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

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.

Synchronized Phasor Measurement Applications in Power Systems

Permanent magnet AC (PMAC) motor drives are finding expanded use in high-performance applications where torque smoothness is essential. This paper reviews a wide range of motor- and controller-based design techniques that have been described in the literature for minimizing the generation of cogging and ripple torques in both sinusoidal and trapezoidal PMAC motor drives. Sinusoidal PMAC drives generally show the greatest potential for pulsating torque minimization using well-known motor design techniques such as skewing and fractional slot pitch windings. In contrast, trapezoidal PMAC drives pose more difficult trade-offs in both the motor and controller design which may require compromises in drive simplicity: and cost to improve torque smoothness. Controller-based techniques for minimizing pulsating torque typically involve the use of active cancellation algorithms which depend on either accurate tuning or adaptive control schemes for effectiveness. In the end, successful suppression of pulsating torque ultimately relies on an orchestrated systems approach to all aspects of the PMAC machine and controller design which often requires a carefully selected combination of minimization techniques.

Pulsating torque minimization techniques for permanent magnet AC motor drives-a review

The influence of various design parameters on the cogging torque developed by permanent magnet machines is investigated. It is shown that the slot and pole number combination has a significant effect on the cogging torque, and influences the optimal value of both skew angle and magnet arc, as well as determining the optimal number of auxiliary teeth/slots. A simple factor, which is proportional to the slot number and the pole number and inversely proportional to their smallest common multiple, has been introduced to indicate the "goodness"/spl beta/ of the slot and pole number combination. In general, the higher the "goodness" factor the larger the cogging torque.

https://eprints.whiterose.ac.uk/889/1/zhuzq20.pdf

Influence of design parameters on cogging torque in permanent magnet machines

An analytical technique for predicting the instantaneous magnetic field distribution in the airgap region of radial-field topologies of brushless permanent-magnet DC motors, under any specified load condition and accounting implicitly for the stator winding current waveform and the effect of stator-slot-openings, has been developed. It is based on the superposition of the component fields due to the permanent magnet and the stator excitation. A 2D analytical method for predicting the open-circuit airgap field distribution in both internal and external rotor radial-field motor topologies is presented. It involves the solution of the governing field equations in polar coordinates in the annular airgap/magnet region of a multipole slotless motor in which the magnets are assumed to have uniform radial magnetization and a constant relative recoil permeability. Results for various radial-field motors are compared with predictions from corresponding finite element analyses. >

Instantaneous magnetic field distribution in brushless permanent magnet DC motors. I. Open-circuit field

An analytical method was developed to determine cogging as well as commutating torque in permanent-magnet machines of both buried and surface-mounted magnet types. A detailed analysis of the torque production in a permanent magnet synchronous motor drive with rectangular current excitation is presented. The effect of skewing is considered. The proposed method takes advantage of the knowledge of the flux density distribution in the air gap as a function of design parameters. The equations can be programmed easily and are very useful for parametric studies and optimization. >

Torque production in permanent-magnet synchronous motors

Catastrophic failures of power systems are phenomena which occur with some regularity throughout the world. It is recognized that these cannot be prevented, although with the use of newer developments in power engineering, in communication systems, and in computer engineering it would be possible to reduce their frequency and their impact on society. Analyses of many blackouts point to some salient features which are common to most such events: power systems under stress because of high load levels or outages of important facilities, some initiating event-usually a fault, often followed by cascading effects due to unwanted operation of some protection systems. In particular, the role of hidden failures (HFs) in protection systems in propagating power system disturbances has become clearer with some of the recent research reported in the literature. This paper explores further the issue of HFs of protection systems and possible countermeasures. Regarding the countermeasures, adapting the protection systems so that they would change their operational logic from OR to a VOTING protocol has been discussed in the literature, and is well within the capability of present technology. Other hardware solutions, such as "Hidden Failure Monitoring and Protection Systems," have also been discussed in the literature. Most of these countermeasures will require intensive use of communication networks. Communication infrastructure will be utilized for real-time data transfer, as well as for slower speed data gathering tasks related to the condition of the power system. In this paper, we concentrate on the communication facilities and their applications for providing countermeasures against catastrophic failures of power systems.

/pdf/catastrophic-failures-in-power-systems-causes-analyses-and-1ascnjycaw.pdf

Catastrophic Failures in Power Systems: Causes, Analyses, and Countermeasures

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 >

Adaptive out-of-step relaying using phasor measurement techniques

Harmonic characteristics of transformer excitation currents under DC bias caused by geomagnetically induced currents (GICs) are presented. A saturation model for a single phase shell-form transformer based on 3-D finite-element analysis is used to calculate the excitation currents. As a consequence, the variation of excitation current harmonics over an extended range of GIC bias is determined. The results of this study are useful in understanding transformers as harmonic sources and their impact on power systems during a solar magnetic disturbance. >

Harmonics generated from a DC biased transformer

This paper explores hidden failures in protection systems, which have been identified as key contributors in the cascading of power system wide-area disturbances. The original definition of hidden failure, which is a failure that remains undetected and is uncovered by another system event, is included as are the developments of hidden failure sequence of events and a methodology for hidden failure identification. This method is based on protection element functionality defects (PEFD). Hidden failures modes are developed based on the relaying implementation for primary protection, back-up protection and special protection systems. Wide-area disturbances based on North American Reliability Council (NERC) reports are analyzed and hidden failures are identified employing the developed methodology. The mechanisms in the wide-area disturbances are summarized. Regions of vulnerability and areas of consequence are important concepts that identify the critical elements from the point of view of hidden failures.

J. De La Ree

Papers

Torque production in permanent-magnet synchronous motors

Catastrophic Failures in Power Systems: Causes, Analyses, and Countermeasures

Adaptive out-of-step relaying using phasor measurement techniques

Harmonics generated from a DC biased transformer

Hidden failures in protection systems and their impact on wide-area disturbances