Real time identification of coherent groups for controlled islanding based on graph theory

Recently, several smart grid applications have been designed to improve monitoring, protection and control of power systems in real time. Most of these emerging approaches exploit the capabilities of wide-area technologies (wide area monitoring, protection and control - WAMPAC). Since WAMPAC implementation requires distributed phasor measurements throughout the system, phasor measurement units (PMUs) have to be adequately located depending on the real-time application. This paper addresses the problem of PMU placement with the aim of achieving high observability of system dynamics that are associated to transient and other short-term phenomena, in order to perform reliable real-time dynamic vulnerability assessment. Thus, a hybrid approach to determine suitable PMU locations that allows ensuring observability of slow and fast dynamic phenomena is proposed. The proposal uses Monte Carlo-based simulations to iteratively evaluate the system fast dynamic coherency, as well as the bus oscillatory modal observability. The methodology is tested on the IEEE New England 39-bus test system. Results show the feasibility of the methodology for orienting the selection of buses that offer the best PMU location in terms of dynamic observability.

Now a days, there are several smart grid applications have been designed for the improvement of monitoring, protection and control of power systems in real time. Out of which most of the emerging approaches exploit the capabilities of wide-area technologies (wide area monitoring, protection and control - WAMPAC). Since WAMPAC implementation requires distributed phasor measurements throughout the system, phasor measurement units (PMUs) have to be adequately located depending on the real-time application. This paper addresses the Role of Phasor Measurement unit (PMU) technology and its application in the power system.

The dynamic monitoring, control, and protection of modern power systems in real time require time-stamped electrical measurements to accurately estimate the bus voltage phasors using the state estimation function under normal and abnormal conditions. These measurements can be acquired by time-synchronized devices, known as phasor measurement units (PMUs). PMUs can measure bus voltage and branch current phasors of a three-phase network, as well as the frequency and the rate of change of frequency (ROCOF), with high speed, accuracy and time stamping provided by global positioning system (GPS) at the coordinated universal time (UTC). Various phasor estimation algorithms have been proposed in the literature, while most of them are concentrated in the discrete Fourier transform (DFT) algorithm, where an integer number of samples multiple of the nominal frequency is required for the computations. In cases where the frequency of the power grid deviates from its nominal value, the raw application of the DFT approach can lead to large errors during phasor estimation. Another approach of the phasor estimation is based on the phase-locked loop (PLL) techniques, widely used in grid tie inverters. PLL techniques can track dynamically (continuous time) the estimated frequency to the time-variant frequency of the power grid. A brief introduction to the basic concepts of the synchrophasor definition is provided, while the main DFT methods for synchrophasor estimation according to recent literature are mentioned. PLL-based PMU techniques are reviewed for both steady-state and dynamic conditions according to IEEE standards. In conclusion, the performance of PLL-based PMU algorithms presented in this literature review is discussed.

Power system oscillation monitoring and control in real-time is an important issue to be taken into consideration in modern interconnected power systems operation. This paper proposes a method to find the system damping and identification of coherent groups in the system following a disturbance in real-time using Artificial Neural Network. The first four cycles of post disturbance data comprising of bus voltage magnitudes and angles measured from optimally placed Phasor Measurement Units using Integer Linear Programming. The dimensionality reduction is also done using Principal Component Analysis. The results show that the proposed method is very fast and predict the damping and coherent groups accurately in real-time for all operating conditions including topological variations, with very less computational burden. The effectiveness of proposed approach is tested on IEEE 39-bus test system.

The electrical power system is becoming more and more complex with the increasing demand of the electricity across the world, as the world is becoming the global village. The electrical power system must be reliable and safe enough to fulfil the energy requirements with the continuous supply of energy. The chances of power system's blackouts and outages are increasing with its increased complexity. So, there is a need of an efficient control system to make the power system more safe, efficient and reliable. Wide Area Monitoring, Protection and Control system (WAMPAC) is becoming an emerging technology for an efficient monitoring, protection and control of power system. Phasor measurement unit (PMU) is an integrated part of wide area monitoring, protection and control (WAMPAC) system, which can be used for monitoring, protection and control of complex electrical power systems. PMU gives the synchronized phasor measurements of voltage and current and can easily monitor and control even small disturbances in power system to protect the power system from any blackouts and outages before any fault occurs. In the proposed paper a PMU model is designed in MATLAB/Simulink and then PMU is used for power system protection and the comparative analysis are done with the conventional protection technique for an interconnected two-area network power system.

