(1) A New Transient Stability Analysis with Automatic Voltage Regulators, Turbine-Speed Governors, and Saturation Effect via Trapezoidal Method Dr. M.F. Al-Kababji Mr.Ahmad Nasser B. Al-Sammak B.Sc., M.Sc, Ph.D. B.Sc., M.Sc. Electrical Engineering Department University of Mosul Mosul - Iraq Abstract In this paper, step-by-step Trapezoidal method is applied to a power system to solve the differential equations those relate the actions of the transient stability, in which generators are installed with automatic voltage regulator (AVR), turbine-speed governor (TSG), and the effect of the saturation is also included. The results compare the individual and combined effects of those controllers. Saturation is modeled by two parts, i.e. excitation and generator saturation. The action of the inertia constant on the swing curve is shown in results. List of Symbols Vt = Terminal voltage. Ei’ = internal voltage(Ef ). X’ d = Direct-axis transient reactance. X’ ds = Direct-axis transient reactance with saturation effect. X P = Potier reactance. δ = generator rotor angle. V t = generator terminal voltage. Pm = mechanical power. Pe = electrical power. Qe = Reactive power. ω = Speed. K A , KE = Regulator and exciter gain. T A , TE = Regulator and exciter time constant. 1 Introduction The main object of this paper is to study the system transient stability by including the general AVR and TSG aided with the saturation effect. Upon a time, many attempts have been made in such a field of work. A historical review to the previous works would be made to get a better understanding for the methods available and used for such a kind of work. However, each method has its merits and demerits according to the task and available auxiliary tools to perform that job, e.g. computers. In general, there are many models that simulate the power system stability problem. The models could be classified according to the system basic equipment inclusion, regarding less the used numerical method for solving the transient stability problem. In all the Refs. [1-13] the saturation effect did not included. The authors, in generic, could be divided into two groups. The first group made their study by AVR adoption only [1-4] , the best one among them is given in Ref. [2] which used the most famous practical model of AVR modeling (AVR type one). While the second group did include the AVR and TSG [5 -9] . The best one among this group of literatures is given by Ref. [9] , to which the results are made for only one-machine-system with a simplified method for the modeling of the AVR and TSG. Recently, authors provide a better understanding for power system transient stability problems and more specifically for the construction of computationally feasible transient stability algorithms associated with power system changes [10 -13] . In fact, AVR effect is embodied; while TSG is not included despite its role and great effect on system. Saturation effect is another neglected parameter in spite of its influence K F , TF = Feedback gain and time constant of AVR. S E = Saturation function of the exciter. S G = Saturation function of the generator. R = Governor drop. T1, T2, T3 = Governor time constant. T4 = Turbine time constant. T w = Water flow time constant. tc = Period of the disturbance. Tmax = Maximum simulation time. dt = Time interval. T = Time constant. H = Inertia constant. D = Damping coefficient. f o = Rated frequency. The Scientific Journal of Tikrit University, Vol.6, No.5,1999