LOAD FLOW IN A 330KV GRID NETWORK BY FAST DECOUPLED METHOD
The Nigerian 330kV grid network is characterized with major problems like voltage instability (voltage profile violation), long transmission lines, nature of transmission lines and high power losses which affect power generation and distribution systems. This paper considered the load-flow study of the Nigerian 330-kV consisting of 32 buses, 11 generating stations and 36 transmission lines using fast coupled method. Load flow study is a numerical analysis of the flow of power in an inter- connected power system. This analysis has been done at the state of planning, operation, control and economic scheduling. Results of such an analysis have been presented in terms of active power, reactive power, voltage magnitude have been required for solving these equations. Objective of this paper is to develop a MATLAB program to calculate voltage magnitude and phase angle, active power & reactive power at each bus. In this work fast decoupled method was used for load flow analysis: Fast-Decoupled method, have been used and the method has been analysed on the basis of number of iterations obtained.
CHAPTER ONE
1.0 INTRODUCTION
Since Electrical Energy is the pivotal upon which a country’s development is anchored, hence, the ever-increasing demand of electric power. Power is usually generated at specific locations far from load centers before it is delivered to consumers through transmission and distribution systems. The Nigerian power system network, like any other networks elsewhere is made up of the large interconnected network that spans across the country nationwide. One of the main challenges combating this network is the fact that most Northern parts of the system usually experience poor voltage profile as a result of shortage of reactive power support. Other challenges include fragile transmission lines, inability of transmission lines to transport more than 400MW of power, radial network and high losses 1. This study classifies buses whose voltages are extremely below statutory limit of ±5% (346.6kV [1.05pu] to 313.5kV [0.95pu] as a result of reactive power shortage as “weak buses”. This problem is more amplified in relatively weak networks having high resistance to reactance ratios.
In load flow study, the main objective is to determine the complex bus voltages, and real and reactive power injected into the transmission system as well as real and reactive power at the slack bus with other parameters being specified. Load flow analysis usually finds its application during power network design and planning. It is also useful for obtaining the system behavior during operation in order to predict the loading conditions of transmission lines and equipment’s within the system. The system is usually assumed to be operating under a balance condition such that the analysis can be carried out using a balanced single-phase representation 3 .
The on-going reform in the Nigeria Power sector, among its numerous objectives, is to produce radical expansion of the existing grid network. It is expected that in the next few years, a much larger, fortified and stable grid will replace the scanty, unstable and fragile grid that exists presently. This is a major objective of the on-going reform in the power sector. As a solution to the country’s present power crisis, caused majorly by a weak grid network, the Nigerian government has mapped out a reform program for the power sector which has in its short term plan the objective of expanding the grid to a total generation capacity of 10,000MW by the year 2011. The proposed grid network has 49 buses, 17 generating stations of 10,000MW total power generation capacity and 9,156km transmission lines. When this is compared with the existing network with only 31 buses, 6,000MW total installed power generation capacity and 4889.2km transmission lines, the expansion process would be regarded as a radical one. The rapid increase in the demand for electricity as a result of population growth, industrial development and rise in consumer electrical appliances have necessitated the stepping up of generation and transmission capabilities of the grid network to deliver quality power supply to the consumers. Various researches have shown that the existing grid network is inadequate and lacks the capacity to provide the right quantity and quality of power for the whole country [1-4]. It must be noted however that most of the solutions proffered by these researchers demand moderate expansion and changes in the grid network. The detailed load flow study of the emerging grid was carried out on the Nigerian power grid with focus on the 330kV power transmission lines, all generating stations and 330kV substations.
|
Pre- |
Post- Reform 330kV Network |
Number of Generators |
11 |
17 |
Total capacity(MW) |
6,000 |
10,000 |
Number of Buses |
31 |
49 |
Length of Transmission |
4889 |
9156 |
Number of Single Lines |
16 |
37 |
Number of Double Lines |
13 |
27 |
Number of Loops |
3 |
9 |
1.2 OBJECTIVE OF THE STUDY
The main objective of this work is to solve power flow problem by determine the steady- state complex voltages at all buses of the network, from which the active and reactive power flows in every transmission line and transformer using fast decoupled method.
1.3 PURPOSE OF THE STUDY
The purpose of any load flow analysis is to compute precise steady-state voltages magnitudes and angles of all buses in the network, the real and reactive power flows into every line and transformer, under the assumption of known generation and load.
1.4 SCOPE OF THE PROJECT
This study presented the method to analyze power flow of power system consisted of HVDC system. HVDC was modeled as the complex power injections. The presented complex power injected was incorporated into the existing power flow program based on fast decoupled method. The presented method was tested on the multi-machine power system.
1.5 SIGNIFICANCE OF THE STUDY
The Fast Decoupled method presented a slight increase in number of iterations with increasing number of buses but with faster convergence, when compared to other methods.
Since active power P is closely associated with power angle but it is less associated with bus voltage magnitude. An important characteristic of any practical electric power transmissions system operating in steady state is the strong interdependence between real powers and bus voltages angles and between reactive powers and voltage magnitudes .This interesting property of weak coupling between P - and Q-V variables gave the necessary motivation in developing the decoupled load flow (DLF) method, in which P−and Q-V problem are solved separately .In any conventional Newton method, half of the elements of the Jacobean matrix represent the weak coupling, and therefore may be ignored' Any such approximation reduces the true quadratic convergence to geometric one.
The main advantage of the Decoupled Load Flow (DLF) as compared to the NR method is its reduced memory requirement in storing the Jacobian. There is not much of an advantage from the point of view of speed since the time per iteration of the DLF is almost the same as that of NR method and it always takes a number of iterations to converge because of the approximation.
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