Compensation Of Transmission Lines

Management of reactive power and voltage control constitute part of the major challenge in power system industry. Adequate reactive power control solves power quality problems like voltage profile maintenance at all power transmission levels, transmission efficiency and system stability. Power demand increases steadily while the expansion of power generation and transmission has been severely limited due to the inadequate resources and environmental forces. These give cause for concern as they contribute to the constant power failure in the Nigeria power system. In this work the Nigeria 330KV network, 30 bus system is considered. To alleviate/eradicate some of these problems mentioned, compensation in power system becomes very essential. Compensation reduces generating MVA and MVAR. The reduction in MVAR helps electrical companies to transmit more power and absorbing more customers without expanding their power networks. Newton-Raphson’s solution method was used to carry out the analysis because of its sparsity, fast convergence and simplicity attribute as compared to other solution methods using the relevant data as obtained from power holding company of Nigeria (PHCN). MAT LAB/SIMULINK method was used to carry out the simulation analysis. The results obtained showed that the bus voltages outside the statutory limit of 0.95 – 1.05p.u that is 313.5 – 346.5KV were buses 14(Jos) with value 0.8171pu, bus 17(Gombe) 0.8144p.u bus 18(Abuja) 0.9402pu, bus 19(Maiduguri) 0.8268pu, bus 22(Kano) 0.7609pu, bus 29(Kaduna) 0.8738pu, and bus 30(Makurdi) 0.8247pu under normal uncompensated condition. Capacitive shunt compensation because of its advantages was implemented on these buses, and the results then came up to tolerable values. Results obtained after compensation reveal acceptable voltage levels at the problem buses. For instance bus 14(Jos) is now 0.9823p.u, bus 17(Gombe) 1.0242p.u, bus 18(Abuja) 0.9667p.u, bus 19(Maiduguri) 1.0455p.u, bus 22(Kano) which is heavily loaded was linked to Jos and a 60 percent compensation on Kano bus yielded an increase of 0.7609pu to 0.947p.u. System efficiency improved from 65% (uncompensated) to 85% after compensation. On the application of 20% over compensation, overvoltages (>1.05pu) resulted which may cause system collapse if not controlled. From the results obtained, installing compensation devices, make it possible to control the amount of active and reactive power flowing through the lines thereby controlling the voltage. It is clear from the results that the use or incorporation of system compensation will lead to many benefits like increasing transmission lines loadability which enables electrical company to transmit more power with the existing transmission lines as well absorb more customers without increasing the network.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

1.0   INTRODUCTION

1.1   BACKGROUND OF THE PROJECT

• PROBLEM STATEMENT
• OBJECTIVE OF THE PROJECT
• PURPOSE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• APPLICATION OF THE PROJECT
• SCOPE OF THE PROJECT
• DEFINITION OF TERMS

CHAPTER TWO

LITERATURE REVIEW

• REVIEW OF THE STUDY
• COMPENSATION IN TRANSMISSIONNETWORK
• POWER FLOW THROUGH A TRANSMISSIONLINE
• PRODUCTION AND ABSORPTION OF REACTIVE POWER
• EFFECT OF REACTIVE POWER FLOW ON LINE VOLTAGEDROP
• RELEVANCE TO HV TRANSMISSIONSYSTEM
• DEVICES USED FORCOMPENSATION
• FLEXIBLE AC TRANSMISSION SYSTEM (FACTS)
• CONTROL OF POWER FLOW
• LOAD COMPENSATION
• EFFECT OF COMPENSATION ON LINE VOLTAGE
• ADVANTAGES OF COMPENSATION

 

