A. P. Sakis Meliopoulos

Smart Grid Technologies for Autonomous Operation and Control

This paper presents a new smart grid infrastructure for active distribution systems that will allow continuous and accurate monitoring of distribution system operations and customer utilization of electric power. The infrastructure allows a complete array of applications. The paper discusses four specific applications: a) protection against downed conductors; b) load levelization; c) loss minimization; and d) reliability enhancement.

Multiphase power flow and state estimation for power distribution systems

A multiphase power flow model and state estimation for distribution systems are formulated and solution methods are presented. The multiphase power flow model is based on fully asymmetric modeling of the power distribution system. The state estimation uses this model in conjunction with synchronized measurements. The method provides an estimate of the total electric load for each distribution circuit without the requirement of knowledge of the individual loads along the circuit. The paper addresses the following issues: (a) modeling; (b) implementation; (c) observability; and (d) performance. The overall performance of the method is described in terms of confidence level versus error. The concepts are illustrated with a simplified distribution system.

Incorporation of Switching Operations in Power System Corrective Control Computations

This paper presents a linear programming based methodology for corrective controls computations. The methodology computes adjustments of unit real power output, VAR source output, transformer tap settings, capacitor/reactor switching, branch switching or line sectionalization, and if necessary, load shedding. A previous publication presented the basic algorithm for computing adjustments of continuous controls such as generator real power, transformer tap setting, etc. This paper addresses the problem of incorporating discrete controls such as capacitor/reactor switching and line switching/sectionalization into the overall procedure. Efficient algorithms are presented for the computation of discrete controls such as capacitor bank and transmission line switching. The methodology is illustrated with typical results obtained with the Georgia Power Companys 500 kV/230 kV/115 kV system. The network representation of this system comprises 981 buses and 1175 circuits.

Advanced Distribution Management System

This paper proposes an advanced distribution management system (DMS) that a) monitors each component and performs protection functions using a dynamic state estimation, b) the estimated states are transmitted to the DMS where the real time model of the entire feeder is synthesized, c) uses the real time model to perform upper level optimization (operations planning) and lower level optimization (real time control) via a hierarchical optimization procedure; and d) applies proper controls to operate the system at optimal points. The proposed approach for protection, operations planning, and real time control of the system provides the infrastructure for additional important applications. As an example, the paper presents a novel application for monitoring available reserves from all resources in the system. We propose the concept of Reserve-O-Meter that monitors in real time the available reserves from all resources (utility and customer owned).

The supercalibrator — A fully distributed state estimator

This paper describes a new approach that led to the development of a fully distributed state estimator, named the SuperCalibrator (SC). The SC is a three-phase state estimator that operates at the substation level and requires at least one PMU at each substation. The computed substation state estimate is transferred to the control center where the overall system state is synthesized from the substation states. The SC-based distributed state estimator has been implemented on the US Virgin Islands St. Thomas and St. John power system of the USVI Water and Power Authority. The most significant performance characteristics of the system are: (a) High update rate up to four system wide state estimation solutions per second, (b) High Accuracy - typically 0.05 degrees in phase and 0.1% in magnitude, (c) Scalability, (d) No need for tuning of the state estimation process.

A Breaker-Oriented, Three-Phase IEEE 24-Substation Test System

Accurate bus-oriented, three-phase modeling of power systems is desirable for advanced applications and has become practical due to increased computational capability. To assist research activities in this area, this paper presents a benchmark three-phase test system. The proposed system is based on the 24-bus IEEE Reliability Test System that has been converted into a 24-substation, breaker-oriented, three-phase model. The model is available in electronic form at the site: http://pscal.ece.gatech.edu/testsys/. The proposed model is intended for use in research for three-phase power flow analysis, reliability analysis, fault analysis, transient stability, evaluation of fault currents through specific breakers, risk assessment of breaker failures, and other applications.

