Phasor Measurement Units Measurements Research Articles

Estimation Methods of Short Circuit Current using Normal PMU Measurements and Field Testing

This paper proposes estimation methods of short circuit current using phasor measurement unit (PMU) measurements (phasors). The methods follow the basic notion of representing the source side of a power system by an equivalent circuit with a voltage behind back impedance, and employ a set of voltage and current phasors measured at substations during the normal variation of loads in their estimation. In order to improve the estimation accuracy of the proposed methods, the concept of using the changes between the consecutive phasors is introduced. Furthermore, to make the methods applicable to the real world system, a reference phasor concept to remove the effects of system wide frequency variations and a filtering process to filter out the outlier phasors, are proposed and implemented. The validity and effectiveness of the proposed methods were checked and confirmed using experiments and field tests.

Optimal Placement of Phasor Measurement Units for Improving Power System State Estimation Accuracy: A Heuristic Approach

Optimal Placement of Phasor Measurement Units for Improving Power System State Estimation Accuracy: A Heuristic Approach This paper describes a heuristic approach for optimal placement of phasor measurement units (PMUs) in power system for improving state estimation accuracy. PMUs are able to measure highly accurate bus voltage phasors as well as branch current phasors incident to the buses at which PMUs are installed. Due to cost consideration of PMU placement, power grid utilities are interested in the knowledge of how to add a limited number of PMUs to their existing network in order to improve state estimation performance. State estimation results are calculated by the weighted least square (WLS) state estimation method. In the problem of adding PMU measurements into the estimator, two methods are investigated. Method I is to mix PMU measurements with conventional measurements in the estimator, and method II is to add PMU measurements through a post-processing step. These two methods can achieve very similar state estimation results, but method II is a more time-efficient approach without modifying the existing state estimation software. The proposed PMU placement approach is tested using IEEE 14-bus system, and the obtained figure and table might help planning engineering determine the optimal placement of PMUs when they want to place a few PMUs in their systems.

State estimation and bad data processing for systems including PMU and SCADA measurements

Conventional state estimators (SE) are based on real-time measurements, consisting of bus voltages and active and reactive power flows and injections, and estimate the voltage phasors of the network buses. Until recently, these measurements were obtained only through SCADA. With the advent of GPS synchronized measurements obtained by phasor measurement units (PMU), effective techniques are required to incorporate the extremely accurate PMU measurements into state estimation, in order to improve its performance and observability. This paper develops a non-linear weighted least squares estimator by modeling the current phasor measurements either in rectangular or in polar coordinates and compares the two approaches. Any numerical problems arised at flat start or for lightly loaded lines, are resolved. The error amplification, due to the current phasor measurement transformation from polar into rectangular coordinates, is also investigated. The normalized residual test is used to effectively identify any bad data in the conventional and phasor measurements. The proposed techniques are tested with the IEEE 14-bus system.

Construction of System Restoration Strategy with PMU Measurements

Power system restoration is well-recognized as one of the major technologies to improve system reliability. A high efficient restoration strategy is established and implemented with accurate information acquisition. Phasor measurement unit (PMU) provides a state-of-the-art information monitoring technology. In this paper, with PMU measurements, several algorithms are proposed to ensure complete observability of systems under regular operating conditions and during system restoration process. Case studies on IEEE 14, 30, 57, 118 and 300 – bus systems validate efficiency of the proposed algorithms.

A dynamic state estimation method for power systems

GPS based Phasor Measurement Units (PMUs) are prevailing in power systems. This paper introduces a dynamic state estimation method for power systems. As installation of PMUs at all buses is impractical, this method employs SCADA data that covers the whole system and PMU data that covers part of the system. The PMU samples are interpolated into the SCADA data to increase the measuring density. An iterative state estimation algorithm is established with the coordination of PMU and SCADA measurements. Example shows that the method can increase the estimating precision and provide more information on power system dynamics.

