Phasor Measurement Techniques.- Phasor Estimation of Nominal Frequency Inputs.- Phasor Estimation at Off-Nominal Frequency Inputs.- Frequency Estimation.- Phasor Measurement Units and Phasor Data Concentrators.- Transient Response of Phasor Measurement Units.- Phasor Measurement Applications.- State Estimation.- Control with Phasor Feedback.- Protection Systems with Phasor Inputs.- Electromechanical Wave Propagation.

Synchronized Phasor Measurements and Their Applications

A power system state estimation based on (a) multiphase model, (b) voltage and current waveform measurements, (c) synchronized measurements and (d) multifrequency model (i.e. the approach accounts for waveform distortion or harmonics) is formulated. The paper focuses on the following: (a) modeling, (b) implementation, (c) observability and (d) performance. Sensitivity analysis is used to show how transmission line modeling and measurement schemes affect the performance of harmonic state estimation. The overall performance of the system is described in terms of confidence level versus error. These concepts are illustrated with simple systems. The overall harmonic measurement system is scheduled for installation and field evaluation on the NYPA/New York Power Pool transmission system by the end of 1993. >

Power system harmonic state estimation

The technology of the optical measurement of current is reviewed. Several fundamentallydifferent approaches are described. Implementations from a number of manufacturers are examinedso as to highlight the similarities and the differences. Experience with optical current transducers isreported. The question of interfacing to an optical current transducer is discussed. The specialproblems posed by calibration of this kind of instrument are reviewed.

Optical Current Transducers for Power Systems: A Review

Transmission lines are designed to transfer electric power from source locations to distribution networks. However, their lengths are exposed to various faults. Protective relay and fault recorder systems, based on fundamental power frequency signals, are installed to isolate and the faulty line and provide the fault position. However, the error is high especially in transmission lines. This thesis investigates the problem of fault localization using traveling wave current signals obtained at a single-end of a transmission line and/or at multi-ends of a transmission network. A review of various signal processing techniques is presented. The wavelet transform is found to be more accurate than conventional signal processing techniques for extracting the traveling wave signals from field measurements.

In this thesis, an optimization method has been developed to select the best wavelet candidate from several mother wavelets. The optimum mother wavelet was selected and used to analyze the fault signal at different details' levels. The best details' level, which carries the fault features, was selected according to its energy content. From the line and network data, the traveling wave speed is calculated for each line using the optimum mother wavelet at different detail levels. Accurate determination fault location depends on the proper details wavelet level as well as the propagation speed. A high frequency current transformer model has been verified experimentally using impulse current signals at the high voltage laboratory, Helsinki University of Technology.

Single-end method has been studied for several transmission line configurations, including lines equipped with/without overhead ground wires, counterpoises, or overhead ground wires and counterpoises. The time difference between the aerial and ground mode has also been investigated for these line configurations.

Multi-ended method, using recordings sparsely located in the transmission network, has been proposed to overcome the weakness of the single-end method. The method is based on extracting the fault transient signals from at least two monitored buses and using the double-end method assisted by the shortest path algorithm is used to find the minimum travel time of these signals to the nearest bus.

Validation of the fault location is performed using the ATP/EMTP transient simulations. The method is verified using field data from five traveling wave recorders installed at pre-selected buses of the Finnish 400-kV transmission network.

The algorithm will allow utilities to accurately locate line faults the knowledge of transient current signals, network topology, and the shortest-path algorithm. The thesis, which genuinely provides an economic approach to fault location of transmission systems consistent with today's needs, provides a good foundation for further developments.

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Power transmission line fault location based on current traveling waves

State estimation has been introduced to power systems and implemented in the 60s, using a single frequency, balanced and symmetric power system model under steady state conditions. This implementation is still prevalent today. The single frequency, balanced and symmetric system assumptions have simplified the implementation but have generated practical problems. This paper examines these simplified assumptions and their impact on the state estimation performance. It provides a theoretical basis for the well-known fact that the reliability of the state estimator algorithms has been below expectations. Specifically, sensitivity analysis methods are used to quantify the impact of modeling simplifications and measurement schemes on the performance of state estimation. The results clearly illustrate that the traditional state estimation algorithm is biased. These biases affect the accuracy of state estimation and its convergence characteristics.The paper also reviews the traditional state estimation approach against recent technological advances that have enabled synchronized measurements. The implications and possibilities of this new technology are discussed in this paper. Specifically, an example application of the new technology for a Three Phase State Estimator is described. A power system state estimation based on a) multiphase model, b) voltage and current waveform measurements, and c) synchronized measurements is formulated. The paper focuses on the following: a) modeling, b) implementation, c) observability and d) performance. The overall performance of the system is described in terms of confidence level versus error. These concepts are illustrated with simple systems. In addition, we demonstrate the performance of the proposed methods on an actual system (New York Power Authority system) using actual synchronized measurements. The paper concludes with a commentary on the implications of improved state estimation methods on the security/reliability monitoring and control of an electric power system.

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Power system state estimation: modeling error effects and impact on system operation

A technique for laboratory characterization of instrument transformers designed for transmission level voltage and current measurements is presented. The technique is also extended to transient event recorders (TERs). The objective of the method is to determine the suitability of existing substation instrument transformers for harmonic measurements, particularly in the frequency range of 60 to 1500 Hz covering the first 25 harmonics. Specifically, the following characteristics are of interest: transfer function magnitude and phase, linearity, and sensitivity of the frequency response to burdens. The measurement technique is based on exciting the instrument transformer primary with an impulsive waveform. Both input and output waveforms are recorded using laboratory grade probes and digitizers. Digital signal processing techniques are used to compute the instrument transformer frequency response. Several voltage transformers and current transformers in the 230 kV-765 kV voltage range were tested. The results are described. >

J. McBride

Papers

Transmission level instrument transformers and transient event recorders characterization for harmonic measurements