Effects of Protection System Hidden Failures on Bulk Power System Reliability

Protection system hidden failures have been recognized as a contributing factor to power system cascading outages. However, in the current bulk power system reliability assessment practice, protection systems are generally assumed to be perfect, and the effects of hidden failures in protection systems are not taken into account. In this paper, the impact of protection system hidden failures on bulk power system reliability is investigated. A breaker-oriented bulk power system network model is developed to include detailed system substation configurations and associated protection system schemes. Protection system constituents, such as transducers, relays, circuit breakers, may suffer from hidden failures. Hidden failures existing in transducers and relays can be detected by the advanced system real time monitoring and analysis technologies. Thus, the major concern of this work focuses on the analysis of hidden failures in circuit breakers. The hidden failure effects analysis shows that some initial system disturbances can result in the unnecessary outages of intact power system equipment because of hidden failures in circuit breaker trip mechanisms. Contingencies resulting from hidden failure outages are further evaluated by a security-constrained adequacy evaluation methodology to obtain their influence on system reliability. The proposed analysis procedure is demonstrated with a breaker- oriented 24-substation reliability test system, which is developed based on the IEEE 24-bus reliability test system and integrates explicit substation and protection system models in the network model. Evaluation results show that protection system hidden failures downgrade the system reliability level because they lead to the outages of undamaged equipment following initial system disturbances.

Setting-Less Protection: Feasibility Study

A new protection scheme is proposed that does not require settings or the settings are simple and the need to coordinate with other protective devices has been removed. The approach can be viewed as a generalization of differential protection and it is enabled with dynamic state estimation. Specifically, the proposed protection scheme is based on continuously monitoring terminal voltages and currents of the component and other possible quantities such as tap setting, temperature, etc. as appropriate for the component under protection. The monitored data are utilized in a dynamic state estimation that continuously provides the dynamic state of the component by fitting the data to the basic model equations of the device under protection. The dynamic state is then used to determine the health of the component. Tripping or no tripping is decided on the basis of the health of the component. The basic approach, the analytics and the requirements for successful implementation of this concept are presented. Numerical experiments are presented to validate the method as well as an example comparison with conventional protection. Finally an evaluation of feasibility is provided based on present day microprocessor capabilities and it is concluded that present day microprocessors do have the computational power required by the proposed approach.

GPS-Synchronized Data Acquisition: Technology Assessment and Research Issues

GPS-synchronized equipment (PMUs) is in general higher precision equipment as compared to typical SCADA systems. Conceptually, PMU data are time tagged with accuracy of better than 1 microsecond and magnitude accuracy that is better than 0.1%. This potential performance is not achieved in an actual field installation due to errors from instrumentation channels and system imbalances. Presently, PMU data precision from substation installed devices is practically unknown. On the other hand, specific applications of PMU data require specific accuracy of data. Applications vary from simple system monitoring to wide area protection and control to voltage instability prediction. Each application may have different accuracy requirements. For example for simple system monitoring in steady state highly accurate data may not be critical while for transient instability prediction high precision may be critical. For addressing data precision requirements for a variety of applications, it is necessary to quantify the accuracy of the collected PMU data. We discuss data precision requirements for a variety of applications and we propose a methodology for characterizing data errors. In particular, we propose a new approach for improving data accuracy via estimation methods. The proposed methodology quantifies the expected error of the filtered data. Examples are provided that define the instrumentation requirements for specific applications.

Role of laboratory education in power engineering: is the virtual laboratory feasible? III. Virtual power system laboratories: is the technology ready

For pt.III see ibid., p.1478-83 (2000). IEEE PES sponsors a panel session in the summer power meeting in Seattle on laboratory education in power engineering. Six short papers and one full paper summarize the opinion of the panelists. This is the full paper. The evolution of software engineering, multitasking environment, object-oriented programming and symbolically assisted simulation methods have enabled the creation of interactive simulation environments that come close to providing a virtual experience of the actual system. The initial attempts at utilizing this technology are impressive and yet the degree to which they achieve virtual status is questionable. This paper examines the pros and cons of the present status of this technology. We discuss the minimum requirements for a virtual environment. We present our approach and compare it to the general requirements of a virtual laboratory. We conclude that the technology exists today to generate a virtual power system laboratory. Yet much work remains to be done for claiming that we have achieved the objective of having a true virtual laboratory for power systems. At the same time, virtual environments have certain advantages that cannot be achieved in a physical laboratory.