Over the last decade, there has been a considerable increase in deploying phasor measurement units (PMUs) in wide-area monitoring, protection, and control of power systems, as well as the development of smart transmission and distribution grid applications. This chapter is focused on the demonstration of capabilities of DIgSILENT PowerFactory software for solving the problem of optimal PMU placement in power networks. The optimal placement has been viewed from the perspective of satisfying the observability requirement of power system state estimator. Optimal placement of PMU is formulated as a practical design task, considering some technical challenges like complete network observability, enough redundancy, and the concept of zero injection buses under PMU and tie-line critical contingencies. Furthermore, the meta-heuristic techniques on the basis of evolutionary computations are programmed as an optimisation toolbox in DIgSILENT Programming Language (DPL). A distinctive characteristic of the presented module is that the evolutionary algorithm is only coded in DPL without using the time-consuming process of interlinking DIgSILENT PowerFactory with another software package like MATLAB. In summary, the bus adjacency relationship matrix, zero injection bus (ZIB), observability in the presence of ZIB, and PMU/line contingencies are programmed in different DPLs and combined together with the DPL of an evolutionary algorithm to create the optimal PMU placement module. Also, the proposed toolbox is not case-dependent and can be run with the user-defined test systems, what is contributing to the proposed tool flexibility. Finally, the applicability and efficiency of the proposed optimal PMU placement module are investigated on the DIgSILENT PowerFactory version of IEEE 14- and 39-bus test systems.

Power system monitoring and control in real time is a challenging task for modern power system due to large operational constraints. The deployment of phasor measurement units (PMUs) at key locations provides an opportunity for devising effective power system monitoring and control measures. In this study, a new method is proposed to determine the real-time transient stability status and identification of the coherent generator groups by predicting the rotor angle values following a large disturbance through radial basis function neural network. The first six cycles of synchronously sampled post-fault data measurements from PMUs consisting of rotor angles and voltages of generators are taken as the input to the neural network to predict the future state of the system. The proposed method can also determine the synchronism state of the individual machine in real time. The proposed scheme is demonstrated on the IEEE-39 bus test system at different operating conditions.

Optimal phasor measurement unit placement for power system observability using teaching–learning based optimization

Phasor measurement units (PMUs) are considered as a promising tool for future monitoring, protection and control of power systems. In this paper, a unified approach is proposed in order to determine the optimal number and locations of PMUs to make the system measurement model observable and thereby can be used for power system state estimation. The PMU placement problem is formulated as a binary integer linear programming (BILP), in which the binary decision variables (0,1) determine whether to install a PMU at each bus, while preserving the system observability and lowest system metering economy. The proposed approach integrates the impacts of both existing conventional power injection/flow measurements (if any) and the possibility of single or multiple PMU loss into the decision strategy of the optimal PMU allocation. Unlike other available techniques, the network topology remains unaltered for the inclusion of conventional measurements, and therefore the network connectivity matrix is built only once based on the original network topology. The mathematical formulation of the problem maintains the original bus ordering of the system under study, and therefore the solution directly points at the optimal PMU locations. Simulations using Matlab are conducted on a simple testing 7-bus system, as well as on different IEEE systems (14bus, 30-bus, 57-bus and 118-bus) to prove the validity of the proposed method. The results obtained in this paper are compared with those published before in literature.

Continuous and efficient operation of a power system has become an issue of paramount importance in modern society. As such the Synchrophasor technology employing the Phasor Measurement Units (PMU) has emerged as a prime candidate for ensuring the goal of monitoring and controlling a power system in real time, which in effect ensures minimization of power system failures. But the existing network configuration which connects different PMUs to PDC (Phasor Data Concentrators) is prone to failure in the event of damage to the dedicated communication path between PMU and PDC. The system proposed in this paper aims to use GSM/GPRS (Global System for Mobile) communication between PMUs to establish alternate pathways of communication to ensure smooth operation until the original communication pathway is established. As a by-product it can also be used for dedicated monitoring of an individual PMU using a ‘Smart Phone’. This paper proposes a hybrid communication topology which can improve the reliability of PMU based monitoring system.

