A fast recursive solution for induction motor transients

A fast and accurate algorithm for determining induction-motor transient behavior is presented. The fast components of the stator transients are decoupled from the machine flux linkage equations by a linear transformation. The resulting differential equations are then solved by using recursive algebraic equations, which require considerably less computational effort than existing methods. An example shows that the method is very accurate and yet uses less than 40% of the CPU time required by the exact model. The method could be useful in studies that involve simultaneous responses of many machines, such as power system stability studies, where optimal computational efficiency is desirable     

Simulation of induction machinery for power system studies

A simple, fast, and accurate algorithm for determining induction-machine transient behavior is presented. The differential equations for the full-order model of induction machines are simplified and solved using linear system techniques. Examples show that the algorithm is accurate for large disturbances and requires as little as 29% of the CPU time required by the full-order model. The algorithm may offer computational advantages in some studies of large-scale power systems where the detailed induction machine models can not be used due to the complexity of the overall system and where the overall CPU time may be costly     

Voltage-dependent model for teaching transformer core nonlinearity

A voltage-dependent model for transformer core nonlinearity suitable for undergraduate instruction is proposed. The model is based on Fourier series representation of the excitation current, and its parameters are determined with the aid of computer software and measured data. Laboratory experiments are performed to determine the model and verify its validity. The experiment shed light on transformer nonlinearity when used as part of the classical experiment on transformer saturation in the undergraduate energy conversion/power systems laboratory course     

Calculations and measurements of the Unity Plus three-phaseinduction motor

The Unity Plus induction motor configuration for three-phase motors is described and analyzed. In the Unity Plus winding method only one set of windings, called the power winding, is connected directly to the source. The second set of windings is connected to capacitors and is coupled to the power winding through transformer action. The equivalent circuit of the Unity Plus motor for steady-state operation is obtained through standard induction motor analysis methods. Laboratory experiments on a 10 hp three-phase induction motor, both as a conventional winding configuration and as a Unity Plus configuration after rewinding by Unity Plus representatives, verified the accuracy of the circuit model and showed that the Unity Plus winding configuration did not result in higher efficiencies than that obtainable from conventional winding methods     

Analysis of three-phase transformer no-load characteristics

The traditional laboratory experiment on three-phase transformer connections consists of a qualitative observation of current and phase voltage waveforms by means of an oscilloscope, with emphasis placed on the dominant third harmonic component. Some recorded waveshapes, however, cannot be explained in simple terms without considering other harmonic components and the quality of power supply. This paper outlines an improved lecture/experiment that quantitatively analyzes the waveforms of various transformer connections under steady-state no-load conditions while taking into account the nonideal voltage supply. The experimental data obtained with the aid of a harmonic analyzer are then compared to the qualitative predictions and the discrepancies are discussed     

An accurate solution to line harmonic distortion produced by AC/DCconverters with overlap and DC ripple

A method to determine harmonic distortion levels produced by AC/DC converters with overlap and DC current ripple is provided. The exact values of individual harmonic magnitudes are calculated easily from waveform discontinuity points by using algebraic additions instead of integrations. The total harmonic distortion (THD) of the line voltage at the coupling point is expressed in closed form. The expressions derived can be used with confidence when investigating accurate harmonic levels produced by converter-fed DC drives     

Evaluating temporal variability in the spectral reflectance response of annual ryegrass to changes in nitrogen applications and leaching fractions

A two‐year study was conducted in 2002 and 2003 at the University of Nevada, Las Vegas's center for urban water conservation to assess canopy spectral response of annual ryegrass (Lolium multiflorum Lam.) grown under various combinations of N and irrigation (based on leaching fraction: LF) treatments. Multispectral measurements were acquired using a ground‐based spectroradiometer (200–1100 nm) on a biweekly basis during the growing season (October–May) in 2002 and 2003. Multispectral parameters were correlated with soil–plant parameters and temporal variability was investigated. Results showed that the normalized difference vegetation index (NDVI), stress index (SI), photochemical reflectance index (PRI) and canopy reflectance at 693 nm, were highly correlated with tissue N concentration (TN), tissue moisture content (TM), TN×TM and canopy colour, as influenced by N and LF treatment combinations. Coefficients of determination ranged from 0.50 to 0.79 (P<0.001) based on single‐day correlations and correlations established over the entire growing period in 2002 and in 2003. TN was mainly predicted from wavelengths in the VIS portion of the spectrum, while TM was predicted from wavelengths in the VIS and NIR. Correlations were inconsistent between spectral parameters and physiological parameters throughout the study confirming the problem of temporal variation associated with spectral signatures of turfgrass species. However, spectral reflectance showed significant potential for monitoring turfgrass N and moisture status, and was able to capture temporal variability over the same growing period and from one year to another. The results provide a sound basis for future validation of ground‐based remote sensing for turfgrass management on golf courses.     

Discussion of power definitions contained in the IEEE Dictionary

This tutorial paper discusses the drawbacks of the definitions of various types of powers found in the IEEE Standard Dictionary of Electrical and Electronics Terms (IEEE Std. 100-88). With the exceptions of instantaneous power and active power, all remaining kinds of “powers” are nonphysical. The concept of power factor in polyphase circuits is ambiguous. Examples that illustrate the shortcomings of many power definitions are included. The impact of these definitions on current power/energy metering practices are discussed. It is recommended that some definitions be either changed or eliminated from the IEEE Dictionary     

Optimal efficiency speed control of induction motors by variablerotor impedance

An optimal method to control the speed of a wound-rotor induction motor by variable external rotor impedance is presented. The rotor impedance is adjusted so that, for any desired torque and slip values, the total copper losses are minimized. Motor efficiency is improved compared with the case of conventional speed control by variable rotor resistance only. An example illustrates the copper loss reduction and dynamic behavior of the drive. Simulation study results that show the percentage copper loss reduction is generally likely to be higher for lighter loads. For constant-torque loads, the reduction percentage reaches a peak at the lower slip values, whereas for fan-type loads the most significant percentage copper-loss reduction occurs at both the higher and lower slip values. The response time of the rotor speed for startup or a sudden change in the speed setting is considerably smaller than that achieved by pure rotor resistance control     

Shunt capacitor sizing for radial distribution feeders withdistorted substation voltages

An algorithm for optimizing shunt capacitor sizes on radial distribution lines with nonsinusoidal substation voltages such that the RMS voltages and their corresponding total harmonic distortion lie within prescribed values is presented. The problem is formulated as a combinatorial optimization problem with inequality constraints. A simple heuristic numerical algorithm that is based on the method of local variations is proposed to determine an optimal solution. An example shows that optimal capacitor sizes found by neglecting the harmonic components may result in unacceptable voltage distortion levels