Virgilio Centeno

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.

An Alternative for Including Phasor Measurements in State Estimators

With the increasing use of real-time synchronized phasor measurement units, it is necessary to consider applications of these measurements in greater detail. One of the most natural applications of these measurements is in the area of state estimation. A straightforward application of state estimation theory treats phasor measurements of currents and voltages as additional measurements to be appended to traditional measurements now being used in most energy management system (EMS) state estimators. The resulting state estimator is once again nonlinear and requires significant modifications to existing EMS software. This paper proposes an alternative approach, which leaves the traditional state estimation software in place, and discusses a novel method of incorporating the phasor measurements and the results of the traditional state estimator in a postprocessing linear estimator. This paper presents the underlying theory and provides verification through simulations of the two alternative strategies. It is shown that the new technique provides the same results as the nonlinear state estimator and does not require modification of the existing EMS software

Power system frequency monitoring network (FNET) implementation

Frequency dynamics is one of the most important measures of an electrical power system status. To better understand power system dynamics, an accurately measured wide-area frequency is needed. The concept of building an Internet-based real-time GPS-synchronized wide-area frequency monitoring network (FNET) was proposed in 2000 by Qiu et al., and this concept has been realized. The FNET system consists of frequency disturbance recorders and an information management system. The FNET has made the synchronized observations of the entire U.S. power network possible with very little cost for the first time. This paper summarizes the implementation of the FNET system and shows some preliminary observations and analyses of the data that have been collected from the FNET.

Synchronized phasor measurements of a power system event

The paper describes one of the first field measurements of positive sequence voltage phasors at key system buses during a switching operation at Plant Scherer of the Georgia Power Company. The phasor measurements were synchronized using time transmissions from the Global Positioning System (GPS) satellites. The data show the first ever observation of power swings recorded via synchronized phasors at several points on an integrated power network. Measurements were made on the Georgia Power Company (GPC) system, the Florida Power and Light (FPL) system, and on the Tennessee Valley Authority (TVA) system. The disturbance was also simulated on a stability program. Results of the simulation, and a comparison with the observed field data are also included. >

An information architecture for future power systems and its reliability analysis

Analysis of 162 disturbances from 1979-1995 reported by the North American Electric Reliability Council (NERC) indicates the importance of information systems under the regulated and competitive environment. This paper points out the major deficiencies in current communication and information systems and proposes a new power system information architecture aimed at correcting these deficiencies. The proposed architecture includes automation and control systems at all levels, from substation control system to independent system operator (ISO) operating center, taking into account the requirements of real-time data, security, availability, scalability, and appropriate quality of service. It uses multiple communication channels employing a wide variety of technologies to transmit real-time operating data and control signals. The real-time operating and control system is modeled with various redundancy configurations. The reliabilities of different configurations are studied and compared for practical values of component failure rates and repair rates.

Comparative testing of synchronized phasor measurement units

This work reports the result of a comparative testing done on four phasor measurement units (PMU) from different manufacturers. Phase shift and attenuation at fundamental frequency, performance under system balanced and unbalanced conditions and performance under system variable frequency are the issues addressed for this comparative assessment. The results are presented in a comparative evaluation of features and performance of the PMU units. The results of this work reveal that data from the tested PMU units is of comparable accuracy only under nominal frequency operating conditions. At off-nominal frequency operation every tested PMU unit yielded a different phase and magnitude for the common measured voltage signal. The existing Synchrophasor standard does not specify phase or magnitude performance for off-nominal frequency operation. The standard is in the process of revision, and it is expected that the revised standard will specifically address performance requirements at off-nominal frequencies.

An adaptive out-of-step relay [for power system protection]

The paper describes the development of an adaptive out-of-step relay, from the formulation of its concept to its field implementation at the Florida-Georgia interface. Adaptive relaying seeks to make adjustments to the relay characteristics as power system conditions change, thereby making the relay more attuned to the prevailing power system conditions. The work described here began as a theoretical examination of the out-of-step relaying application, its possible shortcomings, and the opportunities to make adaptive improvements. It is shown that for a system that behaves primarily as a two-machine power system, the out-of-step relay could be made more secure by applying the principle of equal area criterion. The paper describes the theory of such a relay, its hardware configuration, and the system as it is installed in the field. The newly developed technology of synchronized phasor measurements plays an important role in the realization of this relay. The paper includes a summary of the field experience gathered over a period of one year.

Adaptive out-of-step relaying using phasor measurement techniques

Adaptive relaying proposes to provide protection functions that will adapt to changing power system conditions. The adaptive out-of-step relay presented recognizes power system changes and uses a modified system impedance matrix to change relay settings. An investigation of a Florida-Georgia 500 kV interconnection initially, used a simple two-machine mode to represent the interconnection. After this approach is tested a three-machine Florida model will be constructed. The results from the two approaches will then be compared. The configuration used to implement the relay consists of two or more phasor measurement units (PMUs), which provide synchronized real-time information regarding the state of the system. These PMUs are discussed and data provided by the PMUs is analyzed.<<ETX>>

Methodology for a Security/Dependability Adaptive Protection Scheme Based on Data Mining

Recent blackouts offer testimonies of the crucial role played by protection relays in a reliable power system. It is argued that embracing the paradigm shift of adaptive protection is a fundamental step toward a reliable power grid. The purpose of this paper is to present a methodology to implement a security/dependability adaptive protection scheme. The advocated methodology aims to reduce the likelihood of manifestation of hidden failures and potential cascading events by adjusting the security/dependability balance of protection systems. The proposed methodology is based on wide-area measurements obtained with the aid of phasor measurement units. A data-mining algorithm, known as decision trees, is used to classify the power system state and to predict the optimal security/dependability bias of a critical protection scheme. The methodology is tested on a detailed 4000-bus system.

An Adaptive Out-of-Step Relay

The paper describes the development of an adaptive out-of-step relay, from the formulation of its concept to its field implementation at the Florida-Georgia interface. Adaptive relaying seeks to make adjustments to the relay characteristics as system conditions change, thereby making the relay more attuned to the prevailing power system conditions. The work described here began as a theoretical examination of the out-of-step relaying application, its possible shortcomings, and the opportunities to make adaptive improvements. It is shown that for a system that behaves primarily as a two-machine power system, the out-of-step relay could be made more secure by applying the principle of equal area criterion. The paper describes the theory of such a relay, its hardware configuration, and the system as it is installed in the field. The newly developed technology of synchronized phasor measurements plays an important role in the realization of this relay. The paper includes a summary of the field experience gathered over a period of one year.