CHAPTER THREE

3.0     POWER FLOW PROBLEMS AND METHOD OF ANALYSIS

3.1     THE CHALLENGES IN AC POWER SYSTEM

3.2   METHOD USED

3.3   FORMULATION OF POWER FLOW PROBLEM (NODAL ADMITTANCE MATRIX)

3.4   NEWTON-RAPHSON’S METHOD

3.5    METHODS OF VOLTAGE CONTROL

3.6 MODELING OF REACTIVE COMPENSATING DEVICES

3.7    COMPENSATION EFFECT ON MAXIMUM POWER

3.8     CAPACITOR RATING CALCULATIONS

3.9                 RELATIONSHIP BETWEEN REACTIVE POWER, VOLTAGE AND CAPACITOR (Q,V & C) IN AC POWER SYSTEM

3.10  INPUT DATA USED FOR THE ANALYSIS

CHAPTER FOUR

4.0   NIGERIA POWER SYSTEM AND SIMULATION

• MODELING EFFECT ON POWER SYSTEMOPERATION
• RESULT
• DISCUSSION

CHAPTER FIVE

• CONCLUSION
• CONTRIBUTION
• RECOMMENDATION
• REFERENCES

CHAPTER ONE

1.0                              INTRODUCTION

• BACKGROUND OF THE STUDY

The current incessant power failure in Nigeria has reached an unprecedented level that the public is almost demanding for a state of emergency in respect of electricity supply. The projected power demand for the year 2009/2010 was 10,000 MW but the actual available supply was 3,500 MW. The various efforts made to rescue the power short fall did not yield any meaningful outcome [1].

The research work is to provide a reversal of the above previous situation by looking into the problems and proffer a solution that will minimize if not completely eradicate the problems. In power flow study the frequency should remain nearly constant, because considerable drop in frequency could result  in high magnetizing    currents in induction motors and transformers [2]. The flows of active and reactive powers in a transmission network are fairly independent of each other and are influenced by different control       actions.       Active   power control is closely related        to frequency control, and reactive power control is closely related to voltage control [3]. Since constancy of frequency and voltage are important factors in determining the quality of power supply, then the control of active and reactive power is vital to the satisfactory performance of power system [2]. In this work, the Nigeria integrated power network system is presented in its current state and its parameters are tabulated and examined. After compiling          the generators,        lines, load data, and other parameters, equations for the power flow analysis are then formulated incorporating these parameters. These equations are solved using MATLAB/SIMULINK [3, 4].

Because electrical energy is normally generated at the power stations far away from the urban areas where consumers are located and are delivered

to the ultimate consumers through a network of transmission and distribution, the terminal voltage vary substantially. Wider variation in voltage may cause erratic operation or even malfunctioning of consumers’ appliances.

The main cause for voltage variation is the variation in load on the supply system. With the increase in load on the supply system the voltage at the consumer premises falls due to increase in voltage drop in:

• Alternator synchronous impedance
• Transmission lines
• Feeders and Distributors [5].

A power system is said to be well designed if it gives good quality and reliable supply. By good quality is meant the voltage levels being within reasonable limits. Naturally all the equipment on the power system are designed to operate satisfactorily only when the voltage levels on the system correspond to the rated voltage or at the most the variation are within ±5% of rated value. When the voltage variation is more than a normal value, the performance of the equipment suffers and the life of most of the equipment will be at risk. Due to variation in bus voltages, the fluorescent tube refuse to glow, the picture on a television set starts rolling if the voltage is below a certain level. The torque of an induction motor (which forms about 70% of the total load on power system) varies as the square of the terminal voltage and so on. Thus controlling the voltage on the power system becomes very vital [5, 6].

For reduction of cost and to improve reliability, most of the world’s electric power systems are interconnected. This takes advantage of diversity of loads, availability of sources and fuel prices to supply power to loads at minimum cost.

These days, greater demands have been placed on the transmission network by way of continual addition of load and it will continue to rise because of the increasing number of consumers.

Increased demands on transmission, absence of long-term planning, and the need to provide open access to generating companies and consumers have resulted in less security and reduced quality of supply.

To alleviate/eradicate some of these problems mentioned, compensation in power system becomes very essential. A Compensator can be connected in the power system in two ways that is in series and in shunt at the line ends or even in the midpoint between buses. It is necessary to regulate the voltage of the system at various buses within prescribed limits; else the voltage decreases in magnitude due to the load and the phase angles displaced as a result of the nature of the load (reactive) and the system characteristics.

Control of voltage at each bus is essential for several reasons, some of which include:

• The control    of    the    kilowatts    and    kilovar   flows    over   a    line interconnecting two generating
• The adjustment of consumers’ voltage within the statutory
• Seasonal (5-15%), daily (3-5%) or short period (1-2%) regulation of the voltage at various parts of the system [5, 6].

Flexible AC Transmission System (FACTS), Static Synchronous Compensator (STATCOM), Unified Power Flow Controller (UPFC) are among the newest technology for carrying out compensation in power system to maintain stability.

