ELSEVIER Electrical Power & Energy Systems, Vol. 19, No. 1, pp. 11-17, 1997 Copyright © 1996 Elsevier Science Ltd Printed in Great Britain. All fights reserved PH: S0142-0615(96)00021-X O142-0615/97/$17.00 +0.oo Effect of generation rescheduling on voltage stability margin K N Srivastava E.R.D.A., Baroda, Power System Cell, Post Box 760, Vadodara-390010, India S C Srivastava* Asian Institute of Technology, EPSM, Energy Program, G.P.O. Box 2754, Bangkok 10501, Thailand One of the recent concerns that power utilities are facing is to maintain the required' system voltage stability margin. This paper investigates the effect of generation reschedul- ing in enhancing the overall system voltage stability margin. A new formulation of generation rescheduling in view of minimization of the slack reactive power injection has been suggested. In addition, conventional optimal power flow (OPF) formulations, with their objectives being the minimization of total generation cost and mini- mization of total system transmission loss, and another formulation of generatwn rescheduling in view of the maximization of the minimum singular value of the power flow Jacobian have been studied. All the four formulations have a more realistic voltage dependent model of the generators and the synchronous condensers. The study has been carried out on three sample systems. Copyright © 1996 Elsevier Science Ltd Keywords: voltage stability, generation rescheduling, margin enhancement I. Introduction The economic recession coupled with environmental and ecological pressures has compelled electric utilities all over the world to serve the !increasing load demand without corresponding increases in their transmission and genera- tion facilities. However, under these stressed conditions the utilities are now facing the problem of maintaining required voltages in some parts of the power system net- work and the increased probability of voltage collapse. While both static and dynamic factors are involved in the phenomena of voltage instability/collapse 1, the static aspects have been conve~fiently used for assessment of the system security and stability. *On leave from the Department of Electrical Engineering, Indian Institute of Technology, Kan~ur-208016, India Received 18 January 1996; accepted2 May 1996 Extensive work exists in the area of steady state voltage stability analysis and margin predictions 1-3. Some of the indices suggested for the static voltage sta- bility are reactive power sensitivity to bus voltage 4'5 stability margin in terms of real or reactive power 6'7, voltage collapse proximity indicator (VCPI) derived from the sensitivity of total reactive power generation to real or reactive load increase s'9, voltage instability proximity indicator (VIPI) based on the closeness of multiple load flow solutions 1°'11, minimum singular value, eigenvalue or 12 19 condition number of the power flow Jacobian - . Tiranuchit et al. 12 proposed an optimal generation scheduling scheme to maximize the minimum singular value of the Jacobian using a linear programming tech- nique. Generators and condensers were modeled by their fixed real and reactive power limits and their voltage dependent capabilities were not considered. Begovic et al.2° demonstrated that by using an optimal power flow strategy to minimize the weighted sum of the abso- lute values of the control actions, the voltage stability can be improved. Traditionally, generation scheduling is performed in view of the minimization of the total fuel cost of genera- tion and/or system transmission loss. These schemes form part of a modern energy management system. Reference 21 presents a review of various optimal power flow strategies being used in practice. However, the effect of these conventional optimal power flow schemes on the voltage stability margin has not been reported in the literature. Hence, the objective behind the work reported in this paper has been: (1) To explore a new scheme of generation rescheduling in view of the minimization of slack bus reactive power injection. (2) To consider the relative impact of the above scheme along with the following OPF models for generation rescheduling on voltage stability enhancement. • Minimization of the total fuel cost of the generation 11