VOLTAGE STABILITY may be improved by various control functions. In this paper, it is shown that how High Side VOLTAGE Control (HIVC) may be employed for this purpose. Two test systems, namely a 22- bus and IEEE U8-bus systems are used to demonstrate the proposed tuning strategy for HSVC control parameters.

This paper presents a new fault location method for radial distribution networks with distributed generations. The proposed fault location algorithm uses the VOLTAGE and current data obtained by digital fault recorder installed at the head of the network main feeder, with or without the data from any digital fault recorders installed at DG connection points. The algorithm is based on fundamental frequency calculations and includes novel subroutines of current calculation of DG contained laterals and average loading factor and power factor estimation of the network transformers to solve the fault location problem. The method has been tested by simulation studies using EMTP on a 205-node 20 kV radial distribution network containing three DG's for different data acquisition scenarios. The results verify accuracy of the method under different fault conditions even with only one measuring point at the head of the main feeder.

VOLTAGE STABILITY assessment is one of the critical topics concerning the STABILITY of power systems. With the increasing loading of transmission networks and its impact on downstream networks, the importance of studying this issue has gained attention even more. By presenting a new index, this paper evaluates the VOLTAGE STABILITY of transmission systems. Employing the proposed index, network lines can be assessed in terms of VOLTAGE STABILITY, and this means identifying weak network lines. Besides decreasing the calculation burden, the proposed index can boost accuracy. The index has been extended to consider the impact of the presence of distributed generations (DGs) and on-load tap changers (OLTC). To analyze and calculate the efficiency of the proposed index, two standard 9-bus and 14-bus transmission networks are utilized and the results are compared with other indices, showing that the results related to this index are reasonable and acceptable in comparison with those of other indices and impose a lower computational burden.

This paper presents a new approach for estimating and improving VOLTAGE STABILITY margin from phase and magnitude profiles of bus VOLTAGEs using sensitivity analysis of VOLTAGE STABILITY Assessment Neural Network (VSANN). Bus VOLTAGE profile contains useful information about system STABILITY margin including the effect of loadgeneration pattern, line outage and reactive power compensation, so it is adopted as input pattern of VSANN. In fact, VSANN establishes a functionality for VSM with respect to VOLTAGE profile. Sensitivity analysis of VSM with respect to VOLTAGE profile and reactive power compensation extracted from information stored in the weighting factor of VSANN is the most dominant feature of the proposed approach. Sensitivity of VSM helps one to select the most effective buses for reactive power compensation aimed enhancing VSM. The proposed approach has been applied to IEEE 39-bus test system which demonstrated applicability of the proposed approach.

VOLTAGE inSTABILITY is a major threat for security of power systems. Preserving VOLTAGE STABILITY margin at a certain limit is a vital requirement for today’s power systems. Assessment of VOLTAGE STABILITY margin is a challenging task demanding sophisticated indices. In this paper, for the purpose of on line VOLTAGE STABILITY assessment a new index based on the correlation characteristic of network VOLTAGE profile is proposed. VOLTAGE profile comprising all bus VOLTAGEs contains the effect of network topoloy, load-generation patterns and reactive power compensation on the system behavior and VOLTAGE STABILITY margin. Therefore, the proposed index is capable to clearly reveal the effect of all system characteristics and events on the VOLTAGE STABILITY margin. The most attractive feature for this index is its fast and easy calculation from synchronously measured VOLTAGE profile without any need to system modeling and simulation and without any dependency on network size. At any instant of system operation by merely measuring network VOLTAGE profile and no further simulation calculation this index could be evaluated with respect to a specific reference profile. The results show that the behavior of this index with respect to the change in system security is independent of the selected reference profile. The simplicity and easy calculation make this index very suitable for on line application. The proposed approach has been demonstrated on IEEE 39 bus test system with promising results showing its effectiveness and applicability.

STABILITY challenges in Microgrids (MGs) usually arise from low inertia of Distributed Generation (DG). In this paper, a VOLTAGE STABILITY improvement method is proposed in order to improve MG operation. VOLTAGE STABILITY Index (VSI) is applied to evaluate and improve VOLTAGE STABILITY of MGs including different types of DGs. A new hybrid optimization is introduced to find the optimal operation of autonomous MG and to improve VSI. Operational optimization is performed by finding optimal droop parameters of DGs and sitting wind DGs to reduce energy generation cost. Optimization is defined as a multi-objective function and a hybrid HS-GA algorithm is applied to solve the optimization problem. A new power flow formulation is also proposed in which the steady state frequency, reference frequency, droop coefficients and, reference VOLTAGE of droop based DGs are considered as optimization variables. Results of proposed approach are compared with other methods for 33 and 69-bus IEEE systems using MATLAB software. Results prove the efficiency of proposed approach for operational improvement of MGs.

Methods for calculating Available Transfer Capability (ATC) of the transmission systems may be grouped under Static and Dynamic methods. This paper presents a fast dynamic method for ATC calculations, which considers both Transient STABILITY Limits and VOLTAGE STABILITY Limits as terminating criteria. A variation of Energy Function Method is used to determine the transient STABILITY limit and the determinant of the Jacobian matrix of the system is used as an index to determine the VOLTAGE STABILITY limit. A novel method is used to approximately calculate this determinant. Combining these two methods, an algorithm that calculates ATC, based on both VOLTAGE and angle dynamic STABILITY is presented The advantage of this algorithm, besides considering both VOLTAGE and angle dynamic STABILITY, is its high speed This-speed of calculation makes the algorithm a perfect candidate to be used in screening contingencies and determining those cases that need to be further analyzed. To demonstrate the validity, efficiency, and the speed of the new method, it is used to calculate ATC for numerical examples with 1, 3, 7 (CIGREE), 10,30 (IEEE) and US (Iowa State) buses.