Krishna S

Undervoltage load shedding serves to maintain voltage stability when a majority of loads are fast acting. An undervoltage load shedding scheme should address two tasks: The detection of voltage instability following a large disturbance and the determination of the amount of load to be shed. Additionally, in case of short-term voltage instability, the scheme should be fast. This paper proposes a method to predict voltage instability arising due to a large disturbance. The amount of load to be shed to maintain voltage stability is then determined from the Thevenin equivalent of the network as seen from the local bus. The proposed method uses local measurements of bus voltage and power, and does not require knowledge of the network. The method is validated by simulation of three test systems subjected to a large disturbance. The proposed scheme is fairly accurate in estimating the minimum amount of load to be shed to maintain stability. The method is also successful in maintaining stability in cases where voltage collapse is detected at multiple buses.

Voltage stability is an important aspect in power system planning and operation. In this paper, the applicability of first-order eigenvalue sensitivity for preventive control and planning of reactive power compensator for voltage stability is investigated. First-order eigenvalue sensitivity is used to determine the most suitable generator for rescheduling and to find the best location for shunt reactive power compensation. The change in generation and the amount of shunt compensation required are determined from the sensitivities obtained. Voltage stability depends on load dynamics. Loads are therefore represented by a dynamic model. Analysis is carried out on the 17-generator, 162-bus system and the results are presented. © 2012 IEEE.

The problem of voltage stability is closely related to load dynamics. In this paper, voltage instability due to small disturbances is analysed using eigenvalue method taking into account the dynamics of the generators and the load. Participation factor analysis is employed to find out the participation of different state variables in eigenvalues of the system. In small disturbance voltage stability studies, the eigenvalues of importance are those corresponding to the loads. The paper discusses how the method of selective computation can be employed to quickly compute the eigenvalues associated with loads. A study is performed to determine whether the selective computation of eigenvalue performed by retaining a state variable results in the eigenvalue in which the retained state variable has maximum participation. Voltage instability, when eigenvalue associated with load is positive, is demonstrated using simulation of two test systems subjected to a small disturbance.