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.

This paper presents some results on the accuracy of normal form analysis for large deviations from the stable equilibrium point (SEP) in a power system. The results of studies on the region of convergence of Neumann series, which is required for normal form analysis, are presented. A polynomial function approximation is proposed to model the generator exciter limiter. Studies on the accuracy of higher order normal form analysis for large deviations from SEP are presented. Use of Prony analysis in addition to simulation is proposed for the verification of accuracy.

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.

This paper investigates the accuracy of normal form analysis applied to power systems. The steps involved in the method of normal forms are described. The approximations involved in the method of normal forms which can lead to inaccurate results are given. The accuracy of the method is dependent on the convergence of Neumann series used to obtain the inverse of a matrix in one of the steps. Studies on the convergence of Neumann series are conducted on a SMIB system. The region of convergence of Neumann series in the phase plane is determined.

Underfrequency load shedding (UFLS) is a common practice to protect a power system during large generation deficit. The adaptive UFLS schemes proposed in the literature have the drawbacks such as requirement of transmission of local frequency measurements to a central location and knowledge of system parameters, such as inertia constant H and load damping constant D. In this paper, a UFLS scheme that uses only the local frequency measurements is proposed. The proposed method does not require prior knowledge of H and D. The scheme is developed for power systems with and without spinning reserve. The proposed scheme requires frequency measurements free from the oscillations at the swing mode frequencies. Use of an elliptic low pass filter to remove these oscillations is proposed. The scheme is tested on a 2 generator system and the 10 generator New England system. Performance of the scheme with power system stabilizer is also studied.

During a false data injection attack (FDIA), the attacker compromises the meter readings to corrupt the state estimator's output. One method of managing FDIA is by securing meters that are most vulnerable to attacks. The existing methods may not secure the most vulnerable meters, and may not work in practical scenarios where the utility has budget and time constraints. To solve these issues, a novel vulnerability index is proposed in this paper. The advantage of using the proposed index in finding meters to be secured is demonstrated using IEEE test systems.

Online dynamic security assessment involves analyzing the effect of a large number of contingencies in a short time. This is a computationally demanding task, and use of energy function method reduces the computational burden. Energy function method involves determination of a quantity called critical energy which requires system simulation for a short duration. In spite of the use of energy function method, there is a significant computational requirement since a large number of contingencies have to be analyzed. In this paper, a comparison of the performance, in terms of accuracy and speed, of different numerical methods in the determination of critical energy, is presented.

One major cyber-threat to energy management system is false data injection attack, where an attacker corrupts a set of meters maliciously in such a way that the conventional methods cannot detect it. For an n bus power system, a method to prevent such threats is by securing a set of (n-1) meters, called a basic measurement set (BMS). We prove, in this paper, that the failure in the protection system of a single meter in a BMS is sufficient to create the most vulnerable form of attacks, if the BMS is not chosen appropriately. Selecting the appropriate BMS (called optimal BMS) is formulated as a multi-objective combinatorial optimization problem. First, a greedy algorithm is developed to find the optimal BMS. Second, if all the necessary meters cannot be secured, a greedy algorithm is developed for securing less than (n-1) meters in an optimal BMS, in such a way that the vulnerability of attack is minimum. Our simulation results confirm that there is a significant improvement in security when the optimal BMS is chosen.

The conventional derivation of the expression for inductance of power transmission lines given in books is more a recipe than a derivation starting from a law of physics. The serious shortcomings of the traditional approach are that the defi nition of flux linkage lacks strong connection to Faraday's law, and unnecessary assumptions are made. This paper gives a complete rigorous derivation of the expression for inductance of power transmission lines. This paper will help instructors as well as students, since it addresses the defi ciencies present in the derivation given in textbooks.

In a false data injection attack to compromise the results of state estimation, the attacker intends to alter the meter readings communicated to the control center to his/her desired values to realize an objective. However, to avoid detection, the manipulated readings should not violate physical laws. Therefore, even if an attacker is able to attack a set of meters, he/she may not be able to inject an arbitrary magnitude of attack into all meters of this set. In this paper, we study the degrees of freedom in the attack vectors available to the attacker; higher degrees of freedom pose a higher risk to the utility. We propose an algorithm to determine the degrees of freedom in attack vectors and a method to find the set of meters to be secured in order to minimize the degrees of freedom in all attack vectors. Our results show that a significant reduction in degrees of freedom in all attack vectors is possible by securing a small set of meters.