Generation Transmission Congestion For Improved Stability

ABSTRACT

In the expanding transmission network, Congestion management and voltage stability are significant issues to be handled. Congestion management can be improved by increasing the power transfer capability or by reducing the system losses. With proper VAR support, the issue of voltage instability can be vanquished. Adaption of Flexible AC Transmission System (FACTS) devices is a techno-commercial manner to overcome the above issues. Unified Power Flow Controller (UPFC) is a pliable FACTS device which can control active power, reactive power and voltage injections concurrently in an efficient manner. In this paper power flow model of UPFC is described, location of UPFC is determined by Line Utilization Factor (LUF) and Line Voltage Stability Index (Lmn index) in order to find out the lines which are more vulnerable for congestion and voltage instability. The effectiveness of UPFC is tested on IEEE-14 bus system using MATLAB software. The results are compared with Placement and without placement of FACTS device.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

GLOSSARY

CHAPTER ONE

• INTRODUCTION
• AIM OF THE STUDY
• SCOPE OF THE STUDY
• STATEMENT OF PROBLEM
• SIGNIFICANCE OF THE STUDY
• CAUSES OF POWER CONGESTION
• IMPACTS OF GENERATION AND TRANSMISSION CONGESTION

CHAPTER TWO

LITERATURE REVIEW

• OVERVIEW OF THE STUDY
• REVIEW OF THE RELATED STUDIES
• STUDY OF VARIOUS CASES FOR CONGESTION MANAGEMENT IN DIFFERENT COUNTRIES
• CONGESTION MANAGEMENT TECHNIQUES

CHAPTER THREE

3.0     METHODOLOGY

3.1     PLACEMENT OF UPFC

3.2      POWER FLOW MODEL OF UPFC

CHAPTER FOUR

• RESULTS

CHAPTER FIVE

• CONCLUSION
• REFERENCES

GLOSSARY

FACTS = Flexible AC Transmission   Systems

TCSC = Thyristor         Controlled Series  Capacitor

UPFC = Unified    Power    Flow Controller

GA = Genetic Algorithms.

OPF = Optimal Power Flow

CHAPTER ONE

1.1                                              INTRODUCTION

With the significant increase in power demand in the few past decades, the size of the power transmission network have been improved in vertically integrated environment as well as deregulated power sector. However, the Congestion management and voltage instability problems are challenging issues for the secured and reliable operation of power system.

Congestion in transmission refers to inability of transmission line to deliver power to  the desired customer due to simultaneous transactions or insufficient transmission capacity of transmission line [1]. In deregulated power market congestion management is very complex task for system operator when compared to regulated system [2]. The literatures [3-4] have explained different methods and techniques of congestion management. Different problems due to congestion and congestion management by FACTS devices are explained in [5].

We have variant definitions for Voltage stability in literature, as per IEEE/CIGRE voltage stability is defined as ability of a system to take care of voltage in order that once load admittance is raised, load power can increase and that each power and voltage square measure manageable [6]. Voltage instability problem raises due to heavily loads, inability to meet VAR demand, line outages etc., [7]. Voltage stability analysis, assessment techniques and control methods are explained in references [8-10].

If the transmission system is incapable of handling congestion management and voltage stability it leads to problems of outages, block-outs etc., which dangers the system security and reliability [11]. In order to overcome the above problems FACTS devices are to be allocated in optimal places [12]. M. Esmaili [13] proposed a method for optimal location and sizing of series FACTS device Thyristor Controlled Switched Capacitor (TCSC) based on priority list and Locational Marginal Pricing (LMP).Based on reactive power loss and real power flow performance index TCSC is placed [14]. UPFC have been placed for congestion management based upon Power transmission congestion distribution factor [15], sensitivity analysis and LMP [16]. Voltage stability index also used for congestion management [17] and the voltage stability have been improved by UPFC placement [18]. Based on Newton-Rapshon Optimal Power Flow (NR-OPF) method UPFC have been placed, which enhances the voltage profile and power transfer capability simultaneously[19].

In this paper Line Utilization Factor (LUF) and Line Stability Index (Lmn- index) are used for placement of UPFC. Also Voltage Collapse Proximity Index (VCPI) and Active Power Performance Index (APPI) are calculated before and after placement of UPFC in order to observe the performance of UPFC in congestion management and voltage stability. The performance of FACTS device is tested on IEEE-14 bus system for different loading conditions.

1.2                                         AIM OF THE PROJECT

Power generation and Transmission congestion is a vital problem in the power system security and reliability sector. To ensure the stable operation of the system, a congestion free power network is desirable. The aim of this work is to discuss and apply techniques used in clearing congestion in power system.

1.3                                      SCOPE OF THE STUDY

In this paper, a new Congestion Management (CM) technique, the FACTS devices are  a handy FACTS device named Unified Power Flow Conditioner (UPFC) is used. We have placed the UPFC based upon line burden and voltage stability indices namely Line Utilization Factor (LUF) and Lmn-index. The impact of UPFC in congestion relief and Voltage stability improvement are assayed through Active Power Performance Index (APPI) and Voltage Collapse Proximity Indicator (VCPI).

