Reactive power management at high voltage long AC transmission line.

This is to certify that this thesis entitled "Reactive power management at high voltage long AC transmission line." is done by the following students under my direct supervision and this work was carried out by them in the laboratories of the Department of Electrical and Electronic Engineering under the Faculty of Engineering of Daffodil International University in partial fulfillment of the requirements for the degree of Bachelor of Science in Electrical and Electronic Engineering. We hereby declare that this thesis is based on the result found by us. This thesis is submitted to Daffodil International University for partial fulfillment of the requirement of the degree of B.Sc.

This thesis has not been submitted in whole or in part previously for any degree. I would remain forever grateful to the Department of Electrical and Electronics Engineering, Daffodil International University, Bangladesh for giving me the space to carry out this dissertation. It was his guidance and continuous motivation during the course of any doubts that helped me immensely to move forward with this dissertation.

Mohammad Tawhidul Alam Associate Professor of the Department of Electrical and Electronics Engineering for his guidance and support.

LIST OF ABBREVIATIONS

In a high-voltage long AC transmission system, the system voltage changes continuously with the changes of load. The reactive power also changes with the change of load which affects the system voltage, for this reason it is important to analyze the power system to determine system parameters and its variation under various load conditions. Reactive power compensation is defined as the management of reactive power to improve the performance of AC power systems.

In general, the problem of reactive power compensation is related to load and voltage support. Voltage support is generally required to reduce the voltage fluctuation at a particular terminal of a transmission line. Reactive power compensation in transmission systems also improves AC system stability by increasing the maximum active power that can be transmitted.

It also features reactive power compensation by using capacitor banks at different sections of the transmission line.

CHAPTER-1

Introduction
Reactive power
Analogy to explain the reactive power
Necessity of reactive power in power system
Thesis objectives

Voltage management and reactive power management are two aspects of one activity, each supporting reliability and facilitating commercial transactions over transmission networks. On an AC power system, voltage is controlled by managing production and absorption of reactive power. To maximize the amount of real power that can be transferred across a full transmission interface, reactive power flow must be minimized.

The loss of a generator or a serious conductor will have the combined impact of reducing the reactive supply and, at an equivalent time, reconfiguring flow specified the system is intense extra reactive power. A minimum of some reactive supply must be able to respond quickly to ever-changing reactive power requirements and to maintain acceptable voltages throughout the system. Thus, even if an electrical system needs real power reserves to return to contingencies, it must also maintain reactive power reserves.

The reactive power decreases due to inductive load and the maturation of reactive power under inductive load will be observed.

Fig 1.4: Analogy to explain the reactive power [3] Fig 1.5: reactive power explain [3]

CHAPTER-2

Reactive power compensation

Reactive power compensation in power system
Benefits of reactive power compensation
Compensation technique with power electronics device
Types of compensation

Synchronous Condenser

These categories are primarily based on the processes by which the capacitor bank is connected to the system. All the previous advantages arise from the fact that the impact of the capacitor reduces the reactive current flowing through the entire system. A shunt capacitor draws an almost fixed amount of leading current which is superimposed on the load current and consequently reduces the reactive parts of the load and thereby improves the power factor of the system.

Since these are connected in series with the load, the load current always flows through the series capacitor bank. Actually, the capacitive reactance of the series capacitor neutralizes the inductive reactance of the path. Synchronous Capacitor Just like a capacitor bank, we can use an excited synchronous motor to improve the poor power factor of an influencing system.

The main advantage of using synchronous motor is that the progression of power factor is smooth. Suppose that due to a reactive load of the power system, the system draws a current IL from the supply at a lag angle θL with respect to voltage. At present, the overall current drawn from the supply is the resultant of the load current IL and motor current IM.

Therefore, the power factor of the system cosθ is currently over the power the facility of the system before we tend to connect the synchronous condenser to the system. The synchronous condenser is that the additional advanced technique of power output than a static condenser bank, but the improvement of power issues by synchronous condenser below five hundred kVAR is not economical than that by a static capacitor bank. The advantages of a synchronous condenser area unit that we can smoothly manage the power factor of the system while not stepping as per demand.

Just in case of a static capacitor bank, these fine changes of power factor may not be possible, rather a capacitor bank improves the power factor incrementally. Basic schematic of synchronous capacitor and power factor improvement diagram shown in Figure 2.2 and load curve for under- and over-excitation in Figure 2.3.

