Effect of speed governor on transient stability of multimachine power system

Abstract

The ,implementation of modern electronic and micro-processor based control system has made the response of speed gov- ' ernors very fast. In this study we have shown the effect of this type of governors on transient stability of a power systern. The interconnected grid system of Bangladesh Power Development Board is taken as a model for this study. The steady state conditions prior to the fault are taken from the drawing no. 3754 N-7013 TO 03' studied by Lahmeyer International, GMBH. Lumping all the generators operating in a power station to a single unit, the set of swing equations for each equivalent.unit are deduced consdering the effect of damper winding and speed governors. In solving the swing equations, the variation of shaft power with rotor speed is calculated from the equations derived for speed control mechanism ,(governor). This derived differential equations are represented in the form of a block diagram. To obtaine the power transfer between different pairs of machines, the driving point and transfer admittances between hypothetical machine internal-voltage-buses were calculated eliminating all other nodes by matrix node elimination method. All the loads were replaced by constant shunt addmittance between ! the corresponding bus ill1dground. Swing equations were solved by Runge -Kutta fourth order approximation method. Three-phase short circuit of four different types covering *- major disturbances, such as generation rejection, load rejection and loss of transmission facilities at four different points were studied considering governor action and also neglecting governor action. Each fault was studied with three different modes of CB operations; (a) without autorecloser, (b) unsustained fault and use of autorecloser and (c) sustained fault and use of autorecloser. Taking Ghorasal-132 equivalent machines as the reference the relative rotor angles of all the equivalent machines were plotted by the computer. The fOllowing facilities are available in the generalized computer program developed for the proposed work: (1) Determination of driving point and transfer admittance at pre-fault, during fault and post-fault conditions. (2) Determination of driving point and transfer impedances at pre-fault, during fault and post fault conditions. (3) Solution of the swing equations by Rungee-Kutta fourth order approximation with or without governor action. (4) Plotting of the swing curves. This program can be used for any number of buses, generators, and CB/Autorecloser time setting.