1.4                                    STATEMENT OF PROBLEM

The occurrence of congestion in power systems leads to system disturbances that cause further outages in an interconnected system. Congestion is also caused by grave damage to power system components if system outages frequently occur. It is not only equipment which is harmed by congestion, but also the power quality [8]. To prevent power system equipment from being damaged and to enhance power quality, congestion systems need to function immediately.

1.5                                 SIGNIFICANCE OF THE STUDY

The importance of congestion management is discussed in reference [6], which identify the congestion management as one the key issues to maintain security and reliability of transmission networks. Congestion management balances the system and solves financial issues arising from the congestion. Lack of attention to congestion in the system may lead to widespread blackouts associated with negative social and economic consequences.

1.6                              CAUSES OF POWER CONGESTION

In deregulated environment, the term Transmission Open-Access (TOA) indicates that the transmission network is freely available to the other market participants such as generators, customers, or other utilities that want to use the transmission network for power transaction between them and thus creates a situation in which transmission network is not able to accommodate all the desired transaction due to violations of some system constraint, this is known as congestion. The congestion may be caused due to various reasons, such as:

1. transmission line outages
2. generator outages and

• change in energy demand.

Other reasons, due to which congestion problem has increased in recent years, are as follows:-

1. Deregulation of power industry has caused the electricity price to be lower, better service quality and electricity in bulk can be sent across-border in competitive electricity markets. Such transmission of bulk power may cause the electricity networks to reach their physical limits.
2. In deregulated environments, if transmission capacity is not enough then there is a lack of investment in electricity networks in order to meet the demand and generation. Or, it can be said that transmission capacity relative to peak load, has become less in many countries.
3. Due to the integration of wind generation into electricity transmission networks, it is difficult to manage congestion because of fast changing power flows of electricity networks caused by wind power fluctuations.

1.7       IMPACTS OF GENERATION AND TRANSMISSION CONGESTION

In the deregulated power industry, generation and transmission congestion is a major problem for the electricity markets. The congestion has a wide range of impacts on the entire electricity market as well as the individual market players i.e. sellers and buyers.

Without congestion lowest-priced resources are used to meet the demand but if the congestion is present in the transmission network then it prevents the demand to be met by the lowest-priced resources due to transmission constraints and some energy is purchased from alternative sources at higher prices. But if this price exceeded than the willingness to pay of the buyers, then some of the demand is not fulfilled in the particular market. This condition occurs especially in area where demand exceeds the local generation. This demand can be met by the imports of electricity from other areas. The suppliers at the import side may raise their prices as high as they want and results in an increase in Locational Marginal Prices & creates market power.

The LMP at a location is the marginal cost of supplying the next MW of load to the location using the lowest production cost of all available generation without violating any system security limit. Market power is defined as the conditions where a market participant can profitably maintain prices above a competitive level for a significant period of time. Market power results a decrease in competition and exercising market power can raise price and lower market efficiency. There are two sources for the occurrence of market power i.e. market dominance and congestion. In the electricity market, a supplier can exercise market power by either physical withholding or economical withholding.

As the presence of congestion on the grid prevents the use of the lowest-priced resources to met the load, therefore change of the generation/demand schedule is required that will result in higher cost than that for the unconstrained market and hence a loss in the market efficiency occurs due to the change in the generation/demand schedule.

1. Congestion Impact On Market Efficiency

To show the impact of congestion on market efficiency a two zone system connected by an interface is considered. Let each zone have a 100 MW constant load. Zone A has a 200 MW generator with an incremental cost of $10/MWh and Zone B has a 200 MW generator with an incremental cost of $20/MWh.

Without any transfer limit between zones (without congestion), all 200 MW of load will be bought from generator A at $10/MWh, and the cost will be $2000/h, as shown in Fig. 1(a). If there is a 50Mw transfer limit, then 150 MW will be bought from A at $10/MWh and the remaining 50 MW must be bought from generator B at $20/MWh, at a total cost of $2500/h. Thus Congestion has created a market inefficiency of 25% of the optimal costs.

Fig.1 Without Transmission Congestion

Fig.2 With 50MW transfer limit Two zone system

Congestion has also created unlimited market power for generator B. Generator B can increase its bid as much as it wants, because the loads must still buy 50 MW from it.

1. Congestion Impact on Market Players

Congestion affects virtually each market players either in a positive or in a negative way.

At the import side buyer may suffer a decrease in consumer surplus because due to transmission constraints it has limited access of energy from other resources, therefore he has to buy energy from the higher-price seller located at the import side. This lack of choice causes either the higher payment prices or reduced purchases of energy. Therefore, the buyer’s consumer surplus decreases. However, a seller located at the import side may offer his output at higher prices, and if the demand is fixed and buyer can afford the price them seller may sell more energy, resulting in an increased producer surplus.

Conversely, a buyer at the export side will have an increase in his consumer surplus because it may increase its energy purchases if the buyer’s willingness to pay is high. However, a seller located at the export side may suffer a decrease in his producer surplus.