Fig 2.1: Compensation technique with power electronics device [4]

Chapter-3

FACTS devices

Flexible AC Transmission Systems (FACTS)
Reactive Power Compensation in Power Transmission System by using FACTS: Consumer load needs reactive power that varies continuously and will
Types of FACTS devices
Series compensation

Static Synchronous series compensator (SSSC)
Thyristor-controlled series compensation (TCSC)
Thyristor Controlled Series Reactor (TCSR)
Thyristor Switched Series Capacitor (TSSC)

Shunt Compensation

Shunt capacitive compensation
Shunt inductive compensation

Types of shunt compensator

Static VAR compensator (SVC)
Static synchronous compensator (STATCOM)

Interline Power Flow Controller (IPFC)
Unified power flow controller

In different words, in series compensation, reactive power is inserted non-parallel to the line to increase the impedance of the system. It is capable of transferring every active and reactive power to the system, allowing it to compensate for the resistive and reactive voltage drop – maintaining high effective X/R that is independent of the degree of series compensation. This will reduce the cost of the thyristor and reduce the cost of the controller.

SVCs are part of the flexible AC transmission system family, which regulate voltage, power factor, harmonics and stabilize the system. Before the invention of the SVC, power factor compensation was reserved for large rotating machines such as synchronous capacitors or switched capacitor banks. Then it controls the reactive power flow by changing the DC capacitor input voltage, just because the fundamental element of the converter output voltage is proportional to the DC voltage.

Unlike the GTO-based type, the IGBT-based VSC uses a set DC voltage and changes its output AC voltage by changing the modulation index of the PWM modulator. Furthermore, harmonic voltage is mitigated by installing shunt filters on the AC side of the VSC. Based on this principle, a STATCOM will be used to regulate the reactive power flow by changing the output voltage of the voltage source converter with reference to the system voltage.

This is due to the fact that the maximum capacitive reactive power produced by a STATCOM falls linearly with the system voltage, while the power of an SVC is proportional to the square of the voltage. However, the inverters must be physically close to each other due to the connection of the inverter area unit via a common DC link. Unified Power Flow Controller (UPFC), as a representative of the third generation of FACTS devices, is by far the most comprehensive FACTS device, in the stationary state of the power system, it can perform power flow regulation, reasonably control the active and reactive power of the network, improve the transmission capacity of the power system, and in the transient state of the power system system can realize fast-acting reactive power compensation, dynamically support access point voltage and improve system voltage stability, in addition, it can improve system damping and power angle stability.

The UPFC is a combination of a static synchronous compensator (STATCOM) and a static synchronous series compensator (SSSC) coupled via a common DC connection. The main advantage of the UPFC is to control the active and reactive current flows in the transmission line. The adjustable parameters of the UPFC are in-line reactance, phase angle and voltage. Gyugyi from Westinghouse. The UPFC enables a secondary but important function, such as stability control, to suppress power system oscillations, thereby improving the transient stability of the power system.

The main advantage of the solution is the ability to manage the flow of bulk power within the line while actively processing only a small part of the bulk power.

Chapter-4

Analysis reactive power Application

Generator
Zigzag Transformer
Long Transmission line
RLC loads
Bus-Bar
Analysis 1
Analysis 2(compensation at Generator end)
Analysis 4(Compensation at receiving end Transformer)

Used in electrical networks, the zigzag connection has a number of features of star(Y) and delta(∆) connections. The zigzag transformer connected above MATLAB circuit design for harmonic current and voltage reduction, to provide low resistance to zero sequence currents, for phase shift detection between primary and secondary winding with this connection, gives extra. The last sending transformer absorbed the 33 kv line-to-line voltage and the 500 kv line supply.

A load that draws current during a sinusoidal rise-and-fall pattern along with a sinusoidal change in voltage—that is, the maximum, minimum, and zero points of the voltage and current values over time—is purely resistive and has no other parts. They are usually included in electrical substations to increase the overall "power factor" of the system. Inductive loads increase the cost of a given power system and reduce the amount of energy that is converted to another form of energy.

Power busses are defined as a conductor or group of conductors used to collect electrical energy from incoming feeders and distribute it to outgoing feeders. When a fault occurs, the circuit breaker is tripped, and the faulty part of the bus is also definitely disconnected from the circuit. Electrical busbars are available in rectangular, cross, round and various shapes.

The choice of the busbar depends on the various factors such as reliability, flexibility, cost, etc. Here it is seen that the different portion of power decreases with varying inductive load. The receiving end transformer power is very low and this power also decreases with varying inductive load.

From the figure above, we can say that when we connect the capacitor bank to the output terminal transformer, the output power of the generator and the output terminal power of the transformer are greatly increased. For this reason, a capacitor bank should never be used on a transmitting final transformer. From the figure above, it can be seen that the power levels increase on each section of the transmission line and also increase the power flow through the TX receiving end or the load end.

Figure shows that there is minimum change of power in this system. There is very small change of power with varying capacitor

Chapter-5

Conclusion