• 2                               STATEMENT OF THE PROBLEM

Power flow problem is the inability to have the required voltage values and angle at each bus in a power system under balanced three-phase steady- state conditions. Power flow studies involve the computation of voltage

magnitude and phase angle at each bus in a power system. They are essential in planning the future expansion of the system because satisfactory operation of the system depends on knowing the effects of interconnections with other power stations and to have an idea of the effect of new transmission lines before they are installed. It also involves the determination of the voltage magnitude and angle at each bus of the power system network under specified operating conditions. Main consideration in this project will be focused on delivering the reactive power directly to buses in a transmission system, by installing sources of reactive power. The reason is that transmission lines can be operated with varying load and nearly constant voltage at both ends if adequate sources of reactive power are available at both ends. We are required to find the voltage at all the buses and the real and reactive power that flow in all the branches, the losses etc.

• 3                     OBJECTIVE OF THE STUDY

Electricity generation and consumption have always been a basic platform for economic growth and development of any nation. It has been generally accepted that the economy of any nation depends very much on the level of industrialization attained by that country. So to sustain industrial output and ensure rapid growth, there is a great need for a reliable and efficient supply of electrical energy. With the introduction of micro- computer into the market, computations of varying complexities can easily be carried out. It is now the concern of the system engineer or designer to generate a fast method to solve the power flow problem to ensure efficient and durable service.

The main objective of the study is to generate a reliable algorithm using MATLAB 2010 version with Newton-Raphson’s method that will be used to solve power flow calculations, generating the voltage magnitude and angles at each bus for both on-line and off-line applications.

The assessment of the power flow result to find out those buses that are outside the stipulated range, that need to be compensated. The specific objectives of this thesis are;

• To develop a fast power-flow program using MATLAB/SIMULINK network that will be used to solve large network of Nigeria power system with Newton-Raphson’s solution
• To assess the voltage limit at each bus detecting those that are outside the tolerance level. Identification of weak buses in the
• Also the provision of compensation on those buses to improve the system
• To access the limit of compensation that can go with
  • 4                               SIGNIFICANCE OF THE STUDY

In transmission lines receiving end voltage and power factor are two very important aspects to be considered. This study is important in that it used to keep voltage within tolerable limit and to improve power factor, transmission line compensation is done.

1.5                           APPLICATION OF THE STUDY

Power flow is used for line loading, generation adequacy, economic dispatching and unit commitment, all for planning and stability of power system. The implementation of this work would be beneficial to the following group of people.

• Power holding company of Nigeria,
• The Research students
• The ministry of power and energy for policy formulation

It will also offer some economic benefits by way of reducing fault level and improve steady state performance for expansion alternative.

• 6                                 SCOPE OF THE STUDY

Power system control and line compensation are essential for the effective working of power system. Voltage, frequency and power factor are the main items to be controlled. To get the desired voltage at the consumer end voltage control is necessary. Frequency control is done to form a synchronous link between two systemsu having different frequencies. The control of reactive vars will automatically control the power factor of the system. This research work is limited to the study of 330KV, 30 bus system of the Nigeria network in order to alleviate some of the problems hampering the grid network.

1.7                                       PURPOSE OF THE STUDY

The main purpose transmission line compensation is to improve the system stability and voltage control, in increasing the efficiency of power transmission, facilitating line energization and reducing temporary and transient over-voltages.

• 8                                 DEFINITION OF TERMS
• Flexible AC Transmission System (FACTS) is defined as alternating current transmission systems incorporating power electronics-based and other static controllers to enhance controllability and increase power transfer capability [7].

Unified Power Flow Controller (UPFC): It is a compensator that consists of STATCOM and static synchronous series compensator (SSSC) which are coupled via a dc link to allow a bidirectional flow of real power between the series output terminals of the SSSC and the shunt output terminals of the STATCOM. It has the unique ability to control real and reactive power flow independently [7, 8].

• Stability: It is the ability of the power system to remain at stable operation after being subjected to a sudden power change [9].
• FACTS controller: This is a power electronics-based system or other static equipment that provides control of one or more AC transmission system parameters [7].
• Static synchronous compensator (STATCOM): Is a static synchronous generator operated as a shunt connected static Var compensator whose capacitive or inductive output current can be controlled independent of ac system voltage. It is based on a voltage source or current-sourced converter [7].

Transient stability limit refers to the maximum flow of power through a point without loss of stability when sudden disturbance occurs [9].