CHAPTER ONE
INTRODUCTION
1.1 PREAMBLE
Electrical energy is an essential ingredient for the industrial and all-round development of any country. The quality of life in any country is highly dependent on a reliable electricity supply. The frequent system collapses in the Nigerian power sector have severally thrown or plunged the nation into darkness due to system instability in the Nigeria electric power system. The epileptic nature of the supply has led to low economic growth and dissatisfaction among the citizenry. To assist in overcoming the instability problems, analysis of the Nigerian electric power system transient stability is carried out employing Newton-Raphson method of load flow solution and fourth order Runge Kutta method in mat-lab software package environment [1, 2, 3].
The objective of any electrical power system is to generate electric energy in sufficient quantities at most suitable locality, transmit it in bulk quantities to the load centre, which is then distributed to the individual consumers. In carrying out the desired objectives, the electric power system is faced with unforeseen circumstances such as faults. Under this condition, the system voltage collapses resulting in a dangerous high current. This causes instability within the system which can result in system breakdown if adequate care is not taken [4, 5].
In order to avoid these undesirable situations, it becomes necessary to, before hand; predict with a very good accuracy, the extent of voltage, current and power distribution within the system at anytime so as to know the protective devices to be incorporated to handle the abnormal conditions. Hence under these dangerous situations, the transformers, lines, generators, cables, bus-bars etc. need to be protected [2, 6, and 7].
The transient stability analysis which is the main concern of this work, deals with the state of the synchronous machine during a fault in the system. It gives the state and position of the load. The digital computer is an indispensable tool for power system analysis, computational algorithms for various system studies such as load flow, fault-level analysis, stability studies etc. It gives an acceptable working accuracy to the ever widening complex power system of modern times [8, 9].
- THE OBJECTIVES OF THE STUDY.
These include the following:
i To determine the critical clearing angle and time of the Nigerian
330KV protection system.
ii To determine the behavior of the Nigerian power system during
large scale disturbance and make necessary recommendations.
iii To specify the circuit break speeds in the system
iv To determine the available transfer capability (ATC) of the
Nigerian 330KV grid system during fault and make
recommendation for improvement such that the system is
transiently stable.
1.3 SCOPE OF STUDY
The dissertation work covers the Nigerian 330KV power system. All the thirty-four (34) buses in the network are critically examined and analyzed with regard to transient stability .
1.4 Methodology
In this work, the composition of the Nigerian 330KV Electric power
system (the national grid) is looked into and the critical clearing time
and angle evaluated and determined using fourth (4th) order Runge
Kutta method after obtaining power flow solution results with
Ifnewton power flow program(Newton-Raphson Method) and other
programs such as Lfybus, Busout, Trstab, Afpek, Dfpek, Ybusaf,
Ybusbf and Ybusdf in Matlab software package environment such that
the probability of total system collapse is reduced to the barest
minimum.
Power holding company Plc. 330KV electrical network
single Line diagram is used for this study. The generators,
transmission lines and transformer parameters are taken from the most
up-to-date data from National control centre, Oshogbo System
Planning unit and system operations department. The subtransient
reactance X11 of the synchronous machines is used to give maximum
fault levels at the instant of fault.
The MATLAB function ode 23 will be employed to solve the 2m
first order swing equation to give the desired result.
The performance of protective system during transient period will be
Evaluated. Heavy Egbin – Ikeja West 330KV line will be faulted
And be removed and the system critical clearing time and angle
determined such that the Nigerian power system is transiently stable
thereby averting widespread black-out
1.5 NEED FOR STABILITY STUDIES
In general, stability studies are very important primarily from the stand point of determining the maximum amount of power that can be transmitted without instability being incurred under steady state conditions or as a result of load changes or faults. Potential stability problems are still the most critical impediments to maximizing power transfers across interconnected power systems like the Nigerian national grid. Occurrence of transient instability problems may result to large excursions of the system machines rotor angle, and if corrective action fails, loss of synchronism among generators may result in total system collapse. Recall that in the summer of 1996, two major transient disturbances occurred in the Western system co-ordinating council in United States of America which resulted in partial black-outs that cost the power utilities and their customers several Millions Dollars[13].
In Nigeria, two system collapses within a three-day interval in March 2000, plunged the entire nation into darkness. The nation was without electricity for up to 72 hours in some areas with serious social, economic and security implications. This incident led to the sacking of the power utility [NEPA] board and the appointment of a Technical Board to oversee the day to day activities of the Authority [13, 18].
The transient stability of a power system is normally taken as very important and a major determinant of the stability of the power system because of its non-linear character, its fast evolution and its disastrous practical implications.
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