Joint Controller-Communication Topology Design for Distributed Wide-Area Damping Control of Power Systems

AbstractThe recent development and deployment of the synchronized phasor measurement units (PMU) is allowing the wide-area monitoring and control of large-scale power systems. Furthermore, the integration of more communication technologies into the power system is giving an additional degree of freedom to the control design that may improve the performance of the overall system. Small-signal stability is an important requirement for power systems with the increasing number of distributed generation units. The oscillation modes of the power system have to be well damped in order to avoid contingencies such as blackouts. Wide-area controllers based on the real-time PMU measurements operating in centralized, distributed and decentralized manner have been widely proposed to damp the low-frequency oscillation of the large-scale interconnected power system. It has been shown that the damping performance can be improved by using the synchronized PMU data transmitted in real-time via communication network. However, only a few of the proposed methods take the structural constraint of the measurement data transmission into account. In this paper, we propose a method to design a distributed wide-area damping controller together with the communication topology in order to improve the damping performance of the power system. As a design strategy, first a decentralized controller that stabilizes the overall system is designed. Then, the damping performance is improved by designing the distributed control law, i.e. allowing the local controllers to exchange information. The problem is formulated as a mixed-integer optimization. Finally the proposed approach is evaluated in a five machine power system via a numerical simulation.

Application of Phasor Measurement Unit on Locating Disturbance Source for Low-Frequency Oscillation

A smart power grid is an integration of the advanced measurement, communication, computer, and control techniques. Among all the state-of-the-art technologies in building a smart power grid, the phasor measurement unit (PMU) is an important and promising one. Nowadays in China, most ultrahigh- and high-voltage buses are all equipped with PMUs. This paper reports an application of PMU data on locating the disturbance source for the low-frequency oscillation that has happened several times in the interconnected big power grids in China recently. The posterior analysis by the Electric Power System Research Institute of China (CEPRI) has confirmed that these low-frequency oscillations are caused by the resonance phenomena. It is urgent to find the disturbance source in case it happens again. However, there have been no systematic and effective methods to locate the disturbance in a very large power system. The trial and error method has been implemented via the digital simulations, but in vain. To overcome this problem, a novel method is developed in this paper to locate the disturbance source with the help of PMUs. The method takes advantage of the PMU measurements to reduce the searching area for locating the disturbance source. Case studies show the efficiency of the proposed method.

Synchronized Phasor Measurement Applications in Power Systems

Synchronized phasor measurements have become a mature technology with several international manufacturers offering commercial phasor measurement units (PMUs) which meet the prevailing industry standard for synchrophasors. With the occurrence of major blackouts in many power systems around the world, the value of data provided by PMUs has been recognized, and installation of PMUs on power transmission networks of most major power systems has become an important current activity. This paper provides a brief introduction to the PMU and wide-area measurement system (WAMS) technology and discusses the uses of these measurements for improved monitoring, protection, and control of power networks.

Inclusion of PMU current phasor measurements in a power system state estimator

Three different methods of inclusion of current measurements by phasor measurement units (PMUs) in a power system state estimator is investigated. A comprehensive formulation of the hybrid state estimator incorporating conventional, as well as PMU measurements, is presented for each of the three methods. The behaviour of the elements because of the current measurements in the measurement Jacobian matrix is examined for any possible ill-conditioning of the state estimator gain matrix. The performances of the state estimators are compared in terms of the convergence properties and the variance in the estimated states. The IEEE 14-bus and IEEE 300-bus systems are used as test beds for the study.

Wide-area phasor power oscillation damping controller: a new approach to handling time-varying signal latency

Using the present technology, latency associated with remote feedback signals can be determined from the time stamp information at both the phasor measurement unit (PMU) location and the control centre. This study illustrates how this latency could be accounted for in the implementation of a wide-area phasor power oscillation damping controller (phasor POD). The basic idea is to adjust the position of the rotating reference frame – used for phasor extraction – to account for the extra phase shift introduced because of latency. The oscillatory component of the original PMU measurement is retrieved out of the delayed signal received at the control centre. Thus, continuous compensation is achieved without requiring any Pade approximation and/or gain scheduling, unlike the techniques reported in the literature. With the proposed modification, a phasor POD is shown to continuously adapt to the actual latency and maintain the desired dynamic performance over a range of different operating conditions.

