Volume 14, Issue 2 -

: In this paper, we make an attempt to describe the phenomenon of wave propagation when a disturbance is introduced in an electromechanical system. The focus is mainly on generator trips in a power system. Ordering of the generators is first done using a sensitivity matrix. Thereafter, orthogonal decomposition of the ordered generators is done to group them based on their participation in different modes. Finally, we find the velocity of propagation of the wave and the transport delay associated with it using the ESPRIT method. The analysis done on generators from the eastern and western regions of India. 1

: For the assessment of voltage instability which comprises the detection of voltage instability and identification of critical buses, two indices namely, system wide Qtax, and bus-specific qtax, are proposed. The Qtax, based on the sensitivity of the reactive power injections to the loading in the system provides early detection of impending voltage instability. The computed qtax indices identify the critcal buses among the load buses in the system. The identified critical buses provided optimal lacations for the corrective control actions for averting voltage instability. Additionally, for voltage stability monitoring, determining the poing of exhaustion of the reactive reserves in system is also crucial. This is addressed by proposed Q-Monitoring Index (QMI), which is the ratio of the reactive component of the source current to the sink current that flows through the adjacent transmission line. These proposed indices together can provide early indication to impending voltage instability. This has been illustrated on IEEE-39 bus system. The reactive support on identified critical buses results in maximum increase in the loadability of the system.

: A New Voltage Source Converter (VSC) based on neutral clamped three-level circuit is proposed for High Voltage DC (HVDC) system. The proposed VSC is designed in a multipulse configuration. The converter is operated by Fundamental Frequency Switching (FFS). A new control method is developed for achieving all the necessary control aspects of HVDC system such as independent real and reactive power control, bidirectional real and reactive power control. The basic of the control method is varying the pulse width and by keeping the dc link voltage constant. The steady state and dynamic performances of HVDC system interconnecting two different frequencies network are demonstrated for active and reactive power control. Total number of transformers used in this system are reduced to half in comparison with the two-level VSCs for both active and reactive power control. The performance of the HVDC system is improved in terms of reduced harmonics level even at fundamental frequency switching. The harmonic performance of the designed converter is also studied for different value of the dead angle ( β ), and the optimized range of the dead angle is achieved for varying reactive power requirement. Simulation results are presented for the designed three level multipulse voltage source converters with the proposed control algorithm.

The aim of this paper is to present an algorithm for analysing the actual spatial characterization of the dynamic responses of frequencies for large-scale power system. Based on the distribution feature of disturbance power, the measure of interaction (MI) is employed to analyse and quantify the strength of connection among the busses and generation units. The MI takes into account the interconnection constraints among network structure and parameters. In particular, only the network parameters are used in the proposed structural partition procedure. Case Studies carried out on the IEEE 68-bus system are presented to demonstrate the application and effectiveness of the technique developed. Investigations show that the spatial characterization of the dynamic responses of frequencies can be accurately obtained with the procedure, independent of fault location and the size of disturbance, since the proposed technique is based on the structural feature of the system.

: Active Power Filters (APF) are more effective than conventional passive filters with regard to mitigating harmonics and compensating reactive power. As a result, deployment of APF in the distribution network is ever increasing. The performance of APF mainly depends on the reference extraction technique adopted. This work proposes sliding Discrete Fourier Transform (DFT) assisted single phase p-q theory for the extraction of reference current. The proposed algorithm exploits the inherent ability of sliding DFT (SDFT) to provide the fundamental and its quadrature component of signal (voltage or current) to derive the reference current with the help of a single-phase p-q theory. Furthermore, the algorithm involves the phase shifting of the fundamental component alone, and is suitable even for distorted utility voltage. Effectiveness of the proposed method is demonstrated through simulation results.

This paper demonstrates a systematic and objective approach for dimensioning of current transformers (CT) for biased differential relay. The paper proposes some mathematical formulae which allow protection engineers to dimension CT for meeting requirements imposed by sensitivity, and yet maintain stability for through fault. The formulae can be extended to CT with antiremanence magnetic paths. The suitability for the method is demonstrated for various sensitivity objectives and system conditions. The paper also discusses the implementation for different measurement algorithms.

: This article presents a systematic approach to construct the zonal dynamic equivalents of a large-power system based on the concept of relative electrical distance (RED). The task of dynamic equivalencing is to eliminate the full model of the external system and replace it with an equivalent model, which has dynamic characteristics close enough to the full model. The dynamic equivalent models are used for large-scale power system offline transient stability analysis with large disturbance. Dynamic equivalencing also helps in reducing the computation burden and memory requirements in wide area monitoring system (WAMS) for online stability assessment. The procedure is illustrated on IEEE 39 bus system and on a practical 205 bus system consisting of three zones of Indian Southern grid, where an equivalent of a zone has been constructed. The simulation results of the original system and equivalent system are compared. The proposed approach is also compared with the existing Ward equivalent method and the results are found to be similar. The simulation results show that the developed equivalent system has close accuracy in representing the dynamic characteristics of the original system.

This paper uses a small power system, consisting of two hydropower stations and a fixed-speed wind farm as sources of power, to study the influence of type of speed governor of hydropower stations on the frequency stabilization of the fixed-speed wind farm. As an example, two types of speed governors are selected which are (1) mechanical-hydraulic speed governor and (2) electrical-hydraulic speed governor. Rest of the speed governors can be also examined following the same methodology presented in the research. Two transfer functions, which correspond to the two speed governors, are developed for each hydropower station. The overall transfer function of the test power system is developed, and different study cases are presented. The frequency response analysis of the different transfer functions is used to compare the two speed governors based on their ability to stabilize the frequency deviation of the fixed-speed wind resulting from electrical or mechanical disturbances in the power systems. Time-domain simulations under a mechanical disturbance, represented by a wind gust, and an electrical disturbance, represented by three-phase to ground fault, are performed to validate the results of the frequency response analysis.

High-power photovoltaic (PV) plants are usually constituted of the connection of different PV subfields, each of them with its interface transformer. Different solutions have been studied to improve the efficiency of the whole generation system. In particular, transformerless configurations are the more attractive one from efficiency and costs point of view. This paper focuses on transformerless PV configurations characterised by the parallel connection of interface inverters. The problem of zero sequence current due to both the parallel connection and the presence of undesirable parasitic earth capacitances is considered and a solution, which consists of the synchronisation of pulse-width modulation triangular carrier, is proposed and theoretically analysed. The theoretical analysis has been validated through simulation and experimental results.