bus 85.129 - 4.8 68.
  • 17 Load Bus 85.116 - 4.8 66.
  • 18 Load Bus 85.110 - 4.9 70.
  • 19 Load Bus 85.416 - 4.9 61.
  • 20 Load Bus 76.747 - 9.3 67.
  • 21 Load Bus 81.932 - 6.7 70.
  • 22 Load Bus 82.863 - 5.7 75.
  • 23 Load Bus 80.874 - 7.2 65.
  • 24 Load Bus 79.266 - 9.1 78.
  • 25 Load Bus 77.474 - 9.5 70.
  • 26 Load Bus 79.511 - 8.8 72.
  • 27 Load Bus 80.147 - 7.5 64.
  • 28 Load Bus 79.804 - 8.4 70.
  • 29 Load Bus 78.101 - 10.2 74.
  • 30 Load Bus 78.909 - 8.7 70.
  • 31 Load Bus 78.488 - 9.5 70.
  • 32 Load Bus 78.444 - 8.9 71.
  • 33 Load Bus 76.979 - 9.5 72.
  • 34 Load Bus 76.674 - 9.5 70.
  • 35 Load Bus 77.168 - 9.8 74.
  • 36 Slack Bus 100.00 0.0 62.
• Total Losses 8.407 48. Total Demand 143.465 180.335 230.440 62.26 lagging
• 25 Load Bus 83.709 - 8 5 70.
• 26 Load Bus 85.603 - 7 9 72.
• 27 Load Bus 86.192 - 6 8 64.
• 28 Load Bus 85.875 - 7 .6 70.
• 29 Load Bus 84.303 - 9 2 74.
• 30 Load Bus 85.036 - 7 8 70.
• 31 Load Bus 84.656 - 8 .6 70.
• 32 Load Bus 84.606 - 8.1 71.
• 33 Load Bus 83.260 - 8.6 72.
• 34 Load Bus 82.977 - 8.6 70.
• 35 Load Bus 83.440 - 8.9 74.
• 36 Slack Bus 105.000 0.0 63.

Figure ( 4 ): Load flow analysis after Changing the Tap of the transformers.

Bus Number Bus Type Nominal Voltage PF % Angle 1 Load Bus 99.474 - 4.7 70. 2 Load Bus 97.123 - 4.4 70. 3 Load Bus 96.813 - 4.3 70. 4 Load Bus 96.813 - 4.4 75. 5 Load Bus 96.757 - 4.3 64. 6 Load Bus 96.7 30 - 4.3 74. 7 Load Bus 96.736 - 4.3 67. 8 Load Bus 96.822 - 4.3 74. 9 Load Bus 96.933 - 4.3 61. 10 Load Bus 96.793 - 4.3 69. 11 Load Bus 96.998 - 4.4 71. 12 Load Bus 96.201 - 4.2 68. 13 Load Bus 97.092 - 4.3 69.

14 Load Bus 96.231 - 4.2 68. 15 Load Bus 96.663 - 4.3 68. 16 Load Bus 95.859 - 4.1 68. 17 Load Bus 95.848 - 4.1 67. 18 Load Bus 95.842 - 4.2 71. 19 Load Bus 96.124 - 4.1 62. 20 Load Bus 89.357 - 7.6 67. 21 Load Bus 93.912 - 5.6 70. 22 Load Bus 94.748 - 4.8 75. 23 Load Bus 92.965 - 6.0 65. 24 Load Bus 91.561 - 7.5 78. 25 Load Bus 89.990 - 7.8 70. 26 Load Bus 91.772 - 7.3 72. 27 Load Bus 92.323 - 6.2 64. 28 Load Bus 92.026 - 6.9 70. 29 Load Bus 90.564 - 8.4 74. 30 Load Bus 91.222 - 7.2 70. 31 Load Bus 90.891 - 7.8 70. 32 Load Bus 90.819 - 7.4 71. 33 Load Bus 89.556 - 7.9 72. 34 Load Bus 89.290 - 7.8 70. 35 Load Bus 89.728 - 8.1 74. 36 Slack Bus 105.00 0 63.

Table (7)

Summary of total generation, loading and demand are shown in the following table:

MW Mvar MVA PF

Source (Swing Bus) 147.947 177.921 231. 396 63.94 lagging

Total Demand 147.947 177.921 231. 396 63.94 lagging

Total Losses 7.045 40.

Table (8)

The changing of the tap on the transformers still didn’t achieve the required, so we have to add

shunt capacitor banks.

2.3.1.3 Improvement by Using Shunt Capacitor Banks:

After running the ETAP the load flow results obtained are shown in the tables 9 and 10, other

results are shown in the appendix D, Figure 5 shows the network after adding the capacitor

bank and Figure 6 shows the load flow analysis after installing the capacitor banks.