Real Time Wide Area Voltage Stability Index in the Korean Metropolitan Area

Through the development of phasor measurement units (PMU), various aspects of power system dynamic behavior could be monitored and diagnosed. Monitoring dynamic voltage stability has become one of the achievements we can obtain from PMUs. It is very important to select the most appropriate method for the Korea Electric Power Corporation (KEPCO) system since there are many voltage stability indices. In this paper, we propose an advanced WAVI (Wide Area Voltage Stability) that is well suited for the purposes of monitoring the dynamic voltage stability of KEPCO’s PMU installation plan. The salient features of the proposed index are: i) it uses only PMU measurements without coupling with EMS data; ii) it is computationally unburdened and can be applied to real-time situations. The proposed index is applied to the KEPCO test system and the results show that it successfully predicts voltage instability through comparative studies.

Decision Tree-Based Online Voltage Security Assessment Using PMU Measurements

Voltage collapse is a critical problem that impacts power system operational security. Timely and accurate assessment of voltage security is necessary to detect post-contingency voltage problems in order to prevent a large scale blackout. This paper presents an online voltage security assessment scheme using synchronized phasor measurements and periodically updated decision trees (DTs). The DTs are first trained offline using detailed voltage security analysis conducted using the past representative and forecasted 24-h ahead operating conditions. The DTs are also updated every hour by including newly predicted system conditions for robustness improvement. The associated synchronized critical attributes are obtained in real time from phasor measurement units (PMUs) and compared with the offline thresholds determined by the DTs to assess security. This approach is tested on the American Electric Power (AEP) system and properly trained DTs perform well in assessing voltage security. Several new ideas to improve DT performance are also introduced.

PMU Measurement Uncertainty Considerations in WLS State Estimation

A method to assign weights to the measurements obtained through phasor measurement units (PMUs) in a weighted least squares (WLS) state estimation is presented in this paper. The uncertainties for direct measurements are obtained from the manufacturer's specifications. For pseudo-measurements, the uncertainties are evaluated by using the classical uncertainty propagation theory. The propagation of measurement uncertainty as a function of line length and conductor type is also investigated. The lower and upper bounds of the estimated states considering the measurement uncertainties are found by using linear programming. The proposed method is applied on the IEEE 14-, 30-, 57-, and 118-bus test systems, and the state estimation results including the lower and upper bounds of the estimated states are presented.

A novel hybrid state estimator for including synchronized phasor measurements

State estimator is crucial for on-line power system monitoring, analysis and control. With the increasing use of synchronized phasor measurement units (PMU) in power grids, how to utilize phasor measurements to improve the precision of state estimator becomes imperative. Since there are lots of traditional measurements in SCADA system and it is hard for phasor measurements to replace them in the near future, the best way is to develop hybrid state estimator which includes both phasor and traditional measurements to get better behavior. In this paper, a novel state estimator for including voltage phasors, branch current phasors and traditional measurements is proposed. The detailed model and how to calculate covariance matrix of PMU measurements are described in detail. New England 39-bus system and IEEE 118-bus system are used as test systems and the simulation results demonstrate that the proposed state estimation algorithm improves the precision greatly and gets better behavior as compared with other state estimators with or without phasor measurements.

04/02797 Effects of unbalances and harmonics on optimalcapacitor placement in distribution system: Ghose, T. and Goswami, S. K. Electric Power Systems Research, 2004,68, (2), 167–173

State estimator is crucial for on-line power system monitoring, analysis and control. With the increasing use of synchronized phasor measurement units (PMU) in power grids, how to utilize phasor measurements to improve the precision of state estimator becomes imperative. Since there are lots of traditional measurements in SCADA system and it is hard for phasor measurements to replace them in the near future, the best way is to develop hybrid state estimator which includes both phasor and traditional measurements to get better behavior. In this paper, a novel state estimator for including voltage phasors, branch current phasors and traditional measurements is proposed. The detailed model and how to calculate covariance matrix of PMU measurements are described in detail. New England 39-bus system and IEEE 118-bus system are used as test systems and the simulation results demonstrate that the proposed state estimation algorithm improves the precision greatly and gets better behavior as compared with other state estimators with or without phasor measurements.