Several major blackouts in the past have shown the need for advanced wide‐area monitoring and control (WAMC) techniques. Advanced synchrophasor visualization and monitoring can be realized with time‐referenced power system data that are collected by phasor measurement units (PMUs) using synchronized clocks. Presently, PMUs are being deployed around the world at a rapid rate for various power system applications. When a necessary number of PMUs are installed at optimal locations throughout the network, the complete state of the system can be observed. PMUs take real‐time measurements to determine the state of the power system and can be used to enhance state estimation efficiency. With PMUs in place, there are many control and protection schemes that can be implemented successfully to take preventive and corrective actions. These remedial action schemes (RASs) are classified by the IEEE Power System Relaying Committee (PSRC) as system integrity protection schemes (SIPSs). This work involved the development of a real‐time hardware test bed in order to analyze the transient stability of a simulated power system by using synchrophasors to visualize system stress across a transmission line with and without load‐shedding schemes. The real time digital simulator (RTDS®) was used to model the power system in real time. PMUs, a satellite‐synchronized clock, and a synchrophasor vector processor (SVP) were used to test the synchrophasor application. Copyright © 2010 John Wiley & Sons, Ltd.

In this paper graph theory is used to identify coherent groups of generators and to locate PMUs for Inter-Area monitoring. Initially, the problem of identifying coherent groups is presented as a graphical problem. Then, three graph clustering methods are implemented to group coherent generators. Finally, when the electric network is separated in coherent regions, a placement of PMU based on centrality criteria is proposed. This can be used as a first stage in the implementation of a plan of monitoring in a large electric power system. Dynamic simulations and phasorial representation of simulations are done with the reduced order equivalent of the interconnected New England system (NETS) and New York power system (NYPS). The results show that graph theory can be applied to identify coherent groups and to locate PMUs to Inter-area monitoring.

Phasor measurement units (PMUs) are essential tools for monitoring, protection and control of power systems. The optimal PMU placement (OPP) problem refers to the determination of the minimal number of PMUs and their corresponding locations in order to achieve full network observability. This paper introduces a recursive Tabu search (RTS) method to solve the OPP problem. More specifically, the traditional Tabu search (TS) metaheuristic algorithm is executed multiple times, while in the initialisation of each TS the best solution found from all previous executions is used. The proposed RTS is found to be the best among three alternative TS initialisation schemes, in regard to the impact on the success rate of the algorithm. A numerical method is proposed for checking network observability, unlike most existing metaheuristic OPP methods, which are based on topological observability methods. The proposed RTS method is tested on the IEEE 14, 30, 57 and 118‐bus test systems, on the New England 39‐bus test system and on the 2383‐bus power system. The obtained results are compared with other reported PMU placement methods. The simulation results show that the proposed RTS method finds the minimum number of PMUs, unlike earlier methods which may find either the same or even higher number of PMUs.

Frequency is an important parameter that plays a crucial role in the monitoring, protection and control of power system. It provides an indication of the interconnection's generation/load balance. Normally nominal frequency is either 50 Hz or 60 Hz in most of the countries. Any deviation of frequency from nominal is an indication of abnormal condition or generation/load imbalance. Synchronized phasor measurement unit (PMUs) are providing a promising future for accurate phasor and frequency estimation. Initially Synchrophasor estimation was the main thrust and after amendments in IEEE standards researchers could able to provide solution for frequency and rate of change of frequency (ROCOF) estimation. The main concern now is to achieve accurate, fast, less computationally complex and economic frequency and ROCOF estimation algorithm. So far different algorithms have been proposed for commercial PMUs and are being claimed as in compliance with IEEE standards C37.118.2011. These standards are providing benchmark for justifying accuracy of commercial PMUs. For effective monitoring and control of these PMUs, their operation under transient and large dynamic oscillation demands quick and highly accurate estimation without any discrepancy in estimated phasor value, irrespective of different manufacturers. This paper presents a comparative analysis of fundamental phasor estimation algorithms namely Basic FFT, Recursive DFT and Non-Recursive DFT under normal operating condition and in presence of noise and harmonics.

Phaser measurement units (PMUs) have become indispensable elements of a reliable power system network and the ability to make precise time synchronized measurements with the best possible accuracy have made these devices to be the best choice for wide area operation, protection and control in a large power system. Due to the widespread use of synchrophasor measurements, it becomes necessary to characterize each PMU based on their performance and select the appropriate device for the required application. Furthermore, the IEEE Std C37.118.1a-2014 mandates the latest performance standards for the commercial PMUs and classifies them based on their performance. This necessitates the development of a test-bed which is capable of testing different PMUs to check whether they comply with the latest IEEE standard and also to characterize the devices in terms of their accuracy and precision. This paper describes a LabVIEW based PMU testing and calibration system that was developed at Virginia Tech with the support of NIST and is capable of performing the latest steady state, dynamic and latency tests as described in the IEEE Synchrophasor standard. The testing system also provides flexibility by automatic and manual modes of operation to allow the characterization of PMUs based on the requirements of the test operator.