Torsional interaction between non-identical generating units with a coincident torsional mode is investigated. The generators are electrically identical but have differences in their mechanical parameters. The mechanical system of each generator in the two-machine model is represented by. the modal model; this enables independent variation of mode damping, inertia and frequency which is not possible to achieve with the conventional spring-mass representation.The studies show that in a system without series capacitance, differences in mode damping affect the phase deviatioa but not the relative amplitude of torsional oscillations; the opposite being true for mode inertia and frequency differences. The amplitude and phase characteristics are both greatly affected by series capacitance for a difference in any mechanical parameter.
Power System Stabilizers (PSS) work well at the particular network configuration and steady state conditions for which they were designed. Once conditions change the performance degrades. This can be overcome by an intelligent nonlinear PSS based on fuzzy logc. Such a fuzzy logic power system stabilizer (FLPSS) is developed, using speed and power deviation, as inputs and provides an auxiliary signal for the excitation system of a synchronous motor, in a multimachine power system environment. The FLPSS's effect on the system damping is then compared with a conventional power system stabilizer's (CPSS) effect on the system. The results demonstrate an improved system performance with the FLPSS and also that the FLPSS is robust. Synchronous Motor 0.02ljo.67 5 Synchronous generator
The paper investigates the effect of adding a second 1072 MVA turbogenerator to an existing one in a power station feeding a series capacitor compensated transmission line. In carrying out the investigation, the new two-generator system is modelled as one equivalent generator with increased capacity, and also as a multimachine system with two separate generators. A comparison of these models shows that, for this type of stability study and this transmission system configuration, there is no advantage gained in modelling the two generators separately rather than as one equivalent generator. The results further show that conditions can exist where the system is stable with one generator but unstable with two, and vice versa. List of principal symbols d, q = d, g-axis of a machine rotating reference frame D, Q = D, Q-axis of the synchronously rotating reference frame [D] = shaft damping matrix [G] = rotational voltage inductance matrix H = inertia constant in seconds i = vector of axis currents [/] = identity matrix [J] = shaft inertia matrix [X] = shaft stiffness matrix [L] = machine inductance matrix N = compensation level p = derivative operator d/dt P t = generator terminal power [A] = machine resistance matrix s ( = ith natural frequency T = forcing torque vector T e = electric torque T m = shaft mechanical torque v = vector of axis voltages V b = infinite bus voltage V t = generator terminal voltage H>,-= ith mode shape vector X c = transmission line capacitive reactance 0 = null vector q> = flux linkage A = small change operator ) H = ith eigenvalue 8 = rotor angle vector co 0 = system frequency in rad/s (electrical) co = angular velocity of rotor in rad/s (electrical)
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